Add project restore files and NuGet cache for GsaViewer

- Created project.nuget.cache to store NuGet package cache information.
- Added project.packagespec.json to define project restore settings and dependencies.
- Included rider.project.restore.info for Rider IDE integration.

.idea/.idea.GsaViewer/.idea/.gitignore

@@ -0,0 +1,13 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Rider ignored files
+/modules.xml
+/contentModel.xml
+/projectSettingsUpdater.xml
+/.idea.GsaViewer.iml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/.idea.GsaViewer/.idea/avalonia.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AvaloniaProject">
+    <option name="projectPerEditor">
+      <map>
+        <entry key="Views/MainWindow.axaml" value="GsaViewer.csproj" />
+      </map>
+    </option>
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/copilot.data.migration.agent.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AgentMigrationStateService">
+    <option name="migrationStatus" value="COMPLETED" />
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/copilot.data.migration.ask.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AskMigrationStateService">
+    <option name="migrationStatus" value="COMPLETED" />
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/copilot.data.migration.ask2agent.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Ask2AgentMigrationStateService">
+    <option name="migrationStatus" value="COMPLETED" />
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/copilot.data.migration.edit.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="EditMigrationStateService">
+    <option name="migrationStatus" value="COMPLETED" />
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/encodings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding" addBOMForNewFiles="with BOM under Windows, with no BOM otherwise" />
+</project>

.idea/.idea.GsaViewer/.idea/indexLayout.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="UserContentModel">
+    <attachedFolders />
+    <explicitIncludes />
+    <explicitExcludes />
+  </component>
+</project>

.idea/.idea.GsaViewer/.idea/material_theme_project_new.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MaterialThemeProjectNewConfig">
+    <option name="metadata">
+      <MTProjectMetadataState>
+        <option name="userId" value="24a2abbf:19d72afb14b:-7ffd" />
+      </MTProjectMetadataState>
+    </option>
+  </component>
+</project>

App.axaml

@@ -0,0 +1,10 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="GsaViewer.App"
+             RequestedThemeVariant="Default">
+             <!-- "Default" ThemeVariant follows system theme variant. "Dark" or "Light" are other available options. -->
+  
+    <Application.Styles>
+        <FluentTheme />
+    </Application.Styles>
+</Application>

App.axaml.cs

@@ -0,0 +1,47 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Data.Core;
+using Avalonia.Data.Core.Plugins;
+using System.Linq;
+using Avalonia.Markup.Xaml;
+using GsaViewer.ViewModels;
+using GsaViewer.Views;
+
+namespace GsaViewer;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            // Avoid duplicate validations from both Avalonia and the CommunityToolkit. 
+            // More info: https://docs.avaloniaui.net/docs/guides/development-guides/data-validation#manage-validationplugins
+            DisableAvaloniaDataAnnotationValidation();
+            desktop.MainWindow = new MainWindow
+            {
+                DataContext = new MainWindowViewModel(),
+            };
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+
+    private void DisableAvaloniaDataAnnotationValidation()
+    {
+        // Get an array of plugins to remove
+        var dataValidationPluginsToRemove =
+            BindingPlugins.DataValidators.OfType<DataAnnotationsValidationPlugin>().ToArray();
+
+        // remove each entry found
+        foreach (var plugin in dataValidationPluginsToRemove)
+        {
+            BindingPlugins.DataValidators.Remove(plugin);
+        }
+    }
+}

GsaEditor.Core/Compression/ZlibHelper.cs

@@ -0,0 +1,88 @@
+using System.IO.Compression;
+
+namespace GsaEditor.Core.Compression;
+
+/// <summary>
+/// Provides zlib compression and decompression utilities for GSA archive entries.
+/// The GSA format stores zlib-wrapped data: 2-byte header (CMF+FLG) + deflate stream + 4-byte Adler-32 checksum.
+/// This helper skips the 2-byte zlib header and uses <see cref="DeflateStream"/> for the core deflate data.
+/// </summary>
+public static class ZlibHelper
+{
+    /// <summary>
+    /// Decompresses zlib-wrapped data into a byte array of the specified original size.
+    /// Skips the 2-byte zlib header before feeding data to <see cref="DeflateStream"/>.
+    /// </summary>
+    /// <param name="compressedData">The zlib-wrapped compressed data (header + deflate + checksum).</param>
+    /// <param name="originalLength">The expected decompressed size in bytes.</param>
+    /// <returns>The decompressed byte array.</returns>
+    /// <exception cref="InvalidDataException">Thrown when decompression fails or data is corrupt.</exception>
+    public static byte[] Decompress(byte[] compressedData, uint originalLength)
+    {
+        if (compressedData.Length < 2)
+            throw new InvalidDataException("Compressed data is too short to contain a zlib header.");
+
+        // Skip the 2-byte zlib header (typically 0x78 0x9C for default compression)
+        using var ms = new MemoryStream(compressedData, 2, compressedData.Length - 2);
+        using var deflate = new DeflateStream(ms, CompressionMode.Decompress);
+
+        var result = new byte[originalLength];
+        int totalRead = 0;
+        while (totalRead < result.Length)
+        {
+            int bytesRead = deflate.Read(result, totalRead, result.Length - totalRead);
+            if (bytesRead == 0)
+                break;
+            totalRead += bytesRead;
+        }
+
+        return result;
+    }
+
+    /// <summary>
+    /// Compresses data using zlib format: 2-byte header + deflate stream + 4-byte Adler-32 checksum.
+    /// </summary>
+    /// <param name="data">The uncompressed data to compress.</param>
+    /// <returns>The zlib-wrapped compressed byte array.</returns>
+    public static byte[] Compress(byte[] data)
+    {
+        using var output = new MemoryStream();
+
+        // Write zlib header: CMF=0x78 (deflate method, 32K window), FLG=0x9C (default level, valid check bits)
+        output.WriteByte(0x78);
+        output.WriteByte(0x9C);
+
+        using (var deflate = new DeflateStream(output, CompressionLevel.Optimal, leaveOpen: true))
+        {
+            deflate.Write(data, 0, data.Length);
+        }
+
+        // Write Adler-32 checksum in big-endian byte order
+        uint adler = ComputeAdler32(data);
+        output.WriteByte((byte)(adler >> 24));
+        output.WriteByte((byte)(adler >> 16));
+        output.WriteByte((byte)(adler >> 8));
+        output.WriteByte((byte)adler);
+
+        return output.ToArray();
+    }
+
+    /// <summary>
+    /// Computes the Adler-32 checksum of the given data.
+    /// </summary>
+    /// <param name="data">The data to checksum.</param>
+    /// <returns>The 32-bit Adler-32 checksum value.</returns>
+    private static uint ComputeAdler32(byte[] data)
+    {
+        const uint MOD_ADLER = 65521;
+        uint a = 1, b = 0;
+
+        for (int i = 0; i < data.Length; i++)
+        {
+            a = (a + data[i]) % MOD_ADLER;
+            b = (b + a) % MOD_ADLER;
+        }
+
+        return (b << 16) | a;
+    }
+}

GsaEditor.Core/GsaEditor.Core.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+  </PropertyGroup>
+</Project>

GsaEditor.Core/IO/GsaIndexReader.cs

@@ -0,0 +1,70 @@
+using System.Xml.Linq;
+
+namespace GsaEditor.Core.IO;
+
+/// <summary>
+/// Represents a single entry parsed from a .idx NML index file.
+/// </summary>
+public class GsaIndexEntry
+{
+    /// <summary>
+    /// The file alias (relative path) of the entry.
+    /// </summary>
+    public string Id { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Compression method: 0 = raw, 1 = zlib.
+    /// </summary>
+    public int Method { get; set; }
+
+    /// <summary>
+    /// Original (decompressed) size in bytes.
+    /// </summary>
+    public uint Length { get; set; }
+
+    /// <summary>
+    /// Compressed size in bytes.
+    /// </summary>
+    public uint CompressedLength { get; set; }
+
+    /// <summary>
+    /// Byte offset of the data block within the archive.
+    /// </summary>
+    public long Offset { get; set; }
+}
+
+/// <summary>
+/// Parses .idx NML index files (XML-compatible format) into a list of <see cref="GsaIndexEntry"/>.
+/// </summary>
+public static class GsaIndexReader
+{
+    /// <summary>
+    /// Reads index entries from the specified .idx file.
+    /// </summary>
+    /// <param name="filePath">The path to the .idx file.</param>
+    /// <returns>A list of parsed index entries.</returns>
+    public static List<GsaIndexEntry> Read(string filePath)
+    {
+        var doc = XDocument.Load(filePath);
+        var entries = new List<GsaIndexEntry>();
+
+        var root = doc.Root;
+        if (root == null || root.Name.LocalName != "Index")
+            return entries;
+
+        foreach (var entryEl in root.Elements("Entry"))
+        {
+            var entry = new GsaIndexEntry
+            {
+                Id = entryEl.Element("Id")?.Value ?? string.Empty,
+                Method = int.TryParse(entryEl.Element("Method")?.Value, out var m) ? m : 0,
+                Length = uint.TryParse(entryEl.Element("Len")?.Value, out var l) ? l : 0,
+                CompressedLength = uint.TryParse(entryEl.Element("CompLen")?.Value, out var cl) ? cl : 0,
+                Offset = long.TryParse(entryEl.Element("Offset")?.Value, out var o) ? o : 0
+            };
+            entries.Add(entry);
+        }
+
+        return entries;
+    }
+}

GsaEditor.Core/IO/GsaIndexWriter.cs

@@ -0,0 +1,36 @@
+using System.Xml.Linq;
+using GsaEditor.Core.Models;
+
+namespace GsaEditor.Core.IO;
+
+/// <summary>
+/// Writes a .idx NML index file from a <see cref="GsaArchive"/>.
+/// The index file is XML-compatible and lists each entry with its alias, compression method,
+/// sizes, and data offset for fast lookup without a full sequential scan.
+/// </summary>
+public static class GsaIndexWriter
+{
+    /// <summary>
+    /// Writes the index file for the given archive to the specified path.
+    /// </summary>
+    /// <param name="archive">The archive whose entries will be indexed.</param>
+    /// <param name="filePath">The output .idx file path.</param>
+    public static void Write(GsaArchive archive, string filePath)
+    {
+        var doc = new XDocument(
+            new XElement("Index",
+                archive.Entries.Select(e =>
+                    new XElement("Entry",
+                        new XElement("Id", e.Alias),
+                        new XElement("Method", e.IsCompressed ? 1 : 0),
+                        new XElement("Len", e.OriginalLength),
+                        new XElement("CompLen", e.CompressedLength),
+                        new XElement("Offset", e.DataOffset)
+                    )
+                )
+            )
+        );
+
+        doc.Save(filePath);
+    }
+}

GsaEditor.Core/IO/GsaReader.cs

@@ -0,0 +1,163 @@
+using System.Text;
+using GsaEditor.Core.Models;
+
+namespace GsaEditor.Core.IO;
+
+/// <summary>
+/// Reads a .gsa binary archive from a stream or file and produces a <see cref="GsaArchive"/>.
+/// Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+/// </summary>
+public static class GsaReader
+{
+    /// <summary>Magic word for the NARC (legacy) format.</summary>
+    private const uint MAGIC_NARC = 0x4E415243;
+
+    /// <summary>Magic word for the NARD (enhanced) format.</summary>
+    private const uint MAGIC_NARD = 0x4E415244;
+
+    /// <summary>Maximum allowed alias length in characters.</summary>
+    private const int MAX_ALIAS_LENGTH = 511;
+
+    /// <summary>
+    /// Reads a GSA archive from the specified file path.
+    /// </summary>
+    /// <param name="filePath">The path to the .gsa archive file.</param>
+    /// <returns>A fully populated <see cref="GsaArchive"/>.</returns>
+    /// <exception cref="InvalidDataException">Thrown if the file has an invalid magic word.</exception>
+    public static GsaArchive Read(string filePath)
+    {
+        using var stream = File.OpenRead(filePath);
+        return Read(stream);
+    }
+
+    /// <summary>
+    /// Reads a GSA archive from a stream by performing a sequential scan of all entries.
+    /// </summary>
+    /// <param name="stream">A readable, seekable stream positioned at the start of the archive.</param>
+    /// <returns>A fully populated <see cref="GsaArchive"/>.</returns>
+    /// <exception cref="InvalidDataException">Thrown if the stream has an invalid magic word.</exception>
+    public static GsaArchive Read(Stream stream)
+    {
+        using var reader = new BinaryReader(stream, Encoding.ASCII, leaveOpen: true);
+        var archive = new GsaArchive();
+
+        // Read global header
+        uint magic = reader.ReadUInt32();
+        if (magic == MAGIC_NARC)
+        {
+            archive.Format = GsaFormat.NARC;
+        }
+        else if (magic == MAGIC_NARD)
+        {
+            archive.Format = GsaFormat.NARD;
+            archive.OffsetPadding = reader.ReadInt32();
+            archive.SizePadding = reader.ReadInt32();
+        }
+        else
+        {
+            throw new InvalidDataException(
+                $"Invalid GSA magic word: 0x{magic:X8}. Expected NARC (0x{MAGIC_NARC:X8}) or NARD (0x{MAGIC_NARD:X8}).");
+        }
+
+        // Sequentially read all entries until EOF
+        while (stream.Position < stream.Length)
+        {
+            var entry = ReadEntry(reader, archive);
+            if (entry == null)
+                break;
+            archive.Entries.Add(entry);
+        }
+
+        return archive;
+    }
+
+    /// <summary>
+    /// Reads a single file entry from the current stream position.
+    /// </summary>
+    /// <param name="reader">The binary reader positioned at the start of an entry.</param>
+    /// <param name="archive">The parent archive (used for NARD padding alignment).</param>
+    /// <returns>A populated <see cref="GsaEntry"/>, or null if no more entries can be read.</returns>
+    private static GsaEntry? ReadEntry(BinaryReader reader, GsaArchive archive)
+    {
+        var stream = reader.BaseStream;
+
+        if (stream.Position >= stream.Length)
+            return null;
+
+        // NARD: align stream position before reading entry header
+        if (archive.Format == GsaFormat.NARD && archive.OffsetPadding > 0)
+            AlignStream(stream, archive.OffsetPadding);
+
+        // Check if enough bytes remain for the alias length field
+        if (stream.Length - stream.Position < 4)
+            return null;
+
+        // Read alias
+        uint aliasLength = reader.ReadUInt32();
+        if (aliasLength == 0 || aliasLength > MAX_ALIAS_LENGTH)
+            return null;
+
+        if (stream.Length - stream.Position < aliasLength)
+            return null;
+
+        byte[] aliasBytes = reader.ReadBytes((int)aliasLength);
+        string alias = Encoding.ASCII.GetString(aliasBytes);
+
+        // Read compression flag (bit 0: 1=compressed, 0=raw)
+        byte compressionByte = reader.ReadByte();
+        bool isCompressed = (compressionByte & 0x01) != 0;
+
+        // Read original (decompressed) length
+        uint originalLength = reader.ReadUInt32();
+
+        // Read compressed length (only present if compressed)
+        uint compressedLength;
+        if (isCompressed)
+        {
+            compressedLength = reader.ReadUInt32();
+        }
+        else
+        {
+            compressedLength = originalLength;
+        }
+
+        // NARD: align stream position before reading the data block
+        if (archive.Format == GsaFormat.NARD && archive.OffsetPadding > 0)
+            AlignStream(stream, archive.OffsetPadding);
+
+        // Read raw data
+        long dataOffset = stream.Position;
+        uint dataSize = isCompressed ? compressedLength : originalLength;
+
+        if (stream.Length - stream.Position < dataSize)
+            return null;
+
+        byte[] rawData = reader.ReadBytes((int)dataSize);
+
+        return new GsaEntry
+        {
+            Alias = alias,
+            IsCompressed = isCompressed,
+            OriginalLength = originalLength,
+            CompressedLength = compressedLength,
+            RawData = rawData,
+            DataOffset = dataOffset
+        };
+    }
+
+    /// <summary>
+    /// Advances the stream position to the next aligned boundary.
+    /// </summary>
+    /// <param name="stream">The stream to align.</param>
+    /// <param name="alignment">The alignment boundary in bytes.</param>
+    private static void AlignStream(Stream stream, int alignment)
+    {
+        if (alignment <= 1) return;
+        long pos = stream.Position;
+        long remainder = pos % alignment;
+        if (remainder != 0)
+        {
+            stream.Position = pos + (alignment - remainder);
+        }
+    }
+}

GsaEditor.Core/IO/GsaWriter.cs

@@ -0,0 +1,114 @@
+using System.Text;
+using GsaEditor.Core.Models;
+
+namespace GsaEditor.Core.IO;
+
+/// <summary>
+/// Writes a <see cref="GsaArchive"/> to a binary .gsa stream or file.
+/// Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+/// </summary>
+public static class GsaWriter
+{
+    /// <summary>Magic word for the NARC (legacy) format.</summary>
+    private const uint MAGIC_NARC = 0x4E415243;
+
+    /// <summary>Magic word for the NARD (enhanced) format.</summary>
+    private const uint MAGIC_NARD = 0x4E415244;
+
+    /// <summary>
+    /// Writes the archive to the specified file path.
+    /// </summary>
+    /// <param name="archive">The archive to write.</param>
+    /// <param name="filePath">The output file path.</param>
+    public static void Write(GsaArchive archive, string filePath)
+    {
+        using var stream = File.Create(filePath);
+        Write(archive, stream);
+    }
+
+    /// <summary>
+    /// Writes the archive to the given stream.
+    /// Each entry's <see cref="GsaEntry.DataOffset"/> is updated to reflect the new position in the output.
+    /// </summary>
+    /// <param name="archive">The archive to write.</param>
+    /// <param name="stream">A writable stream.</param>
+    public static void Write(GsaArchive archive, Stream stream)
+    {
+        using var writer = new BinaryWriter(stream, Encoding.ASCII, leaveOpen: true);
+
+        // Write global header
+        if (archive.Format == GsaFormat.NARC)
+        {
+            writer.Write(MAGIC_NARC);
+        }
+        else
+        {
+            writer.Write(MAGIC_NARD);
+            writer.Write(archive.OffsetPadding);
+            writer.Write(archive.SizePadding);
+        }
+
+        // Write each entry sequentially
+        foreach (var entry in archive.Entries)
+        {
+            WriteEntry(writer, entry, archive);
+        }
+    }
+
+    /// <summary>
+    /// Writes a single file entry at the current stream position.
+    /// </summary>
+    /// <param name="writer">The binary writer.</param>
+    /// <param name="entry">The entry to write.</param>
+    /// <param name="archive">The parent archive (used for NARD padding alignment).</param>
+    private static void WriteEntry(BinaryWriter writer, GsaEntry entry, GsaArchive archive)
+    {
+        // NARD: align stream position before writing entry header
+        if (archive.Format == GsaFormat.NARD && archive.OffsetPadding > 0)
+            WritePadding(writer, archive.OffsetPadding);
+
+        // Write alias
+        byte[] aliasBytes = Encoding.ASCII.GetBytes(entry.Alias);
+        writer.Write((uint)aliasBytes.Length);
+        writer.Write(aliasBytes);
+
+        // Write compression flag
+        writer.Write((byte)(entry.IsCompressed ? 1 : 0));
+
+        // Write original (decompressed) length
+        writer.Write(entry.OriginalLength);
+
+        // Write compressed length (only if compressed)
+        if (entry.IsCompressed)
+        {
+            writer.Write(entry.CompressedLength);
+        }
+
+        // NARD: align stream position before writing the data block
+        if (archive.Format == GsaFormat.NARD && archive.OffsetPadding > 0)
+            WritePadding(writer, archive.OffsetPadding);
+
+        // Update the entry's data offset to reflect the new position
+        entry.DataOffset = writer.BaseStream.Position;
+
+        // Write raw data
+        writer.Write(entry.RawData);
+    }
+
+    /// <summary>
+    /// Writes zero-bytes to pad the stream to the next aligned boundary.
+    /// </summary>
+    /// <param name="writer">The binary writer.</param>
+    /// <param name="alignment">The alignment boundary in bytes.</param>
+    private static void WritePadding(BinaryWriter writer, int alignment)
+    {
+        if (alignment <= 1) return;
+        long pos = writer.BaseStream.Position;
+        long remainder = pos % alignment;
+        if (remainder != 0)
+        {
+            int paddingBytes = (int)(alignment - remainder);
+            writer.Write(new byte[paddingBytes]);
+        }
+    }
+}

GsaEditor.Core/Models/GsaArchive.cs

@@ -0,0 +1,27 @@
+namespace GsaEditor.Core.Models;
+
+/// <summary>
+/// Represents a loaded GSA archive with its global header information and file entries.
+/// </summary>
+public class GsaArchive
+{
+    /// <summary>
+    /// The format variant of this archive (NARC or NARD).
+    /// </summary>
+    public GsaFormat Format { get; set; } = GsaFormat.NARC;
+
+    /// <summary>
+    /// (NARD only) Byte alignment for data offsets. Zero or unused for NARC.
+    /// </summary>
+    public int OffsetPadding { get; set; }
+
+    /// <summary>
+    /// (NARD only) Byte alignment for data sizes. Zero or unused for NARC.
+    /// </summary>
+    public int SizePadding { get; set; }
+
+    /// <summary>
+    /// The ordered list of file entries in the archive.
+    /// </summary>
+    public List<GsaEntry> Entries { get; set; } = new();
+}

GsaEditor.Core/Models/GsaEntry.cs

@@ -0,0 +1,77 @@
+using GsaEditor.Core.Compression;
+
+namespace GsaEditor.Core.Models;
+
+/// <summary>
+/// Represents a single file entry within a GSA archive.
+/// </summary>
+public class GsaEntry
+{
+    /// <summary>
+    /// Relative path (alias) of the file within the archive, using '/' as separator.
+    /// Maximum 511 characters.
+    /// </summary>
+    public string Alias { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether this entry's data is zlib-compressed.
+    /// </summary>
+    public bool IsCompressed { get; set; }
+
+    /// <summary>
+    /// Original (decompressed) size of the file in bytes.
+    /// </summary>
+    public uint OriginalLength { get; set; }
+
+    /// <summary>
+    /// Compressed size of the file in bytes. Equal to <see cref="OriginalLength"/> if not compressed.
+    /// </summary>
+    public uint CompressedLength { get; set; }
+
+    /// <summary>
+    /// Raw data as stored in the archive (compressed bytes if <see cref="IsCompressed"/> is true).
+    /// </summary>
+    public byte[] RawData { get; set; } = Array.Empty<byte>();
+
+    /// <summary>
+    /// Byte offset of this entry's data block within the archive file.
+    /// </summary>
+    public long DataOffset { get; set; }
+
+    /// <summary>
+    /// Returns the decompressed data for this entry.
+    /// If the entry is not compressed, returns <see cref="RawData"/> directly.
+    /// </summary>
+    /// <returns>The decompressed file content.</returns>
+    public byte[] GetDecompressedData()
+    {
+        if (!IsCompressed)
+            return RawData;
+
+        return ZlibHelper.Decompress(RawData, OriginalLength);
+    }
+
+    /// <summary>
+    /// Sets the entry data from uncompressed bytes, optionally compressing with zlib.
+    /// Updates <see cref="OriginalLength"/>, <see cref="CompressedLength"/>,
+    /// <see cref="IsCompressed"/>, and <see cref="RawData"/>.
+    /// </summary>
+    /// <param name="uncompressedData">The uncompressed file content.</param>
+    /// <param name="compress">Whether to compress the data with zlib.</param>
+    public void SetData(byte[] uncompressedData, bool compress)
+    {
+        OriginalLength = (uint)uncompressedData.Length;
+        IsCompressed = compress;
+
+        if (compress)
+        {
+            RawData = ZlibHelper.Compress(uncompressedData);
+            CompressedLength = (uint)RawData.Length;
+        }
+        else
+        {
+            RawData = uncompressedData;
+            CompressedLength = OriginalLength;
+        }
+    }
+}

GsaEditor.Core/Models/GsaFormat.cs

@@ -0,0 +1,18 @@
+namespace GsaEditor.Core.Models;
+
+/// <summary>
+/// Identifies the archive format variant.
+/// </summary>
+public enum GsaFormat
+{
+    /// <summary>
+    /// Legacy format with no padding support. Magic word = 0x4E415243 ("NARC").
+    /// </summary>
+    NARC,
+
+    /// <summary>
+    /// Enhanced format with offset and size padding for console DVD alignment.
+    /// Magic word = 0x4E415244 ("NARD").
+    /// </summary>
+    NARD
+}

GsaEditor.Core/bin/Debug/net8.0/GsaEditor.Core.deps.json

@@ -0,0 +1,23 @@
+{
+  "runtimeTarget": {
+    "name": ".NETCoreApp,Version=v8.0",
+    "signature": ""
+  },
+  "compilationOptions": {},
+  "targets": {
+    ".NETCoreApp,Version=v8.0": {
+      "GsaEditor.Core/1.0.0": {
+        "runtime": {
+          "GsaEditor.Core.dll": {}
+        }
+      }
+    }
+  },
+  "libraries": {
+    "GsaEditor.Core/1.0.0": {
+      "type": "project",
+      "serviceable": false,
+      "sha512": ""
+    }
+  }
+}

GsaEditor.Core/bin/Debug/net8.0/GsaEditor.Core.xml

@@ -0,0 +1,276 @@
+<?xml version="1.0"?>
+<doc>
+    <assembly>
+        <name>GsaEditor.Core</name>
+    </assembly>
+    <members>
+        <member name="T:GsaEditor.Core.Compression.ZlibHelper">
+            <summary>
+            Provides zlib compression and decompression utilities for GSA archive entries.
+            The GSA format stores zlib-wrapped data: 2-byte header (CMF+FLG) + deflate stream + 4-byte Adler-32 checksum.
+            This helper skips the 2-byte zlib header and uses <see cref="T:System.IO.Compression.DeflateStream"/> for the core deflate data.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Decompress(System.Byte[],System.UInt32)">
+            <summary>
+            Decompresses zlib-wrapped data into a byte array of the specified original size.
+            Skips the 2-byte zlib header before feeding data to <see cref="T:System.IO.Compression.DeflateStream"/>.
+            </summary>
+            <param name="compressedData">The zlib-wrapped compressed data (header + deflate + checksum).</param>
+            <param name="originalLength">The expected decompressed size in bytes.</param>
+            <returns>The decompressed byte array.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown when decompression fails or data is corrupt.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Compress(System.Byte[])">
+            <summary>
+            Compresses data using zlib format: 2-byte header + deflate stream + 4-byte Adler-32 checksum.
+            </summary>
+            <param name="data">The uncompressed data to compress.</param>
+            <returns>The zlib-wrapped compressed byte array.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.ComputeAdler32(System.Byte[])">
+            <summary>
+            Computes the Adler-32 checksum of the given data.
+            </summary>
+            <param name="data">The data to checksum.</param>
+            <returns>The 32-bit Adler-32 checksum value.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexEntry">
+            <summary>
+            Represents a single entry parsed from a .idx NML index file.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Id">
+            <summary>
+            The file alias (relative path) of the entry.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Method">
+            <summary>
+            Compression method: 0 = raw, 1 = zlib.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Length">
+            <summary>
+            Original (decompressed) size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.CompressedLength">
+            <summary>
+            Compressed size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Offset">
+            <summary>
+            Byte offset of the data block within the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexReader">
+            <summary>
+            Parses .idx NML index files (XML-compatible format) into a list of <see cref="T:GsaEditor.Core.IO.GsaIndexEntry"/>.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexReader.Read(System.String)">
+            <summary>
+            Reads index entries from the specified .idx file.
+            </summary>
+            <param name="filePath">The path to the .idx file.</param>
+            <returns>A list of parsed index entries.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexWriter">
+            <summary>
+            Writes a .idx NML index file from a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            The index file is XML-compatible and lists each entry with its alias, compression method,
+            sizes, and data offset for fast lookup without a full sequential scan.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the index file for the given archive to the specified path.
+            </summary>
+            <param name="archive">The archive whose entries will be indexed.</param>
+            <param name="filePath">The output .idx file path.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaReader">
+            <summary>
+            Reads a .gsa binary archive from a stream or file and produces a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAX_ALIAS_LENGTH">
+            <summary>Maximum allowed alias length in characters.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.String)">
+            <summary>
+            Reads a GSA archive from the specified file path.
+            </summary>
+            <param name="filePath">The path to the .gsa archive file.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the file has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.IO.Stream)">
+            <summary>
+            Reads a GSA archive from a stream by performing a sequential scan of all entries.
+            </summary>
+            <param name="stream">A readable, seekable stream positioned at the start of the archive.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the stream has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.ReadEntry(System.IO.BinaryReader,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Reads a single file entry from the current stream position.
+            </summary>
+            <param name="reader">The binary reader positioned at the start of an entry.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+            <returns>A populated <see cref="T:GsaEditor.Core.Models.GsaEntry"/>, or null if no more entries can be read.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.AlignStream(System.IO.Stream,System.Int32)">
+            <summary>
+            Advances the stream position to the next aligned boundary.
+            </summary>
+            <param name="stream">The stream to align.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaWriter">
+            <summary>
+            Writes a <see cref="T:GsaEditor.Core.Models.GsaArchive"/> to a binary .gsa stream or file.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the archive to the specified file path.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="filePath">The output file path.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.IO.Stream)">
+            <summary>
+            Writes the archive to the given stream.
+            Each entry's <see cref="P:GsaEditor.Core.Models.GsaEntry.DataOffset"/> is updated to reflect the new position in the output.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="stream">A writable stream.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WriteEntry(System.IO.BinaryWriter,GsaEditor.Core.Models.GsaEntry,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Writes a single file entry at the current stream position.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="entry">The entry to write.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WritePadding(System.IO.BinaryWriter,System.Int32)">
+            <summary>
+            Writes zero-bytes to pad the stream to the next aligned boundary.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaArchive">
+            <summary>
+            Represents a loaded GSA archive with its global header information and file entries.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Format">
+            <summary>
+            The format variant of this archive (NARC or NARD).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.OffsetPadding">
+            <summary>
+            (NARD only) Byte alignment for data offsets. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.SizePadding">
+            <summary>
+            (NARD only) Byte alignment for data sizes. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Entries">
+            <summary>
+            The ordered list of file entries in the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaEntry">
+            <summary>
+            Represents a single file entry within a GSA archive.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.Alias">
+            <summary>
+            Relative path (alias) of the file within the archive, using '/' as separator.
+            Maximum 511 characters.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.IsCompressed">
+            <summary>
+            Whether this entry's data is zlib-compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.OriginalLength">
+            <summary>
+            Original (decompressed) size of the file in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.CompressedLength">
+            <summary>
+            Compressed size of the file in bytes. Equal to <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/> if not compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.RawData">
+            <summary>
+            Raw data as stored in the archive (compressed bytes if <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/> is true).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.DataOffset">
+            <summary>
+            Byte offset of this entry's data block within the archive file.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.GetDecompressedData">
+            <summary>
+            Returns the decompressed data for this entry.
+            If the entry is not compressed, returns <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/> directly.
+            </summary>
+            <returns>The decompressed file content.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.SetData(System.Byte[],System.Boolean)">
+            <summary>
+            Sets the entry data from uncompressed bytes, optionally compressing with zlib.
+            Updates <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/>, <see cref="P:GsaEditor.Core.Models.GsaEntry.CompressedLength"/>,
+            <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/>, and <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/>.
+            </summary>
+            <param name="uncompressedData">The uncompressed file content.</param>
+            <param name="compress">Whether to compress the data with zlib.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaFormat">
+            <summary>
+            Identifies the archive format variant.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARC">
+            <summary>
+            Legacy format with no padding support. Magic word = 0x4E415243 ("NARC").
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARD">
+            <summary>
+            Enhanced format with offset and size padding for console DVD alignment.
+            Magic word = 0x4E415244 ("NARD").
+            </summary>
+        </member>
+    </members>
+</doc>

GsaEditor.Core/obj/Debug/net8.0/.NETCoreApp,Version=v8.0.AssemblyAttributes.cs

@@ -0,0 +1,4 @@
+// <autogenerated />
+using System;
+using System.Reflection;
+[assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v8.0", FrameworkDisplayName = ".NET 8.0")]

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.AssemblyInfo.cs

@@ -0,0 +1,22 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+using System;
+using System.Reflection;
+
+[assembly: System.Reflection.AssemblyCompanyAttribute("GsaEditor.Core")]
+[assembly: System.Reflection.AssemblyConfigurationAttribute("Debug")]
+[assembly: System.Reflection.AssemblyFileVersionAttribute("1.0.0.0")]
+[assembly: System.Reflection.AssemblyInformationalVersionAttribute("1.0.0")]
+[assembly: System.Reflection.AssemblyProductAttribute("GsaEditor.Core")]
+[assembly: System.Reflection.AssemblyTitleAttribute("GsaEditor.Core")]
+[assembly: System.Reflection.AssemblyVersionAttribute("1.0.0.0")]
+
+// Généré par la classe MSBuild WriteCodeFragment.
+

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.AssemblyInfoInputs.cache

@@ -0,0 +1 @@
+68387796343863a0e5c11cd0f612a1b364816551cf5816c6d556d410439a3710

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.GeneratedMSBuildEditorConfig.editorconfig

@@ -0,0 +1,15 @@
+is_global = true
+build_property.TargetFramework = net8.0
+build_property.TargetPlatformMinVersion = 
+build_property.UsingMicrosoftNETSdkWeb = 
+build_property.ProjectTypeGuids = 
+build_property.InvariantGlobalization = 
+build_property.PlatformNeutralAssembly = 
+build_property.EnforceExtendedAnalyzerRules = 
+build_property._SupportedPlatformList = Linux,macOS,Windows
+build_property.RootNamespace = GsaEditor.Core
+build_property.ProjectDir = C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\
+build_property.EnableComHosting = 
+build_property.EnableGeneratedComInterfaceComImportInterop = 
+build_property.EffectiveAnalysisLevelStyle = 8.0
+build_property.EnableCodeStyleSeverity = 

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.GlobalUsings.g.cs

@@ -0,0 +1,8 @@
+// <auto-generated/>
+global using global::System;
+global using global::System.Collections.Generic;
+global using global::System.IO;
+global using global::System.Linq;
+global using global::System.Net.Http;
+global using global::System.Threading;
+global using global::System.Threading.Tasks;

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.csproj.CoreCompileInputs.cache

@@ -0,0 +1 @@
+f57ab49a8539dcd5eaae9903c06c691e87a9ead2bd6a913638151d11a0b5901a

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.csproj.FileListAbsolute.txt

@@ -0,0 +1,13 @@
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\bin\Debug\net8.0\GsaEditor.Core.deps.json
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\bin\Debug\net8.0\GsaEditor.Core.dll
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\bin\Debug\net8.0\GsaEditor.Core.pdb
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\bin\Debug\net8.0\GsaEditor.Core.xml
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.GeneratedMSBuildEditorConfig.editorconfig
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.AssemblyInfoInputs.cache
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.AssemblyInfo.cs
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.csproj.CoreCompileInputs.cache
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.dll
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\refint\GsaEditor.Core.dll
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.xml
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\GsaEditor.Core.pdb
+C:\Users\simulateur\Desktop\GsaViewer\GsaEditor.Core\obj\Debug\net8.0\ref\GsaEditor.Core.dll

GsaEditor.Core/obj/Debug/net8.0/GsaEditor.Core.xml

@@ -0,0 +1,276 @@
+<?xml version="1.0"?>
+<doc>
+    <assembly>
+        <name>GsaEditor.Core</name>
+    </assembly>
+    <members>
+        <member name="T:GsaEditor.Core.Compression.ZlibHelper">
+            <summary>
+            Provides zlib compression and decompression utilities for GSA archive entries.
+            The GSA format stores zlib-wrapped data: 2-byte header (CMF+FLG) + deflate stream + 4-byte Adler-32 checksum.
+            This helper skips the 2-byte zlib header and uses <see cref="T:System.IO.Compression.DeflateStream"/> for the core deflate data.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Decompress(System.Byte[],System.UInt32)">
+            <summary>
+            Decompresses zlib-wrapped data into a byte array of the specified original size.
+            Skips the 2-byte zlib header before feeding data to <see cref="T:System.IO.Compression.DeflateStream"/>.
+            </summary>
+            <param name="compressedData">The zlib-wrapped compressed data (header + deflate + checksum).</param>
+            <param name="originalLength">The expected decompressed size in bytes.</param>
+            <returns>The decompressed byte array.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown when decompression fails or data is corrupt.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Compress(System.Byte[])">
+            <summary>
+            Compresses data using zlib format: 2-byte header + deflate stream + 4-byte Adler-32 checksum.
+            </summary>
+            <param name="data">The uncompressed data to compress.</param>
+            <returns>The zlib-wrapped compressed byte array.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.ComputeAdler32(System.Byte[])">
+            <summary>
+            Computes the Adler-32 checksum of the given data.
+            </summary>
+            <param name="data">The data to checksum.</param>
+            <returns>The 32-bit Adler-32 checksum value.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexEntry">
+            <summary>
+            Represents a single entry parsed from a .idx NML index file.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Id">
+            <summary>
+            The file alias (relative path) of the entry.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Method">
+            <summary>
+            Compression method: 0 = raw, 1 = zlib.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Length">
+            <summary>
+            Original (decompressed) size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.CompressedLength">
+            <summary>
+            Compressed size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Offset">
+            <summary>
+            Byte offset of the data block within the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexReader">
+            <summary>
+            Parses .idx NML index files (XML-compatible format) into a list of <see cref="T:GsaEditor.Core.IO.GsaIndexEntry"/>.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexReader.Read(System.String)">
+            <summary>
+            Reads index entries from the specified .idx file.
+            </summary>
+            <param name="filePath">The path to the .idx file.</param>
+            <returns>A list of parsed index entries.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexWriter">
+            <summary>
+            Writes a .idx NML index file from a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            The index file is XML-compatible and lists each entry with its alias, compression method,
+            sizes, and data offset for fast lookup without a full sequential scan.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the index file for the given archive to the specified path.
+            </summary>
+            <param name="archive">The archive whose entries will be indexed.</param>
+            <param name="filePath">The output .idx file path.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaReader">
+            <summary>
+            Reads a .gsa binary archive from a stream or file and produces a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAX_ALIAS_LENGTH">
+            <summary>Maximum allowed alias length in characters.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.String)">
+            <summary>
+            Reads a GSA archive from the specified file path.
+            </summary>
+            <param name="filePath">The path to the .gsa archive file.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the file has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.IO.Stream)">
+            <summary>
+            Reads a GSA archive from a stream by performing a sequential scan of all entries.
+            </summary>
+            <param name="stream">A readable, seekable stream positioned at the start of the archive.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the stream has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.ReadEntry(System.IO.BinaryReader,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Reads a single file entry from the current stream position.
+            </summary>
+            <param name="reader">The binary reader positioned at the start of an entry.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+            <returns>A populated <see cref="T:GsaEditor.Core.Models.GsaEntry"/>, or null if no more entries can be read.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.AlignStream(System.IO.Stream,System.Int32)">
+            <summary>
+            Advances the stream position to the next aligned boundary.
+            </summary>
+            <param name="stream">The stream to align.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaWriter">
+            <summary>
+            Writes a <see cref="T:GsaEditor.Core.Models.GsaArchive"/> to a binary .gsa stream or file.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the archive to the specified file path.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="filePath">The output file path.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.IO.Stream)">
+            <summary>
+            Writes the archive to the given stream.
+            Each entry's <see cref="P:GsaEditor.Core.Models.GsaEntry.DataOffset"/> is updated to reflect the new position in the output.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="stream">A writable stream.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WriteEntry(System.IO.BinaryWriter,GsaEditor.Core.Models.GsaEntry,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Writes a single file entry at the current stream position.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="entry">The entry to write.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WritePadding(System.IO.BinaryWriter,System.Int32)">
+            <summary>
+            Writes zero-bytes to pad the stream to the next aligned boundary.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaArchive">
+            <summary>
+            Represents a loaded GSA archive with its global header information and file entries.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Format">
+            <summary>
+            The format variant of this archive (NARC or NARD).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.OffsetPadding">
+            <summary>
+            (NARD only) Byte alignment for data offsets. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.SizePadding">
+            <summary>
+            (NARD only) Byte alignment for data sizes. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Entries">
+            <summary>
+            The ordered list of file entries in the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaEntry">
+            <summary>
+            Represents a single file entry within a GSA archive.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.Alias">
+            <summary>
+            Relative path (alias) of the file within the archive, using '/' as separator.
+            Maximum 511 characters.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.IsCompressed">
+            <summary>
+            Whether this entry's data is zlib-compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.OriginalLength">
+            <summary>
+            Original (decompressed) size of the file in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.CompressedLength">
+            <summary>
+            Compressed size of the file in bytes. Equal to <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/> if not compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.RawData">
+            <summary>
+            Raw data as stored in the archive (compressed bytes if <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/> is true).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.DataOffset">
+            <summary>
+            Byte offset of this entry's data block within the archive file.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.GetDecompressedData">
+            <summary>
+            Returns the decompressed data for this entry.
+            If the entry is not compressed, returns <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/> directly.
+            </summary>
+            <returns>The decompressed file content.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.SetData(System.Byte[],System.Boolean)">
+            <summary>
+            Sets the entry data from uncompressed bytes, optionally compressing with zlib.
+            Updates <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/>, <see cref="P:GsaEditor.Core.Models.GsaEntry.CompressedLength"/>,
+            <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/>, and <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/>.
+            </summary>
+            <param name="uncompressedData">The uncompressed file content.</param>
+            <param name="compress">Whether to compress the data with zlib.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaFormat">
+            <summary>
+            Identifies the archive format variant.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARC">
+            <summary>
+            Legacy format with no padding support. Magic word = 0x4E415243 ("NARC").
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARD">
+            <summary>
+            Enhanced format with offset and size padding for console DVD alignment.
+            Magic word = 0x4E415244 ("NARD").
+            </summary>
+        </member>
+    </members>
+</doc>

GsaEditor.Core/obj/GsaEditor.Core.csproj.nuget.dgspec.json

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GsaEditor.Core/obj/GsaEditor.Core.csproj.nuget.g.props

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+    <RestoreSuccess Condition=" '$(RestoreSuccess)' == '' ">True</RestoreSuccess>
+    <RestoreTool Condition=" '$(RestoreTool)' == '' ">NuGet</RestoreTool>
+    <ProjectAssetsFile Condition=" '$(ProjectAssetsFile)' == '' ">$(MSBuildThisFileDirectory)project.assets.json</ProjectAssetsFile>
+    <NuGetPackageRoot Condition=" '$(NuGetPackageRoot)' == '' ">$(UserProfile)\.nuget\packages\</NuGetPackageRoot>
+    <NuGetPackageFolders Condition=" '$(NuGetPackageFolders)' == '' ">C:\Users\simulateur\.nuget\packages\</NuGetPackageFolders>
+    <NuGetProjectStyle Condition=" '$(NuGetProjectStyle)' == '' ">PackageReference</NuGetProjectStyle>
+    <NuGetToolVersion Condition=" '$(NuGetToolVersion)' == '' ">6.14.0</NuGetToolVersion>
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+  <ItemGroup Condition=" '$(ExcludeRestorePackageImports)' != 'true' ">
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GsaEditor.Core/obj/GsaEditor.Core.csproj.nuget.g.targets

@@ -0,0 +1,2 @@
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+<Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" />

GsaEditor.Core/obj/project.assets.json

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+        "runtimeIdentifierGraphPath": "C:\\Program Files\\dotnet\\sdk\\9.0.306/PortableRuntimeIdentifierGraph.json"
+      }
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+}

GsaEditor.Core/obj/project.nuget.cache

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+    "C:\\Users\\simulateur\\.nuget\\packages\\microsoft.aspnetcore.app.ref\\8.0.21\\microsoft.aspnetcore.app.ref.8.0.21.nupkg.sha512"
+  ],
+  "logs": []
+}

GsaEditor.sln

@@ -0,0 +1,25 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.0.31903.59
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GsaEditor", "GsaEditor\GsaEditor.csproj", "{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "GsaEditor.Core", "GsaEditor.Core\GsaEditor.Core.csproj", "{B2C3D4E5-F6A7-8901-BCDE-F12345678901}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

GsaEditor/App.axaml

@@ -0,0 +1,9 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="GsaEditor.App"
+             RequestedThemeVariant="Default">
+
+    <Application.Styles>
+        <FluentTheme />
+    </Application.Styles>
+</Application>

GsaEditor/App.axaml.cs

@@ -0,0 +1,35 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Data.Core.Plugins;
+using Avalonia.Markup.Xaml;
+using GsaEditor.ViewModels;
+using GsaEditor.Views;
+
+namespace GsaEditor;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            // Avoid duplicate validations from both Avalonia and the CommunityToolkit.
+            var dataValidationPluginsToRemove =
+                BindingPlugins.DataValidators.OfType<DataAnnotationsValidationPlugin>().ToArray();
+            foreach (var plugin in dataValidationPluginsToRemove)
+                BindingPlugins.DataValidators.Remove(plugin);
+
+            desktop.MainWindow = new MainWindow
+            {
+                DataContext = new MainWindowViewModel()
+            };
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}

GsaEditor/GsaEditor.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <ApplicationManifest>app.manifest</ApplicationManifest>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <AvaloniaResource Include="Assets\**"/>
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="11.3.6"/>
+    <PackageReference Include="Avalonia.Desktop" Version="11.3.6"/>
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.3.6"/>
+    <PackageReference Include="Avalonia.Fonts.Inter" Version="11.3.6"/>
+    <PackageReference Include="Avalonia.Diagnostics" Version="11.3.6">
+      <IncludeAssets Condition="'$(Configuration)' != 'Debug'">None</IncludeAssets>
+      <PrivateAssets Condition="'$(Configuration)' != 'Debug'">All</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.2.1"/>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\GsaEditor.Core\GsaEditor.Core.csproj"/>
+  </ItemGroup>
+</Project>

GsaEditor/Helpers/Dialogs.cs

@@ -0,0 +1,204 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Layout;
+
+namespace GsaEditor.Helpers;
+
+/// <summary>
+/// Provides simple dialog utilities (confirm, message, input) using programmatically-created Avalonia windows.
+/// No third-party controls or custom themes are used.
+/// </summary>
+public static class Dialogs
+{
+    /// <summary>
+    /// Shows a confirmation dialog with Yes/No buttons.
+    /// </summary>
+    /// <param name="parent">The parent window.</param>
+    /// <param name="title">Dialog title.</param>
+    /// <param name="message">Message to display.</param>
+    /// <returns>True if the user clicked Yes, false otherwise.</returns>
+    public static async Task<bool> ConfirmAsync(Window parent, string title, string message)
+    {
+        var result = false;
+
+        var dialog = new Window
+        {
+            Title = title,
+            Width = 420,
+            Height = 170,
+            WindowStartupLocation = WindowStartupLocation.CenterOwner,
+            CanResize = false,
+            ShowInTaskbar = false
+        };
+
+        var messageBlock = new TextBlock
+        {
+            Text = message,
+            TextWrapping = Avalonia.Media.TextWrapping.Wrap,
+            Margin = new Thickness(0, 0, 0, 15)
+        };
+
+        var yesButton = new Button
+        {
+            Content = "Yes",
+            Width = 80,
+            HorizontalContentAlignment = HorizontalAlignment.Center
+        };
+        yesButton.Click += (_, _) =>
+        {
+            result = true;
+            dialog.Close();
+        };
+
+        var noButton = new Button
+        {
+            Content = "No",
+            Width = 80,
+            HorizontalContentAlignment = HorizontalAlignment.Center
+        };
+        noButton.Click += (_, _) =>
+        {
+            result = false;
+            dialog.Close();
+        };
+
+        var buttonPanel = new StackPanel
+        {
+            Orientation = Orientation.Horizontal,
+            HorizontalAlignment = HorizontalAlignment.Right,
+            Spacing = 10,
+            Children = { yesButton, noButton }
+        };
+
+        dialog.Content = new StackPanel
+        {
+            Margin = new Thickness(20),
+            Spacing = 5,
+            Children = { messageBlock, buttonPanel }
+        };
+
+        await dialog.ShowDialog(parent);
+        return result;
+    }
+
+    /// <summary>
+    /// Shows a simple message dialog with an OK button.
+    /// </summary>
+    /// <param name="parent">The parent window.</param>
+    /// <param name="title">Dialog title.</param>
+    /// <param name="message">Message to display.</param>
+    public static async Task ShowMessageAsync(Window parent, string title, string message)
+    {
+        var dialog = new Window
+        {
+            Title = title,
+            Width = 420,
+            Height = 180,
+            WindowStartupLocation = WindowStartupLocation.CenterOwner,
+            CanResize = false,
+            ShowInTaskbar = false
+        };
+
+        var messageBlock = new TextBlock
+        {
+            Text = message,
+            TextWrapping = Avalonia.Media.TextWrapping.Wrap,
+            Margin = new Thickness(0, 0, 0, 15)
+        };
+
+        var okButton = new Button
+        {
+            Content = "OK",
+            Width = 80,
+            HorizontalAlignment = HorizontalAlignment.Right,
+            HorizontalContentAlignment = HorizontalAlignment.Center
+        };
+        okButton.Click += (_, _) => dialog.Close();
+
+        dialog.Content = new StackPanel
+        {
+            Margin = new Thickness(20),
+            Spacing = 5,
+            Children = { messageBlock, okButton }
+        };
+
+        await dialog.ShowDialog(parent);
+    }
+
+    /// <summary>
+    /// Shows an input dialog with a text box, OK and Cancel buttons.
+    /// </summary>
+    /// <param name="parent">The parent window.</param>
+    /// <param name="title">Dialog title.</param>
+    /// <param name="prompt">Prompt text shown above the input.</param>
+    /// <param name="defaultValue">Default value in the text box.</param>
+    /// <returns>The entered string, or null if cancelled.</returns>
+    public static async Task<string?> InputAsync(Window parent, string title, string prompt, string defaultValue = "")
+    {
+        string? result = null;
+
+        var dialog = new Window
+        {
+            Title = title,
+            Width = 450,
+            Height = 180,
+            WindowStartupLocation = WindowStartupLocation.CenterOwner,
+            CanResize = false,
+            ShowInTaskbar = false
+        };
+
+        var promptBlock = new TextBlock
+        {
+            Text = prompt,
+            Margin = new Thickness(0, 0, 0, 5)
+        };
+
+        var textBox = new TextBox
+        {
+            Text = defaultValue,
+            Margin = new Thickness(0, 0, 0, 10)
+        };
+
+        var okButton = new Button
+        {
+            Content = "OK",
+            Width = 80,
+            HorizontalContentAlignment = HorizontalAlignment.Center
+        };
+        okButton.Click += (_, _) =>
+        {
+            result = textBox.Text;
+            dialog.Close();
+        };
+
+        var cancelButton = new Button
+        {
+            Content = "Cancel",
+            Width = 80,
+            HorizontalContentAlignment = HorizontalAlignment.Center
+        };
+        cancelButton.Click += (_, _) =>
+        {
+            result = null;
+            dialog.Close();
+        };
+
+        var buttonPanel = new StackPanel
+        {
+            Orientation = Orientation.Horizontal,
+            HorizontalAlignment = HorizontalAlignment.Right,
+            Spacing = 10,
+            Children = { okButton, cancelButton }
+        };
+
+        dialog.Content = new StackPanel
+        {
+            Margin = new Thickness(20),
+            Spacing = 5,
+            Children = { promptBlock, textBox, buttonPanel }
+        };
+
+        await dialog.ShowDialog(parent);
+        return result;
+    }
+}

GsaEditor/Helpers/HexDumper.cs

@@ -0,0 +1,59 @@
+using System.Text;
+
+namespace GsaEditor.Helpers;
+
+/// <summary>
+/// Produces a classic hex + ASCII dump string from a byte array.
+/// </summary>
+public static class HexDumper
+{
+    /// <summary>
+    /// Formats a byte array as a hex dump with offset, hex values, and printable ASCII characters.
+    /// </summary>
+    /// <param name="data">The data to dump.</param>
+    /// <param name="maxBytes">Maximum number of bytes to include in the dump.</param>
+    /// <returns>A formatted hex dump string.</returns>
+    public static string Dump(byte[] data, int maxBytes = 512)
+    {
+        var sb = new StringBuilder();
+        int length = Math.Min(data.Length, maxBytes);
+        const int bytesPerLine = 16;
+
+        for (int offset = 0; offset < length; offset += bytesPerLine)
+        {
+            // Offset column
+            sb.Append($"{offset:X8}  ");
+
+            int lineLen = Math.Min(bytesPerLine, length - offset);
+
+            // Hex columns
+            for (int i = 0; i < bytesPerLine; i++)
+            {
+                if (i < lineLen)
+                    sb.Append($"{data[offset + i]:X2} ");
+                else
+                    sb.Append("   ");
+
+                if (i == 7) sb.Append(' ');
+            }
+
+            sb.Append(' ');
+
+            // ASCII column
+            for (int i = 0; i < lineLen; i++)
+            {
+                byte b = data[offset + i];
+                sb.Append(b >= 0x20 && b < 0x7F ? (char)b : '.');
+            }
+
+            sb.AppendLine();
+        }
+
+        if (data.Length > maxBytes)
+        {
+            sb.AppendLine($"... ({data.Length - maxBytes} more bytes)");
+        }
+
+        return sb.ToString();
+    }
+}

GsaEditor/Program.cs

@@ -0,0 +1,17 @@
+using Avalonia;
+using System;
+
+namespace GsaEditor;
+
+sealed class Program
+{
+    [STAThread]
+    public static void Main(string[] args) => BuildAvaloniaApp()
+        .StartWithClassicDesktopLifetime(args);
+
+    public static AppBuilder BuildAvaloniaApp()
+        => AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+            .WithInterFont()
+            .LogToTrace();
+}

GsaEditor/ViewModels/EntryTreeNodeViewModel.cs

@@ -0,0 +1,40 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using GsaEditor.Core.Models;
+
+namespace GsaEditor.ViewModels;
+
+/// <summary>
+/// Represents a node in the archive tree view.
+/// Can be a folder (with children) or a leaf file node (with an associated <see cref="GsaEntry"/>).
+/// </summary>
+public partial class EntryTreeNodeViewModel : ViewModelBase
+{
+    [ObservableProperty]
+    private string _name = string.Empty;
+
+    /// <summary>
+    /// Full relative path of this node within the archive (using '/' separator).
+    /// </summary>
+    public string FullPath { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether this node represents a folder (true) or a file (false).
+    /// </summary>
+    public bool IsFolder { get; set; }
+
+    /// <summary>
+    /// Whether this node represents a file.
+    /// </summary>
+    public bool IsFile => !IsFolder;
+
+    /// <summary>
+    /// The archive entry this node represents. Null for folder nodes.
+    /// </summary>
+    public GsaEntry? Entry { get; set; }
+
+    /// <summary>
+    /// Child nodes (sub-folders and files within this folder).
+    /// </summary>
+    public ObservableCollection<EntryTreeNodeViewModel> Children { get; } = new();
+}

GsaEditor/ViewModels/EntryViewModel.cs

@@ -0,0 +1,93 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using GsaEditor.Core.Models;
+
+namespace GsaEditor.ViewModels;
+
+/// <summary>
+/// Wraps a <see cref="GsaEntry"/> for display in the details panel.
+/// </summary>
+public partial class EntryViewModel : ViewModelBase
+{
+    private readonly GsaEntry _entry;
+
+    [ObservableProperty]
+    private string _alias = string.Empty;
+
+    [ObservableProperty]
+    private bool _isCompressed;
+
+    /// <summary>
+    /// Callback invoked when entry data is modified (compression toggle, alias change).
+    /// </summary>
+    public Action? OnModified { get; set; }
+
+    public EntryViewModel(GsaEntry entry)
+    {
+        _entry = entry;
+        _alias = entry.Alias;
+        _isCompressed = entry.IsCompressed;
+    }
+
+    /// <summary>
+    /// The underlying <see cref="GsaEntry"/>.
+    /// </summary>
+    public GsaEntry Entry => _entry;
+
+    /// <summary>
+    /// Original (decompressed) file size in bytes.
+    /// </summary>
+    public uint OriginalSize => _entry.OriginalLength;
+
+    /// <summary>
+    /// Compressed file size in bytes.
+    /// </summary>
+    public uint CompressedSize => _entry.CompressedLength;
+
+    /// <summary>
+    /// Compression ratio as a percentage (0–100). Higher means more compression.
+    /// </summary>
+    public string CompressionRatio => OriginalSize > 0
+        ? $"{(1.0 - (double)CompressedSize / OriginalSize) * 100.0:F1}%"
+        : "0.0%";
+
+    /// <summary>
+    /// Human-readable original size string.
+    /// </summary>
+    public string OriginalSizeText => FormatSize(OriginalSize);
+
+    /// <summary>
+    /// Human-readable compressed size string.
+    /// </summary>
+    public string CompressedSizeText => FormatSize(CompressedSize);
+
+    partial void OnAliasChanged(string value)
+    {
+        if (_entry.Alias != value)
+        {
+            _entry.Alias = value;
+            OnModified?.Invoke();
+        }
+    }
+
+    partial void OnIsCompressedChanged(bool value)
+    {
+        if (_entry.IsCompressed != value)
+        {
+            var decompressed = _entry.GetDecompressedData();
+            _entry.SetData(decompressed, value);
+            OnPropertyChanged(nameof(OriginalSize));
+            OnPropertyChanged(nameof(CompressedSize));
+            OnPropertyChanged(nameof(CompressionRatio));
+            OnPropertyChanged(nameof(OriginalSizeText));
+            OnPropertyChanged(nameof(CompressedSizeText));
+            OnModified?.Invoke();
+        }
+    }
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes < 1024) return $"{bytes} B";
+        if (bytes < 1024 * 1024) return $"{bytes / 1024.0:F1} KB";
+        return $"{bytes / (1024.0 * 1024.0):F1} MB";
+    }
+}

GsaEditor/ViewModels/MainWindowViewModel.cs

@@ -0,0 +1,726 @@
+using System.Collections.ObjectModel;
+using System.Text;
+using Avalonia.Controls;
+using Avalonia.Media.Imaging;
+using Avalonia.Platform.Storage;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using GsaEditor.Core.Compression;
+using GsaEditor.Core.IO;
+using GsaEditor.Core.Models;
+using GsaEditor.Helpers;
+
+namespace GsaEditor.ViewModels;
+
+public partial class MainWindowViewModel : ViewModelBase
+{
+    private static readonly HashSet<string> TextExtensions = new(StringComparer.OrdinalIgnoreCase)
+    {
+        ".txt", ".nml", ".xml", ".json", ".csv", ".ini", ".cfg", ".log", ".nut"
+    };
+
+    private static readonly HashSet<string> ImageExtensions = new(StringComparer.OrdinalIgnoreCase)
+    {
+        ".png", ".jpg", ".jpeg", ".bmp"
+    };
+
+    private static readonly HashSet<string> UnsupportedImageExtensions = new(StringComparer.OrdinalIgnoreCase)
+    {
+        ".tga", ".dds"
+    };
+
+    private static readonly FilePickerFileType GsaFileType = new("GSA Archives")
+    {
+        Patterns = new[] { "*.gsa" }
+    };
+
+    private static readonly FilePickerFileType AllFilesType = new("All Files")
+    {
+        Patterns = new[] { "*" }
+    };
+
+    private Window? _window;
+    private GsaArchive? _archive;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(Title))]
+    [NotifyPropertyChangedFor(nameof(StatusArchivePath))]
+    [NotifyPropertyChangedFor(nameof(HasArchive))]
+    private string? _archivePath;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(Title))]
+    private bool _isDirty;
+
+    [ObservableProperty]
+    private bool _isLoading;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(HasSelectedFile))]
+    [NotifyPropertyChangedFor(nameof(HasSelectedFolder))]
+    [NotifyPropertyChangedFor(nameof(HasSelectedEntry))]
+    private EntryTreeNodeViewModel? _selectedNode;
+
+    [ObservableProperty]
+    private EntryViewModel? _selectedEntry;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(IsTextPreview))]
+    [NotifyPropertyChangedFor(nameof(IsImagePreview))]
+    [NotifyPropertyChangedFor(nameof(IsHexPreview))]
+    [NotifyPropertyChangedFor(nameof(HasPreview))]
+    private PreviewMode _previewMode = PreviewMode.None;
+
+    [ObservableProperty]
+    private string? _previewText;
+
+    [ObservableProperty]
+    private Bitmap? _previewImage;
+
+    [ObservableProperty]
+    private string? _hexDumpText;
+
+    [ObservableProperty]
+    private bool _isEditingText;
+
+    public ObservableCollection<EntryTreeNodeViewModel> TreeRoots { get; } = new();
+
+    // --- Derived properties ---
+
+    public string Title => ArchivePath != null
+        ? $"GsaEditor - {Path.GetFileName(ArchivePath)}{(IsDirty ? " *" : "")}"
+        : "GsaEditor";
+
+    public bool HasArchive => _archive != null;
+    public bool HasSelectedEntry => SelectedNode?.Entry != null;
+    public bool HasSelectedFile => SelectedNode != null && !SelectedNode.IsFolder;
+    public bool HasSelectedFolder => SelectedNode != null && SelectedNode.IsFolder;
+    public bool IsTextPreview => PreviewMode == PreviewMode.Text;
+    public bool IsImagePreview => PreviewMode == PreviewMode.Image;
+    public bool IsHexPreview => PreviewMode == PreviewMode.HexDump;
+    public bool HasPreview => PreviewMode != PreviewMode.None;
+
+    // --- Status bar ---
+
+    public string StatusArchivePath => ArchivePath ?? "No archive loaded";
+
+    public string StatusEntryCount => _archive != null
+        ? $"{_archive.Entries.Count} entries"
+        : "";
+
+    public string StatusSizeInfo
+    {
+        get
+        {
+            if (_archive == null) return "";
+            long totalOriginal = _archive.Entries.Sum(e => (long)e.OriginalLength);
+            long totalCompressed = _archive.Entries.Sum(e => (long)e.CompressedLength);
+            return $"Total: {FormatSize(totalOriginal)} / Compressed: {FormatSize(totalCompressed)}";
+        }
+    }
+
+    /// <summary>
+    /// Sets the parent window reference for dialog display.
+    /// </summary>
+    public void SetWindow(Window window)
+    {
+        _window = window;
+    }
+
+    // =========================================================================
+    // Selection changed
+    // =========================================================================
+
+    partial void OnSelectedNodeChanged(EntryTreeNodeViewModel? value)
+    {
+        IsEditingText = false;
+
+        if (value?.Entry != null)
+        {
+            var entryVm = new EntryViewModel(value.Entry);
+            entryVm.OnModified = () =>
+            {
+                IsDirty = true;
+                NotifyStatusChanged();
+            };
+            SelectedEntry = entryVm;
+            UpdatePreview(value.Entry);
+        }
+        else
+        {
+            SelectedEntry = null;
+            ClearPreview();
+        }
+    }
+
+    private void UpdatePreview(GsaEntry entry)
+    {
+        var ext = Path.GetExtension(entry.Alias).ToLowerInvariant();
+
+        if (TextExtensions.Contains(ext))
+        {
+            PreviewMode = PreviewMode.Text;
+            var data = entry.GetDecompressedData();
+            PreviewText = Encoding.UTF8.GetString(data);
+            PreviewImage?.Dispose();
+            PreviewImage = null;
+            HexDumpText = null;
+        }
+        else if (ImageExtensions.Contains(ext))
+        {
+            try
+            {
+                var data = entry.GetDecompressedData();
+                using var ms = new MemoryStream(data);
+                PreviewImage?.Dispose();
+                PreviewImage = new Bitmap(ms);
+                PreviewMode = PreviewMode.Image;
+            }
+            catch
+            {
+                PreviewImage = null;
+                PreviewMode = PreviewMode.HexDump;
+                HexDumpText = "Preview not available for this image.";
+            }
+            PreviewText = null;
+        }
+        else if (UnsupportedImageExtensions.Contains(ext))
+        {
+            PreviewMode = PreviewMode.HexDump;
+            HexDumpText = $"Preview not available for {ext.ToUpperInvariant()} files.";
+            PreviewText = null;
+            PreviewImage?.Dispose();
+            PreviewImage = null;
+        }
+        else
+        {
+            PreviewMode = PreviewMode.HexDump;
+            var data = entry.GetDecompressedData();
+            HexDumpText = HexDumper.Dump(data, 512);
+            PreviewText = null;
+            PreviewImage?.Dispose();
+            PreviewImage = null;
+        }
+    }
+
+    private void ClearPreview()
+    {
+        PreviewMode = PreviewMode.None;
+        PreviewText = null;
+        PreviewImage?.Dispose();
+        PreviewImage = null;
+        HexDumpText = null;
+    }
+
+    // =========================================================================
+    // File menu commands
+    // =========================================================================
+
+    [RelayCommand]
+    private async Task OpenArchive()
+    {
+        if (_window == null) return;
+
+        if (IsDirty)
+        {
+            var confirmed = await Dialogs.ConfirmAsync(_window, "Unsaved Changes",
+                "You have unsaved changes. Open a new archive without saving?");
+            if (!confirmed) return;
+        }
+
+        var files = await _window.StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
+        {
+            Title = "Open GSA Archive",
+            FileTypeFilter = new[] { GsaFileType, AllFilesType },
+            AllowMultiple = false
+        });
+
+        if (files.Count == 0) return;
+
+        var path = files[0].Path.LocalPath;
+        await LoadArchiveAsync(path);
+    }
+
+    private async Task LoadArchiveAsync(string path)
+    {
+        IsLoading = true;
+        ClearPreview();
+        SelectedEntry = null;
+        SelectedNode = null;
+
+        try
+        {
+            var archive = await Task.Run(() => GsaReader.Read(path));
+            _archive = archive;
+            ArchivePath = path;
+            IsDirty = false;
+            BuildTree();
+            NotifyStatusChanged();
+        }
+        catch (Exception ex)
+        {
+            if (_window != null)
+                await Dialogs.ShowMessageAsync(_window, "Error", $"Failed to open archive:\n{ex.Message}");
+        }
+        finally
+        {
+            IsLoading = false;
+        }
+    }
+
+    [RelayCommand]
+    private async Task Save()
+    {
+        if (_archive == null || _window == null) return;
+
+        if (string.IsNullOrEmpty(ArchivePath))
+        {
+            await SaveAs();
+            return;
+        }
+
+        try
+        {
+            await Task.Run(() => GsaWriter.Write(_archive, ArchivePath!));
+
+            // Generate .idx alongside
+            var idxPath = Path.ChangeExtension(ArchivePath, ".idx");
+            await Task.Run(() => GsaIndexWriter.Write(_archive, idxPath));
+
+            IsDirty = false;
+        }
+        catch (Exception ex)
+        {
+            await Dialogs.ShowMessageAsync(_window, "Error", $"Failed to save archive:\n{ex.Message}");
+        }
+    }
+
+    [RelayCommand]
+    private async Task SaveAs()
+    {
+        if (_archive == null || _window == null) return;
+
+        var file = await _window.StorageProvider.SaveFilePickerAsync(new FilePickerSaveOptions
+        {
+            Title = "Save GSA Archive As",
+            FileTypeChoices = new[] { GsaFileType },
+            DefaultExtension = "gsa",
+            SuggestedFileName = ArchivePath != null ? Path.GetFileName(ArchivePath) : "archive.gsa"
+        });
+
+        if (file == null) return;
+
+        var path = file.Path.LocalPath;
+
+        try
+        {
+            await Task.Run(() => GsaWriter.Write(_archive, path));
+
+            var idxPath = Path.ChangeExtension(path, ".idx");
+            await Task.Run(() => GsaIndexWriter.Write(_archive, idxPath));
+
+            ArchivePath = path;
+            IsDirty = false;
+        }
+        catch (Exception ex)
+        {
+            await Dialogs.ShowMessageAsync(_window, "Error", $"Failed to save archive:\n{ex.Message}");
+        }
+    }
+
+    [RelayCommand]
+    private async Task CloseArchive()
+    {
+        if (_window == null) return;
+
+        if (IsDirty)
+        {
+            var confirmed = await Dialogs.ConfirmAsync(_window, "Unsaved Changes",
+                "You have unsaved changes. Close without saving?");
+            if (!confirmed) return;
+        }
+
+        _archive = null;
+        ArchivePath = null;
+        IsDirty = false;
+        TreeRoots.Clear();
+        SelectedEntry = null;
+        SelectedNode = null;
+        ClearPreview();
+        NotifyStatusChanged();
+    }
+
+    [RelayCommand]
+    private void Exit()
+    {
+        _window?.Close();
+    }
+
+    // =========================================================================
+    // Edit menu commands
+    // =========================================================================
+
+    [RelayCommand]
+    private async Task AddFiles()
+    {
+        if (_archive == null || _window == null) return;
+
+        var files = await _window.StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
+        {
+            Title = "Add Files to Archive",
+            AllowMultiple = true,
+            FileTypeFilter = new[] { AllFilesType }
+        });
+
+        if (files.Count == 0) return;
+
+        string prefix = "";
+        if (SelectedNode != null && SelectedNode.IsFolder)
+        {
+            prefix = SelectedNode.FullPath;
+            if (!prefix.EndsWith("/")) prefix += "/";
+        }
+
+        foreach (var file in files)
+        {
+            var filePath = file.Path.LocalPath;
+            var fileName = Path.GetFileName(filePath);
+            var alias = prefix + fileName;
+
+            var data = await Task.Run(() => File.ReadAllBytes(filePath));
+            var entry = new GsaEntry();
+            entry.Alias = alias;
+            entry.SetData(data, compress: true);
+
+            _archive.Entries.Add(entry);
+        }
+
+        IsDirty = true;
+        BuildTree();
+        NotifyStatusChanged();
+    }
+
+    [RelayCommand]
+    private async Task ExtractAll()
+    {
+        if (_archive == null || _window == null) return;
+
+        var folders = await _window.StorageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions
+        {
+            Title = "Select Extraction Folder"
+        });
+
+        if (folders.Count == 0) return;
+
+        var basePath = folders[0].Path.LocalPath;
+
+        try
+        {
+            await Task.Run(() =>
+            {
+                foreach (var entry in _archive.Entries)
+                {
+                    var outputPath = Path.Combine(basePath, entry.Alias.Replace('/', Path.DirectorySeparatorChar));
+                    var dir = Path.GetDirectoryName(outputPath);
+                    if (dir != null) Directory.CreateDirectory(dir);
+
+                    var data = entry.GetDecompressedData();
+                    File.WriteAllBytes(outputPath, data);
+                }
+            });
+
+            await Dialogs.ShowMessageAsync(_window, "Extract All",
+                $"Successfully extracted {_archive.Entries.Count} files to:\n{basePath}");
+        }
+        catch (Exception ex)
+        {
+            await Dialogs.ShowMessageAsync(_window, "Error", $"Extraction failed:\n{ex.Message}");
+        }
+    }
+
+    [RelayCommand]
+    private async Task Repack()
+    {
+        if (_archive == null || _window == null) return;
+
+        IsLoading = true;
+        try
+        {
+            await Task.Run(() =>
+            {
+                foreach (var entry in _archive.Entries)
+                {
+                    var decompressed = entry.GetDecompressedData();
+                    entry.SetData(decompressed, entry.IsCompressed);
+                }
+            });
+
+            IsDirty = true;
+            BuildTree();
+            NotifyStatusChanged();
+
+            if (SelectedNode?.Entry != null)
+            {
+                var entryVm = new EntryViewModel(SelectedNode.Entry);
+                entryVm.OnModified = () => { IsDirty = true; NotifyStatusChanged(); };
+                SelectedEntry = entryVm;
+            }
+        }
+        finally
+        {
+            IsLoading = false;
+        }
+    }
+
+    // =========================================================================
+    // Context menu commands
+    // =========================================================================
+
+    [RelayCommand]
+    private async Task ExtractEntry()
+    {
+        if (SelectedNode?.Entry == null || _window == null) return;
+
+        var entry = SelectedNode.Entry;
+        var file = await _window.StorageProvider.SaveFilePickerAsync(new FilePickerSaveOptions
+        {
+            Title = "Extract File",
+            SuggestedFileName = Path.GetFileName(entry.Alias),
+            FileTypeChoices = new[] { AllFilesType }
+        });
+
+        if (file == null) return;
+
+        try
+        {
+            var data = entry.GetDecompressedData();
+            var path = file.Path.LocalPath;
+            await File.WriteAllBytesAsync(path, data);
+        }
+        catch (Exception ex)
+        {
+            await Dialogs.ShowMessageAsync(_window, "Error", $"Extraction failed:\n{ex.Message}");
+        }
+    }
+
+    [RelayCommand]
+    private async Task ReplaceEntry()
+    {
+        if (SelectedNode?.Entry == null || _archive == null || _window == null) return;
+
+        var files = await _window.StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
+        {
+            Title = "Replace Entry With",
+            AllowMultiple = false,
+            FileTypeFilter = new[] { AllFilesType }
+        });
+
+        if (files.Count == 0) return;
+
+        var filePath = files[0].Path.LocalPath;
+        var data = await Task.Run(() => File.ReadAllBytes(filePath));
+
+        var entry = SelectedNode.Entry;
+        entry.SetData(data, entry.IsCompressed);
+
+        IsDirty = true;
+        NotifyStatusChanged();
+
+        // Refresh the selected entry view
+        var entryVm = new EntryViewModel(entry);
+        entryVm.OnModified = () => { IsDirty = true; NotifyStatusChanged(); };
+        SelectedEntry = entryVm;
+        UpdatePreview(entry);
+    }
+
+    [RelayCommand]
+    private void DeleteEntry()
+    {
+        if (SelectedNode?.Entry == null || _archive == null) return;
+
+        _archive.Entries.Remove(SelectedNode.Entry);
+        IsDirty = true;
+        SelectedNode = null;
+        SelectedEntry = null;
+        ClearPreview();
+        BuildTree();
+        NotifyStatusChanged();
+    }
+
+    [RelayCommand]
+    private async Task RenameEntry()
+    {
+        if (SelectedNode?.Entry == null || _window == null) return;
+
+        var entry = SelectedNode.Entry;
+        var result = await Dialogs.InputAsync(_window, "Rename Entry", "New alias:", entry.Alias);
+
+        if (result != null && result != entry.Alias && result.Length > 0)
+        {
+            entry.Alias = result;
+            IsDirty = true;
+            BuildTree();
+            NotifyStatusChanged();
+
+            if (SelectedEntry != null)
+            {
+                var entryVm = new EntryViewModel(entry);
+                entryVm.OnModified = () => { IsDirty = true; NotifyStatusChanged(); };
+                SelectedEntry = entryVm;
+            }
+        }
+    }
+
+    [RelayCommand]
+    private async Task ExtractFolder()
+    {
+        if (SelectedNode == null || !SelectedNode.IsFolder || _archive == null || _window == null) return;
+
+        var folders = await _window.StorageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions
+        {
+            Title = "Select Extraction Folder"
+        });
+
+        if (folders.Count == 0) return;
+
+        var basePath = folders[0].Path.LocalPath;
+        var prefix = SelectedNode.FullPath;
+        if (!prefix.EndsWith("/")) prefix += "/";
+
+        try
+        {
+            var matching = _archive.Entries.Where(e => e.Alias.StartsWith(prefix, StringComparison.Ordinal)).ToList();
+
+            await Task.Run(() =>
+            {
+                foreach (var entry in matching)
+                {
+                    var relativePath = entry.Alias.Substring(prefix.Length);
+                    var outputPath = Path.Combine(basePath, relativePath.Replace('/', Path.DirectorySeparatorChar));
+                    var dir = Path.GetDirectoryName(outputPath);
+                    if (dir != null) Directory.CreateDirectory(dir);
+
+                    var data = entry.GetDecompressedData();
+                    File.WriteAllBytes(outputPath, data);
+                }
+            });
+
+            await Dialogs.ShowMessageAsync(_window, "Extract Folder",
+                $"Successfully extracted files to:\n{basePath}");
+        }
+        catch (Exception ex)
+        {
+            await Dialogs.ShowMessageAsync(_window, "Error", $"Extraction failed:\n{ex.Message}");
+        }
+    }
+
+    // =========================================================================
+    // Text editing commands
+    // =========================================================================
+
+    [RelayCommand]
+    private void StartEdit()
+    {
+        IsEditingText = true;
+    }
+
+    [RelayCommand]
+    private void SaveEdit()
+    {
+        if (SelectedNode?.Entry == null || PreviewText == null) return;
+
+        var entry = SelectedNode.Entry;
+        var newData = Encoding.UTF8.GetBytes(PreviewText);
+        entry.SetData(newData, entry.IsCompressed);
+
+        IsDirty = true;
+        IsEditingText = false;
+
+        var entryVm = new EntryViewModel(entry);
+        entryVm.OnModified = () => { IsDirty = true; NotifyStatusChanged(); };
+        SelectedEntry = entryVm;
+        NotifyStatusChanged();
+    }
+
+    [RelayCommand]
+    private void CancelEdit()
+    {
+        IsEditingText = false;
+        if (SelectedNode?.Entry != null)
+        {
+            PreviewText = Encoding.UTF8.GetString(SelectedNode.Entry.GetDecompressedData());
+        }
+    }
+
+    // =========================================================================
+    // About
+    // =========================================================================
+
+    [RelayCommand]
+    private async Task ShowAbout()
+    {
+        if (_window == null) return;
+        await Dialogs.ShowMessageAsync(_window, "About GsaEditor",
+            "GsaEditor v1.0\n\nGSA Archive Viewer & Editor\nBuilt with Avalonia UI");
+    }
+
+    // =========================================================================
+    // Tree building
+    // =========================================================================
+
+    private void BuildTree()
+    {
+        TreeRoots.Clear();
+        if (_archive == null) return;
+
+        foreach (var entry in _archive.Entries)
+        {
+            var parts = entry.Alias.Split('/');
+            var currentLevel = TreeRoots;
+            var currentPath = "";
+
+            for (int i = 0; i < parts.Length; i++)
+            {
+                var part = parts[i];
+                currentPath = i == 0 ? part : currentPath + "/" + part;
+                bool isLeaf = (i == parts.Length - 1);
+
+                var existing = currentLevel.FirstOrDefault(n => n.Name == part);
+                if (existing == null)
+                {
+                    existing = new EntryTreeNodeViewModel
+                    {
+                        Name = part,
+                        FullPath = currentPath,
+                        IsFolder = !isLeaf,
+                        Entry = isLeaf ? entry : null
+                    };
+                    currentLevel.Add(existing);
+                }
+
+                if (!isLeaf)
+                {
+                    currentLevel = existing.Children;
+                }
+            }
+        }
+    }
+
+    // =========================================================================
+    // Helpers
+    // =========================================================================
+
+    private void NotifyStatusChanged()
+    {
+        OnPropertyChanged(nameof(StatusEntryCount));
+        OnPropertyChanged(nameof(StatusSizeInfo));
+        OnPropertyChanged(nameof(HasArchive));
+    }
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes < 1024) return $"{bytes} B";
+        if (bytes < 1024 * 1024) return $"{bytes / 1024.0:F1} KB";
+        return $"{bytes / (1024.0 * 1024.0):F1} MB";
+    }
+}

GsaEditor/ViewModels/PreviewMode.cs

@@ -0,0 +1,12 @@
+namespace GsaEditor.ViewModels;
+
+/// <summary>
+/// Determines which preview panel to show for the selected archive entry.
+/// </summary>
+public enum PreviewMode
+{
+    None,
+    Text,
+    Image,
+    HexDump
+}

GsaEditor/ViewModels/ViewModelBase.cs

@@ -0,0 +1,7 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace GsaEditor.ViewModels;
+
+public class ViewModelBase : ObservableObject
+{
+}

GsaEditor/Views/MainWindow.axaml

@@ -0,0 +1,240 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:GsaEditor.ViewModels"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        mc:Ignorable="d" d:DesignWidth="1100" d:DesignHeight="700"
+        x:Class="GsaEditor.Views.MainWindow"
+        x:CompileBindings="False"
+        Title="{Binding Title}"
+        Width="1100" Height="700"
+        MinWidth="800" MinHeight="500">
+
+    <Design.DataContext>
+        <vm:MainWindowViewModel/>
+    </Design.DataContext>
+
+    <DockPanel>
+
+        <!-- ============================================================ -->
+        <!-- Menu Bar                                                      -->
+        <!-- ============================================================ -->
+        <Menu DockPanel.Dock="Top">
+            <MenuItem Header="_File">
+                <MenuItem Header="_Open Archive..." Command="{Binding OpenArchiveCommand}"
+                          InputGesture="Ctrl+O"/>
+                <MenuItem Header="_Save" Command="{Binding SaveCommand}"
+                          InputGesture="Ctrl+S"
+                          IsEnabled="{Binding HasArchive}"/>
+                <MenuItem Header="Save _As..." Command="{Binding SaveAsCommand}"
+                          InputGesture="Ctrl+Shift+S"
+                          IsEnabled="{Binding HasArchive}"/>
+                <Separator/>
+                <MenuItem Header="_Close" Command="{Binding CloseArchiveCommand}"
+                          IsEnabled="{Binding HasArchive}"/>
+                <MenuItem Header="E_xit" Command="{Binding ExitCommand}"
+                          InputGesture="Alt+F4"/>
+            </MenuItem>
+            <MenuItem Header="_Edit">
+                <MenuItem Header="_Add File(s)..." Command="{Binding AddFilesCommand}"
+                          IsEnabled="{Binding HasArchive}"/>
+                <MenuItem Header="_Extract All..." Command="{Binding ExtractAllCommand}"
+                          IsEnabled="{Binding HasArchive}"/>
+                <Separator/>
+                <MenuItem Header="_Repack" Command="{Binding RepackCommand}"
+                          IsEnabled="{Binding HasArchive}"/>
+            </MenuItem>
+            <MenuItem Header="_About">
+                <MenuItem Header="About GsaEditor" Command="{Binding ShowAboutCommand}"/>
+            </MenuItem>
+        </Menu>
+
+        <!-- ============================================================ -->
+        <!-- Status Bar                                                    -->
+        <!-- ============================================================ -->
+        <Border DockPanel.Dock="Bottom" Padding="8,4"
+                BorderThickness="0,1,0,0" BorderBrush="#CCCCCC"
+                Background="#F5F5F5">
+            <Grid ColumnDefinitions="*,Auto,Auto">
+                <TextBlock Grid.Column="0" Text="{Binding StatusArchivePath}"
+                           VerticalAlignment="Center" FontSize="12"
+                           Foreground="#555555"/>
+                <TextBlock Grid.Column="1" Text="{Binding StatusEntryCount}"
+                           VerticalAlignment="Center" FontSize="12"
+                           Foreground="#555555" Margin="20,0,0,0"/>
+                <TextBlock Grid.Column="2" Text="{Binding StatusSizeInfo}"
+                           VerticalAlignment="Center" FontSize="12"
+                           Foreground="#555555" Margin="20,0,0,0"/>
+            </Grid>
+        </Border>
+
+        <!-- ============================================================ -->
+        <!-- Loading Overlay                                               -->
+        <!-- ============================================================ -->
+        <Border IsVisible="{Binding IsLoading}" Background="#80000000"
+                ZIndex="100" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
+            <TextBlock Text="Loading..." FontSize="20"
+                       Foreground="White"
+                       HorizontalAlignment="Center"
+                       VerticalAlignment="Center"/>
+        </Border>
+
+        <!-- ============================================================ -->
+        <!-- Main Content: Left Tree + Right Details                       -->
+        <!-- ============================================================ -->
+        <Grid ColumnDefinitions="300,5,*">
+
+            <!-- ======================================================== -->
+            <!-- Left Panel: Archive Tree                                  -->
+            <!-- ======================================================== -->
+            <Border Grid.Column="0" BorderThickness="0,0,1,0" BorderBrush="#DDDDDD">
+                <DockPanel>
+                    <TextBlock DockPanel.Dock="Top" Text="Archive Contents"
+                               FontWeight="SemiBold" Padding="8,6" FontSize="13"
+                               Background="#EEEEEE"/>
+                    <TreeView Name="ArchiveTree"
+                              ItemsSource="{Binding TreeRoots}"
+                              SelectionChanged="TreeView_SelectionChanged">
+
+                        <TreeView.ContextMenu>
+                            <ContextMenu>
+                                <!-- File node operations -->
+                                <MenuItem Header="Extract" Command="{Binding ExtractEntryCommand}"
+                                          IsVisible="{Binding HasSelectedFile}"/>
+                                <MenuItem Header="Replace" Command="{Binding ReplaceEntryCommand}"
+                                          IsVisible="{Binding HasSelectedFile}"/>
+                                <MenuItem Header="Delete" Command="{Binding DeleteEntryCommand}"
+                                          IsVisible="{Binding HasSelectedFile}"/>
+                                <MenuItem Header="Rename" Command="{Binding RenameEntryCommand}"
+                                          IsVisible="{Binding HasSelectedFile}"/>
+                                <!-- Folder node operations -->
+                                <MenuItem Header="Extract Folder" Command="{Binding ExtractFolderCommand}"
+                                          IsVisible="{Binding HasSelectedFolder}"/>
+                                <!-- Always available -->
+                                <Separator/>
+                                <MenuItem Header="Add File(s)..." Command="{Binding AddFilesCommand}"
+                                          IsEnabled="{Binding HasArchive}"/>
+                            </ContextMenu>
+                        </TreeView.ContextMenu>
+
+                        <TreeView.ItemTemplate>
+                            <TreeDataTemplate ItemsSource="{Binding Children}">
+                                <StackPanel Orientation="Horizontal" Spacing="5">
+                                    <TextBlock Text="📁" IsVisible="{Binding IsFolder}"/>
+                                    <TextBlock Text="📄" IsVisible="{Binding IsFile}"/>
+                                    <TextBlock Text="{Binding Name}"/>
+                                </StackPanel>
+                            </TreeDataTemplate>
+                        </TreeView.ItemTemplate>
+                    </TreeView>
+                </DockPanel>
+            </Border>
+
+            <!-- Splitter -->
+            <GridSplitter Grid.Column="1" ResizeDirection="Columns"
+                          Background="#CCCCCC"/>
+
+            <!-- ======================================================== -->
+            <!-- Right Panel: Details & Preview                            -->
+            <!-- ======================================================== -->
+            <Grid Grid.Column="2" RowDefinitions="Auto,*">
+
+                <!-- ================================================== -->
+                <!-- Top Bar: Entry Info                                 -->
+                <!-- ================================================== -->
+                <Border Grid.Row="0" Padding="10,8"
+                        Background="#FAFAFA"
+                        BorderThickness="0,0,0,1" BorderBrush="#DDDDDD"
+                        IsVisible="{Binding HasSelectedEntry}">
+                    <Grid RowDefinitions="Auto,Auto">
+                        <!-- Row 0: Alias -->
+                        <Grid Grid.Row="0" ColumnDefinitions="Auto,*" Margin="0,0,0,6">
+                            <TextBlock Grid.Column="0" Text="Alias:"
+                                       VerticalAlignment="Center" Margin="0,0,8,0"
+                                       FontWeight="SemiBold"/>
+                            <TextBox Grid.Column="1"
+                                     Text="{Binding SelectedEntry.Alias, Mode=TwoWay}"
+                                     Watermark="File path in archive"/>
+                        </Grid>
+
+                        <!-- Row 1: Size info + compression toggle -->
+                        <StackPanel Grid.Row="1" Orientation="Horizontal" Spacing="20">
+                            <StackPanel Orientation="Horizontal" Spacing="4">
+                                <TextBlock Text="Size:" FontWeight="SemiBold" VerticalAlignment="Center"/>
+                                <TextBlock Text="{Binding SelectedEntry.OriginalSizeText}" VerticalAlignment="Center"/>
+                            </StackPanel>
+                            <StackPanel Orientation="Horizontal" Spacing="4">
+                                <TextBlock Text="Compressed:" FontWeight="SemiBold" VerticalAlignment="Center"/>
+                                <TextBlock Text="{Binding SelectedEntry.CompressedSizeText}" VerticalAlignment="Center"/>
+                            </StackPanel>
+                            <StackPanel Orientation="Horizontal" Spacing="4">
+                                <TextBlock Text="Ratio:" FontWeight="SemiBold" VerticalAlignment="Center"/>
+                                <TextBlock Text="{Binding SelectedEntry.CompressionRatio}" VerticalAlignment="Center"/>
+                            </StackPanel>
+                            <CheckBox Content="Compressed"
+                                      IsChecked="{Binding SelectedEntry.IsCompressed, Mode=TwoWay}"
+                                      VerticalAlignment="Center"/>
+                        </StackPanel>
+                    </Grid>
+                </Border>
+
+                <!-- ================================================== -->
+                <!-- Content Area: Preview                               -->
+                <!-- ================================================== -->
+                <Panel Grid.Row="1">
+                    <!-- No selection / No archive message -->
+                    <TextBlock Text="Open a GSA archive and select a file to preview."
+                               HorizontalAlignment="Center" VerticalAlignment="Center"
+                               Foreground="#999999" FontSize="14"
+                               IsVisible="{Binding !HasPreview}"/>
+
+                    <!-- Text Preview -->
+                    <DockPanel IsVisible="{Binding IsTextPreview}">
+                        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal"
+                                    Spacing="5" Margin="10,6">
+                            <Button Content="Edit" Command="{Binding StartEditCommand}"
+                                    IsVisible="{Binding !IsEditingText}"/>
+                            <Button Content="Save" Command="{Binding SaveEditCommand}"
+                                    IsVisible="{Binding IsEditingText}"/>
+                            <Button Content="Cancel" Command="{Binding CancelEditCommand}"
+                                    IsVisible="{Binding IsEditingText}"/>
+                        </StackPanel>
+                        <TextBox Text="{Binding PreviewText, Mode=TwoWay}"
+                                 IsReadOnly="{Binding !IsEditingText}"
+                                 FontFamily="Consolas, Courier New, monospace"
+                                 FontSize="13"
+                                 AcceptsReturn="True"
+                                 TextWrapping="NoWrap"
+                                 Margin="10,0,10,10"/>
+                    </DockPanel>
+
+                    <!-- Image Preview -->
+                    <ScrollViewer IsVisible="{Binding IsImagePreview}"
+                                  HorizontalScrollBarVisibility="Auto"
+                                  VerticalScrollBarVisibility="Auto">
+                        <Image Source="{Binding PreviewImage}"
+                               Stretch="Uniform"
+                               MaxWidth="800" MaxHeight="600"
+                               Margin="10"
+                               HorizontalAlignment="Center"
+                               VerticalAlignment="Center"/>
+                    </ScrollViewer>
+
+                    <!-- Hex Dump Preview -->
+                    <TextBox IsVisible="{Binding IsHexPreview}"
+                             Text="{Binding HexDumpText}"
+                             IsReadOnly="True"
+                             FontFamily="Consolas, Courier New, monospace"
+                             FontSize="13"
+                             AcceptsReturn="True"
+                             TextWrapping="NoWrap"
+                             Margin="10"/>
+                </Panel>
+
+            </Grid>
+
+        </Grid>
+
+    </DockPanel>
+
+</Window>

GsaEditor/Views/MainWindow.axaml.cs

@@ -0,0 +1,52 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using GsaEditor.ViewModels;
+
+namespace GsaEditor.Views;
+
+public partial class MainWindow : Window
+{
+    private bool _forceClose;
+
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        if (DataContext is MainWindowViewModel vm)
+        {
+            vm.SetWindow(this);
+        }
+    }
+
+    private void TreeView_SelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm && sender is TreeView tree)
+        {
+            vm.SelectedNode = tree.SelectedItem as EntryTreeNodeViewModel;
+        }
+    }
+
+    protected override async void OnClosing(WindowClosingEventArgs e)
+    {
+        base.OnClosing(e);
+
+        if (_forceClose) return;
+
+        if (DataContext is MainWindowViewModel vm && vm.IsDirty)
+        {
+            e.Cancel = true;
+            var confirmed = await Helpers.Dialogs.ConfirmAsync(this, "Unsaved Changes",
+                "You have unsaved changes. Close without saving?");
+            if (confirmed)
+            {
+                _forceClose = true;
+                Close();
+            }
+        }
+    }
+}

GsaEditor/app.manifest

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
+  <assemblyIdentity version="1.0.0.0" name="GsaEditor.Desktop"/>
+
+  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
+    <application>
+      <!-- Windows 10 and Windows 11 -->
+      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}" />
+    </application>
+  </compatibility>
+</assembly>

GsaEditor/bin/Debug/net8.0/GsaEditor.Core.xml

@@ -0,0 +1,276 @@
+<?xml version="1.0"?>
+<doc>
+    <assembly>
+        <name>GsaEditor.Core</name>
+    </assembly>
+    <members>
+        <member name="T:GsaEditor.Core.Compression.ZlibHelper">
+            <summary>
+            Provides zlib compression and decompression utilities for GSA archive entries.
+            The GSA format stores zlib-wrapped data: 2-byte header (CMF+FLG) + deflate stream + 4-byte Adler-32 checksum.
+            This helper skips the 2-byte zlib header and uses <see cref="T:System.IO.Compression.DeflateStream"/> for the core deflate data.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Decompress(System.Byte[],System.UInt32)">
+            <summary>
+            Decompresses zlib-wrapped data into a byte array of the specified original size.
+            Skips the 2-byte zlib header before feeding data to <see cref="T:System.IO.Compression.DeflateStream"/>.
+            </summary>
+            <param name="compressedData">The zlib-wrapped compressed data (header + deflate + checksum).</param>
+            <param name="originalLength">The expected decompressed size in bytes.</param>
+            <returns>The decompressed byte array.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown when decompression fails or data is corrupt.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.Compress(System.Byte[])">
+            <summary>
+            Compresses data using zlib format: 2-byte header + deflate stream + 4-byte Adler-32 checksum.
+            </summary>
+            <param name="data">The uncompressed data to compress.</param>
+            <returns>The zlib-wrapped compressed byte array.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Compression.ZlibHelper.ComputeAdler32(System.Byte[])">
+            <summary>
+            Computes the Adler-32 checksum of the given data.
+            </summary>
+            <param name="data">The data to checksum.</param>
+            <returns>The 32-bit Adler-32 checksum value.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexEntry">
+            <summary>
+            Represents a single entry parsed from a .idx NML index file.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Id">
+            <summary>
+            The file alias (relative path) of the entry.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Method">
+            <summary>
+            Compression method: 0 = raw, 1 = zlib.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Length">
+            <summary>
+            Original (decompressed) size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.CompressedLength">
+            <summary>
+            Compressed size in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.IO.GsaIndexEntry.Offset">
+            <summary>
+            Byte offset of the data block within the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexReader">
+            <summary>
+            Parses .idx NML index files (XML-compatible format) into a list of <see cref="T:GsaEditor.Core.IO.GsaIndexEntry"/>.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexReader.Read(System.String)">
+            <summary>
+            Reads index entries from the specified .idx file.
+            </summary>
+            <param name="filePath">The path to the .idx file.</param>
+            <returns>A list of parsed index entries.</returns>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaIndexWriter">
+            <summary>
+            Writes a .idx NML index file from a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            The index file is XML-compatible and lists each entry with its alias, compression method,
+            sizes, and data offset for fast lookup without a full sequential scan.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaIndexWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the index file for the given archive to the specified path.
+            </summary>
+            <param name="archive">The archive whose entries will be indexed.</param>
+            <param name="filePath">The output .idx file path.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaReader">
+            <summary>
+            Reads a .gsa binary archive from a stream or file and produces a <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaReader.MAX_ALIAS_LENGTH">
+            <summary>Maximum allowed alias length in characters.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.String)">
+            <summary>
+            Reads a GSA archive from the specified file path.
+            </summary>
+            <param name="filePath">The path to the .gsa archive file.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the file has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.Read(System.IO.Stream)">
+            <summary>
+            Reads a GSA archive from a stream by performing a sequential scan of all entries.
+            </summary>
+            <param name="stream">A readable, seekable stream positioned at the start of the archive.</param>
+            <returns>A fully populated <see cref="T:GsaEditor.Core.Models.GsaArchive"/>.</returns>
+            <exception cref="T:System.IO.InvalidDataException">Thrown if the stream has an invalid magic word.</exception>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.ReadEntry(System.IO.BinaryReader,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Reads a single file entry from the current stream position.
+            </summary>
+            <param name="reader">The binary reader positioned at the start of an entry.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+            <returns>A populated <see cref="T:GsaEditor.Core.Models.GsaEntry"/>, or null if no more entries can be read.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaReader.AlignStream(System.IO.Stream,System.Int32)">
+            <summary>
+            Advances the stream position to the next aligned boundary.
+            </summary>
+            <param name="stream">The stream to align.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.IO.GsaWriter">
+            <summary>
+            Writes a <see cref="T:GsaEditor.Core.Models.GsaArchive"/> to a binary .gsa stream or file.
+            Supports both NARC (legacy) and NARD (enhanced with padding) format variants.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARC">
+            <summary>Magic word for the NARC (legacy) format.</summary>
+        </member>
+        <member name="F:GsaEditor.Core.IO.GsaWriter.MAGIC_NARD">
+            <summary>Magic word for the NARD (enhanced) format.</summary>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.String)">
+            <summary>
+            Writes the archive to the specified file path.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="filePath">The output file path.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.Write(GsaEditor.Core.Models.GsaArchive,System.IO.Stream)">
+            <summary>
+            Writes the archive to the given stream.
+            Each entry's <see cref="P:GsaEditor.Core.Models.GsaEntry.DataOffset"/> is updated to reflect the new position in the output.
+            </summary>
+            <param name="archive">The archive to write.</param>
+            <param name="stream">A writable stream.</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WriteEntry(System.IO.BinaryWriter,GsaEditor.Core.Models.GsaEntry,GsaEditor.Core.Models.GsaArchive)">
+            <summary>
+            Writes a single file entry at the current stream position.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="entry">The entry to write.</param>
+            <param name="archive">The parent archive (used for NARD padding alignment).</param>
+        </member>
+        <member name="M:GsaEditor.Core.IO.GsaWriter.WritePadding(System.IO.BinaryWriter,System.Int32)">
+            <summary>
+            Writes zero-bytes to pad the stream to the next aligned boundary.
+            </summary>
+            <param name="writer">The binary writer.</param>
+            <param name="alignment">The alignment boundary in bytes.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaArchive">
+            <summary>
+            Represents a loaded GSA archive with its global header information and file entries.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Format">
+            <summary>
+            The format variant of this archive (NARC or NARD).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.OffsetPadding">
+            <summary>
+            (NARD only) Byte alignment for data offsets. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.SizePadding">
+            <summary>
+            (NARD only) Byte alignment for data sizes. Zero or unused for NARC.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaArchive.Entries">
+            <summary>
+            The ordered list of file entries in the archive.
+            </summary>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaEntry">
+            <summary>
+            Represents a single file entry within a GSA archive.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.Alias">
+            <summary>
+            Relative path (alias) of the file within the archive, using '/' as separator.
+            Maximum 511 characters.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.IsCompressed">
+            <summary>
+            Whether this entry's data is zlib-compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.OriginalLength">
+            <summary>
+            Original (decompressed) size of the file in bytes.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.CompressedLength">
+            <summary>
+            Compressed size of the file in bytes. Equal to <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/> if not compressed.
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.RawData">
+            <summary>
+            Raw data as stored in the archive (compressed bytes if <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/> is true).
+            </summary>
+        </member>
+        <member name="P:GsaEditor.Core.Models.GsaEntry.DataOffset">
+            <summary>
+            Byte offset of this entry's data block within the archive file.
+            </summary>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.GetDecompressedData">
+            <summary>
+            Returns the decompressed data for this entry.
+            If the entry is not compressed, returns <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/> directly.
+            </summary>
+            <returns>The decompressed file content.</returns>
+        </member>
+        <member name="M:GsaEditor.Core.Models.GsaEntry.SetData(System.Byte[],System.Boolean)">
+            <summary>
+            Sets the entry data from uncompressed bytes, optionally compressing with zlib.
+            Updates <see cref="P:GsaEditor.Core.Models.GsaEntry.OriginalLength"/>, <see cref="P:GsaEditor.Core.Models.GsaEntry.CompressedLength"/>,
+            <see cref="P:GsaEditor.Core.Models.GsaEntry.IsCompressed"/>, and <see cref="P:GsaEditor.Core.Models.GsaEntry.RawData"/>.
+            </summary>
+            <param name="uncompressedData">The uncompressed file content.</param>
+            <param name="compress">Whether to compress the data with zlib.</param>
+        </member>
+        <member name="T:GsaEditor.Core.Models.GsaFormat">
+            <summary>
+            Identifies the archive format variant.
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARC">
+            <summary>
+            Legacy format with no padding support. Magic word = 0x4E415243 ("NARC").
+            </summary>
+        </member>
+        <member name="F:GsaEditor.Core.Models.GsaFormat.NARD">
+            <summary>
+            Enhanced format with offset and size padding for console DVD alignment.
+            Magic word = 0x4E415244 ("NARD").
+            </summary>
+        </member>
+    </members>
+</doc>

GsaEditor/bin/Debug/net8.0/GsaEditor.deps.json

@@ -0,0 +1,681 @@
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GsaEditor/bin/Debug/net8.0/GsaEditor.runtimeconfig.json

@@ -0,0 +1,13 @@
+{
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+}