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src/Concelier/__Libraries/StellaOps.Concelier.Federation/Compression/ZstdCompression.cs

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+using ZstdSharp;
+
+namespace StellaOps.Concelier.Federation.Compression;
+
+/// <summary>
+/// ZStandard compression utilities for federation bundles.
+/// </summary>
+public static class ZstdCompression
+{
+    /// <summary>Default compression level (balanced speed/ratio).</summary>
+    public const int DefaultLevel = 3;
+
+    /// <summary>Minimum compression level.</summary>
+    public const int MinLevel = 1;
+
+    /// <summary>Maximum compression level.</summary>
+    public const int MaxLevel = 19;
+
+    /// <summary>
+    /// Create a compression stream wrapping the output.
+    /// </summary>
+    /// <param name="output">Target stream for compressed data.</param>
+    /// <param name="level">Compression level (1-19, default 3).</param>
+    /// <returns>Stream that compresses data written to it.</returns>
+    public static CompressionStream CreateCompressionStream(Stream output, int level = DefaultLevel)
+    {
+        ValidateLevel(level);
+        return new CompressionStream(output, level);
+    }
+
+    /// <summary>
+    /// Create a decompression stream wrapping the input.
+    /// </summary>
+    /// <param name="input">Source stream of compressed data.</param>
+    /// <returns>Stream that decompresses data read from it.</returns>
+    public static DecompressionStream CreateDecompressionStream(Stream input)
+    {
+        return new DecompressionStream(input);
+    }
+
+    /// <summary>
+    /// Compress data in memory.
+    /// </summary>
+    /// <param name="data">Uncompressed data.</param>
+    /// <param name="level">Compression level (1-19, default 3).</param>
+    /// <returns>Compressed data.</returns>
+    public static byte[] Compress(ReadOnlySpan<byte> data, int level = DefaultLevel)
+    {
+        ValidateLevel(level);
+        using var compressor = new Compressor(level);
+        return compressor.Wrap(data).ToArray();
+    }
+
+    /// <summary>
+    /// Decompress data in memory.
+    /// </summary>
+    /// <param name="compressed">Compressed data.</param>
+    /// <returns>Decompressed data.</returns>
+    public static byte[] Decompress(ReadOnlySpan<byte> compressed)
+    {
+        using var decompressor = new Decompressor();
+        return decompressor.Unwrap(compressed).ToArray();
+    }
+
+    /// <summary>
+    /// Compress a file to another file.
+    /// </summary>
+    public static async Task CompressFileAsync(
+        string inputPath,
+        string outputPath,
+        int level = DefaultLevel,
+        CancellationToken ct = default)
+    {
+        ValidateLevel(level);
+        await using var input = File.OpenRead(inputPath);
+        await using var output = File.Create(outputPath);
+        await using var compressor = CreateCompressionStream(output, level);
+        await input.CopyToAsync(compressor, ct);
+    }
+
+    /// <summary>
+    /// Decompress a file to another file.
+    /// </summary>
+    public static async Task DecompressFileAsync(
+        string inputPath,
+        string outputPath,
+        CancellationToken ct = default)
+    {
+        await using var input = File.OpenRead(inputPath);
+        await using var decompressor = CreateDecompressionStream(input);
+        await using var output = File.Create(outputPath);
+        await decompressor.CopyToAsync(output, ct);
+    }
+
+    /// <summary>
+    /// Decompress from one stream to another.
+    /// </summary>
+    public static async Task DecompressAsync(
+        Stream input,
+        Stream output,
+        CancellationToken ct = default)
+    {
+        await using var decompressor = CreateDecompressionStream(input);
+        await decompressor.CopyToAsync(output, ct);
+    }
+
+    /// <summary>
+    /// Compress from one stream to another.
+    /// </summary>
+    public static async Task CompressAsync(
+        Stream input,
+        Stream output,
+        int level = DefaultLevel,
+        CancellationToken ct = default)
+    {
+        ValidateLevel(level);
+        await using var compressor = CreateCompressionStream(output, level);
+        await input.CopyToAsync(compressor, ct);
+    }
+
+    private static void ValidateLevel(int level)
+    {
+        if (level < MinLevel || level > MaxLevel)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(level),
+                level,
+                $"Compression level must be between {MinLevel} and {MaxLevel}");
+        }
+    }
+}