I'm pretending that I know what I'm doing

fxl.codes.kisekae.data/Archives/LHArchiveDecoder.cs

@@ -0,0 +1,81 @@
+namespace fxl.codes.kisekae.data.Archives;
+
+/**
+ * Ported from https://github.com/kisekae/UltraKiss/blob/master/src/Kisekae/Lhhuf.java
+ */
+public class LhArchiveDecoder
+{
+    private const int Buffer = 4096;
+    private const int BufferSize = 60;
+    private const int Threshold = 2;
+    private const int EndOfFile = -1;
+    private const int NChar = 256 - Threshold + BufferSize; // For some reason????
+    private const int TableSize = NChar * 2 - 1;
+    private const int RootPosition = TableSize - 1;
+    private const int MaxFreq = 0x8000;
+    private readonly int[] _child = new int[TableSize];
+    private readonly int[] _frequency = new int[TableSize];
+    private readonly int[] _parent = new int[TableSize + NChar];
+
+    private int _bytesProcessed;
+    private int[] _data = new int[Buffer + 1];
+    private int _lastBytesProcessed;
+    private int[] _leftChild = new int[Buffer + 1];
+    private int[] _rightChild = new int[Buffer * 2 + 1];
+    private int[] _same = new int[Buffer + 1];
+    private byte[] _textBuffer = new byte[Buffer + BufferSize - 1];
+    private int putlen, getlen, putbuf, getbuf;
+
+    private void Initialize()
+    {
+        for (var i = 0; i < NChar; i++)
+        {
+            _frequency[i] = 1;
+            _child[i] = i + TableSize;
+            _parent[i + TableSize] = i;
+        }
+
+        for (int i = 0, j = NChar; j <= RootPosition; i += 2, j++)
+        {
+            _frequency[j] = _frequency[i] + _frequency[i + 1];
+            _child[j] = i;
+            _parent[i] = _parent[i + 1] = j;
+        }
+
+        _frequency[TableSize] = 0xffff;
+        _parent[RootPosition] = 0;
+    }
+
+    private void Reconstruct()
+    {
+        int k;
+        for (int i = 0, j = 0; i < TableSize; i++, j++)
+        {
+            if (_child[i] < TableSize) continue;
+
+            _frequency[j] = (_frequency[i] + 1) / 2;
+            _child[j] = _child[i];
+        }
+
+        for (int i = 0, j = NChar; j < TableSize; i += 2, j++)
+        {
+            k = i + 1;
+            var f = _frequency[j] = _frequency[i] + _frequency[k];
+            for (k = j - 1; f < _frequency[k]; k--);
+            k++;
+
+            for (int p = j, e = k; p > e; p--) _frequency[p] = _frequency[p - 1];
+            _frequency[k] = f;
+
+            for (var p = j; p > k; p--) _child[p] = _child[p - 1];
+            _child[k] = i;
+        }
+
+        /* link parents */
+        for (var i = 0; i < TableSize; i++)
+            if ((k = _child[i]) >= TableSize)
+                _parent[k] = i;
+            else
+                _parent[k] = _parent[k + 1] = i;
+    }
+}

fxl.codes.kisekae.data/Archives/LzhExtractor.cs

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+using System.Text;
+
+namespace fxl.codes.kisekae.data.Archives;
+
+public class LzhExtractor
+{
+    public async void Open(Stream stream, string filename)
+    {
+        var headerSize = stream.ReadByte();
+        var headerSum = stream.ReadByte();
+        var methodBytes = new byte[5];
+        await stream.ReadExactlyAsync(methodBytes);
+
+        var method = Encoding.ASCII.GetString(methodBytes);
+        var skipSize = await ReadLittleEndian(stream);
+        var origSize = await ReadLittleEndian(stream);
+        var time = await ReadLittleEndian(stream);
+        var attribute = stream.ReadByte();
+        var level = stream.ReadByte();
+    }
+
+    private static async Task<int> ReadLittleEndian(Stream stream, int length = 4)
+    {
+        var buffer = new byte[length];
+        await stream.ReadExactlyAsync(buffer);
+        var x = BitConverter.ToInt32(buffer);
+
+        var b0 = (x >> 24) & 255;
+        var b1 = (x >> 16) & 255;
+        var b2 = (x >> 8) & 255;
+        var b3 = (x >> 0) & 255;
+        return (b0 << 0) + (b1 << 8) + (b2 << 16) + (b3 << 24);
+    }
+}