WIP, but reading more about this

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

@@ -4,19 +4,115 @@ namespace fxl.codes.kisekae.data.Archives;
 
 public class LzhExtractor
 {
-    public async void Open(Stream stream, string filename)
+    private int _crc16 = -1;
+    private int _crc32 = -1;
+    private DateTime _created;
+    private string _method;
+    private string _name;
+    private int _sizeCompressed;
+    private int _sizeCompressedExtended;
+    private int _sizeExtension;
+    private int _sizeHeader;
+    private int _sizeUncompressed;
+    public long DataPosition;
+
+    public async Task ReadHeader(Stream stream)
     {
-        var headerSize = stream.ReadByte();
+        _sizeHeader = stream.ReadByte();
+        if (_sizeHeader <= 0) throw new Exception("Zero sized LHA file");
+
         var headerSum = stream.ReadByte();
         var methodBytes = new byte[5];
         await stream.ReadExactlyAsync(methodBytes);
+        _method = Encoding.ASCII.GetString(methodBytes);
+        if (string.IsNullOrEmpty(_method) || !_method.StartsWith('-')) throw new Exception("Invalid LHA file signature");
 
-        var method = Encoding.ASCII.GetString(methodBytes);
-        var skipSize = await ReadLittleEndian(stream);
-        var origSize = await ReadLittleEndian(stream);
+        _sizeExtension = 0;
+        _sizeCompressedExtended = await ReadLittleEndian(stream);
+        _sizeUncompressed = await ReadLittleEndian(stream);
         var time = await ReadLittleEndian(stream);
+        _created = GetDateTime(time);
+
         var attribute = stream.ReadByte();
         var level = stream.ReadByte();
+        int next;
+
+        switch (level)
+        {
+            case 0:
+                _sizeCompressed = _sizeCompressedExtended;
+                _name = await GetStringValue(stream, stream.ReadByte());
+                _crc16 = await ReadLittleEndian(stream, 2);
+                next = 0;
+                break;
+            case 1:
+                _name = await GetStringValue(stream, stream.ReadByte());
+                _crc16 = await ReadLittleEndian(stream, 2);
+                stream.Position++;
+                next = await ReadLittleEndian(stream, 2);
+                break;
+            case 2:
+                _sizeCompressed = _sizeCompressedExtended;
+                _crc16 = await ReadLittleEndian(stream, 2);
+                stream.Position++;
+                next = await ReadLittleEndian(stream, 2);
+                break;
+            default: throw new Exception("Invalid LHA file header");
+        }
+
+        if (level > 0)
+            while (next != 0)
+            {
+                _sizeExtension += next;
+                var type = stream.ReadByte();
+                var size = next - 3;
+
+                switch (type)
+                {
+                    case 0: break;
+                    case 1:
+                        _name = "";
+                        for (; size > 0; size--) _name += (char)stream.ReadByte();
+                        break;
+                    case 2:
+                    case 0x52:
+                    case 0x53:
+                        stream.Position += size;
+                        size = 0;
+                        break;
+                    case 0x3f: break;
+                    case 0x40:
+                    case 0x50:
+                        stream.Position += 2;
+                        size -= 2;
+                        break;
+                    case 0x51:
+                    case 0x54:
+                        stream.Position += 4;
+                        size -= 4;
+                        break;
+                }
+
+                stream.Position += size;
+                next = await ReadLittleEndian(stream, 2);
+            }
+
+        if (level == 1) _sizeCompressed = _sizeCompressedExtended - _sizeExtension;
+
+        DataPosition = level switch
+        {
+            0 => _sizeHeader + 2,
+            1 => _sizeHeader + _sizeExtension + 2,
+            2 => _sizeHeader,
+            _ => DataPosition
+        };
+    }
+
+    private static async Task<string> GetStringValue(Stream stream, int length)
+    {
+        var buffer = new byte[length];
+        await stream.ReadExactlyAsync(buffer);
+        return Encoding.ASCII.GetString(buffer);
     }
 
     private static async Task<int> ReadLittleEndian(Stream stream, int length = 4)
@@ -31,4 +127,18 @@ public class LzhExtractor
         var b3 = (x >> 0) & 255;
         return (b0 << 0) + (b1 << 8) + (b2 << 16) + (b3 << 24);
     }
+
+    private static DateTime GetDateTime(int t)
+    {
+        var year = ((t >> 25) & 0x7f) + 1980;
+        var month = (t >> 21) & 0x0f;
+        var day = (t >> 16) & 0x1f;
+        var hour = (t >> 11) & 0x1f;
+        var minute = (t >> 5) & 0x3f;
+        var second = (t & 0x1f) * 2;
+
+        if (month is < 1 or > 12 || day is < 1 or > 31 || hour >= 24 || minute >= 60 || second > 60) return DateTime.MinValue;
+
+        return new DateTime(year, month, day, hour, minute, second);
+    }
 }