add custom chess engine

2026-06-08 13:58:22 -06:00
parent d2ae34f530
commit c3280aa6d3
42 changed files with 3033 additions and 168 deletions
@@ -0,0 +1,118 @@
+using JoshHeaps.Net.Services.Interfaces;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Middleman wrapper over the native custom chess engine (chess_engine.dll / libchess_engine.so).
+/// Shares <see cref="IChessEngine"/> with <see cref="Stockfish"/> so the two are swappable.
+/// The boundary contract is FEN string in, UCI move string out — identical to Stockfish.
+/// </summary>
+public sealed partial class CustomChessEngine : IChessEngine
+{
+    private readonly EngineSafeHandle _handle;
+
+    public int Skill { get; }
+
+    public CustomChessEngine(int skill = 20)
+    {
+        Skill = skill;
+
+        var handle = NativeMethods.engine_create($"skill={skill}");
+
+        if (handle == IntPtr.Zero)
+            throw new InvalidOperationException("Native chess engine failed to initialize (engine_create returned null).");
+
+        _handle = new EngineSafeHandle(handle);
+    }
+
+    public Task<string> GetBestMoveAsync(string fen) => Task.Run(() => GetBestMove(fen));
+
+    private unsafe string GetBestMove(string fen)
+    {
+        const int bufferLength = 16;            // longest UCI move is 5 chars ("e7e8q") + NUL
+        byte* buffer = stackalloc byte[bufferLength];
+
+        var added = false;
+
+        try
+        {
+            _handle.DangerousAddRef(ref added);
+            var code = NativeMethods.engine_best_move(_handle.DangerousGetHandle(), fen, buffer, bufferLength);
+
+            if (code != 0)
+                throw new InvalidOperationException($"Native chess engine failed to produce a move for FEN '{fen}' (engine_best_move returned {code}).");
+
+            return Marshal.PtrToStringUTF8((IntPtr)buffer)
+                ?? throw new InvalidOperationException("Native chess engine returned an empty move.");
+        }
+        finally
+        {
+            if (added)
+                _handle.DangerousRelease();
+        }
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        _handle.Dispose();
+        return ValueTask.CompletedTask;
+    }
+
+    /// <summary>Guarantees the native handle is released exactly once via engine_destroy.</summary>
+    private sealed class EngineSafeHandle : SafeHandle
+    {
+        public EngineSafeHandle(IntPtr handle) : base(IntPtr.Zero, ownsHandle: true) => SetHandle(handle);
+
+        public override bool IsInvalid => handle == IntPtr.Zero;
+
+        protected override bool ReleaseHandle()
+        {
+            NativeMethods.engine_destroy(handle);
+            return true;
+        }
+    }
+
+    /// <summary>
+    /// P/Invoke surface for chess_engine.(dll|so). The resolver maps the logical name
+    /// "chess_engine" to the platform binary in the Resources folder (mirrors Stockfish).
+    /// </summary>
+    private static partial class NativeMethods
+    {
+        private const string LibName = "chess_engine";
+
+        static NativeMethods() =>
+            NativeLibrary.SetDllImportResolver(typeof(NativeMethods).Assembly, Resolve);
+
+        private static IntPtr Resolve(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
+        {
+            if (libraryName != LibName)
+                return IntPtr.Zero;
+
+            var fileName = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                ? "chess_engine.dll"
+                : "libchess_engine.so";
+
+            var path = Path.Combine(AppContext.BaseDirectory, "Resources", fileName);
+
+            if (NativeLibrary.TryLoad(path, out var handle))
+                return handle;
+
+            return NativeLibrary.Load(libraryName, assembly, searchPath);
+        }
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial IntPtr engine_create(string? options);
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static unsafe partial int engine_best_move(IntPtr engine, string fen, byte* outBuffer, int outLength);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void engine_destroy(IntPtr engine);
+    }
+}