v0.1.0 chess game in go, using external stockfish engine

internal/board/board.go

@@ -0,0 +1,88 @@
+// FILE: internal/board/board.go
+package board
+
+import (
+	"fmt"
+	"strings"
+
+	"chess/internal/core"
+)
+
+const (
+	StartingFEN = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+)
+
+type Board struct {
+	squares   [8][8]byte
+	turn      core.Color
+	castling  string
+	enPassant string
+	halfmove  int
+	fullmove  int
+}
+
+func FEN(fen string) (*Board, error) {
+	parts := strings.Fields(fen)
+	if len(parts) != 6 {
+		return nil, fmt.Errorf("invalid FEN: expected 6 parts, got %d", len(parts))
+	}
+
+	b := &Board{}
+
+	// Parse board
+	ranks := strings.Split(parts[0], "/")
+	if len(ranks) != 8 {
+		return nil, fmt.Errorf("invalid FEN: expected 8 ranks")
+	}
+
+	for r := 0; r < 8; r++ {
+		file := 0
+		for _, ch := range ranks[r] {
+			if ch >= '1' && ch <= '8' {
+				file += int(ch - '0')
+			} else {
+				if file >= 8 {
+					return nil, fmt.Errorf("invalid FEN: too many pieces in rank %d", r+1)
+				}
+				b.squares[r][file] = byte(ch)
+				file++
+			}
+		}
+		if file != 8 {
+			return nil, fmt.Errorf("invalid FEN: rank %d has %d files", r+1, file)
+		}
+	}
+
+	// Parse game state with validation
+	if len(parts[1]) != 1 || (parts[1][0] != 'w' && parts[1][0] != 'b') {
+		return nil, fmt.Errorf("invalid FEN: turn must be 'w' or 'b'")
+	}
+	b.turn = core.Color(parts[1][0])
+	b.castling = parts[2]
+	b.enPassant = parts[3]
+
+	if _, err := fmt.Sscanf(parts[4], "%d", &b.halfmove); err != nil {
+		return nil, fmt.Errorf("invalid FEN: halfmove counter")
+	}
+	if _, err := fmt.Sscanf(parts[5], "%d", &b.fullmove); err != nil {
+		return nil, fmt.Errorf("invalid FEN: fullmove counter")
+	}
+
+	return b, nil
+}
+
+func (b *Board) Turn() core.Color {
+	return b.turn
+}
+
+func (b *Board) GetPieceAt(square string) byte {
+	if len(square) != 2 {
+		return 0
+	}
+	if square[0] < 'a' || square[0] > 'h' || square[1] < '1' || square[1] > '8' {
+		return 0
+	}
+	file := square[0] - 'a'
+	rank := '8' - square[1]
+	return b.squares[rank][file]
+}