From 7aa65f4ec0547bbc385c9fce7571425ce71d3d1b Mon Sep 17 00:00:00 2001
From: ekzyis <ekzyis@ekzy.is>
Date: Thu, 26 Sep 2024 10:21:09 +0200
Subject: [PATCH] Add kingside castle

---
 chess/board.go      | 55 +++++++++++++++++++++++++++++++++++++++++++--
 chess/board_test.go | 20 +++++++++++++++++
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/chess/board.go b/chess/board.go
index fd497c5..82e8275 100644
--- a/chess/board.go
+++ b/chess/board.go
@@ -278,6 +278,7 @@ func (b *Board) Move(move string) error {
 		fromX          int
 		fromY          int
 		promotion      string
+		castle         = false
 		collisionPiece *Piece
 		err            error
 	)
@@ -291,6 +292,14 @@ func (b *Board) Move(move string) error {
 		return err
 	}
 
+	if move == "O-O" {
+		castle = true
+		if b.turn == Dark {
+			to = "g8"
+			fromY = 0
+		}
+	}
+
 	// TODO: parse ambiguous captures for all pieces
 	// TODO: parse checkmates e.g. e5#
 	// TODO: parse O-O as kingside castle and O-O-O as queenside castle
@@ -316,7 +325,7 @@ func (b *Board) Move(move string) error {
 		case "q":
 			return b.moveQueen(to)
 		case "k":
-			return b.moveKing(to)
+			return b.moveKing(to, castle)
 		default:
 			return fmt.Errorf("invalid move %s: %v", move, err)
 		}
@@ -356,6 +365,10 @@ func parseMove(move string) (string, int, int, string, error) {
 		from  string
 	)
 
+	if move == "O-O" {
+		return "K", 5, 7, "g1", nil
+	}
+
 	if strings.Contains(move, "x") {
 		return parseCaptureMove(move)
 	}
@@ -1113,7 +1126,7 @@ func (b *Board) moveQueen(position string) error {
 	return fmt.Errorf("no queen found that can move to %s", position)
 }
 
-func (b *Board) moveKing(position string) error {
+func (b *Board) moveKing(position string, castle bool) error {
 	var (
 		x     int
 		y     int
@@ -1127,6 +1140,44 @@ func (b *Board) moveKing(position string) error {
 		return err
 	}
 
+	if castle {
+		// TODO: check if castle is allowed
+
+		y := 7
+		if b.turn == Dark {
+			y = 0
+		}
+
+		if (b.turn == Light && position == "g1") || (b.turn == Dark && position == "g8") {
+			// kingside castle
+
+			king := b.getPiece(4, y)
+			if king == nil || king.Color != b.turn || king.Name != King {
+				return fmt.Errorf("invalid castle move")
+			}
+
+			if b.getPiece(5, y) != nil {
+				return fmt.Errorf("invalid castle move")
+			}
+
+			if b.getPiece(6, y) != nil {
+				return fmt.Errorf("invalid castle move")
+			}
+
+			rook := b.getPiece(7, y)
+			if rook == nil || rook.Color != b.turn || rook.Name != Rook {
+				return fmt.Errorf("invalid castle move")
+			}
+
+			b.tiles[6][y] = king
+			b.tiles[4][y] = nil
+			b.tiles[5][y] = rook
+			b.tiles[7][y] = nil
+
+			return nil
+		}
+	}
+
 	// ^
 	xPrev = x + 0
 	yPrev = y - 1
diff --git a/chess/board_test.go b/chess/board_test.go
index 88d821e..b06a3d4 100644
--- a/chess/board_test.go
+++ b/chess/board_test.go
@@ -482,6 +482,26 @@ func TestBoardPin(t *testing.T) {
 	assertMoveError(t, b, "Ne4", "invalid move Ne4: king is in check")
 }
 
+func TestBoardCastle(t *testing.T) {
+	t.Parallel()
+
+	b := chess.NewBoard()
+
+	assertParse(t, b, "e4 e5 Nf3 Nf6 Be2 Be7 O-O")
+
+	assertPiece(t, b, "f1", chess.Rook, chess.Light)
+	assertPiece(t, b, "g1", chess.King, chess.Light)
+	assertNoPiece(t, b, "h1")
+	assertNoPiece(t, b, "e1")
+
+	assertParse(t, b, "O-O")
+
+	assertPiece(t, b, "f8", chess.Rook, chess.Dark)
+	assertPiece(t, b, "g8", chess.King, chess.Dark)
+	assertNoPiece(t, b, "h8")
+	assertNoPiece(t, b, "e8")
+}
+
 func assertParse(t *testing.T, b *chess.Board, moves string) {
 	assert.NoError(t, b.Parse(moves))
 }