Implement bishop moves

chess/board.go

@@ -221,7 +221,89 @@ func (b *Board) moveRook(position string) error {
 }
 
 func (b *Board) moveBishop(position string) error {
-	return nil
+	var (
+		x     int
+		y     int
+		xPrev int
+		yPrev int
+		piece *Piece
+		err   error
+	)
+
+	if x, y, err = getXY(position); err != nil {
+		return err
+	}
+
+	xPrev = x
+	yPrev = y
+	for xPrev >= 0 && xPrev < 8 && yPrev >= 0 && yPrev < 8 {
+		xPrev++
+		yPrev--
+		piece = b.getPiece(xPrev, yPrev)
+		if piece != nil {
+			if piece.Name == Bishop && piece.Color == b.turn {
+				b.tiles[xPrev][yPrev] = nil
+				b.tiles[x][y] = piece
+				return nil
+			} else {
+				// direction blocked by other piece
+				break
+			}
+		}
+	}
+
+	xPrev = x
+	yPrev = y
+	for xPrev >= 0 && xPrev < 8 && yPrev >= 0 && yPrev < 8 {
+		xPrev++
+		yPrev++
+		piece = b.getPiece(xPrev, yPrev)
+		if piece != nil {
+			if piece.Name == Bishop && piece.Color == b.turn {
+				b.tiles[xPrev][yPrev] = nil
+				b.tiles[x][y] = piece
+				return nil
+			} else {
+				break
+			}
+		}
+	}
+
+	xPrev = x
+	yPrev = y
+	for xPrev >= 0 && xPrev < 8 && yPrev >= 0 && yPrev < 8 {
+		xPrev--
+		yPrev++
+		piece = b.getPiece(xPrev, yPrev)
+		if piece != nil {
+			if piece.Name == Bishop && piece.Color == b.turn {
+				b.tiles[xPrev][yPrev] = nil
+				b.tiles[x][y] = piece
+				return nil
+			} else {
+				break
+			}
+		}
+	}
+
+	xPrev = x
+	yPrev = y
+	for xPrev >= 0 && xPrev < 8 && yPrev >= 0 && yPrev < 8 {
+		xPrev--
+		yPrev--
+		piece = b.getPiece(xPrev, yPrev)
+		if piece != nil {
+			if piece.Name == Bishop && piece.Color == b.turn {
+				b.tiles[xPrev][yPrev] = nil
+				b.tiles[x][y] = piece
+				return nil
+			} else {
+				break
+			}
+		}
+	}
+
+	return fmt.Errorf("no bishop found that can move to %s", position)
 }
 
 func (b *Board) moveKnight(position string) error {

chess/board_test.go

@@ -109,6 +109,27 @@ func TestBoardMoveKnight(t *testing.T) {
 	assertNoPiece(t, b, "g8")
 }
 
+func TestBoardMoveBishop(t *testing.T) {
+	b := chess.NewBoard()
+
+	b.Move("Bc4")
+
+	assertMoveError(t, b, "Bc4", "no bishop found that can move to c4")
+
+	b.Move("e3")
+	b.Move("e6")
+
+	b.Move("Bc4")
+
+	assertPiece(t, b, "c4", chess.Bishop, chess.Light)
+	assertNoPiece(t, b, "f1")
+
+	b.Move("Bc5")
+
+	assertPiece(t, b, "c5", chess.Bishop, chess.Dark)
+	assertNoPiece(t, b, "f8")
+}
+
 func assertPiece(t *testing.T, b *chess.Board, position string, name chess.PieceName, color chess.Color) {
 	p := b.At(position)