private Color blockTypeColor(BlockType blockType) {
        switch (blockType) {
            case I: return Color.CYAN;
            case J: return Color.BLUE;
            case L: return Color.ORANGE;
            case O: return Color.YELLOW;
            case S: return Color.GREEN;
            case T: return PURPLE_COLOR;
            case Z: return Color.RED;
            default: throw new AssertionError();
        }
    }