Simple snake implementation

Snake.ts

interface IVec2 {
    x: number;
    y: number;
}

interface IBounds {
    min: IVec2;
    max: IVec2;
}

/**
 * 方向。
 */
enum Direction {
    up,
    down,
    left,
    right,
}

interface ISnakeBodySegment {
    /**
     * 身子的方向。起点是头部或者上一段身子的尾部。
     */
    direction: Direction;

    /**
     * 身子的长度。
     */
    length: number;
}

/**
 * 贪吃蛇的抽象定义。
 */
interface ISnake {
    /**
     * 蛇的头部点。
     */
    head: IVec2;

    /**
     * 蛇身子的每一段。
     */
    body: ISnakeBodySegment[];
}

/**
 * 让贪吃蛇前进一步。
 * @param snake 
 */
function step(snake: ISnake) {
    const firstBody = snake.body[0];
    switch (firstBody.direction) {
        case Direction.left: --snake.head.x; break;
        case Direction.right: ++snake.head.y; break;
        case Direction.up: ++snake.head.y; break;
        case Direction.down: --snake.head.y; break;
    }
}

/**
 * 让贪吃蛇转个弯。
 * @param snake 
 * @param direction 
 */
function turn(snake: ISnake, direction: Direction) {
    const firstBody = snake.body[0];
    let isValid = false;
    switch (direction) {
        case Direction.left:
        case Direction.right:
            if (firstBody.direction !== Direction.left &&
                firstBody.direction !== Direction.right) {
                isValid = true;
            }
            break;
        case Direction.up:
        case Direction.down:
            if (firstBody.direction !== Direction.up &&
                firstBody.direction !== Direction.down) {
                isValid = true;
            }
            break;
    }

    if (isValid) {
        // 添加一节身体到最前面，长度是 1
        snake.body.unshift({ direction, length: 1 });
        // 减去最后一节身体的长度
        const lastBody = snake.body[snake.body.length - 1];
        --lastBody.length;
        // 如果最后一节身体长度是 0，就销毁它
        if (lastBody.length === 0) {
            snake.body.pop();
        }
    }
}

/**
 * 判断贪吃蛇是否自杀了（咬到自己了）。
 * @param snake 
 */
function selfKilled(snake: ISnake) {
    return ifSomeBodyPoint(snake, (bodyPoint) => bodyPoint.x === snake.head.x && bodyPoint.y === snake.head.y);
}

/**
 * 判断贪吃蛇是否触碰到边界了。
 * @param snake 
 * @param bounds 
 */
function touchBounds(snake: ISnake, bounds: IBounds) {
    return ifSomeBodyPoint(snake, (bodyPoint) => isVec2OutOfBounds(bodyPoint, bounds));

    function isVec2OutOfBounds(point: IVec2, bounds: IBounds) {
        return isNumberOutOfBounds(point.x, bounds.min.x, bounds.max.x) ||
            isNumberOutOfBounds(point.y, bounds.min.y, bounds.max.y);
    }

    function isNumberOutOfBounds(v: number, min: number, max: number) {
        return v <= min || v >= max;
    }
}

function ifSomeBodyPoint(snake: ISnake, visitor: (bodyPoint: IVec2) => boolean) {
    let bodyPoint = Object.assign({}, snake.head);
    for (const segment of snake.body) {
        for (let i = 0; i < segment.length; ++i) {
            switch (segment.direction) {
                case Direction.left:
                    ++bodyPoint.x;
                    break;
                case Direction.right:
                    --bodyPoint.x;
                    break;
                case Direction.up:
                    --bodyPoint.y;
                    break;
                case Direction.down:
                    ++bodyPoint.y;
                    break;
            }
            if (visitor(bodyPoint)) {
                return true;
            }
        }
    }
    return false;
}