import {GameOver} from "./Game.js";

export class Snake {
    /**
     * The snake of the game
     * @param options
     */
    constructor({startPos = [8,8], size = 4, startDirection = directions.RIGHT} = {}) {
        if (startPos && Array.isArray(startPos) && startPos.length === 2 && startPos.filter(s => typeof s === "number" && s > 0 && s % 1 === 0).length === startPos.length)
            this.body = [startPos];
        else
            throw new InvalidSnakeOption("startPos");

        if (size && typeof size === "number" && size > 1 && size % 1 === 0)
            this.size = size;
        else
            throw new InvalidSnakeOption("size");

        // Generate snake body
        for (let s = 1; s < this.size; s++) {
            const pos = this.body[this.body.length - 1].map((n, i) => n - startDirection[i]);
            if (pos.find(v => v < 0))
                throw new InvalidSnakeOption("startPos too small");
            this.body.push(pos);
        }

        this.eating = false;
        this.narrowing = false;
    }

    /**
     * Move the snake body
     * @param {directions} direction
     */
    move(direction) {
        if (!this.eating)
            this.body.pop();
        else
            this.eating = false;

        const pos = this.body[0].map((n, i) => n + direction[i]);

        if (this.body.find(([x,y]) => pos[0] === x && pos[1] === y))
            throw new GameOver();

        if (!this.narrowing)
            this.body.unshift(pos);
        else
            this.narrowing = false;
    }

    /**
     * Enable eating
     */
    eat() {
        this.eating = true;
    }

    /**
     * Enable narrowing
     */
    shrink() {
        this.narrowing = true;
    }
}

export const directions = {
    UP: [0, -1],
    RIGHT: [1, 0],
    DOWN: [0, 1],
    LEFT: [-1, 0]
};

export class InvalidSnakeOption extends Error {
    /**
     * @param {string} name
     */
    constructor(name) {
        super(`Invalid Snake option: ${name}`);
    }
}