var canvas;
var context;
var game;

function initialize() {

    canvas = document.getElementById("canvas");
    context = canvas.getContext("2d");

    game = new theGame();

    document.addEventListener('keydown', function(evt) {

        var key = evt.which;
        game.input(key);
    }, false);


    mainLoop();
}

function theGame() {

    this.currentKey = null;
    this.lastKey = null;

    this.w = 20;

    this.score = 0;

    this.starting = { x: Math.floor((canvas.width / this.w) * 0.5) * this.w, y: Math.floor((canvas.height / this.w) * 0.5) * this.w }

    this.snake = new Rectangle(0, 0, this.w, this.w); this.snake.boxColor = "green";

    this.snake.x = this.starting.x
    this.snake.y = this.starting.y

    this.tail = new Array();
    this.tail.push(this.snake);

    this.re = 5;
    this.limit = this.re;
    this.spawnFood();
}

theGame.prototype.spawnFood = function() {

    var x = Math.floor(Math.random() * (canvas.width / this.w)) * this.w;
    var y = Math.floor(Math.random() * (canvas.height / this.w)) * this.w;
    this.food = new Rectangle(x, y, this.w, this.w); this.food.boxColor = "red";
}

theGame.prototype.reset = function() {

    this.currentKey = null;
    this.lastKey = null;
    this.snake.x = this.starting.x
    this.snake.y = this.starting.y
    this.tail = new Array();
    this.score = 0;
    this.tail.push(this.snake);
}


theGame.prototype.input = function(key) {

    switch(key) {

        case 38 : if (this.lastKey != "down") { this.currentKey = "up"; }
        break;
        case 40 : if (this.lastKey != "up") { this.currentKey = "down"; }
        break;
        case 37 : if (this.lastKey != "right") { this.currentKey = "left"; }
        break;
        case 39 : if (this.lastKey != "left") { this.currentKey = "right"; }
        break;

    }
}

theGame.prototype.update = function() {

    this.limit--;
    if (this.limit <= 0) {

        for (var i = this.tail.length - 1; i > 0; i--) {

            if (i != 0) { this.tail[i].x = this.tail[i - 1].x; this.tail[i].y = this.tail[i - 1].y; }
        }

        if (this.currentKey == "up") { this.lastKey = "up";
            this.snake.y -= this.w; if (this.snake.y < 0) { this.reset(); }
        }
        if (this.currentKey == "down") { this.lastKey = "down";
            this.snake.y += this.w; if (this.snake.y > canvas.height - this.w) { this.reset(); }
        }
        if (this.currentKey == "left") { this.lastKey = "left";
            this.snake.x -= this.w; if (this.snake.x < 0) { this.reset(); }
        }
        if (this.currentKey == "right") { this.lastKey = "right";
            this.snake.x += this.w; if (this.snake.x > canvas.width - this.w) { this.reset(); }
        }

        for (var i = 0; i < this.tail.length; i++) {

            if (i != 0 && this.snake.contains(this.tail[i].middle())) {

                this.reset();
            }
        }

        if (this.snake.contains(this.food.middle())) {

            rect = new Rectangle(-100, -100, this.w, this.w); rect.boxColor = "green";
            this.tail.push(rect);

            this.spawnFood();
        }
        this.limit = this.re;
    }
}

theGame.prototype.draw = function() {

    context.clearRect(0,0,canvas.width, canvas.height);

    for (var i = 0; i < this.tail.length; i++) {

        this.tail[i].draw();
    }

    this.food.draw();
    context.fillStyle = "white";
    context.font = "15px Arial";
    context.fillText(this.score, canvas.width * 0.5, 16);
}




function mainLoop() {

    game.update();
    game.draw();

    requestAnimationFrame(mainLoop);
}