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

window.addEventListener('keydown', function(evt) { onKeyDown(evt); }, false);
window.addEventListener('keyup', function(evt) { onKeyUp(evt); }, false);

var startFrameMillis = Date.now();
var endFrameMillis = Date.now();
function getDeltaTime()	// Only call this function once per frame
{
	endFrameMillis = startFrameMillis;
	startFrameMillis = Date.now();
	var deltaTime = (startFrameMillis - endFrameMillis) * 0.001;
	if (deltaTime > 1)	// Validate that the delta is within range
	{
		deltaTime = 1;
	}
	return deltaTime;
}

var SCREEN_WIDTH = canvas.width;
var SCREEN_HEIGHT = canvas.height;
var ASTEROID_SPEED = 0.8;
var PLAYER_SPEED = 1;
var PLAYER_TURN_SPEED = 0.04;
var BULLET_SPEED = 1.5;

var KEY_SPACE = 32;
var KEY_LEFT = 37;
var KEY_UP = 38;
var KEY_RIGHT = 39;
var KEY_DOWN = 40;

var grass = document.createElement("img");
grass.src = "Assets/Sprites/grass.png";

var background = [];

for(var y=0;y<15;y++)
{
	background[y] = [];
	for(var x=0; x<20; x++)
		background[y][x] = grass;
}

var player = {
	image: document.createElement("img"),
	x: SCREEN_WIDTH/2,
	y: SCREEN_HEIGHT/2,
	width: 93,
	height: 80,
	directionX: 0,
	directionY: 0,
	angularDirection: 0,
	rotation: 0
};

player.image.src = "Assets/Sprites/ship.png";

var asteroids = [];

function rand(floor, ceil)
{
	return Math.floor( (Math.random()* (ceil-floor)) +floor );
}

function spawnAsteroid()
{

	var type = rand(0, 3);


	var asteroid = {};

	asteroid.image = document.createElement("img");
	asteroid.image.src = "rock_large.png";
	asteroid.width = 69;
	asteroid.height = 75;
	var x = SCREEN_WIDTH/2;
	var y = SCREEN_HEIGHT/2;

	var dirX = rand(-10,10);
	var dirY = rand(-10,10);
	var magnitude = (dirX * dirX) + (dirY * dirY);
	if(magnitude != 0)
	{
		var oneOverMag = 1 / Math.sqrt(magnitude);
		dirX *= oneOverMag;
		dirY *= oneOverMag;
	}

	var movX = dirX * SCREEN_WIDTH;
	var movY = dirY * SCREEN_HEIGHT;

	asteroid.x = x + movX;
	asteroid.y = y + movY;

	asteroid.velocityX = -dirX * ASTEROID_SPEED;
	asteroid.velocityY = -dirY * ASTEROID_SPEED;

	asteroids.push(asteroid);
}

var bullet = [];

function playerShoot()
{
	var bullet = {
		image: document.createElement("img"),
		x: player.x,
		y: player.y,
		width: 5,
		height: 5,
		velocityX: 0,
		velocityY: 0
	};

	bullet.image.src = "bullet.png";

	var velX = 0;
	var velY = 1;

	var s = Math.sin(player.rotation);
	var c = Math.cos(player.rotation);

	var xVel = (velX * c) - (velY * s);
	var yVel = (velX * s) + (velY * c);

	bullet.velocityX = xVel * BULLET_SPEED;
	bullet.velocityY = yVel * BULLET_SPEED;

	bullets.push(bullet);
}

function onKeyDown(event)
{
	if(event.keyCode == KEY_UP)
	{
		player.directionY = 1;
	}
	if(event.keyCode == KEY_DOWN)
	{
		player.directionY = -1;
	}
	if(event.keyCode == KEY_LEFT)
	{
		player.angularDirection = -1;
	}
	if(event.keyCode == KEY_RIGHT)
	{
		player.angularDirection = 1;
	}
}

function onKeyUp(event)
{
	if(event.keyCode == KEY_UP)
	{
		player.directionY = 0;
	}
	if(event.keyCode == KEY_DOWN)
	{
		player.directionY = 0;
	}
	if(event.keyCode == KEY_LEFT)
	{
		player.angularDirection = 0;
	}
	if(event.keyCode == KEY_RIGHT)
	{
		player.angularDirection = 0;
	}

	if(event.keyCode == KEY_SPACE)
	{
		playerShoot();
	}
}

function intersects(x1, y1, w1, h1, x2, y2, w2, h2)
{
	if(y2 + h2 < y1 ||
		x2 + w2 < x1 ||
		x2 > x1 + w1 ||
		y2 > y1 + h1)
	{
		return false;
	}
	return true;
}

function run()
{
	context.fillStyle = "#ccc";
	context.fillRect(0, 0, canvas.width, canvas.height);

	var deltaTime = getDeltaTime();

	for(var y=0; y<15; y++)
	{
		for(var x=0; x<20; x++)
		{
			context.drawImage(background[y][x], x*32, y*32);
		}
	}

	if(bullet.isDead == false)
	{
		bullet.x += bullet.velocityX;
		bullet.y += bullet.velocityY;
		context.drawImage(bullet.image,
				bullet.x - bullet.width/2,bullet.y - bullet.height/2);
	}

	var s = Math.sin(player.rotation);
	var c = Math.cos(player.rotation);

	var xDir = (player.directionX * c) - (player.directionY * s);
	var yDir = (player.directionX * s) + (player.directionY * c);
	var xVel = xDir * PLAYER_SPEED;
	var yVel = yDir * PLAYER_SPEED;

	player.x += xVel;
	player.y += yVel;

	player.rotation += player.angularDirection * PLAYER_TURN_SPEED;

	context.save();
		context.translate(player.x, player.y);
		context.rotate(player.rotation);
		context.drawImage(
			player.image, -player.width/2, -player.height/2);
	context.restore();

	var velocityX = asteroid.directionX * ASTEROID_SPEED;
	var velocityY = asteroid.directionY * ASTEROID_SPEED;
	asteroid.x += velocityX;
	asteroid.y += velocityY;
	context.drawImage(asteroid.image,
			asteroid.x - asteroid.width/2,
			asteroid.y - asteroid.height/2);

	for(var i=0; i<asteroids.length; i++)
	{
			asteroids[i].x = asteroids[i].x + asteroids[i].velocityX;
			asteroids[i].y = asteroids[i].y + asteroids[i].velocityY;
	}

	for(var i=0; i<asteroids.length; i++)
	{
			context.drawImage(asteroids[i].image, asteroids[i].x, asteroids[i].y);
	}

	spawnTimer -= deltaTime;
	if(spawnTimer <= 0)
	{
			spawnTimer = 1;
			spawnAsteroid();
	}

		for(var i=0; i<asteroids.length; i++)
		{
			for(var j=0; j<bullets.length; j++)
			{
				if(intersects(
					bullets[j].x, bullets[j].y,
					bullets[j].width, bullets[j].height,
					asteroids[i].x, asteroids[i].y,
					asteroids[i].width, asteroids[i].height) == true)
				{
					asteroids.splice(i, 1);
					bullets.splice(j, 1);
					break;
				}
			}
		}
	}

//60FPS framework
(function()
{
var onEachFrame;

if (window.requestAnimationFrame)
{
  onEachFrame = function(cb)
  {
   var _cb = function() { cb(); window.requestAnimationFrame(_cb); }
   _cb();
  };

}
else if (window.mozRequestAnimationFrame)
	{
	onEachFrame = function(cb) {
		var _cb = function() { cb(); window.mozRequestAnimationFrame(_cb); }
		_cb();
	};

}
else
{
	onEachFrame = function(cb)
	{
		setInterval(cb, 1000 / 60);
	}
}

	window.onEachFrame = onEachFrame;
})();

window.onEachFrame(run);