// window.addEventListener('resize', function()
// {
//   jsCanvasSnow.resize(document.documentElement.clientWidth, 3600);
//     jsCanvasSnow.init();
// }, false);

window.addEventListener('load', function()
{
  jsCanvasSnow.init();
  jsCanvasSnow.start();
}, false);
function microtime()
{
	return new Date().getTime()*0.01;
}

// returns a random integer from min to max
function irand(min, max)
{
	return Math.floor((min||0) + Math.random() * ((max+1||100) - (min||0)));
}

// returns a random float from min to max
function frand(min, max)
{
	return (min||0) + Math.random() * ((max||1) - (min||0));
}

function clamp(value, min, max)
{
	return Math.min(Math.max(value, min), max);
}

// Two component vector class
function Vector2(x, y)
{
	this.x = x || 0;
	this.y = y || 0;
	
	this.add = function(other)
	{
		this.x += other.x;
		this.y += other.y;
	}
	
	this.magnitude = function()
	{
		return Math.sqrt(this.x * this.x + this.y * this.y);
	}
}

function Color(r, g, b)
{
	this.r = r || 0;
	this.g = g || 0;
	this.b = b || 0;
}
function jsParticle(origin, velocity, size, amplitude)
{
	this.origin = origin;
	this.position = new Vector2(origin.x, origin.y);
	this.velocity = velocity || new Vector2(0, 0);
	this.size = size;
	this.amplitude = amplitude;
	
	// randomize start values a bit
	this.dx = Math.random() * 100;
	
	this.update = function(delta_time)
	{
		this.position.y += this.velocity.y * delta_time;
		
		// oscilate the x value between -amplitude and +amplitude
		this.dx += this.velocity.x*delta_time;		
		this.position.x = this.origin.x + (this.amplitude * Math.sin(this.dx));
	};
}

var jsCanvasSnow = 
{
	canvas : null,
	ctx : null,
	particles : [],
	running : false,
	
	start_time : 0,
	frame_time : 0,

	init : function( )
	{
		// use the container width and height
		this.canvas = document.getElementById('snowing');
		this.ctx = this.canvas.getContext('2d');
    this.resize(document.documentElement.clientWidth, 3600);

		// change these values
    // the 2 element arrays represent min and max values
		this.pAmount = 1200;         // amount of particles
		this.pSize = [0.1 , 3];    // min and max size
		this.pSwing = [0.1, 0.5];      // min and max oscilation speed for x movement
		this.pSpeed = [5, 10],     // min and max y speed
		this.pAmplitude = [20, 30];  // min and max distance for x movement
		
    this._init_particles();
	},
	
	start : function()
	{
		this.running = true;
		this.start_time = this.frame_time = microtime();
		this._loop();
	},
	
	stop : function()
	{
		this.running = false;
	},
  
  resize : function(w, h)
  {
    this.canvas.width = w;
    this.canvas.height = h;
  },
	
	_loop : function()
	{
		if ( jsCanvasSnow.running )
		{
			jsCanvasSnow._clear();
			jsCanvasSnow._update();
			jsCanvasSnow._draw();
			jsCanvasSnow._queue();
		}
	},	
	
	_init_particles : function()
	{
		// clear the particles array
		this.particles.length = 0;
		
		for ( var i = 0 ; i < this.pAmount ; i++) 
		{
			var origin = new Vector2(frand(0, this.canvas.width), frand(-this.canvas.height, 0));
			var velocity = new Vector2(frand(this.pSwing[0],this.pSwing[1]), frand(this.pSpeed[0],this.pSpeed[1]));
			var size = frand(this.pSize[0], this.pSize[1]);
			var amplitude = frand(this.pAmplitude[0], this.pAmplitude[1]);
			
			this.particles.push(new jsParticle(origin, velocity, size, amplitude));
		}
	},

	_update : function()
	{
		// calculate the time since the last frame
		var now_time = microtime();
		var delta_time = now_time - this.frame_time;
		
		for ( var i = 0 ; i < this.particles.length ; i++)
		{
			var particle = this.particles[i];
			particle.update(delta_time);
			
			if (particle.position.y-particle.size > this.canvas.height)
			{
				// reset the particle to the top and a random x position
				particle.position.y = -particle.size;
				particle.position.x = particle.origin.x = Math.random() * this.canvas.width;
				particle.dx = Math.random() * 100;
			}			
		}
		
		// save this time for the next frame
		this.frame_time = now_time;
	},
	
	_draw : function()
	{
		this.ctx.fillStyle = 'rgb(255,255,255)';
		
		for ( var i = 0 ; i < this.particles.length ; i++)
		{
			var particle = this.particles[i];
			this.ctx.fillRect(particle.position.x, particle.position.y, particle.size, particle.size);
		}
	},
	
	_clear : function()
	{
		this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
	},
	
	_queue : function()
	{
		window.requestAnimationFrame( jsCanvasSnow._loop );
	}
};