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/*!
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 * @class bkcore.threejs.Particles
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 *
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 * Particle system wrapper/helper
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 * 
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 * @author Thibaut 'BKcore' Despoulain <http://bkcore.com>
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 */
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/*!
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 * @package bkcore.threejs
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 */ 
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var bkcore = bkcore || {};
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bkcore.threejs = bkcore.threejs || {};
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/**
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 * Creates a new particle system using given parameters
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 * @param {Object{max, spawnRate, spawn, velocity, randomness, force, spawnRadius, life, friction, color, color2, tint, texture, size, blending, depthTest, transparent, opacity}} opts 
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 */
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bkcore.threejs.Particles = function(opts)
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{
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	this.black = new THREE.Color(0x000000);
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	this.white = new THREE.Color(0xffffff);
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	this.material = new THREE.ParticleBasicMaterial({
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		color: opts.tint == undefined ? 0xffffff : opts.tint,
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		map: opts.texture == undefined ? null : opts.texture,
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		size: opts.size == undefined ? 4 : opts.size,
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		blending: opts.blending == undefined ? THREE.AdditiveBlending : opts.blending,
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		depthTest: opts.depthTest == undefined ? false : opts.depthTest,
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		transparent: opts.transparent == undefined ? true : opts.transparent,
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		vertexColors: true,
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		opacity: opts.opacity == undefined ? 1.0 : opts.opacity,
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		sizeAttenuation: true
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	});
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	this.max = opts.max == undefined ? 1000 : opts.max;
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	this.spawnRate = opts.spawnRate == undefined ? 0 : opts.spawnRate;
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	this.spawn = opts.spawn == undefined ? new THREE.Vector3() : opts.spawn;
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	this.velocity = opts.velocity == undefined ? new THREE.Vector3() : opts.velocity;
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	this.randomness = opts.randomness == undefined ? new THREE.Vector3() : opts.randomness;
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	this.force = opts.force == undefined ? new THREE.Vector3() : opts.force;
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	this.spawnRadius = opts.spawnRadius == undefined ? new THREE.Vector3() : opts.spawnRadius;
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	this.life = opts.life == undefined ? 60 : opts.life;
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	this.ageing = 1 / this.life;
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	this.friction = opts.friction == undefined ? 1.0 : opts.friction;
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	this.color = new THREE.Color(opts.color == undefined ? 0xffffff : opts.color);
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	this.color2 = opts.color2 == undefined ? null : new THREE.Color(opts.color2);
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	this.position = opts.position == undefined ? new THREE.Vector3() : opts.position;
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	this.rotation = opts.rotation == undefined ? new THREE.Vector3() : opts.rotation;
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	this.sort = opts.sort == undefined ? false : opts.sort;
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	this.pool = [];
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	this.buffer = [];
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	this.geometry = null;
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	this.system = null;
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	this.build();
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}
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bkcore.threejs.Particles.prototype.build = function()
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{
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	this.geometry = new THREE.Geometry();
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	this.geometry.dynamic = true;
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	this.pool = [];
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	this.buffer = [];
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	for(var i = 0; i < this.max; ++i)
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	{
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		var p = new bkcore.threejs.Particle();
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		this.pool.push(p);
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		this.buffer.push(p);
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		this.geometry.vertices.push(p.position);
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		this.geometry.colors.push(p.color);
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	}
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	this.system = new THREE.ParticleSystem(this.geometry, this.material);
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	this.system.position = this.position;
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	this.system.rotation = this.rotation;
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	this.system.sort = this.sort;
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}
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/**
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 * Emits given number of particles
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 * @param  int count
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 */
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bkcore.threejs.Particles.prototype.emit = function(count)
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{
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	var emitable = Math.min(count, this.pool.length);
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	for(var i = 0; i < emitable; ++i)
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	{
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		var p = this.pool.pop();
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		p.available = false;
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		p.position.copy(this.spawn)
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			.addSelf(
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				this.randomVector()
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				.multiplySelf(this.spawnRadius)
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			);
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		p.velocity.copy(this.velocity)
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			.addSelf(
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				this.randomVector()
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				.multiplySelf(this.randomness)
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			);
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		p.force.copy(this.force);
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		p.basecolor.copy(this.color);
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		if(this.color2 != undefined) p.basecolor.lerpSelf(this.color2, Math.random());
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		p.life = 1.0;
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	}
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}
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bkcore.threejs.Particles.prototype.randomVector = function()
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{
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	return new THREE.Vector3(
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			Math.random()*2-1,
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			Math.random()*2-1,
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			Math.random()*2-1
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		);
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}
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/**
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 * Updates particles (should be call in a RAF loop)
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 * @param  float dt time delta ~1.0
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 */
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bkcore.threejs.Particles.prototype.update = function(dt)
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{
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	var p, l;
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	var df = new THREE.Vector3();
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	var dv = new THREE.Vector3();
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	for(var i = 0; i < this.buffer.length; ++i)
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	{
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		p = this.buffer[i];
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		if(p.available) continue;
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		p.life -= this.ageing;
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		if(p.life <= 0 && !p.available)
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		{
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			p.reset();
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			this.pool.push(p);
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			continue;
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		}
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		l = p.life > 0.5 ? 1.0 : p.life + 0.5;
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		p.color.setRGB(
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			l * p.basecolor.r, 
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			l * p.basecolor.g, 
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			l * p.basecolor.b
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		);
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		if(this.friction != 1.0)
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			p.velocity.multiplyScalar(this.friction);
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		df.copy(p.force).multiplyScalar(dt);
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		p.velocity.addSelf(df);
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		dv.copy(p.velocity).multiplyScalar(dt);
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		p.position.addSelf(dv);
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	}
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	if(this.spawnRate > 0)
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		this.emit(this.spawnRate);
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	this.geometry.verticesNeedUpdate = true;
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	this.geometry.colorsNeedUpdate = true;
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}
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bkcore.threejs.Particle = function()
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{
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	this.position = new THREE.Vector3(-10000,-10000,-10000);
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	this.velocity = new THREE.Vector3();
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	this.force = new THREE.Vector3();
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	this.color = new THREE.Color(0x000000);
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	this.basecolor = new THREE.Color(0x000000);
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	this.life = 0.0;
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	this.available = true;
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}
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bkcore.threejs.Particle.prototype.reset = function()
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{
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	this.position.set(0,-100000,0);
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	this.velocity.set(0,0,0);
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	this.force.set(0,0,0);
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	this.color.setRGB(0,0,0);
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	this.basecolor.setRGB(0,0,0);
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	this.life = 0.0;
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	this.available = true;
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}
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