//We need few imports for the color
import fl.motion.Color;
import flash.geom.ColorTransform;
 
/*We want 20 particles at the start
particlesArray is used when we animate each particle */
var numberOfParticles:Number = 20;
var particlesArray:Array = new Array();
 
//Each time a hit occurs, we want to create 10 new particles
var numberOfExplosionParticles:uint = 10;
 
//This loop creates the first particles and gives them speed and coordinates
for (var i=0; i < numberOfParticles; i++) {
 
	var particle:Particle = new Particle();
 
	//We want the particles to stay at their original position
	particle.speedX = 0;
	particle.speedY = 0;
 
	//Set the starting position
	particle.y = Math.random() * stage.stageHeight;
	particle.x = Math.random() * stage.stageWidth;
 
	//Add the particle to the stage and push it to array for later use.
	addChild (particle);
	particlesArray.push (particle);
}
 
//Call for the first explosion
startExplosions ();
 
/*This function makes a random particle to explode.
From here, the chain reaction begins.*/
function startExplosions ():void {
 
	//Select a random particle from an array
	var index = Math.round(Math.random() * (particlesArray.length-1));
	var firstParticle:Particle = particlesArray[index];
 
	//Set a random tint
	var ct:Color = new Color();
	ct.setTint (0xFFFFFF * Math.random(),1);
 
	//Create 10 new particles because of explosion
	for (var i=0; i < numberOfExplosionParticles; i++) {
 
		var particle:Particle = new Particle();
 
		/*Give random x and y speed to the particle. 
		Math.random returns a random number n, where 0 <= n < 1. */
		particle.speedX = Math.random()*10 - 5 ;
		particle.speedY = Math.random()*10 - 5;
 
		//Apply the randomly selected tint to each particle
		particle.transform.colorTransform = ct;
 
		//Set the starting position
		particle.y = firstParticle.y;
		particle.x = firstParticle.x;
 
		//Particle is part of an explosion
		particle.partOfExplosion = true;
 
		//Add the particle to the stage and push it to array for later use.
		addChild (particle);
		particlesArray.push (particle);
	}
	//Let's remove the particle that exploded (remove from stage and from the array)
	removeChild (firstParticle);
	particlesArray.splice (index,1);
 
	addEventListener (Event.ENTER_FRAME, enterFrameHandler);
}
 
//This function is responsible for the animation
function enterFrameHandler (e:Event):void {
 
	//Loop through every particle
	for (var i=0; i < particlesArray.length; i++) {
 
		var particleOne:Particle = particlesArray[i];
 
		//Update the particle's coordinates
		particleOne.y += particleOne.speedY;
		particleOne.x += particleOne.speedX;
 
		/*This loop calls a checkForHit function to find if the two particles are colliding*/
		for (var j:uint = i + 1; j < particlesArray.length; j++) {
			var particleTwo:Particle = particlesArray[j];
 
			/*Make sure the particles are on stage, only then check for hits*/
			if (contains(particleOne) && contains(particleTwo)) {
				checkForHit (particleOne, particleTwo);
			}
		}
	}
}
 
/*This function checks whether two particles have collided*/
function checkForHit (particleOne:Particle, particleTwo:Particle):void {
 
	/*Let's make sure we only check those particles, where one is moving and the other
	is stationary. We don't want two moving particles to explode. */
	if ((particleOne.partOfExplosion == false && particleTwo.partOfExplosion == true) ||
	particleOne.partOfExplosion == true && particleTwo.partOfExplosion == false ) {
 
		//Calculate the distance using Pythagorean theorem
		var distanceX:Number = particleOne.x - particleTwo.x;
		var distanceY:Number = particleOne.y - particleTwo.y;
		var distance:Number = Math.sqrt(distanceX*distanceX + distanceY*distanceY);
 
		/* If the distance is smaller than particle's width, we have a hit. 
		Note: if the particles were of different size, the calculation would be:
		distance < ((particleOne.width / 2) + (particleTwo.width / 2))
		*/
		if (distance < particleOne.width) {
 
			//Set a random tint to the particles that explode
			var ct:Color = new Color();
			ct.setTint (0xFFFFFF * Math.random(),1);
 
			//Create 10 new particles because of an explosion
			for (var i=0; i < numberOfExplosionParticles; i++) {
 
				var particle:Particle = new Particle();
 
				particle.speedX = Math.random()*10 - 5 ;
				particle.speedY = Math.random()*10 - 5;
 
				//Apply tint
				particle.transform.colorTransform = ct;
 
				//Set the starting position
				particle.y = particleOne.y;
				particle.x = particleOne.x;
 
				particle.partOfExplosion = true;
 
				//Add the particle to the stage and push it to array for later use.
				addChild (particle);
				particlesArray.push (particle);
			}
 
			/* Check which of the two particles was stationary.
			We'll remove the one that was stationary.
			*/
			if (particleOne.partOfExplosion == false) {
				var temp1 = particlesArray.indexOf(particleOne);
				particlesArray.splice (temp1,1);
				removeChild (particleOne);
			}
			else {
				var temp2 = particlesArray.indexOf(particleTwo);
				particlesArray.splice (temp2,1);
				removeChild (particleTwo);
			}
 
		}
	}
}