<canvas id="screen"></canvas>

canvas{
	background-color: #000000;
  position: absolute;
  top: 0px;
  left: 0px;
}

var screenWidth = window.innerWidth;
var screenHeight = window.innerHeight;
 
var minVx = -10;
var deltaVx = 20;
var minVy = 25
var deltaVy = 15;
var minParticleV = 5;
var deltaParticleV = 5;
 
var gravity = 1;
 
var explosionRadius = 200;
var bombRadius = 10;
var explodingDuration = 100;
var explosionDividerFactor = 10; // I couldn't find a better name. Got any?
 
var nBombs = 1; // initial
var percentChanceNewBomb = 5;
 
// Color utils forked from http://andreasstorm.com/
// (or someone who forked from there)
 
function Color(min) {
  min = min || 0;
  this.r = colorValue(min);
  this.g = colorValue(min);
  this.b = colorValue(min);
  this.style = createColorStyle(this.r, this.g, this.b);
};
 
function colorValue(min) {
  return Math.floor(Math.random() * 255 + min);
}
 
function createColorStyle(r,g,b) {
  return 'rgba(' + r + ',' + g + ',' + b + ', 0.8)';
}
 
// A Bomb. Or firework.
function Bomb(){
  var self = this;
 
  self.radius = bombRadius;
  self.previousRadius = bombRadius;
  self.explodingDuration = explodingDuration;
  self.hasExploded = false;
  self.alive = true;
  self.color = new Color();
 
  self.px = (window.innerWidth / 4) + (Math.random() * window.innerWidth / 2);
  self.py = window.innerHeight;
 
  self.vx = minVx + Math.random() * deltaVx;
  self.vy = (minVy + Math.random() * deltaVy) * -1; // because y grows downwards
 
  self.duration = 
 
  self.update = function(particlesVector){
    if(self.hasExploded){
      var deltaRadius = explosionRadius - self.radius;
      self.previousRadius = self.radius;
      self.radius += deltaRadius / explosionDividerFactor;
      self.explodingDuration--;
      if(self.explodingDuration == 0){
        self.alive = false;
      }
    }
    else{
      self.vx += 0;
      self.vy += gravity;
      if(self.vy >= 0){ // invertion point
        self.explode(particlesVector);
      }
 
      self.px += self.vx;
      self.py += self.vy;
    }
  };
 
  self.draw = function(ctx){
    ctx.beginPath();
    ctx.arc(self.px, self.py, self.previousRadius, 0, Math.PI * 2, false);
    if(self.hasExploded){
    }
    else{
      ctx.fillStyle = self.color.style;
      ctx.lineWidth = 1;
      ctx.fill();
    }
 
  };
 
 
  self.explode = function(particlesVector){
    self.hasExploded = true;
    var e = 3 + Math.floor(Math.random() * 3);
    for(var j = 0; j < e; j++){
      var n = 10 + Math.floor(Math.random() * 21); // 10 - 30
      var speed = minParticleV + Math.random() * deltaParticleV;
      var deltaAngle = 2 * Math.PI / n;
      var initialAngle = Math.random() * deltaAngle;
      for(var i = 0; i < n; i++){
        particlesVector.push(new Particle(self,  i * deltaAngle + initialAngle, speed));
      }
    }
  };
 
}
 
function Particle(parent, angle, speed){
  var self = this;
  self.px = parent.px;
  self.py = parent.py;
  self.vx = Math.cos(angle) * speed;
  self.vy = Math.sin(angle) * speed;
  self.color = parent.color;
  self.duration = 40 + Math.floor(Math.random()*20);
  self.alive = true;
 
  self.update = function(){
    self.vx += 0;
    self.vy += gravity / 10;
 
    self.px += self.vx;
    self.py += self.vy;
    self.radius = 3;
 
    self.duration--;
    if(self.duration <= 0){
      self.alive = false;
    }
  };
 
  self.draw = function(ctx){
    ctx.beginPath();
    ctx.arc(self.px, self.py, self.radius, 0, Math.PI * 2, false);
    ctx.fillStyle = self.color.style;
    ctx.lineWidth = 1;
    ctx.fill();
  };
 
}
 
function Controller(){
  var self = this;
  self.canvas = document.getElementById("screen");
  self.canvas.width = screenWidth;
  self.canvas.height = screenHeight;
  self.ctx = self.canvas.getContext('2d');
 
  function setSpeedParams(){
    var heightReached = 0;
    var vy = 0;
 
    while(heightReached < screenHeight && vy >= 0){
      vy += gravity;
      heightReached += vy;
    }
 
    minVy = vy / 2;
    deltaVy = vy - minVy;
 
    vx = (1 / 4) * screenWidth / (vy / 2);
    minVx = -vx;
    deltaVx = 2*vx;
  };
 
 
 
  self.resize = function(){
    screenWidth = window.innerWidth;
    screenHeight = window.innerHeight;
    self.canvas.width = screenWidth;
    self.canvas.height = screenHeight;
    setSpeedParams();
  };
  self.resize();
 
  window.onresize = self.resize;
 
  self.init = function(){
    self.readyBombs = [];
    self.explodedBombs = [];
    self.particles = [];
 
    for(var i = 0; i < nBombs; i++){ self.readyBombs.push(new Bomb()); } } self.update = function(){ var aliveBombs = []; while(self.explodedBombs.length > 0){
      var bomb = self.explodedBombs.shift();
      bomb.update();
      if(bomb.alive){
        aliveBombs.push(bomb);
      }
    }
    self.explodedBombs = aliveBombs;
 
    var notExplodedBombs = [];
    while(self.readyBombs.length > 0){
      var bomb = self.readyBombs.shift();
      bomb.update(self.particles);
      if(bomb.hasExploded){
        self.explodedBombs.push(bomb);
      }
      else{
        notExplodedBombs.push(bomb);
      }
    }
    self.readyBombs = notExplodedBombs;
 
    var aliveParticles = [];
    while(self.particles.length > 0){
      var particle = self.particles.shift();
      particle.update();
      if(particle.alive){
        aliveParticles.push(particle);
      }
    }
    self.particles = aliveParticles;
  }
 
  self.draw = function(){
    self.ctx.beginPath();
    self.ctx.fillStyle='rgba(0, 0, 0, 0.1)'; // Ghostly effect
    self.ctx.fillRect(0, 0, self.canvas.width, self.canvas.height);
 
 
 
    for(var i = 0; i < self.readyBombs.length; i++){
      self.readyBombs[i].draw(self.ctx);
    }
 
    for(var i = 0; i < self.explodedBombs.length; i++){
      self.explodedBombs[i].draw(self.ctx);
    }
 
    for(var i = 0; i < self.particles.length; i++){
      self.particles[i].draw(self.ctx);
    }
 
  }
 
  self.animation = function(){
    self.update();
    self.draw();
 
   if(Math.random() * 100 < percentChanceNewBomb) {
     self.readyBombs.push(new Bomb());
   }
 
 
    requestAnimationFrame(self.animation);
  }
}
 
var controller = new Controller();
controller.init();
requestAnimationFrame(controller.animation);