window.requestAnimFrame = (function () {
    return window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        function (callback) {
            window.setTimeout(callback, 1000 / 60);
        };
})();

var canvas = null,
    ctx = null,
    cw = window.innerWidth,
    ch = window.innerHeight,
    fireworksLimit = 10,
    fireworksShown = 0,
    fireworks = [],
    particles = [],
    hue = 120,
    timerTotal = 25,
    timerTick = 0,
    animationEnd = true;

function random(min, max) {
    return Math.random() * (max - min) + min;
}

/* To sprawdzic... */
function calculateDistance(p1x, p1y, p2x, p2y) {
    var xDistance = p1x - p2x,
        yDistance = p1y - p2y;
    return Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2));
}

function Firework(sx, sy, tx, ty) {
    this.x = sx;
    this.y = sy;

    this.sx = sx;
    this.sy = sy;

    this.tx = tx;
    this.ty = ty;

    this.distanceToTarget = calculateDistance(sx, sy, tx, ty);
    this.distanceTraveled = 0;

    this.coordinates = [];
    this.coordinateCount = 3;

    while (this.coordinateCount--) {
        this.coordinates.push([this.x, this.y]);
    }

    this.angle = Math.atan2(ty - sy, tx - sx);
    this.speed = 2;
    this.acceleration = 1.05;
    this.brightness = random(50, 70);
    this.targetRadius = 1;
}

Firework.prototype.update = function (index) {
    this.coordinates.pop();
    this.coordinates.unshift([this.x, this.y]);

    if (this.targetRadius < 8) {
        this.targetRadius += 0.3;
    } else {
        this.targetRadius = 1;
    }

    // speed up the firework
    this.speed *= this.acceleration;

    // get the current velocities based on angle and speed
    var vx = Math.cos(this.angle) * this.speed,
        vy = Math.sin(this.angle) * this.speed;
    // how far will the firework have traveled with velocities applied?
    this.distanceTraveled = calculateDistance(this.sx, this.sy, this.x + vx, this.y + vy);

    if (this.distanceTraveled >= this.distanceToTarget) {
        createParticles(this.tx, this.ty);
        // remove the firework, use the index passed into the update function to determine which to remove
        fireworks.splice(index, 1);
    } else {
        // target not reached, keep traveling
        this.x += vx;
        this.y += vy;
    }
}

// draw firework
Firework.prototype.draw = function () {
    ctx.beginPath();
    // move to the last tracked coordinate in the set, then draw a line to the current x and y
    ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]);
    ctx.lineTo(this.x, this.y);
    ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)';
    ctx.stroke();
}

function Particle(x, y) {
    this.x = x;
    this.y = y;
    // track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails
    this.coordinates = [];
    this.coordinateCount = 5;
    while (this.coordinateCount--) {
        this.coordinates.push([this.x, this.y]);
    }
    // set a random angle in all possible directions, in radians
    this.angle = random(0, Math.PI * 2);
    this.speed = random(1, 10);
    // friction will slow the particle down
    this.friction = 0.98;
    // gravity will be applied and pull the particle down
    this.gravity = 1;
    // set the hue to a random number +-50 of the overall hue variable
    this.hue = random(hue - 50, hue + 50);
    this.brightness = random(50, 80);
    this.alpha = 1;
    // set how fast the particle fades out
    this.decay = random(0.015, 0.03);
}

// update particle
Particle.prototype.update = function (index) {
    // remove last item in coordinates array
    this.coordinates.pop();
    // add current coordinates to the start of the array
    this.coordinates.unshift([this.x, this.y]);
    // slow down the particle
    this.speed *= this.friction;
    // apply velocity
    this.x += Math.cos(this.angle) * this.speed;
    this.y += Math.sin(this.angle) * this.speed + this.gravity;
    // fade out the particle
    this.alpha -= this.decay;

    // remove the particle once the alpha is low enough, based on the passed in index
    if (this.alpha <= this.decay) {
        particles.splice(index, 1);
    }

    if (particles.length === 0) {
        if (fireworksShown === fireworksLimit) {
            animationEnd = true;
        }
    }
}

// draw particle
Particle.prototype.draw = function () {
    ctx.beginPath();
    // move to the last tracked coordinates in the set, then draw a line to the current x and y
    ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]);
    ctx.lineTo(this.x, this.y);
    ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')';
    ctx.stroke();
}

// create particle group/explosion
function createParticles(x, y) {
    // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though
    var particleCount = 500;
    while (particleCount--) {
        particles.push(new Particle(x, y));
    }
}

function loop() {
    if (animationEnd === true) {
        animationFinish();
        return true;
    }

    requestAnimationFrame(loop);
    hue = random(0, 360);

    ctx.globalCompositeOperation = 'destination-out';
    ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
    ctx.fillRect(0, 0, cw, ch);
    ctx.globalCompositeOperation = 'lighter';

    var i = fireworks.length;
    while (i--) {
        fireworks[i].draw();
        fireworks[i].update(i);
    }

    var i = particles.length;
    while (i--) {
        particles[i].draw();
        particles[i].update(i);
    }

    if (timerTick >= timerTotal) {
        // start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen
        if (fireworksShown < fireworksLimit) {
            fireworks.push(new Firework(cw / 2, ch, random(0, cw), random(0, ch / 2)));
            fireworksShown++;
            timerTick = 0;
        }
    } else {
        timerTick++;
    }
}

//window.onload = loop;
window.fireworks.start = function () {
    /* Prevent multiple animations */
    if (animationEnd === false) {
        return false;
    }

    fireworksShown = 0;
    animationEnd = false;
    canvas = document.createElement('canvas');
    document.body.appendChild(canvas);
    ctx = canvas.getContext('2d');
    canvas.style.zIndex = 100;
    canvas.style.top = 0;
    canvas.style.left = 0;
    canvas.style.position = 'fixed';
    canvas.width = cw;
    canvas.height = ch;
    //canvas.style.background = "rgba(0,0,0,0.7)";

    loop();

    //setTimeout(function(){animationEnd = true;}, 4500);
}

animationFinish = function () {
    document.body.removeChild(canvas);
};