var w = window.innerWidth;
var h = window.innerHeight;
var ctx = document.getElementById('canvas');

window.addEventListener('load', resize);
window.addEventListener('resize', resize, false);

function resize() {
	ctx.width = w = window.innerWidth;
	ctx.height = h = window.innerHeight;
}

resize();

let ctxfr = ctx.getContext('2d');

// min and max radius, radius threshold and percentage of filled circles
var radMin = 5,
	radMax = 125,
	filledCircle = 60, //percentage of filled circles
	concentricCircle = 30, //percentage of concentric circles
	radThreshold = 25; //IFF special, over this radius concentric, otherwise filled

//min and max speed to move
var speedMin = 0.3,
	speedMax = 2.5;

//max reachable opacity for every circle and blur effect
var maxOpacity = 0.6;

//default palette choice
var colors = ['52,168,83', '117,95,147', '199,108,23', '194,62,55', '0,172,212', '120,120,120'],
	bgColors = ['52,168,83', '117,95,147', '199,108,23', '194,62,55', '0,172,212', '120,120,120'],
	circleBorder = 10,
	backgroundLine = bgColors[0];
var backgroundMlt = 0.85;

//min distance for links
var linkDist = Math.min(canvas.width, canvas.height) / 2.4,
	lineBorder = 2.5;

//most importantly: number of overall circles and arrays containing them
var maxCircles = 12,
	points = [],
	pointsBack = [];

//populating the screen
for (var i = 0; i < maxCircles * 2; i++) points.push(new Circle());
for (var i = 0; i < maxCircles; i++) pointsBack.push(new Circle(true));

//experimental vars
var circleExp = 1,
	circleExpMax = 1.003,
	circleExpMin = 0.997,
	circleExpSp = 0.00004,
	circlePulse = false;

//circle class
function Circle(background) {
	//if background, it has different rules
	this.background = (background || false);
	this.x = randRange(-canvas.width / 2, canvas.width / 2);
	this.y = randRange(-canvas.height / 2, canvas.height / 2);
	this.radius = background ? hyperRange(radMin, radMax) * backgroundMlt : hyperRange(radMin, radMax);
	this.filled = this.radius < radThreshold ? (randint(0, 100) > filledCircle ? false : 'full') : (randint(0, 100) >
		concentricCircle ? false : 'concentric');
	this.color = background ? bgColors[randint(0, bgColors.length - 1)] : colors[randint(0, colors.length - 1)];
	this.borderColor = background ? bgColors[randint(0, bgColors.length - 1)] : colors[randint(0, colors.length - 1)];
	this.opacity = 0.05;
	this.speed = (background ? randRange(speedMin, speedMax) / backgroundMlt : randRange(speedMin, speedMax)); // * (radMin / this.radius);
	this.speedAngle = Math.random() * 2 * Math.PI;
	this.speedx = Math.cos(this.speedAngle) * this.speed;
	this.speedy = Math.sin(this.speedAngle) * this.speed;
	var spacex = Math.abs((this.x - (this.speedx < 0 ? -1 : 1) * (canvas.width / 2 + this.radius)) / this.speedx),
		spacey = Math.abs((this.y - (this.speedy < 0 ? -1 : 1) * (canvas.height / 2 + this.radius)) / this.speedy);
	this.ttl = Math.min(spacex, spacey);
};

Circle.prototype.init = function() {
	Circle.call(this, this.background);
}

//support functions
//generate random int a<=x<=b
function randint(a, b) {
	return Math.floor(Math.random() * (b - a + 1) + a);
}
//generate random float
function randRange(a, b) {
	return Math.random() * (b - a) + a;
}
//generate random float more likely to be close to a
function hyperRange(a, b) {
	return Math.random() * Math.random() * Math.random() * (b - a) + a;
}

//rendering function
function drawCircle(ctx, circle) {
	//circle.radius *= circleExp;
	var radius = circle.background ? circle.radius *= circleExp : circle.radius /= circleExp;
	ctx.beginPath();
	ctx.arc(circle.x, circle.y, radius * circleExp, 0, 2 * Math.PI, false);
	ctx.lineWidth = Math.max(1, circleBorder * (radMin - circle.radius) / (radMin - radMax));
	ctx.strokeStyle = ['rgba(', circle.borderColor, ',', circle.opacity, ')'].join('');
	if (circle.filled == 'full') {
		ctx.fillStyle = ['rgba(', circle.borderColor, ',', circle.background ? circle.opacity * 0.8 : circle.opacity, ')']
			.join('');
		ctx.fill();
		ctx.lineWidth = 0;
		ctx.strokeStyle = ['rgba(', circle.borderColor, ',', 0, ')'].join('');
	}
	ctx.stroke();
	if (circle.filled == 'concentric') {
		ctx.beginPath();
		ctx.arc(circle.x, circle.y, radius / 2, 0, 2 * Math.PI, false);
		ctx.lineWidth = Math.max(1, circleBorder * (radMin - circle.radius) / (radMin - radMax));
		ctx.strokeStyle = ['rgba(', circle.color, ',', circle.opacity, ')'].join('');
		ctx.stroke();
	}
	circle.x += circle.speedx;
	circle.y += circle.speedy;
	if (circle.opacity < (circle.background ? maxOpacity : 1)) circle.opacity += 0.01;
	circle.ttl--;
}

//initializing function
function init() {
	window.requestAnimationFrame(draw);
}

//rendering function
function draw() {

	if (circlePulse) {
		if (circleExp < circleExpMin || circleExp > circleExpMax) circleExpSp *= -1;
		circleExp += circleExpSp;
	}

	ctxfr.globalCompositeOperation = 'destination-over';
	ctxfr.clearRect(0, 0, canvas.width, canvas.height); // clear canvas

	ctxfr.save();
	ctxfr.translate(canvas.width / 2, canvas.height / 2);

	//function to render each single circle, its connections and to manage its out of boundaries replacement
	function renderPoints(ctx, arr) {
		for (var i = 0; i < arr.length; i++) {
			var circle = arr[i];
			//checking if out of boundaries
			if (circle.ttl < 0) {}
			var xEscape = canvas.width / 2 + circle.radius,
				yEscape = canvas.height / 2 + circle.radius;
			if (circle.ttl < -20) arr[i].init(arr[i].background);
			//if (Math.abs(circle.y) > yEscape || Math.abs(circle.x) > xEscape) arr[i].init(arr[i].background);
			drawCircle(ctx, circle);
		}
		for (var i = 0; i < arr.length - 1; i++) {
			for (var j = i + 1; j < arr.length; j++) {
				var deltax = arr[i].x - arr[j].x;
				var deltay = arr[i].y - arr[j].y;
				var dist = Math.pow(Math.pow(deltax, 2) + Math.pow(deltay, 2), 0.5);
				//if the circles are overlapping, no laser connecting them
				if (dist <= arr[i].radius + arr[j].radius) continue;
				//otherwise we connect them only if the dist is < linkDist
				if (dist < linkDist) {
					var xi = (arr[i].x < arr[j].x ? 1 : -1) * Math.abs(arr[i].radius * deltax / dist);
					var yi = (arr[i].y < arr[j].y ? 1 : -1) * Math.abs(arr[i].radius * deltay / dist);
					var xj = (arr[i].x < arr[j].x ? -1 : 1) * Math.abs(arr[j].radius * deltax / dist);
					var yj = (arr[i].y < arr[j].y ? -1 : 1) * Math.abs(arr[j].radius * deltay / dist);
					ctx.beginPath();
					ctx.moveTo(arr[i].x + xi, arr[i].y + yi);
					ctx.lineTo(arr[j].x + xj, arr[j].y + yj);
					var samecolor = arr[i].color == arr[j].color;
					ctx.strokeStyle = ["rgba(", arr[i].borderColor, ",", Math.min(arr[i].opacity, arr[j].opacity) * ((linkDist -
						dist) / linkDist), ")"].join("");
					ctx.lineWidth = (arr[i].background ? lineBorder * backgroundMlt : lineBorder) * ((linkDist - dist) / linkDist); //*((linkDist-dist)/linkDist);
					ctx.stroke();
				}
			}
		}
	}

	renderPoints(ctxfr, points);
	ctxfr.restore();

	window.requestAnimationFrame(draw);
}

init();