<template>
    <canvas id="canvas"></canvas>
</template>

<script>
export default {
    props: {
        url: {
            type: String
        }
    },
    data() {
        return {

        }
    },
    mounted() {
        let app=document.querySelector("#app");
        var canvas = document.getElementById('canvas'),
            ctx = canvas.getContext('2d'),
            w = canvas.width = app.clientWidth,
            h = canvas.height = app.clientHeight,

            hue = 217,
            stars = [],
            count = 0,
            maxStars = 1200;

        var canvas2 = document.createElement('canvas'),
            ctx2 = canvas2.getContext('2d');
        canvas2.width = 100;
        canvas2.height = 100;
        var half = canvas2.width / 2,
            gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
        gradient2.addColorStop(0.025, '#fff');
        gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
        gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
        gradient2.addColorStop(1, 'transparent');

        ctx2.fillStyle = gradient2;
        ctx2.beginPath();
        ctx2.arc(half, half, half, 0, Math.PI * 2);
        ctx2.fill();

        // End cache

        function random(min, max) {
            if (arguments.length < 2) {
                max = min;
                min = 0;
            }

            if (min > max) {
                var hold = max;
                max = min;
                min = hold;
            }

            return Math.floor(Math.random() * (max - min + 1)) + min;
        }

        function maxOrbit(x, y) {
            var max = Math.max(x, y),
                diameter = Math.round(Math.sqrt(max * max + max * max));
            return diameter / 2;
        }

        var Star = function () {

            this.orbitRadius = random(maxOrbit(w, h));
            this.radius = random(60, this.orbitRadius) / 5;
            this.orbitX = w / 2;
            this.orbitY = h / 2;
            this.timePassed = random(0, maxStars);
            this.speed = random(this.orbitRadius) / 900000;
            this.alpha = random(2, 10) / 10;

            count++;
            stars[count] = this;
        }

        Star.prototype.draw = function () {
            var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
                y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
                twinkle = random(10);

            if (twinkle === 1 && this.alpha > 0) {
                this.alpha -= 0.05;
            } else if (twinkle === 2 && this.alpha < 1) {
                this.alpha += 0.05;
            }

            ctx.globalAlpha = this.alpha;
            ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
            this.timePassed += this.speed;
        }

        for (var i = 0; i < maxStars; i++) {
            new Star();
        }

        function animation() {
            ctx.globalCompositeOperation = 'source-over';
            ctx.globalAlpha = 0.8;
            ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';
            ctx.fillRect(0, 0, w, h)

            ctx.globalCompositeOperation = 'lighter';
            for (var i = 1, l = stars.length; i < l; i++) {
                stars[i].draw();
            };

            window.requestAnimationFrame(animation);
        }

        animation();
    },
    methods: {

    }
}
</script>
