/**
 * 全站深色岩层背景上的粒子网络效果
 * 固定在视口内（position: fixed），任意页面、任意滚动位置都可见，跟随鼠标移动。
 */
(function () {
    var canvas = document.querySelector('.site-particles');
    if (!canvas) return;

    var ctx = canvas.getContext('2d');
    var DPR = window.devicePixelRatio || 1;
    var prefersReducedMotion = window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    var width = 0;
    var height = 0;
    var particles = [];
    var mouse = { x: null, y: null, active: false };

    var config = {
        density: 9000,
        maxParticles: 130,
        linkDistance: 150,
        mouseLinkDistance: 220,
        mouseForce: 1.1,
        dotRadiusMin: 1.6,
        dotRadiusMax: 3.4,
        dotColor: '124, 211, 252',
        lineColor: '56, 189, 248'
    };

    function resize() {
        width = window.innerWidth;
        height = window.innerHeight;
        canvas.width = Math.max(1, Math.round(width * DPR));
        canvas.height = Math.max(1, Math.round(height * DPR));
        ctx.setTransform(DPR, 0, 0, DPR, 0, 0);
        createParticles();
    }

    function createParticles() {
        var count = Math.min(config.maxParticles, Math.floor((width * height) / config.density));
        particles = new Array(Math.max(count, 30)).fill(null).map(function () {
            return {
                x: Math.random() * width,
                y: Math.random() * height,
                vx: (Math.random() - 0.5) * 0.4,
                vy: (Math.random() - 0.5) * 0.4,
                r: Math.random() * (config.dotRadiusMax - config.dotRadiusMin) + config.dotRadiusMin
            };
        });
    }

    document.addEventListener('mousemove', function (e) {
        mouse.x = e.clientX;
        mouse.y = e.clientY;
        mouse.active = true;
    });
    document.addEventListener('mouseleave', function () { mouse.active = false; });

    function step() {
        particles.forEach(function (p) {
            p.x += p.vx;
            p.y += p.vy;

            if (p.x <= 0 || p.x >= width) p.vx *= -1;
            if (p.y <= 0 || p.y >= height) p.vy *= -1;

            p.x = Math.max(0, Math.min(width, p.x));
            p.y = Math.max(0, Math.min(height, p.y));

            if (mouse.active) {
                var dx = mouse.x - p.x;
                var dy = mouse.y - p.y;
                var dist = Math.hypot(dx, dy);
                if (dist < config.mouseLinkDistance && dist > 0.001) {
                    var pull = (1 - dist / config.mouseLinkDistance) * config.mouseForce;
                    p.x -= (dx / dist) * pull;
                    p.y -= (dy / dist) * pull;
                }
            }
        });
    }

    function render() {
        ctx.clearRect(0, 0, width, height);

        for (var i = 0; i < particles.length; i++) {
            for (var j = i + 1; j < particles.length; j++) {
                var dx = particles[i].x - particles[j].x;
                var dy = particles[i].y - particles[j].y;
                var dist = Math.hypot(dx, dy);
                if (dist < config.linkDistance) {
                    ctx.strokeStyle = 'rgba(' + config.lineColor + ', ' + ((1 - dist / config.linkDistance) * 0.45) + ')';
                    ctx.lineWidth = 0.7;
                    ctx.beginPath();
                    ctx.moveTo(particles[i].x, particles[i].y);
                    ctx.lineTo(particles[j].x, particles[j].y);
                    ctx.stroke();
                }
            }

            if (mouse.active) {
                var mdx = particles[i].x - mouse.x;
                var mdy = particles[i].y - mouse.y;
                var mdist = Math.hypot(mdx, mdy);
                if (mdist < config.mouseLinkDistance) {
                    ctx.strokeStyle = 'rgba(' + config.lineColor + ', ' + ((1 - mdist / config.mouseLinkDistance) * 0.65) + ')';
                    ctx.lineWidth = 0.9;
                    ctx.beginPath();
                    ctx.moveTo(particles[i].x, particles[i].y);
                    ctx.lineTo(mouse.x, mouse.y);
                    ctx.stroke();
                }
            }
        }

        particles.forEach(function (p) {
            ctx.beginPath();
            ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2);
            ctx.fillStyle = 'rgba(' + config.dotColor + ', 0.85)';
            ctx.shadowColor = 'rgba(56, 189, 248, 0.8)';
            ctx.shadowBlur = 7;
            ctx.fill();
            ctx.shadowBlur = 0;
        });

        if (mouse.active) {
            ctx.beginPath();
            ctx.arc(mouse.x, mouse.y, 2.6, 0, Math.PI * 2);
            ctx.fillStyle = 'rgba(255, 255, 255, 0.85)';
            ctx.shadowColor = 'rgba(255, 255, 255, 0.85)';
            ctx.shadowBlur = 12;
            ctx.fill();
            ctx.shadowBlur = 0;
        }
    }

    function loop() {
        step();
        render();
        requestAnimationFrame(loop);
    }

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

    if (!prefersReducedMotion) {
        loop();
    } else {
        render();
    }
})();