/**
 * 文件功能：聊天室烟花特效
 *
 * 使用 Canvas 粒子系统在全屏播放多发烟花爆炸动画。
 * 特效总时长约 4 秒，结束后自动清理并回调。
 */

const FireworksEffect = (() => {
    // 粒子类：模拟一个爆炸后的发光粒子
    class Particle {
        constructor(x, y, color) {
            this.x = x;
            this.y = y;
            this.color = color;
            // 随机方向和速度
            const angle = Math.random() * Math.PI * 2;
            const speed = Math.random() * 6 + 2;
            this.vx = Math.cos(angle) * speed;
            this.vy = Math.sin(angle) * speed;
            this.alpha = 1;
            this.gravity = 0.12;
            this.decay = Math.random() * 0.012 + 0.012; // 透明度每帧衰减量
            this.radius = Math.random() * 3 + 1;
        }

        /** 每帧更新粒子位置和状态 */
        update() {
            this.vy += this.gravity;
            this.x += this.vx;
            this.y += this.vy;
            this.vx *= 0.98; // 空气阻力
            this.vy *= 0.98;
            this.alpha -= this.decay;
        }

        /** 绘制粒子 */
        draw(ctx) {
            ctx.save();
            ctx.globalAlpha = Math.max(0, this.alpha);
            ctx.fillStyle = this.color;
            ctx.beginPath();
            ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2);
            ctx.fill();
            ctx.restore();
        }
    }

    // 预定义烟花颜色组
    const COLORS = [
        "#ff4444",
        "#ff8800",
        "#ffdd00",
        "#44ff44",
        "#44ddff",
        "#8844ff",
        "#ff44cc",
        "#ffffff",
        "#ffaaaa",
        "#aaffaa",
        "#aaaaff",
        "#ffffaa",
    ];

    /**
     * 发射一枚烟花，返回粒子数组
     *
     * @param  {number}  x       爆炸中心 x
     * @param  {number}  y       爆炸中心 y
     * @param  {number}  count   粒子数量
     * @returns {Particle[]}
     */
    function _burst(x, y, count) {
        const color = COLORS[Math.floor(Math.random() * COLORS.length)];
        const particles = [];
        for (let i = 0; i < count; i++) {
            particles.push(new Particle(x, y, color));
        }
        return particles;
    }

    /**
     * 启动烟花特效
     *
     * @param  {HTMLCanvasElement}  canvas   全屏 Canvas
     * @param  {Function}           onEnd    特效结束回调
     */
    function start(canvas, onEnd) {
        const ctx = canvas.getContext("2d");
        const w = canvas.width;
        const h = canvas.height;
        const DURATION = 4500; // 总时长（ms）

        let particles = [];
        let animId = null;
        let launchCount = 0;
        const MAX_LAUNCHES = 8; // 总共发射几枚烟花

        // 定时发射烟花
        const launchInterval = setInterval(() => {
            if (launchCount >= MAX_LAUNCHES) {
                clearInterval(launchInterval);
                return;
            }
            const x = w * (0.15 + Math.random() * 0.7); // 避免贴近边缘
            const y = h * (0.1 + Math.random() * 0.5); // 在屏幕上半区爆炸
            const count = Math.floor(Math.random() * 40) + 60;
            particles = particles.concat(_burst(x, y, count));
            launchCount++;
        }, 500);

        const startTime = performance.now();

        // 动画循环
        function animate(now) {
            // 清除画布（保持透明，不遮挡聊天背景）
            ctx.clearRect(0, 0, w, h);

            // 更新并绘制存活粒子（粒子自带 alpha 衰减，视觉上有淡出效果）
            particles = particles.filter((p) => p.alpha > 0.02);
            particles.forEach((p) => {
                p.update();
                p.draw(ctx);
            });

            if (now - startTime < DURATION) {
                animId = requestAnimationFrame(animate);
            } else {
                // 特效结束：清空 canvas 后回调
                clearInterval(launchInterval);
                cancelAnimationFrame(animId);
                ctx.clearRect(0, 0, w, h);
                onEnd();
            }
        }

        animId = requestAnimationFrame(animate);
    }

    return { start };
})();