/**
 * Particles — Canvas floating math symbols background
 * Full-viewport canvas with slow-drifting math symbols (Σ, π, ∫, ∞, Δ, √, α, β)
 * Respects prefers-reduced-motion, disables on viewports < 768px, caps at 30 FPS.
 */
const Particles = (() => {
  let canvas = null;
  let ctx = null;
  let particles = [];
  let animId = null;
  let lastTime = 0;
  const FPS = 30;
  const FRAME_TIME = 1000 / FPS;

  const SYMBOLS = ['Σ', 'π', '∫', '∞', 'Δ', '√', 'α', 'β', 'λ', 'μ', '∂', '∑'];

  function prefersReducedMotion() {
    return window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  }

  function randomBetween(a, b) {
    return a + Math.random() * (b - a);
  }

  class Particle {
    constructor() {
      this.reset();
    }

    reset() {
      this.x = Math.random() * (canvas ? canvas.width : window.innerWidth);
      this.y = Math.random() * (canvas ? canvas.height : window.innerHeight);
      this.size = randomBetween(16, 32);
      this.symbol = SYMBOLS[Math.floor(Math.random() * SYMBOLS.length)];
      this.vx = randomBetween(-0.2, 0.2);
      this.vy = randomBetween(-0.15, 0.15);
      this.rotation = randomBetween(0, Math.PI * 2);
      this.rotationSpeed = randomBetween(-0.005, 0.005);
      this.opacity = randomBetween(0.4, 0.8);
    }

    update() {
      this.x += this.vx;
      this.y += this.vy;
      this.rotation += this.rotationSpeed;

      const W = canvas ? canvas.width : window.innerWidth;
      const H = canvas ? canvas.height : window.innerHeight;

      if (this.x < -50) this.x = W + 50;
      if (this.x > W + 50) this.x = -50;
      if (this.y < -50) this.y = H + 50;
      if (this.y > H + 50) this.y = -50;
    }

    draw(ctx) {
      ctx.save();
      ctx.translate(this.x, this.y);
      ctx.rotate(this.rotation);
      ctx.font = `${this.size}px "Times New Roman", serif`;
      ctx.fillStyle = `rgba(108, 92, 231, ${this.opacity})`;
      ctx.textAlign = 'center';
      ctx.textBaseline = 'middle';
      ctx.fillText(this.symbol, 0, 0);
      ctx.restore();
    }
  }

  function initCanvas() {
    if (window.innerWidth < 768) return;
    if (prefersReducedMotion()) return;

    canvas = document.getElementById('particles-bg');
    if (!canvas) {
      canvas = document.createElement('canvas');
      canvas.id = 'particles-bg';
      document.body.appendChild(canvas);
    }

    ctx = canvas.getContext('2d');
    resize();
    window.addEventListener('resize', resize);

    // Create particles
    const count = Math.min(40, Math.floor((window.innerWidth * window.innerHeight) / 25000));
    particles = [];
    for (let i = 0; i < count; i++) {
      particles.push(new Particle());
    }

    lastTime = performance.now();
    loop(performance.now());
  }

  function resize() {
    if (!canvas) return;
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
  }

  function loop(timestamp) {
    animId = requestAnimationFrame(loop);

    if (timestamp - lastTime < FRAME_TIME) return;
    lastTime = timestamp;

    if (!ctx || !canvas) return;

    ctx.clearRect(0, 0, canvas.width, canvas.height);

    for (const p of particles) {
      p.update();
      p.draw(ctx);
    }
  }

  function destroy() {
    if (animId) {
      cancelAnimationFrame(animId);
      animId = null;
    }
    if (canvas && canvas.parentElement) {
      canvas.parentElement.removeChild(canvas);
    }
    canvas = null;
    ctx = null;
    particles = [];
    window.removeEventListener('resize', resize);
  }

  // Auto-init on load
  if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', initCanvas);
  } else {
    initCanvas();
  }

  return { init: initCanvas, destroy };
})();