// 粒子系统
import { rand, randInt } from './util.js';

export class Particles {
  constructor() { this.list = []; }
  clear() { this.list.length = 0; }

  spawn(x, y, n, opt = {}) {
    const {
      colors = ['#fff', '#ff5c7a', '#ffc63a'],
      speed = 3, life = 40, size = 3, grav = 0.12, spread = Math.PI * 2, dir = 0,
    } = opt;
    for (let i = 0; i < n; i++) {
      const a = dir + (Math.random() - 0.5) * spread;
      const s = rand(speed * 0.35, speed);
      this.list.push({
        x, y, vx: Math.cos(a) * s, vy: Math.sin(a) * s,
        life: life * rand(0.6, 1.25), max: life,
        c: colors[randInt(0, colors.length - 1)],
        s: size * rand(0.6, 1.3), g: grav,
      });
    }
  }

  burst(x, y, opt = {}) { this.spawn(x, y, opt.n || 18, opt); }

  update() {
    for (let i = this.list.length - 1; i >= 0; i--) {
      const p = this.list[i];
      p.x += p.vx; p.y += p.vy; p.vy += p.g;
      p.vx *= 0.985;
      if (--p.life <= 0) this.list.splice(i, 1);
    }
  }

  draw(ctx) {
    for (const p of this.list) {
      ctx.globalAlpha = Math.min(1, p.life / (p.max * 0.5));
      ctx.fillStyle = p.c;
      ctx.fillRect(p.x | 0, p.y | 0, p.s | 0, p.s | 0);
    }
    ctx.globalAlpha = 1;
  }
}