CosmicDust

"use client";

import { useEffect, useRef, type ReactNode } from "react";

type CosmicDustProps = {
  children?: ReactNode;
  className?: string;
  /** Colour of the fine dust. */
  color?: string;
  /** Colour of the large soft specks. */
  accent?: string;
  background?: string;
  /** Number of specks. */
  count?: number;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
};

type Speck = { x: number; y: number; r: number; vy: number; phase: number; alpha: number; big: boolean };

/* CosmicDust: fine dust and a few soft out-of-focus specks float upward, swaying and flickering. */
export function CosmicDust({
  children,
  className = "",
  color = "#e9e3ff",
  accent = "#a78bfa",
  background = "#07060f",
  count = 220,
  speed = 1,
}: CosmicDustProps) {
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const canvas = canvasRef.current;
    const ctx = canvas?.getContext("2d");
    if (!canvas || !ctx) return;
    const still = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let w = 0;
    let h = 0;
    let raf = 0;
    let last = 0;
    let time = 0;
    let specks: Speck[] = [];

    const draw = () => {
      ctx.clearRect(0, 0, w, h);
      for (const s of specks) {
        ctx.fillStyle = s.big ? accent : color;
        ctx.globalAlpha = s.alpha * (0.6 + 0.4 * Math.sin(time * 2 + s.phase));
        ctx.beginPath();
        ctx.arc(s.x + Math.sin(time * 0.5 + s.phase) * 10, s.y, s.r, 0, Math.PI * 2);
        ctx.fill();
      }
      ctx.globalAlpha = 1;
    };

    const frame = (now: number) => {
      const dt = last ? Math.min((now - last) / 1000, 0.05) * speed : 0;
      last = now;
      time += dt;
      for (const s of specks) {
        s.y -= s.vy * dt;
        if (s.y < -s.r * 2) {
          s.y = h + s.r * 2;
          s.x = Math.random() * w;
        }
      }
      draw();
      raf = requestAnimationFrame(frame);
    };

    const start = () => {
      if (still || raf) return;
      last = 0;
      raf = requestAnimationFrame(frame);
    };
    const stop = () => {
      cancelAnimationFrame(raf);
      raf = 0;
    };

    const resize = () => {
      const dpr = Math.min(window.devicePixelRatio || 1, 2);
      w = canvas.clientWidth;
      h = canvas.clientHeight;
      canvas.width = Math.round(w * dpr);
      canvas.height = Math.round(h * dpr);
      ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
      specks = Array.from({ length: count }, () => {
        const big = Math.random() < 0.08;
        return {
          x: Math.random() * w,
          y: Math.random() * h,
          r: big ? 3 + Math.random() * 4 : 0.5 + Math.random() * 1.1,
          vy: big ? 4 + Math.random() * 6 : 8 + Math.random() * 16,
          phase: Math.random() * Math.PI * 2,
          alpha: big ? 0.15 : 0.4 + Math.random() * 0.5,
          big,
        };
      });
      draw();
    };

    // Redraw on size change; only animate while on screen.
    const ro = new ResizeObserver(resize);
    const io = new IntersectionObserver(([e]) => (e.isIntersecting ? start() : stop()));
    ro.observe(canvas);
    io.observe(canvas);
    return () => {
      stop();
      ro.disconnect();
      io.disconnect();
    };
  }, [color, accent, count, speed]);

  return (
    <div className={`relative overflow-hidden ${className}`} style={{ background }}>
      <canvas ref={canvasRef} aria-hidden className="absolute inset-0 h-full w-full" />
      <div className="relative h-full">{children}</div>
    </div>
  );
}