"use client";

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

type StarDriftProps = {
  children?: ReactNode;
  className?: string;
  /** Number of stars. */
  count?: number;
  color?: string;
  background?: string;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
};

type Star = { x: number; y: number; z: number; phase: number };

/* StarDrift: a field of stars drifting at different depths. Near stars are bigger, brighter and faster. */
export function StarDrift({
  children,
  className = "",
  count = 160,
  color = "#ffffff",
  background = "#04050d",
  speed = 1,
}: StarDriftProps) {
  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 stars: Star[] = [];

    const draw = () => {
      ctx.clearRect(0, 0, w, h);
      ctx.fillStyle = color;
      for (const s of stars) {
        ctx.globalAlpha = (0.3 + 0.7 * s.z) * (0.75 + 0.25 * Math.sin(time * 3 * s.z + s.phase));
        ctx.beginPath();
        ctx.arc(s.x, s.y, 0.4 + s.z * 1.3, 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 stars) {
        s.x += 14 * s.z * dt;
        s.y -= 4 * s.z * dt;
        if (s.x > w + 2) s.x = -2;
        if (s.y < -2) s.y = h + 2;
      }
      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);
      stars = Array.from({ length: count }, () => ({
        x: Math.random() * w,
        y: Math.random() * h,
        z: 0.15 + Math.random() * 0.85,
        phase: Math.random() * Math.PI * 2,
      }));
      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();
    };
  }, [count, color, 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>
  );
}