"use client";

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

type PixelRainProps = {
  children?: ReactNode;
  className?: string;
  color?: string;
  /** Base colour. Also used to fade the trails. */
  background?: string;
  /** Pixel size in pixels. */
  size?: number;
  /** Share of columns raining at once, 0 to 1. */
  density?: number;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
};

type Drop = { y: number; v: number; on: boolean };

/* PixelRain: square pixels fall down a grid and leave fading trails. */
export function PixelRain({
  children,
  className = "",
  color = "#a78bfa",
  background = "#05040b",
  size = 10,
  density = 0.6,
  speed = 1,
}: PixelRainProps) {
  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 drops: Drop[] = [];

    const newDrop = (y: number): Drop => ({ y, v: 8 + Math.random() * 14, on: Math.random() < density });
    const cell = (col: number, row: number) => ctx.fillRect(col * size + 1, row * size + 1, size - 2, size - 2);

    // Still frame: each raining column gets a short fixed trail.
    const drawStill = () => {
      ctx.globalAlpha = 1;
      ctx.fillStyle = background;
      ctx.fillRect(0, 0, w, h);
      ctx.fillStyle = color;
      drops.forEach((d, col) => {
        if (!d.on) return;
        for (let k = 0; k < 8; k++) {
          ctx.globalAlpha = (1 - k / 8) * 0.8;
          cell(col, Math.floor(d.y) - k);
        }
      });
      ctx.globalAlpha = 1;
    };

    const frame = (now: number) => {
      const dt = last ? Math.min((now - last) / 1000, 0.05) * speed : 0;
      last = now;
      ctx.globalAlpha = 1 - Math.pow(0.9, dt * 60);
      ctx.fillStyle = background;
      ctx.fillRect(0, 0, w, h);
      ctx.globalAlpha = 1;
      ctx.fillStyle = color;
      drops.forEach((d, col) => {
        d.y += d.v * dt;
        if (d.y * size > h + size * 10) drops[col] = newDrop(-Math.random() * 20);
        else if (d.on) cell(col, Math.floor(d.y));
      });
      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);
      drops = Array.from({ length: Math.ceil(w / size) }, () => newDrop(Math.random() * (h / size)));
      drawStill();
    };

    // 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, background, size, density, 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>
  );
}