"use client";

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

type HeroCanvasProps = {
  title: string;
  /** Small line above the title. */
  eyebrow?: string;
  subtitle?: string;
  /** Buttons or links under the text. */
  children?: ReactNode;
  /** Dot colour. */
  color?: string;
  /** Colour of the dots lifted by the pointer. */
  accent?: string;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
  /** h1 by default. Use h2 if the page already has an h1. */
  headingAs?: ElementType;
  /** Set the height, background and text colour here. */
  className?: string;
};

const ROWS = 46;
const SPACING = 0.22;
const CAMERA = 1.4;

/* HeroCanvas: a hero over a sea of dots rolling toward you in perspective. The pointer lifts a swell that travels with it. */
export function HeroCanvas({
  title,
  eyebrow,
  subtitle,
  children,
  color = "#8b7fd6",
  accent = "#22d3ee",
  speed = 1,
  headingAs: Heading = "h1",
  className = "min-h-[36rem] bg-[#06060e] text-white",
}: HeroCanvasProps) {
  const id = useId();
  const box = useRef<HTMLElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const section = box.current;
    const canvas = canvasRef.current;
    const ctx = canvas?.getContext("2d");
    if (!section || !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 onScreen = true;
    const pointer = { x: 0, y: 0, power: 0, on: false };

    const draw = () => {
      ctx.clearRect(0, 0, w, h);
      const horizon = h * 0.42;
      const focal = h * 0.42;
      const travel = time * 0.35;
      const flow = travel % SPACING;
      // Far rows first, so near dots land on top.
      for (let r = ROWS; r >= 1; r--) {
        const z = r * SPACING - flow + 0.5;
        const scale = focal / z;
        const groundY = horizon + CAMERA * scale;
        const reach = Math.ceil(w / 2 / (scale * SPACING)) + 1;
        const depth = Math.min(1, (ROWS - r + 1) / 14);
        for (let c = -reach; c <= reach; c++) {
          const worldX = c * SPACING;
          const swell = Math.sin(worldX * 0.9 + time * 0.6) * 0.1 + Math.sin((z + travel) * 1.3 - time * 0.5) * 0.14;
          const x = w / 2 + worldX * scale;
          const dx = (x - pointer.x) / (w * 0.14 + 60);
          const dy = (groundY - pointer.y) / (h * 0.3 + 40);
          const lift = pointer.power * Math.exp(-(dx * dx + dy * dy));
          const y = groundY - (swell + lift * 0.5) * scale;
          const size = Math.max(0.9, Math.min(3, scale * 0.016)) * (1 + lift);
          ctx.globalAlpha = Math.min(1, depth * 0.85 + lift * 0.4);
          ctx.fillStyle = lift > 0.2 ? accent : color;
          ctx.fillRect(x - size / 2, y - size / 2, size, size);
        }
      }
      ctx.globalAlpha = 1;
    };

    const tick = (now: number) => {
      const dt = Math.min(0.05, (now - last) / 1000);
      last = now;
      time += dt * speed;
      pointer.power += ((pointer.on ? 1 : 0) - pointer.power) * Math.min(1, dt * 5);
      draw();
      raf = requestAnimationFrame(tick);
    };
    const start = () => {
      if (still || raf || !onScreen) return;
      last = performance.now();
      raf = requestAnimationFrame(tick);
    };
    const stop = () => {
      cancelAnimationFrame(raf);
      raf = 0;
    };

    const resize = () => {
      const rect = canvas.getBoundingClientRect();
      const dpr = Math.min(2, window.devicePixelRatio || 1);
      w = rect.width;
      h = rect.height;
      canvas.width = Math.round(w * dpr);
      canvas.height = Math.round(h * dpr);
      ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
      draw();
    };

    const move = (e: PointerEvent) => {
      if (still || e.pointerType !== "mouse") return;
      const rect = canvas.getBoundingClientRect();
      pointer.x = e.clientX - rect.left;
      pointer.y = e.clientY - rect.top;
      pointer.on = true;
    };
    const leave = () => {
      pointer.on = false;
    };

    const sizes = new ResizeObserver(resize);
    sizes.observe(canvas);
    const sight = new IntersectionObserver(([entry]) => {
      onScreen = entry.isIntersecting;
      if (onScreen) start();
      else stop();
    });
    sight.observe(canvas);
    section.addEventListener("pointermove", move);
    section.addEventListener("pointerleave", leave);
    start();

    return () => {
      stop();
      sizes.disconnect();
      sight.disconnect();
      section.removeEventListener("pointermove", move);
      section.removeEventListener("pointerleave", leave);
    };
  }, [color, accent, speed]);

  return (
    <section ref={box} aria-labelledby={id} className={`@container relative isolate overflow-hidden ${className}`}>
      <canvas ref={canvasRef} aria-hidden className="absolute inset-0 -z-10 size-full" />
      <div className="flex max-w-2xl flex-col px-5 pt-5 pb-16 @2xl:px-14 @2xl:pt-12 @2xl:pb-24">
        {eyebrow && <p className="mb-2 text-xs font-medium tracking-[0.2em] uppercase opacity-70 @2xl:mb-4 @2xl:text-sm">{eyebrow}</p>}
        <Heading id={id} className="text-[clamp(1.6rem,8cqw,4rem)] leading-[1.06] font-semibold tracking-tight text-balance">
          {title}
        </Heading>
        {subtitle && <p className="mt-3 max-w-lg text-sm text-pretty opacity-70 @2xl:mt-5 @2xl:text-lg">{subtitle}</p>}
        {children && <div className="mt-4 flex flex-wrap gap-3 @2xl:mt-8">{children}</div>}
      </div>
    </section>
  );
}