"use client";

import { useEffect, useRef } from "react";

export interface ParallaxScaleZoomProps {
  imageSrc?: string;
  /** Max zoom multiplier reached at end of section. */
  maxScale?: number;
  eyebrow?: string;
  headline?: string;
  subhead?: string;
}

export default function ParallaxScaleZoom({
  imageSrc = "/heroes/landscape-card-bg.webp",
  maxScale = 1.35,
  eyebrow = "Parallax · 10",
  headline = "Scroll-driven scale",
  subhead =
    "The image zooms IN as you scroll the section. Reverse of Ken Burns — coupled to scroll position, so the viewer drives the motion.",
}: ParallaxScaleZoomProps) {
  const sectionRef = useRef<HTMLElement | null>(null);
  const imgRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    let raf = 0;
    let visible = false;
    const io = new IntersectionObserver(
      (entries) => {
        visible = entries[0]?.isIntersecting ?? false;
      },
      { threshold: 0 }
    );
    if (sectionRef.current) io.observe(sectionRef.current);

    const onScroll = () => {
      if (!visible || !sectionRef.current || !imgRef.current) return;
      cancelAnimationFrame(raf);
      raf = requestAnimationFrame(() => {
        const rect = sectionRef.current!.getBoundingClientRect();
        const winH = window.innerHeight;
        // progress: 0 when section top hits viewport top, 1 when section bottom hits viewport top
        const total = rect.height + winH;
        const p = Math.max(0, Math.min(1, (winH - rect.top) / total));
        const scale = 1 + (maxScale - 1) * p;
        imgRef.current!.style.transform = `scale(${scale})`;
      });
    };

    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => {
      io.disconnect();
      window.removeEventListener("scroll", onScroll);
      cancelAnimationFrame(raf);
    };
  }, [maxScale]);

  return (
    <section
      ref={sectionRef}
      className="relative isolate flex min-h-[120svh] w-full items-center justify-center overflow-hidden bg-slate-900"
    >
      <div
        ref={imgRef}
        className="absolute inset-0 -z-10 will-change-transform"
        style={{
          backgroundImage: `url(${imageSrc})`,
          backgroundSize: "cover",
          backgroundPosition: "center",
          transformOrigin: "center",
        }}
      />
      <div className="absolute inset-0 -z-0 bg-gradient-to-b from-black/40 via-black/20 to-black/75" />
      <div className="relative z-10 mx-auto max-w-3xl px-6 text-center text-white">
        <p className="mb-4 text-xs font-semibold uppercase tracking-[0.3em] text-white/70">
          {eyebrow}
        </p>
        <h1 className="text-balance text-4xl font-semibold leading-[1.1] tracking-tight sm:text-6xl">
          {headline}
        </h1>
        <p className="mx-auto mt-6 max-w-xl text-base leading-relaxed text-white/80 sm:text-lg">
          {subhead}
        </p>
      </div>
    </section>
  );
}