"use client";

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

interface ScrollFadeInProps {
  children: ReactNode;
  className?: string;
  delay?: number;
}

/**
 * Wraps children in a fade-in-up animation triggered by scroll.
 * Unlike Framer Motion's initial={{ opacity: 0 }}, this does NOT
 * render opacity:0 in SSR HTML — content is visible by default
 * and only hidden after JS hydration for the animation effect.
 */
export default function ScrollFadeIn({ children, className = "", delay = 0 }: ScrollFadeInProps) {
  const ref = useRef<HTMLDivElement>(null);
  const [isVisible, setIsVisible] = useState(false);
  const [hasMounted, setHasMounted] = useState(false);
  const [reduceMotion, setReduceMotion] = useState(false);

  useEffect(() => {
    setHasMounted(true);
    setReduceMotion(window.matchMedia("(prefers-reduced-motion: reduce)").matches);
    const el = ref.current;
    if (!el) return;

    // Fallback for browsers without IntersectionObserver
    if (typeof IntersectionObserver === "undefined") {
      setIsVisible(true);
      return;
    }

    const observer = new IntersectionObserver(
      ([entry]) => {
        if (entry.isIntersecting) {
          setIsVisible(true);
          observer.unobserve(el);
        }
      },
      // Start a little before the section is fully in view so it never feels late
      { threshold: 0.1, rootMargin: "0px 0px -60px 0px" }
    );

    observer.observe(el);
    return () => observer.disconnect();
  }, []);

  return (
    <div
      ref={ref}
      className={className}
      style={hasMounted ? {
        opacity: isVisible ? 1 : 0,
        transform: isVisible || reduceMotion ? "translateY(0)" : "translateY(16px)",
        transition: `opacity 0.6s var(--ease-out) ${delay}s, transform 0.6s var(--ease-out) ${delay}s`,
      } : undefined}
    >
      {children}
    </div>
  );
}