"use client";

import { useEffect, useState } from "react";
import Link from "next/link";
import Image from "next/image";

const NAVBAR_HEIGHT = 100; // px — matches h-[6.25rem]
const SCROLL_DURATION = 800; // ms

function smoothScrollTo(targetY: number) {
  const startY = window.scrollY;
  const distance = targetY - startY;
  const startTime = performance.now();

  function step(now: number) {
    const elapsed = now - startTime;
    const progress = Math.min(elapsed / SCROLL_DURATION, 1);
    // ease-in-out cubic
    const ease = progress < 0.5
      ? 4 * progress ** 3
      : 1 - (-2 * progress + 2) ** 3 / 2;
    window.scrollTo(0, startY + distance * ease);
    if (progress < 1) requestAnimationFrame(step);
  }

  requestAnimationFrame(step);
}

const navLinks = [
  { label: "Werkzeuge", href: "#werkzeuge" },
  { label: "Blog", href: "#blog" },
  { label: "Über Björn", href: "#ueber-bjoern" },
  { label: "Shop", href: "/shop" },
];

const anchorIds = navLinks
  .filter((l) => l.href.startsWith("#"))
  .map((l) => l.href.slice(1));

export function Navbar() {
  const [scrolled, setScrolled] = useState(false);
  const [activeSection, setActiveSection] = useState("");

  useEffect(() => {
    const onScroll = () => setScrolled(window.scrollY > 8);
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  useEffect(() => {
    const visible = new Set<string>();

    const updateActive = () => {
      for (const id of anchorIds) {
        if (visible.has(id)) { setActiveSection(id); return; }
      }
      setActiveSection("");
    };

    const observers = anchorIds.map((id) => {
      const el = document.getElementById(id);
      if (!el) return null;
      const obs = new IntersectionObserver(
        ([entry]) => {
          entry.isIntersecting ? visible.add(id) : visible.delete(id);
          updateActive();
        },
        { rootMargin: "-100px 0px -50% 0px" }
      );
      obs.observe(el);
      return obs;
    });

    return () => observers.forEach((o) => o?.disconnect());
  }, []);

  return (
    <header
      className={`sticky top-0 z-50 w-full h-[6.25rem] flex items-center px-[2rem] transition-[background-color,backdrop-filter] duration-300 ${
        scrolled
          ? "bg-[#f5f0e8]/80 backdrop-blur-md"
          : "bg-[#f5f0e8]"
      }`}
    >
      <div className="w-full flex items-center justify-between">

        {/* Logo — smooth scroll to top */}
        <a
          href="/"
          className="shrink-0"
          onClick={(e) => {
            e.preventDefault();
            smoothScrollTo(0);
            history.replaceState(null, "", "/");
          }}
        >
          <Image
            src="/logo.png"
            alt="einfach produktiv"
            width={181}
            height={61}
            priority
          />
        </a>

        {/* Nav links */}
        <nav className="flex items-center gap-[3rem]">
          {navLinks.map((link) =>
            link.href.startsWith("#") ? (
              <a
                key={link.href}
                href={link.href}
                onClick={(e) => {
                  e.preventDefault();
                  const el = document.getElementById(link.href.slice(1));
                  if (el) {
                    const top = el.getBoundingClientRect().top + window.scrollY - NAVBAR_HEIGHT;
                    smoothScrollTo(top);
                  }
                  history.replaceState(null, "", link.href);
                }}
                className={`text-[1.125rem] font-semibold tracking-[0.01125rem] transition-colors cursor-pointer ${
                  activeSection === link.href.slice(1)
                    ? "text-[#f6a701]"
                    : "text-[#222221] hover:text-[#f6a701]"
                }`}
              >
                {link.label}
              </a>
            ) : (
              <Link
                key={link.href}
                href={link.href}
                className="text-[1.125rem] font-semibold text-[#222221] tracking-[0.01125rem] hover:text-[#f6a701] transition-colors"
              >
                {link.label}
              </Link>
            )
          )}
        </nav>

        {/* CTA buttons */}
        <div className="flex items-center gap-[0.75rem] p-[0.5rem]">
          <Link
            href="/newsletter"
            className="px-[1.5rem] py-[1rem] rounded-[0.5rem] border border-[#868686] text-[1.125rem] font-bold text-[#222221] hover:bg-[#222221] hover:text-white transition-colors"
          >
            Newsletter
          </Link>
          <Link
            href="/challenge"
            className="px-[1.5rem] py-[1rem] rounded-[0.5rem] bg-[#f6a701] text-[1.125rem] font-bold text-[#222221] hover:brightness-95 transition-all"
          >
            7-Tage-Challenge
          </Link>
        </div>

      </div>
    </header>
  );
}