"use client";

/**
 * PageHeader — per-page sub-header carrying the page title / breadcrumb.
 *
 * The global SiteHeader (mounted in app/layout.tsx) owns the wordmark,
 * primary nav, search, reading settings, and user menu. PageHeader is now
 * purely typographic — it renders whatever `children` the page passes and
 * applies a subtle bordered band so the page's title area has visual weight
 * separate from the body content.
 *
 * Behaviour preserved from the previous (busier) implementation:
 *   • If sessionStorage has `spsays_from_search`, the first <Link> child is
 *     hidden and replaced with a "← Back to search results" button. This
 *     keeps the cross-page-navigation polish that the search page relies on.
 *
 * Sticky headers collapse on scroll-down and re-appear on scroll-up
 * (mobile-address-bar pattern). Long reading pages get back the vertical
 * real estate without losing the title anchor on demand. Only applies
 * when `sticky` — a non-sticky header has nothing to slide behind.
 *
 * Pages that don't want a sub-header (e.g. the redesigned homepage which
 * paints its own editorial hero) can simply not render PageHeader.
 */

import { useEffect, useRef, useState } from "react";
import { useRouter, usePathname } from "next/navigation";
import { cn } from "@/lib/utils";

const SEARCH_RETURN_KEY = "spsays_from_search";

export function PageHeader({
  children,
  className,
  bare = false,
  sticky = false,
}: {
  children: React.ReactNode;
  /** Drop the bordered chrome — useful for pages that want flush title text. */
  bare?: boolean;
  /**
   * Stick to the top below the global SiteHeader. Used by reading pages
   * so the chapter title stays visible as the user scrolls long content.
   * The offset is `top-12 sm:top-14` — SiteHeader is `h-12 sm:h-14`, so
   * these values land the PageHeader flush with its bottom edge with no
   * visible gap.
   */
  sticky?: boolean;
  className?: string;
}) {
  const router = useRouter();
  const pathname = usePathname();

  // Read (and consume) the search-return flag once on first render.
  const [fromSearch, setFromSearch] = useState(() => {
    if (typeof window === "undefined") return false;
    try {
      if (
        sessionStorage.getItem(SEARCH_RETURN_KEY) === "1" &&
        !pathname.startsWith("/search")
      ) {
        sessionStorage.removeItem(SEARCH_RETURN_KEY);
        return true;
      }
    } catch {
      // sessionStorage unavailable
    }
    return false;
  });

  // Scroll-direction-driven collapse. Hidden when the user is scrolling
  // down past the first viewport-tenth and revealed again as soon as
  // they scroll up. Near the top we always show so quick reading doesn't
  // feel jumpy. Only wired up when `sticky` — that's the only case where
  // the header has a fixed slot to slide behind.
  const [collapsed, setCollapsed] = useState(false);
  const lastScrollYRef = useRef(0);
  useEffect(() => {
    if (!sticky) return;
    lastScrollYRef.current = window.scrollY;
    function onScroll() {
      const y = window.scrollY;
      const delta = y - lastScrollYRef.current;
      // Threshold of ~8px filters out scroll-jitter / momentum noise.
      if (y < 80) setCollapsed(false);
      else if (delta > 8) setCollapsed(true);
      else if (delta < -8) setCollapsed(false);
      lastScrollYRef.current = y;
    }
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, [sticky]);

  return (
    <header
      className={cn(
        "px-4 sm:px-6",
        bare ? "py-6" : "border-b border-border bg-card/85 backdrop-blur py-5",
        sticky &&
          "sticky top-12 sm:top-14 z-20 transition-transform duration-200 ease-out",
        // -translate-y-full tucks the band fully behind the SiteHeader
        // (which sits at a higher z-index), so it visually disappears.
        sticky && collapsed && "-translate-y-full",
        className,
      )}
    >
      <div className="max-w-5xl mx-auto">
        {fromSearch ? (
          <>
            <button
              type="button"
              onClick={() => {
                setFromSearch(false);
                router.back();
              }}
              className="block text-xs text-muted-foreground hover:text-foreground transition-colors mb-2"
            >
              &larr; Back to search results
            </button>
            {/* Hide the page's own breadcrumb link (always the first <a>) */}
            <div className="[&>a:first-child]:hidden">{children}</div>
          </>
        ) : (
          children
        )}
      </div>
    </header>
  );
}