import { lazy, type ReactNode, Suspense, useRef, useState } from "react";
import { Link, useLocation, useNavigate, useSearchParams } from "react-router";
import { t } from "@lingui/core/macro";
import { Trans } from "@lingui/react/macro";
import { useAuth } from "../hooks/useAuth.ts";
import { useWS } from "../hooks/useWS.ts";
import { NotificationBell } from "./NotificationBell.tsx";
import { ChatButton } from "./ChatButton.tsx";
import { UserMenu } from "./UserMenu.tsx";
import { SearchBar } from "./SearchBar.tsx";
import { SITE_EMOJI, SITE_NAME } from "../hooks/useDocumentTitle.ts";

const DumpCreateModal = lazy(() =>
  import("./DumpCreateModal.tsx").then((m) => ({ default: m.DumpCreateModal }))
);

/** Carried in a search entry's history state: the history index of the page
 *  the search started from, so leaving search returns there in one step
 *  however many searches (or result tabs) came in between. */
interface SearchEntryState {
  searchExit?: number;
}

/** React Router's index of the current history entry — 0 for the first page
 *  of the session, which has nothing in the app to go back to. */
function historyIndex(): number {
  return (window.history.state as { idx?: number } | null)?.idx ?? 0;
}

export function AppHeader(
  { centerSlot, disableNew, initialDumpUrl }: {
    centerSlot?: ReactNode;
    disableNew?: boolean;
    initialDumpUrl?: string;
  },
) {
  const { user } = useAuth();
  const { wsStatus, wsErrorMessage } = useWS();
  const navigate = useNavigate();
  const location = useLocation();
  const [searchParams] = useSearchParams();
  // The results page and each of its tabs (/search/~/users…).
  const isSearchPage = location.pathname === "/search" ||
    location.pathname.startsWith("/search/");
  const query = isSearchPage ? searchParams.get("q") ?? "" : "";

  // On the results page the search stays open, holding the query it shows.
  const [searchOpen, setSearchOpen] = useState(false);
  const searchExpanded = isSearchPage || searchOpen;
  const [draft, setDraft] = useState(query);
  const [prevQuery, setPrevQuery] = useState(query);
  if (prevQuery !== query) {
    setPrevQuery(query);
    setDraft(query);
  }

  const [createModalOpen, setCreateModalOpen] = useState(!!initialDumpUrl);
  const searchToggleRef = useRef<HTMLButtonElement>(null);

  function submitSearch(q: string) {
    const here = location.state as SearchEntryState | null;
    // A search from elsewhere remembers that page; one from the results page
    // passes on what it was given, or — for results reached by a link —
    // the page before them. Results that opened the session have nowhere to
    // return to, so a new search just replaces them.
    const searchExit = !isSearchPage
      ? historyIndex()
      : here?.searchExit ?? (historyIndex() > 0 ? historyIndex() - 1 : null);
    const to = `/search?q=${encodeURIComponent(q)}`;
    if (searchExit === null) navigate(to, { replace: true });
    else navigate(to, { state: { searchExit } satisfies SearchEntryState });
  }

  function closeSearch() {
    if (isSearchPage) {
      const exit = (location.state as SearchEntryState | null)?.searchExit;
      if (exit !== undefined) navigate(exit - historyIndex());
      else if (historyIndex() > 0) navigate(-1);
      else navigate("/");
    } else {
      setSearchOpen(false);
      setDraft("");
      searchToggleRef.current?.focus();
    }
  }

  // Escape leaves an opened search, but only reverts an edited query on the
  // results page — leaving that page is the ✕'s job.
  function escapeSearch() {
    if (isSearchPage) setDraft(query);
    else closeSearch();
  }

  function handleSearchToggle() {
    if (searchExpanded) closeSearch();
    else setSearchOpen(true);
  }

  const searchBarProps = {
    expanded: searchExpanded,
    value: draft,
    onValueChange: setDraft,
    onSubmit: submitSearch,
    onCancel: escapeSearch,
  };

  return (
    <>
      <header className="app-header app-header--has-center">
        <Link to="/" className="app-header-brand">
          {SITE_EMOJI}
          <span className="app-header-brand-name">
            {" "}
            {SITE_NAME}
          </span>
        </Link>

        <div className="app-header-center">
          {centerSlot}
          <SearchBar {...searchBarProps} />
        </div>

        <nav className="app-header-nav">
          <button
            ref={searchToggleRef}
            type="button"
            className="nav-search-btn"
            aria-label={searchExpanded ? t`Cancel search` : t`Search`}
            aria-expanded={searchExpanded}
            onClick={handleSearchToggle}
          >
            {searchExpanded ? "✕" : "🔍"}
          </button>
          {user
            ? (
              <>
                {/* Full text links — hidden below the compact breakpoint */}
                <div className="nav-links">
                  <Link
                    to={`/users/${user.username}`}
                    className="app-header-user"
                  >
                    {user.username}
                  </Link>
                  <Link
                    to={`/users/${user.username}/playlists`}
                    className="app-header-user"
                  >
                    <Trans>Playlists</Trans>
                  </Link>
                </div>

                {/* Compact avatar menu — hidden above the compact breakpoint */}
                <div className="nav-compact">
                  <UserMenu user={user} />
                </div>

                <ChatButton />
                <NotificationBell />
                <button
                  type="button"
                  className="btn-primary"
                  onClick={() => setCreateModalOpen(true)}
                  disabled={disableNew}
                  title={disableNew ? t`Server unreachable` : undefined}
                >
                  +<span className="btn-new-label">
                    <Trans>Dump</Trans>
                  </span>
                </button>
              </>
            )
            : (
              <>
                <button type="button" onClick={() => navigate("/login")}>
                  <Trans>Log in</Trans>
                </button>
              </>
            )}
        </nav>
      </header>

      {
        /* Stays mounted so the row can slide open and shut; `inert` keeps the
          collapsed input out of the tab order. */
      }
      <div
        className={`header-search-reveal${
          searchExpanded ? " header-search-reveal--open" : ""
        }`}
        inert={!searchExpanded}
      >
        <div className="header-search-reveal-clip">
          <div className="header-search-below">
            <SearchBar {...searchBarProps} />
          </div>
        </div>
      </div>

      {wsStatus === "disconnected" && wsErrorMessage && (
        <div className="app-header-status" role="alert">
          <strong>
            <Trans>Live updates unavailable.</Trans>
          </strong>{" "}
          {wsErrorMessage}
        </div>
      )}

      {createModalOpen && (
        <Suspense>
          <DumpCreateModal
            onClose={() => setCreateModalOpen(false)}
            initialUrl={initialDumpUrl}
          />
        </Suspense>
      )}
    </>
  );
}