"use client";

import React from "react";
import Link from "next/link";
import { usePathname, useRouter } from "next/navigation";
import { FolderOpen, Search as SearchIcon } from "lucide-react";

import { useAuth } from "@/components/auth/authContext";
import { getBranches } from "@/lib/frontend/apiClient";
import { branchPath, searchPath } from "@/lib/frontend/routes";
import { isValidBranchParam } from "@/lib/frontend/params";
import {
	buildNextUrlForBranchSwitch,
	readRouteBranchFromPathname,
	safeReadLocalStorageBranch,
	safeWriteLocalStorageBranch,
} from "@/lib/frontend/quickNav/branchSwitch";
import {
	getPrimaryNavFromPathname,
	PRIMARY_NAV,
} from "@/lib/frontend/nav/activeRoute";

import { Button } from "@/components/ui/button";
import {
	DropdownMenu,
	DropdownMenuContent,
	DropdownMenuLabel,
	DropdownMenuRadioGroup,
	DropdownMenuRadioItem,
	DropdownMenuSeparator,
	DropdownMenuTrigger,
} from "@/components/ui/dropdown-menu";

const STORAGE_KEY_LAST_BRANCH = "rhl_last_branch";

const BRANCH_LIST_STATE = Object.freeze({
	IDLE: "idle",
	LOADING: "loading",
	READY: "ready",
	ERROR: "error",
});

export default function QuickNav() {
	const router = useRouter();
	const pathname = usePathname() || "/";

	const { status, user, retry } = useAuth();

	const isAuthenticated = status === "authenticated" && user;
	const isAdminDev =
		isAuthenticated && (user.role === "admin" || user.role === "dev");
	const isBranchUser = isAuthenticated && user.role === "branch";

	const canRevalidate = typeof retry === "function";

	// Persisted selection for admin/dev:
	// - Used as the "safe fallback" when the route branch is invalid/non-existent.
	const [selectedBranch, setSelectedBranch] = React.useState(null);

	const [branchList, setBranchList] = React.useState({
		status: BRANCH_LIST_STATE.IDLE,
		branches: null,
	});

	const activePrimaryNav = React.useMemo(() => {
		return getPrimaryNavFromPathname(pathname);
	}, [pathname]);

	const isExplorerActive = activePrimaryNav?.active === PRIMARY_NAV.EXPLORER;
	const isSearchActive = activePrimaryNav?.active === PRIMARY_NAV.SEARCH;

	const routeBranch = React.useMemo(() => {
		return readRouteBranchFromPathname(pathname);
	}, [pathname]);

	const knownBranches =
		branchList.status === BRANCH_LIST_STATE.READY &&
		Array.isArray(branchList.branches)
			? branchList.branches
			: null;

	const isKnownRouteBranch = React.useMemo(() => {
		if (!routeBranch) return false;
		if (!knownBranches) return false; // do not "trust" route until we know the branch list
		return knownBranches.includes(routeBranch);
	}, [routeBranch, knownBranches]);

	React.useEffect(() => {
		if (!isAuthenticated) return;

		// Branch users: fixed branch, no persisted selection needed.
		if (isBranchUser) {
			const own = user.branchId;
			setSelectedBranch(own && isValidBranchParam(own) ? own : null);
			return;
		}

		// Admin/dev: initialize from localStorage only.
		// IMPORTANT:
		// We do NOT initialize from the route branch, because invalid-but-syntactically-valid
		// branches (e.g. NL200) would pollute state and cause thrashing.
		const fromStorage = safeReadLocalStorageBranch(STORAGE_KEY_LAST_BRANCH);

		if (fromStorage && fromStorage !== selectedBranch) {
			setSelectedBranch(fromStorage);
		}
	}, [isAuthenticated, isBranchUser, user?.branchId, selectedBranch]);

	React.useEffect(() => {
		// Fetch the branch list once for admin/dev users (or when the user changes).
		if (!isAdminDev) return;

		let cancelled = false;

		setBranchList({ status: BRANCH_LIST_STATE.LOADING, branches: null });

		(async () => {
			try {
				const res = await getBranches();
				if (cancelled) return;

				const branches = Array.isArray(res?.branches) ? res.branches : [];
				setBranchList({ status: BRANCH_LIST_STATE.READY, branches });
			} catch (err) {
				if (cancelled) return;

				// Fail open: do not block navigation if validation fails.
				console.error("[QuickNav] getBranches failed:", err);
				setBranchList({ status: BRANCH_LIST_STATE.ERROR, branches: null });
			}
		})();

		return () => {
			cancelled = true;
		};
	}, [isAdminDev, user?.userId]);

	React.useEffect(() => {
		// Once we know the branch list, keep selectedBranch valid and stable.
		if (!isAdminDev) return;
		if (!knownBranches || knownBranches.length === 0) return;

		if (!selectedBranch || !knownBranches.includes(selectedBranch)) {
			const next = knownBranches[0];
			setSelectedBranch(next);
			safeWriteLocalStorageBranch(STORAGE_KEY_LAST_BRANCH, next);
		}
	}, [isAdminDev, knownBranches, selectedBranch]);

	React.useEffect(() => {
		// Sync selectedBranch to the current route branch ONLY when that route branch is known to exist.
		// This prevents the "NL200 thrash" while still keeping the dropdown in sync for valid routes.
		if (!isAdminDev) return;
		if (!isKnownRouteBranch) return;
		if (!routeBranch) return;

		if (routeBranch !== selectedBranch) {
			setSelectedBranch(routeBranch);
			safeWriteLocalStorageBranch(STORAGE_KEY_LAST_BRANCH, routeBranch);
		}
	}, [isAdminDev, isKnownRouteBranch, routeBranch, selectedBranch]);

	React.useEffect(() => {
		if (!isAdminDev) return;
		if (!selectedBranch) return;

		// Keep localStorage in sync (defense-in-depth).
		safeWriteLocalStorageBranch(STORAGE_KEY_LAST_BRANCH, selectedBranch);
	}, [isAdminDev, selectedBranch]);

	if (!isAuthenticated) return null;

	// Effective branch for navigation:
	// - Branch users: always their own branch
	// - Admin/dev: always the persisted/validated selection (NOT the route branch)
	//   This guarantees that nav buttons still work even when the user is on /NL200.
	const effectiveBranch = isBranchUser ? user.branchId : selectedBranch;

	const canNavigate = Boolean(
		effectiveBranch && isValidBranchParam(effectiveBranch),
	);

	function navigateToBranchKeepingContext(nextBranch) {
		if (!isValidBranchParam(nextBranch)) return;

		const currentPathname =
			typeof window !== "undefined"
				? window.location.pathname || pathname
				: pathname;

		const currentSearch =
			typeof window !== "undefined" ? window.location.search || "" : "";

		const nextUrl = buildNextUrlForBranchSwitch({
			pathname: currentPathname,
			search: currentSearch,
			nextBranch,
		});

		if (!nextUrl) return;

		// Trigger a session revalidation without causing content flicker.
		if (canRevalidate) retry();

		router.push(nextUrl);
	}

	const explorerVariant = isExplorerActive ? "secondary" : "ghost";
	const searchVariant = isSearchActive ? "secondary" : "ghost";

	return (
		<div className="hidden items-center gap-2 md:flex">
			{isAdminDev ? (
				<DropdownMenu>
					<DropdownMenuTrigger asChild>
						<Button
							variant="outline"
							size="sm"
							type="button"
							title="Niederlassung auswählen"
						>
							{canNavigate ? effectiveBranch : "Niederlassung wählen"}
						</Button>
					</DropdownMenuTrigger>

					<DropdownMenuContent align="end" className="min-w-56">
						<DropdownMenuLabel>Niederlassung</DropdownMenuLabel>
						<DropdownMenuSeparator />

						{branchList.status === BRANCH_LIST_STATE.ERROR ? (
							<div className="px-2 py-2 text-xs text-muted-foreground">
								Konnte nicht geladen werden.
							</div>
						) : (
							<DropdownMenuRadioGroup
								value={canNavigate ? effectiveBranch : ""}
								onValueChange={(value) => {
									if (!value) return;
									if (!isValidBranchParam(value)) return;

									setSelectedBranch(value);
									safeWriteLocalStorageBranch(STORAGE_KEY_LAST_BRANCH, value);

									navigateToBranchKeepingContext(value);
								}}
							>
								{(Array.isArray(branchList.branches)
									? branchList.branches
									: []
								).map((b) => (
									<DropdownMenuRadioItem key={b} value={b}>
										{b}
									</DropdownMenuRadioItem>
								))}
							</DropdownMenuRadioGroup>
						)}
					</DropdownMenuContent>
				</DropdownMenu>
			) : null}

			<Button
				variant={explorerVariant}
				size="sm"
				asChild
				disabled={!canNavigate}
			>
				<Link
					href={canNavigate ? branchPath(effectiveBranch) : "#"}
					title="Explorer öffnen"
					aria-current={isExplorerActive ? "page" : undefined}
				>
					<FolderOpen className="h-4 w-4" />
					Explorer
				</Link>
			</Button>

			<Button variant={searchVariant} size="sm" asChild disabled={!canNavigate}>
				<Link
					href={canNavigate ? searchPath(effectiveBranch) : "#"}
					title="Suche öffnen"
					aria-current={isSearchActive ? "page" : undefined}
				>
					<SearchIcon className="h-4 w-4" />
					Suche
				</Link>
			</Button>
		</div>
	);
}