import type { Cart, Order, CartProduct } from "~/types";
import { trackEvent } from "~/utils/trackEvent";

const CART_STORAGE_KEY = "shop:cart";
const MAX_RETRY_ATTEMPTS = 3;
const RETRY_DELAYS = [1000, 2000, 4000]; // Exponential backoff: 1s, 2s, 4s

// Module-level promise for deduplication (not reactive, just a lock)
let initPromise: Promise<void> | null = null;

export function useCart() {
	const shopApi = useShopApi();

	// Use useState for proper Nuxt SSR/client state management
	const isInitialized = useState<boolean>("cart:initialized", () => false);
	const isInitializing = useState<boolean>("cart:initializing", () => false);
	const hasError = useState<boolean>("cart:hasError", () => false);
	const retryCount = useState<number>("cart:retryCount", () => 0);

	const cart = useState<Cart>("cart", () => ({
		uuid: "",
		products: [],
		productsCount: 0,
		total: 0,
		subtotal: 0,
		VAT: 0,
		delivery: 0,
		deliveryMethod: null,
		emailAddress: "",
		invoiceAddress: "",
		deliveryAddress: "",
		invoiceAddressStructured: null,
		deliveryAddressStructured: null,
		acceptedTermsAndConditionsAt: false
	}));

	function calculateCount(products: CartProduct[] | null) {
		return products ? products.reduce((sum, { count }) => sum + count, 0) : 0;
	}

	function overwrite(order: Order) {
		cart.value.products = (order.cart as CartProduct[] | null) ?? [];
		cart.value.productsCount = calculateCount(cart.value.products);
		cart.value.total = order.total ?? 0;
		cart.value.subtotal = order.subtotal ?? 0;
		cart.value.VAT = order.VAT ?? 0;
		cart.value.delivery = order.delivery?.price ?? 0;
		cart.value.deliveryMethod = order.delivery?.id ?? null;
		cart.value.uuid = order.uuid ?? "";
		cart.value.emailAddress = order.email ?? "";
		cart.value.invoiceAddress = order.invoiceAddress ?? "";
		cart.value.deliveryAddress = order.deliveryAddress ?? "";
		cart.value.invoiceAddressStructured = order.invoiceAddressStructured ?? null;
		cart.value.deliveryAddressStructured = order.deliveryAddressStructured ?? null;
		cart.value.acceptedTermsAndConditionsAt = Boolean(order.acceptedTermsAndConditionsAt);

		// Persist to localStorage (client-only)
		if (import.meta.client) {
			localStorage.setItem(CART_STORAGE_KEY, order.uuid);
		}
	}

	/**
	 * Sleep utility for retry delays
	 */
	function sleep(ms: number): Promise<void> {
		return new Promise((resolve) => setTimeout(resolve, ms));
	}

	/**
	 * Reset cart to empty state
	 */
	function resetCart() {
		cart.value = {
			uuid: "",
			products: [],
			productsCount: 0,
			total: 0,
			subtotal: 0,
			VAT: 0,
			delivery: 0,
			deliveryMethod: null,
			emailAddress: "",
			invoiceAddress: "",
			deliveryAddress: "",
			invoiceAddressStructured: null,
			deliveryAddressStructured: null,
			acceptedTermsAndConditionsAt: false
		};
	}

	/**
	 * Attempt to fetch cart with retry logic
	 */
	async function fetchWithRetry(attempt = 0): Promise<Order | null> {
		const storedUuid = localStorage.getItem(CART_STORAGE_KEY);

		try {
			let order: Order | null = null;

			if (storedUuid) {
				try {
					order = await shopApi.getOrder(storedUuid);
					// If order is paid, we need a fresh cart
					if (order?.paymentAuthorised) {
						order = null;
					}
				} catch {
					// Order not found or error - will create new one
					order = null;
				}
			}

			// Create new order if we don't have a valid one
			if (!order) {
				order = await shopApi.createOrder();
			}

			return order;
		} catch (error) {
			// Track retry attempt
			if (attempt > 0) {
				trackEvent("cart-fetch-retry", { attempt, maxAttempts: MAX_RETRY_ATTEMPTS });
			}

			// Check if we should retry
			if (attempt < MAX_RETRY_ATTEMPTS - 1) {
				const delay = RETRY_DELAYS[attempt] || RETRY_DELAYS[RETRY_DELAYS.length - 1];
				console.warn(`Cart fetch attempt ${attempt + 1} failed, retrying in ${delay}ms...`);
				await sleep(delay);
				return fetchWithRetry(attempt + 1);
			}

			// All retries exhausted
			trackEvent("cart-fetch-failed", { attempts: attempt + 1 });
			throw error;
		}
	}

	async function fetch() {
		// Only run on client
		if (!import.meta.client) return;

		hasError.value = false;
		retryCount.value = 0;

		try {
			const order = await fetchWithRetry();
			if (order) {
				overwrite(order);
			}
		} catch (error) {
			console.error("Error fetching/creating cart after retries:", error);
			localStorage.removeItem(CART_STORAGE_KEY);
			hasError.value = true;
			resetCart();
		}
	}

	/**
	 * Retry cart initialization after an error
	 */
	async function retry() {
		if (!import.meta.client) return;

		hasError.value = false;
		isInitialized.value = false;
		retryCount.value += 1;

		trackEvent("cart-manual-retry", { retryCount: retryCount.value });

		await initialize();
	}

	/**
	 * Initialize cart - ensures cart is fetched exactly once.
	 * Safe to call from multiple components; subsequent calls return the same promise.
	 */
	async function initialize() {
		// Only run on client
		if (!import.meta.client) return;

		// Already initialized
		if (isInitialized.value) return;

		// Already initializing - wait for existing promise
		if (isInitializing.value && initPromise) {
			return initPromise;
		}

		// Start initialization
		isInitializing.value = true;
		initPromise = fetch().finally(() => {
			isInitialized.value = true;
			isInitializing.value = false;
		});

		return initPromise;
	}

	/**
	 * Wait for cart to be ready. Use this in components that need the cart.
	 */
	async function ensureReady() {
		if (!import.meta.client) return;

		if (!isInitialized.value) {
			await initialize();
		}
	}

	async function addProduct(productId: number, count = 1) {
		// Ensure cart is initialized
		if (!cart.value.uuid) {
			await fetch();
		}

		// Verify we have a valid uuid before making the API call
		if (!cart.value.uuid) {
			throw new Error("Failed to initialize cart - no order UUID available");
		}

		const order = await shopApi.addProductToCart(cart.value.uuid, productId, count);
		overwrite(order);
	}

	async function removeProduct(productId: number, count = 1) {
		const order = await shopApi.removeProductFromCart(cart.value.uuid, productId, count);
		overwrite(order);
	}

	async function update(data: Partial<Order>) {
		const order = await shopApi.updateOrder(cart.value.uuid, data);
		overwrite(order);
	}

	async function checkout() {
		return await shopApi.checkoutOrder(cart.value.uuid);
	}

	// Expose individual computed refs for easier access in components
	const uuid = computed(() => cart.value.uuid);
	const products = computed(() => cart.value.products);
	const productsCount = computed(() => cart.value.productsCount);
	const total = computed(() => cart.value.total);
	const subtotal = computed(() => cart.value.subtotal);
	const VAT = computed(() => cart.value.VAT);
	const delivery = computed(() => cart.value.delivery);
	const deliveryMethod = computed(() => cart.value.deliveryMethod);
	const emailAddress = computed(() => cart.value.emailAddress);
	const invoiceAddress = computed(() => cart.value.invoiceAddress);
	const deliveryAddress = computed(() => cart.value.deliveryAddress);
	const invoiceAddressStructured = computed(() => cart.value.invoiceAddressStructured);
	const deliveryAddressStructured = computed(() => cart.value.deliveryAddressStructured);
	const acceptedTermsAndConditionsAt = computed(() => cart.value.acceptedTermsAndConditionsAt);

	return {
		// State
		isInitialized,
		isInitializing,
		hasError,
		retryCount,
		// Individual computed refs for easy template access
		uuid,
		products,
		productsCount,
		total,
		subtotal,
		VAT,
		delivery,
		deliveryMethod,
		emailAddress,
		invoiceAddress,
		deliveryAddress,
		invoiceAddressStructured,
		deliveryAddressStructured,
		acceptedTermsAndConditionsAt,
		// Methods
		initialize,
		ensureReady,
		fetch,
		retry,
		overwrite,
		addProduct,
		removeProduct,
		update,
		checkout
	};
}