import { Injectable, NotFoundException, BadRequestException } from '@nestjs/common';
import { Food } from '../../foods/entities/food.entity';
import { Restaurant } from '../../restaurants/entities/restaurant.entity';
import { EntityManager } from '@mikro-orm/postgresql';
import { CacheService } from '../../utils/cache.service';
import { ulid } from 'ulid';
import { AddItemToCartDto } from '../dto/add-item.dto';
import { BulkAddItemsToCartDto } from '../dto/bulk-add-items.dto';
import { UpdateItemQuantityDto } from '../dto/update-item.dto';
import { ApplyCouponDto } from '../dto/apply-coupon.dto';
import { SetAddressDto } from '../dto/set-address.dto';
import { SetPaymentMethodDto } from '../dto/set-payment-method.dto';
import { UserAddress } from '../../users/entities/user-address.entity';
import { RestaurantPaymentMethod } from '../../payments/entities/restaurant-payment-method.entity';
import { Cart, CartItem, CartCoupon } from '../interfaces/cart.interface';

@Injectable()
export class CartService {
  private readonly CART_TTL = 1200; // 20 minutes in seconds
  private readonly CART_KEY_PREFIX = 'cart';

  constructor(
    private readonly em: EntityManager,
    private readonly cacheService: CacheService,
  ) {}

  /**
   * Get or create cart for user and restaurant
   */
  async getOrCreateCart(userId: string, restaurantId: string): Promise<Cart> {
    const existingCart = await this.getCartByRestaurant(userId, restaurantId);
    if (existingCart) {
      return existingCart;
    }

    // Find restaurant
    const restaurant = await this.em.findOne(Restaurant, { id: restaurantId });
    if (!restaurant) {
      throw new NotFoundException('Restaurant not found');
    }

    // Create new cart
    const now = new Date().toISOString();
    const cart: Cart = {
      userId,
      restaurantId,
      restaurantName: restaurant.name,
      items: [],
      paymentMethodFee: 0,
      totalPrice: 0,
      totalDiscount: 0,
      couponDiscount: 0,
      vatAmount: 0,
      finalPrice: 0,
      totalItems: 0,
      createdAt: now,
      updatedAt: now,
    };

    await this.saveCart(cart);
    return cart;
  }

  /**
   * Find cart by user and restaurant
   */
  async findOne(userId: string, restaurantId: string): Promise<Cart> {
    const cart = await this.getCartByRestaurant(userId, restaurantId);
    if (!cart) {
      throw new NotFoundException('Cart not found');
    }
    return cart;
  }

  /**
   * Add item to cart (increment quantity if item exists, otherwise create new)
   */
  async addItem(userId: string, restaurantId: string, addItemDto: AddItemToCartDto): Promise<Cart> {
    const cart = await this.getOrCreateCart(userId, restaurantId);

    // Find food
    const food = await this.em.findOne(Food, { id: addItemDto.foodId }, { populate: ['restaurant'] });
    if (!food) {
      throw new NotFoundException(`Food with ID ${addItemDto.foodId} not found`);
    }

    // Check if food belongs to the restaurant
    if (food.restaurant.id !== restaurantId) {
      throw new BadRequestException(`Food ${food.title || food.id} does not belong to restaurant ${restaurantId}`);
    }

    // Check stock availability
    if (food.stock < addItemDto.quantity) {
      throw new BadRequestException(`Insufficient stock for food ${food.title}. Available: ${food.stock}`);
    }

    // Check if item already exists in cart
    const existingItemIndex = cart.items.findIndex(item => item.foodId === addItemDto.foodId);

    if (existingItemIndex >= 0) {
      // Update existing item quantity
      const existingItem = cart.items[existingItemIndex];
      const newQuantity = existingItem.quantity + addItemDto.quantity;

      // Check stock for new total quantity
      if (food.stock < newQuantity) {
        throw new BadRequestException(`Insufficient stock for food ${food.title}. Available: ${food.stock}`);
      }

      const itemPrice = food.price || 0;
      const itemDiscount = food.discount || 0;
      const itemTotalPrice = itemPrice * newQuantity;
      const itemTotalDiscount = itemDiscount * newQuantity;
      const itemFinalPrice = itemTotalPrice - itemTotalDiscount;

      cart.items[existingItemIndex] = {
        ...existingItem,
        quantity: newQuantity,
        totalPrice: itemFinalPrice,
      };
    } else {
      // Create new item
      const itemPrice = food.price || 0;
      const itemDiscount = food.discount || 0;
      const itemTotalPrice = itemPrice * addItemDto.quantity;
      const itemTotalDiscount = itemDiscount * addItemDto.quantity;
      const itemFinalPrice = itemTotalPrice - itemTotalDiscount;

      const cartItem: CartItem = {
        itemId: ulid(),
        foodId: food.id,
        foodTitle: food.title,
        quantity: addItemDto.quantity,
        price: itemPrice,
        discount: itemDiscount,
        totalPrice: itemFinalPrice,
      };

      cart.items.push(cartItem);
    }

    // Recalculate cart totals
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Bulk add items to cart (increments quantity if items exist)
   */
  async bulkAddItems(userId: string, restaurantId: string, bulkAddItemsDto: BulkAddItemsToCartDto): Promise<Cart> {
    const cart = await this.getOrCreateCart(userId, restaurantId);

    // Process each item
    for (const addItemDto of bulkAddItemsDto.items) {
      // Find food
      const food = await this.em.findOne(Food, { id: addItemDto.foodId }, { populate: ['restaurant'] });
      if (!food) {
        throw new NotFoundException(`Food with ID ${addItemDto.foodId} not found`);
      }

      // Check if food belongs to the restaurant
      if (food.restaurant.id !== restaurantId) {
        throw new BadRequestException(`Food ${food.title || food.id} does not belong to restaurant ${restaurantId}`);
      }

      // Check stock availability
      if (food.stock < addItemDto.quantity) {
        throw new BadRequestException(`Insufficient stock for food ${food.title}. Available: ${food.stock}`);
      }

      // Check if item already exists in cart
      const existingItemIndex = cart.items.findIndex(item => item.foodId === addItemDto.foodId);

      if (existingItemIndex >= 0) {
        // Update existing item quantity
        const existingItem = cart.items[existingItemIndex];
        const newQuantity = existingItem.quantity + addItemDto.quantity;

        // Check stock for new total quantity
        if (food.stock < newQuantity) {
          throw new BadRequestException(`Insufficient stock for food ${food.title}. Available: ${food.stock}`);
        }

        const itemPrice = food.price || 0;
        const itemDiscount = food.discount || 0;
        const itemTotalPrice = itemPrice * newQuantity;
        const itemTotalDiscount = itemDiscount * newQuantity;
        const itemFinalPrice = itemTotalPrice - itemTotalDiscount;

        cart.items[existingItemIndex] = {
          ...existingItem,
          quantity: newQuantity,
          totalPrice: itemFinalPrice,
        };
      } else {
        // Create new item
        const itemPrice = food.price || 0;
        const itemDiscount = food.discount || 0;
        const itemTotalPrice = itemPrice * addItemDto.quantity;
        const itemTotalDiscount = itemDiscount * addItemDto.quantity;
        const itemFinalPrice = itemTotalPrice - itemTotalDiscount;

        const cartItem: CartItem = {
          itemId: ulid(),
          foodId: food.id,
          foodTitle: food.title,
          quantity: addItemDto.quantity,
          price: itemPrice,
          discount: itemDiscount,
          totalPrice: itemFinalPrice,
        };

        cart.items.push(cartItem);
      }
    }

    // Recalculate cart totals once after all items are added
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Update item quantity in cart
   */
  async updateItemQuantity(
    userId: string,
    restaurantId: string,
    itemId: string,
    updateItemDto: UpdateItemQuantityDto,
  ): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    const itemIndex = cart.items.findIndex(item => item.itemId === itemId);
    if (itemIndex < 0) {
      throw new NotFoundException(`Item with ID ${itemId} not found in cart`);
    }

    const item = cart.items[itemIndex];

    // Find food to check stock
    const food = await this.em.findOne(Food, { id: item.foodId }, { populate: ['restaurant'] });
    if (!food) {
      throw new NotFoundException(`Food with ID ${item.foodId} not found`);
    }

    // Check stock availability
    if (food.stock < updateItemDto.quantity) {
      throw new BadRequestException(`Insufficient stock for food ${food.title}. Available: ${food.stock}`);
    }

    // Update quantity
    const itemPrice = food.price || 0;
    const itemDiscount = food.discount || 0;
    const itemTotalPrice = itemPrice * updateItemDto.quantity;
    const itemTotalDiscount = itemDiscount * updateItemDto.quantity;
    const itemFinalPrice = itemTotalPrice - itemTotalDiscount;

    cart.items[itemIndex] = {
      ...item,
      quantity: updateItemDto.quantity,
      totalPrice: itemFinalPrice,
    };

    // Recalculate cart totals
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Remove item from cart
   */
  async removeItem(userId: string, restaurantId: string, itemId: string): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    const itemIndex = cart.items.findIndex(item => item.itemId === itemId);
    if (itemIndex < 0) {
      throw new NotFoundException(`Item with ID ${itemId} not found in cart`);
    }

    // Remove item
    cart.items.splice(itemIndex, 1);

    // Recalculate cart totals
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Apply coupon to cart
   */
  async applyCoupon(userId: string, restaurantId: string, applyCouponDto: ApplyCouponDto): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    // TODO: Implement actual coupon validation logic
    // For now, this is a placeholder implementation
    // You should validate the coupon code against your coupon/discount system

    // Example coupon structure (replace with your actual coupon validation)
    const coupon: CartCoupon = {
      code: applyCouponDto.code,
      discount: 10, // Example: 10% discount
      discountType: 'percentage', // or 'amount'
    };

    cart.coupon = coupon;

    // Recalculate cart totals
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Remove coupon from cart
   */
  async removeCoupon(userId: string, restaurantId: string): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    cart.coupon = undefined;

    // Recalculate cart totals
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Set address for cart
   */
  async setAddress(userId: string, restaurantId: string, setAddressDto: SetAddressDto): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    // Find and validate address belongs to user
    const address = await this.em.findOne(UserAddress, { id: setAddressDto.addressId }, { populate: ['user'] });
    if (!address) {
      throw new NotFoundException(`Address with ID ${setAddressDto.addressId} not found`);
    }

    // Verify address belongs to the user
    if (address.user.id !== userId) {
      throw new BadRequestException('Address does not belong to the current user');
    }

    cart.addressId = setAddressDto.addressId;
    cart.updatedAt = new Date().toISOString();

    await this.saveCart(cart);

    return cart;
  }

  /**
   * Set payment method for cart
   */
  async setPaymentMethod(
    userId: string,
    restaurantId: string,
    setPaymentMethodDto: SetPaymentMethodDto,
  ): Promise<Cart> {
    const cart = await this.findOne(userId, restaurantId);

    // Find and validate payment method belongs to restaurant
    const restaurantPaymentMethod = await this.em.findOne(
      RestaurantPaymentMethod,
      {
        restaurant: { id: restaurantId },
        paymentMethod: { id: setPaymentMethodDto.paymentMethodId },
      },
      { populate: ['restaurant', 'paymentMethod'] },
    );

    if (!restaurantPaymentMethod) {
      throw new NotFoundException(
        `Payment method with ID ${setPaymentMethodDto.paymentMethodId} not found for restaurant ${restaurantId}`,
      );
    }

    // Verify payment method is active
    if (!restaurantPaymentMethod.isActive) {
      throw new BadRequestException('Payment method is not active for this restaurant');
    }

    // Verify the payment method itself is active
    if (!restaurantPaymentMethod.paymentMethod.isActive) {
      throw new BadRequestException('Payment method is not active');
    }

    cart.paymentMethodId = setPaymentMethodDto.paymentMethodId;
    // cart.paymentMethodFee = Number(restaurantPaymentMethod.price) || 0;

    // Recalculate cart totals to include payment method fee
    await this.recalculateCartTotals(cart);
    await this.saveCart(cart);

    return cart;
  }

  /**
   * Recalculate cart totals (including coupon discount and VAT)
   */
  private async recalculateCartTotals(cart: Cart): Promise<void> {
    let totalPrice = 0;
    let totalDiscount = 0;
    let totalItems = 0;

    for (const item of cart.items) {
      const itemPrice = item.price * item.quantity;
      const itemDiscount = item.discount * item.quantity;
      totalPrice += itemPrice;
      totalDiscount += itemDiscount;
      totalItems += item.quantity;
    }

    cart.totalPrice = totalPrice;
    cart.totalDiscount = totalDiscount;

    // Calculate coupon discount
    let couponDiscount = 0;
    if (cart.coupon) {
      if (cart.coupon.discountType === 'percentage') {
        const priceAfterItemDiscount = totalPrice - totalDiscount;
        couponDiscount = (priceAfterItemDiscount * cart.coupon.discount) / 100;
      } else {
        // amount discount
        const priceAfterItemDiscount = totalPrice - totalDiscount;
        couponDiscount = Math.min(cart.coupon.discount, priceAfterItemDiscount);
      }
    }

    cart.couponDiscount = couponDiscount;
    const priceAfterDiscounts = totalPrice - totalDiscount - couponDiscount;

    // Calculate VAT if restaurant has VAT rate > 0
    let vatAmount = 0;
    const restaurant = await this.em.findOne(Restaurant, { id: cart.restaurantId });
    if (restaurant && restaurant.vat && restaurant.vat > 0) {
      // VAT is calculated on the price after discounts and coupons
      vatAmount = (priceAfterDiscounts * Number(restaurant.vat)) / 100;
    }

    cart.vatAmount = vatAmount;

    // Get payment method fee if payment method is set
    let paymentMethodFee = 0;
    // if (cart.paymentMethodId) {
    //   const restaurantPaymentMethod = await this.em.findOne(RestaurantPaymentMethod, {
    //     restaurant: { id: cart.restaurantId },
    //     paymentMethod: { id: cart.paymentMethodId },
    //   });
    //   if (restaurantPaymentMethod) {
    //     paymentMethodFee = Number(restaurantPaymentMethod.price) || 0;
    //     paymentMethodFee = 1;
    //   }
    // }
    cart.paymentMethodFee = paymentMethodFee;

    // Final price includes items, discounts, VAT, and payment method fee
    cart.finalPrice = priceAfterDiscounts + vatAmount + paymentMethodFee;
    cart.totalItems = totalItems;
    cart.updatedAt = new Date().toISOString();
  }

  /**
   * Type guard to check if an object is a Cart
   */
  private isCart(obj: unknown): obj is Cart {
    if (typeof obj !== 'object' || obj === null) {
      return false;
    }
    const cart = obj as Record<string, unknown>;
    return (
      typeof cart.userId === 'string' &&
      typeof cart.restaurantId === 'string' &&
      Array.isArray(cart.items) &&
      typeof cart.totalPrice === 'number' &&
      typeof cart.totalDiscount === 'number' &&
      typeof cart.couponDiscount === 'number' &&
      typeof cart.vatAmount === 'number' &&
      typeof cart.finalPrice === 'number' &&
      typeof cart.totalItems === 'number' &&
      typeof cart.createdAt === 'string' &&
      typeof cart.updatedAt === 'string'
    );
  }

  /**
   * Get cart by restaurant for a user
   */
  private async getCartByRestaurant(userId: string, restaurantId: string): Promise<Cart | null> {
    const cacheKey = `${this.CART_KEY_PREFIX}:${userId}:${restaurantId}`;
    const cachedCart = await this.cacheService.get<string>(cacheKey);

    if (cachedCart) {
      try {
        const parsed: unknown = JSON.parse(cachedCart);
        if (this.isCart(parsed) && parsed.userId === userId && parsed.restaurantId === restaurantId) {
          return parsed;
        }
      } catch {
        // If parsing fails, return null
      }
    }

    return null;
  }

  /**
   * Save cart to cache
   */
  private async saveCart(cart: Cart): Promise<void> {
    const cacheKey = `${this.CART_KEY_PREFIX}:${cart.userId}:${cart.restaurantId}`;
    await this.cacheService.set(cacheKey, JSON.stringify(cart), this.CART_TTL);
  }
}