import { Injectable, NotFoundException, BadRequestException, Logger } from '@nestjs/common';
import { EntityManager } from '@mikro-orm/postgresql';
import { Order } from '../entities/order.entity';
import { OrderItem } from '../entities/order-item.entity';
import { User } from '../../users/entities/user.entity';
import { Restaurant } from '../../restaurants/entities/restaurant.entity';
import { Food } from '../../foods/entities/food.entity';
import { CartService } from '../../cart/providers/cart.service';
import { OrderStatus, OrderUserAddress, OrderCarAddress } from '../interface/order.interface';
import { PaymentMethodEnum, PaymentStatusEnum } from '../../payments/interface/payment';
import { Cart } from '../../cart/interfaces/cart.interface';
import { PaymentMethod } from '../../payments/entities/payment-method.entity';
import { PaymentsService } from '../../payments/services/payments.service';
import { DeliveryMethodEnum } from '../../delivery/interface/delivery';
import { Delivery } from '../../delivery/entities/delivery.entity';
import { OrderRepository } from '../repositories/order.repository';
import { FindOrdersDto } from '../dto/find-orders.dto';
import { PaginatedResult } from 'src/common/interfaces/pagination.interface';
import { Payment } from 'src/modules/payments/entities/payment.entity';
import { InventoryService } from 'src/modules/inventory/inventory.service';
import { BulkReserveFoodDto } from 'src/modules/inventory/dto/bulk-reserve-food.dto';
import { StatusTransitionRef } from '../interface/order.interface';
import { EventEmitter2 } from '@nestjs/event-emitter';
import { OrderCreatedEvent, OrderStatusChangedEvent } from '../events/order.events';
type OrderItemData = { food: Food; quantity: number; unitPrice: number; discount: number };

type ValidatedCartForOrder = {
  user: User;
  restaurant: Restaurant;
  delivery: Delivery;
  userAddress: OrderUserAddress | null;
  carAddress: OrderCarAddress | null;
  paymentMethod: PaymentMethod;
  orderItemsData: OrderItemData[];
};

@Injectable()
export class OrdersService {
  private readonly logger = new Logger(OrdersService.name);

  private static readonly STATUS_TRANSITIONS: Record<OrderStatus, readonly OrderStatus[]> = {
    [OrderStatus.PENDING_PAYMENT]: [OrderStatus.PAID, OrderStatus.CANCELED, OrderStatus.CONFIRMED],
    [OrderStatus.PAID]: [OrderStatus.CONFIRMED, OrderStatus.CANCELED],
    [OrderStatus.CONFIRMED]: [OrderStatus.PREPARING, OrderStatus.CANCELED],
    [OrderStatus.PREPARING]: [OrderStatus.READY, OrderStatus.SHIPPED, OrderStatus.CANCELED],
    [OrderStatus.READY]: [OrderStatus.COMPLETED, OrderStatus.CANCELED],
    [OrderStatus.SHIPPED]: [OrderStatus.COMPLETED, OrderStatus.CANCELED],
    [OrderStatus.COMPLETED]: [OrderStatus.CANCELED],
    [OrderStatus.CANCELED]: [],
  };

  constructor(
    private readonly em: EntityManager,
    private readonly cartService: CartService,
    private readonly orderRepository: OrderRepository,
    private readonly paymentsService: PaymentsService,
    private readonly inventoryService: InventoryService,
    private readonly eventEmitter: EventEmitter2,
  ) {}

  async checkout(userId: string, restaurantId: string) {
    const cart = await this.cartService.findOneOrFail(userId, restaurantId);
    const validated = await this.validateCartForOrder(userId, restaurantId, cart);

    const order = await this.em.transactional(async em => {
      const order = em.create(Order, {
        user: validated.user,
        restaurant: validated.restaurant,
        deliveryMethod: validated.delivery,
        userAddress: validated.userAddress,
        carAddress: validated.carAddress,
        paymentMethod: validated.paymentMethod,
        couponDiscount: cart.couponDiscount || 0,
        itemsDiscount: cart.itemsDiscount || 0,
        totalDiscount: cart.totalDiscount || 0,
        subTotal: cart.subTotal || 0,
        tax: cart.tax || 0,
        deliveryFee: cart.deliveryFee || 0,
        total: cart.total || 0,
        totalItems: cart.totalItems || 0,
        description: cart.description,
        tableNumber: cart.tableNumber,
        status: OrderStatus.PENDING_PAYMENT,
        history: [{ status: OrderStatus.PENDING_PAYMENT, changedAt: new Date() }],
      });

      em.persist(order);

      for (const itemData of validated.orderItemsData) {
        const { food, quantity, unitPrice, discount } = itemData;

        this.assertFoodHasSufficientStock(food, quantity);

        const totalPrice = (unitPrice - discount) * quantity;

        const orderItem = em.create(OrderItem, {
          order,
          food,
          quantity,
          unitPrice,
          discount,
          totalPrice,
        });

        em.persist(orderItem);
      }

      const payment = em.create(Payment, {
        order,
        amount: order.total,
        status: PaymentStatusEnum.Pending,
        method: order.paymentMethod.method,
        gateway: order.paymentMethod.gateway ?? null,
      });

      em.persist(payment);
      // reserve stock based on payment method.
      const bulkReserveFoodDto: BulkReserveFoodDto = {
        items: validated.orderItemsData.map(item => ({
          foodId: item.food.id,
          quantity: item.quantity,
        })),
      };
      await this.inventoryService.deductFromInventory(em, bulkReserveFoodDto);
      await em.flush();
      this.logger.debug(`Order ${order.id} created for user ${userId} (restaurant ${restaurantId})`);
      this.eventEmitter.emit(
        OrderCreatedEvent.name,
        new OrderCreatedEvent(order.id, restaurantId, String(order?.orderNumber) || ''),
      );
      return order;
    });

    await this.cartService.clearCart(userId, restaurantId);

    const { paymentUrl } = await this.paymentsService.payOrder(order.id);

    return { paymentUrl, order };
  }

  /**
   * Validates cart and prepares all required data for order creation
   */
  private async validateCartForOrder(userId: string, restaurantId: string, cart: Cart): Promise<ValidatedCartForOrder> {
    this.assertCartHasItems(cart);
    this.assertCartHasDeliveryMethod(cart);
    this.assertCartHasPaymentMethod(cart);

    const [user, restaurant, delivery] = await Promise.all([
      this.getUserOrFail(userId),
      this.getRestaurantOrFail(restaurantId),
      this.getDeliveryOrFail(cart.deliveryMethodId!),
    ]);

    this.assertMeetsMinOrderForDelivery(cart, delivery);
    this.assertDeliveryMethodRequirements(cart, delivery);

    const paymentMethod = await this.getPaymentMethodOrFail(cart.paymentMethodId!, restaurantId);
    this.assertPaymentMethodEnabled(paymentMethod);

    const orderItemsData = await this.buildOrderItemsData(cart, restaurantId);

    return {
      user,
      restaurant,
      delivery,
      paymentMethod,
      userAddress: delivery.method === DeliveryMethodEnum.DeliveryCourier ? (cart?.userAddress ?? null) : null,
      carAddress: delivery.method === DeliveryMethodEnum.DeliveryCar ? (cart?.carAddress ?? null) : null,
      orderItemsData,
    };
  }

  async findAllForUser(restId: string, dto: FindOrdersDto, userId: string): Promise<PaginatedResult<Order>> {
    const result = await this.orderRepository.findAllPaginated(restId, {
      page: dto.page,
      limit: dto.limit,
      status: dto.status,
      paymentStatus: dto.paymentStatus,
      search: dto.search,
      startDate: dto.startDate,
      endDate: dto.endDate,
      orderBy: dto.orderBy,
      order: dto.order,
      userId,
    });

    return result;
  }

  async findAllForAdmin(restId: string, dto: FindOrdersDto): Promise<PaginatedResult<Order>> {
    const result = await this.orderRepository.findAllPaginated(restId, {
      page: dto.page,
      limit: dto.limit,
      status: dto.status,
      paymentStatus: dto.paymentStatus,
      search: dto.search,
      startDate: dto.startDate,
      endDate: dto.endDate,
      orderBy: dto.orderBy,
      order: dto.order,
    });

    return result;
  }

  async findOne(id: string, restId: string): Promise<Order> {
    const order = await this.orderRepository.findOne(
      { id, restaurant: { id: restId } },
      {
        populate: [
          'user',
          'restaurant',
          'deliveryMethod',
          'userAddress',
          'carAddress',
          'paymentMethod',
          'items',
          'items.food',
        ],
      },
    );
    if (!order) {
      throw new NotFoundException('Order not found');
    }
    return order;
  }

  // async confirmOrder(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.CONFIRMED);
  // }

  // async prepareOrder(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.PREPARING);
  // }

  // just admin can reject the order any time
  // async rejectOrder(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.CANCELED, { skipTransitionValidation: true });
  // }

  // async readyForDelivery(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.READY);
  // }

  // async cancelOrderAsUser(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.CANCELED);
  // }

  // async markAsDelivered(orderId: string, restId: string) {
  //   return this.changeOrderStatus(orderId, restId, OrderStatus.COMPLETED);
  // }

  // async updateStatus(orderId: string, restId: string, status: OrderStatus, ref: StatusTransitionRef) {
  //   return this.changeOrderStatus(orderId, restId, status, ref);
  // }

  async changeOrderStatus(
    orderId: string,
    restId: string,
    toStatus: OrderStatus,
    ref: StatusTransitionRef,
    desc?: string,
  ): Promise<Order> {
    const order = await this.getOrderOrFail(orderId, restId);

    this.assertStatusTransitionAllowed(order, toStatus, ref);

    order.status = toStatus;
    order.history.push({ status: toStatus, changedAt: new Date(), desc: desc || null });
    await this.em.persistAndFlush(order);

    this.eventEmitter.emit(
      OrderStatusChangedEvent.name,
      new OrderStatusChangedEvent(
        orderId,
        order.user?.id || '',
        String(order?.orderNumber) || '',
        restId,
        order.status,
        toStatus,
        ref,
      ),
    );
    return order;
  }
  /*               Helpers              */
  private assertStatusTransitionAllowed(order: Order, to: OrderStatus, ref: StatusTransitionRef) {
    const paymentMethod = order.paymentMethod?.method;
    if (!paymentMethod) {
      throw new BadRequestException('Order payment method is missing');
    }

    if (!this.canTransition(order.status, to, paymentMethod, ref)) {
      throw new BadRequestException(`Invalid status transition: ${order.status} -> ${to}`);
    }
  }

  private canTransition(from: OrderStatus, to: OrderStatus, paymentMethod: PaymentMethodEnum, ref: 'user' | 'admin') {
    if (!OrdersService.STATUS_TRANSITIONS[from]?.includes(to)) return false;

    if (to === OrderStatus.CANCELED) {
      // only allow orders with status of PENDING_PAYMENT and PAID are allowed to be canceled by user
      if (ref === 'user' && ![OrderStatus.PENDING_PAYMENT, OrderStatus.PAID, OrderStatus.CONFIRMED].includes(from)) {
        return false;
      } else if (ref === 'admin') {
        return true;
      }
    }
    // only allow orders with status of PENDING_PAYMENT and payment
    // method of cash are allowed to move to  CONFIRMED directly
    if (
      from == OrderStatus.PENDING_PAYMENT &&
      to == OrderStatus.CONFIRMED &&
      paymentMethod !== PaymentMethodEnum.Cash
    ) {
      return false;
    }
    // if (paymentMethod === PaymentMethodEnum.Cash) {
    //   if ([OrderStatus.PENDING_PAYMENT, OrderStatus.PAID].includes(to)) return false;
    // }

    if (paymentMethod === PaymentMethodEnum.Online) {
      if (to === OrderStatus.CONFIRMED && from !== OrderStatus.PAID) return false;
    }

    return true;
  }

  private async getOrderOrFail(orderId: string, restId: string): Promise<Order> {
    const order = await this.em.findOne(
      Order,
      { id: orderId, restaurant: { id: restId } },
      { populate: ['paymentMethod'] },
    );
    if (!order) throw new NotFoundException('Order not found');
    return order;
  }

  private assertCartHasItems(cart: Cart) {
    if (!cart.items || cart.items.length === 0) {
      throw new BadRequestException('Cart is empty. Add items to cart before creating an order.');
    }
  }

  private assertCartHasDeliveryMethod(cart: Cart) {
    if (!cart.deliveryMethodId) {
      throw new NotFoundException('Delivery method not found');
    }
  }

  private assertCartHasPaymentMethod(cart: Cart) {
    if (!cart.paymentMethodId) {
      throw new BadRequestException(
        'Payment method is required. Please set a payment method before creating an order.',
      );
    }
  }

  private async getUserOrFail(userId: string): Promise<User> {
    const user = await this.em.findOne(User, { id: userId });
    if (!user) throw new NotFoundException('User not found');
    return user;
  }

  private async getRestaurantOrFail(restaurantId: string): Promise<Restaurant> {
    const restaurant = await this.em.findOne(Restaurant, { id: restaurantId });
    if (!restaurant) throw new NotFoundException('Restaurant not found');
    return restaurant;
  }

  private async getDeliveryOrFail(deliveryId: string): Promise<Delivery> {
    const delivery = await this.em.findOne(Delivery, { id: deliveryId });
    if (!delivery) throw new NotFoundException('Delivery not found');
    return delivery;
  }

  private assertMeetsMinOrderForDelivery(cart: Cart, delivery: Delivery) {
    const minOrderPrice = Number(delivery.minOrderPrice) || 0;
    if (minOrderPrice > 0 && cart.total < minOrderPrice) {
      throw new BadRequestException(
        `Minimum order amount for this delivery method is ${minOrderPrice}. Current total is ${cart.total}.`,
      );
    }
  }

  private assertDeliveryMethodRequirements(cart: Cart, delivery: Delivery) {
    if (delivery.method === DeliveryMethodEnum.DineIn) {
      if (!cart.tableNumber || cart.tableNumber.trim() === '') {
        throw new BadRequestException('Table number is required when delivery method is DineIn');
      }
    }

    if (delivery.method === DeliveryMethodEnum.DeliveryCourier && !cart.userAddress) {
      throw new BadRequestException('Address is required. Please set a delivery address before creating an order.');
    }

    if (delivery.method === DeliveryMethodEnum.DeliveryCar && !cart.carAddress) {
      throw new BadRequestException('Car address is required. Please set a car address before creating an order.');
    }
  }

  private async getPaymentMethodOrFail(paymentMethodId: string, restaurantId: string): Promise<PaymentMethod> {
    const paymentMethod = await this.em.findOne(
      PaymentMethod,
      {
        id: paymentMethodId,
        restaurant: { id: restaurantId },
      },
      { populate: ['restaurant'] },
    );

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

    return paymentMethod;
  }

  private assertPaymentMethodEnabled(paymentMethod: PaymentMethod) {
    if (!paymentMethod.enabled) {
      throw new BadRequestException('Payment method is not enabled for this restaurant');
    }
  }

  private async buildOrderItemsData(cart: Cart, restaurantId: string): Promise<OrderItemData[]> {
    const orderItemsData: OrderItemData[] = [];

    for (const cartItem of cart.items) {
      const food = await this.em.findOne(Food, { id: cartItem.foodId }, { populate: ['restaurant', 'inventory'] });
      if (!food) throw new NotFoundException(`Food with ID ${cartItem.foodId} not found`);

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

      this.assertFoodHasSufficientStock(food, cartItem.quantity);

      orderItemsData.push({
        food,
        quantity: cartItem.quantity,
        unitPrice: food.price || 0,
        discount: food.discount || 0,
      });
    }

    return orderItemsData;
  }

  private assertFoodHasSufficientStock(food: Food, quantity: number) {
    const availableStock = food.inventory?.availableStock ?? 0;
    if (availableStock < quantity) {
      throw new BadRequestException(
        `Insufficient stock for food ${food.title || food.id}. Available: ${availableStock}, Requested: ${quantity}`,
      );
    }
  }
}