import {
  BadRequestException,
  ForbiddenException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { ContentStatus, Prisma } from '@prisma/client';
import { AuthUser } from '../auth/auth.types';
import { PermissionsService } from '../auth/permissions.service';
import { PrismaService } from '../prisma/prisma.service';
import {
  AddCartItemDto,
  CheckoutCartDto,
  ShippingAddressDto,
  UpdateCartItemDto,
} from './dto/cart.dto';
import { OrdersService } from '../orders/orders.service';
import { PaymentsService } from '../payments/payments.service';
import { TransactionType } from '@prisma/client';
import { BusinessSettingsService } from '../business-settings/business-settings.service';
import type { PaymentGatewayId } from '../business-settings/business-settings.types';
import { listPublicPaymentGateways } from '../business-settings/business-settings.util';
import { ShippingCostGroupsService } from '../store/shipping-cost-groups.service';

const cartVariantInclude = {
  storeItem: {
    include: {
      product: {
        include: {
          featuredMedia: true,
        },
      },
    },
  },
  selections: {
    include: {
      variation: true,
      option: true,
    },
  },
} satisfies Prisma.StoreItemVariantInclude;

type CartWithItems = Prisma.CartGetPayload<{
  include: {
    items: {
      include: {
        storeItemVariant: {
          include: typeof cartVariantInclude;
        };
      };
    };
  };
}>;

@Injectable()
export class CartService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly permissions: PermissionsService,
    private readonly orders: OrdersService,
    private readonly payments: PaymentsService,
    private readonly businessSettings: BusinessSettingsService,
    private readonly shippingCostGroups: ShippingCostGroupsService,
  ) {}

  async getCart(businessIdRaw: string, actor: AuthUser) {
    const businessId = BigInt(businessIdRaw);
    await this.assertCustomerAccess(businessId, actor);

    const cart = await this.getOrCreateCart(businessId, actor.id);
    return { cart: await this.serializeCart(cart) };
  }

  async addItem(businessIdRaw: string, dto: AddCartItemDto, actor: AuthUser) {
    const businessId = BigInt(businessIdRaw);
    const storeItemVariantId = BigInt(dto.storeItemVariantId);
    const quantity = dto.quantity ?? 1;
    await this.assertCustomerAccess(businessId, actor);

    const variant = await this.loadPurchasableVariant(businessId, storeItemVariantId);
    this.assertStockAvailable(variant.stockQuantity, quantity);

    const cart = await this.getOrCreateCart(businessId, actor.id);
    const existing = cart.items.find(
      (item) => item.storeItemVariantId === storeItemVariantId,
    );

    if (existing) {
      const newQuantity = existing.quantity + quantity;
      this.assertStockAvailable(variant.stockQuantity, newQuantity);

      await this.prisma.cartItem.update({
        where: { id: existing.id },
        data: { quantity: newQuantity },
      });

      await this.bumpProductCartAdd(variant.storeItem.productId, quantity);

      const refreshed = await this.loadCart(cart.id);
      return {
        message: 'Cart item quantity updated',
        cart: await this.serializeCart(refreshed),
      };
    }

    await this.prisma.cartItem.create({
      data: {
        cartId: cart.id,
        storeItemVariantId,
        quantity,
      },
    });

    await this.bumpProductCartAdd(variant.storeItem.productId, quantity);

    const refreshed = await this.loadCart(cart.id);
    return {
      message: 'Item added to cart',
      cart: await this.serializeCart(refreshed),
    };
  }

  async updateItem(
    businessIdRaw: string,
    itemIdRaw: string,
    dto: UpdateCartItemDto,
    actor: AuthUser,
  ) {
    const businessId = BigInt(businessIdRaw);
    const itemId = BigInt(itemIdRaw);
    await this.assertCustomerAccess(businessId, actor);

    const cart = await this.getOrCreateCart(businessId, actor.id);
    const item = cart.items.find((entry) => entry.id === itemId);

    if (!item) {
      throw new NotFoundException('Cart item not found');
    }

    this.assertStockAvailable(item.storeItemVariant.stockQuantity, dto.quantity);

    await this.prisma.cartItem.update({
      where: { id: itemId },
      data: { quantity: dto.quantity },
    });

    const refreshed = await this.loadCart(cart.id);
    return {
      message: 'Cart item updated',
      cart: await this.serializeCart(refreshed),
    };
  }

  async removeItem(businessIdRaw: string, itemIdRaw: string, actor: AuthUser) {
    const businessId = BigInt(businessIdRaw);
    const itemId = BigInt(itemIdRaw);
    await this.assertCustomerAccess(businessId, actor);

    const cart = await this.getOrCreateCart(businessId, actor.id);
    const item = cart.items.find((entry) => entry.id === itemId);

    if (!item) {
      throw new NotFoundException('Cart item not found');
    }

    await this.prisma.cartItem.delete({ where: { id: itemId } });

    const refreshed = await this.loadCart(cart.id);
    return {
      message: 'Cart item removed',
      cart: await this.serializeCart(refreshed),
    };
  }

  async clear(businessIdRaw: string, actor: AuthUser) {
    const businessId = BigInt(businessIdRaw);
    await this.assertCustomerAccess(businessId, actor);

    const cart = await this.getOrCreateCart(businessId, actor.id);
    await this.prisma.cartItem.deleteMany({ where: { cartId: cart.id } });

    const refreshed = await this.loadCart(cart.id);
    return {
      message: 'Cart cleared',
      cart: await this.serializeCart(refreshed),
    };
  }

  async checkout(
    businessIdRaw: string,
    dto: CheckoutCartDto,
    actor: AuthUser,
  ) {
    const businessId = BigInt(businessIdRaw);
    await this.assertCustomerAccess(businessId, actor);

    const cart = await this.getOrCreateCart(businessId, actor.id);

    if (!cart.items.length) {
      throw new BadRequestException('Cart is empty');
    }

    const shippingAddress = await this.resolveShippingAddress(
      actor.id,
      dto.addressId,
      dto.shippingAddress,
    );

    const deliveryMode =
      dto.deliveryMode === 'pickup' || dto.deliveryMode === 'delivery'
        ? dto.deliveryMode
        : dto.addressId
          ? 'delivery'
          : 'pickup';

    const selectedMethodsByGroupId: Record<string, string> = {};
    for (const group of dto.shippingGroups ?? []) {
      if (group.methodId?.trim()) {
        selectedMethodsByGroupId[group.groupId] = group.methodId.trim();
      }
    }

    const productIds = [
      ...new Set(
        cart.items.map((item) => item.storeItemVariant.storeItem.product.id),
      ),
    ];
    const assignments =
      productIds.length === 0
        ? []
        : await this.prisma.categoryAssignment.findMany({
            where: {
              businessId,
              entityType: 'product',
              entityId: { in: productIds },
            },
            select: { entityId: true, categoryId: true },
          });
    const categoryIdsByProduct = new Map<string, string[]>();
    for (const row of assignments) {
      const key = row.entityId.toString();
      const list = categoryIdsByProduct.get(key) ?? [];
      list.push(row.categoryId.toString());
      categoryIdsByProduct.set(key, list);
    }

    const shippingQuote = await this.shippingCostGroups.quoteForCheckout({
      businessId,
      deliveryMode,
      provinceName:
        deliveryMode === 'delivery' ? String(shippingAddress.province ?? '') : null,
      cartItems: cart.items.map((item) => {
        const product = item.storeItemVariant.storeItem.product;
        const content = this.asRecord(product.content);
        const nameFa = (content.nameFa as string | null | undefined)?.trim();
        return {
          productName: nameFa || product.title,
          categoryIds:
            categoryIdsByProduct.get(product.id.toString()) ?? [],
        };
      }),
      selectedMethodsByGroupId,
    });

    const enrichedShippingAddress = {
      ...shippingAddress,
      deliveryMode,
      shipping: {
        total: shippingQuote.total,
        groups: shippingQuote.groups,
      },
    };

    const isEPayment = dto.payment.type === TransactionType.e_payment_gate;
    let gatewayType: PaymentGatewayId | undefined;

    if (isEPayment) {
      if (!dto.returnUrl?.trim()) {
        throw new BadRequestException(
          'returnUrl is required for e-payment checkout',
        );
      }

      const settings =
        await this.businessSettings.getNormalizedSettings(businessId);
      const publicMethods = listPublicPaymentGateways(settings.store.ePayment);
      if (!publicMethods.enabled) {
        throw new BadRequestException(
          'Online payment is not enabled for this store',
        );
      }
      gatewayType = this.payments.resolveGatewayType(
        dto.payment.gatewayType,
        publicMethods,
      );
    }

    const order = await this.orders.createFromCart({
      businessId,
      userId: actor.id,
      createdBy: actor.id,
      source: 'website',
      cartItems: cart.items,
      shippingAddress: enrichedShippingAddress,
      shippingTotal: shippingQuote.total,
      addressId: dto.addressId ? BigInt(dto.addressId) : null,
      customerNotes: dto.customerNotes?.trim() || null,
      adminNotes: null,
      status: 'pending',
      payment: {
        type: dto.payment.type,
        posType: dto.payment.posType,
        gatewayType: isEPayment ? gatewayType : dto.payment.gatewayType,
        transferAccount: dto.payment.transferAccount,
        transferRefNumber: dto.payment.transferRefNumber,
        notes: dto.payment.notes?.trim() || null,
      },
    });

    if (isEPayment && gatewayType) {
      const payment = await this.payments.initiateForCheckout({
        businessId,
        order: {
          id: order.id,
          total: order.total,
          transactions: order.transactions,
        },
        gatewayType,
        returnUrl: dto.returnUrl!.trim(),
      });

      await this.prisma.cartItem.deleteMany({ where: { cartId: cart.id } });

      return {
        message: 'Redirect customer to payment gateway',
        order,
        payment: {
          gatewayType: payment.gatewayType,
          transactionId: payment.transactionId,
          redirect: payment.redirect,
        },
      };
    }

    await this.prisma.cartItem.deleteMany({ where: { cartId: cart.id } });

    return {
      message: 'Order placed successfully',
      order,
    };
  }

  private async getOrCreateCart(businessId: bigint, userId: bigint) {
    // Concurrent GETs (e.g. React Strict Mode) can race on create; upsert is safe.
    const cart = await this.prisma.cart.upsert({
      where: {
        businessId_userId: { businessId, userId },
      },
      create: { businessId, userId },
      update: {},
    });

    return this.loadCart(cart.id);
  }

  private async loadCart(cartId: bigint): Promise<CartWithItems> {
    return this.prisma.cart.findUniqueOrThrow({
      where: { id: cartId },
      include: {
        items: {
          orderBy: { createdAt: 'asc' },
          include: {
            storeItemVariant: {
              include: cartVariantInclude,
            },
          },
        },
      },
    });
  }

  private async bumpProductCartAdd(productId: bigint, quantity: number) {
    if (!Number.isFinite(quantity) || quantity <= 0) return;
    await this.prisma.product.update({
      where: { id: productId },
      data: { cartAddCount: { increment: quantity } },
    });
  }

  private async loadPurchasableVariant(
    businessId: bigint,
    storeItemVariantId: bigint,
  ) {
    const variant = await this.prisma.storeItemVariant.findFirst({
      where: { id: storeItemVariantId, businessId, isActive: true },
      include: {
        storeItem: {
          include: {
            product: true,
          },
        },
      },
    });

    if (!variant) {
      throw new NotFoundException('Store item variant not found or unavailable');
    }

    if (variant.storeItem.product.status !== ContentStatus.published) {
      throw new BadRequestException('Product is not available for purchase');
    }

    if (variant.price === null) {
      throw new BadRequestException('Store item variant has no price configured');
    }

    return variant;
  }

  private async resolveShippingAddress(
    userId: bigint,
    addressIdRaw: string | undefined,
    inline: ShippingAddressDto | undefined,
  ) {
    if (addressIdRaw) {
      const address = await this.prisma.address.findFirst({
        where: { id: BigInt(addressIdRaw), userId },
      });

      if (!address) {
        throw new NotFoundException('Shipping address not found');
      }

      return {
        province: address.province,
        city: address.city,
        address: address.address,
        postalCode: address.postalCode,
        landline: address.landline,
      };
    }

    if (!inline) {
      throw new BadRequestException(
        'Provide addressId or shippingAddress for checkout',
      );
    }

    return {
      province: inline.province.trim(),
      city: inline.city.trim(),
      address: inline.address.trim(),
      postalCode: inline.postalCode?.trim() || null,
      landline: inline.landline?.trim() || null,
    };
  }

  private assertStockAvailable(stockQuantity: number | null, requested: number) {
    if (stockQuantity !== null && requested > stockQuantity) {
      throw new BadRequestException('Insufficient stock for this quantity');
    }
  }

  private async serializeCart(cart: CartWithItems) {
    const productIds = [
      ...new Set(
        cart.items.map((item) => item.storeItemVariant.storeItem.product.id),
      ),
    ];

    const assignments =
      productIds.length === 0
        ? []
        : await this.prisma.categoryAssignment.findMany({
            where: {
              businessId: cart.businessId,
              entityType: 'product',
              entityId: { in: productIds },
            },
            select: { entityId: true, categoryId: true },
          });

    const categoryIdsByProduct = new Map<string, string[]>();
    for (const row of assignments) {
      const key = row.entityId.toString();
      const list = categoryIdsByProduct.get(key) ?? [];
      list.push(row.categoryId.toString());
      categoryIdsByProduct.set(key, list);
    }

    const items = cart.items.map((item) => {
      const productId = item.storeItemVariant.storeItem.product.id.toString();
      return this.serializeCartItem(
        item,
        categoryIdsByProduct.get(productId) ?? [],
      );
    });
    const subtotal = items.reduce((sum, item) => sum + item.lineTotal, 0);

    return {
      id: cart.id.toString(),
      businessId: cart.businessId.toString(),
      items,
      itemCount: items.reduce((sum, item) => sum + item.quantity, 0),
      subtotal,
      updatedAt: cart.updatedAt,
    };
  }

  private serializeCartItem(
    item: CartWithItems['items'][number],
    categoryIds: string[],
  ) {
    const variant = item.storeItemVariant;
    const product = variant.storeItem.product;
    const content = this.asRecord(product.content);
    const price = Number(variant.price);
    const compareAtPrice =
      variant.compareAtPrice === null ? null : Number(variant.compareAtPrice);
    const effectivePrice =
      compareAtPrice !== null && compareAtPrice < price ? compareAtPrice : price;
    const selections = variant.selections.map((selection) => ({
      variationId: selection.variation.id.toString(),
      variationName: selection.variation.name,
      optionId: selection.option.id.toString(),
      value: selection.option.label,
    }));

    return {
      id: item.id.toString(),
      storeItemId: variant.storeItemId.toString(),
      storeItemVariantId: variant.id.toString(),
      productId: product.id.toString(),
      productTitle: product.title,
      productNameFa: (content.nameFa as string | null | undefined) ?? '',
      productImage: product.featuredMedia?.publicUrl ?? null,
      categoryIds,
      sku: variant.sku,
      selections,
      label: selections.map((entry) => entry.value).join(' · ') || product.title,
      quantity: item.quantity,
      unitPrice: effectivePrice,
      compareAtPrice: price,
      lineTotal: effectivePrice * item.quantity,
      stockQuantity: variant.stockQuantity,
    };
  }

  private asRecord(value: unknown): Record<string, unknown> {
    if (value && typeof value === 'object' && !Array.isArray(value)) {
      return value as Record<string, unknown>;
    }
    return {};
  }

  private async assertCustomerAccess(businessId: bigint, actor: AuthUser) {
    if (await this.permissions.isSuperAdmin(actor.id)) {
      return;
    }

    const membership = await this.prisma.businessCustomer.findUnique({
      where: {
        businessId_userId: { businessId, userId: actor.id },
      },
    });

    if (!membership) {
      throw new ForbiddenException('You are not a customer of this business');
    }
  }
}