import { Injectable, Logger, NotFoundException } from '@nestjs/common';
import { OrderChannel, OrderStatus, Prisma } from '@prisma/client';
import { PrismaService } from '../../prisma/prisma.service';
import { CatalogService } from '../catalog/catalog.service';
import { LedgerService } from '../accounting/ledger.service';
import { CreateOrderDto } from './dto/create-order.dto';

interface ComputedItem {
  productVariantId: string;
  quantity: number;
  rashWeightGramsSnapshot: Prisma.Decimal;
  wagePercentSnapshot: Prisma.Decimal;
  discountPercentSnapshot: Prisma.Decimal;
  computedWeightGrams: Prisma.Decimal;
  flatRialCharge: Prisma.Decimal;
}

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

  constructor(
    private readonly prisma: PrismaService,
    private readonly catalog: CatalogService,
    private readonly ledger: LedgerService,
  ) {}

  /**
   * Places a stock order. Per line item:
   *   w = rashWeightGrams * (1 + (wagePercent - discountPercent) / 100)
   * mirrors legacy ApiMobileController::setOrder. Debt is NOT posted here —
   * only once the order reaches DELIVERED_TO_AGENT (see updateStatus).
   */
  /**
   * @param customerId taken from the caller's token by the controller, NEVER
   *   from the request body. The body's `customerId` is ignored; see the note
   *   on CreateOrderDto.
   */
  async createOrder(dto: CreateOrderDto, customerId: string) {
    const customer = await this.prisma.customer.findUnique({ where: { id: customerId } });
    if (!customer) throw new NotFoundException(`Customer ${customerId} not found`);

    // The apps still send customerId in the body (removed from them in Phase 2).
    // It is not used for anything; a mismatch means either a stale client or an
    // attempt to order on someone else's account, and both are worth seeing.
    if (dto.customerId && dto.customerId !== customerId) {
      this.logger.warn(
        `Order body carried customerId=${dto.customerId} but the token is ${customerId}; ` +
          `the token wins.`,
      );
    }

    const computedItems: ComputedItem[] = await Promise.all(
      dto.items.map(async (item) => {
        const variant = await this.catalog.getVariantOrThrow(item.productVariantId);
        const rashWeight = new Prisma.Decimal(variant.rashWeightGrams);
        const wagePercent = new Prisma.Decimal(item.wagePercent);
        const discountPercent = new Prisma.Decimal(item.discountPercent ?? 0);
        const netPercent = wagePercent.sub(discountPercent);
        const computedWeightGrams = rashWeight.mul(netPercent.div(100).add(1));

        return {
          productVariantId: variant.id,
          quantity: item.quantity,
          rashWeightGramsSnapshot: rashWeight,
          wagePercentSnapshot: wagePercent,
          discountPercentSnapshot: discountPercent,
          computedWeightGrams,
          flatRialCharge: new Prisma.Decimal(item.flatRialCharge ?? 0),
        };
      }),
    );

    const totalGoldWeightGrams = computedItems.reduce(
      (sum, item) => sum.add(item.computedWeightGrams.mul(item.quantity)),
      new Prisma.Decimal(0),
    );
    const totalRashWeightGrams = computedItems.reduce(
      (sum, item) => sum.add(item.rashWeightGramsSnapshot.mul(item.quantity)),
      new Prisma.Decimal(0),
    );
    const wageWeightGrams = totalGoldWeightGrams.sub(totalRashWeightGrams);
    const flatRialCharge = computedItems.reduce(
      (sum, item) => sum.add(item.flatRialCharge.mul(item.quantity)),
      new Prisma.Decimal(0),
    );

    // legacy: inValidOrder = (allGram + customer.remain) > customer.gram_level
    const isSuspendedOverCreditLimit = totalGoldWeightGrams
      .add(customer.goldDebtGrams)
      .gt(customer.goldCreditLimitGrams);
    const initialStatus = isSuspendedOverCreditLimit ? OrderStatus.SUSPENDED : OrderStatus.PLACED;

    return this.prisma.$transaction(async (tx) => {
      const order = await tx.order.create({
        data: {
          orderNumber: this.generateOrderNumber(),
          customerId,
          branchId: dto.branchId,
          channel: dto.channel ?? OrderChannel.RETAIL,
          status: initialStatus,
          totalGoldWeightGrams,
          wageWeightGrams,
          flatRialCharge,
          isSuspendedOverCreditLimit,
          items: {
            create: computedItems.map((item) => ({
              productVariantId: item.productVariantId,
              quantity: item.quantity,
              rashWeightGramsSnapshot: item.rashWeightGramsSnapshot,
              wagePercentSnapshot: item.wagePercentSnapshot,
              discountPercentSnapshot: item.discountPercentSnapshot,
              computedWeightGrams: item.computedWeightGrams,
              flatRialCharge: item.flatRialCharge,
            })),
          },
          statusEvents: {
            create: { toStatus: initialStatus, note: isSuspendedOverCreditLimit ? 'Credit limit exceeded' : undefined },
          },
        },
        include: { items: true, statusEvents: true },
      });

      return order;
    });
  }

  async updateStatus(orderId: string, newStatus: OrderStatus, actorAdminUserId?: string, note?: string) {
    return this.prisma.$transaction(async (tx) => {
      const order = await tx.order.findUnique({ where: { id: orderId } });
      if (!order) throw new NotFoundException(`Order ${orderId} not found`);

      const updated = await tx.order.update({
        where: { id: orderId },
        data: {
          status: newStatus,
          deliveredAt: newStatus === OrderStatus.DELIVERED_TO_CUSTOMER ? new Date() : order.deliveredAt,
        },
      });

      await tx.orderStatusEvent.create({
        data: { orderId, fromStatus: order.status, toStatus: newStatus, note, actorAdminUserId },
      });

      // Debt recognition point — mirrors legacy sts>4, which first becomes true
      // at sts=5 ("تحویل مسئول فروش" / delivered to agent), not sts=6 (delivered
      // to customer). Only fires once: a second transition into this status
      // (e.g. a data-fix re-save) would double-post debt, so guard on the order
      // not already having deliveredAt.
      if (newStatus === OrderStatus.DELIVERED_TO_AGENT && !order.deliveredAt) {
        await this.ledger.postOrderDebt(orderId, tx);
      }

      return updated;
    });
  }

  /** Unscoped read. Only reachable from the admin-guarded route. */
  getById(orderId: string) {
    return this.prisma.order.findUnique({
      where: { id: orderId },
      include: { items: true, statusEvents: true, ledgerEntries: true },
    });
  }

  /**
   * A customer reading one of their own orders.
   *
   * Someone else's order is reported as 404, not 403: a 403 would confirm the
   * id exists, which is the same enumeration leak the id-addressed customer
   * routes had.
   */
  async getOwnedById(orderId: string, customerId: string) {
    const order = await this.prisma.order.findFirst({
      where: { id: orderId, customerId },
      include: { items: true, statusEvents: true, ledgerEntries: true },
    });
    if (!order) throw new NotFoundException('سفارش یافت نشد');
    return order;
  }

  private generateOrderNumber(): string {
    const random = Math.random().toString(36).slice(2, 8).toUpperCase();
    return `ORD-${Date.now()}-${random}`;
  }
}