import { Injectable } from '@nestjs/common';
import type { Prisma } from '@prisma/client';
import { calcBenefitAmount, calcBenefitSummary, generateCouponNo } from '@dukang/domain';
import { PrismaService } from '../../common/prisma/prisma.module';
import { serializeBigInt } from '../../common/decorators/current-user.decorator';
import { buildBenefitLedgerEvent, benefitLedgerWhere } from '../../common/event/event.helpers';

export type CouponAllocation = { couponId: string; amount: number };

@Injectable()
export class BenefitService {
  constructor(private readonly prisma: PrismaService) {}

  async grantOnOrderPaid(orderId: bigint) {
    const order = await this.prisma.order.findUniqueOrThrow({
      where: { id: orderId },
    });

    const product = await this.prisma.commonProductItem.findUnique({ where: { id: order.productId } });
    const unitBenefit = calcBenefitAmount({
      price: Number(order.listUnitPrice),
      benefitAmount: product?.benefitAmount ? Number(product.benefitAmount) : null,
    });
    const totalBenefit = unitBenefit * order.quantity;

    const coupon = await this.prisma.benefitCoupon.create({
      data: {
        couponNo: generateCouponNo(),
        userId: order.userId,
        orderId: order.id,
        totalAmount: totalBenefit,
        balance: totalBenefit,
        sourceProduct: order.productName,
      },
    });

    await this.prisma.commonEvent.create({
      data: buildBenefitLedgerEvent({
        userId: order.userId,
        couponId: coupon.id,
        type: 'GRANT',
        amount: totalBenefit,
        balanceAfter: totalBenefit,
        refType: 'ORDER',
        refId: order.id,
        remark: '购酒赠券',
      }),
    });

    return serializeBigInt(coupon);
  }

  async listCoupons(userId: bigint) {
    const list = await this.prisma.benefitCoupon.findMany({
      where: { userId, status: { in: ['ACTIVE', 'USED_UP'] } },
      orderBy: { createdAt: 'desc' },
    });
    return serializeBigInt(list);
  }

  async getSummary(userId: bigint) {
    const coupons = await this.prisma.benefitCoupon.findMany({
      where: { userId, status: 'ACTIVE' },
      orderBy: { createdAt: 'asc' },
    });
    const summary = calcBenefitSummary(
      coupons.map((c) => Number(c.balance)),
    );
    return serializeBigInt(summary);
  }

  async getLedger(userId: bigint, couponId?: bigint) {
    const list = await this.prisma.commonEvent.findMany({
      where: benefitLedgerWhere(userId, couponId),
      orderBy: { createdAt: 'desc' },
    });
    return serializeBigInt(list);
  }

  async getCoupon(userId: bigint, couponId: bigint) {
    const coupon = await this.prisma.benefitCoupon.findFirst({
      where: { id: couponId, userId },
    });
    if (!coupon) return null;
    const ledgers = await this.prisma.commonEvent.findMany({
      where: benefitLedgerWhere(undefined, couponId),
      orderBy: { createdAt: 'desc' },
    });
    return serializeBigInt({ coupon, ledgers });
  }

  /** 核销扣减券余额（乐观锁），由 redeem 模块调用 */
  async deductCoupons(
    tx: Prisma.TransactionClient,
    allocations: CouponAllocation[],
    refType: 'STORE',
    refId: bigint,
  ) {
    for (const alloc of allocations) {
      const coupon = await tx.benefitCoupon.findUniqueOrThrow({
        where: { id: BigInt(alloc.couponId) },
      });
      const allocAmount = alloc.amount;
      const updated = await tx.benefitCoupon.updateMany({
        where: { id: coupon.id, version: coupon.version, balance: { gte: allocAmount } },
        data: {
          usedAmount: { increment: allocAmount },
          balance: { decrement: allocAmount },
          version: { increment: 1 },
          status: Number(coupon.balance) - allocAmount <= 0 ? 'USED_UP' : 'ACTIVE',
        },
      });
      if (updated.count === 0) throw new Error('BENEFIT_DEDUCT_CONFLICT');

      const newBalance = Number(coupon.balance) - allocAmount;
      await tx.commonEvent.create({
        data: buildBenefitLedgerEvent({
          userId: coupon.userId,
          couponId: coupon.id,
          type: 'REDEEM',
          amount: -allocAmount,
          balanceAfter: newBalance,
          refType,
          refId,
        }),
      });
    }
  }

  /** 退款作废权益 */
  async voidCouponsOnRefund(orderId: bigint) {
    const coupons = await this.prisma.benefitCoupon.findMany({
      where: { orderId, status: { in: ['ACTIVE', 'USED_UP'] } },
    });
    for (const coupon of coupons) {
      const balance = Number(coupon.balance);
      if (balance <= 0 && coupon.status === 'USED_UP') continue;
      await this.prisma.$transaction(async (tx) => {
        await tx.benefitCoupon.update({
          where: { id: coupon.id },
          data: { status: 'VOID', balance: 0 },
        });
        if (balance > 0) {
          await tx.commonEvent.create({
            data: buildBenefitLedgerEvent({
              userId: coupon.userId,
              couponId: coupon.id,
              type: 'REFUND_VOID',
              amount: -balance,
              balanceAfter: 0,
              refType: 'ORDER',
              refId: orderId,
              remark: '退款作废权益',
            }),
          });
        }
      });
    }
  }
}