/**
 * 钱包服务 - 余额查询、扣费（原子事务）、充值、入账
 */
import { Injectable, Logger } from '@nestjs/common';
import { PrismaService } from '../prisma/prisma.service';
import { InsufficientBalanceException } from './exceptions/insufficient-balance.exception';

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

  constructor(private readonly prisma: PrismaService) {}

  async getWallet(userId: string) {
    const user = await this.prisma.user.findUnique({
      where: { id: userId },
      select: { balanceCents: true, currency: true },
    });
    if (!user) {
      throw new Error('用户不存在');
    }

    const transactions = await this.prisma.balanceTransaction.findMany({
      where: { userId },
      orderBy: { createdAt: 'desc' },
      take: 20,
      select: {
        id: true,
        amountCents: true,
        type: true,
        refId: true,
        createdAt: true,
      },
    });

    return {
      balanceCents: Number(user.balanceCents),
      currency: user.currency,
      transactions: transactions.map((t) => ({
        ...t,
        amountCents: Number(t.amountCents),
        refId: t.refId ?? null,
        createdAt: t.createdAt.toISOString(),
      })),
    };
  }

  /**
   * 原子扣费 - 使用 UPDATE WHERE 保证余额充足
   * 返回值 { count: 0 } 表示余额不足，抛出 InsufficientBalanceException
   * 插入 BalanceTransaction type='usage'
   */
  async deduct(
    userId: string,
    amountCents: bigint,
    refId: string,
    _model?: string,
  ): Promise<{ newBalance: bigint }> {
    const result = await this.prisma.$transaction(async (tx) => {
      // 原子扣减：仅当 balanceCents >= amountCents 时更新
      const updateResult = await tx.user.updateMany({
        where: {
          id: userId,
          balanceCents: { gte: amountCents },
        },
        data: {
          balanceCents: { decrement: amountCents },
        },
      });

      if (updateResult.count === 0) {
        const user = await tx.user.findUnique({
          where: { id: userId },
          select: { balanceCents: true },
        });
        throw new InsufficientBalanceException(
          '余额不足，无法完成扣费',
          amountCents,
          user?.balanceCents ?? 0n,
        );
      }

      // 记录交易
      await tx.balanceTransaction.create({
        data: {
          userId,
          amountCents: -amountCents,
          type: 'usage',
          refId,
        },
      });

      // 读取新余额
      const updated = await tx.user.findUniqueOrThrow({
        where: { id: userId },
        select: { balanceCents: true },
      });

      return { newBalance: updated.balanceCents };
    });

    this.logger.debug(`Deducted user=${userId} amount=${amountCents} ref=${refId}`);
    return result;
  }

  /**
   * 入账（充值/退款）- 直接增加余额并记录交易
   */
  async credit(
    userId: string,
    amountCents: bigint,
    refId: string,
    type: string,
  ): Promise<{ newBalance: bigint }> {
    const result = await this.prisma.$transaction(async (tx) => {
      const updated = await tx.user.update({
        where: { id: userId },
        data: {
          balanceCents: { increment: amountCents },
        },
        select: { balanceCents: true },
      });

      await tx.balanceTransaction.create({
        data: {
          userId,
          amountCents,
          type,
          refId,
        },
      });

      return { newBalance: updated.balanceCents };
    });

    this.logger.debug(`Credited user=${userId} amount=${amountCents} ref=${refId} type=${type}`);
    return result;
  }
}