P2-14: Deposit installment tracking + refund approval flow

- Add DepositInstallment entity (id, depositId, amount, dueDate, paidDate, status, createdAt)
- Add installments OneToMany relation to Deposit entity with cascade+eager
- Add refund approval fields: refundStatus, refundRequestedAt, refundApprovedBy, refundApprovedAt
- Add installment DTOs (CreateInstallmentDto, UpdateInstallmentDto)
- Add refund approval DTOs (ApproveRefundDto, CreateDepositWithInstallmentsDto)
- Service: add/create/update/delete installments, requestRefund, approveRefund, findPendingRefunds
- Controller: GET deposits/:id, GET pending-refunds, POST :id/installments, PUT installments/:id, DELETE installments/:id, POST :id/request-refund, PUT :id/approve-refund
- Frontend: detail modal with installment list, refund request button, pending refunds tab with approve actions

apps/server/src/deposits/deposits.service.ts

@@ -2,33 +2,84 @@ import { Injectable, NotFoundException, BadRequestException } from '@nestjs/comm
 import { InjectRepository } from '@nestjs/typeorm';
 import { Repository } from 'typeorm';
 import { Deposit } from '../entities/deposit.entity';
-import { CreateDepositDto, RefundDepositDto } from './dto/deposit.dto';
+import { DepositInstallment } from '../entities/deposit-installment.entity';
+import { CreateDepositDto, RefundDepositDto, CreateDepositWithInstallmentsDto } from './dto/deposit.dto';
 
 @Injectable()
 export class DepositsService {
-  constructor(@InjectRepository(Deposit) private repo: Repository<Deposit>) {}
+  constructor(
+    @InjectRepository(Deposit) private repo: Repository<Deposit>,
+    @InjectRepository(DepositInstallment)
+    private installmentRepo: Repository<DepositInstallment>,
+  ) {}
 
   async findAll(query?: { studentId?: number; status?: string }) {
     const qb = this.repo
       .createQueryBuilder('d')
       .leftJoinAndSelect('d.student', 'student')
+      .leftJoinAndSelect('d.installments', 'installments')
       .orderBy('d.createdAt', 'DESC');
     if (query?.studentId) qb.andWhere('d.studentId = :studentId', { studentId: query.studentId });
     if (query?.status) qb.andWhere('d.status = :status', { status: query.status });
     return qb.getMany();
   }
 
+  async findOne(id: number) {
+    const deposit = await this.repo.findOne({ where: { id }, relations: ['student', 'installments'] });
+    if (!deposit) throw new NotFoundException('押金记录不存在');
+    return deposit;
+  }
+
   async create(dto: CreateDepositDto, userId?: number) {
-    return this.repo.save(
-      this.repo.create({
-        studentId: dto.studentId,
-        amount: dto.amount,
-        paidDate: dto.paidDate,
-        notes: dto.notes,
-        status: 'paid',
-        recordedBy: userId,
-      }),
-    );
+    const deposit = this.repo.create({
+      studentId: dto.studentId,
+      amount: dto.amount,
+      paidDate: dto.paidDate,
+      notes: dto.notes,
+      status: 'paid',
+      recordedBy: userId,
+    });
+
+    if (dto instanceof CreateDepositWithInstallmentsDto && dto.installments?.length) {
+      deposit.installments = dto.installments.map((i) =>
+        this.installmentRepo.create({
+          amount: i.amount,
+          dueDate: i.dueDate,
+          status: 'pending',
+        }),
+      );
+    }
+
+    return this.repo.save(deposit);
+  }
+
+  async addInstallment(depositId: number, amount: number, dueDate: string) {
+    const deposit = await this.repo.findOne({ where: { id: depositId } });
+    if (!deposit) throw new NotFoundException('押金记录不存在');
+
+    const installment = this.installmentRepo.create({
+      depositId,
+      amount,
+      dueDate,
+      status: 'pending',
+    });
+    return this.installmentRepo.save(installment);
+  }
+
+  async updateInstallment(id: number, data: { paidDate?: string; status?: string }) {
+    const installment = await this.installmentRepo.findOne({ where: { id } });
+    if (!installment) throw new NotFoundException('分期记录不存在');
+
+    if (data.paidDate !== undefined) installment.paidDate = data.paidDate;
+    if (data.status !== undefined) installment.status = data.status;
+    return this.installmentRepo.save(installment);
+  }
+
+  async deleteInstallment(id: number) {
+    const installment = await this.installmentRepo.findOne({ where: { id } });
+    if (!installment) throw new NotFoundException('分期记录不存在');
+    await this.installmentRepo.delete(id);
+    return { message: '删除成功' };
   }
 
   async refund(id: number, dto: RefundDepositDto, userId?: number) {
@@ -48,9 +99,69 @@ export class DepositsService {
       deduction > 0 ? (refundAmount > 0 ? 'partial_refund' : 'deducted') : 'refunded';
     if (dto.notes) deposit.notes = dto.notes;
 
+    // Clear refund approval flow if direct refund
+    deposit.refundStatus = null;
+    deposit.refundRequestedAt = null;
+    deposit.refundApprovedBy = null;
+    deposit.refundApprovedAt = null;
+
     return this.repo.save(deposit);
   }
 
+  // ---- Refund approval flow ----
+
+  async requestRefund(id: number) {
+    const deposit = await this.repo.findOne({ where: { id } });
+    if (!deposit) throw new NotFoundException('押金记录不存在');
+    if (deposit.status !== 'paid') throw new BadRequestException('该押金已处理');
+    if (deposit.refundStatus) throw new BadRequestException('已提交退款申请，请等待审批');
+
+    deposit.refundStatus = 'pending';
+    deposit.refundRequestedAt = new Date();
+    return this.repo.save(deposit);
+  }
+
+  async approveRefund(id: number, userId: number) {
+    const deposit = await this.repo.findOne({ where: { id } });
+    if (!deposit) throw new NotFoundException('押金记录不存在');
+
+    if (!deposit.refundStatus || deposit.refundStatus === 'refunded') {
+      throw new BadRequestException('未找到待审批的退款申请');
+    }
+
+    const transitions: Record<string, string> = {
+      pending: 'head_teacher_approved',
+      head_teacher_approved: 'finance_approved',
+      finance_approved: 'refunded',
+    };
+
+    const nextStatus = transitions[deposit.refundStatus];
+    if (!nextStatus) throw new BadRequestException(`无效的退款状态: ${deposit.refundStatus}`);
+
+    deposit.refundStatus = nextStatus;
+    deposit.refundApprovedBy = userId;
+    deposit.refundApprovedAt = new Date();
+
+    if (nextStatus === 'refunded') {
+      deposit.status = 'refunded';
+      deposit.refundDate = new Date().toISOString().slice(0, 10);
+      deposit.refundAmount = Number(deposit.amount) - Number(deposit.deductionAmount || 0);
+    }
+
+    return this.repo.save(deposit);
+  }
+
+  async findPendingRefunds() {
+    return this.repo.find({
+      where: [
+        { refundStatus: 'pending' },
+        { refundStatus: 'head_teacher_approved' },
+      ],
+      relations: ['student', 'installments'],
+      order: { refundRequestedAt: 'DESC' },
+    });
+  }
+
   async remove(id: number) {
     const deposit = await this.repo.findOne({ where: { id } });
     if (!deposit) throw new NotFoundException('押金记录不存在');