feat: add student wallet utility billing

apps/server/src/wallets/wallets.service.spec.ts

@@ -0,0 +1,52 @@
+import { BadRequestException } from '@nestjs/common';
+import { WalletsService } from './wallets.service';
+import { Bill } from '../entities/bill.entity';
+
+const manager = (walletBalance: number) => {
+  const wallet = { id: 1, studentId: 10, balance: walletBalance };
+  const saved: any[] = [];
+  return {
+    wallet,
+    saved,
+    value: {
+      findOne: jest.fn(async () => wallet),
+      findOneByOrFail: jest.fn(async () => wallet),
+      save: jest.fn(async (value: any) => { saved.push(value); return value; }),
+      create: jest.fn((_entity: unknown, value: unknown) => value),
+      createQueryBuilder: jest.fn(),
+    },
+  };
+};
+
+describe('WalletsService payment rules', () => {
+  const service = new WalletsService({} as any, {} as any, {} as any, {} as any);
+
+  it('partially pays a bill when balance is insufficient', async () => {
+    const ctx = manager(40);
+    const bill = { id: 9, studentId: 10, totalAmount: 100, paidAmount: 0, outstandingAmount: 100, status: 'unpaid' } as Bill;
+    const result = await service.debitBill(ctx.value as any, bill, 1);
+    expect(result.status).toBe('partially_paid');
+    expect(Number(result.paidAmount)).toBe(40);
+    expect(Number(result.outstandingAmount)).toBe(60);
+    expect(Number(ctx.wallet.balance)).toBe(0);
+    expect(ctx.saved.some((row) => row.type === 'bill_payment' && Number(row.amount) === -40)).toBe(true);
+  });
+
+  it('marks a bill paid when balance covers it', async () => {
+    const ctx = manager(120);
+    const bill = { id: 9, studentId: 10, totalAmount: 100, paidAmount: 0, outstandingAmount: 100, status: 'unpaid' } as Bill;
+    const result = await service.debitBill(ctx.value as any, bill);
+    expect(result.status).toBe('paid');
+    expect(Number(result.outstandingAmount)).toBe(0);
+    expect(Number(ctx.wallet.balance)).toBe(20);
+  });
+
+  it('refunds paid amount and cancels the bill', async () => {
+    const ctx = manager(10);
+    const bill = { id: 9, studentId: 10, totalAmount: 100, paidAmount: 40, outstandingAmount: 60, status: 'partially_paid' } as Bill;
+    const result = await service.refundBill(ctx.value as any, bill, '录入错误', 1);
+    expect(result.status).toBe('cancelled');
+    expect(Number(ctx.wallet.balance)).toBe(50);
+    expect(ctx.saved.some((row) => row.type === 'bill_refund' && Number(row.amount) === 40)).toBe(true);
+  });
+});