backend/src/modules/banking/bank-cards/domain/bank-card.calculations.spec.ts

import {
  bankBalance,
  bankSummary,
  isCalendarDate,
  moscowToday,
} from './bank-card.calculations';

describe('bank card calculations', () => {
  it('uses Moscow midnight for today and the current month', () => {
    expect(moscowToday(new Date('2026-08-31T20:59:59.999Z'))).toBe(
      '2026-08-31',
    );
    expect(moscowToday(new Date('2026-08-31T21:00:00.000Z'))).toBe(
      '2026-09-01',
    );
  });

  it.each([
    '0001-01-01',
    '9999-12-31',
    '2024-02-29',
    '2000-02-29',
    '2026-09-12',
  ])('accepts calendar date %s', (value) => {
    expect(isCalendarDate(value)).toBe(true);
  });

  it.each([
    '0000-01-01',
    '10000-01-01',
    '2026-02-29',
    '1900-02-29',
    '2026-04-31',
    '2026-00-01',
    '2026-13-01',
    '2026-01-00',
    '2026-01-32',
    '2026-1-01',
    '2026-09-12\n',
    '2026-09-12T00:00:00Z',
    '',
  ])('rejects invalid calendar date %s', (value) => {
    expect(isCalendarDate(value)).toBe(false);
  });

  it('folds expenses, topups, refunds and both transfer sides exactly', () => {
    const operations = [
      { kind: 'expense', cardId: 'a', targetCardId: null, amountKopecks: 10n },
      { kind: 'expense', cardId: 'a', targetCardId: null, amountKopecks: 20n },
      { kind: 'topup', cardId: 'a', targetCardId: null, amountKopecks: 15n },
      { kind: 'refund', cardId: 'a', targetCardId: null, amountKopecks: 5n },
      { kind: 'transfer', cardId: 'a', targetCardId: 'b', amountKopecks: 120n },
      { kind: 'expense', cardId: 'c', targetCardId: null, amountKopecks: 300n },
    ];
    expect(bankBalance('a', 100n, operations.slice(0, 2))).toBe(70n);
    expect(bankBalance('a', 100n, operations)).toBe(-30n);
    expect(bankBalance('b', 0n, operations)).toBe(120n);
    expect(bankBalance('unused', -1n, operations)).toBe(-1n);
  });

  it('does not bound computed balances by the storage range', () => {
    expect(
      bankBalance('a', 2n ** 63n - 1n, [
        { kind: 'topup', cardId: 'a', targetCardId: null, amountKopecks: 1n },
      ]),
    ).toBe(2n ** 63n);
    expect(
      bankBalance('a', -(2n ** 63n), [
        { kind: 'expense', cardId: 'a', targetCardId: null, amountKopecks: 1n },
      ]),
    ).toBe(-(2n ** 63n) - 1n);
  });

  it('counts refunds in their own month and inherited category, excluding transfers and topups', () => {
    const operations = [
      {
        kind: 'expense',
        date: '2026-08-31',
        categoryId: 'food',
        amountKopecks: 1000n,
      },
      {
        kind: 'refund',
        date: '2026-09-01',
        categoryId: 'food',
        amountKopecks: 500n,
      },
      {
        kind: 'expense',
        date: '2026-09-30',
        categoryId: 'food',
        amountKopecks: 100n,
      },
      {
        kind: 'expense',
        date: '2026-09-03',
        categoryId: 'travel',
        amountKopecks: 20n,
      },
      {
        kind: 'transfer',
        date: '2026-09-03',
        categoryId: null,
        amountKopecks: 2000n,
      },
      {
        kind: 'topup',
        date: '2026-09-03',
        categoryId: null,
        amountKopecks: 3000n,
      },
      {
        kind: 'expense',
        date: '2026-10-01',
        categoryId: 'travel',
        amountKopecks: 5000n,
      },
    ];
    expect(
      bankSummary({ from: '2026-09-01', to: '2026-09-30' }, operations),
    ).toEqual({
      expenses: 120n,
      refunds: 500n,
      net: -380n,
      categories: [
        { categoryId: 'food', expenses: 100n, refunds: 500n, net: -400n },
        { categoryId: 'travel', expenses: 20n, refunds: 0n, net: 20n },
      ],
    });
    expect(
      bankSummary({ from: '2026-07-01', to: '2026-07-31' }, operations),
    ).toEqual({
      expenses: 0n,
      refunds: 0n,
      net: 0n,
      categories: [],
    });
  });

  it('keeps summary sums beyond signed 64-bit exact', () => {
    const operation = {
      kind: 'expense',
      date: '2026-09-01',
      categoryId: 'food',
      amountKopecks: 2n ** 63n - 1n,
    };
    const total = 2n * (2n ** 63n - 1n);
    expect(
      bankSummary({ from: '2026-09-01', to: '2026-09-30' }, [
        operation,
        operation,
      ]),
    ).toEqual({
      expenses: total,
      refunds: 0n,
      net: total,
      categories: [
        { categoryId: 'food', expenses: total, refunds: 0n, net: total },
      ],
    });
  });
});