const { computeDonationRemaining } = require('../src/utils/donationUtils');

describe('computeDonationRemaining', () => {
  test('a donation with no legs has its full amount remaining', () => {
    expect(computeDonationRemaining(500, [])).toBe(500);
  });

  test('an allocation leg reduces the remaining balance', () => {
    const legs = [{ amount: 200 }];
    expect(computeDonationRemaining(500, legs)).toBe(300);
  });

  test('multiple allocation legs reduce the remaining balance cumulatively', () => {
    const legs = [{ amount: 200 }, { amount: 150 }];
    expect(computeDonationRemaining(500, legs)).toBe(150);
  });

  test('the 1.4.2 regression: refunding the donation itself (a negative-amount leg) reduces remaining balance, not inflates it', () => {
    // 500 donation, never allocated, R200 of it refunded directly back to the donor
    // (a leg with amount: -200). That R200 is no longer available to allocate — remaining
    // must drop to 300. The pre-1.4.2 bug summed legs without Math.abs(), so
    // remaining = 500 - (-200) = 700 (inflated) instead of 500 - 200 = 300 (correct).
    const legs = [{ amount: -200 }];
    expect(computeDonationRemaining(500, legs)).toBe(300);
  });

  test('an allocation and a separate direct refund both reduce the remaining balance', () => {
    // 500 donation: R200 allocated to a registration, R100 separately refunded to the donor.
    // Remaining = 500 - 200 - 100 = 200.
    const legs = [{ amount: 200 }, { amount: -100 }];
    expect(computeDonationRemaining(500, legs)).toBe(200);
  });

  test('unassigning an allocation removes its leg entirely rather than adding an offsetting one', () => {
    // unassignDonationFromRegistration deletes the leg row outright (confirmed in
    // paymentController.js), so the "leg no longer exists" case — not a negative-amount
    // leg — is how an unassigned allocation becomes available again.
    const legsAfterUnassign = [];
    expect(computeDonationRemaining(500, legsAfterUnassign)).toBe(500);
  });

  test('handles a null/undefined legs array', () => {
    expect(computeDonationRemaining(500, null)).toBe(500);
    expect(computeDonationRemaining(500, undefined)).toBe(500);
  });
});