edr-platform/apps/edr-passenger-api/src/modules/upgrade/upgrade.service.spec.ts

import { computeUpgradeAmounts } from './upgrade.service';

// Pure arithmetic only, mirroring reschedule.service.spec.ts — no Nest test module, no mocks.
describe('computeUpgradeAmounts', () => {
  const free = { feePercent: 0, feeMinMinor: 0, feeWaived: false };
  const waived = { feePercent: 30, feeMinMinor: 50000, feeWaived: true };
  const percentOnly = { feePercent: 10, feeMinMinor: 0, feeWaived: false };
  const flooredFee = { feePercent: 10, feeMinMinor: 50000, feeWaived: false };

  it('charges only the fare difference when the class has no fee', () => {
    // RS 1752.34 → EBC 2336.46, as seeded on dev
    expect(computeUpgradeAmounts(free, 175234, 233646)).toEqual({
      feeMinor: 0,
      fareDifferenceMinor: 58412,
      amountDueMinor: 58412,
    });
  });

  it('ignores a configured fee when the policy waives it (US-17 §5)', () => {
    expect(computeUpgradeAmounts(waived, 175234, 233646)).toEqual({
      feeMinor: 0,
      fareDifferenceMinor: 58412,
      amountDueMinor: 58412,
    });
  });

  it('takes the fee as a percentage of the ORIGINAL fare, not of the difference', () => {
    const r = computeUpgradeAmounts(percentOnly, 175234, 233646);
    expect(r.feeMinor).toBe(17523); // 10% of 175234, not of 58412
    expect(r.amountDueMinor).toBe(17523 + 58412);
  });

  it('applies the fee floor when the percentage falls below it', () => {
    const r = computeUpgradeAmounts(flooredFee, 100000, 150000);
    expect(r.feeMinor).toBe(50000); // max(10% of 100000 = 10000, floor 50000)
    expect(r.amountDueMinor).toBe(100000);
  });

  it('never lets a negative difference reduce the amount due', () => {
    // Refused upstream, but the arithmetic must not produce a credit if it ever gets here.
    const r = computeUpgradeAmounts(percentOnly, 200000, 150000);
    expect(r.fareDifferenceMinor).toBe(-50000);
    expect(r.amountDueMinor).toBe(r.feeMinor);
    expect(r.amountDueMinor).toBeGreaterThanOrEqual(0);
  });

  it('charges the full target fare for a free child', () => {
    const r = computeUpgradeAmounts(free, 0, 233646);
    expect(r.feeMinor).toBe(0); // a percentage of zero is zero
    expect(r.amountDueMinor).toBe(233646);
  });
});