const test = require('node:test');
const assert = require('node:assert/strict');
const {
  buildDefaultAccount,
  alignAccountToCurrentCycle,
  getAvailableCredits,
  consumeCredits,
  ensureSufficientCredits,
  getMonthlyAllowanceForPlan,
} = require('../lib/billing');

const NOW = new Date('2026-07-06T12:00:00Z');

const freeAccount = (overrides = {}) => ({
  ...buildDefaultAccount('user-1', NOW),
  ...overrides,
});

test('free plan gets 3 monthly credits', () => {
  assert.equal(getMonthlyAllowanceForPlan('free'), 3);
  assert.equal(buildDefaultAccount('u', NOW).monthlyAllowance, 3);
});

test('free account has available credits', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 1 });
  assert.equal(getAvailableCredits(account), 2);
});

test('free account topup balance counts as available', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 3, topupBalance: 10 });
  assert.equal(getAvailableCredits(account), 10);
});

test('consumeCredits charges a free account from the monthly allowance', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 0 });
  const charged = consumeCredits(account, 1);
  assert.equal(charged, 1);
  assert.equal(account.usedThisCycle, 1);
});

test('consumeCredits throws 402 for an exhausted free account', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 3, topupBalance: 0 });
  assert.throws(() => consumeCredits(account, 1), (error) => {
    assert.equal(error.code, 'INSUFFICIENT_CREDITS');
    assert.equal(error.status, 402);
    assert.deepEqual(error.metadata, { required: 1, available: 0 });
    return true;
  });
});

test('legacy free account with allowance 0 is migrated to 3', () => {
  const account = freeAccount({ monthlyAllowance: 0 });
  const aligned = alignAccountToCurrentCycle(account, NOW);
  assert.equal(aligned.monthlyAllowance, 3);
});

test('pro and trial allowances are unchanged', () => {
  assert.equal(getMonthlyAllowanceForPlan('pro'), 100);
  const trial = freeAccount({ plan: 'pro', monthlyAllowance: 30, usedThisCycle: 5 });
  const aligned = alignAccountToCurrentCycle(trial, NOW);
  assert.equal(aligned.monthlyAllowance, 30); // trial allowance stays allowed
  assert.equal(getAvailableCredits(aligned), 25);
});

test('monthly cycle rollover resets free usage', () => {
  const account = freeAccount({
    monthlyAllowance: 3,
    usedThisCycle: 3,
    cycleEndsAt: '2026-07-01T00:00:00.000Z',
  });
  const aligned = alignAccountToCurrentCycle(account, NOW);
  assert.equal(aligned.usedThisCycle, 0);
  assert.equal(aligned.monthlyAllowance, 3);
  assert.equal(getAvailableCredits(aligned), 3);
});

test('ensureSufficientCredits throws 402 when balance is below cost', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 2, topupBalance: 0 });
  assert.throws(() => ensureSufficientCredits(account, 2), (error) => {
    assert.equal(error.code, 'INSUFFICIENT_CREDITS');
    assert.equal(error.status, 402);
    assert.deepEqual(error.metadata, { required: 2, available: 1 });
    return true;
  });
});

test('ensureSufficientCredits passes when balance covers cost', () => {
  const account = freeAccount({ monthlyAllowance: 3, usedThisCycle: 1, topupBalance: 0 });
  assert.doesNotThrow(() => ensureSufficientCredits(account, 2));
});