trip-plan/tests/costs.test.js

import { test, beforeEach, afterEach } from 'node:test';
import assert from 'node:assert/strict';
import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
import request from 'supertest';
import { createApp } from '../src/server/app.js';
import { computeCosts } from '../src/server/util/costs.js';

let tmpDir;
let app;

beforeEach(() => {
  tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'tripplan-costs-'));
  app = createApp({ dbPath: path.join(tmpDir, 'test.db'), sessionSecret: 'test-secret' });
});

afterEach(() => {
  try {
    if (app.locals.db) app.locals.db.close();
  } catch {
    /* ignore */
  }
  fs.rmSync(tmpDir, { recursive: true, force: true });
});

async function createAccount() {
  const agent = request.agent(app);
  const res = await agent.post('/api/auth/account').send({});
  assert.equal(res.status, 201);
  return { agent, user: res.body.user, token: res.body.token };
}

// Build a trip owned by `owner`; each member agent joins via the join code.
async function costTrip(owner, memberAccounts = []) {
  const trip = (await owner.agent.post('/api/trips').send({
    name: 'Costs', start_date: '2026-08-01', end_date: '2026-08-05', currency: 'USD',
  })).body.trip;
  for (const m of memberAccounts) {
    const res = await m.agent.post('/api/trips/join').send({ code: trip.join_code });
    assert.equal(res.status, 200);
  }
  return trip;
}

function findUser(costs, userId) {
  return costs.perUser.find((u) => u.userId === userId);
}

// ---------------------------------------------------------------------------
// Currency
// ---------------------------------------------------------------------------

test('currency: defaults to USD, validates format, patchable', async () => {
  const { agent } = await createAccount();

  const def = await agent.post('/api/trips').send({ name: 'T', start_date: '2026-08-01', end_date: '2026-08-05' });
  assert.equal(def.status, 201);
  assert.equal(def.body.trip.currency, 'USD');

  const bad = await agent.post('/api/trips').send({ name: 'T', start_date: '2026-08-01', end_date: '2026-08-05', currency: 'us' });
  assert.equal(bad.status, 400);

  const eur = await agent.post('/api/trips').send({ name: 'T', start_date: '2026-08-01', end_date: '2026-08-05', currency: 'EUR' });
  assert.equal(eur.status, 201);
  assert.equal(eur.body.trip.currency, 'EUR');

  const patched = await agent.patch(`/api/trips/${eur.body.trip.id}`).send({ currency: 'THB' });
  assert.equal(patched.status, 200);
  assert.equal(patched.body.trip.currency, 'THB');

  const listed = await agent.get('/api/trips');
  assert.ok(listed.body.trips.every((t) => typeof t.currency === 'string'));
});

// ---------------------------------------------------------------------------
// Costs & splitting (endpoint)
// ---------------------------------------------------------------------------

test('costs: equal split with payer produces net balances and a settlement', async () => {
  const anna = await createAccount();
  const ben = await createAccount();
  const trip = await costTrip(anna, [ben]);

  // anna pays 950 (stay), ben pays 500 (transport); both split equally between the two.
  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'stay', title: 'Hotel', price: 950, paid_by: anna.user.id,
  });
  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-02', type: 'transport', title: 'Van', price: 500, paid_by: ben.user.id,
  });

  const res = await anna.agent.get(`/api/trips/${trip.id}/costs`);
  assert.equal(res.status, 200);
  const c = res.body;
  assert.equal(c.currency, 'USD');
  assert.equal(c.totalCost, 1450);
  assert.deepEqual(c.byType, { stay: 950, transport: 500 });
  assert.equal(c.unassigned, 0);

  const a = findUser(c, anna.user.id);
  const b = findUser(c, ben.user.id);
  assert.equal(typeof a.displayName, 'string');
  assert.deepEqual([a.share, a.paid, a.net], [725, 950, 225]);
  assert.deepEqual([b.share, b.paid, b.net], [725, 500, -225]);

  assert.equal(c.settlements.length, 1);
  assert.deepEqual(c.settlements[0], { fromUserId: ben.user.id, toUserId: anna.user.id, amount: 225 });
});

test('costs: own mode creates no debt and totals price x participants', async () => {
  const anna = await createAccount();
  const ben = await createAccount();
  const trip = await costTrip(anna, [ben]);

  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'flight', title: 'Flights', price: 300, split_mode: 'own',
  });

  const c = (await anna.agent.get(`/api/trips/${trip.id}/costs`)).body;
  assert.equal(c.totalCost, 600); // 300 per person x 2
  assert.deepEqual(c.byType, { flight: 600 });
  for (const u of c.perUser) {
    assert.deepEqual([u.share, u.paid, u.net], [300, 300, 0]);
  }
  assert.deepEqual(c.settlements, []);
  assert.equal(c.unassigned, 0);
});

test('costs: payer mode is a personal expense (requires paid_by)', async () => {
  const anna = await createAccount();
  const ben = await createAccount();
  const trip = await costTrip(anna, [ben]);

  // payer without paid_by -> validation error
  const bad = await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'activity', title: 'Solo tour', price: 100, split_mode: 'payer',
  });
  assert.equal(bad.status, 400);

  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'activity', title: 'Solo tour', price: 100, split_mode: 'payer', paid_by: ben.user.id,
  });

  const c = (await anna.agent.get(`/api/trips/${trip.id}/costs`)).body;
  assert.equal(c.totalCost, 100);
  const a = findUser(c, anna.user.id);
  const b = findUser(c, ben.user.id);
  assert.deepEqual([a.share, a.paid, a.net], [0, 0, 0]);
  assert.deepEqual([b.share, b.paid, b.net], [100, 100, 0]);
  assert.deepEqual(c.settlements, []);
});

test('costs: participants subset only splits among the chosen members', async () => {
  const anna = await createAccount();
  const ben = await createAccount();
  const carol = await createAccount();
  const trip = await costTrip(anna, [ben, carol]);

  // 90 split equally between anna & ben only (carol excluded), anna pays.
  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'transport', title: 'Taxi', price: 90, paid_by: anna.user.id,
    participants: [anna.user.id, ben.user.id],
  });

  const c = (await anna.agent.get(`/api/trips/${trip.id}/costs`)).body;
  assert.equal(c.totalCost, 90);
  const a = findUser(c, anna.user.id);
  assert.deepEqual([a.share, a.paid, a.net], [45, 90, 45]);
  assert.deepEqual([findUser(c, ben.user.id).share, findUser(c, ben.user.id).net], [45, -45]);
  assert.deepEqual([findUser(c, carol.user.id).share, findUser(c, carol.user.id).net], [0, 0]);
  assert.equal(c.settlements.length, 1);
  assert.deepEqual(c.settlements[0], { fromUserId: ben.user.id, toUserId: anna.user.id, amount: 45 });
});

test('costs: equal with no payer accumulates into unassigned', async () => {
  const anna = await createAccount();
  const ben = await createAccount();
  const trip = await costTrip(anna, [ben]);

  await anna.agent.post(`/api/trips/${trip.id}/entries`).send({
    date: '2026-08-01', type: 'stay', title: 'Hotel', price: 200, // paid_by omitted (null)
  });

  const c = (await anna.agent.get(`/api/trips/${trip.id}/costs`)).body;
  assert.equal(c.totalCost, 200);
  assert.equal(c.unassigned, 200);
  assert.deepEqual(c.byType, { stay: 200 });
  for (const u of c.perUser) {
    assert.deepEqual([u.share, u.paid, u.net], [100, 0, -100]);
  }
  // Nobody paid, so there is no creditor to settle toward.
  assert.deepEqual(c.settlements, []);
});

// ---------------------------------------------------------------------------
// Costs computation (pure unit test — greedy minimal-transfer)
// ---------------------------------------------------------------------------

test('computeCosts: greedy settlement matches largest debtor with largest creditor', () => {
  const members = [
    { id: 1, display_name: 'brave-otter' },
    { id: 2, display_name: 'calm-heron' },
    { id: 3, display_name: 'wise-lynx' },
  ];
  // id 1 pays 300 for a 3-way equal split (100 each); id 1 is owed 200 total.
  const c = computeCosts({
    currency: 'USD',
    members,
    entries: [{ type: 'stay', price: 300, paid_by: 1, split_mode: 'equal', participants: [] }],
  });
  assert.equal(c.totalCost, 300);
  assert.equal(findUser(c, 1).displayName, 'brave-otter');
  assert.equal(findUser(c, 1).net, 200);
  assert.equal(findUser(c, 2).net, -100);
  assert.equal(findUser(c, 3).net, -100);
  // Two transfers of 100 into the single creditor (id 1).
  assert.equal(c.settlements.length, 2);
  assert.ok(c.settlements.every((s) => s.toUserId === 1 && s.amount === 100));
});