comparison.js

/**
 * Returns a Comparison of 2 Tasks
 * @param {string} projectId the Project ID
 * @param {Array<string>} taskIds a list of Task IDs
 * @returns {Promise<Object>}
 */
const fetchComparison = (projectId, leftTaskId, rightTaskId) => (
  new Promise(resolve => (
    R.composeP(
      resolve,
      buildComparisonTable
    )(projectId, [leftTaskId, rightTaskId])
  ))
);

const buildComparisonTable = (projectId, taskIds) => (
  R.composeP(
    buildTable,
    R.map(mapComparisonTask),
    () => Promise.all(getImages(projectId, taskIds))
  )()
);

const getImages = (projectId, taskIds) => R.map(fetchData(projectId), taskIds);

const fetchData = R.curry((projectId, taskId) => (
  R.composeP(
    addImagesToTask(projectId, taskId),
    callBizApi
  )([`/tasks/${taskId}`])
));

const addImagesToTask = R.curry((projectId, taskId, task) => (
  fetchImages(projectId, taskId).then(setImages(task))
));

const setImages = R.flip(R.compose(
  R.prop('task'),
  R.assocPath(['task', 'images'])
));

comparison.test.js

import test from 'ava';
import { get, validate } from '../tests/support';
import { webSchemas } from '../tests/schemas';

test('the Web API payload matches its schema', async t => {
  const PROJECT_ID = 175; // Fancy IAT
  const TASK_LEFT = 688; // Brand X
  const TASK_RIGHT = 689; // Your Colour
  const payload = await get(
    `/projects/${PROJECT_ID}/comparison?taskLeftId=${TASK_LEFT}&taskRightId=${TASK_RIGHT}`
  );

  t.true(validate(webSchemas.comparisonTable, payload.body));
});

routes.js

import R from 'ramda';
import express from 'express';

const router = express.Router();

router.route('/projects/:projectId/comparison')
  .get((req, res) => {
    fetchComparison(
      req.params.projectId,
      ...R.props(['leftTaskId', 'rightTaskId'], req.query)
    )
      .then(comparison => res.json(comparison));
  });