Practical solution to https://github.com/onzo-com/etc-kata

index.js

"use strict";

const _ = require("lodash");

function groupByTimeWindow(start, end) {
  return function(o) {
    const date = new Date(o.timestamp);
    if (date.getUTCHours() >= start && date.getUTCHours() <= end)
      return o.consumption_Wh;
    return 0;
  };
}

module.exports.getSensorData = (data, id) => _.groupBy(data, x => x.sensor_id)[id];
module.exports.getConsumptionByTimeWindow = (sensorData, start, end) =>
  _.sumBy(sensorData, groupByTimeWindow(start, end));

index.test.js

"use strict";

const t = require("tap");
const test = t.test;

/**
 * Date and time information in ISO 8601 format
 * Electricity consumption in **Wh**
 */
const rawData = require("./consumption_data.json");
const lib = require("./");
const data = lib.getSensorData(rawData, "b08c6195-8cd9-43ab-b94d-e0b887dd73d2");

test("Calculate the sensor's total daily consumption in kWh", t => {
  t.plan(1);
  let result = lib.getConsumptionByTimeWindow(data, 0, 24) * 10e-4
  result = +result.toFixed(3)
  t.strictEqual(result, 10.713);
});

test("Calculate the sensor's average hourly consumption from 00:00 to 07:00 inclusive", t => {
  t.plan(1);
  let result = lib.getConsumptionByTimeWindow(data, 0, 7) / 8 * 10e-4
  result = +result.toFixed(6)
  t.strictEqual(result, 0.322875);
});

test("Calculate the sensor's average hourly consumption from 08:00 to 15:00 inclusive", t => {
  t.plan(1);
  let result = lib.getConsumptionByTimeWindow(data, 8, 15) / 8 * 10e-4
  result = +result.toFixed(5)
  t.strictEqual(result, 0.44925);
});

test("Calculate the sensor's average hourly consumption from 16:00 to 23:00 inclusive", t => {
  t.plan(1);
  let result = lib.getConsumptionByTimeWindow(data, 16, 23) / 8 * 10e-4
  result = +result.toFixed(3)
  t.strictEqual(result, 0.567);
});