[My Motivational Coach] - A DialogFlow-powered add-on for Google Home Assistant that replies with a randomly generated motivational quote.

index.js

/**
 * @fileoverview Handles a DialogFlow request and returns a motivational quote.
 *
 * In order to deploy, run:
 * gcloud beta functions deploy getMotivationQuote --trigger-http
 */

 const /** boolean */ EQUAL_PROBABILITY = true;

/**
 * Quotes are not owned by author or code.
 * Just a sample extracted from multiple sources.
 */
const /** !Array */ QUOTE_LIST = [
  [  // Music and songs.
    [  // Chojin (translated).
      [  // Rie cuando puedas.
        `Smile whenever you can. Cry whenever you need it.`,
      ],
    ],
  ],

  [  // TV Shows.
    [  // How I Met Your Mother.
      `Your problem is all you do is think, think think.
        I am teaching you how to do, do do.`,
    ],
  ],

  [  // Movies.
    [  // The pursuit of happiness.
      `Don't ever let somebody tell you you can't do something.
        You got a dream, you gotta protect it.
        People who can't do something themselves,
          they wanna tell you you can't do it.
        If you want something, go get it.`,
    ],
    [  // Star Wars.
      `Do or do not. There is no try.`,
    ],
  ],

  [  // Books and book authors.
    [  // Jack Welch - Winning.
      `Every day is a new challenge.`,
    ],
  ],

  [  // Personalities.
    [  // Albert Einstein.
      `During crisis, only imagination is more important than wisdom.`,
      `Become not a man of success, but a man of value.`,
    ],
    [  // Warren Buffet.
      `It takes twenty years to build a reputation and five minutes to run it.`,
    ],
    [  // Steve Jobs.
      `Keep hungry. Stay foolish.`,
    ],
  ],
];

/**
 * Deep flattens an array.
 * Merges all sub levels of an array into one array.
 * @param {!Array} array Array to be flatten.
 * @return {!Array} Flatten array with all values at array level.
 */
const flattenDeepArray = (arrayToFlat) => {
   return arrayToFlat.reduce((accumulator, currentValue) =>
    Array.isArray(currentValue) ?
      accumulator.concat(flattenDeepArray(currentValue)) :
      accumulator.concat(currentValue), []);
};

/**
 * Gets a random number using a uniform distribution.
 * @param {number} min Lower range for number generation.
 * @param {number} max Upper range for number generation.
 * @return {number} Random number uniformly generated.
 */
const getRandomInt = (min, max) => {
  return Math.floor(Math.random() * (max - min)) + min;
};

/**
 * Exports a given text as a JSON response for DialogFlow.
 * @param {string} text Text to export as JSON for response.
 * @param {!HTTPResponse} response HTTP Response generate from request.
 * @return {!HTTPResponse} HTTP Response with given types and JSON data.
 */
function exportAsJson(text, response) {
  if (response.json) { // DialogFlow API V2.
    response.json({ fulfillmentText: text});
  } else {  // DialogFlow API V1.
    response.setHeader('Content-Type', 'application/json');
    response.send(JSON.stringify({
      'speech': text,
      'displayText': text,
    }));
  }
  return response;
};

/**
 * Handles HTTP Requests and produces a response with a quote in JSON.
 * @param {!HTTPRequest} request Node HTTP DialogFlow Request.
 * @param {!HTTPResponse} response Node HTTP DialogFlow Response.
 */
exports.getMotivationQuote = function getMotivationQuote (request, response) {
  let quoteText = QUOTE_LIST;

  if (EQUAL_PROBABILITY) quoteText = flattenDeepArray(quoteText);

  while(Array.isArray(quoteText)) {
    const randomSelection = getRandomInt(0, quoteText.length - 1);
    quoteText = quoteText[randomSelection];
  }

  response = exportAsJson(quoteText, response);
};