helperFunctions.js

const fetch = require('node-fetch'); // JS's default fetch doesn't work server side in Node.js

/**
 * @param {Object[]} searchArray Array of objects, each with an id property, to search
 * @param {Number[]} idArray Array of ids to search with
 * @return {Object[]} Array of objects from searchArray with an id value in idArray
 */
module.exports.searchId = function (searchArray, idArray) {
  const results = [];
  for (const item of searchArray) {
    if (idArray.includes(item.id)) {
      results.push(item);
    }
  }
  return results;
};

/**
 * @param {Object[]} searchArray Array of objects, each with an id property, to search
 * @param {String | undefined} paramId Id provided to API via URL parameter as a String (takes precedence over queryIds) (i.e. '1' from /cards/1)
 * @param {String} queryIds Comma-separated list of ids provided to API via ids query string in URL (i.e. '1,2,3' from /cards?ids=1,2,3)
 * @return {Object[]} Array of objects from searchArray with an id value either matching paramId or, failing that, in queryIds
 */
module.exports.handleIdUrl = function (searchArray, paramId, queryIds) {
  if (paramId !== undefined) { // req.params.id in app.js will return undefined if user didn't provide a parameter in the url
    const paramIdNum = Number(paramId);
    return module.exports.searchId(searchArray, [paramIdNum]); // searchId(...) requires idArray to be an Array
  } else if (queryIds) {
    // split queryIds string by commas using RegExp and mapping while also converting each id to a Number
    const commaSplitRegExp = /, */;
    const queryIdsArray = queryIds.split(commaSplitRegExp).map((s) => Number(s));
    return module.exports.searchId(searchArray, queryIdsArray);
  } else {
    return searchArray;
  }
};

/**
 * @param {String} redditUrl Basic Reddit URL to fetch data from (without any .json added - the function does this)
 * @return {Promise<{score: Number, author: String, replies: Object[] | String} | undefined>} Required data (more is returned than is typed here) from Reddit's JSON API (redditJSON[1].data.children[0].data) if no error occurred during fetching process (e.g. url doesn't exist); else, undefined
 */
module.exports.getRedditData = async function (redditUrl) {
  const redditJSONUrl = redditUrl + '.json';
  const redditResponse = await fetch(redditJSONUrl);
  const redditJSON = await redditResponse.json();
  if (!redditJSON.error) {
    return redditJSON[1].data.children[0].data;
  } else {
    return undefined;
  }
};

/**
 * @param {Object} cardObj The card object to modify with the newRedditData provided
 * @param {{score: Number, author: String, replies: Object[] | String}} newRedditData The Object returned by getRedditData(...) above; including score, author and replies properties
 */
module.exports.updateCardRedditData = function (cardObj, newRedditData) {
  cardObj.redditData = {};
  cardObj.redditData.score = newRedditData.score;
  cardObj.redditData.author = newRedditData.author;

  if (newRedditData.replies !== '') { // Reddit inserts an empty string (rather than an empty Array) if a comment has no replies
    // noinspection JSUnresolvedVariable - otherwise I would have to type to end of the earth to satisfy WebStorm
    cardObj.redditData.replies = newRedditData.replies.data.children.length;
  } else {
    cardObj.redditData.replies = 0;
  }
};

/**
 * @param {Object[]} currentArray Array containing all current objects (each with an id property) to consider
 * @return {Number} The largest currently in use index + 1 - i.e. this new id can be safely used for a new object to add to currentArray
 */
module.exports.getNewId = function (currentArray) {
  if (currentArray.length > 0) {
    const usedIds = currentArray.map(e => e.id); // creates an array of all the objects' ids
    return Math.max(...usedIds) + 1; // new id generated by adding 1 to max element in current cards list
  } else {
    return 0; // list is empty so start the ids at 0
  }
};

/**
 * @param {Object} reqBody JS Object returned from req.body
 * @param {String[]} propertiesArray Array of property names reqBody should possess
 * @param {Response} response express Response object to set status on and return json to client through
 * @returns Boolean true if reqBody has all the properties specified in propertiesArray; else, false
 */
module.exports.requestBodyIsValid = function (reqBody, propertiesArray, response) {
  for (const prop of propertiesArray) {
    if (!Object.prototype.hasOwnProperty.call(reqBody, prop)) {
      response.status(400); // 400 Bad Request
      response.json({
        error: 'request-body-field-missing',
        message: `The request body did not include all the expected fields of ${propertiesArray.join(', ')}`
      });
      return false; // return false to abort the processing of this request
    }
  }
  return true; // body is valid, continue processing
};