Utils.js

/**
 * Filters a set based on the given expression
 * @param {Set} set The set to filter the elements of
 * @param {Function} expression The predicate to match against
 * @returns {Array} The filtered elements
 */
function filter (set, expression) {
  const results = [];
  set.forEach(item => expression(item) && results.push(item));
  return results;
}


/**
 * Filters the given set by the given predicate and returns the first match, if any.
 * @param {Set} set The set to filter the elements of
 * @param {Function} expression The predicate to match elements against
 * @returns {Any|Null} The first match, if any
 */
function findFirst (set, expression) {
  return filter(set, expression)[0];
}


/**
 * Gets the first websocket client with the given user ID
 * @param {Set<WebSocket>|WebSocket[]} clients The clients to filter
 * @param {String} userId The userId to find
 * @returns {Array<WebSocket>} The matching clients
 */
function getClientsById (clients, userId) {
  return filter(clients, (ws) => ws.isAuthenticated && ws.user.id === userId);
}


/**
 * Parses a string into an object and suppresses any errors thrown
 * @param {String} data The string to convert to an object
 */
function safeParse (data) {
  try {
    return JSON.parse(data);
  } catch (exception) {
    return null;
  }
}


/**
 * De-duplicates an array by converting it to a set and back
 * @param {Array<*>} array The array to deduplicate
 * @param {*} append Elements to append to the array before deduplicating
 * @returns {Array<*>} The deduplicated array
 */
function deduplicate (array, ...append) {
  array.push(...append);
  const arraySet = new Set(array);
  return [...arraySet.values()];
}


/**
 * Removes an element from an array
 * @param {Array<*>} array The array to remove the item from
 * @param {*} item The item to remove
 */
function remove (array, item) {
  const ind = array.indexOf(item);

  if (-1 < ind) {
    array.splice(ind, 1);
  }
}


/**
 * Gets the number of sessions of the given user ID
 * @param {String} userId The user ID to get the sessions of
 * @param {Set<WebSocket>} clients The clients to filter
 */
function getSessionsOf (userId, clients) {
  return filter(clients, ws => ws.user && ws.user.id === userId).length;
}


module.exports = {
  deduplicate,
  filter,
  findFirst,
  safeParse,
  getClientsById,
  getSessionsOf,
  remove
};