mjackson/mach

var d = require('describe-property');
var makeToken = require('../../utils/makeToken');
var Promise = require('../../utils/Promise');

function makeUniqueKey(sessions, keyLength) {
  var key;
  do {
    key = makeToken(keyLength);
  } while (sessions[key]);

  return key;
}

function pruneStore(store, interval) {
  var timer = setInterval(function () {
    var now = Date.now();

    var session;
    for (var key in store.sessions) {
      session = store.sessions[key];

      if (session._expiry && session._expiry < now)
        store.purge(key);
    }
  }, interval);

  // Don't let this timer keep the event loop running.
  timer.unref();

  return timer;
}

/**
 * Basic server-side storage for sessions that exist within a single process.
 * This should never be used in production, but can be useful in development
 * and testing scenarios when there is only a single server instance.
 *
 * Accepts the following options:
 *
 * - keyLength        The length (in bytes) that will be used for unique cache keys.
 *                    Defaults to 32
 * - purgeInterval    The interval (in milliseconds) at which the cache is
 *                    purged of expired sessions. Defaults to 5000
 * - expireAfter      The number of seconds after which sessions expire.
 *                    Defaults to 0 (no expiration)
 */
function MemoryStore(options) {
  options = options || {};

  this.sessions = {};
  this.timer = pruneStore(this, options.purgeInterval || 5000);
  this.keyLength = options.keyLength || 32;
  this.ttl = options.expireAfter
    ? (1000 * options.expireAfter) // expireAfter is given in seconds
    : 0;
}

Object.defineProperties(MemoryStore.prototype, {

  load: d(function (value) {
    var session = this.sessions[value];

    if (!session)
      return Promise.resolve({});

    // Verify the session is not expired.
    if (session._expiry && session._expiry <= Date.now())
      return Promise.resolve({});

    return Promise.resolve(session);
  }),

  save: d(function (session) {
    var key = session._id;
    if (!key)
      key = session._id = makeUniqueKey(this.sessions, this.keyLength);

    if (this.ttl)
      session._expiry = Date.now() + this.ttl;

    this.sessions[key] = session;

    return Promise.resolve(key);
  }),

  purge: d(function (key) {
    if (key) {
      delete this.sessions[key];
    } else {
      this.sessions = {};
    }
  }),

  destroy: d(function () {
    delete this.sessions;

    if (this.timer) {
      clearInterval(this.timer);
      delete this.timer;
    }
  })

});

module.exports = MemoryStore;