amadeus4dev/amadeus-node

import EventEmitter from 'events';

// The number of seconds before the token expires, when
// we will already try to refresh it
const TOKEN_BUFFER = 10;

/**
  * A helper library to create and maintain the OAuth2 AccessTokens between
  * requests. Keeps track of the expiry time and automatically tries to fetch
  * a new token if needed.
  *
  * @property {string} accessToken the cached current access token (bearer)
  * @property {number} expiresAt the aproximate time this token expires at
  * @protected
  */
class AccessToken {
  constructor() {
    this.accessToken;
    this.expiresAt;
  }

  // PROTECTED

  /**
   * Fetches or returns a cached bearer token. Used by the Client to get a
   * token before making an API call.
   *
   * @param  {Client} client the Amadeus Client to make an API call with
   * @return {Promise.<Response,ResponseError>} a Promise
   * @protected
   */
  bearerToken(client) {
    let emitter = new EventEmitter();
    let promise = this.promise(emitter);
    this.emitOrLoadAccessToken(client, emitter);
    return promise;
  }

  // PRIVATE

  /**
   * Builds a promise to be returned to the API user
   *
   * @param  {type} emitter the EventEmitter used to notify the Promise of
   * @return {Promise} a promise
   * @private
   */
  promise(emitter) {
    return new Promise((resolve, reject) => {
      emitter.on('resolve', response => resolve(response));
      emitter.on('reject', error => reject(error));
    });
  }


  /**
   * Checks if the token needs a refresh, if not emits the cached token,
   * otherwise tries to load a new access token
   *
   * @param  {Client} client the Amadeus Client to make an API call with
   * @param  {type} emitter the EventEmitter used to emit the token
   * @private
   */
  emitOrLoadAccessToken(client, emitter) {
    if (this.needsLoadOrRefresh()) { this.loadAccessToken(client, emitter); }
    else { emitter.emit('resolve', this.accessToken); }
  }

  /**
   * Checks if the token needs a refresh or first load
   *
   * @return {boolean} wether the token needs a refresh
   * @private
   */
  needsLoadOrRefresh() {
    return !this.accessToken || ((Date.now() + TOKEN_BUFFER) > this.expiresAt);
  }


  /**
   * Loads the access token using the client, emits the token when it's loaded
   *
   * @param  {Client} client the Amadeus Client to make an API call with
   * @param  {type} emitter the EventEmitter used to emit the token
   * @private
   */
  loadAccessToken(client, emitter) {
    client.unauthenticatedRequest('POST', '/v1/security/oauth2/token', {
      'grant_type' : 'client_credentials',
      'client_id' : client.clientId,
      'client_secret' : client.clientSecret
    }).then((response) => {
      this.storeAccessToken(response);
      this.emitOrLoadAccessToken(client, emitter);
    }).catch((error) => {
      emitter.emit('reject', error);
    });
  }

  /**
   * Stores a loaded access token, calculating the expiry date
   *
   * @param  {Response} response the response object received from the client
   * @private
   */
  storeAccessToken(response) {
    this.accessToken = response.result['access_token'];
    this.expiresAt = Date.now() + (response.result['expires_in'] * 1000);
  }
}

export default AccessToken;