var AWS = require('../core');

/**
 * Represents credentials from a JSON file on disk.
 * If the credentials expire, the SDK can {refresh} the credentials
 * from the file.
 *
 * The format of the file should be similar to the options passed to
 * {AWS.Config}:
 *
 * ```javascript
 * {accessKeyId: 'akid', secretAccessKey: 'secret', sessionToken: 'optional'}
 * ```
 *
 * @example Loading credentials from disk
 *   var creds = new AWS.FileSystemCredentials('./configuration.json');
 *   creds.accessKeyId == 'AKID'
 *
 * @!attribute filename
 *   @readonly
 *   @return [String] the path to the JSON file on disk containing the
 *     credentials.
 * @!macro nobrowser
 */
AWS.FileSystemCredentials = AWS.util.inherit(AWS.Credentials, {

  /**
   * @overload AWS.FileSystemCredentials(filename)
   *   Creates a new FileSystemCredentials object from a filename
   *
   *   @param filename [String] the path on disk to the JSON file to load.
   */
  constructor: function FileSystemCredentials(filename) {
    AWS.Credentials.call(this);
    this.filename = filename;
    this.get(function() {});
  },

  /**
   * Loads the credentials from the {filename} on disk.
   *
   * @callback callback function(err)
   *   Called after the JSON file on disk is read and parsed. When this callback
   *   is called with no error, it means that the credentials information
   *   has been loaded into the object (as the `accessKeyId`, `secretAccessKey`,
   *   and `sessionToken` properties).
   *   @param err [Error] if an error occurred, this value will be filled
   * @see get
   */
  refresh: function refresh(callback) {
    if (!callback) callback = function(err) { if (err) throw err; };
    try {
      var creds = JSON.parse(AWS.util.readFileSync(this.filename));
      AWS.Credentials.call(this, creds);
      if (!this.accessKeyId || !this.secretAccessKey) {
        throw new Error('Credentials not set in ' + this.filename);
      }
      this.expired = false;
      callback();
    } catch (err) {
      callback(err);
    }
  }

});
