var _ = require('./utility');

/*
 * Notifier - the internal object responsible for delegating between the client exposed API, the
 * chain of transforms necessary to turn an item into something that can be sent to Rollbar, and the
 * queue which handles the communcation with the Rollbar API servers.
 *
 * @param queue - an object that conforms to the interface: addItem(item, callback)
 * @param options - an object representing the options to be set for this notifier, this should have
 * any defaults already set by the caller
 */
function Notifier(queue, options) {
  this.queue = queue;
  this.options = options;
  this.transforms = [];
  this.diagnostic = {};
}

/*
 * configure - updates the options for this notifier with the passed in object
 *
 * @param options - an object which gets merged with the current options set on this notifier
 * @returns this
 */
Notifier.prototype.configure = function(options) {
  this.queue && this.queue.configure(options);
  var oldOptions = this.options;
  this.options = _.merge(oldOptions, options);
  return this;
};

/*
 * addTransform - adds a transform onto the end of the queue of transforms for this notifier
 *
 * @param transform - a function which takes three arguments:
 *    * item: An Object representing the data to eventually be sent to Rollbar
 *    * options: The current value of the options for this notifier
 *    * callback: function(err: (Null|Error), item: (Null|Object)) the transform must call this
 *    callback with a null value for error if it wants the processing chain to continue, otherwise
 *    with an error to terminate the processing. The item should be the updated item after this
 *    transform is finished modifying it.
 */
Notifier.prototype.addTransform = function(transform) {
  if (_.isFunction(transform)) {
    this.transforms.push(transform);
  }
  return this;
};

/*
 * log - the internal log function which applies the configured transforms and then pushes onto the
 * queue to be sent to the backend.
 *
 * @param item - An object with the following structure:
 *    message [String] - An optional string to be sent to rollbar
 *    error [Error] - An optional error
 *
 * @param callback - A function of type function(err, resp) which will be called with exactly one
 * null argument and one non-null argument. The callback will be called once, either during the
 * transform stage if an error occurs inside a transform, or in response to the communication with
 * the backend. The second argument will be the response from the backend in case of success.
 */
Notifier.prototype.log = function(item, callback) {
  if (!callback || !_.isFunction(callback)) {
    callback = function() {};
  }

  if (!this.options.enabled) {
    return callback(new Error('Rollbar is not enabled'));
  }

  this.queue.addPendingItem(item);
  var originalError = item.err;
  this._applyTransforms(item, function(err, i) {
    if (err) {
      this.queue.removePendingItem(item);
      return callback(err, null);
    }
    this.queue.addItem(i, callback, originalError, item);
  }.bind(this));
};

/* Internal */

/*
 * _applyTransforms - Applies the transforms that have been added to this notifier sequentially. See
 * `addTransform` for more information.
 *
 * @param item - An item to be transformed
 * @param callback - A function of type function(err, item) which will be called with a non-null
 * error and a null item in the case of a transform failure, or a null error and non-null item after
 * all transforms have been applied.
 */
Notifier.prototype._applyTransforms = function(item, callback) {
  var transformIndex = -1;
  var transformsLength = this.transforms.length;
  var transforms = this.transforms;
  var options = this.options;

  var cb = function(err, i) {
    if (err) {
      callback(err, null);
      return;
    }

    transformIndex++;

    if (transformIndex === transformsLength) {
      callback(null, i);
      return;
    }

    transforms[transformIndex](i, options, cb);
  };

  cb(null, item);
};

module.exports = Notifier;