// used to set a flash message for next request
exports.flash = function() {
  return function(req, res, next) {
    if (req.flash) {
      return next();
    }

    req.flash = _flash;
    next();
  };
};

// used on new requests to check for flash messages stored in session
exports.flashRead = function() {
  return function(req, res, next) {
    if (typeof req.session.flash !== 'undefined') {
      res.locals.flash = req.session.flash;
    }

    next();
  };
};

/**
 * Sets a session-based flash message.
 *
 * @this req
 * @param {string} type - user-defined type of flash message
 * @param {string} msg - message to be displayed to the user
 */
function _flash(type, msg) {
  // verify that express-session has been enabled
  if (this.session === undefined) throw Error('req.flash() requires sessions');

  // set session properties
  this.session.flash = {
    type: type,
    msg: msg,
  };
}