controller.es6

import Ember from 'ember';

var { computed, get } = Ember;

export default Ember.ArrayController.extend({
  selectedUsers        : Ember.A([]),
  remainingUsers       : computed.setDiff('model', 'selectedUsers'),
  remainingUsersLength : computed.alias('remainingUsers.length'),

  actions: {
    addUser(userId) {
      var selectedUsers = get(this, 'selectedUsers');
      var user          = get(this, 'model').findBy('id', parseInt(userId));

      if (!selectedUsers.contains(user)) {
        return selectedUsers.pushObject(user);
      }
    },

    addAllUsers() {
      var remainingUsers = get(this, 'remainingUsers')
      return get(this, 'selectedUsers').pushObjects(remainingUsers);
    },

    removeUser(user) {
      return get(this, 'selectedUsers').removeObject(user);
    },

    removeAllUsers() {
      return get(this, 'selectedUsers').clear();
    }
  }
});