Wizard framework

Looking ahead to Migrate 2.6, the main theme of that release will be developing a framework for building user-friendly UIs for migration. This will be a significant step forward towards addressing #1123538: UI for defining migrations, at least for particular scenarios that implement this framework. Work has already begun - the adventurously curious can see the current state by checking out the wizard_api branches of Migrate and migrate_d2d.

The idea is to support a wizard approach to the UI - leading the user through a series of steps to choose what to migrate and how to map it to the destination Drupal environment, ultimately registering a set of migrations to perform the actual import. The existing migrate_ui dashboard would then be used to run the import, rollback, etc. I expect we'll want to do some redesign here - the existing UI was designed with developers in mind, I think we'll want to simplify it some for the use of non-technical folks. In particular, we'll want to do a better job of leveraging groups - finally implementing #1350284: Display Migration's group on UI for one thing.

Modules implementing migrations from particular sources (Drupal, WordPress, Ning, etc.) would extend the new MigrateUIWizard class, providing forms and validation functions for each step. The extended class will be registered via the 'wizard classes' attribute in hook_migrate_api(), and the steps supported registered in the class constructor:

  public function __construct() {
    parent::__construct();
    $this->addStep(t('Overview'), 'overviewForm');
    $this->addStep(t('Credentials'), 'sourceDataForm');
    $this->addStep(t('Users'), 'userForm');
    $this->addStep(t('Taxonomy'), 'taxonomyForm');
    $this->addStep(t('Content Types'), 'contentTypeForm');
    $this->addStep(t('Review'), 'reviewForm');
  }

The form methods registered here would build and return a form array in the usual way - each one is expected to also have a validation function (overviewFormValidate(), sourceDataFormValidate(), etc.) which will save any data needed by subsequent steps, and of course validate that the user input makes sense. The final Review form will present the choices made by the user, and on Submit register migrations reflecting those choices, redirecting to the Dashboard.

Feedback is, of course, welcome.