class MigrateDrupalHooks

class MigrateDrupalHooks {
    
    /**
     * Implements hook_help().
     */
    public function help($route_name, RouteMatchInterface $route_match) {
        switch ($route_name) {
            case 'help.page.migrate_drupal':
                $output = '';
                $output .= '<h2>' . t('About') . '</h2>';
                $output .= '<p>' . t('The Migrate Drupal module provides a framework based on the <a href=":migrate">Migrate module</a> to facilitate migration from a Drupal (6, 7, or 8) site to your website. It does not provide a user interface. For more information, see the <a href=":migrate_drupal">online documentation for the Migrate Drupal module</a>.', [
                    ':migrate' => Url::fromRoute('help.page', [
                        'name' => 'migrate',
                    ])->toString(),
                    ':migrate_drupal' => 'https://www.drupal.org/documentation/modules/migrate_drupal',
                ]) . '</p>';
                return $output;
        }
    }
    
    /**
     * Implements hook_migration_plugins_alter().
     */
    public function migrationPluginsAlter(array &$definitions) {
        $module_handler = \Drupal::service('module_handler');
        $migration_plugin_manager = \Drupal::service('plugin.manager.migration');
        // This is why the deriver can't do this: the 'd6_taxonomy_vocabulary'
        // definition is not available to the deriver as it is running inside
        // getDefinitions().
        if (isset($definitions['d6_taxonomy_vocabulary'])) {
            $vocabulary_migration_definition = [
                'source' => [
                    'ignore_map' => TRUE,
                    'plugin' => 'd6_taxonomy_vocabulary',
                ],
                'destination' => [
                    'plugin' => 'null',
                ],
                'idMap' => [
                    'plugin' => 'null',
                ],
            ];
            $vocabulary_migration = $migration_plugin_manager->createStubMigration($vocabulary_migration_definition);
            $translation_active = $module_handler->moduleExists('content_translation');
            try {
                $source_plugin = $vocabulary_migration->getSourcePlugin();
                if ($source_plugin instanceof RequirementsInterface) {
                    $source_plugin->checkRequirements();
                }
                $executable = new MigrateExecutable($vocabulary_migration);
                $process = [
                    'vid' => $definitions['d6_taxonomy_vocabulary']['process']['vid'],
                ];
                foreach ($source_plugin as $row) {
                    $executable->processRow($row, $process);
                    $source_vid = $row->getSourceProperty('vid');
                    $plugin_ids = [
                        'd6_term_node:' . $source_vid,
                        'd6_term_node_revision:' . $source_vid,
                    ];
                    if ($translation_active) {
                        $plugin_ids[] = 'd6_term_node_translation:' . $source_vid;
                    }
                    foreach (array_intersect($plugin_ids, array_keys($definitions)) as $plugin_id) {
                        // Match the field name derivation in d6_vocabulary_field.yml.
                        $field_name = substr('field_' . $row->getDestinationProperty('vid'), 0, 32);
                        // The Forum module is expecting 'taxonomy_forums' as the field name
                        // for the forum nodes. The 'forum_vocabulary' source property is
                        // evaluated in Drupal\taxonomy\Plugin\migrate\source\d6\Vocabulary
                        // and is set to true if the vocabulary vid being migrated is the
                        // same as the one in the 'forum_nav_vocabulary' variable on the
                        // source site.
                        $destination_vid = $row->getSourceProperty('forum_vocabulary') ? 'taxonomy_forums' : $field_name;
                        $definitions[$plugin_id]['process'][$destination_vid] = 'tid';
                    }
                }
            } catch (RequirementsException $e) {
                // This code currently runs whenever the definitions are being loaded and
                // if you have a Drupal 7 source site then the requirements will not be
                // met for the d6_taxonomy_vocabulary migration.
            } catch (DatabaseExceptionWrapper $e) {
                // When the definitions are loaded it is possible the tables will not
                // exist.
            }
        }
        if (!$module_handler->moduleExists('node')) {
            return;
        }
        $connection = \Drupal::database();
        // We need to get the version of the source database in order to check
        // if the classic or complete node tables have been used in a migration.
        if (isset($definitions['system_site'])) {
            // Use the source plugin of the system_site migration to get the
            // database connection.
            $migration = $definitions['system_site'];
            
            /** @var \Drupal\migrate\Plugin\migrate\source\SqlBase $source_plugin */
            $source_plugin = $migration_plugin_manager->createStubMigration($migration)
                ->getSourcePlugin();
            try {
                $source_connection = $source_plugin->getDatabase();
                $version = NodeMigrateType::getLegacyDrupalVersion($source_connection);
            } catch (\Exception $e) {
                \Drupal::messenger()->addError(t('Failed to connect to your database server. The server reports the following message: %error.<ul><li>Is the database server running?</li><li>Does the database exist, and have you entered the correct database name?</li><li>Have you entered the correct username and password?</li><li>Have you entered the correct database hostname?</li></ul>', [
                    '%error' => $e->getMessage(),
                ]));
            }
        }
        // If this is a complete node migration then for all migrations, except the
        // classic node migrations, replace any dependency on a classic node migration
        // with a dependency on the complete node migration.
        if (NodeMigrateType::getNodeMigrateType($connection, $version ?? FALSE) === NodeMigrateType::NODE_MIGRATE_TYPE_COMPLETE) {
            $classic_migration_match = '/d([67])_(node|node_translation|node_revision|node_entity_translation)($|:.*)/';
            $replace_with_complete_migration = function (&$value, $key, $classic_migration_match) {
                if (is_string($value)) {
                    $value = preg_replace($classic_migration_match, 'd$1_node_complete$3', $value);
                }
            };
            foreach ($definitions as &$definition) {
                $is_node_classic_migration = preg_match($classic_migration_match, $definition['id']);
                if (!$is_node_classic_migration && isset($definition['migration_dependencies'])) {
                    array_walk_recursive($definition['migration_dependencies'], $replace_with_complete_migration, $classic_migration_match);
                }
            }
        }
    }

}