class MigrateUpgradeImportBatch

class MigrateUpgradeImportBatch {
    
    /**
     * Maximum number of previous messages to display.
     */
    const MESSAGE_LENGTH = 20;
    
    /**
     * The processed items for one batch of a given migration.
     *
     * @var int
     */
    protected static $numProcessed = 0;
    
    /**
     * Ensure we only add the listeners once per request.
     *
     * @var bool
     */
    protected static $listenersAdded = FALSE;
    
    /**
     * The maximum length in seconds to allow processing in a request.
     *
     * @see self::run()
     *
     * @var int
     */
    protected static $maxExecTime;
    
    /**
     * MigrateMessage instance to capture messages during the migration process.
     *
     * @var \Drupal\migrate_drupal_ui\Batch\MigrateMessageCapture
     */
    protected static $messages;
    
    /**
     * The follow-up migrations.
     *
     * @var \Drupal\migrate\Plugin\MigrationInterface[]
     */
    protected static $followUpMigrations;
    
    /**
     * Runs a single migrate batch import.
     *
     * @param int[] $initial_ids
     *   The full set of migration IDs to import.
     * @param array $config
     *   An array of additional configuration from the form.
     * @param array $context
     *   The batch context.
     */
    public static function run($initial_ids, $config, &$context) {
        if (!static::$listenersAdded) {
            $event_dispatcher = \Drupal::service('event_dispatcher');
            $event_dispatcher->addListener(MigrateEvents::POST_ROW_SAVE, [
                static::class,
                'onPostRowSave',
            ]);
            $event_dispatcher->addListener(MigrateEvents::POST_IMPORT, [
                static::class,
                'onPostImport',
            ]);
            $event_dispatcher->addListener(MigrateEvents::MAP_SAVE, [
                static::class,
                'onMapSave',
            ]);
            $event_dispatcher->addListener(MigrateEvents::IDMAP_MESSAGE, [
                static::class,
                'onIdMapMessage',
            ]);
            static::$maxExecTime = ini_get('max_execution_time');
            if (static::$maxExecTime <= 0) {
                static::$maxExecTime = 60;
            }
            // Set an arbitrary threshold of 3 seconds (e.g., if max_execution_time is
            // 45 seconds, we will quit at 42 seconds so a slow item or cleanup
            // overhead don't put us over 45).
            static::$maxExecTime -= 3;
            static::$listenersAdded = TRUE;
        }
        if (!isset($context['sandbox']['migration_ids'])) {
            $context['sandbox']['max'] = count($initial_ids);
            $context['sandbox']['current'] = 1;
            // Total number processed for this migration.
            $context['sandbox']['num_processed'] = 0;
            // migration_ids will be the list of IDs remaining to run.
            $context['sandbox']['migration_ids'] = $initial_ids;
            $context['sandbox']['messages'] = [];
            $context['results']['failures'] = 0;
            $context['results']['successes'] = 0;
        }
        // Number processed in this batch.
        static::$numProcessed = 0;
        $migration_id = reset($context['sandbox']['migration_ids']);
        $definition = \Drupal::service('plugin.manager.migration')->getDefinition($migration_id);
        $configuration = [];
        // @todo Find a way to avoid this in https://www.drupal.org/node/2804611.
        if ($definition['destination']['plugin'] === 'entity:file') {
            // Make sure we have a single trailing slash.
            if ($definition['source']['plugin'] === 'd7_file_private') {
                $configuration['source']['constants']['source_base_path'] = rtrim($config['source_private_file_path'], '/') . '/';
            }
            $configuration['source']['constants']['source_base_path'] = rtrim($config['source_base_path'], '/') . '/';
        }
        
        /** @var \Drupal\migrate\Plugin\Migration $migration */
        $migration = \Drupal::service('plugin.manager.migration')->createInstance($migration_id, $configuration);
        if ($migration) {
            static::$messages = new MigrateMessageCapture();
            $executable = new MigrateExecutable($migration, static::$messages);
            $migration_name = $migration->label() ? $migration->label() : $migration_id;
            try {
                $migration_status = $executable->import();
            } catch (\Exception $e) {
                \Drupal::logger('migrate_drupal_ui')->error($e->getMessage());
                $migration_status = MigrationInterface::RESULT_FAILED;
            }
            switch ($migration_status) {
                case MigrationInterface::RESULT_COMPLETED:
                    // Store the number processed in the sandbox.
                    $context['sandbox']['num_processed'] += static::$numProcessed;
                    $message = new PluralTranslatableMarkup($context['sandbox']['num_processed'], 'Upgraded @migration (processed 1 item total)', 'Upgraded @migration (processed @count items total)', [
                        '@migration' => $migration_name,
                    ]);
                    $context['sandbox']['messages'][] = (string) $message;
                    \Drupal::logger('migrate_drupal_ui')->notice($message);
                    $context['sandbox']['num_processed'] = 0;
                    $context['results']['successes']++;
                    // If the completed migration has any follow-up migrations, add them
                    // to the batch migrations.
                    // @see onPostImport()
                    if (!empty(static::$followUpMigrations)) {
                        foreach (static::$followUpMigrations as $migration_id => $migration) {
                            if (!in_array($migration_id, $context['sandbox']['migration_ids'], TRUE)) {
                                // Add the follow-up migration ID to the batch migration IDs for
                                // later execution.
                                $context['sandbox']['migration_ids'][] = $migration_id;
                                // Increase the number of migrations in the batch to update the
                                // progress bar and keep it accurate.
                                $context['sandbox']['max']++;
                                // Unset the follow-up migration to make sure it won't get added
                                // to the batch twice.
                                unset(static::$followUpMigrations[$migration_id]);
                            }
                        }
                    }
                    break;
                case MigrationInterface::RESULT_INCOMPLETE:
                    $context['sandbox']['messages'][] = (string) new PluralTranslatableMarkup(static::$numProcessed, 'Continuing with @migration (processed 1 item)', 'Continuing with @migration (processed @count items)', [
                        '@migration' => $migration_name,
                    ]);
                    $context['sandbox']['num_processed'] += static::$numProcessed;
                    break;
                case MigrationInterface::RESULT_STOPPED:
                    $context['sandbox']['messages'][] = (string) new TranslatableMarkup('Operation stopped by request');
                    break;
                case MigrationInterface::RESULT_FAILED:
                    $context['sandbox']['messages'][] = (string) new TranslatableMarkup('Operation on @migration failed', [
                        '@migration' => $migration_name,
                    ]);
                    $context['results']['failures']++;
                    \Drupal::logger('migrate_drupal_ui')->error('Operation on @migration failed', [
                        '@migration' => $migration_name,
                    ]);
                    break;
                case MigrationInterface::RESULT_SKIPPED:
                    $context['sandbox']['messages'][] = (string) new TranslatableMarkup('Operation on @migration skipped due to unfulfilled dependencies', [
                        '@migration' => $migration_name,
                    ]);
                    \Drupal::logger('migrate_drupal_ui')->error('Operation on @migration skipped due to unfulfilled dependencies', [
                        '@migration' => $migration_name,
                    ]);
                    break;
                case MigrationInterface::RESULT_DISABLED:
                    // Skip silently if disabled.
                    break;
            }
            // Unless we're continuing on with this migration, take it off the list.
            if ($migration_status != MigrationInterface::RESULT_INCOMPLETE) {
                array_shift($context['sandbox']['migration_ids']);
                $context['sandbox']['current']++;
            }
            // Add and log any captured messages.
            foreach (static::$messages->getMessages() as $message) {
                $context['sandbox']['messages'][] = (string) $message;
                \Drupal::logger('migrate_drupal_ui')->error($message);
            }
            // Only display the last MESSAGE_LENGTH messages, in reverse order.
            $message_count = count($context['sandbox']['messages']);
            $context['message'] = '';
            for ($index = max(0, $message_count - self::MESSAGE_LENGTH); $index < $message_count; $index++) {
                $context['message'] = $context['sandbox']['messages'][$index] . "<br />\n" . $context['message'];
            }
            if ($message_count > self::MESSAGE_LENGTH) {
                // Indicate there are earlier messages not displayed.
                $context['message'] .= '&hellip;';
            }
            // At the top of the list, display the next one (which will be the one
            // that is running while this message is visible).
            if (!empty($context['sandbox']['migration_ids'])) {
                $migration_id = reset($context['sandbox']['migration_ids']);
                $migration = \Drupal::service('plugin.manager.migration')->createInstance($migration_id);
                $migration_name = $migration->label() ? $migration->label() : $migration_id;
                $context['message'] = (string) new TranslatableMarkup('Currently upgrading @migration (@current of @max total tasks)', [
                    '@migration' => $migration_name,
                    '@current' => $context['sandbox']['current'],
                    '@max' => $context['sandbox']['max'],
                ]) . "<br />\n" . $context['message'];
            }
        }
        else {
            array_shift($context['sandbox']['migration_ids']);
            $context['sandbox']['current']++;
        }
        $context['finished'] = 1 - count($context['sandbox']['migration_ids']) / $context['sandbox']['max'];
    }
    
    /**
     * Callback executed when the Migrate Upgrade Import batch process completes.
     *
     * @param bool $success
     *   TRUE if batch successfully completed.
     * @param array $results
     *   Batch results.
     * @param array $operations
     *   An array of methods run in the batch.
     * @param string $elapsed
     *   The time to run the batch.
     */
    public static function finished($success, $results, $operations, $elapsed) {
        $successes = $results['successes'];
        $failures = $results['failures'];
        // If we had any successes log that for the user.
        if ($successes > 0) {
            \Drupal::messenger()->addStatus(\Drupal::translation()->formatPlural($successes, 'Completed 1 upgrade task successfully', 'Completed @count upgrade tasks successfully'));
        }
        // If we had failures, log them and show the migration failed.
        if ($failures > 0) {
            \Drupal::messenger()->addError(\Drupal::translation()->formatPlural($failures, '1 upgrade failed', '@count upgrades failed'));
            \Drupal::messenger()->addError(t('Upgrade process not completed'));
        }
        else {
            // Everything went off without a hitch. We may not have had successes
            // but we didn't have failures so this is fine.
            \Drupal::messenger()->addStatus(t('Congratulations, you upgraded Drupal!'));
        }
        if (\Drupal::moduleHandler()->moduleExists('dblog')) {
            $url = Url::fromRoute('migrate_drupal_ui.log');
            \Drupal::messenger()->addMessage(Link::fromTextAndUrl(new TranslatableMarkup('Review the detailed upgrade log'), $url), $failures ? 'error' : 'status');
        }
    }
    
    /**
     * Reacts to item import.
     *
     * @param \Drupal\migrate\Event\MigratePostRowSaveEvent $event
     *   The post-save event.
     */
    public static function onPostRowSave(MigratePostRowSaveEvent $event) {
        // We want to interrupt this batch and start a fresh one.
        if (time() - REQUEST_TIME > static::$maxExecTime) {
            $event->getMigration()
                ->interruptMigration(MigrationInterface::RESULT_INCOMPLETE);
        }
    }
    
    /**
     * Adds follow-up migrations.
     *
     * @param \Drupal\migrate\Event\MigrateImportEvent $event
     *   The import event.
     */
    public static function onPostImport(MigrateImportEvent $event) {
        $migration = $event->getMigration();
        if ($migration instanceof MigrationWithFollowUpInterface) {
            // After the migration on which they depend has been successfully
            // executed, the follow-up migrations are immediately added to the batch
            // and removed from the $followUpMigrations property. This means that the
            // $followUpMigrations property is always empty at this point and it's OK
            // to override it with the next follow-up migrations.
            static::$followUpMigrations = $migration->generateFollowUpMigrations();
        }
    }
    
    /**
     * Reacts to item deletion.
     *
     * @param \Drupal\migrate\Event\MigrateRowDeleteEvent $event
     *   The post-save event.
     */
    public static function onPostRowDelete(MigrateRowDeleteEvent $event) {
        // We want to interrupt this batch and start a fresh one.
        if (time() - REQUEST_TIME > static::$maxExecTime) {
            $event->getMigration()
                ->interruptMigration(MigrationInterface::RESULT_INCOMPLETE);
        }
    }
    
    /**
     * Counts up any map save events.
     *
     * @param \Drupal\migrate\Event\MigrateMapSaveEvent $event
     *   The map event.
     */
    public static function onMapSave(MigrateMapSaveEvent $event) {
        static::$numProcessed++;
    }
    
    /**
     * Counts up any map delete events.
     *
     * @param \Drupal\migrate\Event\MigrateMapDeleteEvent $event
     *   The map event.
     */
    public static function onMapDelete(MigrateMapDeleteEvent $event) {
        static::$numProcessed++;
    }
    
    /**
     * Displays any messages being logged to the ID map.
     *
     * @param \Drupal\migrate\Event\MigrateIdMapMessageEvent $event
     *   The message event.
     */
    public static function onIdMapMessage(MigrateIdMapMessageEvent $event) {
        if ($event->getLevel() == MigrationInterface::MESSAGE_NOTICE || $event->getLevel() == MigrationInterface::MESSAGE_INFORMATIONAL) {
            $type = 'status';
        }
        else {
            $type = 'error';
        }
        $source_id_string = implode(',', $event->getSourceIdValues());
        $message = t('Source ID @source_id: @message', [
            '@source_id' => $source_id_string,
            '@message' => $event->getMessage(),
        ]);
        static::$messages->display($message, $type);
    }

}