API Add extension points to MigrateFileTask (#8994)

* API Add extension points to MigrateFileTask

* Apply suggestions from code review

Co-Authored-By: Guy Marriott <guy@scopey.co.nz>

docs/en/02_Developer_Guides/14_Files/05_File_Migration.md

@@ -55,7 +55,7 @@ but will no longer be attached to a dataobject anymore, and should be cleaned up
 To disable this, set the following config:
 
 ```yaml
-SilverStripe\Assets\FileMigrationHelper:
+SilverStripe\Assets\Dev\Tasks\FileMigrationHelper:
   delete_invalid_files: false
 ```
 
@@ -113,3 +113,71 @@ Use the following estimates to decide how you will run your file migration:
 | 10000+ | Command Line or contact support | n/a | n/a |
 
 Your exact experience will vary based on your host server, the size of your files and other conditions. If your site is hosted on a managed environement (e.g.: [Common Web Platform](https://www.cwp.govt.nz/service-desk) or [SilverStripe Platform](https://docs.platform.silverstripe.com/support/)), you may not have access to the command line to manually run the migration task. Contact your hosting provider's helpdesk if that's your case.
+
+## Customise the File Migration Task (Advanced)
+
+In some context, you may want to disable some other process when the file migration is running. For example, if you have a module that indexes files when they get modified, you'll probably want to wait until the file migration is done to reindex.
+
+The `MigrateFileTask` exposes 4 extension point that can be use to detect the progress of the migration.
+* `preFileMigration` that gets fired at the start of the task
+* `postFileMigration` that gets fired at the end of the task
+* `preFileMigrationSubtask`  that gets fired at the start of each subtasks
+* `postFileMigrationSubtask` that gets fired at the end of each subtasks.
+
+`preFileMigrationSubtask` and `postFileMigrationSubtask` will provide a single string parameter matching the name of the subtask (e.g.: `move-files`)
+
+### Example migrate file task extension
+```php
+<?php
+
+use Psr\Log\LoggerInterface;
+use SilverStripe\Core\Extension;
+
+class MigrateFileTaskExtension extends Extension
+{
+
+    private static $dependencies = [
+        'logger' => '%$' . LoggerInterface::class . '.quiet',
+    ];
+
+    /** @var LoggerInterface */
+    private $logger;
+
+    /**
+     * @param LoggerInterface $logger
+     */
+    public function setLogger(LoggerInterface $logger)
+    {
+        $this->logger = $logger;
+    }
+
+    public function preFileMigration()
+    {
+        $this->logger->info('Run some extension code BEFORE the Migrate File Task');
+    }
+
+    public function postFileMigration()
+    {
+        $this->logger->info('Run some extension code AFTER the Migrate File Task');
+    }
+
+    public function preFileMigrationSubtask($subtaskName)
+    {
+        $this->logger->info(sprintf('Run some extension code BEFORE the %s subtask', $subtaskName));
+    }
+
+    public function postFileMigrationSubtask($subtaskName)
+    {
+        $this->logger->info(sprintf('Run some extension code AFTER the %s subtask', $subtaskName));
+    }
+
+}
+```
+
+Add the following snippet to your YML config to enable the extension.
+
+```yaml
+SilverStripe\Dev\Tasks\MigrateFileTask:
+  extensions:
+    - MigrateFileTaskExtension
+```

src/Dev/Tasks/MigrateFileTask.php

@@ -46,85 +46,102 @@ class MigrateFileTask extends BuildTask
         $args = $request->getVars();
         $this->validateArgs($args);
 
+        $this->extend('preFileMigration');
+
         $subtasks = !empty($args['only']) ? explode(',', $args['only']) : $this->defaultSubtasks;
 
-        if (in_array('move-files', $subtasks)) {
+        $subtask = 'move-files';
+        if (in_array($subtask, $subtasks)) {
             if (!class_exists(FileMigrationHelper::class)) {
                 $this->logger->error("No file migration helper detected");
-                return;
-            }
-
-            $this->logger->info('### Migrating filesystem and database records (move-files)');
-
-            $this->logger->info('If the task fails or times out, run it again and it will start where it left off.');
-
-            $migrated = FileMigrationHelper::singleton()->run();
-            if ($migrated) {
-                $this->logger->info("{$migrated} File DataObjects upgraded");
             } else {
-                $this->logger->info("No File DataObjects need upgrading");
+                $this->extend('preFileMigrationSubtask', $subtask);
+                $this->logger->info("### Migrating filesystem and database records ({$subtask})");
+                $this->logger->info('If the task fails or times out, run it again and it will start where it left off.');
+
+                $migrated = FileMigrationHelper::singleton()->run();
+                if ($migrated) {
+                    $this->logger->info("{$migrated} File DataObjects upgraded");
+                } else {
+                    $this->logger->info("No File DataObjects need upgrading");
+                }
+                $this->extend('postFileMigrationSubtask', $subtask);
             }
         }
 
-        if (in_array('move-thumbnails', $subtasks)) {
+        $subtask = 'move-thumbnails';
+        if (in_array($subtask, $subtasks)) {
             if (!class_exists(LegacyThumbnailMigrationHelper::class)) {
                 $this->logger->error("LegacyThumbnailMigrationHelper not found");
-                return;
-            }
-
-            $this->logger->info('### Migrating existing thumbnails (move-thumbnails)');
-
-            $moved = LegacyThumbnailMigrationHelper::singleton()
-                ->setLogger($this->logger)
-                ->run($this->getStore());
-
-            if ($moved) {
-                $this->logger->info(sprintf("%d thumbnails moved", count($moved)));
             } else {
-                $this->logger->info("No thumbnails moved");
+                $this->extend('preFileMigrationSubtask', $subtask);
+                $this->logger->info("### Migrating existing thumbnails ({$subtask})");
+
+                $moved = LegacyThumbnailMigrationHelper::singleton()
+                    ->setLogger($this->logger)
+                    ->run($this->getStore());
+
+                if ($moved) {
+                    $this->logger->info(sprintf("%d thumbnails moved", count($moved)));
+                } else {
+                    $this->logger->info("No thumbnails moved");
+                }
+
+                $this->extend('postFileMigrationSubtask', $subtask);
             }
         }
 
-        if (in_array('generate-cms-thumbnails', $subtasks)) {
+        $subtask = 'generate-cms-thumbnails';
+        if (in_array($subtask, $subtasks)) {
             if (!class_exists(ImageThumbnailHelper::class)) {
                 $this->logger->error("ImageThumbnailHelper not found");
-                return;
+            } else {
+                $this->extend('preFileMigrationSubtask', $subtask);
+                $this->logger->info("### Generating new CMS UI thumbnails ({$subtask})");
+                ImageThumbnailHelper::singleton()->run();
+                $this->extend('postFileMigrationSubtask', $subtask);
             }
 
-            $this->logger->info('### Generating new CMS UI thumbnails (generate-cms-thumbnails)');
 
-            ImageThumbnailHelper::singleton()->run();
         }
 
-        if (in_array('fix-folder-permissions', $subtasks)) {
+        $subtask = 'fix-folder-permissions';
+        if (in_array($subtask, $subtasks)) {
             if (!class_exists(FixFolderPermissionsHelper::class)) {
                 $this->logger->error("FixFolderPermissionsHelper not found");
-                return;
-            }
-
-            $this->logger->info('### Fixing folder permissions (fix-folder-permissions)');
-
-            $updated = FixFolderPermissionsHelper::singleton()->run();
-
-            if ($updated > 0) {
-                $this->logger->info("Repaired {$updated} folders with broken CanViewType settings");
             } else {
-                $this->logger->info("No folders required fixes");
+                $this->extend('preFileMigrationSubtask', $subtask);
+
+                $this->logger->info("### Fixing folder permissions ({$subtask})");
+                $updated = FixFolderPermissionsHelper::singleton()->run();
+
+                if ($updated > 0) {
+                    $this->logger->info("Repaired {$updated} folders with broken CanViewType settings");
+                } else {
+                    $this->logger->info("No folders required fixes");
+                }
+
+                $this->extend('postFileMigrationSubtask', $subtask);
             }
         }
 
-        if (in_array('fix-secureassets', $subtasks)) {
+        $subtask = 'fix-secureassets';
+        if (in_array($subtask, $subtasks)) {
             if (!class_exists(SecureAssetsMigrationHelper::class)) {
                 $this->logger->error("SecureAssetsMigrationHelper not found");
-                return;
+            } else {
+                $this->extend('preFileMigrationSubtask', $subtask);
+
+                $this->logger->info("### Fixing secure-assets ({$subtask})");
+                $moved = SecureAssetsMigrationHelper::singleton()
+                    ->setLogger($this->logger)
+                    ->run($this->getStore());
+
+                $this->extend('postFileMigrationSubtask', $subtask);
             }
-
-            $this->logger->info('### Fixing secure-assets (fix-secureassets)');
-
-            $moved = SecureAssetsMigrationHelper::singleton()
-                ->setLogger($this->logger)
-                ->run($this->getStore());
         }
+
+        $this->extend('postFileMigration');
     }
 
     public function getDescription()