Generating SilverStripe 3 assets in SilverStripe 4 for testing File migration

GenerateSS3Assets.php

<?php

use GuzzleHttp\Psr7\StreamWrapper;
use Intervention\Image\AbstractFont;
use Intervention\Image\AbstractShape;
use Intervention\Image\ImageManager;
use SilverStripe\Assets\FilenameParsing\FileIDHelperResolutionStrategy;
use SilverStripe\Assets\FilenameParsing\LegacyFileIDHelper;
use SilverStripe\Assets\Flysystem\FlysystemAssetStore;
use SilverStripe\Assets\Image;
use SilverStripe\Assets\InterventionBackend;
use SilverStripe\Assets\Storage\AssetStore;
use SilverStripe\Core\Environment;
use SilverStripe\Core\Injector\Injector;
use SilverStripe\Dev\BuildTask;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\FieldType\DBText;
use SilverStripe\ORM\Queries\SQLUpdate;


class GenerateSS3Assets extends BuildTask
{

    private static $segment = 'gen-ss3-asset';

    public function run($request)
    {
        Environment::increaseTimeLimitTo();
        Environment::increaseMemoryLimitTo();

        /** @var FlysystemAssetStore $store */
        $store = Injector::inst()->get(AssetStore::class);
        $legacyStrategy = new FileIDHelperResolutionStrategy();
        $legacyStrategy->setDefaultFileIDHelper(new LegacyFileIDHelper());
        $legacyStrategy->setResolutionFileIDHelpers([new LegacyFileIDHelper()]);
        $store->setPublicResolutionStrategy($legacyStrategy);

        DB::get_schema()->schemaUpdate( function() {
            DB::quiet();
            $ss3DBField = new DBText('Filename');
            $ss3DBField->setTable('File');
            $ss3DBField->requireField();
        });

        for ($i = 0; $i < 500; $i++) {
            $imgData = $this->generateImage('Live', "generated/test-image-$i.jpg", 1);
            $jpg = $imgData->stream('jpg');
            $stream = StreamWrapper::getResource($jpg);
            $file = new Image();
            $file->setFromStream($stream, "generated/test-image-$i.jpg", null, null, ['visibility' => AssetStore::VISIBILITY_PUBLIC]);
            $file->write();

            $file->CMSThumbnail();
            $file->PreviewThumbnail();

            SQLUpdate::create(
                'File',
                [
                    'FileFilename' => null,
                    'FileHash' => null,
                    'Filename' => "assets/generated/test-image-$i.jpg"
                ],
                ['ID' => $file->ID]
            )->execute();

            fclose($stream);
            $imgData->destroy();
            InterventionBackend::flush();

            echo "generated/test-image-$i.jpg\n";
        }
    }

    /**
     * Generate a placeholder image
     * @param string $targetedStage
     * @param string $filename
     * @param float $f
     * @return \Intervention\Image\Image
     */
    private function generateImage($targetedStage, $filename, $f=1.0)
    {
        /** @var ImageManager $imageManager */
        $imageManager = Injector::inst()->create(ImageManager::class);
        return $imageManager
            ->canvas(400*$f, 300*$f, '#142237')
            ->text($targetedStage, 20*$f, 170*$f, function (AbstractFont $font) use ($f) {
                $font->file(__DIR__ . '/../fonts/ZillaSlab-SemiBold.ttf');
                $font->size(36*$f);
                $font->color('#44C8F5');
            })->text($filename, 20*$f, 195*$f, function (AbstractFont $font) use ($f) {
                $font->file(__DIR__ . '/../fonts/ZillaSlab-Regular.ttf');
                $font->size(20*$f);
                $font->color('#ffffff');
            })->rectangle(20*$f, 210*$f, 100*$f, 212*$f, function (AbstractShape $shape) {
                $shape->background('#DA1052');
            });
    }

}