fix: Use preview API to generate the previews

This allows to benefit from all the check done by the API.
This also used the newly introduced cacheResult argument to limit disk usage.

Signed-off-by: Louis Chemineau <louis@chmn.me>

Author: artonge

lib/private/Blurhash/Listener/GenerateBlurhashMetadata.php

@@ -19,6 +19,7 @@
 use OCP\FilesMetadata\AMetadataEvent;
 use OCP\FilesMetadata\Event\MetadataBackgroundEvent;
 use OCP\FilesMetadata\Event\MetadataLiveEvent;
+use OCP\IPreview;
 use OCP\Lock\LockedException;
 
 /**
@@ -32,6 +33,11 @@ class GenerateBlurhashMetadata implements IEventListener {
 	private const COMPONENTS_X = 4;
 	private const COMPONENTS_Y = 3;
 
+	public function __construct(
+		private IPreview $preview,
+	) {
+	}
+
 	/**
 	 * @throws NotPermittedException
 	 * @throws GenericFileException
@@ -64,7 +70,9 @@ public function handle(Event $event): void {
 			return;
 		}
 
-		$image = $this->resizedImageFromFile($file);
+		$preview = $this->preview->getPreview($file, 256, 256, cacheResult: false);
+		$image = @imagecreatefromstring($preview->getContent());
+
 		if (!$image) {
 			return;
 		}
@@ -73,35 +81,6 @@ public function handle(Event $event): void {
 			->setEtag('blurhash', $currentEtag);
 	}
 
-	/**
-	 * @param File $file
-	 *
-	 * @return GdImage|false
-	 * @throws GenericFileException
-	 * @throws NotPermittedException
-	 * @throws LockedException
-	 */
-	private function resizedImageFromFile(File $file): GdImage|false {
-		$image = @imagecreatefromstring($file->getContent());
-		if ($image === false) {
-			return false;
-		}
-
-		$currX = imagesx($image);
-		$currY = imagesy($image);
-
-		if ($currX > $currY) {
-			$newX = self::RESIZE_BOXSIZE;
-			$newY = intval($currY * $newX / $currX);
-		} else {
-			$newY = self::RESIZE_BOXSIZE;
-			$newX = intval($currX * $newY / $currY);
-		}
-
-		$newImage = @imagescale($image, $newX, $newY);
-		return ($newImage !== false) ? $newImage : $image;
-	}
-
 	/**
 	 * @param GdImage $image
 	 *