fix(blurhash): Use preview API to generate the previews

This allows to benefit from all the checks done by the preview API.
This also use 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, 64, 64, 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
 	 *