From b46550e2bac461563aa61b73d47bba69df41ef96 Mon Sep 17 00:00:00 2001
From: Frank Karlitschek <karlitschek@users.noreply.github.com>
Date: Sat, 2 May 2026 19:51:50 +0200
Subject: [PATCH] feat(digest): inline file thumbnails in the daily activity
 digest email
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The daily activity digest currently lists each event with the
provider's small icon URL. For file-related events that's a generic
mime-type icon, which makes the digest feel like a server log rather
than a "things that happened to your stuff today" summary. Show the
actual file preview instead, when one is available.

`DigestSender::getPreviewDataUri()` resolves the file as the affected
user (so access mirrors what the recipient sees in the web UI),
generates a 96×96 preview via `IPreview`, and returns a base64 data
URI inlined directly into the email — no public preview endpoint
needed, and the digest renders fully offline.

Returns null on any failure (not a file event, file deleted, no read
permission, preview generation unsupported, anything thrown). The
existing `$event->getIcon()` is the seamless fallback, so existing
behaviour is preserved for non-file or no-preview events.

The 96px cap keeps each thumbnail around 3-5 KB; even at the 20-event
ACTIVITY_LIMIT the digest stays well under common message-size
thresholds.

`IRootFolder` and `IPreview` are auto-wired through standard DI;
`DigestSender` is not explicitly registered in `Application.php`,
so no AppInfo change is needed.

Signed-off-by: Frank Karlitschek <frank@nextcloud.com>
---
 lib/DigestSender.php | 62 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/lib/DigestSender.php b/lib/DigestSender.php
index 0dfe4d380..39d2339c2 100644
--- a/lib/DigestSender.php
+++ b/lib/DigestSender.php
@@ -11,8 +11,13 @@
 use OCP\Activity\IEvent;
 use OCP\Activity\IManager;
 use OCP\Defaults;
+use OCP\Files\File;
+use OCP\Files\IRootFolder;
+use OCP\Files\NotFoundException;
+use OCP\Files\NotPermittedException;
 use OCP\IConfig;
 use OCP\IDateTimeFormatter;
+use OCP\IPreview;
 use OCP\IURLGenerator;
 use OCP\IUser;
 use OCP\IUserManager;
@@ -24,6 +29,14 @@
 class DigestSender {
 	public const ACTIVITY_LIMIT = 20;
 
+	/**
+	 * Maximum size in pixels for embedded preview thumbnails. Kept small so that
+	 * the resulting base64-encoded payload doesn't bloat the email — a 96px PNG
+	 * is typically a few KB, and 20 of them stay well under common message-size
+	 * limits.
+	 */
+	private const PREVIEW_PIXELS = 96;
+
 	public function __construct(
 		private IConfig $config,
 		private Data $data,
@@ -37,6 +50,8 @@ public function __construct(
 		private IFactory $l10nFactory,
 		private IDateTimeFormatter $dateTimeFormatter,
 		private LoggerInterface $logger,
+		private IRootFolder $rootFolder,
+		private IPreview $previewManager,
 	) {
 	}
 
@@ -181,7 +196,8 @@ public function sendDigestForUser(IUser $user, int $now, string $timezone, strin
 				$l10n
 			);
 
-			$template->addBodyListItem($this->getHTMLSubject($event), $relativeDateTime, $event->getIcon(), $event->getParsedSubject());
+			$icon = $this->getPreviewDataUri($event, $uid) ?? $event->getIcon();
+			$template->addBodyListItem($this->getHTMLSubject($event), $relativeDateTime, $icon, $event->getParsedSubject());
 		}
 
 		if ($skippedCount) {
@@ -215,6 +231,50 @@ public function sendDigestForUser(IUser $user, int $now, string $timezone, strin
 		}
 	}
 
+	/**
+	 * Returns a data: URI with a base64-encoded PNG preview of the file the
+	 * activity is about, or null if no preview is available — for any reason
+	 * (not a file event, file deleted, no read permission, preview generation
+	 * unsupported, etc.). The caller falls back to the regular event icon.
+	 *
+	 * Resolved as the affected user, so the resulting access mirrors what the
+	 * recipient could see in the web UI.
+	 */
+	private function getPreviewDataUri(IEvent $event, string $uid): ?string {
+		if ($event->getObjectType() !== 'files' || $event->getObjectId() <= 0) {
+			return null;
+		}
+
+		try {
+			$userFolder = $this->rootFolder->getUserFolder($uid);
+			$node = $userFolder->getFirstNodeById($event->getObjectId());
+			if (!$node instanceof File) {
+				return null;
+			}
+
+			if (!$this->previewManager->isAvailable($node)) {
+				return null;
+			}
+
+			$preview = $this->previewManager->getPreview($node, self::PREVIEW_PIXELS, self::PREVIEW_PIXELS, true);
+			$content = $preview->getContent();
+			if ($content === '') {
+				return null;
+			}
+			$mime = $preview->getMimeType() ?: 'image/png';
+			return 'data:' . $mime . ';base64,' . base64_encode($content);
+		} catch (NotFoundException|NotPermittedException) {
+			return null;
+		} catch (\Throwable $e) {
+			$this->logger->debug('Could not generate digest preview', [
+				'app' => 'activity',
+				'exception' => $e,
+				'object_id' => $event->getObjectId(),
+			]);
+			return null;
+		}
+	}
+
 	/**
 	 * @param IEvent $event
 	 * @return string