Storage limit: 80% warning and limit in the web interface

- after each successful backup the stored size is recorded; at 80% of a
  location's limit administrators get a notification (once a day)
- locations list shows stored size and limit; the add form has a
  'maximum size' field that explains that empty means unlimited and
  billed by the provider; PUT /api/targets/{id}/limit (password
  confirmation)

Tested on NC34 with the OVH test bucket: a backup above the limit stops,
a successful one at 81% sends the warning.

lib/Controller/AdminApiController.php

@@ -55,7 +55,8 @@ class AdminApiController extends Controller {
 		$targets = [];
 		foreach ($this->targets->list() as $t) {
 			$targets[] = ['id' => $t->getId(), 'name' => $t->getName(), 'backend' => $t->getBackend(), 'path' => $t->getBasePath(),
-				'repositoryId' => $t->getRepositoryId(), 'createdAt' => $t->getCreatedAt()];
+				'repositoryId' => $t->getRepositoryId(), 'createdAt' => $t->getCreatedAt(), 'appendOnly' => (bool)$t->getAppendOnly(),
+				'maxBytes' => $t->getMaxBytes(), 'storedBytes' => $this->alerts->lastStoredBytes($t)];
 		}
 		$runs = array_map(fn (Run $r) => $this->runJson($r), $this->runs->findRecent(15));
 		return new JSONResponse([
@@ -167,15 +168,25 @@ class AdminApiController extends Controller {
 		return new JSONResponse($this->targets->availableBackends());
 	}
 
-	public function addTarget(string $name, string $backend, string $auth, array $options = [], string $path = 'ng_backup'): JSONResponse {
+	public function addTarget(string $name, string $backend, string $auth, array $options = [], string $path = 'ng_backup', ?float $maxGb = null): JSONResponse {
 		try {
 			$r = $this->targets->add($name, $backend, $auth, $options, $path);
+			if ($maxGb !== null && $maxGb > 0) {
+				$this->targets->setMaxBytes($r['target'], (int)round($maxGb * 1073741824));
+			}
 		} catch (\Throwable $e) {
 			return new JSONResponse(['error' => $e->getMessage()], Http::STATUS_BAD_REQUEST);
 		}
 		return new JSONResponse(['id' => $r['target']->getId(), 'created' => $r['created']]);
 	}
 
+	/** Size limit in GiB; null or 0 = unlimited. */
+	#[PasswordConfirmationRequired]
+	public function setTargetLimit(int $id, ?float $maxGb = null): JSONResponse {
+		$t = $this->targets->setMaxBytes($this->targets->get((string)$id), ($maxGb !== null && $maxGb > 0) ? (int)round($maxGb * 1073741824) : null);
+		return new JSONResponse(['maxBytes' => $t->getMaxBytes()]);
+	}
+
 	#[PasswordConfirmationRequired]
 	public function removeTarget(int $id): JSONResponse {
 		$target = $this->targets->get((string)$id);

lib/Notification/Notifier.php

@@ -42,6 +42,10 @@ class Notifier implements INotifier {
 					: $l->t('Backup to %s failed', [$p['target']]));
 				$notification->setParsedMessage((string)($p['error'] ?? ''));
 				break;
+			case 'quota_warning':
+				$notification->setParsedSubject($l->t('Backup location %1$s is at %2$s%% of its limit (%3$s of %4$s)', [$p['target'], $p['percent'], $p['used'], $p['limit']]));
+				$notification->setParsedMessage($l->t('Backups stop when the limit is reached. Raise the limit, or let the retention policy remove older backups.'));
+				break;
 			case 'backup_stale':
 				$notification->setParsedSubject($l->t('No successful backup to %1$s since %2$s', [$p['target'], $p['since']]));
 				$notification->setParsedMessage($l->t('Check the backup settings and the server log.'));

lib/Service/AlertService.php

@@ -54,6 +54,36 @@ class AlertService {
 			['kind' => $run->getKind(), 'target' => $targetName, 'error' => mb_strimwidth((string)$run->getError(), 0, 300, '…')]);
 	}
 
+	/**
+	 * Remember how much is stored on a location (for the settings page) and warn administrators
+	 * once a day when it is at 80% of its limit or more.
+	 */
+	public function storedBytes(Target $target, int $bytes): void {
+		$this->appConfig->setValueString(Application::APP_ID, 'stored_' . $target->getId(), (string)$bytes);
+		$limit = $target->getMaxBytes();
+		if ($limit === null || $limit <= 0 || $bytes < 0.8 * $limit) {
+			return;
+		}
+		$key = 'quota_notified_' . $target->getId();
+		if ($this->appConfig->getValueString(Application::APP_ID, $key, '') === date('Y-m-d')) {
+			return;
+		}
+		$this->appConfig->setValueString(Application::APP_ID, $key, date('Y-m-d'));
+		$this->notifyAdmins('quota_warning', 'quota-' . $target->getId() . '-' . date('Y-m-d'), [
+			'target' => $target->getName(), 'percent' => (string)round($bytes / $limit * 100),
+			'used' => self::gib($bytes), 'limit' => self::gib($limit)]);
+	}
+
+	private static function gib(int $bytes): string {
+		$g = $bytes / 1073741824;
+		return sprintf($g < 10 ? '%.2f GiB' : '%.1f GiB', $g);
+	}
+
+	public function lastStoredBytes(Target $target): ?int {
+		$v = $this->appConfig->getValueString(Application::APP_ID, 'stored_' . $target->getId(), '');
+		return $v === '' ? null : (int)$v;
+	}
+
 	/** At most one notification per location per day. */
 	public function checkStale(Target $target): void {
 		$last = $this->runs->lastFinished($target->getId(), BackupService::KIND_FULL);

lib/Service/BackupService.php

@@ -149,6 +149,7 @@ class BackupService {
 				$state['files'] = BackupRun::step($repo, $state['files'], $deadline);
 				if ($state['files']['phase'] === 'done') {
 					$this->recordSnapshot($run, $state['files']);
+					$this->alerts->storedBytes($target, $repo->storedBytes());
 					$run->setStatus(Run::DONE);
 					$run->setPhase('done');
 					$run->setFinishedAt(time());