Don't query user settings unnecessarily

lib/UserSettings.php

@@ -71,6 +71,10 @@ public function getUserSetting($user, $method, $type) {
 		}
 
 		$defaultSetting = $this->getDefaultFromSetting($method, $type);
+		if (!$this->canModifySetting($method, $type)) {
+			return $defaultSetting;
+		}
+
 		if (is_bool($defaultSetting)) {
 			return (bool) $this->config->getUserValue(
 				$user,
@@ -149,12 +153,39 @@ protected function getDefaultFromSetting($method, $type) {
 		}
 	}
 
+	/**
+	 * Get a good default setting for a preference
+	 *
+	 * @param string $method Should be one of 'stream', 'email' or 'setting'
+	 * @param string $type One of the activity types, 'batchtime', 'self' or 'selfemail'
+	 * @return bool
+	 */
+	protected function canModifySetting($method, $type) {
+		if ($method === 'setting') {
+			return true;
+		}
+
+		try {
+			$setting = $this->manager->getSettingById($type);
+			switch ($method) {
+				case 'email':
+					return $setting->canChangeMail();
+				case 'notification':
+					return $setting->canChangeNotification();
+				default:
+					return false;
+			}
+		} catch (\InvalidArgumentException $e) {
+			return false;
+		}
+	}
+
 	/**
 	 * Get a list with all notification types
 	 */
 	public function getNotificationTypes() {
 		$settings = $this->manager->getSettings();
-		
+
 		$return = array_map(function (ActivitySettings $setting) {
 			return $setting->getIdentifier();
 		}, $settings);