user_settings: Extract setting values checks to a function.

We extract the checks for default_language, notification_sound,
and email_notifications_batching_period_seconds setting values
in json_change_settings to a new function check_settings_values.

zerver/lib/validator.py

@@ -582,3 +582,36 @@ def check_string_or_int(var_name: str, val: object) -> Union[str, int]:
         return val
 
     raise ValidationError(_("{var_name} is not a string or integer").format(var_name=var_name))
+
+
+def check_settings_values(
+    notification_sound: Optional[str],
+    email_notifications_batching_period_seconds: Optional[int],
+    default_language: Optional[str],
+) -> None:
+    from zerver.lib.actions import get_available_notification_sounds
+    from zerver.lib.i18n import get_available_language_codes
+
+    # We can't use REQ for this widget because
+    # get_available_language_codes requires provisioning to be
+    # complete.
+    if default_language is not None and default_language not in get_available_language_codes():
+        raise JsonableError(_("Invalid default_language"))
+
+    if (
+        notification_sound is not None
+        and notification_sound not in get_available_notification_sounds()
+        and notification_sound != "none"
+    ):
+        raise JsonableError(_("Invalid notification sound '{}'").format(notification_sound))
+
+    if email_notifications_batching_period_seconds is not None and (
+        email_notifications_batching_period_seconds <= 0
+        or email_notifications_batching_period_seconds > 7 * 24 * 60 * 60
+    ):
+        # We set a limit of one week for the batching period
+        raise JsonableError(
+            _("Invalid email batching period: {} seconds").format(
+                email_notifications_batching_period_seconds
+            )
+        )