Better API for last sync timestamp

src/traits.rs

@@ -2,6 +2,7 @@ use std::error::Error;
 
 use async_trait::async_trait;
 use url::Url;
+use chrono::{DateTime, Utc};
 
 use crate::Calendar;
 
@@ -25,3 +26,11 @@ pub trait CalDavSource {
     async fn get_calendar_mut(&mut self, url: Url) -> Option<&mut Calendar>;
 
 }
+
+pub trait SyncSlave {
+    /// Returns the last time this source successfully synced from a master source (e.g. from a server)
+    /// (or None in case it has never been synchronized)
+    fn get_last_sync(&self) -> Option<DateTime<Utc>>;
+    /// Update the last sync timestamp to now, or to a custom time in case `timepoint` is `Some`
+    fn update_last_sync(&mut self, timepoint: Option<DateTime<Utc>>);
+}