Trait is closer to what caldav servers provide

src/item.rs

@@ -7,6 +7,8 @@ use url::Url;
 
 use crate::resource::Resource;
 
+
+
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub enum Item {
     Event(crate::event::Event),
@@ -35,6 +37,13 @@ impl Item {
         }
     }
 
+    pub fn version_tag(&self) -> &VersionTag {
+        match self {
+            Item::Event(e) => e.version_tag(),
+            Item::Task(t) => t.version_tag(),
+        }
+    }
+
     pub fn is_event(&self) -> bool {
         match &self {
             Item::Event(_) => true,
@@ -109,3 +118,24 @@ impl Display for ItemId {
         write!(f, "{}", self.content)
     }
 }
+
+
+/// A VersionTag is basically a CalDAV `ctag` or `etag`. Whenever it changes, this means the data has changed.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct VersionTag {
+    tag: String
+}
+
+impl From<String> for VersionTag {
+    fn from(tag: String) -> VersionTag {
+        Self { tag }
+    }
+}
+
+impl VersionTag {
+    /// Generate a random VesionTag. This is only useful in tests
+    pub fn random() -> Self {
+        let random = uuid::Uuid::new_v4().to_hyphenated().to_string();
+        Self { tag: random }
+    }
+}