NKDB: UpdateHandler: add method to know if we can upgrade from an epoch

lektor_nkdb/src/database/epoch.rs

@@ -17,14 +17,20 @@ pub struct Epoch {
 
 /// Represent the data contained in an epoch.
 pub type EpochData = HashMap<KId, Kara>;
-pub struct EpochInfos(u64, u64);
+pub struct EpochInfos {
+    pub id: u64,
+    pub validity: u64,
+}
 
 /// Represent the keys of the epoch data, e.g. the ids of the kara in this epoch.
 pub type EpochIds<'a> = hash_map::Keys<'a, KId, Kara>;
 
 impl From<kurisu_api::v2::Infos> for EpochInfos {
     fn from(infos: kurisu_api::v2::Infos) -> Self {
-        Self(infos.epoch(), infos.epoch_validity())
+        Self {
+            id: infos.epoch(),
+            validity: infos.epoch_validity(),
+        }
     }
 }
 
@@ -101,6 +107,11 @@ impl Epoch {
         self.id
     }
 
+    /// Get the validity (version) of the epoch
+    pub fn validity(&self) -> u64 {
+        self.validity
+    }
+
     /// Get the number of karas in the epoch.
     pub fn len(&self) -> usize {
         self.data.len()
@@ -112,7 +123,7 @@ impl Epoch {
     }
 
     pub fn set_infos(&mut self, infos: EpochInfos) {
-        self.id = infos.0;
-        self.validity = infos.1;
+        self.id = infos.id;
+        self.validity = infos.validity;
     }
 }

lektor_nkdb/src/database/update.rs

@@ -44,6 +44,19 @@ impl<'a, Storage: DatabaseStorage> UpdateHandler<'a, Storage> {
         }
     }
 
+    /// If the epoch is updatable from using the repository described at infos,
+    /// then return Some(from), where from is the epoch to start updating from
+    /// (= the epoch id of last_epoch)
+    pub async fn recoverable_since(&self, infos: EpochInfos) -> Option<u64> {
+        match self.last_epoch {
+            None => None,
+            Some(last) if last.validity() != infos.validity => None,
+            Some(last) if last.num() < infos.id => Some(last.num()),
+            _ => None,
+        }
+    }
+
+    /// Set EpochInfos for last_epoch
     pub async fn set_epoch_infos(&self, infos: EpochInfos) {
         self.new_epoch.borrow_mut().content().set_infos(infos)
     }