refactor(indexeddb): add transaction fns for getting the next available media content id

Signed-off-by: Michael Goldenberg <m@mgoldenberg.net>

crates/matrix-sdk-indexeddb/src/event_cache_store/error.rs

@@ -81,7 +81,9 @@ impl From<TransactionError> for EventCacheStoreError {
         match value {
             DomException { .. } => Self::InvalidData { details: value.to_string() },
             Serialization(e) => Self::Serialization(serde_json::Error::custom(e.to_string())),
-            ItemIsNotUnique | ItemNotFound => Self::InvalidData { details: value.to_string() },
+            ItemIsNotUnique | ItemNotFound | NumericalOverflow => {
+                Self::InvalidData { details: value.to_string() }
+            }
             Backend(e) => GenericError::from(e.to_string()).into(),
         }
     }

crates/matrix-sdk-indexeddb/src/media_store/error.rs

@@ -71,7 +71,9 @@ impl From<TransactionError> for MediaStoreError {
         match value {
             DomException { .. } => Self::InvalidData { details: value.to_string() },
             Serialization(e) => Self::Serialization(serde_json::Error::custom(e.to_string())),
-            ItemIsNotUnique | ItemNotFound => Self::InvalidData { details: value.to_string() },
+            ItemIsNotUnique | ItemNotFound | NumericalOverflow => {
+                Self::InvalidData { details: value.to_string() }
+            }
             Backend(e) => GenericError::from(e.to_string()).into(),
         }
     }

crates/matrix-sdk-indexeddb/src/media_store/transaction.rs

@@ -348,6 +348,25 @@ impl<'a> IndexeddbMediaStoreTransaction<'a> {
         self.get_item_by_key_components::<MediaContent, IndexedMediaContentIdKey>(id).await
     }
 
+    /// Query IndexedDB for the maximum [`IndexedMediaContentIdKey`] associated
+    /// with a [`MediaContent`]
+    pub async fn get_max_media_content_key_by_id(
+        &self,
+    ) -> Result<Option<IndexedMediaContentIdKey>, TransactionError> {
+        self.get_max_key::<MediaContent, IndexedMediaContentIdKey>(IndexedKeyRange::all(
+            self.serializer().inner(),
+        ))
+        .await
+    }
+
+    /// Query IndexedDB for the next available [`MediaContent::id`]
+    pub async fn get_next_media_content_id(&self) -> Result<u64, TransactionError> {
+        Ok(match self.get_max_media_content_key_by_id().await? {
+            Some(key) => key.checked_add(1).ok_or(TransactionError::NumericalOverflow)?,
+            None => 0,
+        })
+    }
+
     /// Adds [`MediaContent`] to IndexedDB. If an item with the same key already
     /// exists, it will be rejected.
     pub async fn add_media_content(&self, content: &MediaContent) -> Result<(), TransactionError> {

crates/matrix-sdk-indexeddb/src/transaction/mod.rs

@@ -45,6 +45,8 @@ pub enum TransactionError {
     ItemIsNotUnique,
     #[error("item not found")]
     ItemNotFound,
+    #[error("a numerical operation overflowed")]
+    NumericalOverflow,
     #[error("backend: {0}")]
     Backend(Box<dyn AsyncErrorDeps>),
 }