refactor(indexeddb): add trait for converting between high-level types and indexed types in event cache store

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

Author: mgoldenberg

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

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License
 
+#![allow(unused)]
+
 mod migrations;
 mod serializer;
 mod types;

crates/matrix-sdk-indexeddb/src/event_cache_store/serializer/mod.rs

@@ -12,4 +12,5 @@
 // See the License for the specific language governing permissions and
 // limitations under the License
 
+mod traits;
 mod types;

crates/matrix-sdk-indexeddb/src/event_cache_store/serializer/traits.rs

@@ -0,0 +1,44 @@
+// Copyright 2025 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License
+
+use ruma::RoomId;
+
+use crate::serializer::IndexeddbSerializer;
+
+/// A conversion trait for preparing high-level types into indexed types
+/// which are better suited for storage in IndexedDB.
+///
+/// Note that the functions below take an [`IndexeddbSerializer`] as an
+/// argument, which provides the necessary context for encryption and
+/// decryption, in the case the high-level type must be encrypted before
+/// storage.
+pub trait Indexed: Sized {
+    /// The indexed type that is used for storage in IndexedDB.
+    type IndexedType;
+    /// The error type that is returned when conversion fails.
+    type Error;
+
+    /// Converts the high-level type into an indexed type.
+    fn to_indexed(
+        &self,
+        room_id: &RoomId,
+        serializer: &IndexeddbSerializer,
+    ) -> Result<Self::IndexedType, Self::Error>;
+
+    /// Converts an indexed type into the high-level type.
+    fn from_indexed(
+        indexed: Self::IndexedType,
+        serializer: &IndexeddbSerializer,
+    ) -> Result<Self, Self::Error>;
+}