Add query to get last read receipt for room.

Signed-off-by: Jason Volk <jason@zemos.net>

src/service/rooms/read_receipt/data.rs

@@ -7,7 +7,7 @@ use ruma::{
 	serde::Raw,
 };
 use tuwunel_core::{
-	Result, trace,
+	Result, err, is_equal_to, trace,
 	utils::{ReadyExt, stream::TryIgnore},
 };
 use tuwunel_database::{Deserialized, Interfix, Json, Map};
@@ -84,6 +84,28 @@ impl Data {
 			.ignore_err()
 	}
 
+	#[inline]
+	pub(super) async fn last_receipt_count<'a>(
+		&'a self,
+		room_id: &'a RoomId,
+		since: Option<u64>,
+		user_id: Option<&'a UserId>,
+	) -> Result<u64> {
+		type Key<'a> = (&'a RoomId, u64, &'a UserId);
+
+		let key = (room_id, u64::MAX);
+		self.readreceiptid_readreceipt
+			.rev_keys_prefix(&key)
+			.ignore_err()
+			.ready_take_while(|(_, c, _): &Key<'_>| since.is_none_or(|since| since.gt(&c)))
+			.ready_filter(|(_, _, u): &Key<'_>| user_id.as_ref().is_none_or(is_equal_to!(u)))
+			.map(|(_, c, _): Key<'_>| c)
+			.boxed()
+			.next()
+			.await
+			.ok_or_else(|| err!(Request(NotFound("No receipts found in room"))))
+	}
+
 	#[inline]
 	pub(super) fn private_read_set(&self, room_id: &RoomId, user_id: &UserId, pdu_count: u64) {
 		let key = (room_id, user_id);

src/service/rooms/read_receipt/mod.rs

@@ -146,6 +146,17 @@ impl Service {
 			.await
 	}
 
+	pub async fn last_receipt_count(
+		&self,
+		room_id: &RoomId,
+		user_id: Option<&UserId>,
+		since: Option<u64>,
+	) -> Result<u64> {
+		self.db
+			.last_receipt_count(room_id, since, user_id)
+			.await
+	}
+
 	pub async fn delete_all_read_receipts(&self, room_id: &RoomId) -> Result {
 		self.db.delete_all_read_receipts(room_id).await
 	}