1 files changed, 25 insertions, 3 deletions
diff --git a/syncapi/storage/postgres/memberships_table.go b/syncapi/storage/postgres/memberships_table.go
index 00223c57..939d6b3f 100644
--- a/syncapi/storage/postgres/memberships_table.go
+++ b/syncapi/storage/postgres/memberships_table.go
@@ -66,10 +66,14 @@ const selectMembershipCountSQL = "" +
 const selectHeroesSQL = "" +
 	"SELECT DISTINCT user_id FROM syncapi_memberships WHERE room_id = $1 AND user_id != $2 AND membership = ANY($3) LIMIT 5"
 
+const selectMembershipBeforeSQL = "" +
+	"SELECT membership, topological_pos FROM syncapi_memberships WHERE room_id = $1 and user_id = $2 AND topological_pos <= $3 ORDER BY topological_pos DESC LIMIT 1"
+
 type membershipsStatements struct {
-	upsertMembershipStmt      *sql.Stmt
-	selectMembershipCountStmt *sql.Stmt
-	selectHeroesStmt          *sql.Stmt
+	upsertMembershipStmt        *sql.Stmt
+	selectMembershipCountStmt   *sql.Stmt
+	selectHeroesStmt            *sql.Stmt
+	selectMembershipForUserStmt *sql.Stmt
 }
 
 func NewPostgresMembershipsTable(db *sql.DB) (tables.Memberships, error) {
@@ -82,6 +86,7 @@ func NewPostgresMembershipsTable(db *sql.DB) (tables.Memberships, error) {
 		{&s.upsertMembershipStmt, upsertMembershipSQL},
 		{&s.selectMembershipCountStmt, selectMembershipCountSQL},
 		{&s.selectHeroesStmt, selectHeroesSQL},
+		{&s.selectMembershipForUserStmt, selectMembershipBeforeSQL},
 	}.Prepare(db)
 }
 
@@ -132,3 +137,20 @@ func (s *membershipsStatements) SelectHeroes(
 	}
 	return heroes, rows.Err()
 }
+
+// SelectMembershipForUser returns the membership of the user before and including the given position. If no membership can be found
+// returns "leave", the topological position and no error. If an error occurs, other than sql.ErrNoRows, returns that and an empty
+// string as the membership.
+func (s *membershipsStatements) SelectMembershipForUser(
+	ctx context.Context, txn *sql.Tx, roomID, userID string, pos int64,
+) (membership string, topologyPos int, err error) {
+	stmt := sqlutil.TxStmt(txn, s.selectMembershipForUserStmt)
+	err = stmt.QueryRowContext(ctx, roomID, userID, pos).Scan(&membership, &topologyPos)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return "leave", 0, nil
+		}
+		return "", 0, err
+	}
+	return membership, topologyPos, nil
+}