snc: use local caches for resolving identifiers

Signed-off-by: Sumner Evans <sumner.evans@automattic.com>

pkg/connector/store/scoped_store.go

@@ -56,6 +56,7 @@ const (
 		VALUES ($1, $2)
 		ON CONFLICT (username) DO UPDATE SET entity_id=excluded.entity_id
 	`
+	getByUsernameQuery = "SELECT entity_id FROM telegram_username WHERE LOWER(username)=$1"
 	clearUsernameQuery = `DELETE FROM telegram_username WHERE entity_id=$1`
 
 	// User Phone Number Queries
@@ -196,6 +197,14 @@ func (s *ScopedStore) SetUsername(ctx context.Context, userID int64, username st
 	return
 }
 
+func (s *ScopedStore) GetUserIDByUsername(ctx context.Context, username string) (userID int64, err error) {
+	err = s.db.QueryRow(ctx, getByUsernameQuery, username).Scan(&userID)
+	if errors.Is(err, sql.ErrNoRows) {
+		err = nil
+	}
+	return
+}
+
 func (s *ScopedStore) GetUserIDByPhoneNumber(ctx context.Context, phoneNumber string) (userID int64, err error) {
 	err = s.db.QueryRow(ctx, getEntityIDForPhoneNumber, phoneNumber).Scan(&userID)
 	if errors.Is(err, sql.ErrNoRows) {

pkg/connector/store/upgrades/00-latest.sql

@@ -34,6 +34,7 @@ CREATE TABLE telegram_username (
 );
 
 CREATE INDEX telegram_username_entity_idx ON telegram_username (entity_id);
+CREATE INDEX telegram_username_username_idx ON telegram_username (LOWER(username));
 
 CREATE TABLE telegram_phone_number (
     phone_number  TEXT   NOT NULL,