fix(repository): get the previous epoch by index

Since epochs with no inputs won't be stored in the database, the block range between epochs might be disjointed, breaking this function. Filtering results based on the epoch index alone will be enough.

internal/repository/validator.go

@@ -198,11 +198,6 @@ func (pg *Database) GetLastInputOutputsHash(
 // GetPreviousEpoch returns the epoch that ended one block before the start
 // of the current epoch
 func (pg *Database) GetPreviousEpoch(ctx context.Context, currentEpoch Epoch) (*Epoch, error) {
-	if currentEpoch.FirstBlock == 0 {
-		// if this is the first epoch, there is nothing to return
-		return nil, nil
-	}
-
 	query := `
 	SELECT
 		id,
@@ -216,15 +211,15 @@ func (pg *Database) GetPreviousEpoch(ctx context.Context, currentEpoch Epoch) (*
 	FROM
 		epoch
 	WHERE
-		application_address=@appAddress AND last_block=@lastBlock
+		application_address=@appAddress AND index < @index
 	ORDER BY
 		index DESC
 	LIMIT 1
 	`
 
 	args := pgx.NamedArgs{
 		"appAddress": currentEpoch.AppAddress,
-		"lastBlock":  currentEpoch.FirstBlock - 1,
+		"index":      currentEpoch.Index,
 	}
 
 	var (
@@ -245,6 +240,9 @@ func (pg *Database) GetPreviousEpoch(ctx context.Context, currentEpoch Epoch) (*
 		&status,
 	)
 	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
 		return nil, fmt.Errorf("GetPreviousEpoch failed: %w", err)
 	}
 

internal/repository/validator_test.go

@@ -225,7 +225,7 @@ func (s *RepositorySuite) TestGetPreviousEpoch() {
 	previousEpoch, err = s.database.GetPreviousEpoch(s.ctx, epoch2)
 	s.Require().Nil(err)
 	s.Require().NotNil(previousEpoch)
-	s.Require().Equal(*previousEpoch, epoch)
+	s.Require().Equal(previousEpoch.Id, epoch.Id)
 }
 
 func (s *RepositorySuite) TestSetEpochClaimAndInsertProofsTransaction() {