Port: Check if the statediff is already in progress or completed.

indexer/database/sql/postgres/database.go

@@ -17,6 +17,8 @@
 package postgres
 
 import (
+	"fmt"
+
 	"github.com/cerc-io/plugeth-statediff/indexer/database/sql"
 	"github.com/cerc-io/plugeth-statediff/indexer/shared/schema"
 )
@@ -39,6 +41,10 @@ type DB struct {
 	sql.Driver
 }
 
+func (db *DB) ExistsHeaderStm() string {
+	return fmt.Sprintf("SELECT EXISTS(SELECT 1 from %s WHERE block_number = $1 AND block_hash = $2 LIMIT 1)", schema.TableHeader.Name)
+}
+
 // InsertHeaderStm satisfies the sql.Statements interface
 // Stm == Statement
 func (db *DB) InsertHeaderStm() string {