[V124-specific] semi random asgard vault selection based on tx inhash and block height

closes:#1718 (closed)
hashes tx inhash and block height to generate a semi-random number to be used for Asgard vault selection

common/tx.go

@@ -2,6 +2,7 @@ package common
 
 import (
 	"crypto/sha256"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"strings"
@@ -44,6 +45,17 @@ func (tx TxID) Equals(tx2 TxID) bool {
 	return strings.EqualFold(tx.String(), tx2.String())
 }
 
+func (tx TxID) HashWithAttrs(attrs ...interface{}) int64 {
+	toHash := tx.String()
+	for _, attr := range attrs {
+		toHash = fmt.Sprintf("%s|%s", toHash, attr)
+	}
+
+	checksum := sha256.Sum256([]byte(toHash))
+	// using uint32 to avoid overflows
+	return int64(binary.BigEndian.Uint32(checksum[:4]))
+}
+
 // IsEmpty return true when the tx represent empty string
 func (tx TxID) IsEmpty() bool {
 	return strings.TrimSpace(tx.String()) == ""