core: add claim-specific GetScriptHashesForVerifying()

Claim transactions have different logic in C# node, so we need to
implement it too. It's not the most elegant way to fix it, but let's make it
work first and then refactor if and where needed. Fixes verification of Claim
transactions.

pkg/core/blockchain.go

@@ -883,10 +883,41 @@ func (bc *Blockchain) GetTransationResults(t *transaction.Transaction) []*transa
 	return results
 }
 
+// GetScriptHashesForVerifyingClaim returns all ScriptHashes of Claim transaction
+// which has a different implementation from generic GetScriptHashesForVerifying.
+func (bc *Blockchain) GetScriptHashesForVerifyingClaim(t *transaction.Transaction) ([]util.Uint160, error) {
+	hashes := make([]util.Uint160, 0)
+
+	claim := t.Data.(*transaction.ClaimTX)
+	clGroups := make(map[util.Uint256][]*transaction.Input)
+	for _, in := range claim.Claims {
+		clGroups[in.PrevHash] = append(clGroups[in.PrevHash], in)
+	}
+	for group, inputs := range clGroups {
+		refTx, _, err := bc.GetTransaction(group)
+		if err != nil {
+			return nil, err
+		}
+		for _, input := range inputs {
+			if len(refTx.Outputs) <= int(input.PrevIndex) {
+				return nil, fmt.Errorf("wrong PrevIndex reference")
+			}
+			hashes = append(hashes, refTx.Outputs[input.PrevIndex].ScriptHash)
+		}
+	}
+	if len(hashes) > 0 {
+		return hashes, nil
+	}
+	return nil, fmt.Errorf("no hashes found")
+}
+
 // GetScriptHashesForVerifying returns all the ScriptHashes of a transaction which will be use
 // to verify whether the transaction is bonafide or not.
 // Golang implementation of GetScriptHashesForVerifying method in C# (https://github.com/neo-project/neo/blob/master/neo/Network/P2P/Payloads/Transaction.cs#L190)
 func (bc *Blockchain) GetScriptHashesForVerifying(t *transaction.Transaction) ([]util.Uint160, error) {
+	if t.Type == transaction.ClaimType {
+		return bc.GetScriptHashesForVerifyingClaim(t)
+	}
 	references := bc.References(t)
 	if references == nil {
 		return nil, errors.New("Invalid operation")