support reordering

src/main/java/com/sparrowwallet/drongo/protocol/Transaction.java

@@ -39,8 +39,8 @@ public class Transaction extends ChildMessage {
     private Sha256Hash cachedTxId;
     private Sha256Hash cachedWTxId;
 
-    private ArrayList<TransactionInput> inputs;
+    private List<TransactionInput> inputs;
-    private ArrayList<TransactionOutput> outputs;
+    private List<TransactionOutput> outputs;
 
     public Transaction() {
         version = 1;
@@ -731,4 +731,24 @@ public class Transaction extends ChildMessage {
         outputStream.write(new VarInt(bytes.length).encode());
         outputStream.write(bytes);
     }
+
+    public void moveInput(int fromIndex, int toIndex) {
+        moveItem(inputs, fromIndex, toIndex);
+    }
+
+    public void moveOutput(int fromIndex, int toIndex) {
+        moveItem(outputs, fromIndex, toIndex);
+    }
+
+    private <T> void moveItem(List<T> list, int fromIndex, int toIndex) {
+        if(fromIndex < 0 || fromIndex >= list.size() || toIndex < 0 || toIndex >= list.size()) {
+            throw new IllegalArgumentException("Invalid indices [" + fromIndex + ", " + toIndex + "] provided to list of size " + list.size());
+        }
+
+        T item = list.remove(fromIndex);
+        list.add(toIndex, item);
+
+        cachedTxId = null;
+        cachedWTxId = null;
+    }
 }

src/main/java/com/sparrowwallet/drongo/psbt/PSBT.java

@@ -594,6 +594,28 @@ public class PSBT {
         }
     }
 
+    public void moveInput(int fromIndex, int toIndex) {
+        moveItem(psbtInputs, fromIndex, toIndex);
+        transaction.moveInput(fromIndex, toIndex);
+        for(int i = 0; i < psbtInputs.size(); i++) {
+            psbtInputs.get(i).setIndex(i);
+        }
+    }
+
+    public void moveOutput(int fromIndex, int toIndex) {
+        moveItem(psbtOutputs, fromIndex, toIndex);
+        transaction.moveOutput(fromIndex, toIndex);
+    }
+
+    private <T> void moveItem(List<T> list, int fromIndex, int toIndex) {
+        if(fromIndex < 0 || fromIndex >= list.size() || toIndex < 0 || toIndex >= list.size()) {
+            throw new IllegalArgumentException("Invalid indices [" + fromIndex + ", " + toIndex + "] provided to list of size " + list.size());
+        }
+
+        T item = list.remove(fromIndex);
+        list.add(toIndex, item);
+    }
+
     public List<PSBTInput> getPsbtInputs() {
         return psbtInputs;
     }

src/main/java/com/sparrowwallet/drongo/psbt/PSBTInput.java

@@ -48,7 +48,7 @@ public class PSBTInput {
     private ECKey tapInternalKey;
 
     private final Transaction transaction;
-    private final int index;
+    private int index;
 
     private static final Logger log = LoggerFactory.getLogger(PSBTInput.class);
 
@@ -680,10 +680,14 @@ public class PSBTInput {
     }
 
     public TransactionOutput getUtxo() {
-        int vout = (int)transaction.getInputs().get(index).getOutpoint().getIndex();
+        int vout = (int)getInput().getOutpoint().getIndex();
         return getWitnessUtxo() != null ? getWitnessUtxo() : (getNonWitnessUtxo() != null ?  getNonWitnessUtxo().getOutputs().get(vout) : null);
     }
 
+    void setIndex(int index) {
+        this.index = index;
+    }
+
     public void clearNonFinalFields() {
         partialSignatures.clear();
         sigHash = null;