fix(sdk-coin-ada): mark change outputs with change:true in explainTransaction

modules/sdk-coin-ada/src/ada.ts

@@ -54,6 +54,7 @@ export interface AdaTxInfo {
 
 export interface ExplainTransactionOptions {
   txPrebuild: TransactionPrebuild;
+  changeAddress?: string;
 }
 
 export interface AdaParseTransactionOptions extends BaseParseTransactionOptions {
@@ -204,16 +205,20 @@ export class Ada extends BaseCoin {
    */
   async explainTransaction(params: ExplainTransactionOptions): Promise<AdaTransactionExplanation> {
     const factory = this.getBuilder();
-    let rebuiltTransaction: BaseTransaction;
+    let rebuiltTransaction: Transaction;
     const txRaw = params.txPrebuild.txHex;
 
     try {
       const transactionBuilder = factory.from(txRaw);
-      rebuiltTransaction = await transactionBuilder.build();
+      rebuiltTransaction = (await transactionBuilder.build()) as Transaction;
     } catch {
       throw new Error('Invalid transaction');
     }
 
+    if (params.changeAddress) {
+      rebuiltTransaction.changeAddress = params.changeAddress;
+    }
+
     return rebuiltTransaction.explainTransaction() as unknown as AdaTransactionExplanation;
   }
 

modules/sdk-coin-ada/src/lib/transaction.ts

@@ -101,6 +101,11 @@ export class Transaction extends BaseTransaction {
   private _transaction: CardanoWasm.Transaction;
   private _fee: string;
   private _pledgeDetails?: PledgeDetails;
+  private _changeAddress?: string;
+
+  set changeAddress(address: string) {
+    this._changeAddress = address;
+  }
 
   constructor(coinConfig: Readonly<CoinConfig>) {
     super(coinConfig);
@@ -426,10 +431,12 @@ export class Transaction extends BaseTransaction {
       id: txJson.id,
       outputs: txJson.outputs.map((o) => {
         const multiAssets = Transaction.parseMultiAssets(o.multiAssets as CardanoWasm.MultiAsset | undefined);
+        const isChange = this._changeAddress !== undefined && o.address === this._changeAddress;
         return {
           address: o.address,
           amount: o.amount,
           ...(multiAssets && { multiAssets }),
+          ...(isChange && { change: true }),
         };
       }),
       outputAmount: outputAmount,

modules/sdk-coin-ada/src/lib/transactionBuilder.ts

@@ -227,6 +227,9 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
     this.setMutableSenderAssetList();
     this.addOutputs(outputs);
     this._transaction.transaction = this.prepareAdaTransactionDraft(inputs, outputs, true);
+    if (this._changeAddress) {
+      this._transaction.changeAddress = this._changeAddress;
+    }
     return this.transaction;
   }
 
@@ -573,6 +576,9 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
 
     const finalOutputs = this.buildExplicitOutputsCollection(this._fee);
     this._transaction.transaction = this.prepareAdaTransactionDraft(inputs, finalOutputs, true);
+    if (this._changeAddress) {
+      this._transaction.changeAddress = this._changeAddress;
+    }
     return this.transaction;
   }
 
@@ -924,6 +930,9 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
     });
     witnessSet.set_vkeys(vkeyWitnesses);
     this._transaction.transaction = CardanoWasm.Transaction.new(txRaw, witnessSet);
+    if (this._changeAddress) {
+      this._transaction.changeAddress = this._changeAddress;
+    }
     return this.transaction;
   }
 

modules/sdk-coin-ada/test/unit/transactionBuilder.ts

@@ -549,4 +549,66 @@ describe('ADA Transaction Builder', async () => {
   //     console.log(err);
   //   }
   // });
+
+  describe('explainTransaction change output marking', () => {
+    it('should mark the change output with change: true in explainTransaction', async () => {
+      const txBuilder = factory.getTransferBuilder();
+      txBuilder.input({
+        transaction_id: '3677e75c7ba699bfdc6cd57d42f246f86f63aefd76025006ac78313fad2bba21',
+        transaction_index: 1,
+      });
+      const outputAmount = 7823121;
+      txBuilder.output({
+        address: testData.rawTx.outputAddress1.address,
+        amount: outputAmount.toString(),
+      });
+      const changeAddr = testData.rawTx.outputAddress2.address;
+      const totalInput = 21032023;
+      txBuilder.changeAddress(changeAddr, totalInput.toString());
+      txBuilder.ttl(800000000);
+
+      const tx = (await txBuilder.build()) as Transaction;
+      const explained = tx.explainTransaction();
+
+      const changeOutputs = explained.outputs.filter((o) => o.change === true);
+      const nonChangeOutputs = explained.outputs.filter((o) => !o.change);
+
+      changeOutputs.length.should.equal(1);
+      changeOutputs[0].address.should.equal(changeAddr);
+      nonChangeOutputs.length.should.equal(1);
+      nonChangeOutputs[0].address.should.equal(testData.rawTx.outputAddress1.address);
+    });
+
+    it('should not mark any output as change when no changeAddress is set', async () => {
+      const preBuiltTx = new Transaction(coins.get('tada'));
+      preBuiltTx.fromRawTransaction(testData.rawTx.unsignedTx2);
+      const txBuilder = factory.getTransferBuilder();
+      txBuilder.initBuilder(preBuiltTx);
+
+      const tx = (await txBuilder.build()) as Transaction;
+      const explained = tx.explainTransaction();
+
+      const changeOutputs = explained.outputs.filter((o) => o.change === true);
+      changeOutputs.length.should.equal(0);
+    });
+
+    it('should mark consolidation output with change: true when changeAddress matches the single output', async () => {
+      const txBuilder = factory.getTransferBuilder();
+      txBuilder.input({
+        transaction_id: '3677e75c7ba699bfdc6cd57d42f246f86f63aefd76025006ac78313fad2bba21',
+        transaction_index: 1,
+      });
+      const changeAddr = testData.rawTx.outputAddress1.address;
+      const totalInput = 20000000;
+      txBuilder.changeAddress(changeAddr, totalInput.toString());
+      txBuilder.ttl(800000000);
+
+      const tx = (await txBuilder.build()) as Transaction;
+      const explained = tx.explainTransaction();
+
+      const changeOutputs = explained.outputs.filter((o) => o.change === true);
+      changeOutputs.length.should.equal(1);
+      changeOutputs[0].address.should.equal(changeAddr);
+    });
+  });
 });