refactor(abstract-utxo): simplify entrypoint for explainTx

Issue: BTC-1450

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -76,7 +76,6 @@ import { signAndVerifyPsbt, signAndVerifyWalletTransaction } from './sign';
 import { supportedCrossChainRecoveries } from './config';
 import {
   assertValidTransactionRecipient,
-  explainPsbt,
   explainTx,
   fromExtendedAddressFormat,
   getPsbtTxInputs,
@@ -1535,12 +1534,7 @@ export abstract class AbstractUtxoCoin extends BaseCoin {
     if (typeof txHex !== 'string' || !txHex.match(/^([a-f0-9]{2})+$/i)) {
       throw new Error('invalid transaction hex, must be a valid hex string');
     }
-    const tx = this.decodeTransaction(txHex);
-    if (tx instanceof bitgo.UtxoPsbt) {
-      return explainPsbt(tx, params, this.network);
-    } else {
-      return explainTx(tx, params, this.network);
-    }
+    return explainTx(this.decodeTransaction(txHex), params, this.network);
   }
 
   /**

modules/abstract-utxo/src/transaction/explainTransaction.ts

@@ -135,7 +135,7 @@ function getTxInputSignaturesCount<TNumber extends number | bigint>(
  * Decompose a raw psbt into useful information, such as the total amounts,
  * change amounts, and transaction outputs.
  */
-export function explainPsbt<TNumber extends number | bigint, Tx extends bitgo.UtxoTransaction<bigint>>(
+function explainPsbt<TNumber extends number | bigint, Tx extends bitgo.UtxoTransaction<bigint>>(
   psbt: bitgo.UtxoPsbt<Tx>,
   params: ExplainTransactionOptions<TNumber>,
   network: utxolib.Network
@@ -212,11 +212,7 @@ export function explainPsbt<TNumber extends number | bigint, Tx extends bitgo.Ut
   } as TransactionExplanation;
 }
 
-/**
- * Decompose a raw transaction into useful information, such as the total amounts,
- * change amounts, and transaction outputs.
- */
-export function explainTx<TNumber extends number | bigint>(
+function explainLegacyTx<TNumber extends number | bigint>(
   tx: bitgo.UtxoTransaction<TNumber>,
   params: ExplainTransactionOptions<TNumber>,
   network: utxolib.Network
@@ -229,3 +225,19 @@ export function explainTx<TNumber extends number | bigint>(
     signatures: inputSignaturesCount.reduce((prev, curr) => (curr > prev ? curr : prev), 0),
   } as TransactionExplanation;
 }
+
+/**
+ * Decompose a raw transaction into useful information, such as the total amounts,
+ * change amounts, and transaction outputs.
+ */
+export function explainTx<TNumber extends number | bigint>(
+  tx: bitgo.UtxoTransaction<TNumber> | bitgo.UtxoPsbt,
+  params: ExplainTransactionOptions<TNumber>,
+  network: utxolib.Network
+): TransactionExplanation {
+  if (tx instanceof bitgo.UtxoPsbt) {
+    return explainPsbt(tx, params, network);
+  } else {
+    return explainLegacyTx(tx, params, network);
+  }
+}