feat(abstract-utxo): implement explainTx for descriptor wallets

Issue: BTC-1450

Author: OttoAllmendinger

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

@@ -3,9 +3,12 @@ import * as utxolib from '@bitgo/utxo-lib';
 import { TransactionExplanation } from '../abstractUtxoCoin';
 
 import * as fixedScript from './fixedScript';
+import * as descriptor from './descriptor';
 
-import { IWallet } from '@bitgo/sdk-core';
-import { isDescriptorWallet } from '../descriptor';
+import { isTriple, IWallet } from '@bitgo/sdk-core';
+import { getDescriptorMapFromWallet, isDescriptorWallet } from '../descriptor';
+import { toBip32Triple } from '../keychains';
+import { getPolicyForEnv } from '../descriptor/validatePolicy';
 
 /**
  * Decompose a raw transaction into useful information, such as the total amounts,
@@ -22,7 +25,20 @@ export function explainTx<TNumber extends number | bigint>(
   network: utxolib.Network
 ): TransactionExplanation {
   if (params.wallet && isDescriptorWallet(params.wallet)) {
-    throw new Error('Descriptor wallets are not supported');
+    if (tx instanceof utxolib.bitgo.UtxoPsbt) {
+      if (!params.pubs || !isTriple(params.pubs)) {
+        throw new Error('pub triple is required for descriptor wallets');
+      }
+      const walletKeys = toBip32Triple(params.pubs);
+      const descriptors = getDescriptorMapFromWallet(
+        params.wallet,
+        walletKeys,
+        getPolicyForEnv(params.wallet.bitgo.env)
+      );
+      return descriptor.explainPsbt(tx, descriptors);
+    }
+
+    throw new Error('legacy transactions are not supported for descriptor wallets');
   }
   if (tx instanceof utxolib.bitgo.UtxoPsbt) {
     return fixedScript.explainPsbt(tx, params, network);