From d5c5c7463e5210916822c8030bb59c7b0f3ccc1c Mon Sep 17 00:00:00 2001
From: Florian Dold <florian@dold.me>
Date: Wed, 5 Apr 2023 11:06:22 +0200
Subject: [PATCH] wallet-core: also return top-level fee gap estimate

---
 packages/taler-util/src/wallet-types.ts               | 6 ++++++
 packages/taler-wallet-core/src/operations/pay-peer.ts | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/packages/taler-util/src/wallet-types.ts b/packages/taler-util/src/wallet-types.ts
index a761c5cff..11162df14 100644
--- a/packages/taler-util/src/wallet-types.ts
+++ b/packages/taler-util/src/wallet-types.ts
@@ -2263,6 +2263,12 @@ export interface PayPeerInsufficientBalanceDetails {
    */
   balanceMaterial: AmountString;
 
+  /**
+   * If non-zero, the largest fee gap estimate of an exchange
+   * where we would otherwise have enough balance available.
+   */
+  feeGapEstimate: AmountString;
+
   perExchange: {
     [url: string]: {
       balanceAvailable: AmountString;
diff --git a/packages/taler-wallet-core/src/operations/pay-peer.ts b/packages/taler-wallet-core/src/operations/pay-peer.ts
index 92ec549dd..ebf521079 100644
--- a/packages/taler-wallet-core/src/operations/pay-peer.ts
+++ b/packages/taler-wallet-core/src/operations/pay-peer.ts
@@ -342,6 +342,8 @@ export async function selectPeerCoins(
 
       const perExchange: PayPeerInsufficientBalanceDetails["perExchange"] = {};
 
+      let maxFeeGapEstimate = Amounts.zeroOfCurrency(currency);
+
       for (const exch of exchanges) {
         if (exch.detailsPointer?.currency !== currency) {
           continue;
@@ -361,12 +363,15 @@ export async function selectPeerCoins(
           balanceMaterial: Amounts.stringify(infoExchange.balanceMaterial),
           feeGapEstimate: Amounts.stringify(gap),
         };
+
+        maxFeeGapEstimate = Amounts.max(maxFeeGapEstimate, gap);
       }
 
       const errDetails: PayPeerInsufficientBalanceDetails = {
         amountRequested: Amounts.stringify(instructedAmount),
         balanceAvailable: Amounts.stringify(infoGeneral.balanceAvailable),
         balanceMaterial: Amounts.stringify(infoGeneral.balanceMaterial),
+        feeGapEstimate: Amounts.stringify(maxFeeGapEstimate),
         perExchange,
       };