From 1a14e73f220d989bc3056e3ea9ddc60ee54d4bb1 Mon Sep 17 00:00:00 2001
From: ffranr <robyn@lightning.engineering>
Date: Thu, 19 Jan 2023 11:27:13 +0000
Subject: [PATCH] rpc: batch on-chain fee estimate calc includes account
 version

Account version is taken from a snapshot of spending account states. This is because the account might be updated to a new version within the batch.
---
 rpcserver.go | 39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/rpcserver.go b/rpcserver.go
index f78222197..88e73f497 100644
--- a/rpcserver.go
+++ b/rpcserver.go
@@ -2266,6 +2266,9 @@ func (s *rpcServer) prepareLeasesResponse(ctx context.Context,
 		// paid.
 		totalNumChannels := 0
 
+		// Keep a tally of the total number of channels per account key.
+		accountChannelsCount := make(map[[33]byte]uint32)
+
 		// Keep track of the index for the first lease found for this
 		// batch. We'll use this to know where to start from when
 		// populating the ChainFeeSat field for each lease.
@@ -2282,7 +2285,8 @@ func (s *rpcServer) prepareLeasesResponse(ctx context.Context,
 				}
 
 				// Filter out the account if required.
-				_, ok = accounts[ourOrder.Details().AcctKey]
+				accountKey := ourOrder.Details().AcctKey
+				_, ok = accounts[accountKey]
 				if len(accounts) != 0 && !ok {
 					continue
 				}
@@ -2418,20 +2422,33 @@ func (s *rpcServer) prepareLeasesResponse(ctx context.Context,
 
 				// Count the total number of channels.
 				totalNumChannels++
+
+				// Count the total number of channels per
+				// account.
+				accountChannelsCount[accountKey]++
 			}
 
 			// Estimate the chain fees paid for the number of
 			// channels created in this batch and tally them.
-			//
-			// TODO(guggero): This is just an approximation! We
-			// should properly calculate the fees _per account_ as
-			// that's what we do on the server side. Then we can
-			// also take a look at the actual account version at the
-			// time of the batch.
-			chainFee := order.EstimateTraderFee(
-				uint32(totalNumChannels), batch.BatchTxFeeRate,
-				account.VersionInitialNoVersion,
-			)
+			chainFee := btcutil.Amount(0)
+			for accountKey, numChannels := range accountChannelsCount {
+				// Calculate and sum the account specific chain
+				// fee estimate.
+				//
+				// The account version influences the chain fee.
+				// It is important to use the account version
+				// that was used when the batch was created.
+				// Accounts might be updated within the batch.
+				// Therefore, we query the account version from
+				// an account spending snapshot.
+				spendingAcctSnapshot :=
+					batch.SpendingAccountsSnapshot[accountKey]
+
+				chainFee += order.EstimateTraderFee(
+					numChannels, batch.BatchTxFeeRate,
+					spendingAcctSnapshot.Version,
+				)
+			}
 
 			// We'll need to compute the chain fee paid for each
 			// lease. Since multiple leases can be created within a