Merge #1191

1191: compute payment fee as the difference between inputs/outputs r=KtorZ a=KtorZ

# Issue Number

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#1150 

# Overview

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- [x] I have re-used the existing coin selection function and removing the need for an extra 'estimateFee' function in the core engine


# Comments

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Co-authored-by: KtorZ <matthias.benkort@gmail.com>

lib/core-integration/src/Test/Integration/Scenario/API/Transactions.hs

@@ -935,7 +935,7 @@ spec = do
         wSrc <- fixtureWalletWith ctx [feeMin `div` 2]
         wDest <- emptyWallet ctx
         addr:_ <- listAddresses ctx wDest
-        let amt = 1
+        let amt = 1 :: Natural
 
         let destination = addr ^. #id
         let payload = Json [json|{
@@ -950,7 +950,7 @@ spec = do
         r <- request @ApiFee ctx (postTxFeeEp wSrc) Default payload
         verify r
             [ expectResponseCode HTTP.status202
-            , expectFieldBetween amount (feeMin - amt, feeMax + amt)
+            , expectFieldBetween amount (feeMin, feeMax)
             ]
 
     it "TRANS_ESTIMATE_04 - Not enough money" $ \ctx -> do

lib/core/src/Cardano/Wallet.hs

@@ -85,11 +85,9 @@ module Cardano.Wallet
     -- ** Payment
     , selectCoinsExternal
     , selectCoinsForPayment
-    , estimatePaymentFee
     , signPayment
     , ErrSelectCoinsExternal (..)
     , ErrSelectForPayment (..)
-    , ErrEstimatePaymentFee (..)
     , ErrSignPayment (..)
     , ErrCoinSelection (..)
     , ErrAdjustForFee (..)
@@ -865,30 +863,6 @@ selectCoinsForMigration ctx wid = do
   where
     tl = ctx ^. transactionLayer @t @k
 
--- | Estimate a transaction fee by automatically selecting inputs from
--- the wallet to cover the requested outputs.
-estimatePaymentFee
-    :: forall ctx s t k e.
-        ( HasTransactionLayer t k ctx
-        , HasDBLayer s k ctx
-        , e ~ ErrValidateSelection t
-        )
-    => ctx
-    -> WalletId
-    -> NonEmpty TxOut
-    -> ExceptT (ErrEstimatePaymentFee e) IO Fee
-estimatePaymentFee ctx wid recipients = do
-    (wal, _, pending) <- withExceptT ErrEstimatePaymentFeeNoSuchWallet $
-        readWallet @ctx @s @k ctx wid
-    let bp = blockchainParameters wal
-    let utxo = availableUTxO @s pending wal
-    (sel, _utxo') <- withExceptT ErrEstimatePaymentFeeCoinSelection $ do
-        let opts = coinSelOpts tl (bp ^. #getTxMaxSize)
-        CoinSelection.random opts recipients utxo
-    pure $ computeFee (bp ^. #getFeePolicy) $ estimateSize tl sel
-  where
-    tl = ctx ^. transactionLayer @t @k
-
 -- | Augments the given outputs with new outputs. These new outputs corresponds
 -- to change outputs to which new addresses are being assigned to. This updates
 -- the wallet state as it needs to keep track of new pending change addresses.
@@ -1393,12 +1367,6 @@ data ErrSelectForPayment e
     | ErrSelectForPaymentFee ErrAdjustForFee
     deriving (Show, Eq)
 
--- | Errors that can occur when estimating transaction fees.
-data ErrEstimatePaymentFee e
-    = ErrEstimatePaymentFeeNoSuchWallet ErrNoSuchWallet
-    | ErrEstimatePaymentFeeCoinSelection (ErrCoinSelection e)
-    deriving (Show, Eq)
-
 -- | Errors that can occur when listing UTxO statistics.
 newtype ErrListUTxOStatistics
     = ErrListUTxOStatisticsNoSuchWallet ErrNoSuchWallet

lib/core/src/Cardano/Wallet/Api/Server.hs

@@ -50,7 +50,6 @@ import Cardano.Wallet
     ( ErrAdjustForFee (..)
     , ErrCoinSelection (..)
     , ErrDecodeSignedTx (..)
-    , ErrEstimatePaymentFee (..)
     , ErrFetchRewards (..)
     , ErrJoinStakePool (..)
     , ErrListTransactions (..)
@@ -157,8 +156,6 @@ import Cardano.Wallet.Primitive.AddressDiscovery.Sequential
     ( SeqState (..), defaultAddressPoolGap, mkSeqState )
 import Cardano.Wallet.Primitive.CoinSelection
     ( CoinSelection (..), changeBalance, feeBalance, inputBalance )
-import Cardano.Wallet.Primitive.Fee
-    ( Fee (..) )
 import Cardano.Wallet.Primitive.Model
     ( Wallet, availableBalance, currentTip, getState, totalBalance )
 import Cardano.Wallet.Primitive.Types
@@ -210,7 +207,7 @@ import Control.Monad
 import Control.Monad.IO.Class
     ( MonadIO, liftIO )
 import Control.Monad.Trans.Except
-    ( ExceptT, except, throwE, withExceptT )
+    ( ExceptT, catchE, except, throwE, withExceptT )
 import Data.Aeson
     ( (.=) )
 import Data.Function
@@ -802,13 +799,20 @@ postTransactionFee
     -> Handler ApiFee
 postTransactionFee ctx (ApiT wid) body = do
     let outs = coerceCoin <$> (body ^. #payments)
-    (Fee fee) <- liftHandler $ withWorkerCtx ctx wid liftE $ \wrk ->
-        W.estimatePaymentFee @_ @s @t wrk wid outs
-    return ApiFee
-        { amount = Quantity (fromIntegral fee)
-        }
+    liftHandler $ withWorkerCtx ctx wid liftE $ \wrk ->
+        (apiFee <$> W.selectCoinsForPayment @_ @s @t @k wrk wid outs)
+            `catchE` handleCannotCover wrk
   where
-    liftE = throwE . ErrEstimatePaymentFeeNoSuchWallet
+    apiFee = ApiFee . Quantity . fromIntegral . feeBalance
+    liftE = throwE . ErrSelectForPaymentNoSuchWallet
+    handleCannotCover wrk = \case
+        ErrSelectForPaymentFee (ErrCannotCoverFee missing) -> do
+            (wallet, _, pending) <- withExceptT ErrSelectForPaymentNoSuchWallet $
+                W.readWallet wrk wid
+            let balance = availableBalance pending wallet
+            pure $ ApiFee $ Quantity $ fromIntegral missing + balance
+
+        e -> throwE e
 
 {-------------------------------------------------------------------------------
                                     Stake Pools
@@ -1600,11 +1604,6 @@ instance Buildable e => LiftHandler (ErrSelectForPayment e) where
         ErrSelectForPaymentCoinSelection e -> handler e
         ErrSelectForPaymentFee e -> handler e
 
-instance Buildable e => LiftHandler (ErrEstimatePaymentFee e) where
-    handler = \case
-        ErrEstimatePaymentFeeNoSuchWallet e -> handler e
-        ErrEstimatePaymentFeeCoinSelection e -> handler e
-
 instance LiftHandler ErrListUTxOStatistics where
     handler = \case
         ErrListUTxOStatisticsNoSuchWallet e -> handler e