decouple deposits from 'estimateFee'

  Fees and deposits are closely related but that aren't the same thing. So it's better to keep the fee estimation about fees, and leave deposits out of it.

lib/core/src/Cardano/Wallet.hs

@@ -1987,27 +1987,44 @@ data FeeEstimation = FeeEstimation
     -- ^ Most coin selections will result in a fee higher than this.
     , estMaxFee :: Word64
     -- ^ Most coin selections will result in a fee lower than this.
-    , deposit :: Maybe Word64
-    -- ^ Deposit if stake key was registered,
     } deriving (Show, Eq, Generic)
 
 instance NFData FeeEstimation
 
+-- | Calculate the minimum deposit necessary if a given wallet wanted to
+-- delegate to a pool. Said differently, this return either 0, or the value of
+-- the key deposit protocol parameters if the wallet has no registered stake
+-- key.
+calcMinimumDeposit
+    :: forall ctx s k.
+        ( HasDBLayer s k ctx
+        )
+    => ctx
+    -> WalletId
+    -> ExceptT ErrNoSuchWallet IO Coin
+calcMinimumDeposit ctx wid = db & \DBLayer{..} -> do
+    mapExceptT atomically (isStakeKeyRegistered $ PrimaryKey wid) >>= \case
+        True ->
+            pure $ Coin 0
+        False ->
+            stakeKeyDeposit <$> readWalletProtocolParameters @ctx @s @k ctx wid
+  where
+    db  = ctx ^. dbLayer @s @k
+
 -- | Estimate the transaction fee for a given coin selection algorithm by
 -- repeatedly running it (100 times) and collecting the results. In the returned
 -- 'FeeEstimation', the minimum fee is that which 90% of the sampled fees are
 -- greater than. The maximum fee is the highest fee observed in the samples.
-estimateFeeForCoinSelection
+estimateFee
     :: forall m err. Monad m
-    => Maybe Word64
-    -> ExceptT err m Fee
+    => ExceptT err m Coin
     -> ExceptT err m FeeEstimation
-estimateFeeForCoinSelection deposit'
+estimateFee
     = fmap deciles
     . handleErrors
     . replicateM repeats
     . runExceptT
-    . fmap getFee
+    . fmap unCoin
   where
     -- Use method R-8 from to get top 90%.
     -- https://en.wikipedia.org/wiki/Quantile#Estimating_quantiles_from_a_sample
@@ -2017,7 +2034,7 @@ estimateFeeForCoinSelection deposit'
         . quantiles medianUnbiased (V.fromList [1, 10]) 10
         . V.fromList
         . map fromIntegral
-    mkFeeEstimation [a,b] = FeeEstimation a b deposit'
+    mkFeeEstimation [a,b] = FeeEstimation a b
     mkFeeEstimation _ = error "estimateFeeForCoinSelection: impossible"
 
     -- Remove failed coin selections from samples. Unless they all failed, in

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

@@ -1507,11 +1507,6 @@ mkApiTransactionFromInfo ti (TransactionInfo txid fee ins outs ws meta depth txt
   where
       drop2nd (a,_,c) = (a,c)
 
-apiFee :: FeeEstimation -> ApiFee
-apiFee (FeeEstimation estMin estMax deposit) =
-    ApiFee (qty estMin) (qty estMax) (qty $ fromMaybe 0 deposit)
-  where qty = Quantity . fromIntegral
-
 postTransactionFee
     :: forall ctx s k n.
         ( ctx ~ ApiLayer s k
@@ -1542,7 +1537,7 @@ postTransactionFee ctx (ApiT wid) body = do
                 liftIO $ W.readNextWithdrawal @_ @s @k wrk wid wdrl
 
         fee <- liftHandler $ W.estimateFeeForPayment @_ @s @k wrk wid outs wdrl md
-        pure $ apiFee fee
+        pure $ mkApiFee fee Nothing
 
 joinStakePool
     :: forall ctx s n k.
@@ -2092,6 +2087,11 @@ mkApiCoin
     -> Quantity "lovelace" Natural
 mkApiCoin (Coin c) = Quantity $ fromIntegral c
 
+mkApiFee :: Maybe Coin -> FeeEstimation -> ApiFee
+mkApiFee deposit (FeeEstimation estMin estMax) =
+    ApiFee (qty estMin) (qty estMax) (qty $ unCoin $ fromMaybe (Coin 0) deposit)
+  where qty = Quantity . fromIntegral
+
 mkApiWithdrawal
     :: forall (n :: NetworkDiscriminant). ()
     => (RewardAccount, Coin)