From 07b66682505aa2a6ce7397ac0003b560bfe649b5 Mon Sep 17 00:00:00 2001
From: Pablo Lamela <pablo.lamela@iohk.io>
Date: Wed, 13 Nov 2024 12:11:41 +0100
Subject: [PATCH] Add functional dependency to `ExtendedSigningKeyRole` and
 comments

---
 cardano-api/internal/Cardano/Api/Keys/Mnemonics.hs | 14 +++++++++++---
 .../cardano-api-test/Test/Cardano/Api/Address.hs   |  8 ++++----
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/cardano-api/internal/Cardano/Api/Keys/Mnemonics.hs b/cardano-api/internal/Cardano/Api/Keys/Mnemonics.hs
index e7cd2f91f..557a0dda1 100644
--- a/cardano-api/internal/Cardano/Api/Keys/Mnemonics.hs
+++ b/cardano-api/internal/Cardano/Api/Keys/Mnemonics.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE InstanceSigs #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeApplications #-}
 
 module Cardano.Api.Keys.Mnemonics
@@ -68,10 +68,18 @@ instance Error MnemonicToSigningStakeKeyError where
   prettyError (InvalidAccountNumberError accNo) = "Invalid account number: " <> pretty accNo
   prettyError (InvalidPaymentKeyNoError keyNo) = "Invalid payment key number: " <> pretty keyNo
 
-class ExtendedSigningKeyRole keyrole indexType where
+class ExtendedSigningKeyRole keyrole indexType | keyrole -> indexType where
   -- | Derive an extended private key of the keyrole from an account extended private key
   deriveSigningKeyFromAccount
-    :: AsType keyrole -> Shelley 'AccountK XPrv -> indexType -> Either Word32 (SigningKey keyrole)
+    :: AsType keyrole
+    -- ^ Type of the extended signing key to generate.
+    -> Shelley 'AccountK XPrv
+    -- ^ The account extended private key from which to derivate the private key for the keyrole.
+    -> indexType
+    -- ^ The payment key number in the derivation path (as 'Word32') if applicable for
+    -- the given key role, otherwise '()'. First key is 0.
+    -> Either Word32 (SigningKey keyrole)
+    -- ^ The derived extended signing key or the 'indexType' if it is 'Word32' and it is invalid.
 
 instance ExtendedSigningKeyRole PaymentExtendedKey Word32 where
   deriveSigningKeyFromAccount
diff --git a/cardano-api/test/cardano-api-test/Test/Cardano/Api/Address.hs b/cardano-api/test/cardano-api-test/Test/Cardano/Api/Address.hs
index 85d0afd08..b66d714c2 100644
--- a/cardano-api/test/cardano-api-test/Test/Cardano/Api/Address.hs
+++ b/cardano-api/test/cardano-api-test/Test/Cardano/Api/Address.hs
@@ -74,7 +74,7 @@ exampleMnemonic =
 prop_payment_derivation_is_accurate :: Property
 prop_payment_derivation_is_accurate = H.propertyOnce $ do
   signingKey <-
-    H.evalEither $ signingKeyFromMnemonic AsPaymentExtendedKey exampleMnemonic 0 (0 :: Word32)
+    H.evalEither $ signingKeyFromMnemonic AsPaymentExtendedKey exampleMnemonic 0 0
   let verificationKey =
         getVerificationKey (signingKey :: SigningKey PaymentExtendedKey)
           :: VerificationKey PaymentExtendedKey
@@ -92,7 +92,7 @@ prop_payment_derivation_is_accurate = H.propertyOnce $ do
 prop_stake_derivation_is_accurate :: Property
 prop_stake_derivation_is_accurate = H.propertyOnce $ do
   signingKey <-
-    H.evalEither $ signingKeyFromMnemonic AsStakeExtendedKey exampleMnemonic 0 (0 :: Word32)
+    H.evalEither $ signingKeyFromMnemonic AsStakeExtendedKey exampleMnemonic 0 0
   let verificationKey =
         getVerificationKey (signingKey :: SigningKey StakeExtendedKey) :: VerificationKey StakeExtendedKey
       addr =
@@ -106,9 +106,9 @@ prop_stake_derivation_is_accurate = H.propertyOnce $ do
 prop_payment_with_stake_derivation_is_accurate :: Property
 prop_payment_with_stake_derivation_is_accurate = H.propertyOnce $ do
   paymentSigningKey <-
-    H.evalEither $ signingKeyFromMnemonic AsPaymentExtendedKey exampleMnemonic 0 (0 :: Word32)
+    H.evalEither $ signingKeyFromMnemonic AsPaymentExtendedKey exampleMnemonic 0 0
   stakeSigningKey <-
-    H.evalEither $ signingKeyFromMnemonic AsStakeExtendedKey exampleMnemonic 0 (0 :: Word32)
+    H.evalEither $ signingKeyFromMnemonic AsStakeExtendedKey exampleMnemonic 0 0
   let paymentVerificationKey =
         getVerificationKey (paymentSigningKey :: SigningKey PaymentExtendedKey)
           :: VerificationKey PaymentExtendedKey