refactor(internal): improve clarity and maintainability of alonzoTxOutParser

cardano-api/src/Cardano/Api/Tx/Internal/Output.hs

@@ -586,31 +586,35 @@ instance IsShelleyBasedEra era => FromJSON (TxOut CtxTx era) where
     alonzoTxOutParser
       :: AlonzoEraOnwards era -> Aeson.Object -> Aeson.Parser (TxOut CtxTx era)
     alonzoTxOutParser w o = do
+      -- Parse optional datum fields (both hash and JSON value may be present)
       mDatumHash <- o .:? "datumhash"
-      mDatumVal <- o .:? "datum"
-      case (mDatumVal, mDatumHash) of
-        (Nothing, Nothing) ->
-          TxOut
-            <$> o .: "address"
-            <*> o .: "value"
-            <*> return TxOutDatumNone
-            <*> return ReferenceScriptNone
-        (Just dVal, Just{}) -> do
-          case scriptDataJsonToHashable ScriptDataJsonDetailedSchema dVal of
-            Left e -> fail $ "Error parsing ScriptData: " <> show e
-            Right hashableData ->
-              TxOut
-                <$> o .: "address"
-                <*> o .: "value"
-                <*> return (TxOutSupplementalDatum w hashableData)
-                <*> return ReferenceScriptNone
-        (Nothing, Just dHash) ->
-          TxOut
-            <$> o .: "address"
-            <*> o .: "value"
-            <*> return (TxOutDatumHash w dHash)
-            <*> return ReferenceScriptNone
-        (Just _dVal, Nothing) -> fail "Only datum JSON was found, this should not be possible."
+      mDatumJson <- o .:? "datum"
+
+      -- Parse required fields common to all TxOuts
+      parsedAddress <- o .: "address"
+      parsedValue <- o .: "value"
+
+      -- Parse datum based on which fields are present
+      txOutDatum <-
+        case (mDatumJson, mDatumHash) of
+          -- No datum information provided
+          (Nothing, Nothing) ->
+            pure TxOutDatumNone
+          -- Only datum hash provided (datum not included in tx)
+          (Nothing, Just dHash) ->
+            pure (TxOutDatumHash w dHash)
+          -- Both hash and JSON provided (supplemental datum in tx body)
+          (Just datumJson, Just{}) -> do
+            case scriptDataJsonToHashable ScriptDataJsonDetailedSchema datumJson of
+              Left e -> fail $ "Error parsing ScriptData: " <> show e
+              Right hashableData ->
+                pure (TxOutSupplementalDatum w hashableData)
+          -- Only JSON provided without hash (invalid state)
+          (Just _datumJson, Nothing) ->
+            fail "Only datum JSON was found, this should not be possible."
+
+      -- Note: ReferenceScript is always None for Alonzo-era parsing
+      pure $ TxOut parsedAddress parsedValue txOutDatum ReferenceScriptNone
 
 instance IsShelleyBasedEra era => FromJSON (TxOut CtxUTxO era) where
   parseJSON = withObject "TxOut" $ \o -> do