fix unflatten and simplify flatten

the unflatten needs to merge at the second level

cardano-api/src/Cardano/Api/Value.hs

@@ -135,23 +135,32 @@ instance ToJSON Value where
   toJSON = toJSON . unflatten
 
 unflatten :: Value -> AssetsBundle
-unflatten (Value flatMap) = AssetsBundle [ toBundle aIdq | aIdq <- Map.toList flatMap]
- where
-   toBundle :: (AssetId, Quantity) -> AssetIdBundle
-   toBundle (AssetId pId aName, q) = AssetIdBundle pId $ Map.singleton aName q
-   toBundle (AdaAssetId, q) = AdaAsset q
+unflatten v@(Value flatMap) =
+    -- unflatten all the non-ada assets, and add ada separately
+    AssetsBundle $
+        [ AdaAsset q | let q = selectAsset v AdaAssetId, q /= 0 ]
+     ++ [ AssetIdBundle pId qs | (pId, qs) <- Map.toList nonAdaAssets ]
+  where
+    nonAdaAssets :: Map PolicyId (Map AssetName Quantity)
+    nonAdaAssets =
+      Map.fromListWith (Map.unionWith (<>))
+        [ (pId, Map.singleton aName q)
+        | (AssetId pId aName, q) <- Map.toList flatMap ]
 
 instance FromJSON Value where
   parseJSON jv = flatten <$> parseJSON jv
 
 flatten :: AssetsBundle -> Value
 flatten (AssetsBundle bundles) =
-  Value . Map.fromList $ concat [ convToTuple aIdBundle | aIdBundle <- bundles]
- where
-  convToTuple :: AssetIdBundle -> [(AssetId, Quantity)]
-  convToTuple (AssetIdBundle pId aNameAndQuantityMap) =
-    map (\(aName,q) -> (AssetId pId aName, q)) $ Map.toList aNameAndQuantityMap
-  convToTuple (AdaAsset q) = pure $ (AdaAssetId, q)
+    Value $
+      Map.fromList
+        [ (aId, q)
+        | bundle   <- bundles
+        , (aId, q) <- case bundle of
+                        AdaAsset          q  -> [ (AdaAssetId, q) ]
+                        AssetIdBundle pId qs -> [ (AssetId pId aName, q)
+                                                | (aName, q) <- Map.toList qs ]
+        ]
 
 -- | Intermediate representation used in the JSON parsing\/rendering of 'Value'
 newtype AssetsBundle = AssetsBundle [AssetIdBundle]