Add SqlMarshaller GADT with applicative combinators

orville-sqlite.cabal

@@ -18,6 +18,7 @@ library
       Orville.SQLite.FieldDefinition
       Orville.SQLite.Monad
       Orville.SQLite.RawSql
+      Orville.SQLite.SqlMarshaller
       Orville.SQLite.SqlType
   hs-source-dirs: src
   build-depends:

src/Orville/SQLite/SqlMarshaller.hs

@@ -0,0 +1,166 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Orville.SQLite.SqlMarshaller
+  ( SqlMarshaller
+  , FieldInfo (..)
+  , marshallField
+  , marshallReadOnlyField
+  , marshallMaybe
+  , marshallerFieldInfo
+  , marshallerDerivedColumns
+  , marshallerEncodeWrite
+  , marshallerDecodeRow
+  ) where
+
+import qualified Database.SQLite3 as SQLite3
+import Orville.SQLite.FieldDefinition
+  ( FieldDefinition (..)
+  , Nullability (..)
+  , fieldColumnName
+  , fieldToSqlValue
+  , fieldFromSqlValue
+  , fieldIsNullable
+  , fieldSqlTypeName
+  )
+
+data FieldInfo = FieldInfo
+  { fieldInfoName :: String
+  , fieldInfoType :: String
+  , fieldInfoIsNullable :: Bool
+  }
+
+data SqlMarshaller writeEntity readEntity where
+  MarshallPure :: readEntity -> SqlMarshaller writeEntity readEntity
+  MarshallApply ::
+    SqlMarshaller writeEntity (a -> b) ->
+    SqlMarshaller writeEntity a ->
+    SqlMarshaller writeEntity b
+  MarshallNest ::
+    (writeEntity -> a) ->
+    SqlMarshaller a readEntity ->
+    SqlMarshaller writeEntity readEntity
+  MarshallField ::
+    FieldDefinition nullability a ->
+    SqlMarshaller a a
+  MarshallMaybe ::
+    FieldDefinition 'Nullable a ->
+    SqlMarshaller (Maybe a) (Maybe a)
+  MarshallReadOnly ::
+    SqlMarshaller a readEntity ->
+    SqlMarshaller b readEntity
+
+instance Functor (SqlMarshaller w) where
+  fmap f m = MarshallPure f `MarshallApply` m
+
+instance Applicative (SqlMarshaller w) where
+  pure = MarshallPure
+  (<*>) = MarshallApply
+
+marshallField ::
+  (writeEntity -> a) ->
+  FieldDefinition 'NotNull a ->
+  SqlMarshaller writeEntity a
+marshallField accessor fieldDef =
+  MarshallNest accessor (MarshallField fieldDef)
+
+marshallReadOnlyField ::
+  FieldDefinition nullability a ->
+  SqlMarshaller writeEntity a
+marshallReadOnlyField fieldDef =
+  MarshallReadOnly (MarshallField fieldDef)
+
+marshallMaybe ::
+  (writeEntity -> Maybe a) ->
+  FieldDefinition 'Nullable a ->
+  SqlMarshaller writeEntity (Maybe a)
+marshallMaybe accessor fieldDef =
+  MarshallNest accessor (MarshallMaybe fieldDef)
+
+marshallerFieldInfo ::
+  SqlMarshaller writeEntity readEntity ->
+  [FieldInfo]
+marshallerFieldInfo marshaller =
+  reverse $ go marshaller []
+  where
+    go :: SqlMarshaller w r -> [FieldInfo] -> [FieldInfo]
+    go (MarshallPure _) acc = acc
+    go (MarshallApply m1 m2) acc = go m1 (go m2 acc)
+    go (MarshallNest _ m) acc = go m acc
+    go (MarshallField fieldDef) acc =
+      FieldInfo
+        (fieldColumnName fieldDef)
+        (fieldSqlTypeName fieldDef)
+        (fieldIsNullable fieldDef)
+        : acc
+    go (MarshallMaybe fieldDef) acc =
+      FieldInfo
+        (fieldColumnName fieldDef)
+        (fieldSqlTypeName fieldDef)
+        (True :: Bool)
+        : acc
+    go (MarshallReadOnly m) acc = go m acc
+
+marshallerDerivedColumns ::
+  SqlMarshaller writeEntity readEntity ->
+  [String]
+marshallerDerivedColumns marshaller =
+  reverse $ go marshaller []
+  where
+    go :: SqlMarshaller w r -> [String] -> [String]
+    go (MarshallPure _) acc = acc
+    go (MarshallApply m1 m2) acc = go m1 (go m2 acc)
+    go (MarshallNest _ m) acc = go m acc
+    go (MarshallField fieldDef) acc = fieldColumnName fieldDef : acc
+    go (MarshallMaybe fieldDef) acc = fieldColumnName fieldDef : acc
+    go (MarshallReadOnly m) acc = go m acc
+
+marshallerEncodeWrite ::
+  SqlMarshaller writeEntity readEntity ->
+  writeEntity ->
+  [(String, SQLite3.SQLData)]
+marshallerEncodeWrite marshaller entity =
+  reverse $ go marshaller entity []
+  where
+    go :: SqlMarshaller w r -> w -> [(String, SQLite3.SQLData)] -> [(String, SQLite3.SQLData)]
+    go (MarshallPure _) _ acc = acc
+    go (MarshallApply m1 m2) w acc =
+      go m1 w (go m2 w acc)
+    go (MarshallNest accessor m) w acc =
+      go m (accessor w) acc
+    go (MarshallField fieldDef) a acc =
+      (fieldColumnName fieldDef, fieldToSqlValue a fieldDef) : acc
+    go (MarshallMaybe fieldDef) a acc =
+      case a of
+        Nothing -> (fieldColumnName fieldDef, SQLite3.SQLNull) : acc
+        Just val -> (fieldColumnName fieldDef, fieldToSqlValue val fieldDef) : acc
+    go (MarshallReadOnly _) _ acc = acc
+
+marshallerDecodeRow ::
+  SqlMarshaller writeEntity readEntity ->
+  [(String, SQLite3.SQLData)] ->
+  Either String readEntity
+marshallerDecodeRow marshaller rowData =
+  go marshaller rowData
+  where
+    go :: SqlMarshaller w r -> [(String, SQLite3.SQLData)] -> Either String r
+    go (MarshallPure r) _ = Right r
+    go (MarshallApply m1 m2) rd = do
+      f <- go m1 rd
+      a <- go m2 rd
+      Right (f a)
+    go (MarshallNest _ m) rd = go m rd
+    go (MarshallField fieldDef) rd =
+      case lookup (fieldColumnName fieldDef) rd of
+        Just sqlVal -> fieldFromSqlValue sqlVal fieldDef
+        Nothing ->
+          Left $ "Column '" <> fieldColumnName fieldDef <> "' not found in result row"
+    go (MarshallMaybe fieldDef) rd =
+      case lookup (fieldColumnName fieldDef) rd of
+        Just SQLite3.SQLNull -> Right Nothing
+        Just sqlVal -> Just <$> fieldFromSqlValue sqlVal fieldDef
+        Nothing ->
+          Left $ "Column '" <> fieldColumnName fieldDef <> "' not found in result row"
+    go (MarshallReadOnly m) rd = go m rd