Elm.hs

{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeOperators #-}
{-# OPTIONS_GHC -Wno-partial-type-signatures #-}
module Language.Haskell.To.Elm where

import Protolude hiding (All, Infix, Type)

import qualified Bound
import qualified Data.Aeson as Aeson
import Data.HashMap.Lazy (HashMap)
import qualified Data.HashMap.Lazy as HashMap
import Data.String
import Data.Text (Text)
import Data.Time
import Generics.SOP as SOP

import Language.Elm.Definition (Definition)
import qualified Language.Elm.Definition as Definition
import Language.Elm.Expression (Expression)
import qualified Language.Elm.Expression as Expression
import qualified Language.Elm.Name as Name
import qualified Language.Elm.Pattern as Pattern
import Language.Elm.Type (Type)
import qualified Language.Elm.Type as Type

-------------------------------------------------------------------------------
-- * Classes

-- | Represents that the corresponding Elm type for the Haskell type @a@ is @'elmType' \@a@.
class HasElmType a where
  elmType :: Type v
  default elmType :: Type v
  elmType =
    Type.Global $
      maybe
        (panic "default-implemented 'elmType' without a definition")
        Definition.name $
          elmDefinition @a

  -- | When 'Just', this represents that we can generate the definition for the
  -- Elm type that corresponds to @a@ using @'elmDefinition' \@a@.
  --
  -- See 'deriveElmTypeDefinition' for a way to automatically derive 'elmDefinition'.
  --
  -- When 'Nothing', it means that the type is an already existing Elm type
  -- that does not need to be generated.
  elmDefinition :: Maybe Definition
  elmDefinition =
    Nothing

  {-# minimal elmType | elmDefinition #-}

-- | Represents that the Elm type that corresponds to @a@ has a decoder from
-- @value@, namely @'elmDecoder' \@value \@a@.
class HasElmType a => HasElmDecoder value a where
  elmDecoder :: Expression v
  default elmDecoder :: Expression v
  elmDecoder =
    Expression.Global $
      maybe
        (panic "default-implemented 'elmDecoder' without a definition")
        Definition.name $
          elmDecoderDefinition @value @a

  -- | When 'Just', this represents that we can generate the Elm decoder definition
  -- from @value@ for the Elm type that corresponds to @a@.
  --
  -- See 'deriveElmJSONDecoder' for a way to automatically derive
  -- 'elmDecoderDefinition' when @value = 'Aeson.Value'@.
  elmDecoderDefinition :: Maybe Definition
  elmDecoderDefinition =
    Nothing

  {-# minimal elmDecoder | elmDecoderDefinition #-}

-- | Represents that the Elm type that corresponds to @a@ has an encoder into
-- @value@, namely @'elmEncoder' \@value \@a@.
--
-- This class has a default instance for types that satisfy
-- 'HasElmEncoderDefinition', which refers to the name of that definition.
class HasElmType a => HasElmEncoder value a where
  elmEncoder :: Expression v
  default elmEncoder :: Expression v
  elmEncoder =
    Expression.Global $
      maybe
        (panic "default-implemented 'elmEncoder' without a definition")
        Definition.name $
          elmEncoderDefinition @value @a

  -- | When 'Just', this represents that we can generate the Elm encoder
  -- definition into @value@ for the Elm type that corresponds to @a@.
  --
  -- See 'deriveElmJSONEncoder' for a way to automatically derive
  -- 'elmEncoderDefinition' when @value = 'Aeson.Value'@.
  elmEncoderDefinition :: Maybe Definition
  elmEncoderDefinition =
    Nothing

  {-# minimal elmEncoder | elmEncoderDefinition #-}

-------------------------------------------------------------------------------
-- * Derivers

-- | Elm code generation options
newtype Options = Options
  { fieldLabelModifier :: String -> String -- ^ Use this function to go from Haskell record field name to Elm record field name.
  }

defaultOptions :: Options
defaultOptions =
  Options
    { fieldLabelModifier = identity
    }

-- | Automatically create an Elm definition given a Haskell type.
--
-- This is suitable for use as the 'elmDefinition' in a 'HasElmType' instance:
--
-- @
-- instance 'HasElmType' MyType where
--   'elmDefinition' =
--     'Just' $ 'deriveElmTypeDefinition' \@MyType 'defaultOptions' \"Api.MyType.MyType\"
-- @
deriveElmTypeDefinition :: forall a. (HasDatatypeInfo a, All2 HasElmType (Code a)) => Options -> Name.Qualified -> Definition
deriveElmTypeDefinition options name =
  case datatypeInfo (Proxy @a) of
    ADT _mname _tname (Record _cname fields :* Nil) ->
      Definition.Alias name (Type.Record (recordFields fields))

    ADT _mname _tname cs ->
      Definition.Type name (constructors cs)

    Newtype _mname _tname (Record _cname fields) ->
      Definition.Alias name (Type.Record (recordFields fields))

    Newtype _mname _tname c ->
      Definition.Type name (constructors (c :* Nil))
  where
    recordFields :: All HasElmType xs => NP FieldInfo xs -> [(Name.Field, Type v)]
    recordFields Nil = []
    recordFields (f :* fs) = field f : recordFields fs

    field :: forall x v. HasElmType x => FieldInfo x -> (Name.Field, Type v)
    field (FieldInfo fname) =
      (fromString $ fieldLabelModifier options fname, elmType @x)

    constructors :: All2 HasElmType xss => NP ConstructorInfo xss -> [(Name.Constructor, [Type v])]
    constructors Nil = []
    constructors (c :* cs) = constructor c : constructors cs

    constructor :: forall xs v. All HasElmType xs => ConstructorInfo xs -> (Name.Constructor, [Type v])
    constructor (Constructor cname) = (fromString cname, constructorFields $ shape @_ @xs)
    constructor (Infix _ _ _) = panic "Infix constructors are not supported"
    constructor (Record cname fs) = (fromString cname, [Type.Record $ recordFields fs])

    constructorFields :: All HasElmType xs => Shape xs -> [Type v]
    constructorFields ShapeNil = []
    constructorFields s@(ShapeCons _) = go s
      where
        go :: forall x xs v. (HasElmType x, All HasElmType xs) => Shape (x ': xs) -> [Type v]
        go (ShapeCons s') = elmType @x : constructorFields s'

-- | Automatically create an Elm JSON decoder definition given a Haskell type.
--
-- This is suitable for use as the 'elmDecoderDefinition' in a
-- @'HasElmDecoder' 'Aeson.Value'@ instance:
--
-- @
-- instance 'HasElmDecoder' 'Aeson.Value' MyType where
--   'elmDecoderDefinition' =
--     Just $ 'deriveElmJSONDecoder' \@MyType 'defaultOptions' 'Aeson.defaultOptions' "Api.MyType.decoder"
-- @
--
-- Uses the given 'Aeson.Options' to match the JSON format of derived
-- 'Aeson.FromJSON' and 'Aeson.ToJSON' instances.
deriveElmJSONDecoder
  :: forall a
  . (HasDatatypeInfo a, HasElmType a, All2 (HasElmDecoder Aeson.Value) (Code a))
  => Options
  -> Aeson.Options
  -> Name.Qualified
  -> Definition
deriveElmJSONDecoder options aesonOptions decoderName =
  Definition.Constant decoderName (Type.App "Json.Decode.Decoder" $ elmType @a) $
  case datatypeInfo (Proxy @a) of
    ADT _mname _tname (Record _cname fields :* Nil) ->
      decodeRecord fields $
      Expression.App "Json.Decode.succeed" $
      case Type.appsView (elmType @a) of
        (Type.Record fieldTypes, _) ->
          explicitRecordConstructor $ fst <$> fieldTypes

        _ ->
          Expression.Global typeName

    ADT _mname _tname cs ->
      decodeConstructors $ constructors cs

    Newtype _mname _tname (Record _cname fields) ->
      decodeRecord fields $
      Expression.App "Json.Decode.succeed" $
      case Type.appsView (elmType @a) of
        (Type.Record fieldTypes, _) ->
          explicitRecordConstructor $ fst <$> fieldTypes

        _ ->
          Expression.Global typeName

    Newtype _mname _tname c ->
      decodeConstructors $ constructors (c :* Nil)
  where
    typeName@(Name.Qualified moduleName_ _) =
      case Type.appsView (elmType @a) of
        (Type.Global tname, _) -> tname

        _ ->
          panic "Can't automatically derive JSON decoder for an anonymous Elm type"

    constructors
      :: All2 (HasElmDecoder Aeson.Value) xss
      => NP ConstructorInfo xss
      -> [(String, [Expression v])]
    constructors Nil = []
    constructors (c :* cs) = constructor c : constructors cs

    constructor
      :: forall xs v
      . All (HasElmDecoder Aeson.Value) xs
      => ConstructorInfo xs
      -> (String, [Expression v])
    constructor (Constructor cname) =
      (cname, constructorFields $ shape @_ @xs)
    constructor (Infix _ _ _) =
      panic "Infix constructors are not supported"
    constructor (Record cname fs) =
      (cname, [decodeRecord fs $ explicitRecordConstructor $ recordFieldNames fs])

    constructorFields
      :: All (HasElmDecoder Aeson.Value) xs
      => Shape xs
      -> [Expression v]
    constructorFields ShapeNil = []
    constructorFields s@(ShapeCons _) = go s
      where
        go
          :: forall x xs v
          . (HasElmDecoder Aeson.Value x, All (HasElmDecoder Aeson.Value) xs)
          => Shape (x ': xs)
          -> [Expression v]
        go (ShapeCons s') = elmDecoder @Aeson.Value @x : constructorFields s'

    explicitRecordConstructor
      :: [Name.Field]
      -> Expression v
    explicitRecordConstructor names =
      go mempty names
      where
        go :: HashMap Name.Field v -> [Name.Field] -> Expression v
        go locals fnames =
          case fnames of
            [] ->
              Expression.Record [(name, Expression.Var $ locals HashMap.! name) | name <- names]

            fname:fnames' ->
              Expression.Lam $ Bound.toScope $ go (HashMap.insert fname (Bound.B ()) $ Bound.F <$> locals) fnames'

    decodeRecord
      :: All (HasElmDecoder Aeson.Value) xs
      => NP FieldInfo xs
      -> Expression v
      -> Expression v
    decodeRecord (f :* Nil)
      | Aeson.unwrapUnaryRecords aesonOptions =
        unwrappedRecordField f
    decodeRecord fs =
      recordFields fs

    recordFields
      :: All (HasElmDecoder Aeson.Value) xs
      => NP FieldInfo xs
      -> Expression v
      -> Expression v
    recordFields Nil e = e
    recordFields (f :* fs) e =
      recordFields fs $ recordField f e

    isMaybe :: forall t. HasElmType t => Bool
    isMaybe =
      case Type.appsView $ elmType @t of
        (Type.Global "Maybe.Maybe", _) -> True
        _ -> False

    recordField
      :: forall x v
      . HasElmDecoder Aeson.Value x
      => FieldInfo x
      -> Expression v
      -> Expression v
    recordField (FieldInfo fname) e
      | Aeson.omitNothingFields aesonOptions && isMaybe @x =
        e Expression.|>
          Expression.apps
            "Json.Decode.Pipeline.optional"
            [ jsonFieldName fname
            , elmDecoder @Aeson.Value @x
            , "Maybe.Nothing"
            ]

      | otherwise =
        e Expression.|>
          Expression.apps
            "Json.Decode.Pipeline.required"
            [ jsonFieldName fname
            , elmDecoder @Aeson.Value @x
            ]

    unwrappedRecordField
      :: forall x v
      . HasElmDecoder Aeson.Value x
      => FieldInfo x
      -> Expression v
      -> Expression v
    unwrappedRecordField (FieldInfo _) e =
      e Expression.|> elmDecoder @Aeson.Value @x

    recordFieldNames
      :: All (HasElmDecoder Aeson.Value) xs
      => NP FieldInfo xs
      -> [Name.Field]
    recordFieldNames Nil = []
    recordFieldNames (FieldInfo fname :* fs) =
      elmField fname : recordFieldNames fs

    constructorJSONName :: String -> Text
    constructorJSONName = toS . Aeson.constructorTagModifier aesonOptions

    jsonFieldName :: String -> Expression v
    jsonFieldName = Expression.String . toS . Aeson.fieldLabelModifier aesonOptions

    elmField :: String -> Name.Field
    elmField = fromString . fieldLabelModifier options

    decodeConstructor :: String -> Expression v -> [Expression v] -> Expression v
    decodeConstructor _ constr [] =
      Expression.App "Json.Decode.succeed" constr

    decodeConstructor contentsName constr [constrField] =
      Expression.App "Json.Decode.succeed" constr Expression.|>
        Expression.apps "Json.Decode.Pipeline.required" [Expression.String (toS contentsName), constrField]

    decodeConstructor contentsName constr constrFields =
      Expression.apps
        "Json.Decode.field"
        [ Expression.String (toS contentsName)
        , foldl'
          (Expression.|>)
          (Expression.App "Json.Decode.succeed" constr)
          [ Expression.App
            "Json.Decode.Pipeline.custom"
            (Expression.apps "Json.Decode.index" [Expression.Int index, field])
          | (index, field) <- zip [0..] constrFields
          ]
        ]

    decodeConstructors :: [(String, [Expression v])] -> Expression v
    decodeConstructors [(constr, constrFields)]
      | not $ Aeson.tagSingleConstructors aesonOptions =
        let
          qualifiedConstr =
            Expression.Global $ Name.Qualified moduleName_ $ toS constr
        in
        case constrFields of
          [constrField] ->
            Expression.apps "Json.Decode.map" [qualifiedConstr, constrField]

          _ ->
            foldl'
              (Expression.|>)
              (Expression.App "Json.Decode.succeed" qualifiedConstr)
              [Expression.App
                "Json.Decode.Pipeline.custom"
                (Expression.apps "Json.Decode.index" [Expression.Int index, field])
              | (index, field) <- zip [0..] constrFields
              ]

    decodeConstructors constrs
      | Aeson.allNullaryToStringTag aesonOptions && allNullary constrs =
        "Json.Decode.string" Expression.|> Expression.App "Json.Decode.andThen" (Expression.Lam
          (Bound.toScope $ Expression.Case (pure $ Bound.B ()) $
            [ ( Pattern.String $ constructorJSONName constr
              , Bound.toScope $ Expression.App "Json.Decode.succeed" qualifiedConstr
              )
            | (constr, _) <- constrs
            , let
                qualifiedConstr =
                  Expression.Global $ Name.Qualified moduleName_ $ toS constr
            ]
            ++
            [ ( Pattern.Wildcard
              , Bound.toScope $ Expression.App "Json.Decode.fail" $ Expression.String "No matching constructor"
              )
            ]
          ))

    decodeConstructors constrs =
      case Aeson.sumEncoding aesonOptions of
        Aeson.TaggedObject tagName contentsName ->
          Expression.apps "Json.Decode.field" [Expression.String $ toS tagName, "Json.Decode.string"] Expression.|>
            Expression.App "Json.Decode.andThen" (Expression.Lam
              (Bound.toScope $ Expression.Case (pure $ Bound.B ()) $
                [ ( Pattern.String $ constructorJSONName constr
                  , Bound.toScope $ decodeConstructor contentsName qualifiedConstr (fmap (Bound.F . Bound.F) <$> fields)
                  )
              | (constr, fields) <- constrs
              , let
                  qualifiedConstr =
                    Expression.Global $ Name.Qualified moduleName_ $ toS constr
              ]
              ++
              [ ( Pattern.Wildcard
                , Bound.toScope $ Expression.App "Json.Decode.fail" $ Expression.String "No matching constructor"
                )
              ]
            ))

        _ -> panic "Only the DataAeson.TaggedObject sumEncoding is currently supported"

    allNullary :: forall c f. [(c, [f])] -> Bool
    allNullary = all (null . snd)

-- | Automatically create an Elm JSON encoder definition given a Haskell type.
--
-- This is suitable for use as the 'elmEncoderDefinition' in a @'HasElmEncoder 'Aeson.Value'@ instance:
--
-- @
-- instance 'HasElmEncoder' 'Aeson.Value' MyType where
--   'elmEncoderDefinition' =
--     'Just' $ 'deriveElmJSONEncoder' \@MyType 'defaultOptions' 'Aeson.defaultOptions' "Api.MyType.encoder"
-- @
--
-- Uses the given 'Aeson.Options' to match the JSON format of derived
-- 'Aeson.FromJSON' and 'Aeson.ToJSON' instances.
deriveElmJSONEncoder
  :: forall a
  . (HasDatatypeInfo a, HasElmType a, All2 (HasElmEncoder Aeson.Value) (Code a))
  => Options
  -> Aeson.Options
  -> Name.Qualified
  -> Definition
deriveElmJSONEncoder options aesonOptions encoderName =
  Definition.Constant encoderName (Type.Fun (elmType @a) "Json.Encode.Value") $
  Expression.Lam $ Bound.toScope $
    case datatypeInfo (Proxy @a) of
      ADT _mname _tname (Record _cname fields :* Nil) ->
        encodeRecord fields $ pure $ Bound.B ()

      ADT _mname _tname cs ->
        encodeConstructors (constructors cs) (pure $ Bound.B ())

      Newtype _mname _tname (Record _cname fields) ->
        encodeRecord fields $ pure $ Bound.B ()

      Newtype _mname _tname c ->
        encodeConstructors (constructors (c :* Nil)) (pure $ Bound.B ())
  where
    (Name.Qualified moduleName_ _) =
      case Type.appsView (elmType @a) of
        (Type.Global tname, _) -> tname

        _ ->
          panic "Can't automatically derive JSON encoder for an anonymous Elm type"

    constructors
      :: All2 (HasElmEncoder Aeson.Value) xss
      => NP ConstructorInfo xss
      -> [(String, [Expression v])]
    constructors Nil = []
    constructors (c :* cs) = constructor c : constructors cs

    constructor
      :: forall xs v
      . All (HasElmEncoder Aeson.Value) xs
      => ConstructorInfo xs
      -> (String, [Expression v])
    constructor (Constructor cname) =
      (cname, constructorFields $ shape @_ @xs)
    constructor Infix {} =
      panic "Infix constructors are not supported"
    constructor (Record cname fs) =
      (cname, [Expression.Lam $ Bound.toScope $ encodeRecord fs (pure $ Bound.B ())])

    constructorFields
      :: All (HasElmEncoder Aeson.Value) xs
      => Shape xs
      -> [Expression v]
    constructorFields ShapeNil = []
    constructorFields s@(ShapeCons _) = go s
      where
        go
          :: forall x xs v
          . (HasElmEncoder Aeson.Value x, All (HasElmEncoder Aeson.Value) xs)
          => Shape (x ': xs)
          -> [Expression v]
        go (ShapeCons s') = elmEncoder @Aeson.Value @x : constructorFields s'

    encodeRecord
      :: All (HasElmEncoder Aeson.Value) xs
      => NP FieldInfo xs
      -> Expression v
      -> Expression v
    encodeRecord (f :* Nil) e
      | Aeson.unwrapUnaryRecords aesonOptions =
        unwrappedRecordField f e
    encodeRecord fs e =
      Expression.App "Json.Encode.object" $
        case recordFields fs e of
          (nonNullable, []) ->
            Expression.List nonNullable

          ([], nullable) ->
            Expression.App "List.concat" $ Expression.List nullable

          (nonNullable, nullable) ->
            Expression.apps "Basics.++"
              [ Expression.List nonNullable
              , Expression.App "List.concat" $ Expression.List nullable
              ]

    recordFields
      :: All (HasElmEncoder Aeson.Value) xs
      => NP FieldInfo xs
      -> Expression v
      -> ([Expression v], [Expression v])
    recordFields Nil _ = mempty
    recordFields (f :* fs) e =
      recordField f e <> recordFields fs e

    isMaybe :: forall t. HasElmType t => Bool
    isMaybe =
      case Type.appsView $ elmType @t of
        (Type.Global "Maybe.Maybe", _) -> True
        _ -> False

    recordField
      :: forall x v
      . HasElmEncoder Aeson.Value x
      => FieldInfo x
      -> Expression v
      -> ([Expression v], [Expression v])
    recordField (FieldInfo fname) e
      | Aeson.omitNothingFields aesonOptions && isMaybe @x =
        ( []
        , [ Expression.Case (Expression.App (Expression.Proj $ elmField fname) e)
            [ ( Pattern.Con "Maybe.Nothing" []
              , Bound.toScope $ Expression.List []
              )
            , ( Pattern.Con "Maybe.Just" [Pattern.Var 0]
              , Bound.toScope $
                Expression.App
                  (elmEncoder @Aeson.Value @x)
                  (Expression.App (Expression.Proj $ elmField fname) (Bound.F <$> e))
              )
            ]
          ]
        )

      | otherwise =
        ( [ Expression.tuple
            (jsonFieldName fname)
            (Expression.App (elmEncoder @Aeson.Value @x) (Expression.App (Expression.Proj $ elmField fname) e))
          ]
        , []
        )

    unwrappedRecordField
      :: forall x v
      . HasElmEncoder Aeson.Value x
      => FieldInfo x
      -> Expression v
      -> Expression v
    unwrappedRecordField (FieldInfo _) =
      Expression.App (elmEncoder @Aeson.Value @x)

    constructorJSONName :: String -> Text
    constructorJSONName = toS . Aeson.constructorTagModifier aesonOptions

    jsonFieldName :: String -> Expression v
    jsonFieldName = Expression.String . toS . Aeson.fieldLabelModifier aesonOptions

    elmField :: String -> Name.Field
    elmField = fromString . fieldLabelModifier options

    elmConstr :: String -> Name.Qualified
    elmConstr = Name.Qualified moduleName_ . fromString

    encodeConstructorFields :: [Expression v] -> Expression (Bound.Var Int v)
    encodeConstructorFields [constrField] =
      Expression.App (Bound.F <$> constrField) (pure $ Bound.B 0)

    encodeConstructorFields constrFields =
      Expression.apps
        "Json.Encode.list"
        [ "Basics.identity"
        , Expression.List
          [ Expression.App (Bound.F <$> field) (pure $ Bound.B index)
          | (index, field) <- zip [0..] constrFields
          ]
        ]

    encodeConstructors :: [(String, [Expression v])] -> Expression v -> Expression v
    encodeConstructors [(constr, constrFields)] expr
      | not $ Aeson.tagSingleConstructors aesonOptions =
        Expression.Case expr
          [ ( Pattern.Con (elmConstr constr) (Pattern.Var . fst <$> zip [0..] constrFields)
            , Bound.toScope $ encodeConstructorFields constrFields
            )
          ]

    encodeConstructors constrs expr
      | Aeson.allNullaryToStringTag aesonOptions && allNullary constrs =
        Expression.Case expr
          [ ( Pattern.Con (elmConstr constr) []
            , Bound.toScope $
              Expression.App "Json.Encode.string" $ Expression.String $ constructorJSONName constr
            )
          | (constr, _) <- constrs
          ]

    encodeConstructors constrs expr =
      case Aeson.sumEncoding aesonOptions of
        Aeson.TaggedObject tagName contentsName ->
          Expression.Case expr
            [ ( Pattern.Con (elmConstr constr) (Pattern.Var . fst <$> zip [0..] constrFields)
              , Bound.toScope $
                Expression.App "Json.Encode.object" $
                Expression.List $
                  Expression.tuple
                    (Expression.String (toS tagName))
                    (Expression.App "Json.Encode.string" $ Expression.String $ constructorJSONName constr)
                  :
                  [ Expression.tuple
                    (Expression.String (toS contentsName))
                    (encodeConstructorFields constrFields)
                  | not $ null constrFields
                  ]
              )
            | (constr, constrFields) <- constrs
            ]

        _ -> panic "Only the DataAeson.TaggedObject sumEncoding is currently supported"

    allNullary :: forall c f. [(c, [f])] -> Bool
    allNullary = all (null . snd)

-------------

instance HasElmType Int where
  elmType =
    "Basics.Int"

instance HasElmEncoder Aeson.Value Int where
  elmEncoder =
    "Json.Encode.int"

instance HasElmDecoder Aeson.Value Int where
  elmDecoder =
    "Json.Decode.int"

instance HasElmType Double where
  elmType =
    "Basics.Float"

instance HasElmEncoder Aeson.Value Double where
  elmEncoder =
    "Json.Encode.float"

instance HasElmDecoder Aeson.Value Double where
  elmDecoder =
    "Json.Decode.float"

instance HasElmType Bool where
  elmType =
    "Basics.Bool"

instance HasElmEncoder Aeson.Value Bool where
  elmEncoder =
    "Json.Encode.bool"

instance HasElmDecoder Aeson.Value Bool where
  elmDecoder =
    "Json.Decode.bool"

instance HasElmType Text where
  elmType =
    "String.String"

instance HasElmEncoder Text Text where
  elmEncoder =
    "Basics.identity"

instance HasElmDecoder Text Text where
  elmDecoder =
    "Basics.identity"

instance HasElmEncoder Text Char where
  elmEncoder =
    "String.fromChar"

instance HasElmEncoder Text Int where
  elmEncoder =
    "String.fromInt"

instance HasElmEncoder Text Double where
  elmEncoder =
    "String.fromFloat"

instance HasElmEncoder Aeson.Value Text where
  elmEncoder =
    "Json.Encode.string"

instance HasElmDecoder Aeson.Value Text where
  elmDecoder =
    "Json.Decode.string"

instance HasElmType Char where
  elmType =
    "Char.Char"

instance HasElmEncoder Aeson.Value Char where
  elmEncoder =
    "Json.Encode.string" Expression.<< "String.fromChar"

instance HasElmDecoder Aeson.Value Char where
  elmDecoder =
    "Json.Decode.string" Expression.|>
      Expression.App "Json.Decode.andThen"
      (Expression.Lam $ Bound.toScope $
        Expression.Case
          (Expression.App "String.uncons" $ Expression.Var $ Bound.B ())
          [ ( Pattern.Con "Maybe.Just" [Pattern.tuple (Pattern.Var 0) (Pattern.String "")]
            , Bound.toScope $ Expression.App "Json.Decode.succeed" $ Expression.Var $ Bound.B 0
            )
          , ( Pattern.Wildcard
            , Bound.toScope $ Expression.App "Json.Decode.fail" $ Expression.String "Not a char"
            )
          ]
      )

instance HasElmType UTCTime where
  elmType =
    "Time.Posix"

instance HasElmEncoder Aeson.Value UTCTime where
  elmEncoder =
    "Iso8601.encode"

instance HasElmDecoder Aeson.Value UTCTime where
  elmDecoder =
    "Iso8601.decoder"

instance HasElmEncoder a b => HasElmEncoder (Maybe a) (Maybe b) where
  elmEncoder = Expression.App "Maybe.map" (elmEncoder @a @b)

instance HasElmType a => HasElmType (Maybe a) where
  elmType =
    Type.App "Maybe.Maybe" (elmType @a)

instance HasElmEncoder Aeson.Value a => HasElmEncoder Aeson.Value (Maybe a) where
  elmEncoder =
    Expression.apps "Maybe.Extra.unwrap" ["Json.Encode.null", elmEncoder @Aeson.Value @a]

instance HasElmDecoder Aeson.Value a => HasElmDecoder Aeson.Value (Maybe a) where
  elmDecoder =
    Expression.App "Json.Decode.nullable" (elmDecoder @Aeson.Value @a)

instance HasElmType a => HasElmType [a] where
  elmType =
    Type.App "List.List" (elmType @a)

instance HasElmEncoder Aeson.Value a => HasElmEncoder Aeson.Value [a] where
  elmEncoder =
    Expression.App "Json.Encode.list" (elmEncoder @Aeson.Value @a)

instance HasElmDecoder Aeson.Value a => HasElmDecoder Aeson.Value [a] where
  elmDecoder =
    Expression.App "Json.Decode.list" (elmDecoder @Aeson.Value @a)

instance (HasElmType a, HasElmType b) => HasElmType (a, b) where
  elmType =
    Type.apps "Basics.," [elmType @a, elmType @b]

instance (HasElmEncoder Aeson.Value a, HasElmEncoder Aeson.Value b) => HasElmEncoder Aeson.Value (a, b) where
  elmEncoder =
    Expression.Lam $ Bound.toScope $
      Expression.Case (pure $ Bound.B ())
        [ ( Pattern.tuple (Pattern.Var 0) (Pattern.Var 1)
          , Bound.toScope $
            Expression.apps
              "Json.Encode.list"
              [ "Basics.identity"
              , Expression.List
                  [ Expression.App (elmEncoder @Aeson.Value @a) $ pure $ Bound.B 0
                  , Expression.App (elmEncoder @Aeson.Value @b) $ pure $ Bound.B 1
                  ]
              ]
          )
        ]

instance (HasElmDecoder Aeson.Value a, HasElmDecoder Aeson.Value b) => HasElmDecoder Aeson.Value (a, b) where
  elmDecoder =
    Expression.apps
      "Json.Decode.map2"
      [ "Tuple.pair"
      , Expression.apps "Json.Decode.index" [Expression.Int 0, elmDecoder @Aeson.Value @a]
      , Expression.apps "Json.Decode.index" [Expression.Int 1, elmDecoder @Aeson.Value @b]
      ]

-- | A shorthand for a list of the type definitions for
-- @'jsonDefinitions' \@MyType@ is a shorthand for creating a list of its
-- 'elmDefinition', @'elmEncoderDefinition' \@'Aeson.Value'@, and
-- @'elmDecoderDefinition' \@'Aeson.Value'@.
jsonDefinitions :: forall t. (HasElmEncoder Aeson.Value t, HasElmDecoder Aeson.Value t) => [Definition]
jsonDefinitions =
  catMaybes
  [ elmDefinition @t
  , elmEncoderDefinition @Aeson.Value @t
  , elmDecoderDefinition @Aeson.Value @t
  ]