{-# LANGUAGE ConstrainedClassMethods #-}
{-# LANGUAGE DataKinds               #-}
{-# LANGUAGE LambdaCase              #-}
{-# LANGUAGE NamedFieldPuns          #-}
{-# LANGUAGE OverloadedStrings       #-}
{-# LANGUAGE ScopedTypeVariables     #-}
{-# LANGUAGE TemplateHaskell         #-}
{-# LANGUAGE TypeApplications        #-}
{-# LANGUAGE TypeFamilies            #-}

module Data.Morpheus.Execution.Client.Aeson
  ( deriveFromJSON
  , deriveToJSON
  , takeValueType
  )
where

import           Data.Aeson
import           Data.Aeson.Types
import qualified Data.HashMap.Lazy             as H
                                                ( lookup )
import           Data.Semigroup                 ( (<>) )
import           Data.Text                      ( unpack )
import           Language.Haskell.TH

import           Data.Morpheus.Execution.Internal.Utils
                                                ( nameSpaceType )

--
-- MORPHEUS
import           Data.Morpheus.Types.Internal.AST
                                                ( DataField(..)
                                                , isFieldNullable
                                                , ConsD(..)
                                                , TypeD(..)
                                                , Key
                                                )
import           Data.Morpheus.Types.Internal.TH
                                                ( destructRecord
                                                , instanceFunD
                                                , instanceHeadT
                                                )

-- FromJSON
deriveFromJSON :: TypeD -> Q Dec
deriveFromJSON TypeD { tCons = [] } =
  fail "Type Should Have at least one Constructor"
deriveFromJSON TypeD { tName, tNamespace, tCons = [cons] } = defineFromJSON
  name
  (aesonObject tNamespace)
  cons
  where name = nameSpaceType tNamespace tName
deriveFromJSON typeD@TypeD { tName, tCons, tNamespace }
  | isEnum tCons = defineFromJSON name aesonEnum tCons
  | otherwise    = defineFromJSON name (aesonUnionObject tNamespace) typeD
  where name = nameSpaceType tNamespace tName

aesonObject :: [Key] -> ConsD -> ExpQ
aesonObject tNamespace con@ConsD { cName } = appE
  [|withObject name|]
  (lamE [varP (mkName "o")] (aesonObjectBody tNamespace con))
  where name = unpack $ nameSpaceType tNamespace cName

aesonObjectBody :: [Key] -> ConsD -> ExpQ
aesonObjectBody namespace ConsD { cName, cFields } = handleFields cFields
 where
  consName = mkName $ unpack $ nameSpaceType namespace cName
  ------------------------------------------
  handleFields []     = fail "No Empty Object"
  handleFields fields = startExp fields
  ----------------------------------------------------------------------------------
   where
    defField field@DataField { fieldName }
      | isFieldNullable field = [|o .:? fName|]
      | otherwise             = [|o .: fName|]
      where fName = unpack fieldName
        -------------------------------------------------------------------
    startExp fNames = uInfixE (conE consName)
                              (varE '(<$>))
                              (applyFields fNames)
     where
      applyFields []  = fail "No Empty fields"
      applyFields [x] = defField x
      applyFields (x : xs) =
        uInfixE (defField x) (varE '(<*>)) (applyFields xs)

aesonUnionObject :: [Key] -> TypeD -> ExpQ
aesonUnionObject namespace TypeD { tCons } = appE
  (varE 'takeValueType)
  (lamCaseE (map buildMatch tCons <> [elseCaseEXP]))
 where
  buildMatch cons@ConsD { cName } = match objectPattern body []
   where
    objectPattern = tupP [litP (stringL $ unpack cName), varP $ mkName "o"]
    body          = normalB $ aesonObjectBody namespace cons

takeValueType :: ((String, Object) -> Parser a) -> Value -> Parser a
takeValueType f (Object hMap) = case H.lookup "__typename" hMap of
  Nothing         -> fail "key \"__typename\" not found on object"
  Just (String x) -> pure (unpack x, hMap) >>= f
  Just val ->
    fail $ "key \"__typename\" should be string but found: " <> show val
takeValueType _ _ = fail "expected Object"

defineFromJSON :: Key -> (t -> ExpQ) -> t -> DecQ
defineFromJSON tName parseJ cFields = instanceD (cxt []) iHead [method]
 where
  iHead  = instanceHeadT ''FromJSON tName []
  -----------------------------------------
  method = instanceFunD 'parseJSON [] (parseJ cFields)

isEnum :: [ConsD] -> Bool
isEnum = not . isEmpty . filter (isEmpty . cFields)
  where isEmpty = (0 ==) . length

aesonEnum :: [ConsD] -> ExpQ
aesonEnum cons = lamCaseE handlers
 where
  handlers = map buildMatch cons <> [elseCaseEXP]
   where
    buildMatch ConsD { cName } = match enumPat body []
     where
      enumPat = litP $ stringL $ unpack cName
      body    = normalB $ appE (varE 'pure) (conE $ mkName $ unpack cName)

elseCaseEXP :: MatchQ
elseCaseEXP = match (varP varName) body []
 where
  varName = mkName "invalidValue"
  body    = normalB $ appE
    (varE $ mkName "fail")
    (uInfixE (appE (varE 'show) (varE varName))
             (varE '(<>))
             (stringE " is Not Valid Union Constructor")
    )

-- ToJSON
deriveToJSON :: TypeD -> Q [Dec]
deriveToJSON TypeD { tCons = [] } =
  fail "Type Should Have at least one Constructor"
deriveToJSON TypeD { tName, tCons = [ConsD { cFields }] } =
  pure <$> instanceD (cxt []) appHead methods
 where
  appHead = instanceHeadT ''ToJSON tName []
  ------------------------------------------------------------------
  -- defines: toJSON (User field1 field2 ...)= object ["name" .= name, "age" .= age, ...]
  methods = [funD 'toJSON [clause argsE (normalB body) []]]
   where
    argsE = [destructRecord tName varNames]
    body  = appE (varE 'object) (listE $ map (decodeVar . unpack) varNames)
    decodeVar name = [|name .= $(varName)|] where varName = varE $ mkName name
    varNames = map fieldName cFields
deriveToJSON TypeD { tName, tCons }
  | isEnum tCons
  = pure <$> instanceD (cxt []) (instanceHeadT ''ToJSON tName []) []
  |
    -- enum: uses default aeson instance derivation methods
    otherwise
  = fail "Input Unions are not yet supported"