{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}

-- | This module provides the functions to parse and execute @GraphQL@ queries.
module Language.GraphQL
    ( graphql
    , graphqlSubs
    ) where

import qualified Data.Aeson as Aeson
import qualified Data.Aeson.Types as Aeson
import Data.Either (fromRight)
import qualified Data.Sequence as Seq
import Data.Text (Text)
import Language.GraphQL.AST
import Language.GraphQL.Error
import Language.GraphQL.Execute
import Language.GraphQL.Type.Schema
import Text.Megaparsec (parse)

-- | If the text parses correctly as a @GraphQL@ query the query is
-- executed using the given 'Schema'.
graphql :: Monad m
    => Schema m -- ^ Resolvers.
    -> Text -- ^ Text representing a @GraphQL@ request document.
    -> m Aeson.Value -- ^ Response.
graphql schema = graphqlSubs schema mempty mempty

-- | If the text parses correctly as a @GraphQL@ query the substitution is
-- applied to the query and the query is then executed using to the given
-- 'Schema'.
graphqlSubs :: Monad m
    => Schema m -- ^ Resolvers.
    -> Maybe Text -- ^ Operation name.
    -> Aeson.Object -- ^ Variable substitution function.
    -> Text -- ^ Text representing a @GraphQL@ request document.
    -> m Aeson.Value -- ^ Response.
graphqlSubs schema operationName variableValues document'
    = either parseError executeRequest (parse document "" document')
    >>= formatResponse
  where
    executeRequest parsed
      = fromRight streamReturned
      <$> execute schema operationName variableValues parsed
    streamReturned = singleError "This service does not support subscriptions."
    formatResponse (Response data'' Seq.Empty) =
        pure $ Aeson.object [("data", data'')]
    formatResponse (Response data'' errors') = pure $ Aeson.object
        [ ("data", data'')
        , ("errors", Aeson.toJSON $ fromError <$> errors')
        ]
    fromError Error{ locations = [], ..} =
        Aeson.object [("message", Aeson.toJSON message)]
    fromError Error{..} = Aeson.object
        [ ("message", Aeson.toJSON message)
        , ("locations", Aeson.listValue fromLocation locations)
        ]
    fromLocation Location{..} = Aeson.object
        [ ("line", Aeson.toJSON line)
        , ("column", Aeson.toJSON column)
        ]