{-# LANGUAGE DataKinds         #-}
{-# LANGUAGE DeriveAnyClass    #-}
{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards   #-}
{-# LANGUAGE TypeOperators     #-}

module Main where

import Control.Exception (SomeException)
import Options.Generic (Generic, ParseRecord, type (<?>))

import qualified Control.Exception
import qualified Data.Aeson
import qualified Data.Aeson.Encode.Pretty
import qualified Data.ByteString.Char8
import qualified Data.ByteString.Lazy
import qualified Data.Text.IO
import qualified Dhall
import qualified Dhall.JSON
import qualified GHC.IO.Encoding
import qualified Options.Generic
import qualified System.Exit
import qualified System.IO

data Options = Options
    { explain  :: Bool <?> "Explain error messages in detail"
    , pretty   :: Bool <?> "Pretty print generated JSON"
    , omitNull :: Bool <?> "Omit record fields that are null"
    } deriving (Generic, ParseRecord)

main :: IO ()
main = handle $ do
    GHC.IO.Encoding.setLocaleEncoding GHC.IO.Encoding.utf8
    Options {..} <- Options.Generic.getRecord "Compile Dhall to JSON"

    let encode       = if   Options.Generic.unHelpful pretty
                       then Data.Aeson.Encode.Pretty.encodePretty
                       else Data.Aeson.encode
        explaining   = if Options.Generic.unHelpful explain  then Dhall.detailed      else id
        omittingNull = if Options.Generic.unHelpful omitNull then Dhall.JSON.omitNull else id

    stdin <- Data.Text.IO.getContents

    json  <- omittingNull <$> explaining (Dhall.JSON.codeToValue "(stdin)" stdin)

    Data.ByteString.Char8.putStrLn $ Data.ByteString.Lazy.toStrict $ encode json 

handle :: IO a -> IO a
handle = Control.Exception.handle handler
  where
    handler :: SomeException -> IO a
    handler e = do
        System.IO.hPutStrLn System.IO.stderr ""
        System.IO.hPrint    System.IO.stderr e
        System.Exit.exitFailure