{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards   #-}
module Main where

import Control.Applicative (optional)
import Control.Exception (SomeException)
import Data.Monoid ((<>))
import Dhall.JSON (parseOmission, parseConversion)
import Dhall.Yaml (Options(..), dhallToYaml, parseDocuments, parseQuoted)
import Options.Applicative (Parser, ParserInfo)

import qualified Control.Exception
import qualified Data.ByteString
import qualified Data.Text           as Text
import qualified Data.Text.IO        as Text.IO
import qualified GHC.IO.Encoding
import qualified Options.Applicative as Options
import qualified System.Exit
import qualified System.IO

parseOptions :: Parser Options
parseOptions =
        Options
    <$> parseExplain
    <*> Dhall.JSON.parseOmission
    <*> parseDocuments
    <*> parseQuoted
    <*> Dhall.JSON.parseConversion
    <*> optional parseFile
  where
    parseExplain =
        Options.switch
            (   Options.long "explain"
            <>  Options.help "Explain error messages in detail"
            )

    parseFile =
        Options.strOption
            (   Options.long "file"
            <>  Options.help "Read expression from a file instead of standard input"
            <>  Options.metavar "FILE"
            )

parserInfo :: ParserInfo Options
parserInfo =
    Options.info
        (Options.helper <*> parseOptions)
        (   Options.fullDesc
        <>  Options.progDesc "Compile Dhall to YAML"
        )

main :: IO ()
main = do
    GHC.IO.Encoding.setLocaleEncoding GHC.IO.Encoding.utf8

    options@Options {..} <- Options.execParser parserInfo

    handle $ do
        contents <- case file of
            Nothing   -> Text.IO.getContents
            Just path -> Text.IO.readFile path

        let path = case file of
                Nothing -> "(stdin)"
                Just p  -> Text.pack p

        Data.ByteString.putStr =<< dhallToYaml options path contents

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