module Main (main) where

import Control.Exception   (IOException, try)
import Control.Monad.Error (ErrorT(..), MonadError(..))
import Data.List           (intercalate)
import System.Environment  (getArgs, getProgName)
import System.Exit         (exitFailure, exitSuccess)
import System.IO           (hPutStrLn, stderr)

import Language.Dot (parseDot, renderDot)

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

main :: IO ()
main =
    getArgs >>= run

run :: [String] -> IO ()
run args =
    case args of
      [fp] -> renderDotFile fp
      []   -> displayUsage >> exitSuccess
      _    -> displayUsage >> exitFailure

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

renderDotFile :: FilePath -> IO ()
renderDotFile fp =
    runErrorT (renderDotFileET fp) >>= either exitError putStrLn

renderDotFileET :: FilePath -> ErrorT String IO String
renderDotFileET fp = do
    contents <- readFile fp `liftCatch` show
    graph    <- parseDot fp contents `liftEither` show
    return $ renderDot graph

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

displayUsage :: IO ()
displayUsage = do
    programName <- getProgName
    ePutStrLns
      [ programName ++ ": Pretty-print a Graphviz DOT file."
      , intercalate " " ["Usage:", programName, "FILE"]
      ]

exitError :: String -> IO ()
exitError e = do
    displayUsage
    ePutStrLn ""
    let el = lines e
    if length el == 1
      then ePutStrLn  ("ERROR: " ++ e)
      else ePutStrLns ("ERROR:" : indent el)
    exitFailure
  where
    indent = map ("  "++)

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

liftCatch :: IO a -> (IOException -> e) -> ErrorT e IO a
liftCatch a f = ErrorT $ fmap (either (Left . f) Right) (try a)

liftEither :: (MonadError e m) => Either l r -> (l -> e) -> m r
liftEither e f = either (throwError . f) return e

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

ePutStrLn :: String -> IO ()
ePutStrLn = hPutStrLn stderr

ePutStrLns :: [String] -> IO ()
ePutStrLns = mapM_ (hPutStrLn stderr)