path: root/apps/ListPath.hs

{-
 - Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
 - This file is licensed under the terms of the MIT License.
 - See LICENSE.txt for details.
-}

module Main ( main ) where

import System.Console.GetOpt
import System.Directory ( doesDirectoryExist )
import System.Environment ( getArgs, getProgName )
import System.Exit ( exitFailure, exitSuccess )
import System.IO ( hPutStr, stderr )

import qualified Environment

main :: IO ()
main = do
  rawArgs <- getArgs
  case getOpt Permute optionDescription rawArgs of
    (actions, args, []) -> do
      options <- foldl (>>=) (return defaultOptions) actions
      case args of
        [] -> listPath options
        _ -> invalidNumberOfArguments
    (_, _, errorMessages) -> exitWithUsageErrors errorMessages

listPath :: Options -> IO ()
listPath options = do
  val <- Environment.getEnv $ name options
  mapM_ printPath $ Environment.splitPaths val
    where
      printPath p = do
        exists <- doesDirectoryExist p
        putStrLn $ (if exists then "+" else "-") ++ " " ++ p

data Options = Options { name :: String } deriving (Eq, Show)

defaultOptions :: Options
defaultOptions = Options { name = "PATH" }

buildHelpMessage :: IO String
buildHelpMessage = do
  header <- buildHeader
  return $ usageInfo header optionDescription
    where
      buildHeader :: IO String
      buildHeader = do
        progName <- getProgName
        return $ "Usage: " ++ progName ++ " [OPTIONS...]\nOptions:"

exitWithHelpMessage :: a -> IO b
exitWithHelpMessage _ = do
  helpMessage <- buildHelpMessage
  putStr helpMessage
  exitSuccess

exitWithUsageErrors :: [String] -> IO a
exitWithUsageErrors errorMessages = do
  hPutStr stderr $ concatMap ("Usage error: " ++) errorMessages
  helpMessage <- buildHelpMessage
  hPutStr stderr helpMessage
  exitFailure

invalidNumberOfArguments :: IO a
invalidNumberOfArguments = exitWithUsageErrors ["invalid number of arguments\n"]

optionDescription :: [OptDescr (Options -> IO Options)]
optionDescription = [
    Option "n" ["name"] (ReqArg (\s opts -> return opts { name = s }) "NAME") "set the variable name ('PATH' by default)",
    Option "h" ["help"] (NoArg exitWithHelpMessage) "show this message and exit"
  ]