    {- |
    Module      :  XMonad.Prompt.Shell
    Copyright   :  (C) 2007 Andrea Rossato
    License     :  BSD3

    Maintainer  :  andrea.rossato@unibz.it
    Stability   :  unstable
    Portability :  unportable

    A shell prompt for XMonad
    -}

    module XMonad.Prompt.Shell
        ( -- * Usage
          -- $usage
          Shell (..)
        , shellPrompt
        -- ** Variations on shellPrompt
        -- $spawns
        , prompt
        , safePrompt
        , unsafePrompt

        -- * Utility functions
        , getCommands
        , getBrowser
        , getEditor
        , getShellCompl
        , split
        ) where

    import           Codec.Binary.UTF8.String (encodeString)
    import           Control.Exception        as E
    import           Control.Monad            (forM)
    import           Data.List                (isPrefixOf)
    import           System.Directory         (doesDirectoryExist, getDirectoryContents)
    import           System.Environment       (getEnv)
    import           System.Posix.Files       (getFileStatus, isDirectory)

    import           XMonad                   hiding (config)
    import           XMonad.Prompt
    import           XMonad.Util.Run

    econst :: Monad m => a -> IOException -> m a
    econst = const . return

    {- $usage
    1. In your @~\/.xmonad\/xmonad.hs@:

    > import XMonad.Prompt
    > import XMonad.Prompt.Shell

    2. In your keybindings add something like:

    >   , ((modm .|. controlMask, xK_x), shellPrompt defaultXPConfig)

    For detailed instruction on editing the key binding see
    "XMonad.Doc.Extending#Editing_key_bindings". -}

    data Shell = Shell

    instance XPrompt Shell where
        showXPrompt Shell     = "Run: "
        completionToCommand _ = escape

    shellPrompt :: XPConfig -> X ()
    shellPrompt c = do
        cmds <- io getCommands
        mkXPrompt Shell c (getShellCompl cmds) spawn

    {- $spawns
        See safe and unsafeSpawn in "XMonad.Util.Run".
        prompt is an alias for safePrompt;
        safePrompt and unsafePrompt work on the same principles, but will use
        XPrompt to interactively query the user for input; the appearance is
        set by passing an XPConfig as the second argument. The first argument
        is the program to be run with the interactive input.
        You would use these like this:

        >     , ((modm,               xK_b), safePrompt "firefox" greenXPConfig)
        >     , ((modm .|. shiftMask, xK_c), prompt ("xterm" ++ " -e") greenXPConfig)

        Note that you want to use safePrompt for Firefox input, as Firefox
        wants URLs, and unsafePrompt for the XTerm example because this allows
        you to easily start a terminal executing an arbitrary command, like
        'top'. -}

    prompt, unsafePrompt, safePrompt :: FilePath -> XPConfig -> X ()
    prompt = unsafePrompt
    safePrompt c config = mkXPrompt Shell config (getShellCompl [c]) run
        where run = safeSpawn c . return
    unsafePrompt c config = mkXPrompt Shell config (getShellCompl [c]) run
        where run a = unsafeSpawn $ c ++ " " ++ a

    getShellCompl :: [String] -> String -> IO [String]
    getShellCompl cmds s | s == "" || last s == ' ' = return []
                         | otherwise                = do
        f     <- fmap lines $ runProcessWithInput "bash" [] ("compgen -A file -- "
                                                            ++ s ++ "\n")
        files <- case f of
                   [x] -> do fs <- getFileStatus (encodeString x)
                             if isDirectory fs then return [x ++ "/"]
                                               else return [x]
                   _   -> return f
        return . uniqSort $ files ++ commandCompletionFunction cmds s

    commandCompletionFunction :: [String] -> String -> [String]
    commandCompletionFunction cmds str | '/' `elem` str = []
                                       | otherwise      = filter (isPrefixOf str) cmds

    getCommands :: IO [String]
    getCommands = do
        p  <- getEnv "PATH" `E.catch` econst []
        let ds = filter (/= "") $ split ':' p
        es <- forM ds $ \d -> do
            exists <- doesDirectoryExist d
            if exists
                then getDirectoryContents d
                else return []
        return . uniqSort . filter ((/= '.') . head) . concat $ es

    split :: Eq a => a -> [a] -> [[a]]
    split _ [] = []
    split e l =
        f : split e (rest ls)
            where
              (f,ls) = span (/=e) l
              rest s | s == []   = []
                     | otherwise = tail s

    escape :: String -> String
    escape []       = ""
    escape (x:xs)
        | isSpecialChar x = '\\' : x : escape xs
        | otherwise       = x : escape xs

    isSpecialChar :: Char -> Bool
    isSpecialChar =  flip elem " &\\@\"'#?$*()[]{};"

    -- | Ask the shell environment for the value of a variable in XMonad's environment, with a default value.
    --   In order to /set/ an environment variable (eg. combine with a prompt so you can modify @$HTTP_PROXY@ dynamically),
    --   you need to use 'System.Posix.putEnv'.
    env :: String -> String -> IO String
    env variable fallthrough = getEnv variable `E.catch` econst fallthrough

    {- | Ask the shell what browser the user likes. If the user hasn't defined any
       $BROWSER, defaults to returning \"firefox\", since that seems to be the most
       common X web browser.
       Note that if you don't specify a GUI browser but a textual one, that'll be a problem
       as 'getBrowser' will be called by functions expecting to be able to just execute the string
       or pass it to a shell; so in that case, define $BROWSER as something like \"xterm -e elinks\"
       or as the name of a shell script doing much the same thing. -}
    getBrowser :: IO String
    getBrowser = env "BROWSER" "x-www-browser"

    -- | Like 'getBrowser', but should be of a text editor. This gets the $EDITOR variable, defaulting to \"emacs\".
    getEditor :: IO String
    getEditor = env "EDITOR" "emacs"