{-|
  Copyright (c) 2017 Fritjof Bornebusch <fritjof@alokat.org>
 
  Permission to use, copy, modify, and distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.
 
  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-}

{-# LANGUAGE CPP #-}

import System.Console.GetOpt
import System.Environment      (getArgs)
import System.Exit             (exitFailure, exitSuccess)
import System.IO               (stdout, stderr, hFlush, hPutStr)
#ifdef openbsd_HOST_OS
import System.OpenBSD.Process  (pledge)
#endif 
import System.Random           (randomRIO)

exit_with_message :: String -> IO ()
exit_with_message msg = do
    hPutStr stderr (msg ++ "\n")
    exitFailure

upperCaseLettersList :: [Char]
upperCaseLettersList = ['A'..'Z']

lowerCaseLettersList :: [Char]
lowerCaseLettersList = ['a'..'z']

numbersList :: [Char]
numbersList = ['0'..'9']

specialCharactersList :: [Char]
specialCharactersList = ['!'..'/'] ++ [':'..'@'] ++ ['['..'_'] ++ ['{'..'~']

data Options = Options { optUpperCaseFlag         :: Bool
                        ,optLowerCaseFlag         :: Bool
                        ,optNumbersFlag           :: Bool
                        ,optSpecialCharactersFlag :: Bool
                        ,optLengthValue           :: Int
                        }

startOptions :: Options
startOptions = Options  { optUpperCaseFlag         = False
                        , optLowerCaseFlag         = False 
                        , optNumbersFlag           = False
                        , optSpecialCharactersFlag = False
                        , optLengthValue           = 16
                        }

options :: [ OptDescr (Options -> IO Options) ]
options =
    [ Option "u" []
        (NoArg
            (\opt -> return opt { optUpperCaseFlag = True }))
        "upper case letters"
 
    , Option "l" []
        (NoArg
            (\opt -> return opt { optLowerCaseFlag = True }))
        "lower case letters"
 
    , Option "n" []
        (NoArg
            (\opt -> return opt { optNumbersFlag = True }))
        "numbers"
 
    , Option "s" [] 
        (NoArg
            (\opt -> return opt { optSpecialCharactersFlag = True }))
        "special signs"
 
    , Option "x" []
        (ReqArg
            (\arg opt -> return opt { optLengthValue = read arg })
            "number")
        "password length"
    ]


parse :: [String] -> IO ([Options -> IO Options], [String])
parse args =
    case getOpt RequireOrder options args of
        (actions, nonOptions,[]) -> return (actions, nonOptions)
        (_,_,errors) -> ioError (userError (concat errors ++ header)) 
    where header = "usage: hpg [-ulns]\n" ++ 
                   "           [-x number]"

randomList :: Int -> [Char] -> IO([Int])
randomList 0 _ = return []
randomList n list = do
    let l = length list
    r <- randomRIO (0, l-1)
    rs <- randomList (n-1) list
    return (r:rs)

create_password :: Int -> [Bool] -> IO [Char]
create_password lengthValue flags = do
    let l = create_signs [upperCaseLettersList,
                          lowerCaseLettersList,
                          numbersList,
                          specialCharactersList] flags

    rl <- randomList lengthValue l
    return [l !! i | i <- rl]

add_signs :: [Char] -> ([Char], Bool) -> [Char] 
add_signs list (l, True) = list ++ l
add_signs list (_, False) = list

create_signs :: [[Char]] -> [Bool] -> [Char]
create_signs signs [False, False, False, False] = do
    -- default values are upper case and lower case letters
    create_signs signs [True, True, True, False]

create_signs signs flags = do
    let z = zip signs flags
    foldl (\x y -> add_signs x y) [] z

main :: IO ()
main = do
#ifdef openbsd_HOST_OS
    pledge (Just "stdio") Nothing
#endif
    (actions, _nonOptions) <- getArgs >>= parse
    opts <- foldl (>>=) (return startOptions) actions
    let Options { optUpperCaseFlag          = upperCase
                , optLowerCaseFlag          = lowerCase
                , optNumbersFlag            = numbers
                , optSpecialCharactersFlag  = specialCharacters
                , optLengthValue            = lengthValue } = opts

    if lengthValue > 2^(16::Int)
        then exit_with_message "password too long"
        else do
            pwd <- create_password lengthValue [upperCase,
                                                lowerCase,
                                                numbers,
                                                specialCharacters]
            hPutStr stdout (pwd ++ "\n")
            hFlush stdout
            exitSuccess