MorseCode-0.0.3: Text/Morse.hs

-- Author:     Andy Stewart <lazycat.manatee@gmail.com>
-- Maintainer: Andy Stewart <lazycat.manatee@gmail.com>
-- 
-- Copyright (C) 2010 Andy Stewart, all rights reserved.
-- 
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation, either version 3 of the License, or
-- any later version.
-- 
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU General Public License for more details.
-- 
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see <http://www.gnu.org/licenses/>.

module Text.Morse (
    encodeMorse,
    decodeMorse,
    canEncodeToMorse,
    isMorseChar
    ) where

import Data.Char
import Data.Map (Map)

import qualified Data.Map as M

-- | Morse Code convert map.
morseCode :: Map Char String
morseCode =
  M.fromList
  [('a', ".-")
  ,('b', "-...")
  ,('c', "-.-.")
  ,('d', "-..")
  ,('e', ".")
  ,('f', "..-.")
  ,('g', "--.")
  ,('h', "....")
  ,('i', "..")
  ,('j', ".---")
  ,('k', "-.-")
  ,('l', ".-..")
  ,('m', "--")
  ,('n', "-.")
  ,('o', "---")
  ,('p', ".--.")
  ,('q', "--.-")
  ,('r', ".-.")
  ,('s', "...")
  ,('t', "-")
  ,('u', "..-")
  ,('v', "...-")
  ,('w', ".--")
  ,('x', "-..-")
  ,('y', "-.--")
  ,('z', "--..")
  ,('=', "-...-")
  ,('?', "..--..")
  ,('/', "-..-.")
  ,(',', "--..--")
  ,('.', ".-.-.-")
  ,(':', "---...")
  ,('\'', ".----.")
  ,('-', "-....-")
  ,('(', "-.--.-")
  ,(')', "-.--.-")
  ,('0', "-----")
  ,('1', ".----")
  ,('2', "..---")
  ,('3', "...--")
  ,('4', "....-")
  ,('5', ".....")
  ,('6', "-....")
  ,('7', "--...")
  ,('8', "---..")
  ,('9', "----.")
  ,('@', ".--.-.")]

-- | Convert String to Morse Code.
-- And ignore invalid Morse character.
encodeMorse :: String -> String
encodeMorse =
  concatMap (\x -> 
                 case findMinMatch morseCode (\ k _ -> k == toLower x) of
                   -- Add blank after Morse Code.
                   Just (_, morse) -> morse ++ " "
                   Nothing -> 
                       -- Replace space with '/'
                       -- or ignore invalid character.
                       if isSpace x then "/" else "")

-- | Get string from Morse Code.
-- Invalid Morse Code will skip.
decodeMorse :: String -> String
decodeMorse str = decodeMorse' str ""

decodeMorse' :: String -> String -> String
decodeMorse' [] _ = []
decodeMorse' (x:xs) str 
    | x == '.'
        = decodeMorse' xs (str ++ [x])
    | x == '-'
        = decodeMorse' xs (str ++ [x])
    | x == ' '
        = let char = 
                  case findMinMatch morseCode (\ _ v -> v == str) of
                    Just (c, _) -> c
                    -- Insert blank when got invalid Morse code.
                    Nothing -> x 
          in char : decodeMorse' xs ""
    | x == '/' 
        = ' ' : decodeMorse' xs ""
    -- Ignore invalid Morse character.
    | otherwise
        = decodeMorse' xs ""

-- | Character can encode to Morse Code?
canEncodeToMorse :: Char -> Bool
canEncodeToMorse char = 
  case findMinMatch morseCode (\ k _ -> k == char) of
    Just _  -> True
    Nothing -> False

-- | Is valid Morse character.?
isMorseChar :: Char -> Bool
isMorseChar char = char `elem` ".-/ "

-- | Find min match one.
findMinMatch :: Ord k => Map k a -> (k -> a -> Bool) -> Maybe (k, a)
findMinMatch map fun = match
    where filterMap = M.filterWithKey fun map
          match     = if M.null filterMap
                         then Nothing
                         else Just $ M.findMin filterMap