Utils.hs

module Data.Elocrypt.Utils where

import Data.Char (isAlphaNum, isSpace)
import Data.Maybe (fromMaybe)
import Data.Ratio
import qualified Data.Map as M

import Control.Monad.Random (MonadRandom(), fromList)

-- |A mapping from letters to numbers that look like them
numeralConversions = M.fromList [
  ('o', ['0']),
  ('l', ['1']),
  ('z', ['2']),
  ('e', ['3']),
  ('a', ['4']),
  ('s', ['5']),
  ('g', ['6', '9']),
  ('t', ['7']),
  ('b', ['8'])]

-- |A mapping from letters to symbols that look like them
symbolConversions = M.fromList [
  ('a', ['@']),
  ('l', ['!']),
  ('s', ['$'])]

-- |Map a letter to one or more digits, if possible
toDigit :: Char -> String
toDigit c = fromMaybe [c] (numeralConversions M.!? c)

-- |Map a letter to one or more symbols, if possible
toSymbol :: Char -> String
toSymbol c = fromMaybe [c] (symbolConversions M.!? c)

-- |Selects special characters
isSymbol :: Char -> Bool
isSymbol c = not (isAlphaNum c || isSpace c)

-- |Randomly update characters at the specified probability
updateR
  :: MonadRandom m
  => (Char -> m Char)
  -> Rational
  -> String
  -> m String
updateR f prob = mapM f'
  where f' ch = do
          ch' <- f ch
          fromList [
            (ch, toRational $ denominator prob),
            (ch', toRational $ numerator prob)]

-- |Update character at position pos
update1
  :: Monad m
  => (Char -> m Char) -- ^ Update function
  -> String           -- ^ the string to update
  -> Int              -- ^ the position to update
  -> m String
update1 _ "" _   = return ""
update1 f s  pos = (\ch' -> prefix ++ ch' : suffix) <$> f ch
  where (prefix, ch : suffix) = splitAt pos s