Generator.hs

module Breve.Generator 
( wordID
, hashID
, Word
, Url
) where

import Control.Applicative
import Control.Monad.State
import System.Random
import Crypto.Hash.SHA256     (hash)
import Data.Binary            (decode)
import Data.ByteString.Char8  (pack)
import Data.ByteString.Lazy   (fromStrict)

type Word = String
type Url  = String

-- Choose a random element of a list
choice :: [a] -> State StdGen a
choice xs = (xs !!) <$> randomSt (0, length xs - 1)
  where randomSt = state . randomR

-- Generate a random phonetic string
word :: State StdGen Word
word = replicateM 10 letter where
  vowels     = "aeiou"
  consonants = "bcdfghjklmnpqrstvwxyz"
  letter     = choice [vowels, consonants] >>= choice

-- SHA256 hash to seed a generator
hashID :: Url -> Int
hashID = decode . fromStrict . hash . pack

-- Assing a unique word to the url
wordID :: Url -> Word
wordID = evalState word . mkStdGen . hashID