Generator.hs

module Breve.Generator
( nameHash
, intHash
, Name
, Url
) where

import Control.Monad.State
import System.Random
import Crypto.Hash.SHA256     (hash)
import Data.Binary            (decode)
import Data.ByteString.Lazy   (fromStrict)
import Data.Text              (Text, pack)
import Data.Text.Encoding     (encodeUtf8)

type Name = Text
type Url  = Text

-- 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 Name
word = pack <$> replicateM 10 letter where
  vowels     = "aeiou"
  consonants = "bcdfghjklmnpqrstvwxyz"
  letter     = choice [vowels, consonants] >>= choice

-- SHA256 hash to seed a generator
intHash :: Url -> Int
intHash = decode . fromStrict . hash . encodeUtf8

-- Assign a unique name to the url
nameHash :: Url -> Name
nameHash = evalState word . mkStdGen . intHash