    -- |
    -- Module      : Crypto.Random.Entropy.Unsafe
    -- License     : BSD-style
    -- Maintainer  : Vincent Hanquez <vincent@snarc.org>
    -- Stability   : experimental
    -- Portability : Good
    --
    module Crypto.Random.Entropy.Unsafe
        ( replenish
        , module Crypto.Random.Entropy.Backend
        ) where

    import Data.Word (Word8)
    import Foreign.Ptr (Ptr, plusPtr)
    import Crypto.Random.Entropy.Backend

    -- | Refill the entropy in a buffer
    --
    -- Call each entropy backend in turn until the buffer has
    -- been replenished.
    --
    -- If the buffer cannot be refill after 3 loopings, this will raise
    -- an User Error exception
    replenish :: Int -> [EntropyBackend] -> Ptr Word8 -> IO ()
    replenish _        []       _   = fail "cryptonite: random: cannot get any source of entropy on this system"
    replenish poolSize backends ptr = loop 0 backends ptr poolSize
      where loop :: Int -> [EntropyBackend] -> Ptr Word8 -> Int -> IO ()
            loop retry [] p n | n == 0     = return ()
                              | retry == 3 = error "cryptonite: random: cannot fully replenish"
                              | otherwise  = loop (retry+1) backends p n
            loop _     (_:_)  _ 0 = return ()
            loop retry (b:bs) p n = do
                r <- gatherBackend b p n
                loop retry bs (p `plusPtr` r) (n - r)