module Detect ( detectFileCompression
              ) where

import           Compression
import qualified Data.ByteString      as BS
import qualified Data.ByteString.Lazy as BSL
import           Info

firstChunk :: FilePath -> IO BS.ByteString
firstChunk = fmap (go . BSL.toChunks) . BSL.readFile
    where go []    = error "Empty file; could not detect compression"
          go (x:_) = x

detectFileCompression :: FilePath -> IO Compression
detectFileCompression fp =
    case detectCompression fp of
        None -> identify <$> firstChunk fp
        x    -> pure x