{-# LANGUAGE TemplateHaskell #-}
module Data.FileEmbed
    ( embedFile
    , embedDir
    , getDir
    ) where

import Language.Haskell.TH (runQ,
                            Exp (AppE, ListE, LitE, TupE),
                            Lit (StringL),
                            Q,
                            runIO)
import System.Directory (doesDirectoryExist, doesFileExist,
                         getDirectoryContents)
import Control.Monad (filterM)
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as B8
import Control.Arrow ((&&&), second, first)
import Control.Applicative ((<$>))
import Data.Monoid (mappend)

-- | Embed a single file in your source code.
--
-- > import qualified Data.ByteString
-- >
-- > myFile :: Data.ByteString.ByteString
-- > myFile = $(embedFile "dirName/fileName")
embedFile :: FilePath -> Q Exp
embedFile fp = (runIO $ B.readFile fp) >>= bsToExp

-- | Embed a directory recusrively in your source code.
--
-- > import qualified Data.ByteString
-- >
-- > myDir :: [(FilePath, Data.ByteString.ByteString)]
-- > myDir = $(embedDir "dirName")
embedDir :: FilePath -> Q Exp
embedDir fp = ListE <$> ((runIO $ fileList fp) >>= mapM pairToExp)

-- | Get a directory tree in the IO monad.
--
-- This is the workhorse of 'embedDir'
getDir :: FilePath -> IO [(FilePath, B.ByteString)]
getDir = fileList

pairToExp :: (FilePath, B.ByteString) -> Q Exp
pairToExp (path, bs) = do
    exp' <- bsToExp bs
    return $! TupE [LitE $ StringL path, exp']

bsToExp :: B.ByteString -> Q Exp
bsToExp bs = do
    helper <- runQ [| stringToBs |]
    let chars = B8.unpack bs
    return $! AppE helper $! LitE $! StringL chars

stringToBs :: String -> B.ByteString
stringToBs = B8.pack

notHidden :: FilePath -> Bool
notHidden ('.':_) = False
notHidden _ = True

fileList :: FilePath -> IO [(FilePath, B.ByteString)]
fileList top = map (first tail) <$> fileList' top ""

fileList' :: FilePath -> FilePath -> IO [(FilePath, B.ByteString)]
fileList' realTop top = do
    let prefix1 = top ++ "/"
        prefix2 = realTop ++ prefix1
    allContents <- filter notHidden <$> getDirectoryContents prefix2
    let all' = map (mappend prefix1 &&& mappend prefix2) allContents
    files <- filterM (doesFileExist . snd) all' >>=
             mapM (liftPair2 . second B.readFile)
    dirs <- filterM (doesDirectoryExist . snd) all' >>=
            mapM (fileList' realTop . fst)
    return $ concat $ files : dirs

liftPair2 :: Monad m => (a, m b) -> m (a, b)
liftPair2 (a, b) = b >>= \b' -> return (a, b')