{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE OverloadedStrings #-}
-- | Access files on the filesystem.
module WaiAppStatic.Storage.Filesystem
    ( -- * Types
      ETagLookup
      -- * Settings
    , defaultWebAppSettings
    , defaultFileServerSettings
    , webAppSettingsWithLookup
    ) where

import WaiAppStatic.Types
import System.FilePath ((</>))
import System.Directory (doesFileExist, doesDirectoryExist, getDirectoryContents)
import Data.List (foldl')
import Control.Monad (forM)
import Util
import Data.ByteString (ByteString)
import Control.Exception (SomeException, try)
import qualified Network.Wai as W
import WaiAppStatic.Listing
import Network.Mime
import System.PosixCompat.Files (fileSize, getFileStatus, modificationTime, isRegularFile)
import Data.Maybe (catMaybes)
import qualified Crypto.Hash.Conduit (hashFile)
import Data.Byteable (toBytes)
import Crypto.Hash (MD5, Digest)
import qualified Data.ByteString.Base64 as B64
import qualified Data.Text as T

-- | Construct a new path from a root and some @Pieces@.
pathFromPieces :: FilePath -> Pieces -> FilePath
pathFromPieces = foldl' (\fp p -> fp </> T.unpack (fromPiece p))

-- | Settings optimized for a web application. Files will have aggressive
-- caching applied and hashes calculated, and indices and listings are disabled.
defaultWebAppSettings :: FilePath -- ^ root folder to serve from
                      -> StaticSettings
defaultWebAppSettings root = StaticSettings
    { ssLookupFile = webAppLookup hashFileIfExists root
    , ssMkRedirect  = defaultMkRedirect
    , ssGetMimeType = return . defaultMimeLookup . fromPiece . fileName
    , ssMaxAge  = MaxAgeForever
    , ssListing = Nothing
    , ssIndices = []
    , ssRedirectToIndex = False
    , ssUseHash = True
    , ssAddTrailingSlash = False
    , ss404Handler = Nothing
    }

-- | Settings optimized for a file server. More conservative caching will be
-- applied, and indices and listings are enabled.
defaultFileServerSettings :: FilePath -- ^ root folder to serve from
                          -> StaticSettings
defaultFileServerSettings root = StaticSettings
    { ssLookupFile = fileSystemLookup (fmap Just . hashFile) root
    , ssMkRedirect = defaultMkRedirect
    , ssGetMimeType = return . defaultMimeLookup . fromPiece . fileName
    , ssMaxAge = NoMaxAge
    , ssListing = Just defaultListing
    , ssIndices = map unsafeToPiece ["index.html", "index.htm"]
    , ssRedirectToIndex = False
    , ssUseHash = False
    , ssAddTrailingSlash = False
    , ss404Handler = Nothing
    }

-- | Same as @defaultWebAppSettings@, but additionally uses a specialized
-- @ETagLookup@ in place of the standard one. This can allow you to cache your
-- hash values, or even precompute them.
webAppSettingsWithLookup :: FilePath -- ^ root folder to serve from
                         -> ETagLookup
                         -> StaticSettings
webAppSettingsWithLookup dir etagLookup =
  (defaultWebAppSettings dir) { ssLookupFile = webAppLookup etagLookup dir}

-- | Convenience wrapper for @fileHelper@.
fileHelperLR :: ETagLookup
             -> FilePath -- ^ file location
             -> Piece -- ^ file name
             -> IO LookupResult
fileHelperLR a b c = fmap (maybe LRNotFound LRFile) $ fileHelper a b c

-- | Attempt to load up a @File@ from the given path.
fileHelper :: ETagLookup
           -> FilePath -- ^ file location
           -> Piece -- ^ file name
           -> IO (Maybe File)
fileHelper hashFunc fp name = do
    efs <- try $ getFileStatus fp
    case efs of
        Left (_ :: SomeException) -> return Nothing
        Right fs | isRegularFile fs -> return $ Just File
            { fileGetSize = fromIntegral $ fileSize fs
            , fileToResponse = \s h -> W.responseFile s h fp Nothing
            , fileName = name
            , fileGetHash = hashFunc fp
            , fileGetModified = Just $ modificationTime fs
            }
        Right _ -> return Nothing

-- | How to calculate etags. Can perform filesystem reads on each call, or use
-- some caching mechanism.
type ETagLookup = FilePath -> IO (Maybe ByteString)

-- | More efficient than @fileSystemLookup@ as it only concerns itself with
-- finding files, not folders.
webAppLookup :: ETagLookup -> FilePath -> Pieces -> IO LookupResult
webAppLookup hashFunc prefix pieces =
    fileHelperLR hashFunc fp lastPiece
  where
    fp = pathFromPieces prefix pieces
    lastPiece
        | null pieces = unsafeToPiece ""
        | otherwise = last pieces

-- | MD5 hash and base64-encode the file contents. Does not check if the file
-- exists.
hashFile :: FilePath -> IO ByteString
hashFile fp = do
    h <- Crypto.Hash.Conduit.hashFile fp
    return $ B64.encode $ toBytes (h :: Digest MD5)

hashFileIfExists :: ETagLookup
hashFileIfExists fp = do
    res <- try $ hashFile fp
    return $ case res of
        Left (_ :: SomeException) -> Nothing
        Right x -> Just x

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

-- | Get a proper @LookupResult@, checking if the path is a file or folder.
-- Compare with @webAppLookup@, which only deals with files.
fileSystemLookup :: ETagLookup
                 -> FilePath -> Pieces -> IO LookupResult
fileSystemLookup hashFunc prefix pieces = do
    let fp = pathFromPieces prefix pieces
    fe <- doesFileExist fp
    if fe
        then fileHelperLR hashFunc fp lastPiece
        else do
            de <- doesDirectoryExist fp
            if de
                then do
                    entries' <- fmap (filter isVisible) $ getDirectoryContents fp
                    entries <- forM entries' $ \fpRel' -> do
                        let name = unsafeToPiece $ T.pack fpRel'
                            fp' = fp </> fpRel'
                        de' <- doesDirectoryExist fp'
                        if de'
                            then return $ Just $ Left name
                            else do
                                mfile <- fileHelper hashFunc fp' name
                                case mfile of
                                    Nothing -> return Nothing
                                    Just file -> return $ Just $ Right file
                    return $ LRFolder $ Folder $ catMaybes entries
                else return LRNotFound
  where
    lastPiece
        | null pieces = unsafeToPiece ""
        | otherwise = last pieces
