vervis/src/Data/KeyFile.hs

{- This file is part of Vervis.
 -
 - Written in 2019 by fr33domlover <fr33domlover@riseup.net>.
 -
 - ♡ Copying is an act of love. Please copy, reuse and share.
 -
 - The author(s) have dedicated all copyright and related and neighboring
 - rights to this software to the public domain worldwide. This software is
 - distributed without any warranty.
 -
 - You should have received a copy of the CC0 Public Domain Dedication along
 - with this software. If not, see
 - <http://creativecommons.org/publicdomain/zero/1.0/>.
 -}

module Data.KeyFile
    ( KeyFile (..)
    , loadKeyFile
    )
where

import Prelude

import Data.ByteString (ByteString)
import System.Directory (doesFileExist)

import qualified Data.ByteString as B (readFile, writeFile)

class KeyFile a where
    generateKey :: IO a
    parseKey    :: ByteString -> IO a
    renderKey   :: a -> ByteString

loadKeyFile :: KeyFile a => Bool -> FilePath -> IO a
loadKeyFile setup path = do
    e <- doesFileExist path
    if e
        then if setup
                then fail $ "loadKeyFile: Initial setup but file already exists: " ++ path
                else parseKey =<< B.readFile path
        else if setup
                then do
                    k <- generateKey
                    B.writeFile path $ renderKey k
                    return k
                else fail $ "loadKeyFile: File not found: " ++ path