{- Copyright 2016 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

{-# LANGUAGE DeriveGeneric, BangPatterns #-}

module BackupRecord where

import Types
import Types.Cost
import Types.Server
import GHC.Generics
import Data.Time.Clock.POSIX
import Data.Aeson
import Data.Maybe
import System.FilePath
import System.Directory
import System.Posix.User
import System.Posix.Files
import qualified Data.ByteString.Lazy as B

-- | Record of a backup.
--
-- If an attacker cracks the user's system and finds this stored
-- on it, it should not help them recover keys from keysafe.
-- 
-- That's why the Name used is not included; as knowing the name lets
-- an attacker download shards and start password cracking.
--
-- Including the password entropy does let an attacker avoid trying
-- weak passwords and go right to passwords that are strong enough, but
-- this should only half the password crack time at worst.
data BackupRecord = BackupRecord
	{ backupDate :: POSIXTime
	, backupServers :: [HostName]
	, secretKeySource :: String
	, passwordEntropy :: Int
	} deriving (Show, Generic)

-- BackupRecord is serialized as JSON.
instance ToJSON BackupRecord
instance FromJSON BackupRecord

mkBackupRecord :: [Server] -> SecretKeySource -> Entropy UnknownPassword -> IO BackupRecord
mkBackupRecord servers sks (Entropy n) = BackupRecord
	<$> getPOSIXTime
	<*> pure (map serverName servers)
	<*> pure (show sks)
	<*> pure n

backupRecordFile :: IO FilePath
backupRecordFile = do
	u <- getUserEntryForID =<< getEffectiveUserID
	return $ homeDirectory u </> ".keysafe/backup.log"

readBackupRecords :: IO [BackupRecord]
readBackupRecords = do
	f <- backupRecordFile
	e <- doesFileExist f
	if e
		then fromMaybe [] . decode <$> B.readFile f
		else return []

storeBackupRecord :: BackupRecord -> IO ()
storeBackupRecord r = do
	!rs <- readBackupRecords
	f <- backupRecordFile
	let d = takeDirectory f
	createDirectoryIfMissing True d
	setFileMode d $
		ownerReadMode
			`unionFileModes` ownerWriteMode
			`unionFileModes` ownerExecuteMode
	setPermissions d 
		$ setOwnerReadable True 
			$ setOwnerWritable True 
				$ setOwnerExecutable True emptyPermissions
	B.writeFile f $ encode (r:rs)