git-annex/Types/Key.hs

{- git-annex Key data type
 - 
 - Most things should not need this, using Types instead
 -
 - Copyright 2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Types.Key (
	Key(..),
	stubKey,
	key2file,
	file2key,

	prop_idempotent_key_encode
) where

import System.Posix.Types

import Common
import Utility.QuickCheck

{- A Key has a unique name, is associated with a key/value backend,
 - and may contain other optional metadata. -}
data Key = Key {
	keyName :: String,
	keyBackendName :: String,
	keySize :: Maybe Integer,
	keyMtime :: Maybe EpochTime
} deriving (Eq, Ord, Read, Show)

stubKey :: Key
stubKey = Key {
	keyName = "",
	keyBackendName = "",
	keySize = Nothing,
	keyMtime = Nothing
}

fieldSep :: Char
fieldSep = '-'

{- Converts a key to a string that is suitable for use as a filename.
 - The name field is always shown last, separated by doubled fieldSeps,
 - and is the only field allowed to contain the fieldSep. -}
key2file :: Key -> FilePath
key2file Key { keyBackendName = b, keySize = s, keyMtime = m, keyName = n } =
	b +++ ('s' ?: s) +++ ('m' ?: m) +++ (fieldSep : n)
  where
	"" +++ y = y
	x +++ "" = x
	x +++ y = x ++ fieldSep:y
	c ?: (Just v) = c : show v
	_ ?: _ = ""

file2key :: FilePath -> Maybe Key
file2key s = if key == Just stubKey then Nothing else key
  where
	key = startbackend stubKey s

	startbackend k v = sepfield k v addbackend
		
	sepfield k v a = case span (/= fieldSep) v of
		(v', _:r) -> findfields r $ a k v'
		_ -> Nothing

	findfields (c:v) (Just k)
		| c == fieldSep = Just $ k { keyName = v }
		| otherwise = sepfield k v $ addfield c
	findfields _ v = v

	addbackend k v = Just k { keyBackendName = v }
	addfield 's' k v = Just k { keySize = readish v }
	addfield 'm' k v = Just k { keyMtime = readish v }
	addfield _ _ _ = Nothing

instance Arbitrary Key where
	arbitrary = Key
		<$> arbitrary
		<*> (listOf1 $ elements ['A'..'Z']) -- BACKEND
		<*> ((abs <$>) <$> arbitrary) -- size cannot be negative
		<*> arbitrary

prop_idempotent_key_encode :: Key -> Bool
prop_idempotent_key_encode k = Just k == (file2key . key2file) k