newtype MapLog

Noticed that Semigroup instance of Map is not suitable to use
for MapLog. For example, it behaved like this:

ghci>  parseTrustLog "foo 1 timestamp=10\nfoo 2 timestamp=11" <> parseTrustLog "foo X timestamp=12"
fromList [(UUID "foo",LogEntry {changed = VectorClock 11s, value = SemiTrusted})]

Which was wrong, it lost the newer DeadTrusted value.

Luckily, nothing used that Semigroup when operating on a MapLog. And this
provides a safe instance.

Sponsored-by: Graham Spencer on Patreon

Logs/MapLog.hs

@@ -6,7 +6,7 @@
  -
  - The field names cannot contain whitespace.
  -
- - Copyright 2014, 2019 Joey Hess <id@joeyh.name>
+ - Copyright 2014-2023 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -28,6 +28,8 @@ import qualified Data.Attoparsec.ByteString as A
 import qualified Data.Attoparsec.ByteString.Lazy as AL
 import qualified Data.Attoparsec.ByteString.Char8 as A8
 import Data.ByteString.Builder
+import qualified Data.Semigroup as Sem
+import Prelude
 
 data LogEntry v = LogEntry
 	{ changed :: VectorClock
@@ -37,10 +39,23 @@ data LogEntry v = LogEntry
 instance Arbitrary v => Arbitrary (LogEntry v) where
 	arbitrary = LogEntry <$> arbitrary <*> arbitrary
 
-type MapLog f v = M.Map f (LogEntry v)
+newtype MapLog f v = MapLog (M.Map f (LogEntry v))
+	deriving (Show, Eq)
+
+instance Ord f => Sem.Semigroup (MapLog f v)
+  where
+	a <> MapLog b = foldl' (\m (f, v) -> addMapLog f v m) a (M.toList b)
+
+instance Ord f => Monoid (MapLog f v)
+  where
+	mempty = MapLog M.empty
+
+fromMapLog :: MapLog f v -> M.Map f (LogEntry v)
+fromMapLog (MapLog m) = m
 
 buildMapLog :: (f -> Builder) -> (v -> Builder) -> MapLog f v -> Builder
-buildMapLog fieldbuilder valuebuilder = mconcat . map genline . M.toList
+buildMapLog fieldbuilder valuebuilder (MapLog m) = 
+	mconcat $ map genline $ M.toList m
   where
 	genline (f, LogEntry c v) = 
 		buildVectorClock c <> sp 
@@ -50,25 +65,32 @@ buildMapLog fieldbuilder valuebuilder = mconcat . map genline . M.toList
 	nl = charUtf8 '\n'
 
 parseMapLog :: Ord f => A.Parser f -> A.Parser v -> L.ByteString -> MapLog f v
-parseMapLog fieldparser valueparser = fromMaybe M.empty . AL.maybeResult 
-	. AL.parse (mapLogParser fieldparser valueparser)
+parseMapLog fieldparser valueparser = 
+	parseMapLogWith (mapLogParser fieldparser valueparser)
+
+parseMapLogWith :: Ord f => A.Parser (MapLog f v) -> L.ByteString -> MapLog f v
+parseMapLogWith parser = fromMaybe (MapLog M.empty) 
+	. AL.maybeResult
+	. AL.parse parser
 
 mapLogParser :: Ord f => A.Parser f -> A.Parser v -> A.Parser (MapLog f v)
-mapLogParser fieldparser valueparser = M.fromListWith best <$> parseLogLines go
-  where
-	go = do
-		c <- vectorClockParser
-		_ <- A8.char ' '
-		w <- A8.takeTill (== ' ')
-		f <- either fail return $
-			A.parseOnly (fieldparser <* A.endOfInput) w
-		_ <- A8.char ' '
-		v <- valueparser
-		A.endOfInput
-		return (f, LogEntry c v)
+mapLogParser fieldparser valueparser = mapLogParser' $ do
+	c <- vectorClockParser
+	_ <- A8.char ' '
+	w <- A8.takeTill (== ' ')
+	f <- either fail return $
+		A.parseOnly (fieldparser <* A.endOfInput) w
+	_ <- A8.char ' '
+	v <- valueparser
+	A.endOfInput
+	return (f, LogEntry c v)
+
+mapLogParser' :: Ord f => A.Parser (f, LogEntry v) -> A.Parser (MapLog f v)
+mapLogParser' p = MapLog . M.fromListWith best
+	<$> parseLogLines p
 
 changeMapLog :: Ord f => CandidateVectorClock -> f -> v -> MapLog f v -> MapLog f v
-changeMapLog c f v m = M.insert f (LogEntry c' v) m
+changeMapLog c f v (MapLog m) = MapLog (M.insert f (LogEntry c' v) m)
   where
 	c' = case M.lookup f m of
 		Nothing -> advanceVectorClock c []
@@ -77,13 +99,19 @@ changeMapLog c f v m = M.insert f (LogEntry c' v) m
 {- Only add an LogEntry if it's newer (or at least as new as) than any
  - existing LogEntry for a field. -}
 addMapLog :: Ord f => f -> LogEntry v -> MapLog f v -> MapLog f v
-addMapLog = M.insertWith best
+addMapLog f v (MapLog m) = MapLog (M.insertWith best f v m)
+
+filterMapLogWith :: (f -> LogEntry v -> Bool) -> MapLog f v -> MapLog f v
+filterMapLogWith f (MapLog m) = MapLog (M.filterWithKey f m)
+
+mapLogWithKey :: (f -> LogEntry v -> LogEntry v) -> MapLog f v -> MapLog f v
+mapLogWithKey f (MapLog m) = MapLog (M.mapWithKey f m)
 
 {- Converts a MapLog into a simple Map without the timestamp information.
  - This is a one-way trip, but useful for code that never needs to change
  - the log. -}
 simpleMap :: MapLog f v -> M.Map f v
-simpleMap = M.map value
+simpleMap (MapLog m) = M.map value m
 
 best :: LogEntry v -> LogEntry v -> LogEntry v
 best new old
@@ -93,8 +121,8 @@ best new old
 prop_addMapLog_sane :: Bool
 prop_addMapLog_sane = newWins && newestWins
   where
-	newWins = addMapLog ("foo") (LogEntry (VectorClock 1) "new") l == l2
-	newestWins = addMapLog ("foo") (LogEntry (VectorClock 1) "newest") l2 /= l2
+	newWins = addMapLog "foo" (LogEntry (VectorClock 1) "new") l == l2
+	newestWins = addMapLog "foo" (LogEntry (VectorClock 1) "newest") l2 /= l2
 
-	l = M.fromList [("foo", LogEntry (VectorClock 0) "old")]
-	l2 = M.fromList [("foo", LogEntry (VectorClock 1) "new")]
+	l = MapLog (M.fromList [("foo", LogEntry (VectorClock 0) "old")])
+	l2 = MapLog (M.fromList [("foo", LogEntry (VectorClock 1) "new")])