split out generic git log parser

Sponsored-By: Jack Hill on Patreon

Git/Log.hs

@@ -0,0 +1,107 @@
+{- git log
+ -
+ - Copyright 2023 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Git.Log where
+
+import Common
+import Git
+import Git.Command
+
+import Data.Time
+import Data.Time.Clock.POSIX
+
+-- A change made to a file.
+data RefChange t = RefChange
+	{ changetime :: POSIXTime
+	, changed :: t
+	, changedfile :: FilePath
+	, oldref :: Ref
+	, newref :: Ref
+	}
+	deriving (Show)
+
+-- Get the git log. Note that the returned cleanup action should only be
+-- run after processing the returned list.
+getGitLog
+	:: Ref
+	-> [FilePath]
+	-> [CommandParam]
+	-> (FilePath -> Maybe t)
+	-> Repo
+	-> IO ([RefChange t], IO Bool)
+getGitLog ref fs os fileselector repo = do
+	(ls, cleanup) <- pipeNullSplit ps repo
+	return (parseGitRawLog fileselector (map decodeBL ls), cleanup)
+  where
+	ps =
+		[ Param "log"
+		, Param "-z"
+		, Param ("--pretty=format:"++commitinfoFormat)
+		, Param "--raw"
+		, Param "--no-abbrev"
+		, Param "--no-renames"
+		] ++ os ++
+		[ Param (fromRef ref)
+		, Param "--"
+		] ++ map Param fs 
+
+-- The commitinfo is the timestamp of the commit, followed by
+-- the commit hash and then the commit's parents, separated by spaces.
+commitinfoFormat :: String
+commitinfoFormat = "%ct"
+
+-- Parses chunked git log --raw output generated by getGitLog, 
+-- which looks something like:
+--
+-- [ "commitinfo\n:changeline"
+-- , "filename"
+-- , ""
+-- , "commitinfo\n:changeline"
+-- , "filename"
+-- , ":changeline"
+-- , "filename"
+-- , ""
+-- ]
+--
+-- The commitinfo is not included before all changelines, so
+-- keep track of the most recently seen commitinfo.
+parseGitRawLog :: (FilePath -> Maybe t) -> [String] -> [RefChange t]
+parseGitRawLog fileselector = parse epoch
+  where
+	epoch = toEnum 0 :: POSIXTime
+	parse oldts ([]:rest) = parse oldts rest
+	parse oldts (c1:c2:rest) = case mrc of
+		Just rc -> rc : parse ts rest
+		Nothing -> parse ts (c2:rest)
+	  where
+		(ts, cl) = case separate (== '\n') c1 of
+			(cl', []) -> (oldts, cl')
+			(tss, cl') -> (parseTimeStamp tss, cl')
+	  	mrc = do
+			(old, new) <- parseRawChangeLine cl
+			v <- fileselector c2
+			return $ RefChange
+				{ changetime = ts
+				, changed = v
+				, changedfile = c2
+				, oldref = old
+				, newref = new
+				}
+	parse _ _ = []
+
+-- Parses something like ":100644 100644 oldsha newsha M"
+-- extracting the shas.
+parseRawChangeLine :: String -> Maybe (Git.Ref, Git.Ref)
+parseRawChangeLine = go . words
+  where
+	go (_:_:oldsha:newsha:_) = 
+		Just (Git.Ref (encodeBS oldsha), Git.Ref (encodeBS newsha))
+	go _ = Nothing
+
+parseTimeStamp :: String -> POSIXTime
+parseTimeStamp = utcTimeToPOSIXSeconds . fromMaybe (giveup "bad timestamp") .
+	parseTimeM True defaultTimeLocale "%s"