move commit to Git.Branch

Git/Branch.hs

@@ -58,3 +58,20 @@ fastForward branch (first:rest) repo = do
 				(True, False) -> findbest r rs -- better
 				(False, True) -> findbest c rs -- worse
 				(False, False) -> findbest c rs -- same
+
+{- Commits the index into the specified branch (or other ref), 
+ - with the specified parent refs, and returns the committed sha -}
+commit :: String -> Branch -> [Ref] -> Repo -> IO Sha
+commit message branch parentrefs repo = do
+	tree <- getSha "write-tree" $ asString $
+		pipeRead [Param "write-tree"] repo
+	sha <- getSha "commit-tree" $ asString $
+		ignorehandle $ pipeWriteRead
+			(map Param $ ["commit-tree", show tree] ++ ps)
+			(L.pack message) repo
+	run "update-ref" [Param $ show branch, Param $ show sha] repo
+	return sha
+	where
+		ignorehandle a = snd <$> a
+		asString a = L.unpack <$> a
+		ps = concatMap (\r -> ["-p", show r]) parentrefs