WIP

Added graftTree but it's buggy.

Should use graftTree in Annex.Branch.graftTreeish; it will be faster
than the current implementation there.

Started Annex.Import, but untested and it doesn't yet handle tree
grafting.

Annex/Import.hs

@@ -0,0 +1,71 @@
+{- git-annex import from remotes
+ -
+ - Copyright 2019 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Annex.Import (buildImportCommit) where
+
+import Annex.Common
+import Types.Import
+import Git.Types
+import Git.Tree
+import Git.Branch
+import Git.FilePath
+import Annex.Link
+
+{- Builds a commit on top of a basecommit that reflects changes to the
+ - content of a remote. When there are no changes to commit, returns Nothing.
+ -
+ - When a remote provided a history of versions of files,
+ - builds a corresponding tree of git commits.
+ -
+ - After importing from a remote, exporting the same thing back to the
+ - remote should be a no-op. So, the export log is updated to reflect the
+ - imported tree.
+ -
+ - The files are imported to the top of the git repository, unless a
+ - subdir is specified, then the import will only affect the contents of
+ - the subdir.
+ -
+ - This does not import any content from a remote. But since it needs the
+ - Key of imported files to be known, its caller will have to download
+ - new files in order to generate keys for them.
+ -}
+buildImportCommit
+	:: Ref
+	-> Maybe FilePath
+	-> ImportableContents Key
+	-> CommitMode
+	-> String
+	-> Annex (Maybe Ref)
+buildImportCommit basecommit subdir importable commitmode commitmessage = do
+	go =<< buildImportTrees basetree importable
+  where
+	go (History importedtree hs) = do
+		parents <- mapM go hs
+		
+		inRepo $ commitTree commitmode commitmessage parents tree
+
+data History t = History t [History t]
+
+{- Builds a history of git trees reflecting the ImportableContents. -}
+buildImportTrees
+	:: Maybe FilePath
+	-> ImportableContents Key
+	-> Annex (History Sha)
+buildImportTrees subdir i = History
+	<$> go (importableContents i)
+	<*> mapM (buildImportTrees subdir basetree) (importableHistory i)
+  where
+	go ls = do
+		is <- mapM mktreeitem ls
+		inRepo $ recordTree (treeItemsToTree is)
+	mktreeitem (loc, k) = do
+		let lf = fromImportLocation loc
+		let topf = asTopFilePath $ maybe lf (</> lf) subdir
+		relf <- fromRepo $ fromTopFilePath topf
+		symlink <- calcRepo $ gitAnnexLink relf k
+		linksha <- hashSymlink symlink
+		return $ TreeItem topf (fromTreeItemType TreeSymlink) linksha