remotely-save/docs/algorithm.md

Algorithm

Sources

We have three record sources:

1. Local files
2. Remote files
3. Local "delete-or-rename" history.

Assuming all sources are reliable.

Deal with them

We list all combinations mutually exclusive and collectively exhaustive.

ID	Remote Files	Local files	Local delete rename history	Extra	Decision
1	exist	exist	ignore	mtime_remote > mtime_local	download remote file, create local folder if not exists, clear local history if exists
2	exist	exist	ignore	mtime_remote < mtime_local	upload local file, create remote folder if not exists, clear local history if exists
3	exist	exist	ignore	mtime_remote === mtime_local && size_remote === size_local	clear local history if exists (the file was synced and no changes after last sync)
4	exist	exist	ignore	mtime_remote === mtime_local && size_remote !== size_local	upload local file, clear local history if exists (we always prefer local to remote)
5	exist	exist	ignore	If local is a folder. mtime_local === undefined	clear local history if exists. TODO: what if a folder and a previous file share the same name?
6	exist	not exist	exist	mtime_remote >= delete_time_local	download remote file, create folder if not exists
7	exist	not exist	exist	mtime_remote < delete_time_local	delete remote file, clear local history
8	exist	not exist	not exist		download remote file, create folder if not exists
9	not exist	exist	ignore	If local is a single file.	upload local file, create remote folder if not exists, clear local history if exists
10	not exist	exist	ignore	If local is a folder.	upload local files recursively, create remote folder if not exists, clear local history if exists
11	not exist	not exist	ignore		clear local history if exists