# Synchronisation

Items:

- Have an ID and a timestamp of last update
- Have a "kind" (task, note, etc.) to allow for selective synchronisation
- Have a "deleted" flag
- Are kept long enough (months) on the server after deletion to let all clients know about its removal

Server:

- Has `update` handler to receive new (versions of) items
- New (versions of) an item get timestamped by the server upon persisting
- Has `updated` handler to return items that are updated after a certain timestamp

Client:

- Collects local updates in sync table
- Sends local updates to server
- Requests updates from server since previous sync action
- The just sent updates also get retrieved again, but with server timestamp
- Applies those updates to local state

## Notes

- The server timestamp is the version number
- Local sync table serves as a queue when used offline
- There is only one user
- New items are generated by user and by bots/scripts
- Only the user will modify items, in one client at the time
- Race conditions are therefore very unlikely
- If there is one, last client that sends its updates "wins"
- No conflict resolution left out for simplicity
- Full sync can be achieved by purging local database and sync with zero timestamp