planner/doc/sync.md

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