Sync progress calculation is incorrect (or could be improved)

[achou11]

Related to #550

From Gregor on Slack:

I believe I know what is happening. There are two stages in sync:
"initial sync", which include membership records, device info, project settings, and presets, fields and icons.
"data sync", which includes observations, tracks and photos.

1. stage 1 ("initial sync") happens without user intervention in the background, regardless of what screen the user is on.
2. stage 2 ("data sync") happens when 2 or more users have pressed the "sync" button (enabled data sync).

When designing this, I don't think we had fully considered the amount of data in the "initial sync" stage when two devices are syncing for the first time, because > there are a lot of presets, fields and icons to sync. A couple of things are contributing to the observed behaviour:

3. The progress calculation in the frontend code shows progress across > both initial sync and data sync. The progress of initial sync is hidden from a device that has not yet pressed "sync" (e.g. enabled data sync), but the device that > has enabled data sync (by pressing "sync") will see this progress. If initial sync is still happening, then the device that first presses sync will see this > progress, giving the impression that "sync" is happening, even though it's the initial sync only.

4. The way progress is calculated, specifically [maxDataSyncCount here](https://github.com/digidem/comapeo-mobile/blob/main/src/frontend/hooks/useSyncState.> ts#L131-L138) is not calculated when the user turns on data sync, rather it is continuously updated to the maximum observed value. This means that the progress is > counting background "initial sync" that has happened before the user has pressed "sync". This means that even if "initial sync" is complete when the user presses > "sync", it shows that already complete progress as part of the sync progress. E.g. if the "initial sync" included 90 records, and "data sync" has 10 records, then if > initial sync is complete, and the user presses "sync", they will see sync progress as 90% done.

Suggested solutions:

For (2), progress should start at 0 when the user first presses "sync". This requires an update to [this code](https://github.com/digidem/comapeo-mobile/blob/main/src/> frontend/hooks/useSyncState.ts#L131-L138) to set maxDataSyncCount at the moment the user enables data sync.

For (1) I am not sure how we expose this to the user - this is a UX issue. Do we expose this "initial sync" as a separate progress bar, that all devices see? Do we > hide it from the users completely? I think this requires further discussion. It would be good to start gathering metrics about how long this "initial sync" is taking, > and how frequent it is that a user presses "sync" before initial sync is complete, because it may be so rare that this is a non-issue. Certainly after presets, fields > and icons have synced, very little additional data is added to the database that is included in the "initial sync" stage - only 2 records (membership and deviceInfo) > for each device that has been added or removed from the project.

[achou11]

The progress calculation in the frontend code shows progress across > both initial sync and data sync.

Don't think this is the case? Based on the implementation, it's only doing calculations based on the data sync (no initial).

comapeo-mobile/src/frontend/hooks/useSyncState.ts

Lines 132 to 137 in ebaf02b

	const newSyncCount = state.data.want + state.data.wanted;
	this.#maxDataSyncCount =
	this.#maxDataSyncCount === null
	? newSyncCount
	: Math.max(this.#maxDataSyncCount, newSyncCount);

comapeo-mobile/src/frontend/hooks/useSyncState.ts

Line 107 in ebaf02b

const currentCount = this.#state.data.want + this.#state.data.wanted;

Although the progress probably should include the initial too, I think.