Fix: narrative dataset filters

[joverlee521]

When users change the slide in a narrative, the controls state gets
reset to its default state which updates the filters state to an empty
object. This leads to the bug described in #1492.

This commit extracts the filters creation from modifyStateViaMetadata
into its own function so that it can be reused to recreate the filters
when users change the slide within a narrative.

Resolves #1492.

[jameshadfield]

Nice find on the 🐛 @joverlee521!

Notes looking at the codepaths involved here as part of review:

1. Loading datasets / changing narrative slides happens via a call to changePage, which has 3 cases (description):
   • The initial load is "case3" and doesn't result in the 🐛
   • Moving to a narrative slide which changes the dataset is "case 2" and doesn't result in the 🐛
   • Moving to a narrative slide where the dataset doesn't change is "case 1" and we have the 🐛
2. "case1" triggers a call to createStateFromQueryOrJSONs which supplies existing redux state and a (URL) query and asks for the state to update accordingly
3. This results in the controls state being calculated via:

controls = cloneDeep(oldState.controls);
controls = restoreQueryableStateToDefaults(controls); # only ever called here
controls = modifyStateViaURLQuery(controls, query);

4. Running restoreQueryableStateToDefaults will set controls.filters = {} (src) but it won't affect controls.filtersInFooter as that's not part of controls.defaults (probably by mistake, but oh well!). Logging the state change in this function when we change slides shows:

controls.filters was {"clade_membership":[],"region":[]...} and is now {}
controls.filtersInFooter was [clade_membership,region,...] and is now [clade_membership,region...]

5. An empty controls.filters means that there are no available filters, so the dropdown doesn't work!

The root cause of the bug is in restoreQueryableStateToDefaults. The "default" in this case is not correct, as it is restoring to the "default app state before we have any data" rather than the "default state as determined by the dataset JSON". One way to fix this is to mimic what we do when we first load JSONs, which is a 1-line change here to:

controls = restoreQueryableStateToDefaults(controls);
controls = modifyStateViaMetadata(controls, metadata); # add this line

However a better fix would be (might be?) to rewrite restoreQueryableStateToDefaults. This is along the lines of what you're doing in this PR, but it's the code inside restoreQueryableStateToDefaults which should be changed, rather than modifying it afterwards.

[joverlee521]

Thanks for writing out the codepath notes @jameshadfield, it's really helpful to see it all!

I'm in favor of just doing the 1-line change of adding modifyStateViaMetadata. This ensures that we restore all dataset default controls without worrying about missing something within restoreQueryableStateToDefaults.

[jameshadfield]

Thanks @joverlee521!