[Discover session] State management

[kertal]

📓 Summary

It's been a while since we've took care of Discover state management. And it's about time to simplify it.

The last fundamental change was done in #153528, completing a series of PRs to extract state relevant functionality that was distributed among the UI into a central state container with several subcontainers.

To summarize how it looks like today:

The multiple sources of truth in Discover's state container are the source for confusion and frustration when dealing and expanding Discover's central state. We now have new requirements, we need a simple way to serialize and deserialize state in Discover.

Instead of several sources of truth, currently we have the following state containers under one umbrella

• DiscoverGlobalStateContainer

  kibana/src/platform/plugins/shared/discover/public/application/main/state_management/discover_global_state_container.ts

  Line 20 in bb877cf

  export const getDiscoverGlobalStateContainer = (

• DiscoverAppStateContainer

  kibana/src/platform/plugins/shared/discover/public/application/main/state_management/discover_app_state_container.ts

  Line 47 in bb877cf

  export interface DiscoverAppStateContainer extends ReduxLikeStateContainer<DiscoverAppState> {

• DiscoverDataStateContainer

  kibana/src/platform/plugins/shared/discover/public/application/main/state_management/discover_data_state_container.ts

  Line 77 in df495ce

  export interface DiscoverDataStateContainer {

• DiscoverInternalStateContainer

  kibana/src/platform/plugins/shared/discover/public/application/main/state_management/discover_internal_state_container.ts

  Line 83 in bf9d344

  export type DiscoverInternalStateContainer = ReduxLikeStateContainer<

• DiscoverSavedSearchContainer

  kibana/src/platform/plugins/shared/discover/public/application/main/state_management/discover_saved_search_container.ts

  Line 63 in bf9d344

  export interface DiscoverSavedSearchContainer {

• DiscoverSearchSessionManager https://github.com/elastic/kibana/blob/bb877cff7ef24c3f7295bdcdbdebb960c7db81b3/src/platform/plugins/shared/discover/public/application/main/state_management/discover_search_session.ts

What's more, our UI additional subscribes to various state among the data plugin, like

• timefilter.getTimeUpdate$
  

  kibana/src/platform/packages/shared/kbn-unified-field-list/src/hooks/use_query_subscriber.ts

  Line 84 in bb877cf

  const subscription = timefilter.getTimeUpdate$().subscribe(() => {

• data.query.getState()

  kibana/src/platform/plugins/shared/discover/public/application/main/components/layout/discover_layout.tsx

  Line 82 in fce8a27

  const globalQueryState = data.query.getState();

And there might be more, our poor UI has to listen to lots of different state, even duplicate ones. time to clean this up

✔️ Acceptance criteria

Though shall not have many different State management container, there shall be one state container to rule em all. The next state container should be

• a central source of truth for the UI
• that should be it easy to extend
• simple to mock,
• simple to explain
• simple to serialize and to deserialize (as a whole, as parts) for various targets (URL, localStorage, SavedObject)
• Future proof
• Can be migrated to step by step (if it makes sense and if it's possible)
• URL initialized state initialization should still be functional and backwards compatible

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)