Expose `SeriesState` for simplified charts

[techniq]

Expose SeriesState for simplified charts to enable:

• Setting initial selected series
• Externally controlling selection
• Reading/writing selection to local storage, etc

[cycle4passion]

I would also find it useful to expose BrushState for persisting in localstorage. This allows for persistence of series and selected range.

[techniq]

I would also find it useful to expose BrushState for persisting in localstorage. This allows for persistence of series and selected range.

100% agree, and actually started on this a bit ago and need to resume. Encapsulating the state in a new BrushState class will enable and simplify state management (this is a pattern I plan to lean into with more state management). Also looking at supporting band scales and fixing some element click interop.

Progress here: #605

[cycle4passion]

In addition to exposing SereisState, BrushState, others, what about a prop like ...

<Chart
persist="localStorage"
/ >

and Layerchart goes ahead and does the heavy lifting read/write to localStorage or sessionStorage?

[techniq]

In addition to exposing SereisState, BrushState, others, what about a prop like ...

<Chart persist="localStorage" / >

and Layerchart goes ahead and does the heavy lifting read/write to localStorage or sessionStorage?

Hmm... we would need to generate a unique ID per chart instance (could use $props.id()).

Initially I would prefer to have some callback hooks, similar to SvelteKit snapshots (capture / restore) and leave it to the user where the would like to persist (localStorage, sessionStorage, query string, API/db call, etc).

I think we approach this iteratively - expose the state, expose the hooks, and then maybe add convenient adapters if needed.