Improve view port selection

[tanjjj]

we want to improve SET_SELECTION.

Issue:
selection is a list of the rowIndex values of the rows to be selected.

In a table with frequent inserts and deletes, we might have timing issues. Assume the user has sorted data. Inserts/deletes that occur towards start of sorted keyset will cause rowIndex positions of following rows to be updated. This is where we might see a race condition.
If user sends a SET_SELECTION message with a rowIndex just as we have an insert that triggers an update to rowIndex values, we could select the wrong row (ie based on its previous rowIndex value).

Proposed solution:
use row KEY values rather than rowIndex values to specify rows to select.
Right now, UI sends an array of every single rowIndex value that needs to be selected. If user uses SHIFT+SELECT to select a range, every rowIndex value in that range is included in the selection.
Using row key values, this approach won’t work. If user selects a large range that spans many pages, the UI will not necessarily have all the data for the full set of rows to be selected. This doesn’t stop it building a list of rowIndex values but it will make it impossible to provide the associated row key values.
I suggest the following, we replace the current single selection message with a number of messages
{
type: "SELECT_ROW”;
preserveExistingSelection: boolean;
rowKey: string;
vpId: string;
}

If preserveExistingSelection is true, simply update the target row to be selected. If preserveExistingSelection is false, also remove selection from any other rows that are currently selected
{
type: “DESELECT_ROW”;
preserveExistingSelection: boolean;
rowKey: string;
vpId: string;
}

{
type: “SELECT_ROW_RANGE”;
preserveExistingSelection: boolean;
fromRowKey: string;
toRowKey: string;
vpId: string;
}

{
type: “SELECT_ALL”;
vpId: string;
}

{
type: “DESELECT_ALL”;
vpId: string;
}

The above would allow us to support the full set of extended selection features that we currently have.

Note DESELECT_ROW with preserveExistingSelection:false would be identical to DESELECT_ALL, but API feels lopsided if we omit the preserveExistingSelection

[tanjjj]

Things to consider:

1. when selecting a range or select all, if a new row is inserted, or an existing row is deleted from the range, do we add/remove it from the selection or ignore the change?

2. There is a lock on set selection. Is this enough to prevent the situation of server handling a set selection (of a range) request and front end send in another request to change sorting?

3. how much change required backend/frontend, including the demo code?

[tanjjj]

Currently in the ViewPort, selection is a map of key <-> index. So we can keep it as it is and only change how we set the selection

[tanjjj]

when select all, if new rows inserted, include the new row
when select a range, if new rows are inserted to the range of selection, ignore

when deselect row with preserve flag true, remove the specific key from selection
when deselect row with preserve flag false, remove all selected rows