Group changes based on `action.params` (or allow filtered actions to reset `history.group`)

[josephmturner]

Thank you for redux-undo!

I'd like to group changes based not only on a comparison of prior/current action.type but also prior/current action.params.

Data model:

interface DraftState {
  message: DraftMessageI
  points: {
    [url: string]: PointI
  }
}

Stream of actions looks like:
{ type: 'draftPointCreate', params: { url: 'point1' } }
{ type: 'draftPointUpdate', params: { url: 'point1', content: 'h' } }
{ type: 'draftPointUpdate', params: { url: 'point1', content: 'he' } }
{ type: 'draftPointUpdate', params: { url: 'point1', content: 'hel' } }
{ type: 'draftPointUpdate', params: { url: 'point1', content: 'hell' } }
{ type: 'draftPointUpdate', params: { url: 'point1', content: 'hello' } }
{ type: 'draftPointCreate', params: { url: 'point2' } }
{ type: 'draftPointUpdate', params: { url: 'point2', content: 'w' } }
{ type: 'draftPointUpdate', params: { url: 'point2', content: 'wo' } }
{ type: 'draftPointUpdate', params: { url: 'point2', content: 'wor' } }
{ type: 'draftPointUpdate', params: { url: 'point2', content: 'worl' } }
{ type: 'draftPointUpdate', params: { url: 'point2', content: 'world' } }

I want to filter out changes which result from draftPointCreate actions since there's no need to store empty points in history.past. Additionally, I want to group changes which result from draftPointUpdate actions if and only if their action.params.url are the same. I tried this config:

export default undoable(draftReducer, {
  filter: excludeAction('draftPointCreate'),
  groupBy: groupByActionTypes('draftPointUpdate')
})

If the filtered draftPointCreate actions caused history.group to reset to null, this would work as intended. However, since #171 and #167, history.group is not modified on filtered actions (I agree that redux-undo current behavior makes sense).

Perhaps there's some other solution for my use case!

Thank you for your time!

[josephmturner]

For now, I found that the quickest solution was to reverse the change made in #171 by not passing a value for group to

const filteredState = newHistory(...)

I suppose I'll maintain my own fork with this minor change until redux-undo gets some love in the future. You might consider adding a flag to allow users to choose whether or not filtered actions reset history.group. If that's desired, I'd be happy to submit a PR.

[josephmturner]

Forking redux-undo was an ugly solution. A better solution is to create a custom filter fn:

let pointURL: string | null = null
let justCreated = false
export function customFilter (action: Action<any>, currState: DraftState, prevHistory: StateWithHistory<DraftState>): boolean {
  let unfiltered = true
  switch (action.type) {
    case Actions.draftPointCreate:
      pointURL = action.params.point.url
      justCreated = true
      unfiltered = false
      break
    case Actions.autoDeleteEmptyPoint:
      if (justCreated) {
        [pointURL] = action.params.pointURLs
        justCreated = unfiltered = false
      }
      break
    default:
      // eslint-disable-next-line @typescript-eslint/no-unused-vars
      pointURL = null
      justCreated = false
  }
  return unfiltered
}

and a custom groupBy fn:

export function customGroupBy (action: Action<any>, currState: DraftState, prevHistory: StateWithHistory<DraftState>): string | null {
  switch (action.type) {
    case Actions.draftPointUpdate:
      return action.params.point.url
    case Actions.autoDeleteEmptyPoint:
      return action.params.pointURLs[0]
  }
  return null
}

Then, in my undo/redo function, I recursively skip over items in the past or future arrays which have deep equality with the present object.