static-cms/packages/netlify-cms-core/src/reducers/cursors.js

import { fromJS } from 'immutable';
import { Cursor } from 'netlify-cms-lib-util';
import { ENTRIES_SUCCESS, SORT_ENTRIES_SUCCESS } from 'Actions/entries';

// Since pagination can be used for a variety of views (collections
// and searches are the most common examples), we namespace cursors by
// their type before storing them in the state.
export const selectCollectionEntriesCursor = (state, collectionName) =>
  new Cursor(state.getIn(['cursorsByType', 'collectionEntries', collectionName]));

const cursors = (state = fromJS({ cursorsByType: { collectionEntries: {} } }), action) => {
  switch (action.type) {
    case ENTRIES_SUCCESS: {
      return state.setIn(
        ['cursorsByType', 'collectionEntries', action.payload.collection],
        Cursor.create(action.payload.cursor).store,
      );
    }
    case SORT_ENTRIES_SUCCESS: {
      return state.deleteIn(['cursorsByType', 'collectionEntries', action.payload.collection]);
    }
    default:
      return state;
  }
};

export default cursors;