reducersWithLenses.js

import { lensPath, lensProp, compose } from 'ramda';

// Some new helper functions
const append = item => array => [...(array || []), item];
const findById = id => array => array.find(item => item._id === id);

const sceneLens = lensProp('scene');
const structureLens = lensProp('structure');
const objectsLens = lensProp('objects');
const groupsLens = lensProp('groups');

const structureObjectLens = compose(sceneLens, structureLens, objectsLens);
const structureGroupLens = compose(sceneLens, structureLens, groupsLens);

switch(state = defaultState, action) {
  case ADD_OBJECT_TO_STRUCTURE: return over(structureObjectLens, append({ name: 'New Object' }), state);

  case ADD_OBJECT_TO_GROUP: {
    const oldGroup = view(structureGroupLens, state).find(findById(action.data.id));
    const newGroup = over(objectLens, append({ name: 'New Object' }), group);
    const groups = view(structureGroupLens, state).length > 0 ? view(structureGroupLens, state).map(replaceFully(oldGroup, newGroup)) : [newGroup];
    return set(structureGroupLens, groups, state);
  }
}