cached computed macro

cached-computed.js

import { run } from '@ember/runloop';

import { computed } from '@ember/object';

const { stringify } = JSON;

export default function(...props) {
  const { getState, update } = props.pop();

  const strippedProps = props.map((prop) => {
    let index = prop.indexOf('.[]');
    if (index === -1) {
      index = prop.indexOf('.@each');
    }
    if (index === -1) {
      return prop;
    }

    return prop.slice(0, index);
  });

  function stateHelper() {
    const
      entries = this.getProperties(strippedProps),
      values = Object.values(entries),
      state = getState.apply(this, values);

    return {
      values,
      state: (typeof state === 'string') ? state : stringify(state)
    };
  }

  let cachedState;

  return computed(...props, function() {
    const { state, values } = stateHelper.call(this);

    if (state === cachedState) {
      return;
    }

    run.scheduleOnce('afterRender', null, () => {
      update.apply(this, values);

      const { state } = stateHelper.call(this);

      cachedState = state;
    });
  }).readOnly();
}

example.hbs

{{_projectContactManager}}

example.js

import Controller from '@ember/controller';

import { run } from '@ember/runloop';
import { inject as injectService } from '@ember/service';

import cachedComputed from '../macros/cached-computed';

export default Controller.extend({
  cart: injectService(),

  _projectContactManager: cachedComputed('cart.order.project.contacts.@each.isBlank', {
    getState: contacts => contacts.mapBy('isBlank'),

    update(contacts) {
      const blankContacts = contacts.filterBy('isBlank');

      blankContacts.forEach((blankContact) => {
        // remove any blank contacts from the list
        contacts.removeObject(blankContact);

        // garbage-collect orphaned contacts
        run.later(blankContact, 'rollbackAttributes');
      });

      // create a new blank contact at the end of the list
      contacts.createRecord({ isOwned: true });
    }
  })
});