toggle.js

// This is the toggle helper from Ember composable helper,
// but I'm adding some annotations
// Ref: https://github.com/DockYard/ember-composable-helpers/blob/master/addon/helpers/toggle.js
import { helper } from '@ember/component/helper';
import { get } from '@ember/object';
import { set } from '@ember/object';
import { isPresent } from '@ember/utils';

// FP - First Pass
// SP - Second Pass

// [FP] Looks like this gives us a way to either get the next index
// Or throw a falsey value of 0
function nextIndex(length, currentIdx) {
  if (currentIdx === -1 || currentIdx + 1 === length) {
    return 0;
  }

  return currentIdx + 1;
}

// Keep in mind, here is the API
// <button {{action (toggle "isExpanded" this)}}>
export function toggle([prop, obj, ...values]) {
  return function() {
    // This would be like `get(this, 'nightMode')` in our case
    let currentValue = get(obj, prop);

    // Going to completely ignore this for now since we are not passing in more values
    if (isPresent(values)) {
      let currentIdx = values.indexOf(currentValue);
      let nextIdx = nextIndex(get(values, 'length'), currentIdx);

      return set(obj, prop, values[nextIdx]);
    }

    // This is just doing `set(this, 'nightMode', !currentValue)`
    return set(obj, prop, !currentValue);
  };
}

export default helper(toggle);