missing message implementation for ember-i18n to support default locale "fallback"

missing-message.js

import { getOwner } from '@ember/application';
import { typeOf } from '@ember/utils';

// https://github.com/jamesarosen/ember-i18n/blob/61086238bb507922fbf458f98fd44fd6e0a24a4e/addon/utils/locale.js#L150
function withFlattenedKeys(object) {
  const result = {};

  Object.keys(object).forEach(function(key) {
    var value = object[key];

    if (typeOf(value) === 'object') {
      value = withFlattenedKeys(value);

      Object.keys(value).forEach(function(suffix) {
        result[`${key}.${suffix}`] = value[suffix];
      });
    } else {
      result[key] = value;
    }
  });

  return result;
}

const cachedResults = {};
function constructTranslationsCache(cache, factory) {
  if (Object.keys(cache).length === 0) {
    const translations = factory && factory.class;
    return withFlattenedKeys(translations || {});
  }
}
function persistTranslations(locale, result) {
  if (result) {
    Object.assign(cachedResults[locale], result);
  }
  return cachedResults[locale];
}
function fallbackTranslations(locale, factory) {
  if (cachedResults[locale] === undefined) {
    cachedResults[locale] = {};
  }
  return persistTranslations(locale, constructTranslationsCache(cachedResults[locale], factory));
}

// to help our app "fall back" to a default locale (english)
export default function(locale, key, context) {
  if (locale !== 'en') {
    const factory = getOwner(this).factoryFor('locale:en/translations');
    const translations = fallbackTranslations(locale, factory);
    return translations[key];
  }
  return `translation.missing: ${key}`;
}