decide.nolog.cz/app/components/create-options-dates.js

import Component from '@ember/component';
import { inject as service } from '@ember/service';
import { computed } from '@ember/object';
import { isArray } from '@ember/array';
import { isPresent } from '@ember/utils';
import moment from 'moment';

export default Component.extend({
  i18n: service(),
  store: service('store'),

  selectedDays: computed('options.[]', function() {
    return this.options
      // should be unique
      .uniqBy('day')
      // raw dates
      .map(({ date }) => date)
      // filter out invalid
      .filter(moment.isMoment)
      .toArray();
  }),
  calendarCenterNext: computed('calendarCenter', function() {
    return moment(this.calendarCenter).add(1, 'months');
  }),

  actions: {
    daysSelected({ moment: newMoments }) {
      let { options } = this;

      if (!isArray(newMoments)) {
        // special case: all options are unselected
        options.clear();
        return;
      }

      // array of options that represent days missing in updated selection
      let removedOptions = options.filter((option) => {
        return !newMoments.find((newMoment) => newMoment.format('YYYY-MM-DD') === option.day);
      });

      // array of moments that aren't represented yet by an option
      let addedMoments = newMoments.filter((moment) => {
        return !options.find((option) => moment.format('YYYY-MM-DD') === option.day);
      });

      // remove options that represent deselected days
      options.removeObjects(removedOptions);

      // add options for newly selected days
      let newOptions = addedMoments.map((moment) => {
        return this.store.createFragment('option', {
          title: moment.format('YYYY-MM-DD'),
        })
      });
      newOptions.forEach((newOption) => {
        // options must be insert into options array at correct position
        let insertBefore = options.find(({ date }) => {
          if (!moment.isMoment(date)) {
            // ignore options that do not represent a valid date
            return false;
          }

          return date.isAfter(newOption.date);
        });
        let position = isPresent(insertBefore) ? options.indexOf(insertBefore) : options.length;
        options.insertAt(position, newOption);
      });
    },
    updateCalenderCenter(diff) {
      this.calendarCenter.add(diff, 'months');
      this.notifyPropertyChange('calenderCenter');
    },
  },

  init() {
    this._super(arguments);

    let { selectedDays } = this;
    this.set('calendarCenter', selectedDays.length >= 1 ? selectedDays[0] : moment());
  },
});