Issue #2606934 by tim.plunkett:...

   *   An array of weekdays.

   *

   * @return array

   *   An array of weekdays reordered to match the first day of the week.

   *   An array of weekdays reordered to match the first day of the week. The

   *   keys will remain unchanged. For example, if the first day of the week is

   *   set to be Monday, the array keys will be [1, 2, 3, 4, 5, 6, 0].

   */

  public static function weekDaysOrdered($weekdays) {

    $first_day = \Drupal::config('system.date')->get('first_day');

    if ($first_day > 0) {

      for ($i = 1; $i <= $first_day; $i++) {

        $last = array_shift($weekdays);

        array_push($weekdays, $last);

        // Reset the array to the first element.

        reset($weekdays);

        // Retrieve the first week day value.

        $last = current($weekdays);

        // Store the corresponding key.

        $key = key($weekdays);

        // Remove this week day from the beginning of the array.

        unset($weekdays[$key]);

        // Add this week day to the end of the array.

        $weekdays[$key] = $last;

      }

    }

    return $weekdays;

<?php

/**

 * @file

 * Contains \Drupal\Tests\Core\Datetime\DateHelperTest.

 */

namespace Drupal\Tests\Core\Datetime;

use Drupal\Core\Datetime\DateHelper;

use Drupal\Core\DependencyInjection\ContainerBuilder;

use Drupal\Tests\UnitTestCase;

/**

 * @coversDefaultClass \Drupal\Core\Datetime\DateHelper

 * @group Datetime

 */

class DateHelperTest extends UnitTestCase {

  /**

   * @covers ::weekDaysOrdered

   * @dataProvider providerTestWeekDaysOrdered

   */

  public function testWeekDaysOrdered($first_day, $expected) {

    $container = new ContainerBuilder();

    $config = ['system.date' => ['first_day' => $first_day]];

    $container->set('config.factory', $this->getConfigFactoryStub($config));

    \Drupal::setContainer($container);

    $weekdays = DateHelper::weekDaysUntranslated();

    // self::assertSame() MUST be used here as it checks for array key order.

    $this->assertSame($expected, DateHelper::weekDaysOrdered($weekdays));

  }

  public function providerTestWeekDaysOrdered() {

    $data = [];

    $data[] = [0, [

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

    ]];

    $data[] = [1, [

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

      0 => 'Sunday',

    ]];

    $data[] = [2, [

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

      0 => 'Sunday',

      1 => 'Monday',

    ]];

    $data[] = [3, [

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

    ]];

    $data[] = [4, [

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

    ]];

    $data[] = [5, [

      5 => 'Friday',

      6 => 'Saturday',

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

    ]];

    $data[] = [6, [

      6 => 'Saturday',

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

    ]];

    $data[] = [7, [

      0 => 'Sunday',

      1 => 'Monday',

      2 => 'Tuesday',

      3 => 'Wednesday',

      4 => 'Thursday',

      5 => 'Friday',

      6 => 'Saturday',

    ]];

    return $data;

  }

}