Find first and last week days according to locale

Question

I'm trying to find first and last week days based on the locale.

In U.S.A. a week normally starts on Sunday, but in other countries it could start on another day - e.g. Monday or even Saturday.

setlocale(LC_ALL, "en_US.UTF-8");
date_default_timezone_set("America/New_York");

$start_week = (new DateTimeImmutable());
$start_week = $start_week->modify('this week');
$end_week = $start_week->modify('this week +6 days');

$interval = new DateInterval('P1D');
$week_range = new DatePeriod($start_week, $interval, $end_week);

foreach($week_range as $week_day) {
  // $week_day starts with Monday, supposed to be Sunday
}

Answer 1

One way to do this is to use the IntlCalendar class. It has a method getFirstDayofWeek(), which returns an integer, corresponding to the DOW_ constants in IntlCalendar:

const integer DOW_SUNDAY = 1 ;
const integer DOW_MONDAY = 2 ;
const integer DOW_TUESDAY = 3 ;
const integer DOW_WEDNESDAY = 4 ;
const integer DOW_THURSDAY = 5 ;
const integer DOW_FRIDAY = 6 ;
const integer DOW_SATURDAY = 7 ;

Use that to add days to the start day when calling DateTimeImmutable::modify() for the start day. See it in action with three locales (i.e. en_US, es_ES, sw_KE) in this phpfiddle.

$locale = 'es_ES'; //Spain Spanish locale
$cal1 = IntlCalendar::createInstance(NULL, $locale);
$firstDayOfWeek = $cal1->getFirstDayOfWeek();
$daysToAdd = $firstDayOfWeek - 2; //difference from US M-Sunday 
echo 'locale: '.$local.' first day of week: '.$cal1->getFirstDayOfWeek().' days to add: '.$daysToAdd.'<br />';
$start_week = new DateTimeImmutable();
$start_week = $start_week->modify('this week +'.$daysToAdd.' days');
$end_week = $start_week->modify('+6 days');
$interval = new DateInterval('P1D');
$week_range = new DatePeriod($start_week, $interval, $end_week);

foreach($week_range as $week_day) {
    echo 'week day: '.$week_day->format('l m/d/Y').'<br />';
}