Php week number starting sunday

I know this topic is old, but this is a shorter way to do it with elvis operator and "+7 day" expression for strtotime[]:

$week=date["W",strtotime[date["w"]==1?"+7 day":"+0 day"]];

if $date["w"] returns true means today is a day between tuesday and sunday [1-6], so, we can return today week ['today'].

if returns false, it means is monday [0], so, we should return the next day ['+1 week'].

This way we don't need to care about last or first day of year or check if current year has 52 or 53 weeks.

Edited: the previous answer [and others in this topic] doesn't work for this year because januray 1st is monday, so, it needs to be 1 week ago [-1 week] excluding sunday [day 6].

date["W",strtotime[date["w"]?'-7 day':'+0 day']];

I think a condition asking if januray 1st is monday could work, but I didn't test it yet, I will come back with an answer later

For a custom day you could use this:

$date = strtotime['2018-04-30']; // [it is monday]

if[date["w",strtotime[date['Y',$date].'-01-01']]==1]{ // if first day of year is monday
    $week = strtotime[date['w',$date]?"-7 day":"+0 day",$date]; // and today is sunday, sub a week
    $week = date["W",$week];
}else{ // if is not monday
    $week = strtotime[date['w',$date]==1?"+7 day":"+0 day",$date]; // and today is monday, add a week
    $week = date["W",$week];
}