Php Date Returning Unexpected Week Range - php

Question

Php is returning an unexpected set of week dates given a specific day. For example, given the date 2015-05-20, the days of the week that should be returned are:
array:7 [
0 => "2015-05-17"
1 => "2015-05-18"
2 => "2015-05-19"
3 => "2015-05-20"
4 => "2015-05-21"
5 => "2015-05-22"
6 => "2015-05-23"
]
Or in plain text May 17th to 23rd, 2015. From what I can tell this is correct. Now, given the date 2015-05-17, I get the following results:
array:7 [
0 => "2015-05-10"
1 => "2015-05-11"
2 => "2015-05-12"
3 => "2015-05-13"
4 => "2015-05-14"
5 => "2015-05-15"
6 => "2015-05-16"
]
Which you will notice is the week before the 17th, or May 11th to 16th, 2015.
Here is the function that is pulling my weekdays:
$days_of_week = array();
for($i = 0; $i <= 6; $i ++){
$days_of_week[] = date("Y-m-d", strtotime(date("o", strtotime($date))."W".date("W", strtotime($date)).$i));
}
Basically, for the 7 days in a given week number (which is 20 in this case), push the formatted value to an array (as shown in the two examples above.) Pre-formatted, the values being pushed are:
2015W200
2015W201
2015W202
2015W203
2015W204
2015W205
2015W206
// Year: 2015, Week: 20, Day(In week): 0-6
I think the issue I'm facing is that ISO-8601 week numbers start from Monday and end at Sunday, but I'm trying to pull a week that starts with Sunday and ends with Saturday (for display on a calendar.) Is there another way to accomplish this?

Answer 1

In fact it's a expected result.
2015-05-17 is in 20th week.
Thus days and week day number are respectively: (10 11, 12, 13, 14, 15, 16) and (0, 1, 2, 3, 4, 5, 6)
See Localized Notations section on docs, in format compounds:
Notation
ISO year with ISO week and day:
YY "-"? "W" W "-"? [0-7]
Where the last token stays for a week day number, starting with sunday to saturday.
So when you loop over week numbers you're getting:
2015W20[0] -> That is, a date on sunday (2015-05-10)
2015W20[1] -> That is, a date on monday (2015-05-18)
So you must especify the correct week number of year:
$days_of_week = array();
$week_number = 21;
$year = date('Y');
for($day = 0; $day <= 6; $day++)
{
$format = $year. "W" . $week_number.$day;
print $format . "\n";
array_push($days_of_week, date('Y-m-d', strtotime($format)));
}
print_r($days_of_week);

Answer 2

I figured my problem out. Ignoring ISO-8601 week numbers (1-53), I was able to get a range of seven days based on a given date`s week number (0 Sunday - 6 Saturday).
$day = new DateTime($date); // 2015-05-21
$start = $day->modify("- ".$day->format("w")." days"); // - 4 days - 2015-05-17
$end = clone $start;
$end = $start->modify("+ 7 days"); // 2015-05-24 (foreach ignores last day)
$interval = new DateInterval("P1D");
$week = new DatePeriod($start, $interval, $end);
foreach($week as $key => $val) {
$days_of_week[] = date("Y-m-d", strtotime($val->format("Y-m-d")));
}
This method correctly returns an array of seven days, starting on Sunday and ending on Saturday, based on a given date. Thanks to #Rizier123 for the backbone of this answer.