PHP Compound Date Format Bug - php

Question

I am using the following lines of code to get the dates I am trying to generate for some reports and it seems to work fine except in a few instances and I can't see why that would be.
// what week numbers belong to which period
$adminconfig_periods = array(
1=>array(1,2,3,4),
2=>array(5,6,7,8,9),
3=>array(10,11,12,13),
4=>array(14,15,16,17),
5=>array(18,19,20,21,22),
6=>array(23,24,25,26),
7=>array(27,28,29,30),
8=>array(31,32,33,34,35),
9=>array(36,37,38,39),
10=>array(40,41,42,43),
11=>array(44,45,46,47,48),
12=>array(49,50,51,52,53)
);
/**
* Get period no for week no
*
* #param string week the week
* #return int - the period no
*/
function getPeriodForWeek($week) {
global $adminconfig_periods;
$foundperiod = false;
$period = 1;
while(!$foundperiod) {
if(in_array($week, $adminconfig_periods[$period])) {
$foundperiod = true;
} else {
$period ++;
}
}
return $period;
}
$wA = $_GET['wA'];
$yA = $_GET['yA'];
$prev_period = '';
$next_period = '';
if (!isset($wA) || !isset($yA)) {
// period and year aren't set so do it for current period
// period starts on first Sunday of the first week in the period and ends on the last Saturday of the last week in the period
$week = date('W');
$period = getPeriodForWeek($week);
$wA = date('m');
$yA = date('Y');
}
else {
// period and year are set
// period starts on first Sunday of the first week in the period and ends on the last Saturday of the last week in the period
$period = $wA;
}
// get date of first Sunday of the first week in this period
$period_start_week = $adminconfig_periods[$period][0];
// get the Sunday of this week
$period_start = date('Y-m-d', strtotime($yA . 'W' . $period_start_week . '0'));
// get date of last Saturday of the last week in this period
$period_length = count($adminconfig_periods[$period]);
// array indexes start from 0 so we need to take one off this value
$last_element = $period_length - 1;
$period_end_week = $adminconfig_periods[$period][$last_element];
// get the Saturday of this week
$period_end = date('Y-m-d', strtotime($yA . 'W' . $period_end_week . '6'));
On this page I have some select menu controls for changing the period and year number and when it gets to certain periods I get some bizarre dates.
The periods are quite confusing but if anybody has any questions then feel free to ask.
Period | What it Should Be | Actual Result
11 | 28/10/2012 - 01/12/2012 | 28/10/2012 - 01/12/2012
10 | 30/09/2012 - 27/10/2012 | 30/09/2012 - 27/10/2012
09 | 02/09/2012 - 29/09/2012 | 02/09/2012 - 29/09/2012
08 | 29/07/2012 - 01/09/2012 | 29/07/2012 - 01/09/2012
07 | 01/07/2012 - 28/07/2012 | 01/07/2012 - 28/07/2012
06 | 03/06/2012 - 30/06/2012 | 03/06/2012 - 30/06/2012
05 | 29/04/2012 - 02/06/2012 | 29/04/2012 - 02/06/2012
04 | 01/04/2012 - 28/04/2012 | 01/04/2012 - 28/04/2012
03 | 04/03/2012 - 31/03/2012 | 04/03/2012 - 31/03/2012
02 | 29/01/2012 - 03/02/2012 | 10/12/2012 - 01/01/1970
01 | 01/01/2012 - 28/01/2012 | 05/03/2012 - 12/11/2012
As you can see, it seems to go insane for periods 1 and 2 for some reason and I don't understand why.
The parameters are passed in the following way: ?wA=1&yA=2012 and if those are not set it uses the current month and period.
If I was to guess then I'd say it might have something to do with leap years but I thought the code would be able to handle that automatically? Who knows, hopefully a few extra pairs of eyes will spot something stupid I've missed.
Code that echo's the dates
date("d/m/Y", strtotime($period_start)) . ' - ' . date("d/m/Y", strtotime($period_end)) .')';

Answer 1

The error is from those 2 lines
$period_start = date('Y-m-d', strtotime($yA . 'W' . $period_start_week . '0'));
$period_end = date('Y-m-d', strtotime($yA . 'W' . $period_end_week . '6'));
if the week number is 2 for example, adding a 6 to it, it would be 26 (week 26), so you have to add a zero to the left side for the single digit ones. Let's do that with str_pad():
$period_start = date('Y-m-d', strtotime($yA . 'W' . str_pad($period_start_week, 2, 0, STR_PAD_LEFT) . '0'));
$period_end = date('Y-m-d', strtotime($yA . 'W' . str_pad($period_end_week, 2, 0, STR_PAD_LEFT) . '6'));