PHP minus one week Sunday - php

Question

I'm a newbie in both php and codeigniter.
I have a function which is used to label the x-axis of a chart of weekly sums of kilometers rode on a bicycle. It works (or is supposed to work) by counting back from today's date either zero Sundays or 1, 2, 3, etc as passed by an array.
I am using PHP Version 5.6.19, and this is my code:
In the Model:
public function week_start($date, $counter){
$tstring = strtotime($date);
$wknumber = ($counter + 1);
$start = strtotime("-$wknumber weeks sunday", $tstring);
return array(date('M d', $start));}
In the Controller:
$datenumbers = array(0, 1, 2, 3, 4, 5, 6, 7);
$dateResult = $this->bike_model->week_start(date("Y/m/d"), $datenumber);
In the view:
for ($i = 0; $i < 8; $i++){
echo "<text class = \"axis\" y = \"357\" x = \"";
echo 26 + ($i*70);
echo "\" dy = \".35em\">";
echo $dates_for_table[$i];}
I have had it up for few days and it has been showing Sunday July 3 as the first number on on my x-axis, as it should have. But today, it is Sunday and I expect it to now say Sunday July 10 as my most recent week. However, it is still showing last Sunday!
So my question is, is there a bug here or am I misunderstanding how '- one week Sunday' should work?
My goal is to have my function with zero as the argument return the most recent week start--either the current Sunday if it is Sunday or the past Sunday. I have found a workaround by adding an if else to the function checking if it is Sunday.
if ($tstring == strtotime('this Sunday')){
$wknumber = $counter;}
else{
$wknumber = ($counter + 1);}
However, this feels clunky and I'm looking for a more elegant way. I also want to understand what went wrong with "- one week Sunday" since I thought I had understood how it was working.
Thank you!

Answer 1

Here is how I did something similar using the object oriented DateTime style:
$startDate = new DateTime('NOW'); // can pass date string if not today
# reset start date to last Sunday or today if it is Sunday:
$startDate->sub(new DateInterval('P'.($startDate->format('w')).'D'));
# for debugging, output first Sunday:
echo $startDate->format('Y-m-d H:i:s') . " => full date and time (check for timezone issues) \n\n";
$weeks = 8;
for ($i = 0; $i < $weeks; $i++) {
# don't decrement first pass; sub 1 week on subsequent:
$startDate->sub(new DateInterval('P'. (($i) ? 1 : 0) .'W'));
echo $startDate->format('Y-m-d') . "\n";
};
You should be able to adapt for your purpose.
If you want to get fancy, you can also use DatePeriod instead of using sub within a loop:
$period = new DatePeriod(
$startDate,
DateInterval::createFromDateString('-1 week'),
7
);
foreach ($period as $date) {
echo $date->format('Y-m-d') . "\n";
}