title: Determine if a week is odd or even
body: <p>I have debugged this legacy code, and would like a sanity check on it.</p>
  
  <p>The purpose of it is to allow someone to choose a delivery frequency for shipping a product. If someone wants their product Every Other Week, the system needs to determine if they should get an order next week, or two weeks from now. We call it A week, or B Week.</p>
  
  <p>Keep in mind I did not write this, I am just trying to make sense of it and would like some help evaluating its accuracy:</p>
  
  <pre><code>if (date("l") == "Monday" ) {
              $start = 0;
          } else if (date("l") == "Tuesday" || date("l") == "Wednesday" || date("l") == "Thursday" || date("l") == "Friday" || date("l") == "Saturday"|| date("l") == "Sunday") {
          $start = -1;
      }
  
      // if changing to every other week set to next week's a/b-ness
      $a_week_tid = 34;
      $b_week_tid = 35;
  
      $every_other_week_frequency_id = 32;
  
      if ($delivery_frequency == $every_other_week_frequency_id) {
          $julian = (int) (strtotime('Monday +' . $start . ' week') / 86400);
          $julian_week = ($julian-4) / 7;
          if ($julian_week % 2) {
              $today_a_or_b = $b_week_tid;
              $next_week_a_or_b = $a_week_tid;
              $a_or_b_week_string = '(A Week)';
          } else {
              $today_a_or_b = $a_week_tid;
              $next_week_a_or_b = $b_week_tid;
              $a_or_b_week_string = '(B Week)';
          }
      } else {
          $next_week_a_or_b = NULL;
          $a_or_b_week_string = NULL;
      }
  </code></pre>
  
  <p>This code is not commented or documented. The part that confuses me is:</p>
  
  <ol>
  <li>Why is 4 subtracted from Julian, then divided by 7?</li>
  <li>If today is Monday, $julian_week is 2129, and 2129 % 2 evaluates TRUE. Is that correct?</li>
  <li>Is this even how it should be done? Can't I rewrite this using date('w') a lot easier?</li>
  </ol>