Help! Writing script based on weekdays in a month

[kyra]

I am stuck, and was able to get some great help the last time I came to this forum, so I am hoping for the same luck this time!!

classes
- classid
- weekday (list weekday a class falls on every week)
- startdate

I am trying to write a script that calculates the number of times a weekday falls in each month (will be used every month) starting from the startdate of the class. I have all the other calculations and fomulas written but I am stumped at the best way to calculate this.

In more broken down terms, this is what I am trying to find using "Sue" as an example:

Sue has a class that she started on 10/08/2009 and John started on 10/01/2009, and their lesson weekday is Thursdays, at $10 a lesson. In all of October, there are 5 Thursdays, but Sue should only be billed for 4 since she started a week into October. John, however, should be billed for 5 since he started the first week in October. So Sue's total for October would be $40, but John's should be $50.

---

I have no idea where to even start with this, any help at all is greatly appreciated.

[NogDog]

Here's something I whipped up (I was bored and didn't feel like doing "real" work) which might help:

<?php
/**
 * Get an array of days in a month by weekday
 * @param int $mon  Month number
 * @param int $yr   Year number
 * @return array    ix1 = day of week, 0 = Sunday to 6 = Saturday
 */
function getMonthDays($mon, $yr)
{
   $dates = array();
   $lastDayNum = cal_days_in_month(CAL_GREGORIAN, $mon, $yr);
   $startWeekDayNum = date('w', mktime(1,1,1,$mon,1,$yr));
   for($day = 1, $wkday = $startWeekDayNum; $day <= $lastDayNum; $day++, $wkday++)
   {
      $dates[$wkday % 7][] = $day;
   }
   return $dates;
}

// SAMPLE USAGE:
$test = getMonthDays(10, 2009);
?>
<p>The thursdays in October 2009 are:</p>
<ul>
<?php
foreach($test[4] as $day)
{
   echo "<li>$day</li>\n";
}
?>
</ul>

Output:

The thursdays in October 2009 are:

• 1

• 8

• 15

• 22

• 29