Countdown to a repeating event every four/4 weeks

chmac

I'm trying to create a very simple script which will tell you the number of days to the next Friday. However, the next Friday is set on a 4 week repeating pattern starting from Friday 17 July.

For example, the script could be to track menstrual cycles (it's not, but you get the idea!). An event that happens every 4 weeks, not every month, starting from a specified date.

The script is fairly simple, but I'd appreciate some feedback on the best way to set it up. The options as I see them are:

1] Add 4 weeks to the original date
Add 4 weeks to the original date until the date is in the future, then count the no of days

2] Store the next date somewhere, and if the date is today or in the past, advance it by 4 weeks

Is there another option I'm missing? The only reason I hesitate before using option 1 is that the execution time will increase every 4 weeks. So if the script were to run for say 100 years, it would need 13'000 iterations of the loop!

I'm probably being overly anal here, so any feedback welcome!

Thanks in advance,

CM.

drawmack

stick the original date into a variable:

i.e. $start = 'March 29, 1975'; //my brithdate was the begining

then just do a little date math like this:

<?php
function find_next_occurance($start) {
    $start = strtotime($start);
    $now = time();
    while($start < $now)
        $start += (60*60*24*7);

return $start;
} //end fine_next_occurance
?>

chmac

Hi Drawmack,

Thanks for the suggestion, that looks like a less intensive way of doing option no 1. However, it will still add one iteration of the loop for every 4 weeks over time.

I'm wondering if there is there an alternative?

For example, can you do some sort of single calculation to say find the next date which falls on a date that is 4/8/12/16/etc weeks from a specified date?

Am I getting unnecessarily complicated?

Cheers - CM.

drawmack

As I tell my clients when you're talking programming if the question starts with can the answer is yes, it's just a matter of time and skills.

Therefore you can do that but it'll be a lot harder, though what you could do is, save the starting date to a file and then update that file everytime the next date changes. This way the while loop will only ever run one or two times.

chmac

Hi Drawmack,

Thanks again. That was my second option, but I'm not sure where would be the best place to store it. Some sort of text file would just create unnecessary clutter on the server.

Can a PHP script write back to itself or to an includes file? That could be a cleaner option.

Admittedly, the more I think about this, the more I reallse that the first option is simpler, in 10 years it'll only mean 130 iterations, which will hardly topple my server!

Thanks again for your input,

CM.