Having issues with a simple birthday system (PHP / MySQL) - php

Question

I'm toying with the idea with what happens when conflicting date systems are present in a database and when it happens it causes chaos in PHP. Case in point, if you have part of the database with dates that contains 01/01/2016 but at some other point it contains 1/1/2016, then the date system seems to break. In a proper environment I'd imagine it should be epoch but in this case it isn't.
The following code is messy and maybe I'm over thinking it. But this is what I have:
/*
*
* Dates ($dob) can appear as followed:
* 01-30-2016 | 1-30-2016 | 01-01-2016 | 01/30/2016 or any combination
*
*/
$chpos = 0; // Define Character Position Variable
$replace = false; // Should we replace the 0 after the first dash?
// If the date uses this format: 01/02/2016 then replace the / with - so it looks like 01-02-2016
$dob = preg_replace('/\s+/', '-', $dob);
// Let's find out if the dash occurs on the 3rd character or 4th. We do this so we can replace the 0 in 2-02-2016
// 01-34-6789 *String Array positions* 0-23-5678
if(substr($dob, 0, 3) == 0 && substr($dob, 0, 0) == 0){
$chpos = 3;
$replace == true;
} else if (substr($dob, 0, 0) != 0 && substr($dob, 0, 2) == 0){
$chpos = 2;
$replace == true;
} else {
$replace == false;
}
// Let's replace the 0 after the first dash if necessary
if($replace == true){
$dob = substr_replace($dob, '', $chpos);
}
// Let's replace the 0 from the beginning if necessary
if(substr($dob, 0, 1 ) == 0){
$dob = substr( $dob, 1 );
}
// Let's convert it to a usable date object
$birthday = new DateTime($dob);
// Now let's compare the time from now to when the birthdate happened
$interval = $birthday->diff(new DateTime);
// Return the data over
return $interval->y;
The issue with the code has to do with when it replaces the 0 on the left of things. I could swear the code should work but maybe I made a typo and just can't see it? I don't know, but it's not working at all. The message is:
Uncaught exception 'Exception' with message 'DateTime::__construct(): Failed to parse time string (2-17-1994) at position 0 (2): Unexpected character'
The line in reference is:
$birthday = new DateTime($dob);
My question here is:
Why does the date system break when it has leading zeros?
Why is it so complex to just parse the date?
Am I missing something or is it supposed to be this difficult?
Am I over-thinking this?
Thank you for your time!

Answer 1

Ignoring the issues of data sanitization (the dob should never have made it into the database in different formats; a unix timestamp would have been a better option)... Why not just do the following;
$timedob = strtotime($dob);
$birthday = date('Y-m-d',$timedob);
strtotime takes any string and converts it into a unix timestamp. The date function then converts that unix timestamp into the output format you want.
Note that strtotime interprets the input as follows; if the Month, day, year are separated by a slash '/' - it assumes that the date is in American m/d/y format. If it sees hyphens or periods (- or .), it assumes that the date is in European d-m-y format.

Answer 2

It is very easy to parse a date string in php, which goes to extraordinary lengths to best interpret your strings using functions like strtottime.
http://php.net/manual/en/function.strtotime.php
The problem you are having is that you should store dates in the database as the database date or datetime formats (or whatever equivalent there is for your database). Validation should be done before trying to enter them into the database, as well as testing that any database writes are not rejected for badly formatted date structures. There also should be further validation when converting to a date for output.
It has been a very long time since I have had to manipulate date strings manually like you are doing here, and there certainly is no need to do so. Especially since date pickers are so commonplace that will also format dates browser side via js before sending. (This does not remove the need for server side validation of course.)
If I were you, I would write a short script to convert all your dates to a proper date format for your database, and change the format of that database column to a date format. Then address anywhere that is trying to write strings as dates into the database in your application. In a well structured application this should only be being done in one model function, so should not take too long.
A final benefit of doing this properly, is you can now easily produce reports or query results such as every event that happened before so and so date or between two dates, or on a tuesday, etc.