Converting source text to time with timezone adjustment - php

Question

I have a file of raw text/xml information that lists events occurring on the current day. The start time for each event is expressed in 00:00:00 24-hour format and is based on the Europe/London timezone. What I want to do is convert each event start time found in the file so that it is expressed in 'g:i A' format and is based on the America/New_York timezone.
Playing around, the following code works just fine if I define the source string as a single instance:
//output will be 3:45 PM
$src_tm = '19:45:00';
$src_tz = new DateTimeZone('Europe/London');
$dest_tz = new DateTimeZone('America/New_York');
$tm = new DateTime($src_tm, $src_tz);
$tm->setTimeZone($dest_tz);
$dest_tm = $tm->format('g:i A');
echo $dest_dt;
However as I said above, I want to do this for each instance in the file. I've come up with the following regex to identify each instance: '/\d+:\d+:00/' but I am having extreme difficulty making things work using the regex with preg_replace and DateTime. What do I need to do to ensure that each start time in the file is identified and converted to 'g:i A' and America/New_York?

Answer 1

I would suggest not using regular expressions to manipulate the XML file. This could be error-prone.
Instead, look into something like SimpleXML for parsing the XML file into a object graph whose nodes you can query and manipulate safely. Once you are done updating the date formats and timezones in each of the relevant nodes, you can save the object graph back into the file as an XML string.

Answer 2

Matt was correct on UTC rather than Europe/London. Thank you for pointing it out. And yes, there is no need for assigning to a particular date in my case, as the information I am using is refreshed daily. So the default to the current date is all I need.
With that said, I was able to get things right after reading about preg_replace_callback. Worked a charm!
//adjust event start time for America/New York
$input = preg_replace_callback('/\\d{2}:\\d{2}:\\d{2}/', 'replace_timestamp', $info);
function replace_timestamp($matches)
{
$source_tz = new DateTimeZone('UTC');
$destination_tz = new DateTimeZone('America/New_York');
$time = new Datetime($matches[0], $source_tz);
$time->setTimeZone($destination_tz);
return $time->format('g:i A');
}