Generate start and ending datetimes in UTC based on a PST date - php

Question

I am taking in a parameter that is a date in PST timezone which will be in the format of "YYYY-MM-DD" (e.g. "2011-08-15"). This parameter is optional. I have 2 questions that I've been struggling with.
I need to calculate the start and end datetime in UTC for this date.
So if the inputted date is 2011-08-15, I want to get the start and end datetimes:
2011-08-15 07:00:00
2011-08-15 06:59:59
(These are essentially the beginning and end of day)
Second, is to handle the case when the date is not passed in. I want to default to the current PST date them and start from there. So if the current datetime is 2011-08-01 10:00:00, I want to get the same start and end datetimes similar to the first scenario except it's based on the inputted date.
2011-08-01 07:00:00
2011-08-01 06:59:59
I've been pulling my hair out dealing with date and datetime conversions. I'm sure I'm missing something super straightforward.

Answer 1

Parse the date and assume PST timezone:
$date = new DateTime("2011-08-15", new DateTimeZone("PST"));
Change the timezone to UTC: (this does the all conversions for you)
$date->setTimeZone(new DateTimeZone("UTC"));
Calculate start and end. Start is our $date and end is $date + 1 day
$start = $date;
$end = clone $date;
$end->modify("+1 day"); // now $end is $start + 1 day
Print start/end:
printf("start: %s, end: %s\n", $start->format('Y-m-d H:i:s'), $end->format('Y-m-d Hi:s'));
// this prints start: 2011-08-15 07:00:00, end: 2011-08-16 07:00:00
For the last part of your questions, you can easily compare two dates:
if ($date > new DateTime()) { // if $date is after now
// do something
}
So you could do something like that:
if ($date > new DateTime()) {
$date->setTimeZone(new DateTimeZone("UTC"));
}
If you don't much like the OO syntax you could also use the function aliases:
$date = date_create(...);
date_format($date, ...);
date_modify($date, ...);
// ...

Answer 2

Use setTimezone function
Working example (I'm not in PST timezone, so I have to set it explicitly)
$date_input = "20011-09-15";
//$date_input = null; //That will emulate no-input case
date_default_timezone_set("America/Los_Angeles"); //if you are in PST, you don't need this line
$date_start = new DateTime($date_input);
$date_end = new DateTime($date_input);
$date_end->modify("+1 day");
/*$date_start->setTimezone(new DateTimeZone("America/Los_Angeles"));
$date_end->setTimezone(new DateTimeZone("America/Los_Angeles"));*/
//end of date is equal to start of the next day.
//But, if you need something like 2011-08-11 23:59:59 add $date_end->modify('-1 second')
$date_start->setTime(0,0,0);
$date_end->setTime(0,0,0);
echo "Date Start PST:".$date_start->format("Y-m-d H:i:s")."<br/>";
echo "Date End PST:".$date_end->format("Y-m-d H:i:s")."<br/>";
//UTC is equal to London time. Almost :)
$date_start->setTimezone(new DateTimeZone ('Europe/London'));
$date_end->setTimezone(new DateTimeZone ('Europe/London'));
echo "Date Start UTC:".$date_start->format("Y-m-d H:i:s")."<br/>";
echo "Date End UTC:".$date_end->format("Y-m-d H:i:s")."<br/>";