Perl converting time based on text match - json

Question

I am using Perl to read in variables from a json file and handle them accordingly. The spot I need help with is when I read a time in from the file that could look like the following:
"StartTime":"2015-07-08T03:38:08Z",
"EndTime":"2015-07-10T03:38:08Z"
This is easy to handle, however here is the tricky part:
"StartTime":"now-10",
"EndTime":"now+10"
I have a function which gets these variables from the json file and checks if the string contains the word "now". But after that, I'm not sure what to do. I'm trying to convert "now" to localtime(time), but it's getting ugly fast. Here is my code:
my $_StartTime = getFromJson("StartTime");
my $_EndTime = getFromJson("EndTime");
if($_StartTime =~ /now/) {
(my $sec, my $min, my $hour, my $mday, my $mon, my $year, my $wday, my $yday, my $isdst) = localtime(time);
my $now = sprintf("%04d-%02d-%02dT%02d:%02d:%02dZ", $year+1900, $mon+1, $mday, $hour, $min, $sec);
}
# end time is handled the same way
Am I on the right track? And if so, how can I add the "+/-10" after the "now" in the file? (Note: assume the +/-10 always refers to hours)

Answer 1

There are lots of good modules on the CPAN that could help in this instance. You don't need to use them but it's worth knowing about them nonetheless.
Firstly, JSON might make your life easier when parsing the JSON files as it has easy methods for converting the JSON into native Perl structures.
Secondly, the DateTime family of modules might make it easier to parse and manipulate the dates. Specifically, instead of using sprintf, you could use DateTime::Format::ISO8601 to parse the date:
my $dt = DateTime::Format::ISO8601->parse_datetime( $_StartTime );
DateTime has methods for accessing the day, year, month and so on. These are documented on the main module page.
You could then keep your special case for the now input and do something like:
# work out if it's addition or subtraction and grab the amount
# then use the appropriate DateTime function:
my $dt = DateTime->now()->add( seconds => 10 );
# or
my $dt = DateTime->now()->subtract( seconds => 10 );

Answer 2

Using POSIX::strftime will make your life easier.
use POSIX 'strftime';
my #test_times = qw[now+10 now now-10];
foreach my $start_time (#test_times) {
if (my ($adjust) = $start_time =~ /^now([-+]\d+)?/) {
$adjust //= 0;
$adjust *= 60 * 60; # Convert hours to seconds
my $time = strftime '%Y-%m-%dT%H:%M:%SZ', gmtime(time + $adjust);
say $time;
}
}
Thinking about it further, I think I'd prefer to use Time::Piece. The principle is almost identical.
use Time::Piece;
my #test_times = qw[now+10 now now-10];
foreach my $start_time (#test_times) {
if (my ($adjust) = $start_time =~ /^now([-+]\d+)?/) {
$adjust //= 0;
$adjust *= 60 * 60; # Convert hours to seconds
my $time = gmtime(time + $adjust);
say $time->strftime('%Y-%m-%dT%H:%M:%SZ');
}
}

Answer 3

I would change this to:
my $_StartTime = getFromJson("StartTime");
my $_EndTime = getFromJson("EndTime");
if($_StartTime =~ s/now//) {
my $time = time;
if ($_StartTime =~ /^([-+]?)([0-9]+)/) {
my ($sign, $number) = ($1, $2);
$time += ($sign eq '-' ? -1 : 1) * $number * 3_600;
}
(my $sec, my $min, my $hour, my $mday, my $mon, my $year, my $wday, my $yday, my $isdst) = localtime($rime);
$_StartTime = sprintf("%04d-%02d-%02dT%02d:%02d:%02dZ", $year+1900, $mon+1, $mday, $hour, $min, $sec);
}

Answer 4

You give little information about the format of the original data, and what result you want from this. I assume the code you show is to convert the times formatted with now to one that you recognize so that you can go on from there. But it's best to handle both formats in one place to generate the same final result regardless of the input
This program uses an imaginary JSON data structure and processes all elements inside it. The core is the use of the Time::Piece module, which will parse and format times for you and do date/time arithmetic
I have encapsulated the code that processes both sorts of time values in a subroutine convert_time which returns a Time::Piece object. The code just uses the module's own stringify method to make the value readable, but you can generate any form of string you want using the object's methods
use strict;
use warnings 'all';
use feature 'say';
use JSON 'from_json';
use Time::Piece;
use Time::Seconds 'ONE_HOUR';
my $json = <<END;
[
{
"StartTime": "2015-07-08T03:38:08Z",
"EndTime": "2015-07-10T03:38:08Z"
},
{
"StartTime": "now-10",
"EndTime": "now+10"
}
]
END
my $data = from_json($json);
for my $item ( #$data ) {
for my $key ( keys %$item ) {
my $time = $item->{$key};
say "$key $time";
my $ans = convert_time($time);
print $ans, "\n\n";
}
}
sub convert_time {
my ($time) = #_;
if ( $time =~ /now([+-]\d+)/ ) {
return localtime() + $1 * ONE_HOUR;
}
else {
return Time::Piece->strptime($time, '%Y-%m-%dT%H:%M:%SZ');
}
}
output
StartTime 2015-07-08T03:38:08Z
Wed Jul 8 03:38:08 2015
EndTime 2015-07-10T03:38:08Z
Fri Jul 10 03:38:08 2015
StartTime now-10
Wed Jan 6 05:57:04 2016
EndTime now+10
Thu Jan 7 01:57:04 2016