use strict;
use warnings;
use Test::More tests => 10;
use Date::Parse qw(str2time);
use Time::Zone;
use POSIX qw();

# IST (Indian Standard Time) should resolve to UTC+5:30
{
    my $offset = tz_offset("ist");
    is($offset, 19800, "tz_offset('ist') returns 19800 (UTC+5:30)");

    my $time = str2time("2024-01-15 12:00:00 IST");
    my $time_utc = str2time("2024-01-15 06:30:00 UTC");
    is($time, $time_utc, "IST date parses to correct UTC equivalent");
}

# RT#76968: tz2zone("America/Chicago") doesn't work
# IANA timezone names like "America/Chicago" should be usable with tz_offset
{
  SKIP: {
        # Verify that the system supports IANA timezone names
        my $has_iana = eval {
            local $ENV{TZ} = "Etc/UTC";
            POSIX::tzset();
            my ($std) = POSIX::tzname();
            defined $std && $std =~ /UTC|GMT/i;
        };
        skip "system does not support IANA timezone names", 6 unless $has_iana;

        # tz_offset with IANA name "Etc/UTC" must return 0 (deterministic)
        my $utc_offset = tz_offset("Etc/UTC");
        is($utc_offset, 0, "RT#76968: tz_offset('Etc/UTC') returns 0");

        # tz2zone with IANA name "Etc/UTC" must return a valid abbreviation
        my $utc_name = tz2zone("Etc/UTC", undef, 0);
        ok(defined $utc_name && length($utc_name) > 0,
            "RT#76968: tz2zone('Etc/UTC') returns a defined non-empty name");

        # tz_offset(tz2zone(IANA_name)) must return defined — the key failure in the bug
        my $chicago_abbr = tz2zone("America/New_York", undef, 0);
        ok(defined $chicago_abbr,
            "RT#76968: tz2zone('America/New_York', dst=0) returns defined");

        my $chicago_offset = tz_offset($chicago_abbr);
        ok(defined $chicago_offset,
            "RT#76968: tz_offset(tz2zone('America/New_York')) returns defined");

        # tz_offset of IANA name directly must return defined
        my $ny_offset = tz_offset("America/New_York");
        ok(defined $ny_offset,
            "RT#76968: tz_offset('America/New_York') returns defined");

        # tz_offset("Etc/UTC") via tz2zone round-trip
        my $utc_abbr = tz2zone("Etc/UTC", undef, 0);
        my $utc_offset2 = tz_offset($utc_abbr);
        is($utc_offset2, 0,
            "RT#76968: tz_offset(tz2zone('Etc/UTC')) returns 0");
    }
}

# RT#98949: Moscow Time Change in October 2014
# MSK (Moscow Standard Time) is UTC+3 permanently since 25 Oct 2014.
# Russia eliminated DST in 2011 (UTC+4 year-round), then reverted to UTC+3 in Oct 2014.
{
    my $offset = tz_offset("msk");
    is($offset, 10800, "RT#98949: tz_offset('msk') returns 10800 (UTC+3)");

    my $time     = str2time("2014-10-27 00:00:00 MSK");
    my $time_utc = str2time("2014-10-26 21:00:00 UTC");
    is($time, $time_utc, "RT#98949: MSK date after 2014 change parses to correct UTC");
}