说我想创建一个每日计划，我想把这一天分成15分钟的大块。
轻松吧？从午夜开始，…错误！在美国/圣保罗，由于夏令时变化，每年有一天从01:00开始。
给定时区和日期，如何找到一天开始的时代？
我的第一个想法是使用以下内容，但假设每一天都有23:59。假设每一天都有午夜，这可能不是一个假设。
perl -MDateTime -E'
say
DateTime->new( year => 2013,month => 10,day => 20 )
->subtract( days => 1 )
->set( hour => 23,minute => 59 )
->set_time_zone("America/Sao_Paulo")
->add( minutes => 1 )
->strftime("%H:%M");
'
01:00
有更强大或更直接的替代方案吗？
解决方法
你会认为这是一般需要做的事情！我怀疑那里有很多错误代码
这是一个编码的解决方案，旨在将其纳入DateTime。
use strict;
use warnings;
use DateTime qw( );
use DateTime::TimeZone qw( );
# Assumption:
# There is no dt to which one can add time
# to obtain a dt with an earlier date.
sub day_start {
my $tz = shift;
my $dt = shift;
my $local_rd_days = ( $dt->local_rd_values() )[0];
my $seconds = $local_rd_days * 24*60*60;
my $min_idx;
if ( $seconds < $tz->max_span->[DateTime::TimeZone::LOCAL_END] ) {
$min_idx = 0;
} else {
$min_idx = @{ $tz->{spans} };
$tz->_generate_spans_until_match( $dt->utc_year()+1,$seconds,'local' );
}
my $max_idx = $#{ $tz->{spans} };
my $utc_rd_days;
my $utc_rd_secs;
while (1) {
my $current_idx = int( ( $min_idx + $max_idx )/2 );
my $current = $tz->{spans}[$current_idx];
if ( $seconds < $current->[DateTime::TimeZone::LOCAL_START] ) {
$max_idx = $current_idx - 1;
}
elsif ( $seconds >= $current->[DateTime::TimeZone::LOCAL_END] ) {
$min_idx = $current_idx + 1;
}
else {
my $offset = $current->[DateTime::TimeZone::OFFSET];
# In case of overlaps,always prefer earlier span.
if ($current->[DateTime::TimeZone::IS_DST] && $current_idx) {
my $prev = $tz->{spans}[$current_idx-1];
$offset = $prev->[DateTime::TimeZone::OFFSET]
if $seconds >= $prev->[DateTime::TimeZone::LOCAL_START]
&& $seconds < $prev->[DateTime::TimeZone::LOCAL_END];
}
$utc_rd_days = $local_rd_days;
$utc_rd_secs = -$offset;
DateTime->_normalize_tai_seconds($utc_rd_days,$utc_rd_secs);
last;
}
if ($min_idx > $max_idx) {
$current_idx = $min_idx;
$current = $tz->{spans}[$current_idx];
if (int( $current->[DateTime::TimeZone::LOCAL_START] / (24*60*60) ) != $local_rd_days) {
my $err = 'Invalid local time for date';
$err .= " in time zone: " . $tz->name;
$err .= "\n";
die $err;
}
$utc_rd_secs = $current->[DateTime::TimeZone::UTC_START] % (24*60*60);
$utc_rd_days = int( $current->[DateTime::TimeZone::UTC_START] / (24*60*60) );
last;
}
}
my ($year,$month,$day) = DateTime->_rd2ymd($utc_rd_days);
my ($hour,$minute,$second) = DateTime->_seconds_as_components($utc_rd_secs);
return
$dt
->_new_from_self(
year => $year,month => $month,day => $day,hour => $hour,minute => $minute,second => $second,time_zone => 'UTC',)
->set_time_zone($tz);
}
测试：
sub new_date {
my $y = shift;
my $m = shift;
my $d = shift;
return DateTime->new(
year => $y,month => $m,day => $d,@_,hour => 0,minute => 0,second => 0,nanosecond => 0,time_zone => 'floating'
);
}
{
# No midnight.
my $tz = DateTime::TimeZone->new( name => 'America/Sao_Paulo' );
my $dt = day_start($tz,new_date(2013,10,20));
print($dt->iso8601(),"\n"); # 2013-10-20T01:00:00
$dt->subtract( seconds => 1 );
print($dt->iso8601(),"\n"); # 2013-10-19T23:59:59
}
{
# Two midnights.
my $tz = DateTime::TimeZone->new( name => 'America/Havana' );
my $dt = day_start($tz,11,3));
print($dt->iso8601(),"\n"); # 2013-11-03T00:00:00
$dt->subtract( seconds => 1 );
print($dt->iso8601(),"\n"); # 2013-11-02T23:59:59
}
一个实际的例子，
sub today_as_floating {
return
DateTime
->now( @_ )
->set_time_zone('floating')
->truncate( to => 'day' );
}
{
my $tz = DateTime::TimeZone->new( name => 'local' );
my $dt = today_as_floating( time_zone => $tz );
$dt = day_start($tz,$dt);
print($dt->iso8601(),"\n");
}