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Enable a permanent daylight saving rule for Posix::time_zone

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* See comments in ptz.h for directions and examples.
This commit is contained in:
Howard Hinnant 2023-01-12 18:30:38 -05:00
parent c9169ea310
commit 5f8c904231
1 changed files with 55 additions and 6 deletions
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61
include/date/ptz.h
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@ -41,8 +41,19 @@
// Posix::time_zone tz{"EST5EDT,M3.2.0,M11.1.0"};
// zoned_time zt{tz, system_clock::now()};
//
// If the rule set is missing (everything starting with ','), then the rule is that the
// alternate offset is never enabled.
// Extension to the Posix rules to allow a constant daylight saving offset:
//
// If the rule set is missing (everything starting with ','), then
// there must be exactly one abbreviation (std or daylight) with
// length 3 or greater, and that will be used as the constant offset. If
// there are two, the std abbreviation is silently set to "", and the
// result is constant daylight saving. If there are zero abbreviations
// with no rule set, an exception is thrown.
//
// Example:
// "EST5" yields a constant offset of -5h with 0h save and "EST abbreviation.
// "5EDT" yields a constant offset of -4h with 1h save and "EDT" abbreviation.
// "EST5EDT" and "5EDT4" are both equal to "5EDT".
//
// Note, Posix-style time zones are not recommended for all of the reasons described here:
// https://stackoverflow.com/tags/timezone/info
@ -337,11 +348,22 @@ time_zone::contant_offset() const
using date::January;
using date::December;
using date::last;
using std::chrono::minutes;
sys_info r;
r.begin = sys_days{year::min()/January/1};
r.end = sys_days{year::max()/December/last};
r.abbrev = std_abbrev_;
r.offset = offset_;
if (std_abbrev_.size() > 0)
{
r.abbrev = std_abbrev_;
r.offset = offset_;
r.save = {};
}
else
{
r.abbrev = dst_abbrev_;
r.offset = offset_ + save_;
r.save = date::ceil<minutes>(save_);
}
return r;
}
@ -352,11 +374,14 @@ time_zone::time_zone(const detail::string_t& s)
using detail::read_signed_time;
using detail::throw_invalid;
auto i = read_name(s, 0, std_abbrev_);
auto std_name_i = i;
auto abbrev_name_i = i;
i = read_signed_time(s, i, offset_);
offset_ = -offset_;
if (i != s.size())
{
i = read_name(s, i, dst_abbrev_);
abbrev_name_i = i;
if (i != s.size())
{
if (s[i] != ',')
@ -379,6 +404,32 @@ time_zone::time_zone(const detail::string_t& s)
}
}
}
if (start_rule_.ok())
{
if (std_abbrev_.size() < 3)
throw_invalid(s, std_name_i, "Zone with rules must have a std"
" abbreviation of length 3 or greater");
if (dst_abbrev_.size() < 3)
throw_invalid(s, abbrev_name_i, "Zone with rules must have a daylight"
" abbreviation of length 3 or greater");
}
else
{
if (dst_abbrev_.size() >= 3)
{
std_abbrev_.clear();
}
else if (std_abbrev_.size() < 3)
{
throw_invalid(s, std_name_i, "Zone must have at least one abbreviation"
" of length 3 or greater");
}
else
{
dst_abbrev_.clear();
save_ = {};
}
}
}
template <class Duration>
@ -765,8 +816,6 @@ read_name(const string_t& s, unsigned i, std::string& name)
++i;
}
}
if (name.size() < 3)
throw_invalid(s, i, "Found name to be shorter than 3 characters");
return i;
}