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LibJS+LibTimeZone: Begin handling DST when computing time zone offsets

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This also updates some expectations in a Temporal time zone offset test
that is using a time stamp which is in DST for a few time zones.
This commit is contained in:
Timothy Flynn 2022-01-19 11:17:54 -05:00 • committed by Linus Groh
parent 9dd4602636
commit 42c9c57141
3 changed files with 91 additions and 17 deletions
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58
Meta/Lagom/Tools/CodeGenerators/LibTimeZone/GenerateTimeZoneData.cpp
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@ -450,9 +450,55 @@ static constexpr Array<@type@, @size@> @name@ { {
append_string_conversions("DaylightSavingsRule"sv, "daylight_savings_rule"sv, time_zone_data.dst_offset_names);
generator.append(R"~~~(
static i64 get_dst_offset(TimeZoneOffset const& time_zone_offset, AK::Time time)
{
auto const& dst_rules = s_dst_offsets[time_zone_offset.dst_rule];
DaylightSavingsOffset const* standard_offset = nullptr;
DaylightSavingsOffset const* daylight_offset = nullptr;
auto time_in_effect_for_rule = [&](auto const& dst_rule) {
auto in_effect = dst_rule.in_effect;
in_effect.year = seconds_since_epoch_to_year(time.to_seconds());
return in_effect.time_since_epoch();
};
auto preferred_rule = [&](auto* current_offset, auto& new_offset) {
if (!current_offset)
return &new_offset;
auto new_time_in_effect = time_in_effect_for_rule(new_offset);
return (time >= new_time_in_effect) ? &new_offset : current_offset;
};
for (size_t index = 0; (index < dst_rules.size()) && (!standard_offset || !daylight_offset); ++index) {
auto const& dst_rule = dst_rules[index];
auto year_from = AK::Time::from_timestamp(dst_rule.year_from, 1, 1, 0, 0, 0, 0);
auto year_to = AK::Time::from_timestamp(dst_rule.year_to + 1, 1, 1, 0, 0, 0, 0);
if ((time < year_from) || (time >= year_to))
continue;
if (dst_rule.offset == 0)
standard_offset = preferred_rule(standard_offset, dst_rule);
else
daylight_offset = preferred_rule(daylight_offset, dst_rule);
}
if (!standard_offset || !daylight_offset)
return 0;
auto standard_time_in_effect = time_in_effect_for_rule(*standard_offset);
auto daylight_time_in_effect = time_in_effect_for_rule(*daylight_offset);
if ((time < daylight_time_in_effect) || (time >= standard_time_in_effect))
return standard_offset->offset;
return daylight_offset->offset;
}
Optional<i64> get_time_zone_offset(TimeZone time_zone, AK::Time time)
{
// FIXME: This implementation completely ignores DST.
auto const& time_zone_offsets = s_time_zone_offsets[to_underlying(time_zone)];
size_t index = 0;
@ -464,7 +510,15 @@ Optional<i64> get_time_zone_offset(TimeZone time_zone, AK::Time time)
}
VERIFY(index < time_zone_offsets.size());
return time_zone_offsets[index].offset;
auto const& time_zone_offset = time_zone_offsets[index];
i64 dst_offset = 0;
if (time_zone_offset.dst_rule != -1)
dst_offset = get_dst_offset(time_zone_offset, time);
else
dst_offset = time_zone_offset.dst_offset;
return time_zone_offset.offset + dst_offset;
}
}