282734 - Lunar calendar support

Status: NEW

(Calendar :: Internal Components, enhancement)

Description

[Po-chiang Chao [:bobchao]]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-TW; rv:1.7.5) Gecko/20041119 Firefox/1.0 (ax)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-TW; rv:1.7.5) Gecko/20041119 Firefox/1.0 (ax)

Since Chinese, Koera, Japan still using lunar calendar, we should support lunar
calendar in Mozilla Calendar and Sunbird.

Reproducible: Always

Steps to Reproduce:

Comment 1

[Rod Whiteley]

IMO a better idea is to provide basic support for any calendar scale, allowing
actual scales to be added by extensions.

BTW, this does not mean supporting scales in ICS files.  To allow interchange,
ICS files should always use Gregorian.

Unfortunately, Gregorian is embedded in the present code, so it will be a
difficult task.  It would be a step forward if date calculations could be
handled exclusively by JavaScript.  Then an extension could replace Date with a
custom version, and the whole product would magically work in a different scale.
 The trick is to isolate code that deals with back end data (always Gregorian),
and only convert code that deals with the UI.

Comment 2

[gekacheka]

The recurrence engine would need to understand the scale in order to calculate
recurrences based on different year lengths, month lengths, and week lengths.

For the purpose of exchanging meeting dates, it would need to be possible to
convert to/from different calendar scales when exporting, importing, or emailing. 

Bug 254443 seems to be about general support for other calendar scales than the
western/gregorian calendar scale.

Other calendars are also lunar, such as Islamic and Hebrew calendars, but there
are differences.  

ICU4C may be an open source starting place for calendars.  It doesn't seem to
include the Chinese or Persian (& Afghan) calendar yet.
http://icu.sourceforge.net/charts/comparison/


(Japan switched to Western (Gregorian) solar calendar starting around 1873. 
There are two numberings for years:  years may be numbered based on western era
year, or on the era of the contemporary emperor's reign as before.  The months
and weeks are based on the western calendar.  It is rare to see a reference to a
lunar calendar date today, so it is not a high priority for Japan.  It is still
used for calculating dates of local traditional (night) festivals, astrology,
and sometimes for finding auspicious dates for weddings and other important
meetings.)

Comment 3

[Jungshik Shin]

Also note that Chinese, Korean and Japanese lunar calendars are slightly
different from each other. Their algorithm for the calculation of moon's phase
is virtually identical as far as I know, but they're different from each other
because the standard meridian is different (well, Korean standard time and
Japanese standard time share the standard meridian of 135 deg. East).

For Korean, 'http://www.icalshare.com/article.php?story=20041129072146305'
(except that that's for Chinese and may be off by a day from time to time)
should more or less fulfill the requirement.

Btw, ICU  supports Chinese lunar calendar (I filed a bug report about the need
to support Korean lunar calendar aside from Chinese lunar calendar back in 2002)

Comment 4

[Mike Shaver (:shaver emeritus)]

Unfortunately, I do not have cycles to work on Calendar stuff these days (just as it's getting to the good part!), so I am a bad owner for these bugs.  To delete the tragically-large chunk of bugspam, search for gregorianabdication.