وحدة:Time

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require('Module:No globals')
local getArgs = require('Module:Arguments').getArgs

local p = {}

--[[--------------------------< T I M E Z O N E   P R O P E R T I E S >----------------------------------------

When specifying utc offset do not use the minus character (U+2212) for offsets west of 0 meridian; use the minus-hyphen


]]

local tz = {																	-- these are ordered by UTC offset +HH:MM followed by -HH:MM

------------------------------< E A S T   U T C + H H : M M >--------------------------------------------------

['utc'] = {
	abbr = 'UTC',			-- (required) abbreviation to use during standard time
	dst_abbr = '',			-- abbreviation to use during daylight saving time
	utc_offset = '00:00',	-- (required) hours and minutes offset from UTC for this timezone; '+' is optional; '-' (hyphen-minus) is required for timezones west of 0 meridian
	df = 'dmy',				-- date format typically used in the time zone
	dst_begins = '',		-- daylight saving begins; e.g. 2nd Sunday in March; also last; empty string if not observed
	dst_ends = '',			-- (required if dst_begins is set) daylight saving begins; e.g. 1st Sunday in November; ignored if dst_begins not set
	dst_time = '',			-- (required if dst_begins is set) local time on the day that dst begins/ends; for EU DST rules specify utc time: e.g.: '01:00 UTC'
	dst_e_time = '',		-- local daylight saving time on the day that dst ends; only when different from dst_time; see acst for an example
	article = 'Coordinated Universal Time'	-- (required) name of related Wikipedia article without markup
	},
['gmt'] = {
	abbr = 'GMT',			
	dst_abbr = '',
	utc_offset = '00:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Greenwich Mean Time'
},
['gmt-uk'] = {
	abbr = 'GMT',			
	dst_abbr = 'BST',															-- British Summer Time
	utc_offset = '00:00',
	df = 'dmy',
	dst_begins = 'last Sunday of March',
	dst_ends = 'last Sunday of October',
	dst_time = '01:00 UTC',														-- 01:00 standard time is same as 01:00 UTC
	article = 'Time in the United Kingdom'
},
['gmt-ie'] = {																	-- ist is shared with Indian Standard Time so use gmt-ie
	abbr = 'GMT',																-- winter time
	dst_abbr = 'IST',															-- Irish Standard Time occurs in summer
	utc_offset = '00:00',
	df = 'dmy',
	dst_begins = 'last Sunday of March',
	dst_ends = 'last Sunday of October',
	dst_time = '01:00 UTC',														-- 01:00 standard time is same as 01:00 UTC
	article = 'Time in Ireland'
},
['wet'] = {
	abbr = 'WET',
	dst_abbr = 'WEST',
	utc_offset = '00:00',
	df = 'dmy',
	dst_begins = 'last Sunday of March',
	dst_ends = 'last Sunday of October',
	dst_time = '01:00 UTC',														-- 01:00 standard time is same as 01:00 UTC
	article = 'Western European Time'
},
['cet'] = {
	abbr = 'CET',
	dst_abbr = 'CEST',
	utc_offset = '01:00',
	df = 'dmy',
	dst_begins = 'last Sunday of March',
	dst_ends = 'last Sunday of October',
	dst_time = '01:00 UTC',														-- 02:00 standard time is same as 01:00 UTC
	article = 'Central European Time'
},
['eet'] = {
	abbr = 'EET',
	dst_abbr = 'EEST',
	utc_offset = '02:00',
	df = 'dmy',
	dst_begins = 'last Sunday of March',
	dst_ends = 'last Sunday of October',
	dst_time = '01:00 UTC',														-- 03:00 standard time is same as 01:00 UTC
	article = 'Eastern European Time'
},
['usz1'] = {
	abbr = 'USZ1',
	dst_abbr = '',
	utc_offset = '02:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Kaliningrad Time'
},
['msk'] = {
	abbr = 'MSK',
	dst_abbr = '',
	utc_offset = '03:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Moscow Time'
},
['samt'] = {
	abbr = 'SAMT',
	dst_abbr = '',
	utc_offset = '04:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Samara Time'
},
['yekt'] = {
	abbr = 'YEKT',
	dst_abbr = '',
	utc_offset = '05:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Yekaterinburg Time'
},
['ist'] = {
	abbr = 'IST',
	utc_offset = '05:30',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Indian Standard Time'
},
['npt'] = {
	abbr = 'NPT',
	dst_abbr = '',
	utc_offset = '05:45',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Nepal Time'
},
['bst'] = {
	abbr = 'BST',
	utc_offset = '06:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Bangladesh Standard Time'
},
['omst'] = {
	abbr = 'OMST',
	dst_abbr = '',
	utc_offset = '06:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Omsk Time'
},
['krat'] = {
	abbr = 'KRAT',
	dst_abbr = '',
	utc_offset = '07:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Krasnoyarsk Time'
},
['wib'] = {																		-- western indonesia
	abbr = 'WIB',
	dst_abbr = '',
	utc_offset = '07:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Time in Indonesia'
},
['awst'] = {
	abbr = 'AWST',
	dst_abbr = '',
	utc_offset = '08:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Time in Australia'
},
['bt'] = {																		-- same as China standard time (CST)
	abbr = 'BT',
	dst_abbr = '',
	utc_offset = '08:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Time in China'
},
['irkt'] = {
	abbr = 'IRKT',
	dst_abbr = '',
	utc_offset = '08:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Irkutsk Time'
},
['wita'] = {		-- central
	abbr = 'WITA',
	dst_abbr = '',
	utc_offset = '08:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Time in Indonesia'
},
['jst'] = {
	abbr = 'JST',
	dst_abbr = '',
	utc_offset = '09:00',
	df = 'iso',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Japan Standard Time'
},
['wit'] = {																		-- eastern Indonesia (same as old template's eit)
	abbr = 'WIT',
	dst_abbr = '',
	utc_offset = '09:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Time in Indonesia'
},
['yakt'] = {
	abbr = 'YAKT',
	dst_abbr = '',
	utc_offset = '09:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Yakutsk Time'
},
['acst'] = {																	-- Northern, Territory, South Australia time
	abbr = 'ACST',
	dst_abbr = 'ACDT',
	utc_offset = '09:30',
	df = 'dmy',
	dst_begins = 'first Sunday in October',
	dst_ends = 'first Sunday in April',
	dst_time = '02:00',
	dst_e_time = '03:00',
	article = 'Time in Australia'
},
['aest'] = {		-- QLD, NSW, TAS, VIC, ACT
	abbr = 'AEST',
	dst_abbr = 'AEDT',
	utc_offset = '10:00',
	df = 'dmy',
	dst_begins = 'first Sunday in October',
	dst_ends = 'first Sunday in April',
	dst_time = '02:00',															-- begins at 02:00 AEST
	dst_e_time = '03:00',														-- ends at 02:00 AEST which is 03:00 AEDT
	article = 'Time in Australia'
},
['chst'] = {
	abbr = 'ChST',
	dst_abbr = '',
	utc_offset = '10:00',
	df = 'mdy',																	-- because a US territory?
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Chamorro Time Zone'
},
['vlat'] = {
	abbr = 'VLAT',
	dst_abbr = '',
	utc_offset = '10:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Vladivostok Time'
},
['sret'] = {
	abbr = 'SRET',
	dst_abbr = '',
	utc_offset = '11:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Srednekolymsk Time'
},
['nzst'] = {
	abbr = 'NZST',
	dst_abbr = 'NZDT',
	utc_offset = '12:00',
	df = 'dmy',
	dst_begins = 'last Sunday in September',
	dst_ends = 'first Sunday in April',
	dst_time = '02:00',															-- begins at 02:00 NZST
	dst_e_time = '03:00',														-- ends at 02:00 NZST which is 03:00 NZDT
	article = 'Time in New Zealand'
},
['pett'] = {
	abbr = 'PETT',
	dst_abbr = '',
	utc_offset = '12:00',
	df = 'dmy',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Kamchatka Time'
},
['idle'] = {																	-- international dateline east
	abbr = 'IDLE',
	dst_abbr = '',
	utc_offset = '12:00',
	df = 'iso',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'UTC+12:00'
},


------------------------------< W E S T   U T C - H H : M M >--------------------------------------------------

['pmst'] = {
	abbr = 'PMST',
	dst_abbr = 'PMDT',
	utc_offset = '-03:00',
	df = 'dmy',																	-- because France
	dst_begins = '2nd Sunday in March',											-- North American rules
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'UTC−03:00'
},
['wgt'] = {																		-- western greenland time?  Not for Thule Airbase which observes US DST rules; requires own properties
	abbr = 'WGT',
	dst_abbr = 'WGST',															-- ??? what is the correct abbreviation?
	utc_offset = '-03:00',
	df = 'dmy',
	dst_begins = 'last Sunday in March',
	dst_ends = 'last Sunday in October',
	dst_time = '01:00 UTC',
	article = 'Time in Denmark'
},
['nst'] = {
	abbr = 'NST',
	dst_abbr = 'NDT',
	utc_offset = '-03:30',
	df = 'dmy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Newfoundland Standard Time'
},
['ast'] = {
	abbr = 'AST',
	dst_abbr = 'ADT',
	utc_offset = '-04:00',
	df = 'dmy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Atlantic Time Zone'
},
['est'] = {
	abbr = 'EST',
	dst_abbr = 'EDT',
	utc_offset = '-05:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Eastern Time Zone'
},
['cst'] = {
	abbr = 'CST',
	dst_abbr = 'CDT',
	utc_offset = '-06:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Central Time Zone'
},
['mst'] = {
	abbr = 'MST',
	dst_abbr = 'MDT',
	utc_offset = '-07:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Mountain Time Zone'
},
['pst'] = {
	abbr = 'PST',
	dst_abbr = 'PDT',
	utc_offset = '-08:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Pacific Time Zone'
},
['akst'] = {
	abbr = 'AKST',
	dst_abbr = 'AKDT',
	utc_offset = '-09:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Alaska Time Zone'
},
['hast'] = {	-- same as AleutST and HST
	abbr = 'HAST',
	dst_abbr = 'HADT',
	utc_offset = '-10:00',
	df = 'mdy',
	dst_begins = '2nd Sunday in March',
	dst_ends = '1st Sunday in November',
	dst_time = '02:00',
	article = 'Hawaii–Aleutian Time Zone'
},
['idlw'] = {																	-- international dateline west
	abbr = 'IDLW',
	dst_abbr = '',
	utc_offset = '-12:00',
	df = 'iso',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'UTC−12:00'
},
['aoe'] = {																		-- last location for any date
	abbr = 'AoE',
	dst_abbr = '',
	utc_offset = '-12:00',
	df = 'iso',
	dst_begins = '',
	dst_ends = '',
	dst_time = '',
	article = 'Anywhere on Earth'
},

------------------------------< M I L I T A R Y >--------------------------------------------------------------
-- {{cite web |url=http://wwp.greenwichmeantime.com/info/timezone.htm |title=Military and Civilian Time Designations |accessdate=2016-03-25 |website=Greenwich Mean Time}}
--http://astro.ukho.gov.uk/nao/miscellanea/WMTZ/Wmtz160224.pdf
['a'] = {abbr = 'A', utc_offset = '01:00', df = 'iso', article = 'List of military time zones'},
['b'] = {abbr = 'B', utc_offset = '02:00', df = 'iso', article = 'List of military time zones'},
['c'] = {abbr = 'C', utc_offset = '03:00', df = 'iso', article = 'List of military time zones'},
['c*'] = {abbr = 'C*', utc_offset = '03:30', df = 'iso', article = 'List of military time zones'},
['d'] = {abbr = 'D', utc_offset = '04:00', df = 'iso', article = 'List of military time zones'},
['d*'] = {abbr = 'D*', utc_offset = '04:30', df = 'iso', article = 'List of military time zones'},
['e'] = {abbr = 'E', utc_offset = '05:00', df = 'iso', article = 'List of military time zones'},
['e*'] = {abbr = 'E*', utc_offset = '05:30', df = 'iso', article = 'List of military time zones'},
['e+'] = {abbr = 'E<span class="plainlinks" style="font-size:120%%;">†</span>', utc_offset = '05:45', df = 'iso', article = 'List of military time zones'},
['f'] = {abbr = 'F', utc_offset = '06:00', df = 'iso', article = 'List of military time zones'},
['f*'] = {abbr = 'F*', utc_offset = '06:30', df = 'iso', article = 'List of military time zones'},
['g'] = {abbr = 'G', utc_offset = '07:00', df = 'iso', article = 'List of military time zones'},
['h'] = {abbr = 'H', utc_offset = '08:00', df = 'iso', article = 'List of military time zones'},
['h*'] = {abbr = 'H*', utc_offset = '08:30', df = 'iso', article = 'List of military time zones'},
['i'] = {abbr = 'I', utc_offset = '09:00', df = 'iso', article = 'List of military time zones'},
['i*'] = {abbr = 'I*', utc_offset = '09:30', df = 'iso', article = 'List of military time zones'},
['k'] = {abbr = 'K', utc_offset = '10:00', df = 'iso', article = 'List of military time zones'},
['k*'] = {abbr = 'K*', utc_offset = '10:30', df = 'iso', article = 'List of military time zones'},
['l'] = {abbr = 'L', utc_offset = '11:00', df = 'iso', article = 'List of military time zones'},
['l*'] = {abbr = 'L*', utc_offset = '11:30', df = 'iso', article = 'List of military time zones'},
['m'] = {abbr = 'M', utc_offset = '12:00', df = 'iso', article = 'List of military time zones'},
['m++'] = {abbr = 'M‡', utc_offset = '12:45', df = 'iso', article = 'List of military time zones'},
['m*'] = {abbr = 'M*', utc_offset = '13:00', df = 'iso', article = 'List of military time zones'},
['m+'] = {abbr = 'M†', utc_offset = '14:00', df = 'iso', df = 'iso', article = 'List of military time zones'},
['n'] = {abbr = 'N', utc_offset = '-01:00', df = 'iso', article = 'List of military time zones'},
['o'] = {abbr = 'O', utc_offset = '-02:00', df = 'iso', article = 'List of military time zones'},
['p'] = {abbr = 'P', utc_offset = '-03:00', df = 'iso', article = 'List of military time zones'},
['p*'] = {abbr = 'P*', utc_offset = '-03:30', df = 'iso', article = 'List of military time zones'},
['q'] = {abbr = 'Q', utc_offset = '-04:00', df = 'iso', article = 'List of military time zones'},
['q*'] = {abbr = 'Q*', utc_offset = '-04:30', df = 'iso', article = 'List of military time zones'},
['r'] = {abbr = 'R', utc_offset = '-05:00', df = 'iso', article = 'List of military time zones'},
['s'] = {abbr = 'S', utc_offset = '-06:00', df = 'iso', article = 'List of military time zones'},
['t'] = {abbr = 'T', utc_offset = '-07:00', df = 'iso', article = 'List of military time zones'},
['u'] = {abbr = 'U', utc_offset = '-08:00', df = 'iso', article = 'List of military time zones'},
['u*'] = {abbr = 'U*', utc_offset = '-08:30', df = 'iso', article = 'List of military time zones'},
['v'] = {abbr = 'V', utc_offset = '-09:00', df = 'iso', article = 'List of military time zones'},
['v*'] = {abbr = 'V*', utc_offset = '-09:30', df = 'iso', article = 'List of military time zones'},
['w'] = {abbr = 'W', utc_offset = '-10:00', df = 'iso', article = 'List of military time zones'},
['x'] = {abbr = 'X', utc_offset = '-11:00', df = 'iso', article = 'List of military time zones'},
['y'] = {abbr = 'Y', utc_offset = '-12:00', df = 'iso', article = 'List of military time zones'},
['z'] = {abbr = 'Z', utc_offset = '±00:00', df = 'iso', article = 'List of military time zones'},

------------------------------< U T C   O F F S E T S >--------------------------------------------------------
-- this table entry filled by the code in p.time()

['utc_offsets'] = {abbr = '', utc_offset = '', df = 'iso', article = ''},
}																				-- end of tz table

--[[--------------------------< I S _ S E T >------------------------------------------------------------------

Whether variable is set or not.  A variable is set when it is not nil and not empty.

]]

local function is_set( var )
	return not (var == nil or var == '');
end


--[[--------------------------< D E C O D E _ D S T _ E V E N T >----------------------------------------------

extract ordinal, day-name, and month from daylight saving start/end definition string as digits:
	Second Sunday in March
returns
	2 0 3

Casing doesn't matter but the form of the string does:
	<ordinal> <day> <any single word> <month> – all are separated by spaces

]]

local function decode_dst_event (dst_event_string)
	local ord, day, month;
	
	local ordinals = {['1st'] = 1, ['first'] = 1, ['2nd'] = 2, ['second'] = 2, ['3rd'] = 3, ['third'] = 3, ['4th'] = 4, ['fourth'] = 4, ['5th'] = 5, ['fifth'] = 5, ['last'] = -1};
	local days = {['sunday'] = 0, ['monday'] = 1, ['tuesday'] = 2, ['wednesday'] = 3, ['thursday'] = 4, ['friday'] = 5, ['saturday'] = 6};
	local months = {['january'] = 1, ['february'] = 2, ['march'] = 3, ['april'] = 4, ['may'] = 5, ['june'] = 6,
		['july'] = 7, ['august'] = 8, ['september'] = 9, ['october'] = 10, ['november'] = 11, ['december'] = 12};
	
	dst_event_string = dst_event_string:lower();								-- force the string to lower case because that is how the tables above are indexed
	ord, day, month = dst_event_string:match ('([%a%d]+)%s+(%a+)%s+%a+%s+(%a+)');
	
	if not (is_set (ord) and is_set (day) and is_set (month)) then				-- if one or more of these not set, then pattern didn't match
		return nil;
	end
	
	return ordinals[ord], days[day], months[month];
end


--[[--------------------------< G E T _ D A Y S _ I N _ M O N T H >--------------------------------------------

Returns the number of days in the month where month is a number 1–12 and year is four-digit Gregorian calendar.
Accounts for leap year.

]]

local function get_days_in_month (year, month)
	local days_in_month = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	
	year = tonumber (year);														-- force these to be numbers just in case
	month = tonumber (month);

	if (2 == month) then														-- if February
		if (0 == (year%4) and (0 ~= (year%100) or 0 == (year%400))) then		-- is year a leap year?
			return 29;															-- if leap year then 29 days in February
		end
	end
	return days_in_month [month];
end


--[[--------------------------< G E T _ D S T _ M O N T H _ D A Y >--------------------------------------------

Return the date (month and day of the month) for the day that is the ordinal (nth) day-name in month (second
Friday in June) of the current year

timestamp is today's date-time number from os.time(); used to supply year
timezone is the timezone parameter value from the template call

Equations used in this function taken from Template:Weekday_in_month

]]

local function get_dst_month_day (timestamp, timezone, start)
	local ord, weekday_num, month;
	local first_day_of_dst_month_num;
	local last_day_of_dst_month_num;
	local days_in_month;
	local year;

	if true == start then
		ord, weekday_num, month = decode_dst_event (tz[timezone].dst_begins);	-- get start string and convert to digits
	else
		ord, weekday_num, month = decode_dst_event (tz[timezone].dst_ends);		-- get end string and convert to digits
	end
	
	if not (is_set (ord) and is_set (weekday_num) and is_set (month)) then
		return nil;																-- could not decode event string
	end
	
	year = os.date ('%Y', timestamp);

	if -1 == ord then		-- j = t + 7×(n + 1) - (wt - w) mod 7				-- if event occurs on the last day-name of the month ('last Sunday of October')
		days_in_month = get_days_in_month (year, month);
		last_day_of_dst_month_num =  os.date ('%w', os.time ({['year']=year, ['month']=month, ['day']=days_in_month}));
		return month, days_in_month + 7*(ord + 1) - ((last_day_of_dst_month_num - weekday_num) % 7);
	else	-- j = 7×n - 6 + (w - w1) mod 7
		first_day_of_dst_month_num = os.date ('%w', os.time ({['year']=year, ['month']=month, ['day']=1}))
		return month, 7 * ord - 6 + (weekday_num - first_day_of_dst_month_num) % 7;		-- return month and calculated date
	end
end


--[[--------------------------< G E T _ U T C _ O F F S E T >--------------------------------------------------

Get utc offset in hours and minutes, convert to seconds.  If the offset can't be converted return 0.
TODO: return error message?
TODO: limit check this? +/-n hours?
]]

local function get_utc_offset (timezone)
	local sign;
	local hours;
	local minutes;
	
	sign, hours, minutes = mw.ustring.match (tz[timezone].utc_offset, '([%+%-±−]?)(%d%d):(%d%d)');
	
	if '-' == sign then sign = -1; else sign = 1; end
	if is_set (hours) and is_set (minutes) then
		return sign * ((hours * 3600) + (minutes * 60));
	else
		return nil;																-- we require that all timezone table have what appears to be a valid offset
	end
end


--[[--------------------------< M A K E _ D S T _ T I M E S T A M P S >----------------------------------------

Return UTC timestamps for the date/time of daylight saving time events (beginning and ending).  These timestamps
will be compared to current UTC time.  A dst timestamp is the date/time in seconds UTC for the timezone at the
hour of the dst event.

For dst rules that specify local event times, the timestamp is the sum of:
	timestamp = current year + dst_month + dst_day + dst_time (all in seconds) local time
Adjust local time to UTC by subtracting utc_offset:
	timestamp = timestamp - utc_offset (in seconds)
For dst_end timestamp, subtract an hour for DST
	timestamp = timestamp - 3600 (in seconds)

For dst rules that specify utc event time the process is the same except that utc offset is not subtracted.


]]

local function make_dst_timestamps (timestamp, timezone)
	local dst_begin, dst_end;													-- dst begin and end time stamps 
	local year;																	-- current year
	local dst_b_month, dst_e_month, dst_day;									-- month and date of dst event
	local dst_hour, dst_minute;													-- hour and minute of dst event on year-dst_month-dst_day
	local invert = false;														-- flag to pass on when dst_begin month is numerically larger than dst_end month (southern hemisphere)
	local utc_offset;
	local utc_flag;

	year = os.date ('%Y', timestamp);											-- current year
	utc_offset = get_utc_offset (timezone);
	if not is_set (utc_offset) then												-- utc offset is a required timezone property
		return nil;
	end

	dst_b_month, dst_day = get_dst_month_day (timestamp, timezone, true);		-- month and day that dst begins
	if not is_set (dst_b_month) then
		return nil;
	end
	
	dst_hour, dst_minute = tz[timezone].dst_time:match ('(%d%d):(%d%d)');		-- get dst time
	utc_flag = tz[timezone].dst_time:find ('[Uu][Tt][Cc]%s*$');					-- set flag when dst events occur at a specified utc time

	dst_begin = os.time ({['year'] = year, ['month'] = dst_b_month, ['day'] = dst_day, ['hour'] = dst_hour, ['min'] = dst_minute});	-- form start timestamp
	if not is_set (utc_flag) then												-- if dst events are specified to occur at local time
		dst_begin = dst_begin - utc_offset;										-- adjust local time to utc by subtracting utc offset
	end

	dst_e_month, dst_day = get_dst_month_day (timestamp, timezone, false);		-- month and day that dst ends
	if not is_set (dst_e_month) then
		return nil;
	end
	
	if is_set (tz[timezone].dst_e_time) then
		dst_hour, dst_minute = tz[timezone].dst_e_time:match ('(%d%d):(%d%d)');	-- get ending dst time; this one for those locales that use different start and end times
		utc_flag = tz[timezone].dst_e_time:find ('[Uu][Tt][Cc]%s*$');			-- set flag if dst is pegged to utc time
	end	

	dst_end = os.time ({['year'] = year, ['month'] = dst_e_month, ['day'] = dst_day, ['hour'] = dst_hour, ['min'] = dst_minute});	-- form end timestamp
	if not is_set (utc_flag) then												-- if dst events are specified to occur at local time
		dst_end = dst_end - 3600;												-- assume that local end time is DST so adjust to local ST
		dst_end = dst_end - utc_offset;											-- adjust local time to utc by subtracting utc offset
	end


	if dst_b_month > dst_e_month then
		invert = true;															-- true for southern hemisphere eg: start September YYYY end April YYYY+1
	end

	return dst_begin, dst_end, invert;
end


--[[--------------------------< G E T _ T E S T _ T I M E >----------------------------------------------------

decode ISO formatted date/time into a table suitable for os.time().  For testing, this time is utc just as is
returned by the os.time() function.

]]

local function get_test_time (iso_date)
	local year, month, day, hour, minute, second;

	year, month, day, hour, minute, second = iso_date:match ('(%d%d%d%d)\-(%d%d)\-(%d%d)T(%d%d):(%d%d):(%d%d)');
	if not year then
		return nil;																-- test time did not match the specified pattern
	end
	return {['year'] = year, ['month'] = month, ['day'] = day, ['hour'] = hour, ['min'] = minute, ['sec'] = second};
end


--[=[-------------------------< P . T I M E >------------------------------------------------------------------

This template takes several parameters; none are required:
	1. the time zone abbreviation (positional, always the first unnamed parameter)
	2. a date format flag; second positional parameter or |df=; can have one of several assigned values:
		y – display output time in dmy format
		dmy – same as 'y'
		mdy – default; included for completeness
		iso – display output time in YYYY-MM-DDTHH:mm format
	3. |dst= when set to 'no' disables dst calculations for locations that do not observe dst – Arizona in MST
	4. |_TEST_TIME_= a specific utc time in ISO date time format used for testing this code
	
TODO: convert _TEST_TIME_ to |time=?

Timezone abbreviations can be found here: [[List_of_time_zone_abbreviations]]

]=]

function p.time (frame)
	local args = getArgs(frame);
	local utc_timestamp, timestamp;												-- current or _TEST_TIME_ timestamps; timestamp is local ST or DST time used in output
	local dst_begin_ts, dst_end_ts;												-- DST begin and end timestamps in UTC
	local tz_abbr;																-- select ST or DST timezone abbreviaion used in output 
	local tz_string;															-- output time in |df= format
	local utc_offset;
	local invert;																-- true when southern hemisphere
	local df;																	-- date format flag; the |df= parameter

	if args[1] then
		args[1] = args[1]:lower();												-- make lower case because tz table member indexes are lower case

		if mw.ustring.match (args[1], 'utc[%+%-±−]?%d%d:%d%d') then				-- if rendering time for a UTC offset timezone
			tz['utc_offsets'].abbr = args[1]:upper():gsub('%-', '−');			-- set the link label to upper case and replace hyphen with a minus character (U+2212)
			tz['utc_offsets'].article = tz['utc_offsets'].abbr;					-- article title same as abbreviation
			tz['utc_offsets'].utc_offset = mw.ustring.match (args[1], 'utc([%+%-±−]?%d%d:%d%d)'):gsub('−', '%-');	-- extract the offset value; replace minus character with hyphen
			args[1] = 'utc_offsets';											-- point to the generic utc offsets table 
		end
		if not is_set (tz[args[1]]) then
			return '<span style="font-size:100%" class="error">{{time}} – unknown timezone ([[Template:Time#Error messages|help]])</span>';
		end
	else
		args[1] = 'utc';														-- default to utc
	end
	
	df = args.df or args[2] or tz[args[1]].df or '';							-- template |df= overrides typical df from tz properties TODO: error check these values?
	if is_set (df) then
		df = df:lower();														-- lower case because we will compare to lower case values later
	end

	if is_set (args._TEST_TIME_) then											-- typically used to test the code at a specific utc time
		local test_time = get_test_time (args._TEST_TIME_);
		if not test_time then
			return '<span style="font-size:100%" class="error">{{time}} – malformed or incomplete _TEST_TIME_ ([[Template:Time#Error messages|help]])</span>';
		end

--		utc_timestamp = os.time(get_test_time (args._TEST_TIME_));
		utc_timestamp = os.time(test_time);
	else
		utc_timestamp = os.time ();												-- get current server time (UTC)
	end
	utc_offset = get_utc_offset (args[1]);										-- utc offset for specified timezone
	timestamp = utc_timestamp + utc_offset;										-- make local time timestamp

	if 'no' == args.dst then													-- for timezones that DO observe dst but for this location ...
		tz_abbr = tz[args[1]].abbr;												-- ... dst is not observed (|dst=no) show time as standard time
	else
		if is_set (tz[args[1]].dst_begins) and is_set (tz[args[1]].dst_ends) and is_set (tz[args[1]].dst_time) then		-- make sure we have all of the parts
			dst_begin_ts, dst_end_ts, invert = make_dst_timestamps (timestamp, args[1]);	-- get begin and end dst timestamps and invert flag

			if nil == dst_begin_ts or nil == dst_end_ts then
				return '<span style="font-size:100%" class="error">{{time}} – error calculating dst timestamps ([[Template:Time#Error messages|help]])</span>';
			end
	
			if invert then														-- southern hemisphere; use beginning and ending of standard time in the comparison
				if utc_timestamp >= dst_end_ts and utc_timestamp < dst_begin_ts then	-- is current date time standard time?
					tz_abbr = tz[args[1]].abbr;									-- standard time abbreviation
				else		
					timestamp = timestamp + 3600;								-- add an hour for 
					tz_abbr = tz[args[1]].dst_abbr;								-- dst abbreviation
				end
			else																-- northern hemisphere
				if utc_timestamp >= dst_begin_ts and utc_timestamp < dst_end_ts then	-- all timestamps are UTC
					timestamp = timestamp + 3600;								-- add an hour
					tz_abbr = tz[args[1]].dst_abbr;
				else
					tz_abbr = tz[args[1]].abbr;
				end
			end
		elseif is_set (tz[args[1]].dst_begins) or is_set (tz[args[1]].dst_ends) or is_set (tz[args[1]].dst_time) then	-- if some but not all not all parts then emit error message
			return '<span style="font-size:100%" class="error">{{time}} – incomplete definition for ' .. args[1]:upper() .. ' ([[Template:Time#Error messages|help]])</span>';
		else
			tz_abbr = tz[args[1]].abbr;											-- dst not observed for this timezone
		end
	end
	
	if 'y' == df or 'dmy' == df then											-- format the output (|df=y is legacy from original template)
		tz_string = os.date ('%R, %e %B %Y', timestamp);						-- dmy
	elseif 'iso' == df then
		tz_string = os.date ('%FT%R', timestamp);								-- iso
	else
		tz_string = os.date ('%R, %B %e, %Y', timestamp);						-- mdy (legacy default)
	end
	
	if not is_set (tz[args[1]].article) then									-- if some but not all not all parts then emit error message
		return '<span style="font-size:100%" class="error">{{time}} – incomplete definition for ' .. args[1]:upper() .. ' ([[Template:Time#Error messages|help]])</span>';
	end

	local refreshLink = mw.title.getCurrentTitle():fullUrl{action = 'purge'}	-- create a refresh link
	return string.format ('%s [[%s|%s]] <span class="plainlinks" style="font-size:80%%;">[[%s refresh]]</span>', tz_string, tz[args[1]].article, tz_abbr, refreshLink);
end

return p;
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