Mô đun:Citation/CS1/Date validation

--[[--------------------------< F O R W A R D   D E C L A R A T I O N S >--------------------------------------
]]

local add_prop_cat, is_set, in_array, set_message, substitute, wrap_style;		-- imported functions from selected Module:Citation/CS1/Utilities
local cfg;																		-- table of tables imported from selected Module:Citation/CS1/Configuration


--[[--------------------------< F I L E - S C O P E   D E C L A R A T I O N S >--------------------------------

File-scope variables are declared here

]]

local lang_object = mw.getContentLanguage();									-- used by is_valid_accessdate(), is_valid_year(), date_name_xlate(); TODO: move to ~/Configuration?
local year_limit;																-- used by is_valid_year()


--[=[-------------------------< I S _ V A L I D _ A C C E S S D A T E >----------------------------------------

returns true if:
	Wikipedia start date <= accessdate < today + 2 days

Wikipedia start date is 2001-01-15T00:00:00 UTC which is 979516800 seconds after 1970-01-01T00:00:00 UTC (the start of Unix time)
accessdate is the date provided in |access-date= at time 00:00:00 UTC
today is the current date at time 00:00:00 UTC plus 48 hours
	if today is 2015-01-01T00:00:00 then
		adding 24 hours gives 2015-01-02T00:00:00 – one second more than today
		adding 24 hours gives 2015-01-03T00:00:00 – one second more than tomorrow

This function does not work if it is fed month names for languages other than English.  Wikimedia #time: parser
apparently doesn't understand non-English date month names. This function will always return false when the date
contains a non-English month name because good1 is false after the call to lang.formatDate().  To get around that
call this function with YYYY-MM-DD format dates.

]=]

local function is_valid_accessdate (accessdate)
	local good1, good2;
	local access_ts, tomorrow_ts;												-- to hold Unix time stamps representing the dates

	good1, access_ts = pcall (lang_object.formatDate, lang_object, 'U', accessdate );			-- convert accessdate value to Unix timestamp 
	good2, tomorrow_ts = pcall (lang_object.formatDate, lang_object, 'U', 'today + 2 days' );	-- today midnight + 2 days is one second more than all day tomorrow
	
	if good1 and good2 then														-- lang.formatDate() returns a timestamp in the local script which which tonumber() may not understand
		access_ts = tonumber (access_ts) or lang_object:parseFormattedNumber (access_ts);		-- convert to numbers for the comparison;
		tomorrow_ts = tonumber (tomorrow_ts) or lang_object:parseFormattedNumber (tomorrow_ts);
	else
		return false;															-- one or both failed to convert to Unix time stamp
	end

	if 979516800 <= access_ts and access_ts < tomorrow_ts then					-- Wikipedia start date <= accessdate < tomorrow's date
		return true;
	else
		return false;															-- accessdate out of range
	end
end


--[[--------------------------< I S _ V A L I D _ E M B A R G O _ D A T E >------------------------------------

returns true and date value if that value has proper dmy, mdy, ymd format.

returns false and 9999 (embargoed forever) when date value is not proper format; assumes that when |pmc-embargo-date= is
set, the editor intended to embargo a PMC but |pmc-embargo-date= does not hold a single date.

]]

local function is_valid_embargo_date (v)
	if v:match ('^%d%d%d%d%-%d%d%-%d%d$') or									-- ymd
		v:match ('^%d%d?%s+%a+%s+%d%d%d%d$') or									-- dmy
		v:match ('^%a+%s+%d%d?%s*,%s*%d%d%d%d$') then							-- mdy
			return true, v;
	end
	return false, '9999';														-- if here not good date so return false and set embargo date to long time in future
end


--[[--------------------------< G E T _ M O N T H _ N U M B E R >----------------------------------------------

returns a number according to the month in a date: 1 for January, etc.  Capitalization and spelling must be correct.
If not a valid month, returns 0

]]

local function get_month_number (month)
	return cfg.date_names['local'].long[month] or cfg.date_names['local'].short[month] or	-- look for local names first
			cfg.date_names['en'].long[month] or	cfg.date_names['en'].short[month] or		-- failing that, look for English names
			0;																				-- not a recognized month name
end


--[[--------------------------< G E T _ S E A S O N _ N U M B E R >--------------------------------------------

returns a number according to the sequence of seasons in a year: 21 for Spring, etc.  Capitalization and spelling
must be correct. If not a valid season, returns 0.
	21-24 = Spring, Summer, Autumn, Winter, independent of “Hemisphere”

returns 0 when <param> is not |date=

Season numbering is defined by Extended Date/Time Format (EDTF) specification (https://www.loc.gov/standards/datetime/)
which became part of ISO 8601 in 2019.  See '§Sub-year groupings'.  The standard defines various divisions using
numbers 21-41.  cs1|2 only supports generic seasons.  EDTF does support the distinction between north and south
hemisphere seasons but cs1|2 has no way to make that distinction.

These additional divisions not currently supported:
	25-28 = Spring - Northern Hemisphere, Summer- Northern Hemisphere, Autumn - Northern Hemisphere, Winter - Northern Hemisphere
	29-32 = Spring – Southern Hemisphere, Summer– Southern Hemisphere, Autumn – Southern Hemisphere, Winter - Southern Hemisphere
	33-36 = Quarter 1, Quarter 2, Quarter 3, Quarter 4 (3 months each)
	37-39 = Quadrimester 1, Quadrimester 2, Quadrimester 3 (4 months each)
	40-41 = Semestral 1, Semestral-2 (6 months each)

]]

local function get_season_number (season, param)
	if 'date' ~= param then
		return 0;																-- season dates only supported by |date=
	end
	return cfg.date_names['local'].season[season] or							-- look for local names first
			cfg.date_names['en'].season[season] or								-- failing that, look for English names
			0;																	-- not a recognized season name
end


--[[--------------------------< G E T _ Q U A R T E R _ N U M B E R >------------------------------------------

returns a number according to the sequence of quarters in a year: 33 for first quarter, etc.  Capitalization and spelling
must be correct. If not a valid quarter, returns 0.
	33-36 = Quarter 1, Quarter 2, Quarter 3, Quarter 4 (3 months each)

returns 0 when <param> is not |date=

Quarter numbering is defined by Extended Date/Time Format (EDTF) specification (https://www.loc.gov/standards/datetime/)
which became part of ISO 8601 in 2019.  See '§Sub-year groupings'.  The standard defines various divisions using
numbers 21-41.  cs1|2 only supports generic seasons and quarters.

These additional divisions not currently supported:
	37-39 = Quadrimester 1, Quadrimester 2, Quadrimester 3 (4 months each)
	40-41 = Semestral 1, Semestral-2 (6 months each)

]]

local function get_quarter_number (quarter, param)
	if 'date' ~= param then
		return 0;																-- quarter dates only supported by |date=
	end
	quarter = mw.ustring.gsub (quarter, ' +', ' ');								-- special case replace multiple space chars with a single space char
	return cfg.date_names['local'].quarter[quarter] or							-- look for local names first
			cfg.date_names['en'].quarter[quarter] or							-- failing that, look for English names
			0;																	-- not a recognized quarter name
end


--[[--------------------------< G E T _ P R O P E R _ N A M E _ N U M B E R >----------------------------------

returns a non-zero number if date contains a recognized proper-name.  Capitalization and spelling must be correct.

returns 0 when <param> is not |date=

]]

local function get_proper_name_number (name, param)
	if 'date' ~= param then
		return 0;																-- proper-name dates only supported by |date=
	end
	return cfg.date_names['local'].named[name] or								-- look for local names dates first
			cfg.date_names['en'].named[name] or									-- failing that, look for English names
			0;																	-- not a recognized named date
end


--[[--------------------------< G E T _ E L E M E N T _ N U M B E R <------------------------------------------

returns true if month or season or quarter or proper name is valid (properly spelled, capitalized, abbreviated)

]]

local function get_element_number (element, param)
	local num;
	
	local funcs = {get_month_number, get_season_number, get_quarter_number, get_proper_name_number};	-- list of functions to execute in order
	
	for _, func in ipairs (funcs) do											-- spin through the function list
		num = func (element, param);											-- call the function and get the returned number
		if 0 ~= num then														-- non-zero when valid month season quarter 
			return num;															-- return that number
		end
	end
	return nil;																	-- not valid
end


--[[--------------------------< I S _ V A L I D _ Y E A R >----------------------------------------------------

Function gets current year from the server and compares it to year from a citation parameter.  Years more than one
year in the future are not acceptable.

]]

local function is_valid_year (year)
	if not is_set(year_limit) then
		year_limit = tonumber(os.date("%Y"))+1;									-- global variable so we only have to fetch it once
	end

	year = tonumber (year) or lang_object:parseFormattedNumber (year);			-- convert to numbers for the comparison;
	return year and (year <= year_limit) or false;
end


--[[--------------------------< I S _ V A L I D _ D A T E >----------------------------------------------------

Returns true if day is less than or equal to the number of days in month and year is no farther into the future
than next year; else returns false.

Assumes Julian calendar prior to year 1582 and Gregorian calendar thereafter. Accounts for Julian calendar leap
years before 1582 and Gregorian leap years after 1582. Where the two calendars overlap (1582 to approximately
1923) dates are assumed to be Gregorian.

]]

local function is_valid_date (year, month, day)
local days_in_month = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
local month_length;
	if not is_valid_year(year) then												-- no farther into the future than next year
		return false;
	end
	
	month = tonumber(month);													-- required for YYYY-MM-DD dates
	
	if (2 == month) then														-- if February
		month_length = 28;														-- then 28 days unless
		if 1582 > tonumber(year) then											-- Julian calendar
			if 0 == (year%4) then												-- is a leap year?
				month_length = 29;												-- if leap year then 29 days in February
			end
		else																	-- Gregorian calendar
			if (0 == (year%4) and (0 ~= (year%100) or 0 == (year%400))) then	-- is a leap year?
				month_length = 29;												-- if leap year then 29 days in February
			end
		end
	else
		month_length = days_in_month[month];
	end

	if tonumber (day) > month_length then
		return false;
	end
	return true;
end


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

Months in a range are expected to have the same style: Jan–Mar or October–December but not February–Mar or Jul–August. 
There is a special test for May because it can be either short or long form.

Returns true when style for both months is the same

]]

local function is_valid_month_range_style (month1, month2)
local len1 = month1:len();
local len2 = month2:len();
local viet1 = mw.ustring.match(month1, "[Tt]háng (.*)")
local viet2 = mw.ustring.match(month2, "[Tt]háng (.*)")
	if tonumber(viet1) and tonumber(viet2) then
		return true;
	elseif viet1 and viet2 and not tonumber(viet1) and not tonumber(viet2) then
		return true;
	elseif viet1 or viet2 then
		return false;
	elseif len1 == len2 then
		return true;															-- both months are short form so return true
	elseif 'May' == month1 or 'May'== month2 then -- ToDo: I18N
		return true;															-- both months are long form so return true
	elseif 3 == len1 or 3 == len2 then
		return false;															-- months are mixed form so return false
	else
		return true;															-- both months are long form so return true
	end
end


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

Check a pair of months or seasons to see if both are valid members of a month or season pair.

Month pairs are expected to be left to right, earliest to latest in time.

All season ranges are accepted as valid because there are publishers out there who have published a Summer–Spring YYYY issue, hence treat as ok

]]

local function is_valid_month_season_range(range_start, range_end, param)
	local range_start_number = get_month_number (range_start);
	local range_end_number;

	if 0 == range_start_number then												-- is this a month range?
		range_start_number = get_season_number (range_start, param);			-- not a month; is it a season? get start season number
		range_end_number = get_season_number (range_end, param);				-- get end season number

		if (0 ~= range_start_number) and (0 ~= range_end_number) and (range_start_number ~= range_end_number) then
			return true;														-- any season pairing is accepted except when both are the same
		end
		return false;															-- range_start and/or range_end is not a season
	end
																				-- here when range_start is a month
	range_end_number = get_month_number (range_end);							-- get end month number
	if range_start_number < range_end_number and								-- range_start is a month; does range_start precede range_end?
		is_valid_month_range_style (range_start, range_end) then				-- do months have the same style?
			return true;														-- proper order and same style
	end
	return false;																-- range_start month number is greater than or equal to range end number; or range end isn't a month
end


--[[--------------------------< M A K E _ C O I N S _ D A T E >------------------------------------------------

This function receives a table of date parts for one or two dates and an empty table reference declared in
Module:Citation/CS1.  The function is called only for |date= parameters and only if the |date=<value> is 
determined to be a valid date format.  The question of what to do with invalid date formats is not answered here.

The date parts in the input table are converted to an ISO 8601 conforming date string:
	single whole dates:		yyyy-mm-dd
	month and year dates:	yyyy-mm
	year dates:				yyyy
	ranges:					yyyy-mm-dd/yyyy-mm-dd
							yyyy-mm/yyyy-mm
							yyyy/yyyy

Dates in the Julian calendar are reduced to year or year/year so that we don't have to do calendar conversion from
Julian to Proleptic Gregorian.

The input table has:
	year, year2 – always present; if before 1582, ignore months and days if present
	month, month2 – 0 if not provided, 1-12 for months, 21-24 for seasons; 99 Christmas
	day, day2 –  0 if not provided, 1-31 for days
	
the output table receives:
	rftdate:	an ISO 8601 formatted date
	rftchron:	a free-form version of the date, usually without year which is in rftdate (season ranges and proper-name dates)
	rftssn:		one of four season keywords: winter, spring, summer, fall (lowercase)
	rftquarter:	one of four values: 1, 2, 3, 4

]]

local function make_COinS_date (input, tCOinS_date)
	local date;																	-- one date or first date in a range
	local date2 = '';															-- end of range date
-- start temporary Julian / Gregorian calendar uncertainty detection
	local year = tonumber(input.year);											-- this temporary code to determine the extent of sources dated to the Julian/Gregorian
	local month = tonumber(input.month);										-- interstice 1 October 1582 – 1 January 1926
	local day = tonumber (input.day);
	if (0 ~= day) and															-- day must have a value for this to be a whole date
		(((1582 == year) and (10 <= month) and (12 >= month)) or				-- any whole 1582 date from 1 October to 31 December or
			((1926 == year) and (1 == month) and (1 == input.day)) or			-- 1 January 1926 or
				((1582 < year) and (1925 >= year))) then						-- any date 1 January 1583 – 31 December 1925
					tCOinS_date.inter_cal_cat = true;							-- set category flag true
	end
-- end temporary Julian / Gregorian calendar uncertainty detection
	
	if 1582 > tonumber(input.year) or 20 < tonumber(input.month) then			-- Julian calendar or season so &rft.date gets year only
		date = input.year;
		if 0 ~= input.year2 and input.year ~= input.year2 then					-- if a range, only the second year portion when not the same as range start year
			date = string.format ('%.4d/%.4d', tonumber(input.year), tonumber(input.year2))		-- assemble the date range
		end
		if 20 < tonumber(input.month) then										-- if season or proper-name date
			local season = {[24] = 'winter', [21] = 'spring', [22] = 'summer', [23] = 'fall', [33] = '1', [34] = '2', [35] = '3', [36] = '4', [98] = 'Easter', [99] = 'Christmas'};	-- seasons lowercase, no autumn; proper-names use title case
			if 0 == input.month2 then											-- single season date
				if 40 < tonumber(input.month) then
					tCOinS_date.rftchron = season[input.month];					-- proper-name dates
				elseif 30 < tonumber(input.month) then
					tCOinS_date.rftquarter = season[input.month];				-- quarters
				else
					tCOinS_date.rftssn = season[input.month];					-- seasons
				end
			else																-- season range with a second season specified
				if input.year ~= input.year2 then								-- season year – season year range or season year–year
					tCOinS_date.rftssn = season[input.month];					-- start of range season; keep this?
					if 0~= input.month2 then
						tCOinS_date.rftchron = string.format ('%s %s – %s %s', season[input.month], input.year, season[input.month2], input.year2);
					end
				else															-- season–season year range
					tCOinS_date.rftssn = season[input.month];					-- start of range season; keep this?
					tCOinS_date.rftchron = season[input.month] .. '–' .. season[input.month2];	-- season–season year range
				end
			end
		end
		tCOinS_date.rftdate = date;
		return;																	-- done
	end
	
	if 0 ~= input.day then
		date = string.format ('%s-%.2d-%.2d', input.year, tonumber(input.month), tonumber(input.day));	-- whole date
	elseif 0 ~= input.month then
		date = string.format ('%s-%.2d', input.year, tonumber(input.month));	-- year and month
	else
		date = string.format ('%s', input.year);								-- just year
	end

	if 0 ~= input.year2 then
		if 0 ~= input.day2 then
			date2 = string.format ('/%s-%.2d-%.2d', input.year2, tonumber(input.month2), tonumber(input.day2));		-- whole date
		elseif 0 ~= input.month2 then
			date2 = string.format ('/%s-%.2d', input.year2, tonumber(input.month2));	-- year and month
		else
			date2 = string.format ('/%s', input.year2);							-- just year
		end
	end
	
	tCOinS_date.rftdate = date .. date2;										-- date2 has the '/' separator
	return;
end


--[[--------------------------< P A T T E R N S >--------------------------------------------------------------

this is the list of patterns for date formats that this module recognizes.  Approximately the first half of these
patterns represent formats that might be reformatted into another format.  Those that might be reformatted have
'indicator' letters that identify the content of the matching capture: 'd' (day), 'm' (month), 'a' (anchor year),
'y' (year); second day, month, year have a '2' suffix.

These patterns are used for both date validation and for reformatting.  This table should not be moved to ~/Configuration
because changes to this table require changes to check_date() and to reformatter() and reformat_date()

]]

local patterns = {
	 																			-- year-initial numerical year-month-day
	['ymd'] = {'^(%d%d%d%d)%-(%d%d)%-(%d%d)$', 'y', 'm', 'd'},
																				-- month-initial: month day, year
	['Mdy'] = {'^(%D-) +([1-9]%d?), +((%d%d%d%d?)%a?)$', 'm', 'd', 'a', 'y'},
																				-- month-initial day range: month day–day, year; days are separated by endash
	['Md-dy'] = {'^(%D-) +([1-9]%d?)[%-–]([1-9]%d?), +((%d%d%d%d)%a?)$', 'm', 'd', 'd2', 'a', 'y'},
																				-- day-initial: day month year
	['dMy'] = {'^([1-9]%d?) +(%D-) +((%d%d%d%d?)%a?)$', 'd', 'm', 'a', 'y'},
	['dMy_v1'] = {'^([1-9]%d?) +(%a+ +[%a%d]+) +năm +((%d%d%d%d?)%a?)$', 'd', 'm', 'a', 'y'},
	['dMy_v2'] = {'^([1-9]%d?) +(%a+ +[%a%d]+), +((%d%d%d%d?)%a?)$', 'd', 'm', 'a', 'y'},
																				-- year-initial: year month day; day: 1 or 2 two digits, leading zero allowed; not supported at en.wiki
	--	['yMd'] = {'^((%d%d%d%d?)%a?) +(%D-) +(%d%d?)$', 'a', 'y', 'm', 'd'},
																				-- day-range-initial: day–day month year; days are separated by endash
	['d-dMy'] = {'^([1-9]%d?)[%-–]([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'd2', 'm', 'a', 'y'},
	['d-dMy_v1'] = {'^([1-9]%d?)[%-–]([1-9]%d?) +(%a+ +[%a%d]+) +năm +((%d%d%d%d)%a?)$', 'd', 'd2', 'm', 'a', 'y'},
	['d-dMy_v2'] = {'^([1-9]%d?)[%-–]([1-9]%d?) +(%a+ +[%a%d]+), +((%d%d%d%d)%a?)$', 'd', 'd2', 'm', 'a', 'y'},
																				-- day initial month-day-range: day month - day month year; uses spaced endash
	['dM-dMy'] = {'^([1-9]%d?) +(%D-) +[%-–] +([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'm', 'd2', 'm2', 'a', 'y'},
	['dM-dMy_v1'] = {'^([1-9]%d?) +(%a+ +[1-9]%d?) +[%-–] +([1-9]%d?) +(%a+ +[%a%d]+) +năm +((%d%d%d%d)%a?)$', 'd', 'm', 'd2', 'm2', 'a', 'y'},
	['dM-dMy_v2'] = {'^([1-9]%d?) +(%a+ +[1-9]%d?) +[%-–] +([1-9]%d?) +(%a+ +[%a%d]+), +((%d%d%d%d)%a?)$', 'd', 'm', 'd2', 'm2', 'a', 'y'},
																				-- month initial month-day-range: month day – month day, year;  uses spaced endash
	['Md-Mdy'] = {'^(%D-) +([1-9]%d?) +[%-–] +(%D-) +([1-9]%d?), +((%d%d%d%d)%a?)$','m', 'd', 'm2', 'd2', 'a', 'y'},
																				-- day initial month-day-year-range: day month year - day month year; uses spaced endash
	['dMy-dMy'] = {'^([1-9]%d?) +(%D-) +(%d%d%d%d) +[%-–] +([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'm', 'y', 'd2', 'm2', 'a', 'y2'},
	['dMy-dMy_v1'] = {'^([1-9]%d?) +(%a+ +[%a%d]+) +năm +(%d%d%d%d) +[%-–] +([1-9]%d?) +(%a+ +[%a%d]+) +năm +((%d%d%d%d)%a?)$', 'd', 'm', 'y', 'd2', 'm2', 'a', 'y2'},
	['dMy-dMy_v2'] = {'^([1-9]%d?) +(%a+ +[%a%d]+), +(%d%d%d%d) +[%-–] +([1-9]%d?) +(%a+ +[%a%d]+), +((%d%d%d%d)%a?)$', 'd', 'm', 'y', 'd2', 'm2', 'a', 'y2'},
																				-- month initial month-day-year-range: month day, year – month day, year;  uses spaced endash
	['Mdy-Mdy'] = {'^(%D-) +([1-9]%d?), +(%d%d%d%d) +[%-–] +(%D-) +([1-9]%d?), +((%d%d%d%d)%a?)$', 'm', 'd', 'y', 'm2', 'd2', 'a', 'y2'},

																				-- these date formats cannot be converted, per se, but month name can be rendered short or long
																				-- month/season year - month/season year; separated by spaced endash
	['My-My'] = {'^(%D-) +(%d%d%d%d) +[%-–] +(%D-) +((%d%d%d%d)%a?)$', 'm', 'y', 'm2', 'a', 'y2'},
	['My-My_v1'] = {'^(%a+ +[%a%d]+) +năm +(%d%d%d%d) +[%-–] +(%a+ +[%a%d]+) +năm +((%d%d%d%d)%a?)$', 'm', 'y', 'm2', 'a', 'y2'},
																				-- month/season range year; months separated by endash
	['M-My'] = {'^(%D-)[%-–](%D-) +((%d%d%d%d)%a?)$', 'm', 'm2', 'a', 'y'},
	['M-My_v1'] = {'^([Tt]háng +[%a%d]+)[%-–]([%a%d]+) +năm +((%d%d%d%d)%a?)$', 'm', 'm2', 'a', 'y'},
	['M-My_v2'] = {'^([Tt]háng +[%a%d]+)[%-–]([%a%d]+), +((%d%d%d%d)%a?)$', 'm', 'm2', 'a', 'y'},
																				-- month/season year or proper-name year; quarter year when First Quarter YYYY etc.
	['My'] = {'^([^%d–]-) +((%d%d%d%d)%a?)$', 'm', 'a', 'y'},					-- this way because endash is a member of %D; %D- will match January–March 2019 when it shouldn't
	['My_v1'] = {'^(%a+ +[%a%d]+) +năm +((%d%d%d%d)%a?)$', 'm', 'a', 'y'},
																				-- these date formats cannot be converted
	['Sy4-y2'] = {'^(%D-) +((%d%d)%d%d)[%-–]((%d%d)%a?)$'},						-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
	['Sy4-y2_v1'] = {'^(%a+ +%a+) +năm +((%d%d)%d%d)[%-–]((%d%d)%a?)$'},
	['Sy-y'] = {'^(%D-) +(%d%d%d%d)[%-–]((%d%d%d%d)%a?)$'},						-- special case Winter/Summer year-year; year separated with unspaced endash
	['Sy-y_v1'] = {'^(%a+ +%a+) +năm +(%d%d%d%d)[%-–]((%d%d%d%d)%a?)$'},
	['y-y'] = {'^(%d%d%d%d?)[%-–]((%d%d%d%d?)%a?)$'},							-- year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
	['y4-y2'] = {'^((%d%d)%d%d)[%-–]((%d%d)%a?)$'},								-- year range: YYYY–YY; separated by unspaced endash
	['ymx'] = {'^(%d%d%d%d)%-(%d%d)%-XX$', 'y', 'm'},							-- edtf year-initial numerical year-month-XX
	['y'] = {'^((%d%d%d%d?)%a?)$'},												-- year; here accept either YYY or YYYY
	}


--[[--------------------------< C H E C K _ D A T E >----------------------------------------------------------

Check date format to see that it is one of the formats approved by WP:DATESNO or WP:DATERANGE. Exception: only
allowed range separator is endash.  Additionally, check the date to see that it is a real date: no 31 in 30-day
months; no 29 February when not a leap year.  Months, both long-form and three character abbreviations, and seasons
must be spelled correctly.  Future years beyond next year are not allowed.

If the date fails the format tests, this function returns false and does not return values for anchor_year and
COinS_date.  When this happens, the date parameter is (DEBUG: not?) used in the COinS metadata and the CITEREF identifier gets
its year from the year parameter if present otherwise CITEREF does not get a date value.

Inputs:
	date_string - date string from date-holding parameters (date, year, publication-date, access-date, pmc-embargo-date, archive-date, lay-date)

Returns:
	false if date string is not a real date; else
	true, anchor_year, COinS_date
		anchor_year can be used in CITEREF anchors
		COinS_date is ISO 8601 format date; see make_COInS_date()

]]

local function check_date (date_string, param, tCOinS_date)
	local year;																	-- assume that year2, months, and days are not used;
	local year2 = 0;															-- second year in a year range
	local month = 0;
	local month2 = 0;															-- second month in a month range
	local day = 0;
	local day2 = 0;																-- second day in a day range
	local anchor_year;
	local coins_date;
	local iso_date;
	
	date_string = mw.ustring.gsub(date_string, "^[Nn]gày ", "", 1)

	if date_string:match (patterns['ymd'][1]) then								-- year-initial numerical year month day format
		year, month, day = date_string:match (patterns['ymd'][1]);
		if 12 < tonumber(month) or 1 > tonumber(month) or 1582 > tonumber(year) or 0 == tonumber(day) then return false; end	-- month or day number not valid or not Gregorian calendar
		anchor_year = year;
	
	elseif date_string:match (patterns['ymx'][1]) then							-- year-initial numerical year month edtf format
		year, month = date_string:match (patterns['ymx'][1]);
		if 12 < tonumber(month) or 1 > tonumber(month) or 1582 > tonumber(year) or not is_valid_year(year) then return false; end	-- month number not valid or not Gregorian calendar or future year
		anchor_year = year;

	elseif mw.ustring.match(date_string, patterns['Mdy'][1]) then				-- month-initial: month day, year
		month, day, anchor_year, year = mw.ustring.match(date_string, patterns['Mdy'][1]);
		month = get_month_number (month);
		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
				
	elseif mw.ustring.match(date_string, patterns['Md-dy'][1]) then				-- month-initial day range: month day–day, year; days are separated by endash
		month, day, day2, anchor_year, year = mw.ustring.match(date_string, patterns['Md-dy'][1]);
		if tonumber(day) >= tonumber(day2) then return false; end				-- date range order is left to right: earlier to later; dates may not be the same;
		month = get_month_number (month);
		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
		month2=month;															-- for metadata
		year2 = year;

	elseif (mw.ustring.match(date_string, patterns['dMy'][1]) or
			mw.ustring.match(date_string, patterns['dMy_v1'][1]) or
			mw.ustring.match(date_string, patterns['dMy_v2'][1])) then				-- day-initial: day month year
		day, month, anchor_year, year = mw.ustring.match(date_string, patterns['dMy'][1]);
		if day == nil then day, month, anchor_year, year = mw.ustring.match(date_string, patterns['dMy_v1'][1]) end
		if day == nil then day, month, anchor_year, year = mw.ustring.match(date_string, patterns['dMy_v2'][1]) end
		month = get_month_number (month);
		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months

--[[ NOT supported at en.wiki
	elseif mw.ustring.match(date_string, patterns['yMd'][1]) then				-- year-initial: year month day; day: 1 or 2 two digits, leading zero allowed
		anchor_year, year, month, day = mw.ustring.match(date_string, patterns['yMd'][1]);
		month = get_month_number (month);
		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
-- end NOT supported at en.wiki ]]

	elseif (mw.ustring.match(date_string, patterns['d-dMy'][1]) or
			mw.ustring.match(date_string, patterns['d-dMy_v1'][1]) or
			mw.ustring.match(date_string, patterns['d-dMy_v2'][1])) then				-- day-range-initial: day–day month year; days are separated by endash
		day, day2, month, anchor_year, year = mw.ustring.match(date_string, patterns['d-dMy'][1]);
		if day == nil then day, day2, month, anchor_year, year = mw.ustring.match(date_string, patterns['d-dMy_v1'][1]) end
		if day == nil then day, day2, month, anchor_year, year = mw.ustring.match(date_string, patterns['d-dMy_v2'][1]) end
		if tonumber(day) >= tonumber(day2) then return false; end				-- date range order is left to right: earlier to later; dates may not be the same;
		month = get_month_number (month);
		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
		month2 = month;															-- for metadata
		year2 = year;

	elseif (mw.ustring.match(date_string, patterns['dM-dMy'][1]) or
			mw.ustring.match(date_string, patterns['dM-dMy_v1'][1]) or
			mw.ustring.match(date_string, patterns['dM-dMy_v2'][1])) then			-- day initial month-day-range: day month - day month year; uses spaced endash
		day, month, day2, month2, anchor_year, year = mw.ustring.match(date_string, patterns['dM-dMy'][1]);
		if day == nil then day, month, day2, month2, anchor_year, year = mw.ustring.match(date_string, patterns['dM-dMy_v1'][1]) end
		if day == nil then day, month, day2, month2, anchor_year, year = mw.ustring.match(date_string, patterns['dM-dMy_v2'][1]) end
		if (not is_valid_month_season_range(month, month2)) or not is_valid_year(year) then return false; end	-- date range order is left to right: earlier to later;
		month = get_month_number (month);										-- for metadata
		month2 = get_month_number (month2);
		year2 = year;

	elseif mw.ustring.match(date_string, patterns['Md-Mdy'][1]) then			-- month initial month-day-range: month day – month day, year; uses spaced endash
		month, day, month2, day2, anchor_year, year = mw.ustring.match(date_string, patterns['Md-Mdy'][1]);
		if (not is_valid_month_season_range(month, month2, param)) or not is_valid_year(year) then return false; end
		month = get_month_number (month);										-- for metadata
		month2 = get_month_number (month2);
		year2 = year;

	elseif (mw.ustring.match(date_string, patterns['dMy-dMy'][1]) or
			mw.ustring.match(date_string, patterns['dMy-dMy_v1'][1]) or
			mw.ustring.match(date_string, patterns['dMy-dMy_v2'][1])) then			-- day initial month-day-year-range: day month year - day month year; uses spaced endash
		day, month, year, day2, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['dMy-dMy'][1]);
		if day == nil then day, month, year, day2, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['dMy-dMy_v1'][1]) end
		if day == nil then day, month, year, day2, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['dMy-dMy_v2'][1]) end
		if tonumber(year2) <= tonumber(year) then return false; end				-- must be sequential years, left to right, earlier to later
		if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end		-- year2 no more than one year in the future; months same style
		month = get_month_number (month);										-- for metadata
		month2 = get_month_number (month2);
		if 0 == month or 0 == month2 then return false; end						-- both must be valid

	elseif mw.ustring.match(date_string, patterns['Mdy-Mdy'][1]) then			-- month initial month-day-year-range: month day, year – month day, year; uses spaced endash
		month, day, year, month2, day2, anchor_year, year2 = mw.ustring.match(date_string, patterns['Mdy-Mdy'][1]);
		if tonumber(year2) <= tonumber(year) then return false; end				-- must be sequential years, left to right, earlier to later
		if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end		-- year2 no more than one year in the future; months same style
		month = get_month_number (month);										-- for metadata
		month2 = get_month_number(month2);
		if 0 == month or 0 == month2 then return false; end						-- both must be valid

	elseif (mw.ustring.match(date_string, patterns['Sy4-y2'][1]) or
			mw.ustring.match(date_string, patterns['Sy4-y2_v1'][1])) then			-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
		local century;
		month, year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy4-y2'][1]);
		if month == nil then month, year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy4-y2_v1'][1]) end
		if 'Winter' ~= month and 'Summer' ~= month and not mw.ustring.match(month, "^[Mm]ùa +[Đđ]ông$") and not mw.ustring.match(month, "^[Mm]ùa +[Hh][ạè]$") then return false end;	-- 'month' can only be Winter or Summer
		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor_year from both years
		year2 = century..year2;													-- add the century to year2 for comparisons
		if 1 ~= tonumber(year2) - tonumber(year) then return false; end			-- must be sequential years, left to right, earlier to later
		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
		month = get_season_number(month, param);

	elseif (mw.ustring.match(date_string, patterns['Sy-y'][1]) or
			mw.ustring.match(date_string, patterns['Sy-y_v1'][1])) then				-- special case Winter/Summer year-year; year separated with unspaced endash
		month, year, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy-y'][1]);
		if month == nil then month, year, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy-y_v1'][1]) end
		if 'Winter' ~= month and 'Summer' ~= month and not mw.ustring.match(month, "^[Mm]ùa +[Đđ]ông$") and not mw.ustring.match(month, "^[Mm]ùa +[Hh][ạè]$") then return false end;		-- 'month' can only be Winter or Summer
		anchor_year = year .. '–' .. anchor_year;										-- assemble anchor_year from both years
		if 1 ~= tonumber(year2) - tonumber(year) then return false; end			-- must be sequential years, left to right, earlier to later
		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
		month = get_season_number (month, param);								-- for metadata

	elseif (mw.ustring.match(date_string, patterns['My-My'][1]) or
			mw.ustring.match(date_string, patterns['My-My_v1'][1])) then				-- month/season year - month/season year; separated by spaced endash
		month, year, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['My-My'][1]);
		if month == nil then month, year, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['My-My_v1'][1]) end
		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor_year from both years
		if tonumber(year) >= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
		if 0 ~= get_month_number(month) and 0 ~= get_month_number(month2) and is_valid_month_range_style(month, month2) then 	-- both must be month year, same month style
			month = get_month_number(month);
			month2 = get_month_number(month2);
		elseif 0 ~= get_season_number(month, param) and 0 ~= get_season_number(month2, param) then	-- both must be season year, not mixed
			month = get_season_number(month, param);
			month2 = get_season_number(month2, param);
		else
			 return false;
		end

	elseif (mw.ustring.match(date_string, patterns['M-My'][1]) or
			mw.ustring.match(date_string, patterns['M-My_v1'][1]) or
			mw.ustring.match(date_string, patterns['M-My_v2'][1])) then				-- month/season range year; months separated by endash
		month, month2, anchor_year, year = mw.ustring.match(date_string, patterns['M-My'][1]);
		local monthNumber2
		if month == nil then month, monthNumber2, anchor_year, year = mw.ustring.match(date_string, patterns['M-My_v1'][1]) end
		if month == nil then month, monthNumber2, anchor_year, year = mw.ustring.match(date_string, patterns['M-My_v2'][1]) end
        if monthNumber2 ~= nil then month2 = 'tháng ' .. monthNumber2 end -- the second “tháng” is implicit
		if (not is_valid_month_season_range(month, month2, param)) or (not is_valid_year(year)) then return false; end
		if 0 ~= get_month_number(month) then									-- determined to be a valid range so just check this one to know if month or season
			month = get_month_number(month);
			month2 = get_month_number(month2);
			if 0 == month or 0 == month2 then return false; end
		else
			month = get_season_number(month, param);
			month2 = get_season_number(month2, param);
		end
		year2 = year;
		
	elseif (mw.ustring.match(date_string, patterns['My'][1]) or
			mw.ustring.match(date_string, patterns['My_v1'][1])) then				-- month/season/quarter/proper-name year
		month, anchor_year, year = mw.ustring.match(date_string, patterns['My'][1]);
		if month == nil then month, anchor_year, year = mw.ustring.match(date_string, patterns['My_v1'][1]) end
		if not is_valid_year(year) then return false; end
		month = get_element_number(month, param);								-- get month season quarter proper-name number or nil
		if not month then return false; end										-- not valid whatever it is

	elseif mw.ustring.match(date_string, patterns['y-y'][1]) then				-- Year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
		year, anchor_year, year2 = mw.ustring.match(date_string, patterns['y-y'][1]);
		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor year from both years
		if tonumber(year) >= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year

	elseif mw.ustring.match(date_string, patterns['y4-y2'][1]) then				-- Year range: YYYY–YY; separated by unspaced endash
		local century;
		year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns['y4-y2'][1]);
		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor year from both years

		if in_array (param, {'date', 'publication-date', 'year'}) then
			add_prop_cat ('year_range_abbreviated');
		end

		if 13 > tonumber(year2) then return false; end							-- don't allow 2003-05 which might be May 2003
		year2 = century .. year2;													-- add the century to year2 for comparisons
		if tonumber(year) >= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year

	elseif mw.ustring.match(date_string, patterns['y'][1]) then					-- year; here accept either YYY or YYYY
		anchor_year, year = mw.ustring.match(date_string, patterns['y'][1]);
		if false == is_valid_year(year) then
			return false;
		end

	else
		return false;															-- date format not one of the MOS:DATE approved formats
	end

	if 'access-date' == param then												-- test accessdate here because we have numerical date parts
		if 0 ~= year and 0 ~= month and 0 ~= day and 							-- all parts of a single date required
			0 == year2 and 0 == month2 and 0 == day2 then						-- none of these; accessdate must not be a range
				if not is_valid_accessdate(year .. '-' .. month .. '-' .. day) then	
					return false;												-- return false when accessdate out of bounds
				end
		else
			return false;														-- return false when accessdate is a range of two dates
		end
	end

	local result=true;															-- check whole dates for validity; assume true because not all dates will go through this test
	if 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 == month2 and 0 == day2 then		-- YMD (simple whole date)
		result = is_valid_date(year, month, day);

	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 == month2 and 0 ~= day2 then	-- YMD-d (day range)
		result = is_valid_date(year, month, day);
		result = result and is_valid_date(year, month, day2);

	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 ~= month2 and 0 ~= day2 then	-- YMD-md (day month range)
		result = is_valid_date(year, month, day);
		result = result and is_valid_date(year, month2, day2);

	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 ~= year2 and 0 ~= month2 and 0 ~= day2 then	-- YMD-ymd (day month year range)
		result = is_valid_date(year, month, day);
		result = result and is_valid_date(year2, month2, day2);
	end
	
	if false == result then return false; end

	if nil ~= tCOinS_date then													-- this table only passed into this function when testing |date= parameter values
		make_COinS_date ({year = year, month = month, day = day, year2 = year2, month2 = month2, day2 = day2}, tCOinS_date);	-- make an ISO 8601 date string for COinS
	end
	
	return true, anchor_year;													-- format is good and date string represents a real date
end	


--[[--------------------------< D A T E S >--------------------------------------------------------------------

Cycle the date-holding parameters in passed table date_parameters_list through check_date() to check compliance with MOS:DATE. For all valid dates, check_date() returns
true. The |date= parameter test is unique, it is the only date holding parameter from which values for anchor_year (used in CITEREF identifiers) and COinS_date (used in
the COinS metadata) are derived.  The |date= parameter is the only date-holding parameter that is allowed to contain the no-date keywords "n.d." or "nd" (without quotes).

Unlike most error messages created in this module, only one error message is created by this function. Because all of the date holding parameters are processed serially,
parameters with errors are added to the <error_list> sequence table as the dates are tested.

]]

local function dates(date_parameters_list, tCOinS_date, error_list)
	local anchor_year;															-- will return as nil if the date being tested is not |date=
	local COinS_date;															-- will return as nil if the date being tested is not |date=
	local embargo_date;															-- if embargo date is a good dmy, mdy, ymd date then holds original value else reset to 9999
	local good_date = false;

	for k, v in pairs(date_parameters_list) do									-- for each date-holding parameter in the list
		if is_set(v.val) then													-- if the parameter has a value
			v.val = mw.ustring.gsub(v.val, '%d', cfg.date_names.local_digits);	-- translate 'local' digits to Western 0-9
			if v.val:match("^c%. [1-9]%d%d%d?%a?$") then						-- special case for c. year or with or without CITEREF disambiguator - only |date= and |year=
				local year = v.val:match("c%. ([1-9]%d%d%d?)%a?");				-- get the year portion so it can be tested
				if 'date' == k then
					anchor_year, COinS_date = v.val:match("((c%. [1-9]%d%d%d?)%a?)");	-- anchor year and COinS_date only from |date= parameter
					good_date = is_valid_year(year);
				elseif 'year' == k then
					good_date = is_valid_year(year);
				end
			elseif 'date' == k then												-- if the parameter is |date=
				if v.val:match("^n%.d%.%a?$") then -- ToDo: I18N								-- if |date=n.d. with or without a CITEREF disambiguator
					good_date, anchor_year, COinS_date = true, v.val:match("((n%.d%.)%a?)"); -- ToDo: I18N	-- "n.d."; no error when date parameter is set to no date
				elseif v.val:match("^nd%a?$") then -- ToDo: I18N								-- if |date=nd with or without a CITEREF disambiguator
					good_date, anchor_year, COinS_date = true, v.val:match("((nd)%a?)"); -- ToDo: I18N	-- "nd";	no error when date parameter is set to no date
				else
					good_date, anchor_year, COinS_date = check_date (v.val, k, tCOinS_date);	-- go test the date
				end
			elseif 'year' == k then												-- if the parameter is |year= it should hold only a year value
				if v.val:match("^[1-9]%d%d%d?%a?$") then						-- if |year = 3 or 4 digits only with or without a CITEREF disambiguator
					good_date, anchor_year, COinS_date = true, v.val:match("((%d+)%a?)");
				end
			elseif 'pmc-embargo-date' == k then											-- if the parameter is |pmc-embargo-date=
				good_date = check_date (v.val, k);								-- go test the date
				if true == good_date then										-- if the date is a valid date
					good_date, embargo_date = is_valid_embargo_date (v.val);	-- is |pmc-embargo-date= date a single dmy, mdy, or ymd formatted date? yes: returns embargo; no: returns 9999
				end
			else																-- any other date-holding parameter
				good_date = check_date (v.val, k);								-- go test the date
			end
			if false == good_date then											-- assemble one error message so we don't add the tracking category multiple times
				table.insert (error_list, wrap_style ('parameter', v.name));	-- make parameter name suitable for error message list
			end
		end
	end
	return anchor_year, embargo_date;											-- and done
end


--[[--------------------------< Y E A R _ D A T E _ C H E C K >------------------------------------------------

Compare the value provided in |year= with the year value(s) provided in |date=.  This function sets a local numeric value:
	0 - year value does not match the year value in date
	1 - (default) year value matches the year value in date or one of the year values when date contains two years
	2 - year value matches the year value in date when date is in the form YYYY-MM-DD and year is disambiguated (|year=YYYYx)

the numernic value in <result> determines the 'output' if any from this function:
	0 – adds error message to error_list sequence table
	1 – adds maint cat
	2 – does nothing

]]

local function year_date_check (year_string, year_origin, date_string, date_origin, error_list)
	local year;
	local date1;
	local date2;
	local result = 1;															-- result of the test; assume that the test passes

	year = year_string:match ('(%d%d%d%d?)');

	if date_string:match ('%d%d%d%d%-%d%d%-%d%d') and year_string:match ('%d%d%d%d%a') then	--special case where both date and year are required YYYY-MM-DD and YYYYx
		date1 = date_string:match ('(%d%d%d%d)');
		year = year_string:match ('(%d%d%d%d)');
		if year ~= date1 then
			result = 0;															-- years don't match
		else
			result = 2;															-- years match; but because disambiguated, don't add to maint cat
		end
		
	elseif date_string:match ("%d%d%d%d?.-%d%d%d%d?") then						-- any of the standard range formats of date with two three- or four-digit years
		date1, date2 = date_string:match ("(%d%d%d%d?).-(%d%d%d%d?)");
		if year ~= date1 and year ~= date2 then
			result = 0;
		end

	elseif mw.ustring.match(date_string, "%d%d%d%d[%-–]%d%d") then				-- YYYY-YY date ranges
		local century;
		date1, century, date2 = mw.ustring.match(date_string, "((%d%d)%d%d)[%-–]+(%d%d)");
		date2 = century..date2;													-- convert YY to YYYY
		if year ~= date1 and year ~= date2 then
			result = 0;
		end

	elseif date_string:match ("%d%d%d%d?") then									-- any of the standard formats of date with one year
		date1 = date_string:match ("(%d%d%d%d?)");
		if year ~= date1 then
			result = 0;
		end
	else																		-- should never get here; this function called only when no other date errors
		result = 0;																-- no recognizable year in date
	end

	if 0 == result then															-- year / date mismatch
		table.insert (error_list, substitute (cfg.messages['mismatch'], {year_origin, date_origin}));	-- add error message to error_list sequence table
	elseif 1 == result then														-- redundant year / date
		set_message ('maint_date_year');										-- add a maint cat
	end
end


--[[--------------------------< R E F O R M A T T E R >--------------------------------------------------------

reformat 'date' into new format specified by format_param if pattern_idx (the current format of 'date') can be
reformatted.  Does the grunt work for reformat_dates().

The table re_formats maps pattern_idx (current format) and format_param (desired format) to a table that holds:
	format string used by string.format()
	identifier letters ('d', 'm', 'y', 'd2', 'm2', 'y2') that serve as indexes into a table t{} that holds captures
		from mw.ustring.match() for the various date parts specified by  patterns[pattern_idx][1]

Items in patterns{} have the general form:
	['ymd'] = {'^(%d%d%d%d)%-(%d%d)%-(%d%d)$', 'y', 'm', 'd'}, where:
		['ymd'] is pattern_idx
		patterns['ymd'][1] is the match pattern with captures for mw.ustring.match()
		patterns['ymd'][2] is an indicator letter identifying the content of the first capture
		patterns['ymd'][3] ... the second capture etc.

when a pattern matches a date, the captures are loaded into table t{} in capture order using the idemtifier
characters as indexes into t{}  For the above, a ymd date is in t{} as:
	t.y = first capture (year), t.m = second capture (month), t.d = third capture (day)

To reformat, this function is called with the pattern_idx that matches the current format of the date and with
format_param set to the desired format.  This function loads table t{} as described and then calls string.format()
with the format string specified by re_format[pattern_idx][format_param][1] using values taken from t{} according
to the capture identifier letters specified by patterns[pattern_idx][format_param][n] where n is 2..

]]

local re_formats = {
	['ymd'] = {																	-- date format is ymd; reformat to:
		['mdy'] = {'%s %s năm %s', 'd', 'm', 'y'},								-- |df=dmy
		['dmy'] = {'%s %s năm %s', 'd', 'm', 'y'},								-- |df=dmy
	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
		},
	['Mdy'] = {																	-- date format is Mdy; reformat to:
		['mdy'] = {'%s %s năm %s', 'd', 'm', 'y'},								-- |df=dmy
		['dmy'] = {'%s %s năm %s', 'd', 'm', 'y'},								-- |df=dmy
		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},									-- |df=ymd
	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
		},
	['dMy'] = {																	-- date format is dMy; reformat to:
		['dmy'] = {'%s %s năm %s', 'd', 'm', 'y'},									-- for long/short reformatting
		['mdy'] = {'%s %s năm %s', 'd', 'm', 'y'},									-- |df=dMy
		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},									-- |df=ymd
	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
		},
	['Md-dy'] = {																-- date format is Md-dy; reformat to:
		['mdy'] = {'%s–%s %s năm %s', 'd', 'd2', 'm', 'y'},							-- |df=dmy -> d-dMy
		['dmy'] = {'%s–%s %s năm %s', 'd', 'd2', 'm', 'y'},							-- |df=dmy -> d-dMy
		},
	['d-dMy'] = {																-- date format is d-d>y; reformat to:
		['dmy'] = {'%s–%s %s năm %s', 'd', 'd2', 'm', 'y'},							-- for long/short reformatting
		['mdy'] = {'%s–%s %s năm %s', 'd', 'd2', 'm', 'y'},						-- |df=mdy -> d-dMy
		},
	['dM-dMy'] = {																-- date format is dM-dMy; reformat to:
		['dmy'] = {'%s %s – %s %s năm %s', 'd', 'm', 'd2', 'm2', 'y'},				-- for long/short reformatting
		['mdy'] = {'%s %s – %s %s năm %s', 'd', 'm', 'd2', 'm2', 'y'},				-- |df=mdy -> dM-dMy
		},
	['Md-Mdy'] = {																-- date format is Md-Mdy; reformat to:
		['mdy'] = {'%s %s – %s %s năm %s', 'd', 'm', 'd2', 'm2', 'y'},				-- |df=dmy -> dM-dMy
		['dmy'] = {'%s %s – %s %s năm %s', 'd', 'm', 'd2', 'm2', 'y'},				-- |df=dmy -> dM-dMy
		},
	['dMy-dMy'] = {																-- date format is dMy-dMy; reformat to:
		['dmy'] = {'%s %s năm %s – %s %s năm %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- for long/short reformatting
		['mdy'] = {'%s %s năm %s – %s %s năm %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},	-- |df=mdy -> dMy-dMy
		},
	['Mdy-Mdy'] = {																-- date format is Mdy-Mdy; reformat to:
		['mdy'] = {'%s %s năm %s – %s %s năm %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- |df=dmy -> dMy-dMy
		['dmy'] = {'%s %s năm %s – %s %s năm %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- |df=dmy -> dMy-dMy
		},
	['My-My'] = {																-- these for long/short reformatting
		['any'] = {'%s năm %s – %s năm %s', 'm', 'y', 'm2', 'y2'},						-- dmy/mdy agnostic
		},
	['M-My'] = {																-- these for long/short reformatting
		['any'] = {'%s–%s năm %s', 'm', 'm2', 'y'},									-- dmy/mdy agnostic
		},
	['My'] = {																	-- these for long/short reformatting
		['any'] = {'%s năm %s', 'm', 'y'},											-- dmy/mdy agnostic
		},
	--	['yMd'] = {																-- not supported at en.wiki
	--		['mdy'] = {'%s %s, %s', 'm', 'd', 'y'},								-- |df=mdy
	--		['dmy'] = {'%s %s %s', 'd', 'm', 'y'},								-- |df=dmy
	--		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},								-- |df=ymd
	--		},
	}


local function reformatter (date, pattern_idx, format_param, mon_len)
	if not in_array (pattern_idx, {'ymd', 'Mdy', 'Md-dy', 'dMy', 'yMd', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy', 'My-My', 'M-My', 'My'}) then
		return;																	-- not in this set of date format patterns then not a reformattable date
	end
	
	if 'ymd' == format_param and in_array (pattern_idx, {'ymd', 'Md-dy', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy', 'My-My', 'M-My', 'My'}) then
		return;																	-- ymd date ranges not supported at en.wiki; no point in reformatting ymd to ymd
	end

	if in_array (pattern_idx, {'My', 'M-My', 'My-My'}) then						-- these are not dmy/mdy so can't be 'reformatted' into either
		format_param = 'any';													-- so format-agnostic 
	end

																				-- yMd is not supported at en.wiki; if yMd is supported at your wiki, uncomment the next line
	--	if 'yMd' == format_param and in_array (pattern_idx, {'yMd', 'Md-dy', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy'}) then	-- these formats not convertable; yMd not supported at en.wiki
	-- if yMd is supported at your wiki, remove or comment-out the next line
	if 'yMd' == format_param then												-- yMd not supported at en.wiki
		return;																	-- not a reformattable date
	end
	
	local c1, c2, c3, c4, c5, c6, c7;											-- these hold the captures specified in patterns[pattern_idx][1]
	c1, c2, c3, c4, c5, c6, c7 = mw.ustring.match (date, patterns[pattern_idx][1]);	-- get the captures

	local t = {																	-- table that holds k/v pairs of date parts from the captures and patterns[pattern_idx][2..]
		[patterns[pattern_idx][2]] = c1;										-- at minimum there is always one capture with a matching indicator letter
		[patterns[pattern_idx][3] or 'x'] = c2;									-- patterns can have a variable number of captures; each capture requires an indicator letter;
		[patterns[pattern_idx][4] or 'x'] = c3;									-- where there is no capture, there is no indicator letter so n in patterns[pattern_idx][n] will be nil;
		[patterns[pattern_idx][5] or 'x'] = c4;									-- the 'x' here spoofs an indicator letter to prevent 'table index is nil' error
		[patterns[pattern_idx][6] or 'x'] = c5;
		[patterns[pattern_idx][7] or 'x'] = c6;
		[patterns[pattern_idx][8] or 'x'] = c7;
		};

	if t.a then																	-- if this date has an anchor year capture
		t.y = t.a;																-- use the anchor year capture when reassembling the date
	end

	if tonumber(t.m) then														-- if raw month is a number (converting from ymd)
		if 's' == mon_len then													-- if we are to use abbreviated month names
			t.m = cfg.date_names['inv_local_s'][tonumber(t.m)];					-- convert it to a month name
		else
			t.m = cfg.date_names['inv_local_l'][tonumber(t.m)];					-- convert it to a month name
		end
		t.d = t.d:gsub ('0(%d)', '%1');											-- strip leading '0' from day if present
	elseif 'ymd' == format_param then											-- when converting to ymd
		t.y = t.y:gsub ('%a', '');												-- strip CITREF disambiguator if present; anchor year already known so process can proceed
		if 1582 > tonumber (t.y) then											-- ymd format dates not allowed before 1582
			return;
		end
		t.m = string.format ('%02d', get_month_number (t.m));					-- make sure that month and day are two digits
		t.d = string.format ('%02d', t.d);
	elseif mon_len then															-- if mon_len is set to either 'short' or 'long'
		for _, mon in ipairs ({'m', 'm2'}) do									-- because there can be two month names, check both 
			if t[mon] then
				t[mon] = get_month_number (t[mon]);								-- get the month number for this month (is length agnostic)
				if 0 == t[mon] then return; end									-- seasons and named dates can't be converted
				t[mon] = (('s' == mon_len) and cfg.date_names['inv_local_s'][t[mon]]) or cfg.date_names['inv_local_l'][t[mon]];	-- fetch month name according to length
			end
		end
	end

	local new_date = string.format (re_formats[pattern_idx][format_param][1],	-- format string
		t[re_formats[pattern_idx][format_param][2]],							-- named captures from t{}
		t[re_formats[pattern_idx][format_param][3]],
		t[re_formats[pattern_idx][format_param][4]],
		t[re_formats[pattern_idx][format_param][5]],
		t[re_formats[pattern_idx][format_param][6]],
		t[re_formats[pattern_idx][format_param][7]],
		t[re_formats[pattern_idx][format_param][8]]
		);

	return new_date;
end


--[[-------------------------< R E F O R M A T _ D A T E S >--------------------------------------------------

Reformats existing dates into the format specified by format.

format is one of several manual keywords: dmy, dmy-all, mdy, mdy-all, ymd, ymd-all.  The -all version includes
access- and archive-dates; otherwise these dates are not reformatted.

This function allows automatic date formatting.  In ~/Configuration, the article source is searched for one of
the {{use xxx dates}} templates.  If found, xxx becomes the global date format as xxx-all.  If |cs1-dates= in
{{use xxx dates}} has legitimate value then that value determines how cs1|2 dates will be rendered.  Legitimate
values for |cs1-dates= are:
	l - all dates are rendered with long month names
	ls - publication dates use long month names; access-/archive-dates use abbreviated month names
	ly - publication dates use long month names; access-/archive-dates rendered in ymd format
	s - all dates are rendered with abbreviated (short) month names
	sy - publication dates use abbreviated month names; access-/archive-dates rendered in ymd format
	y - all dates are rendered in ymd format

the format argument for automatic date formatting will be the format specified by {{use xxx dates}} with the
value supplied by |cs1-dates so one of: xxx-l, xxx-ls, xxx-ly, xxx-s, xxx-sy, xxx-y, or simply xxx (|cs1-dates=
empty, omitted, or invalid) where xxx shall be either of dmy or mdy.

dates are extracted from date_parameters_list, reformatted (if appropriate), and then written back into the
list in the new format.  Dates in date_parameters_list are presumed here to be valid (no errors).  This function
returns true when a date has been reformatted, false else.  Actual reformatting is done by reformatter().

]]

local function reformat_dates (date_parameters_list, format)
	local all = false;															-- set to false to skip access- and archive-dates
	local len_p = 'l';															-- default publication date length shall be long
	local len_a = 'l';															-- default access-/archive-date length shall be long
	local result = false;
	local new_date;																
	
	if format:match('%a+%-all') then											-- manual df keyword; auto df keyword when length not specified in {{use xxx dates}}; 
		format = format:match('(%a+)%-all');									-- extract the format
		all = true;																-- all dates are long format dates because this keyword doesn't specify length
	elseif format:match('%a+%-[lsy][sy]?') then									-- auto df keywords; internal only
		all = true;																-- auto df applies to all dates; use length specified by capture len_p for all dates
		format, len_p, len_a = format:match('(%a+)%-([lsy])([sy]?)');			-- extract the format and length keywords
		if 'y' == len_p then													-- because allowed by MOS:DATEUNIFY (sort of) range dates and My dates not reformatted
			format = 'ymd';														-- override {{use xxx dates}}
		elseif (not is_set(len_a)) or (len_p == len_a) then						-- no access-/archive-date length specified or same length as publication dates then
			len_a = len_p;														-- in case len_a not set
		end
	end																			-- else only publication dates and they are long

	for param_name, param_val in pairs (date_parameters_list) do				-- for each date-holding parameter in the list
		if is_set (param_val.val) then											-- if the parameter has a value
			if not (not all and in_array (param_name, {'access-date', 'archive-date'})) then	-- skip access- or archive-date unless format is xxx-all; yeah, ugly; TODO: find a better way
				for pattern_idx, pattern in pairs (patterns) do
					if mw.ustring.match (param_val.val, pattern[1]) then
						if all and in_array (param_name, {'access-date', 'archive-date'}) then	-- if this date is an access- or archive-date
							new_date = reformatter (param_val.val, pattern_idx, (('y' == len_a) and 'ymd') or format, len_a);	-- choose ymd or dmy/mdy according to len_a setting
						else													-- all other dates
							new_date = reformatter (param_val.val, pattern_idx, format, len_p);
						end
						
						if new_date then										-- set when date was reformatted
							date_parameters_list[param_name].val = new_date;	-- update date in date list
							result = true;										-- and announce that changes have been made
						end
					end	-- if
				end		-- for
			end			-- if
		end				-- if
	end					-- for
return result;																	-- declare boolean result and done
end


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

Loops through the list of date-holding parameters and converts any hyphen to an ndash.  Not called if the cs1|2
template has any date errors.

Modifies the date_parameters_list and returns true if hyphens are replaced, else returns false.

]]

local function date_hyphen_to_dash (date_parameters_list)
	local result = false;
	local n;
	for param_name, param_val in pairs(date_parameters_list) do					-- for each date-holding parameter in the list
		if is_set (param_val.val) and
			not mw.ustring.match (param_val.val, patterns.ymd[1]) then			-- for those that are not ymd dates (ustring because here digits may not be Western)
				param_val.val, n = param_val.val:gsub ('%-', '–');				-- replace any hyphen with ndash
				if 0 ~= n then
					date_parameters_list[param_name].val = param_val.val;		-- update the list
					result = true;
				end
		end
	end
	return result;																-- so we know if any hyphens were replaced
end


--[[--------------------------< E D T F _ T R A N S F O R M >--------------------------------------------------

Loops through the list of date-holding parameters and converts any EDTF formatted dates to MOS compliant dates.
Only YYY-MM-XX supported at this time. Not called if the cs1|2 template has any date errors.

must be done before reformat_dates() and before date_hyphen_to_dash()

Modifies the date_parameters_list and returns true if transformation is performed, else returns false.

]]

local function edtf_transform (date_parameters_list)
	local result = false;
	local source_date = {};

	for param_name, param_val in pairs(date_parameters_list) do					-- for each date-holding parameter in the list
		if is_set(param_val.val) and param_val.val:match (patterns.ymx[1]) then	-- if parameter is set and is an EDTF dates
			source_date.year, source_date.month = param_val.val:match (patterns.ymx[1]);	-- get year and month number
			date_parameters_list[param_name].val = mw.text.trim ("tháng " .. source_date.month .. " năm " .. source_date.year);
			result = true;
		end
	end
	return result;																-- so we know if a transform was done
end


--[[-------------------------< D A T E _ N A M E _ X L A T E >------------------------------------------------

Attempts to translate English month names to local-language month names using names supplied by MediaWiki's
date parser function.  This is simple name-for-name replacement and may not work for all languages.

if xlat_dig is true, this function will also translate Western (English) digits to the local language's digits.
This will also translate ymd dates.

]]

local function date_name_xlate (date_parameters_list, xlt_dig)
	local xlate;
	local mode;																	-- long or short month names
	local modified = false;
	local date;
	
	for param_name, param_val in pairs(date_parameters_list) do					-- for each date-holding parameter in the list
		if is_set(param_val.val) then											-- if the parameter has a value
			date = param_val.val;
			for month in mw.ustring.gmatch (date, '%a+') do						-- iterate through all dates in the date (single date or date range)
				if cfg.date_names.en.long[month] then
					mode = 'F';													-- English name is long so use long local name
				elseif cfg.date_names.en.short[month] then
					mode = 'M';													-- English name is short so use short local name
				else
					mode = nil;													-- not an English month name; could be local language month name or an English season name
				end
		
				if mode then													-- might be a season
					xlate = lang_object:formatDate(mode, '1' .. month);			-- translate the month name to this local language
					date = mw.ustring.gsub (date, month, xlate);				-- replace the English with the translation
					date_parameters_list[param_name].val = date;				-- save the translated date
					modified = true;
				end
			end

			if xlt_dig then														-- shall we also translate digits?
				date = date:gsub ('%d', cfg.date_names.xlate_digits);			-- translate digits from Western to 'local digits'
				date_parameters_list[param_name].val = date;					-- save the translated date
				modified = true;
			end
		end
	end
	
	return modified;
end


--[[--------------------------< S E T _ S E L E C T E D _ M O D U L E S >--------------------------------------

Sets local imported functions table to same (live or sandbox) as that used by the other modules.

]]

local function set_selected_modules (cfg_table_ptr, utilities_page_ptr)
	add_prop_cat = utilities_page_ptr.add_prop_cat ;							-- import functions from selected Module:Citation/CS1/Utilities module
	is_set = utilities_page_ptr.is_set;
	in_array = utilities_page_ptr.in_array;
	set_message = utilities_page_ptr.set_message;
	substitute = utilities_page_ptr.substitute;
	wrap_style = utilities_page_ptr.wrap_style;

	cfg = cfg_table_ptr;														-- import tables from selected Module:Citation/CS1/Configuration
end


--[[--------------------------< A R C H I V E _ D A T E _ C H E C K >------------------------------------------

Compare value in |archive-date= with the timestamp in Wayback machine urls.  Emits an error message with suggested
date from the |archive-url= timestamp in an appropriate format when the value in |archive-date= does not match
the timestamp.

this function never called when any date in a cs1|2 template has errors

error message suggests new |archive-date= value in an appropriate format specified by <df>.  <df> is either 
|df= or cfg.global_df in that order.  If <df> is nil, suggested date has format from |archive-date=.  There is
a caveat: when |df=dmy or |df=mdy, the reformatter leaves |access-date= and |archive-date= formats as they are.
The error message suggested date is passed to the formatter as YYYY-MM-DD so when |df=dmy or |df=mdy, the format
is not changed.

]]

local function archive_date_check (archive_date, archive_url_timestamp, df)
	local archive_date_format = 'dmy-y';										-- holds the date format of date in |archive-date; default to ymd; 'dmy' used here to spoof reformat_dates() 
	
	for _, v_t in ipairs ({{'dMy', 'dmy-all'}, {'Mdy', 'mdy-all'}}) do			-- is |archive-date= format dmy or mdy?
		if archive_date:match (patterns[v_t[1]][1]) then						-- does the pattern match?
			archive_date_format = cfg.keywords_xlate[v_t[2]];					-- get appropriate |df= supported keyword from the i18n translator table
			break;
		end
	end
	
	local dates_t = {};
	dates_t['archive-date'] = {val=archive_date, name=''};						-- setup to call reformat_dates(); never called when errors so <name> unset as not needed
	reformat_dates (dates_t, 'dmy-y');											-- reformat |archive-date= to ymd; 'dmy' used here to spoof reformat_dates()
	local archive_url_date = archive_url_timestamp:gsub ('(%d%d%d%d)(%d%d)(%d%d)%d*', '%1-%2-%3');	-- make ymd format date from timestamp

	if dates_t['archive-date'].val == archive_url_date then						-- are the two dates the same
		return;																	-- yes, done
	else
		dates_t['archive-date'] = {val=archive_url_date, name=''};				-- setup to call reformat_dates() with the timestamp date
		reformat_dates (dates_t, df or archive_date_format);					-- reformat timestamp to format specified by <df> or format used in |archive-date= 
		archive_url_date = dates_t['archive-date'].val;
		set_message ('archive_date không khớp với URL lưu trữ', archive_url_date);		-- emit an error message
	end
end

--[[--------------------------< E X P O R T E D   F U N C T I O N S >------------------------------------------
]]

return {																		-- return exported functions
	archive_date_check = archive_date_check,
	dates = dates,
	year_date_check = year_date_check,
	reformat_dates = reformat_dates,
	date_hyphen_to_dash = date_hyphen_to_dash,
	date_name_xlate = date_name_xlate,
	edtf_transform = edtf_transform,
	set_selected_modules = set_selected_modules
	}