มอดูล:Citation/CS1/Date validation

------------------------------------------------------------------
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
------------------------------------------------------------
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()
--=-----------------------------------------------------------------
returns true if:
	Wikipedia start date ----------------------------------------------
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'.longmonth or cfg.date_names'local'.shortmonth or	-- look for local names first
			cfg.date_names'en'.longmonth or	cfg.date_names'en'.shortmonth or		-- failing that, look for English names
			0;																				-- not a recognized month name
end
--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'.seasonseason or							-- look for local names first
			cfg.date_names'en'.seasonseason or								-- failing that, look for English names
			0;																	-- not a recognized season name
end
--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'.quarterquarter or							-- look for local names first
			cfg.date_names'en'.quarterquarter or							-- failing that, look for English names
			0;																	-- not a recognized quarter name
end
--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'.namedname or								-- look for local names dates first
			cfg.date_names'en'.namedname or									-- failing that, look for English names
			0;																	-- not a recognized named date
end
--pmc-embargo-date=: years more than two years in the future are not acceptable
local function is_valid_year (year, param)
	if not is_set (year_limit) then
		year_limit = tonumber(os.date("%Y"))+544;									-- global variable so we only have to fetch it once
	end
	year = tonumber (year) or lang_object:parseFormattedNumber (year);			-- convert to number for the comparison;
	
	if 'pmc-embargo-date' == param then											-- special case for |pmc-embargo-date=
		return year and (year ----------------------------------------------------
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, param)
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, param) then										-- no farther into the future than next year except |pmc-embargo-date= no more than two years in the future
		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_monthmonth;
	end
	if tonumber (day) > month_length then
		return false;
	end
	return true;
end
------------------------------------------------------
Months in a range are expected to have the same style: Jan–Mar or October–December but not February–Mar or Jul–August. 
This function looks in cfg.date_names{} to see if both month names are listed in the long subtable or both are
listed in the short subtable.  When both have the same style (both are listed in the same table), returns true; false else
local function is_valid_month_range_style (month1, month2)
	if (cfg.date_names.en.longmonth1 and cfg.date_names.en.longmonth2) or					-- are both English names listed in the long subtable?
		(cfg.date_names.en.shortmonth1 and cfg.date_names.en.shortmonth2) or				-- are both English names listed in the short subtable?
		(cfg.date_names'local'.longmonth1 and cfg.date_names'local'.longmonth2) or		-- are both local names listed in the long subtable?
		(cfg.date_names'local'.shortmonth1 and cfg.date_names'local'.shortmonth2) then	-- are both local names listed in the short subtable?
			return true;
	end
	return false;																-- names are mixed
end
----------------------------------------------------
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 ------------------------------------------------
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= 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)) 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))) 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 --------------------------------------------------------------
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'},
																				-- 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'},
																				-- 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?)$', 'd', 'm', 'd2', 'm2', 'a', 'y'},
																				-- month initial month-day-range: month day – month day, year;  uses spaced endash
	'Md-Mdy' = {'^(%D-) +(1-9%d?) +%-– +(%D-) +(1-9%d?), +((%d%d%d%d)%a?)$','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?)$', 'd', 'm', 'y', 'd2', 'm2', 'a', 'y2'},
																				-- month initial month-day-year-range: month day, year – month day, year;  uses spaced endash
	'Mdy-Mdy' = {'^(%D-) +(1-9%d?), +(%d%d%d%d) +%-– +(%D-) +(1-9%d?), +((%d%d%d%d)%a?)$', '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?)$', 'm', 'y', 'm2', 'a', 'y2'},
																				-- month/season range year; months separated by endash
	'M-My' = {'^(%D-)%-–(%D-) +((%d%d%d%d)%a?)$', '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?)$', 'm', 'a', 'y'},					-- this way because endash is a member of %D; %D- will match January–March 2019 when it shouldn't
																				-- these date formats cannot be converted
	'Sy4-y2' = {'^(%D-) +((%d%d)%d%d)%-–((%d%d)%a?)$'},						-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
	'Sy-y' = {'^(%D-) +(%d%d%d%d)%-–((%d%d%d%d)%a?)$'},						-- special case Winter/Summer year-year; year separated with unspaced endash
	'y-y' = {'^(%d%d%d%d?)%-–((%d%d%d%d?)%a?)$'},							-- 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?)$'},								-- year range: YYYY–YY; separated by unspaced endash
	'y' = {'^((%d%d%d%d?)%a?)$'},												-- year; here accept either YYY or YYYY
	}
--pmc-embargo-date= does not hold a single date.
local function is_valid_embargo_date (v)
	if v:match (patterns'ymd'1) or											-- ymd
		v:match (patterns'Mdy'1) or											-- dmy
		v:match (patterns'dMy'1) 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
--------------------------------------------------------------------------------------
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;
	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 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 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) then				-- day-initial: day month year
		day, month, anchor_year, year = mw.ustring.match(date_string, patterns'dMy'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
-- 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) 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 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) 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 (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) 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 tonumber(year2)  can only be winter or summer; also for metadata
		if (month ~= cfg.date_names'en'.season'Winter') and (month ~= cfg.date_names'en'.season'Summer') then
			return false;														-- not Summer or Winter; abandon
		end
		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
	elseif mw.ustring.match(date_string, patterns'My-My'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);
		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) then				-- month/season range year; months separated by endash 
		month, month2, anchor_year, year = mw.ustring.match(date_string, patterns'M-My'1);
		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) then				-- month/season/quarter/proper-name year
		month, anchor_year, year = mw.ustring.match(date_string, patterns'My'1);
		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, param);						--  for |pmc-embargo-date=
	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	
--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  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 date; 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
--year=YYYYx)
the numeric value in  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
------------------------------------------------------------------------------------
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  patternspattern_idx1
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_formatpattern_idxformat_param1 using values taken from t{} according
to the capture identifier letters specified by patternspattern_idxformat_paramn where n is 2..
local re_formats = {
	'ymd' = {																	-- date format is ymd; reformat to:
		'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; not supported at en.wiki
		},
	'Mdy' = {																	-- date format is Mdy; reformat to:
		'mdy' = {'%s %s, %s', 'm', 'd', 'y'},									-- for long/short reformatting
		'dmy' = {'%s %s %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 %s', 'd', 'm', 'y'},									-- for long/short reformatting
		'mdy' = {'%s %s, %s', 'm', 'd', 'y'},									-- |df=mdy
		'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, %s', 'm', 'd', 'd2', 'y'},						-- for long/short reformatting
		'dmy' = {'%s–%s %s %s', 'd', 'd2', 'm', 'y'},							-- |df=dmy -> d-dMy 
		},
	'd-dMy' = {																-- date format is d-d>y; reformat to:
		'dmy' = {'%s–%s %s %s', 'd', 'd2', 'm', 'y'},							-- for long/short reformatting
		'mdy' = {'%s %s–%s, %s', 'm', 'd', 'd2', 'y'},						-- |df=mdy -> Md-dy 
		},
	'dM-dMy' = {																-- date format is dM-dMy; reformat to:
		'dmy' = {'%s %s – %s %s %s', 'd', 'm', 'd2', 'm2', 'y'},				-- for long/short reformatting
		'mdy' = {'%s %s – %s %s, %s', 'm', 'd', 'm2', 'd2', 'y'},				-- |df=mdy -> Md-Mdy 
		},
	'Md-Mdy' = {																-- date format is Md-Mdy; reformat to:
		'mdy' = {'%s %s – %s %s, %s', 'm', 'd',  'm2', 'd2', 'y'},			-- for long/short reformatting
		'dmy' = {'%s %s – %s %s %s', 'd', 'm', 'd2', 'm2', 'y'},				-- |df=dmy -> dM-dMy 
		},
	'dMy-dMy' = {																-- date format is dMy-dMy; reformat to:
		'dmy' = {'%s %s %s – %s %s %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- for long/short reformatting
		'mdy' = {'%s %s, %s – %s %s, %s', 'm', 'd', 'y', 'm2', 'd2', 'y2'},	-- |df=mdy -> Mdy-Mdy 
		},
	'Mdy-Mdy' = {																-- date format is Mdy-Mdy; reformat to:
		'mdy' = {'%s %s, %s – %s %s, %s', 'm', 'd', 'y', 'm2', 'd2', 'y2'},	-- for long/short reformatting
		'dmy' = {'%s %s %s – %s %s %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- |df=dmy -> dMy-dMy 
		},
	'My-My' = {																-- these for long/short reformatting
		'any' = {'%s %s – %s %s', 'm', 'y', 'm2', 'y2'},						-- dmy/mdy agnostic
		},
	'M-My' = {																-- these for long/short reformatting
		'any' = {'%s–%s %s', 'm', 'm2', 'y'},									-- dmy/mdy agnostic
		},
	'My' = {																	-- these for long/short reformatting
		'any' = {'%s %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; when 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' == format_param then												-- yMd not supported at en.wiki; when yMd is supported at your wiki, remove or comment-out this line
		return;																	-- not a reformattable date
	end
	
	local c1, c2, c3, c4, c5, c6, c7;											-- these hold the captures specified in patternspattern_idx1
	c1, c2, c3, c4, c5, c6, c7 = mw.ustring.match (date, patternspattern_idx1);	-- get the captures
	local t = {																	-- table that holds k/v pairs of date parts from the captures and patternspattern_idx2..
		patternspattern_idx2 = c1;										-- at minimum there is always one capture with a matching indicator letter
		patternspattern_idx3 or 'x' = c2;									-- patterns can have a variable number of captures; each capture requires an indicator letter;
		patternspattern_idx4 or 'x' = c3;									-- where there is no capture, there is no indicator letter so n in patternspattern_idxn will be nil;
		patternspattern_idx5 or 'x' = c4;									-- the 'x' here spoofs an indicator letter to prevent 'table index is nil' error
		patternspattern_idx6 or 'x' = c5;
		patternspattern_idx7 or 'x' = c6;
		patternspattern_idx8 or 'x' = c7;
		};
	if t.a then																	-- if this date has an anchor year capture (all convertable date formats except ymd)
		if t.y2 then															-- for year range date formats														
			t.y2 = t.a;															-- use the anchor year capture when reassembling the date
		else																	-- here for single date formats (except ymd)
			t.y = t.a;															-- use the anchor year capture when reassembling the date
		end
	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_short'tonumber(t.m);					-- convert it to a month name
		else
			t.m = cfg.date_names'inv_local_long'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; TODO: maint message?
		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 tmon then
				tmon = get_month_number (tmon);								-- get the month number for this month (is length agnostic)
				if 0 == tmon then return; end									-- seasons and named dates can't be converted
				tmon = (('s' == mon_len) and cfg.date_names'inv_local_short'tmon) or cfg.date_names'inv_local_long'tmon;	-- fetch month name according to length
			end
		end
	end
	local new_date = string.format (re_formatspattern_idxformat_param1,	-- format string
		tre_formatspattern_idxformat_param2,							-- named captures from t{}
		tre_formatspattern_idxformat_param3,
		tre_formatspattern_idxformat_param4,
		tre_formatspattern_idxformat_param5,
		tre_formatspattern_idxformat_param6,
		tre_formatspattern_idxformat_param7,
		tre_formatspattern_idxformat_param8
		);
	return new_date;
end
--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 ; 
		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+%-lsysy?') 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 
		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, pattern1) 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_listparam_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
--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.ymd1) 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_listparam_name.val = param_val.val;		-- update the list
					result = true;
				end
		end
	end
	return result;																-- so we know if any hyphens were replaced
end
---------------------------------------------------------------------------
Attempts to translate English date names to local-language date 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;
	
	local sources_t = {
		{cfg.date_names.en.long, cfg.date_names.inv_local_long},				-- for translating long English month names to long local month names
		{cfg.date_names.en.short, cfg.date_names.inv_local_short},				-- short month names
		{cfg.date_names.en.quarter, cfg.date_names.inv_local_quarter},			-- quarter date names
		{cfg.date_names.en.season, cfg.date_names.inv_local_season},			-- season date nam
		{cfg.date_names.en.named, cfg.date_names.inv_local_named},				-- named dates
		}
	local function is_xlateable (month)											-- local function to get local date name that replaces existing English-language date name
		for _, date_names_t in ipairs (sources_t) do							-- for each sequence table in date_names_t
			if date_names_t1month then										-- if date name is English month (long or short), quarter, season or named and
				if date_names_t2date_names_t1month then					-- if there is a matching local date name
					return date_names_t2date_names_t1month;				-- return the local date name
				end
			end
		end
	end
	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 date names in the date (single date or date range)
				month = mw.text.trim (month);									-- this because quarterly dates contain whitespace
				xlate = is_xlateable (month);									-- get translate ; returns translation or nil
				
--				if cfg.date_names.en.longmonth then							-- long month dates
--					if cfg.date_names.inv_local_longcfg.date_names.en.longmonth then
--						xlate = cfg.date_names.inv_local_longcfg.date_names.en.longmonth;
--					end
----					mode = 'F';													-- English name is long so use long local name
--				elseif cfg.date_names.en.shortmonth then						-- short month dates
--					if cfg.date_names.inv_local_shortcfg.date_names.en.shortmonth then
--						xlate = cfg.date_names.inv_local_shortcfg.date_names.en.shortmonth;
--					end
----					mode = 'M';													-- English name is short so use short local name
--				elseif cfg.date_names.en.quartermonth then					-- quarter dates
--					if cfg.date_names.inv_local_quartercfg.date_names.en.quartermonth then
--						xlate = cfg.date_names.inv_local_quartercfg.date_names.en.quartermonth;
--					end
--				elseif cfg.date_names.en.seasonmonth then						-- season dates
--					if cfg.date_names.inv_local_seasoncfg.date_names.en.seasonmonth then
--						xlate = cfg.date_names.inv_local_seasoncfg.date_names.en.seasonmonth;
--					end
--				elseif cfg.date_names.en.namedmonth then						-- named dates
--					if cfg.date_names.inv_local_namedcfg.date_names.en.namedmonth then
--						xlate = cfg.date_names.inv_local_namedcfg.date_names.en.namedmonth;
--					end
--				else
--					xlate=nil;													-- not an English month name; could be local language month name
----					mode = nil;													-- not an English month name; could be local language month name or an English season name
--				end
				if xlate then		
--				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_listparam_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_listparam_name.val = date;					-- save the translated date
				modified = true;
			end
		end
	end
	
	return modified;
end
------------------------------------------------------------------
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
----------------------------------------------------------------------
return {																		-- return exported functions
	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,
	set_selected_modules = set_selected_modules
	}