Module:Citation/CS1/Date validation

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    < Module:Citation/CS1
    Revision as of 13:06, 16 January 2016 by m>Trappist the monk (Synch from sandbox;)

    Documentation for this module may be created at Module:Citation/CS1/Date validation/doc

    
    local p = {}
    
    
    --[[--------------------------< F O R W A R D   D E C L A R A T I O N S >--------------------------------------
    ]]
    
    local is_set, in_array;																	-- imported function from selected Module:Citation/CS1/Utilities
    
    
    --[[--------------------------< 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 |accessdate= 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
    
    ]]
    
    local function is_valid_accessdate (accessdate)
    	local lang = mw.getContentLanguage();
    	local good1, good2;
    	local access_ts, tomorrow_ts;												-- to hold unix time stamps representing the dates
    		
    	good1, access_ts = pcall( lang.formatDate, lang, 'U', accessdate );			-- convert accessdate value to unix timesatmp 
    	good2, tomorrow_ts = pcall( lang.formatDate, lang, 'U', 'today + 2 days' );	-- today midnight + 2 days is one second more than all day tomorrow
    	
    	if good1 and good2 then
    		access_ts = tonumber (access_ts);										-- convert to numbers for the comparison
    		tomorrow_ts = tonumber (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
    
    --[[--------------------------< 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)
    local long_months = {['January']=1, ['February']=2, ['March']=3, ['April']=4, ['May']=5, ['June']=6, ['July']=7, ['August']=8, ['September']=9, ['October']=10, ['November']=11, ['December']=12};
    local short_months = {['Jan']=1, ['Feb']=2, ['Mar']=3, ['Apr']=4, ['May']=5, ['Jun']=6, ['Jul']=7, ['Aug']=8, ['Sep']=9, ['Oct']=10, ['Nov']=11, ['Dec']=12};
    local temp;
    	temp=long_months[month];
    	if temp then return temp; end				-- if month is the long-form name
    	temp=short_months[month];
    	if temp then return temp; end				-- if month is the short-form name
    	return 0;									-- misspelled, improper case, or not a 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: 1 for Winter, etc.  Capitalization and spelling must be correct. If not a valid season, returns 0
    
    ]]
    
    local function get_season_number (season)
    local season_list = {['Winter']=21, ['Spring']=22, ['Summer']=23, ['Fall']=24, ['Autumn']=24};	-- make sure these numbers do not overlap month numbers
    local temp;
    	temp=season_list[season];
    	if temp then return temp; end												-- if season is a valid name return its number
    	return 0;																	-- misspelled, improper case, or not a season name
    end
    
    --[[--------------------------< I S _ P R O P E R _ N A M E >--------------------------------------------------
    
    returns a non-zero number if date contains a recognized proper name.  Capitalization and spelling must be correct.
    
    ]]
    
    local function is_proper_name (name)
    local name_list = {['Christmas']=31}
    local temp;
    	temp=name_list[name];
    	if temp then return temp; end				-- if name is a valid name return its number
    	return 0;									-- misspelled, improper case, or not a proper name
    end
    
    --[[--------------------------< I S _ V A L I D _ M O N T H _ O R _ S E A S O N >------------------------------
    
    --returns true if month or season is valid (properly spelled, capitalized, abbreviated)
    
    ]]
    
    local function is_valid_month_or_season (month_season)
    	if 0 == get_month_number (month_season) then		-- if month text isn't one of the twelve months, might be a season
    		if 0 == get_season_number (month_season) then	-- not a month, is it a season?
    			return false;								-- return false not a month or one of the five seasons
    		end
    	end
    	return true;
    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 year_limit;
    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
    	return tonumber(year) <= year_limit;				-- false if year is in the future more than one year
    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
    				month_length = 29;
    			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();
    	if len1 == len2 then
    		return true;															-- both months are short form so return true
    	elseif 'May' == month1 or 'May'== month2 then
    		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.
    
    Similarly, seasons are also left to right, earliest to latest in time.  There is an oddity with seasons: winter is assigned a value of 1, spring 2, ...,
    fall and autumn 4.  Because winter can follow fall/autumn at the end of a calender year, a special test is made to see if |date=Fall-Winter yyyy (4-1) is the date.
    
    ]]
    
    local function is_valid_month_season_range(range_start, range_end)
    	local range_start_number = get_month_number (range_start);
    	
    	if 0 == range_start_number then												-- is this a month range?
    		local range_start_number = get_season_number (range_start);				-- not a month; is it a season? get start season number
    		local range_end_number = get_season_number (range_end);					-- get end season number
    
    		if 0 ~= range_start_number then											-- is start of range a season?
    			if range_start_number < range_end_number then						-- range_start is a season
    				return true;													-- return true when range_end is also a season and follows start season; else false
    			end
    			if 24 == range_start_number and 21 == range_end_number then			-- special case when season range is Fall-Winter or Autumn-Winter
    				return true;
    			end
    		end
    		return false;		-- range_start is not a month or a season; or range_start is a season and range_end is not; or improper season sequence
    	end
    
    	local range_end_number = get_month_number (range_end);						-- get end month number
    	if range_start_number < range_end_number then								-- range_start is a month; does range_start precede range_end?
    		if is_valid_month_range_style (range_start, range_end) then				-- do months have the same style?
    			return true;														-- proper order and same style
    		end
    	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; 31– proper name dates
    	day, day2 –  0 if not provided, 1-31 for days
    	
    the output table receives:
    	rftdate:	an IS8601 formatted date
    	rftchron:	a free-form version of the date, usually without year which is in rftdate (season ranges and propername dates)
    	rftssn:		one of four season keywords: winter, spring, summer, fall (lowercase)
    
    ]]
    
    local function make_COinS_date (input, tCOinS_date)
    	local date;																	-- one date or first date in a range
    	local date2 = '';															-- end of range date
    	
    	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 propername date
    			local season = {[21]='winter', [22]='spring', [23]='summer', [24]='fall', [31]='Christmas'};	-- seasons lowercase, no autumn; proper names use title case
    			if 0 == input.month2 then											-- single season date
    				if 30 <tonumber(input.month) then
    					tCOinS_date.rftchron = season[input.month];					-- proper name dates
    				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
    
    
    --[[--------------------------< 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 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, accessdate, embargo, archivedate, etc.)
    
    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, 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("^%d%d%d%d%-%d%d%-%d%d$") then										-- year-initial numerical year month day format
    		year, month, day=string.match(date_string, "(%d%d%d%d)%-(%d%d)%-(%d%d)");
    		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("^%a+ +[1-9]%d?, +[1-9]%d%d%d%a?$") then						-- month-initial: month day, year
    		month, day, anchor_year, year=string.match(date_string, "(%a+)%s*(%d%d?),%s*((%d%d%d%d)%a?)");
    		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 date_string:match("^%a+ +[1-9]%d?–[1-9]%d?, +[1-9]%d%d%d%a?$") then				-- month-initial day range: month day–day, year; days are separated by endash
    		month, day, day2, anchor_year, year=string.match(date_string, "(%a+) +(%d%d?)–(%d%d?), +((%d%d%d%d)%a?)");
    		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 date_string:match("^[1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then						-- day-initial: day month year
    		day, month, anchor_year, year=string.match(date_string, "(%d%d*)%s*(%a+)%s*((%d%d%d%d)%a?)");
    		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 date_string:match("^[1-9]%d?–[1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then				-- day-range-initial: day–day month year; days are separated by endash
    		day, day2, month, anchor_year, year=string.match(date_string, "(%d%d?)–(%d%d?) +(%a+) +((%d%d%d%d)%a?)");
    		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 date_string:match("^[1-9]%d? +%a+ – [1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then		-- day initial month-day-range: day month - day month year; uses spaced endash
    		day, month, day2, month2, anchor_year, year=date_string:match("(%d%d?) +(%a+) – (%d%d?) +(%a+) +((%d%d%d%d)%a?)");
    		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 date_string:match("^%a+ +[1-9]%d? – %a+ +[1-9]%d?, +[1-9]%d%d%d?%a?$") then		-- month initial month-day-range: month day – month day, year;  uses spaced endash
    		month, day, month2, day2, anchor_year, year=date_string:match("(%a+) +(%d%d?) – (%a+) +(%d%d?), +((%d%d%d%d)%a?)");
    		if (not is_valid_month_season_range(month, month2)) 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 date_string:match("^[1-9]%d? +%a+ +[1-9]%d%d%d – [1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then		-- day initial month-day-year-range: day month year - day month year; uses spaced endash
    		day, month, year, day2, month2, anchor_year, year2=date_string:match("(%d%d?) +(%a+) +(%d%d%d%d?) – (%d%d?) +(%a+) +((%d%d%d%d?)%a?)");
    		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);
    
    	elseif date_string:match("^%a+ +[1-9]%d?, +[1-9]%d%d%d – %a+ +[1-9]%d?, +[1-9]%d%d%d%a?$") then		-- month initial month-day-year-range: month day, year – month day, year;  uses spaced endash
    		month, day, year, month2, day2, anchor_year, year2=date_string:match("(%a+) +(%d%d?), +(%d%d%d%d) – (%a+) +(%d%d?), +((%d%d%d%d)%a?)");
    		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);
    
    	elseif date_string:match("^%a+ +[1-9]%d%d%d–%d%d%a?$") then								-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
    		local century;
    		month, year, century, anchor_year, year2=date_string:match("(%a+) +((%d%d)%d%d)–((%d%d)%a?)");
    		if 'Winter' ~= month and 'Summer' ~= month 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);
    
    	elseif date_string:match("^%a+ +[1-9]%d%d%d–[1-9]%d%d%d%a?$") then						-- special case Winter/Summer year-year; year separated with unspaced endash
    		month, year, anchor_year, year2=date_string:match("(%a+) +(%d%d%d%d)–((%d%d%d%d)%a?)");
    		if 'Winter' ~= month and 'Summer' ~= month 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);													-- for metadata
    
    	elseif date_string:match("^%a+ +[1-9]%d%d%d% – %a+ +[1-9]%d%d%d%a?$") then				-- month/season year - month/season year; separated by spaced endash
    		month, year, month2, anchor_year, year2=date_string:match("(%a+) +(%d%d%d%d) – (%a+) +((%d%d%d%d)%a?)");
    		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) and 0 ~= get_season_number(month2) then		-- both must be or season year, not mixed
    			month = get_season_number(month);
    			month2 = get_season_number(month2);
    		else
    			 return false;
    		end
    
    	elseif date_string:match ("^%a+–%a+ +[1-9]%d%d%d%a?$") then					-- month/season range year; months separated by endash 
    		month, month2, anchor_year, year=date_string:match ("(%a+)–(%a+)%s*((%d%d%d%d)%a?)");
    		if (not is_valid_month_season_range(month, month2)) 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);
    		else
    			month = get_season_number(month);
    			month2 = get_season_number(month2);
    		end
    		year2=year;
    		
    	elseif date_string:match("^%a+ +%d%d%d%d%a?$") then							-- month/season year or proper-name year
    		month, anchor_year, year=date_string:match("(%a+)%s*((%d%d%d%d)%a?)");
    		if not is_valid_year(year) then return false; end
    		if not is_valid_month_or_season (month) and 0 == is_proper_name (month) 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);
    		elseif 0 ~= get_season_number(month) then
    			month = get_season_number(month);
    		else
    			month = is_proper_name (month);										-- must be proper name; not supported in COinS
    		end
    
    	elseif date_string:match("^[1-9]%d%d%d?–[1-9]%d%d%d?%a?$") then				-- Year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
    		year, anchor_year, year2=date_string:match("(%d%d%d%d?)–((%d%d%d%d?)%a?)");
    		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 date_string:match("^[1-9]%d%d%d–%d%d%a?$") then						-- Year range: YYYY–YY; separated by unspaced endash
    		local century;
    		year, century, anchor_year, year2=date_string:match("((%d%d)%d%d)–((%d%d)%a?)");
    		anchor_year=year..'–'..anchor_year;										-- assemble anchor year from both years
    		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 date_string:match("^[1-9]%d%d%d?%a?$") then							-- year; here accept either YYY or YYYY
    		anchor_year, year=date_string:match("((%d%d%d%d?)%a?)");
    		if false == is_valid_year(year) then
    			return false;
    		end
    
    	else
    		return false;															-- date format not one of the MOS:DATE approved formats
    	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,
    a single error message is created as the dates are tested.
    
    ]]
    
    local function dates(date_parameters_list, tCOinS_date)
    	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 error_message = "";
    	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) then														-- if the parameter has a value
    			if v:match("^c%. [1-9]%d%d%d?%a?$") then							-- special case for c. year or with or without CITEREF disambiguator - only |date= and |year=
    				local year = v:match("c%. ([1-9]%d%d%d?)%a?");					-- get the year portion so it can be tested
    				if 'date'==k then
    					anchor_year, COinS_date = v:match("((c%. [1-9]%d%d%d?)%a?)");	-- anchor year and COinS_date only from |date= parameter
    					good_date = is_valid_year(year);
    				elseif 'year'==k then
    					good_date = is_valid_year(year);
    				end
    			elseif 'date'==k then												-- if the parameter is |date=
    				if v:match("^n%.d%.%a?") then									-- if |date=n.d. with or without a CITEREF disambiguator
    					good_date, anchor_year, COinS_date = true, v:match("((n%.d%.)%a?)");	--"n.d."; no error when date parameter is set to no date
    				elseif v:match("^nd%a?$") then									-- if |date=nd with or without a CITEREF disambiguator
    					good_date, anchor_year, COinS_date = true, v:match("((nd)%a?)");	--"nd";	no error when date parameter is set to no date
    				else
    					good_date, anchor_year, COinS_date = check_date (v, tCOinS_date);	-- go test the date
    				end
    			elseif 'access-date'==k then										-- if the parameter is |date=
    				good_date = check_date (v);										-- go test the date
    				if true == good_date then										-- if the date is a valid date
    					good_date = is_valid_accessdate (v);						-- is Wikipedia start date < accessdate < tomorrow's date?
    				end
    			else																-- any other date-holding parameter
    				good_date = check_date (v);										-- go test the date
    			end
    			if false==good_date then											-- assemble one error message so we don't add the tracking category multiple times
    				if is_set(error_message) then									-- once we've added the first portion of the error message ...
    					error_message=error_message .. ", ";						-- ... add a comma space separator
    				end
    				error_message=error_message .. "&#124;" .. k .. "=";			-- add the failed parameter
    			end
    		end
    	end
    	return anchor_year, error_message;											-- 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 returns a 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)
    
    ]]
    
    local function year_date_check (year_string, date_string)
    	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 date_string:match ("%d%d%d%d–%d%d") then								-- YYYY-YY date ranges
    		local century;
    		date1, century, date2 = date_string:match ("((%d%d)%d%d)[%s%-–]+(%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
    		result = 0;																-- no recognizable year in date
    	end
    	return result;
    end
    
    
    --[[-------------------------< R E F O R M A T   T A B L E S >------------------------------------------------
    
    These table are used exclusively for reformatting dates
    
    ]]
    
    local source_patterns = {						-- this table holds patterns that match allowed date formats used to extract date components
    	['dmy'] = '(%d%d?)%s+(%a+)%s+(%d%d%d%d)',
    	['mdy'] = '(%a+)%s+(%d%d?),%s+(%d%d%d%d)',
    	['ymd'] = '(%d%d%d%d)%-(%d%d)-(%d%d)',
    	}
    
    local short_formats = {							-- this table holds format strings used by os.date() for short month names
    	['dmy'] = '%e %b %Y',
    	['mdy'] = '%b %e, %Y',
    	['ymd'] = '%F',
    	}
    
    local long_formats = {							-- this table holds format strings used by os.date() for long month names
    	['dmy'] = '%e %B %Y',
    	['mdy'] = '%B %e, %Y',
    	['ymd'] = '%F',
    	}
    
    
    --[[-------------------------< G E T _ D M Y _ D A T E _ P A R T S >------------------------------------------
    
    extracts year, month and day from DMY formatted date, places them in the source_date table, and returns.
    
    ]]
    
    local function get_dmy_date_parts (date, source_date)
    	source_date.day, source_date.month, source_date.year = date:match (source_patterns['dmy']);	-- get date components as strings
    	source_date.month = get_month_number (source_date.month);					-- get month number
    end
    
    
    --[[-------------------------< G E T _ M D Y _ D A T E _ P A R T S >------------------------------------------
    
    extracts year, month and day from MDY formatted date, places them in the source_date table, and returns.
    
    ]]
    
    local function get_mdy_date_parts (date, source_date)
    	source_date.month, source_date.day, source_date.year = date:match (source_patterns['mdy']);	-- get date components as strings
    	source_date.month = get_month_number (source_date.month);					-- get month number
    end
    
    
    --[[-------------------------< G E T _ Y M D _ D A T E _ P A R T S >------------------------------------------
    
    extracts year, month and day from YMD formatted date, places them in the source_date table, and returns.
    
    ]]
    
    local function get_ymd_date_parts (date, source_date)
    	source_date.year, source_date.month, source_date.day = date:match (source_patterns['ymd']);	-- get date components as strings
    end
    
    
    --[[-------------------------< R E F O R M A T _ D A T E S >--------------------------------------------------
    
    Reformats existing dates into the format specified by format and short.
    
    format is one of several keywords: dmy, dmy-all, mdy, mdy-all, ymd, ymd-all.  The all version includes access- and
    archive-dates; otherwise these dates are not reformatted
    
    Date ranges, season dates, proper name dates are not currently supported.
    
    ]]
    
    local function reformat_dates (date_parameters_list, format, short)
    	local all = false;															-- set to false to skip access- and archive-dates
    	local format_str;
    	local source_date = {};
    	
    	if format:match('%a+%-all') then
    		format = format:match('(%a+)%-all');									-- extract the format
    		all = true;																-- set to true to format access- and archive-dates
    	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) then												-- if the parameter has a value
    			if not all and in_array (param_name, {'access-date', 'archive-date'}) then	-- if access- or archive-date and format not xxx-all
    				param_val = '';													-- set to empty string so we don't process this date
    			end
    			for source, pattern in pairs(source_patterns) do
    				if param_val:match(pattern) then
    					if 'ymd' == source then
    						get_ymd_date_parts (param_val, source_date);			-- get the date parts into the source_date table
    					elseif 'dmy' == source then
    						get_dmy_date_parts (param_val, source_date);			-- get the date parts into the source_date table
    					elseif 'mdy' == source then
    						get_mdy_date_parts (param_val, source_date);			-- get the date parts into the source_date table
    					end
    
    					if 'ymd' == format and 1582 > tonumber(source_date.year) then	-- ymd format dates not allowed before 1582
    						return false;											-- abandon reformatting
    					end
    					
    					if short then
    						format_str = short_formats[format];
    					else
    						format_str = long_formats[format];
    					end
    					
    					date_parameters_list[param_name] = os.date (format_str, os.time(source_date));	-- convert date and save
    				end
    			end
    		end
    	end
    	return true;																-- declare success and done
    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 (utilities_page_ptr)
    	is_set = utilities_page_ptr.is_set;											-- import functions from select Module:Citation/CS1/Utilities module
    	in_array = utilities_page_ptr.in_array;											-- import functions from select Module:Citation/CS1/Utilities module
    end
    
    
    
    return {																		-- return exported functions
    	dates = dates,
    	year_date_check = year_date_check,
    	reformat_dates = reformat_dates,
    	set_selected_modules = set_selected_modules
    	}