Module:Citation/CS1/Date validation

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

 localadd_prop_cat,is_set,in_array,set_message,substitute,wrap_style;-- imported functions from selected Module:Citation/CS1/Utilities
 localcfg;-- 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

 ]]

 locallang_object=mw.getContentLanguage();-- used by is_valid_accessdate(), is_valid_year(), date_name_xlate(); TODO: move to ~/Configuration?
 localyear_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年01月15日T00:00:00 UTC which is 979516800 seconds after 1970年01月01日T00:00:00 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年01月01日T00:00:00 then
 		adding 24 hours gives 2015年01月02日T00:00:00 – one second more than today
 		adding 24 hours gives 2015年01月03日T00:00:00 – 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.

 ]=]

 localfunctionis_valid_accessdate(accessdate)
 localgood1,good2;
 localaccess_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

 ifgood1andgood2then-- lang.formatDate() returns a timestamp in the local script which which tonumber() may not understand
 access_ts=tonumber(access_ts)orlang_object:parseFormattedNumber(access_ts);-- convert to numbers for the comparison;
 tomorrow_ts=tonumber(tomorrow_ts)orlang_object:parseFormattedNumber(tomorrow_ts);
 else
 returnfalse;-- one or both failed to convert to Unix time stamp
 end

 if979516800<=access_tsandaccess_ts<tomorrow_tsthen-- Wikipedia start date <= accessdate < tomorrow's date
 returntrue;
 else
 returnfalse;-- 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

 ]]

 localfunctionget_month_number(month)
 returncfg.date_names['local'].long[month]orcfg.date_names['local'].short[month]or-- look for local names first
 cfg.date_names['en'].long[month]orcfg.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)

 ]]

 localfunctionget_season_number(season,param)
 if'date'~=paramthen
 return0;-- season dates only supported by |date=
 end
 returncfg.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)

 ]]

 localfunctionget_quarter_number(quarter,param)
 if'date'~=paramthen
 return0;-- quarter dates only supported by |date=
 end
 quarter=mw.ustring.gsub(quarter,' +',' ');-- special case replace multiple space chars with a single space char
 returncfg.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=

 ]]

 localfunctionget_proper_name_number(name,param)
 if'date'~=paramthen
 return0;-- proper-name dates only supported by |date=
 end
 returncfg.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)

 ]]

 localfunctionget_element_number(element,param)
 localnum;

 localfuncs={get_month_number,get_season_number,get_quarter_number,get_proper_name_number};-- list of functions to execute in order

 for_,funcinipairs(funcs)do-- spin through the function list
 num=func(element,param);-- call the function and get the returned number
 if0~=numthen-- non-zero when valid month season quarter 
 returnnum;-- return that number
 end
 end
 returnnil;-- 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.

 Special case for |pmc-embargo-date=: years more than two years in the future are not acceptable

 ]]

 localfunctionis_valid_year(year,param)
 ifnotis_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)orlang_object:parseFormattedNumber(year);-- convert to number for the comparison
 ifyearand(100>year)then-- years less than 100 not supported
 returnfalse;
 end

 if'pmc-embargo-date'==paramthen-- special case for |pmc-embargo-date=
 returnyearand(year<=tonumber(os.date("%Y"))+2)orfalse;-- years more than two years in the future are not accepted
 end
 returnyearand(year<=year_limit)orfalse;
 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.

 ]]

 localfunctionis_valid_date(year,month,day,param)
 localdays_in_month={31,28,31,30,31,30,31,31,30,31,30,31};
 localmonth_length;
 ifnotis_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
 returnfalse;
 end

 month=tonumber(month);-- required for YYYY-MM-DD dates

 if(2==month)then-- if February
 month_length=28;-- then 28 days unless
 if1582>tonumber(year)then-- Julian calendar
 if0==(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)or0==(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

 iftonumber(day)>month_lengththen
 returnfalse;
 end
 returntrue;
 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. 
 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

 ]]

 localfunctionis_valid_month_range_style(month1,month2)
 if(cfg.date_names.en.long[month1]andcfg.date_names.en.long[month2])or-- are both English names listed in the long subtable?
 (cfg.date_names.en.short[month1]andcfg.date_names.en.short[month2])or-- are both English names listed in the short subtable?
 (cfg.date_names['local'].long[month1]andcfg.date_names['local'].long[month2])or-- are both local names listed in the long subtable?
 (cfg.date_names['local'].short[month1]andcfg.date_names['local'].short[month2])then-- are both local names listed in the short subtable?
 returntrue;
 end
 returnfalse;-- names are mixed
 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

 ]]

 localfunctionis_valid_month_season_range(range_start,range_end,param)
 localrange_start_number=get_month_number(range_start);
 localrange_end_number;

 if0==range_start_numberthen-- 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
 returntrue;-- any season pairing is accepted except when both are the same
 end
 returnfalse;-- 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
 ifrange_start_number<range_end_numberand-- 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?
 returntrue;-- proper order and same style
 end
 returnfalse;-- 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

 ]]

 localfunctionmake_COinS_date(input,tCOinS_date)
 localdate;-- one date or first date in a range
 localdate2='';-- end of range date
 input.year=tonumber(input.year)orlang_object:parseFormattedNumber(input.year);-- language-aware tonumber()
 input.year2=tonumber(input.year2)orlang_object:parseFormattedNumber(input.year2);-- COinS dates are pseudo-ISO 8601 so convert to Arabic numerals

 if((1582==input.year)and(10>tonumber(input.month)))or(1582>input.year)then-- if a Julian calendar date
 tCOinS_date.rftdate=tostring(input.year);-- &rft.date gets year only
 return;-- done
 end
 -- here for all forms of Gregorian dates
 if20<tonumber(input.month)then-- if season, quarter, or proper-name date
 date=input.year;-- &rft.date gets year only
 if0~=input.year2andinput.year~=input.year2then-- if a range, only the second year portion when not the same as range start year
 date=string.format('%.4d/%.4d',input.year,input.year2)-- assemble the date range
 end

 localseason={[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
 if0==input.month2then-- single season, quarter, or proper-name date
 if40<tonumber(input.month)then
 tCOinS_date.rftchron=season[input.month];-- proper-name date; used in journal metadata only
 elseif30<tonumber(input.month)then
 tCOinS_date.rftquarter=season[input.month];-- quarter date; used in journal metadata only
 else
 tCOinS_date.rftssn=season[input.month];-- season date; used in journal metadata only
 end
 else-- season ranges are lumped into &rft.chron; &rft.ssn and &rft.quarter are left blank
 ifinput.year~=input.year2then-- season year – season year range or season year–year
 if0~=input.month2then
 tCOinS_date.rftchron=string.format('%s %s – %s %s',season[input.month],input.year,season[input.month2],input.year2);-- used in journal metadata only
 end
 else-- season–season year range
 tCOinS_date.rftchron=season[input.month]..'–'..season[input.month2];-- season–season year range; used in journal metadata only
 end
 end

 tCOinS_date.rftdate=tostring(date);
 return;-- done
 end
 -- here for gregorian calendar dates
 if0~=input.daythen
 date=string.format('%s-%.2d-%.2d',input.year,tonumber(input.month),tonumber(input.day));-- whole date
 elseif0~=input.monththen
 date=string.format('%s-%.2d',input.year,tonumber(input.month));-- year and month
 else
 date=string.format('%s',input.year);-- just year
 end

 if0~=input.year2then
 if0~=input.day2then
 date2=string.format('/%s-%.2d-%.2d',input.year2,tonumber(input.month2),tonumber(input.day2));-- whole date
 elseif0~=input.month2then
 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 _ T >----------------------------------------------------------

 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()

 ]]

 localpatterns_t={
 -- year-initial numerical year-month-day
 ['ymd']={'^([1-9]%d%d%d)%-(%d%d)%-(%d%d)$','y','m','d'},
 -- month-initial: month day, year
 ['Mdy']={'^(%D-) +([1-9]%d?), +(([1-9]%d%d%d?)%a?)$','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?), +(([1-9]%d%d%d?)%a?)$','m','d','d2','a','y'},
 -- day-initial: day month year
 ['dMy']={'^([1-9]%d?) +(%D-) +(([1-9]%d%d%d?)%a?)$','d','m','a','y'},
 -- year-initial: year month day; day: 1 or 2 two digits, leading zero allowed; not supported at en.wiki
 --	['yMd'] = {'^(([1-9]%d%d%d?)%a?) +(%D-) +(%d%d?)$', 'a', 'y', 'm', 'd'},
 -- day-range-initial: day–day month year; days are separated by endash
 ['d-dMy']={'^([1-9]%d?)[%-–]([1-9]%d?) +(%D-) +(([1-9]%d%d%d?)%a?)$','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-) +(([1-9]%d%d%d?)%a?)$','d','m','d2','m2','a','y'},
 -- month initial month-day-range: month day – month day, year; uses spaced endash
 ['Md-Mdy']={'^(%D-) +([1-9]%d?) +[%-–] +(%D-) +([1-9]%d?), +(([1-9]%d%d%d?)%a?)$','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-) +([1-9]%d%d%d?) +[%-–] +([1-9]%d?) +(%D-) +(([1-9]%d%d%d?)%a?)$','d','m','y','d2','m2','a','y2'},
 -- month initial month-day-year-range: month day, year – month day, year; uses spaced endash
 ['Mdy-Mdy']={'^(%D-) +([1-9]%d?), +([1-9]%d%d%d?) +[%-–] +(%D-) +([1-9]%d?), +(([1-9]%d%d%d?)%a?)$','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-) +([1-9]%d%d%d?) +[%-–] +(%D-) +(([1-9]%d%d%d?)%a?)$','m','y','m2','a','y2'},
 -- month/season range year; months separated by endash
 ['M-My']={'^(%D-)[%-–](%D-) +(([1-9]%d%d%d?)%a?)$','m','m2','a','y'},
 -- month/season year or proper-name year; quarter year when First Quarter YYYY etc.
 ['My']={'^([^%d–]-) +(([1-9]%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-) +(([1-9]%d)%d%d)[%-–]((%d%d)%a?)$'},-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
 ['Sy-y']={'^(%D-) +([1-9]%d%d%d?)[%-–](([1-9]%d%d%d?)%a?)$'},-- special case Winter/Summer year-year; year separated with unspaced endash
 ['y-y']={'^([1-9]%d%d%d?)[%-–](([1-9]%d%d%d?)%a?)$'},-- year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
 ['y4-y2']={'^(([1-9]%d)%d%d)[%-–]((%d%d)%a?)$'},-- year range: YYYY–YY; separated by unspaced endash
 ['y']={'^(([1-9]%d%d%d?)%a?)$'},-- year; here accept either YYY or YYYY
 }


 --[[--------------------------< 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.

 ]]

 localfunctionis_valid_embargo_date(v)
 ifv:match(patterns_t['ymd'][1])or-- ymd
 v:match(patterns_t['Mdy'][1])or-- dmy
 v:match(patterns_t['dMy'][1])then-- mdy
 returntrue,v;
 end
 returnfalse,'9999';-- if here not good date so return false and set embargo date to long time in future
 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 (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()

 ]]

 localfunctioncheck_date(date_string,param,tCOinS_date)
 localyear;-- assume that year2, months, and days are not used;
 localyear2=0;-- second year in a year range
 localmonth=0;
 localmonth2=0;-- second month in a month range
 localday=0;
 localday2=0;-- second day in a day range
 localanchor_year;
 localcoins_date;

 ifdate_string:match(patterns_t['ymd'][1])then-- year-initial numerical year month day format
 year,month,day=date_string:match(patterns_t['ymd'][1]);
 if12<tonumber(month)or1>tonumber(month)or1582>tonumber(year)or0==tonumber(day)thenreturnfalse;end-- month or day number not valid or not Gregorian calendar
 anchor_year=year;

 elseifmw.ustring.match(date_string,patterns_t['Mdy'][1])then-- month-initial: month day, year
 month,day,anchor_year,year=mw.ustring.match(date_string,patterns_t['Mdy'][1]);
 month=get_month_number(month);
 if0==monththenreturnfalse;end-- return false if month text isn't one of the twelve months

 elseifmw.ustring.match(date_string,patterns_t['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_t['Md-dy'][1]);
 iftonumber(day)>=tonumber(day2)thenreturnfalse;end-- date range order is left to right: earlier to later; dates may not be the same;
 month=get_month_number(month);
 if0==monththenreturnfalse;end-- return false if month text isn't one of the twelve months
 month2=month;-- for metadata
 year2=year;

 elseifmw.ustring.match(date_string,patterns_t['dMy'][1])then-- day-initial: day month year
 day,month,anchor_year,year=mw.ustring.match(date_string,patterns_t['dMy'][1]);
 month=get_month_number(month);
 if0==monththenreturnfalse;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_t['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_t['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 ]]

 elseifmw.ustring.match(date_string,patterns_t['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_t['d-dMy'][1]);
 iftonumber(day)>=tonumber(day2)thenreturnfalse;end-- date range order is left to right: earlier to later; dates may not be the same;
 month=get_month_number(month);
 if0==monththenreturnfalse;end-- return false if month text isn't one of the twelve months
 month2=month;-- for metadata
 year2=year;

 elseifmw.ustring.match(date_string,patterns_t['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_t['dM-dMy'][1]);
 if(notis_valid_month_season_range(month,month2))ornotis_valid_year(year)thenreturnfalse;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;

 elseifmw.ustring.match(date_string,patterns_t['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_t['Md-Mdy'][1]);
 if(notis_valid_month_season_range(month,month2,param))ornotis_valid_year(year)thenreturnfalse;end
 month=get_month_number(month);-- for metadata
 month2=get_month_number(month2);
 year2=year;

 elseifmw.ustring.match(date_string,patterns_t['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_t['dMy-dMy'][1]);
 iftonumber(year2)<=tonumber(year)thenreturnfalse;end-- must be sequential years, left to right, earlier to later
 ifnotis_valid_year(year2)ornotis_valid_month_range_style(month,month2)thenreturnfalse;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);
 if0==monthor0==month2thenreturnfalse;end-- both must be valid

 elseifmw.ustring.match(date_string,patterns_t['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_t['Mdy-Mdy'][1]);
 iftonumber(year2)<=tonumber(year)thenreturnfalse;end-- must be sequential years, left to right, earlier to later
 ifnotis_valid_year(year2)ornotis_valid_month_range_style(month,month2)thenreturnfalse;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);
 if0==monthor0==month2thenreturnfalse;end-- both must be valid

 elseifmw.ustring.match(date_string,patterns_t['Sy4-y2'][1])then-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
 localcentury;
 month,year,century,anchor_year,year2=mw.ustring.match(date_string,patterns_t['Sy4-y2'][1]);
 if'Winter'~=monthand'Summer'~=monththenreturnfalseend;-- '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
 if1~=tonumber(year2)-tonumber(year)thenreturnfalse;end-- must be sequential years, left to right, earlier to later
 ifnotis_valid_year(year2)thenreturnfalse;end-- no year farther in the future than next year
 month=get_season_number(month,param);

 elseifmw.ustring.match(date_string,patterns_t['Sy-y'][1])then-- special case Winter/Summer year-year; year separated with unspaced endash
 month,year,anchor_year,year2=mw.ustring.match(date_string,patterns_t['Sy-y'][1]);
 month=get_season_number(month,param);-- <month> 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
 returnfalse;-- not Summer or Winter; abandon
 end
 anchor_year=year..'–'..anchor_year;-- assemble anchor_year from both years
 if1~=tonumber(year2)-tonumber(year)thenreturnfalse;end-- must be sequential years, left to right, earlier to later
 ifnotis_valid_year(year2)thenreturnfalse;end-- no year farther in the future than next year

 elseifmw.ustring.match(date_string,patterns_t['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_t['My-My'][1]);
 anchor_year=year..'–'..anchor_year;-- assemble anchor_year from both years
 iftonumber(year)>=tonumber(year2)thenreturnfalse;end-- left to right, earlier to later, not the same
 ifnotis_valid_year(year2)thenreturnfalse;end-- no year farther in the future than next year
 if0~=get_month_number(month)and0~=get_month_number(month2)andis_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);
 elseif0~=get_season_number(month,param)and0~=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
 returnfalse;
 end

 elseifmw.ustring.match(date_string,patterns_t['M-My'][1])then-- month/season range year; months separated by endash 
 month,month2,anchor_year,year=mw.ustring.match(date_string,patterns_t['M-My'][1]);
 if(notis_valid_month_season_range(month,month2,param))or(notis_valid_year(year))thenreturnfalse;end
 if0~=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);
 if0==monthor0==month2thenreturnfalse;end
 else
 month=get_season_number(month,param);
 month2=get_season_number(month2,param);
 end
 year2=year;

 elseifmw.ustring.match(date_string,patterns_t['My'][1])then-- month/season/quarter/proper-name year
 month,anchor_year,year=mw.ustring.match(date_string,patterns_t['My'][1]);
 ifnotis_valid_year(year)thenreturnfalse;end
 month=get_element_number(month,param);-- get month season quarter proper-name number or nil
 ifnotmonththenreturnfalse;end-- not valid whatever it is

 elseifmw.ustring.match(date_string,patterns_t['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_t['y-y'][1]);
 anchor_year=year..'–'..anchor_year;-- assemble anchor year from both years
 iftonumber(year)>=tonumber(year2)thenreturnfalse;end-- left to right, earlier to later, not the same
 ifnotis_valid_year(year2)thenreturnfalse;end-- no year farther in the future than next year

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

 if13>tonumber(year2)thenreturnfalse;end-- don't allow 2003-05 which might be May 2003
 year2=century..year2;-- add the century to year2 for comparisons
 iftonumber(year)>=tonumber(year2)thenreturnfalse;end-- left to right, earlier to later, not the same
 ifnotis_valid_year(year2)thenreturnfalse;end-- no year farther in the future than next year

 ifin_array(param,{'date','publication-date','year'})then-- here when 'valid' abbreviated year range; if one of these parameters
 add_prop_cat('year-range-abbreviated');-- add properties cat
 end

 elseifmw.ustring.match(date_string,patterns_t['y'][1])then-- year; here accept either YYY or YYYY
 anchor_year,year=mw.ustring.match(date_string,patterns_t['y'][1]);
 iffalse==is_valid_year(year)then
 returnfalse;
 end

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

 ifparam~='date'then-- CITEREF disambiguation only allowed in |date=; |year= & |publication-date= promote to date
 ifanchor_year:match('%l$')then
 returnfalse;
 end
 end

 if'access-date'==paramthen-- test access-date here because we have numerical date parts
 if0~=yearand0~=monthand0~=dayand-- all parts of a single date required
 0==year2and0==month2and0==day2then-- none of these; access-date must not be a range
 ifnotis_valid_accessdate(year..'-'..month..'-'..day)then
 returnfalse;-- return false when access-date out of bounds
 end
 else
 returnfalse;-- return false when access-date is a range of two dates
 end
 end

 if'archive-date'==paramthen-- test archive-date here because we have numerical date parts
 ifnot(0~=yearand0~=monthand0~=dayand-- all parts of a single date required
 0==year2and0==month2and0==day2)then-- none of these; archive-date must not be a range
 returnfalse;-- return false when archive-date is a range of two dates
 end
 end

 localresult=true;-- check whole dates for validity; assume true because not all dates will go through this test
 if0~=yearand0~=monthand0~=dayand0==year2and0==month2and0==day2then-- YMD (simple whole date)
 result=is_valid_date(year,month,day,param);-- <param> for |pmc-embargo-date=

 elseif0~=yearand0~=monthand0~=dayand0==year2and0==month2and0~=day2then-- YMD-d (day range)
 result=is_valid_date(year,month,day);
 result=resultandis_valid_date(year,month,day2);

 elseif0~=yearand0~=monthand0~=dayand0==year2and0~=month2and0~=day2then-- YMD-md (day month range)
 result=is_valid_date(year,month,day);
 result=resultandis_valid_date(year,month2,day2);

 elseif0~=yearand0~=monthand0~=dayand0~=year2and0~=month2and0~=day2then-- YMD-ymd (day month year range)
 result=is_valid_date(year,month,day);
 result=resultandis_valid_date(year2,month2,day2);
 end

 iffalse==resultthenreturnfalse;end

 ifnil~=tCOinS_datethen-- 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

 returntrue,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.

 ]]

 localfunctiondates(date_parameters_list,tCOinS_date,error_list)
 localanchor_year;-- will return as nil if the date being tested is not |date=
 localCOinS_date;-- will return as nil if the date being tested is not |date=
 localembargo_date;-- if embargo date is a good dmy, mdy, ymd date then holds original value else reset to 9999
 localgood_date=false;

 fork,vinpairs(date_parameters_list)do-- for each date-holding parameter in the list
 ifis_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
 ifv.val:match("^c%. [1-9]%d%d%d?%a?$")then-- special case for c. year or with or without CITEREF disambiguator - only |date= and |year=
 localyear=v.val:match("c%. ([1-9]%d%d%d?)%a?");-- get the year portion so it can be tested
 if'date'==kthen
 anchor_year,COinS_date=v.val:match("((c%. [1-9]%d%d%d?)%a?)");-- anchor year and COinS_date only from |date= parameter
 good_date=is_valid_year(year);
 elseif'year'==kthen
 good_date=is_valid_year(year);
 end
 elseif'date'==kthen-- if the parameter is |date=
 ifv.val:match("^n%.d%.%a?$")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
 elseifv.val:match("^nd%a?$")then-- ToDo: I18N								-- if |date=nd with or without a CITEREF disambiguator
 good_date,anchor_year,COinS_date=true,v.val:match("((nd)%a?)");-- ToDo: I18N	-- "nd";	no error when date parameter is set to no date
 else
 good_date,anchor_year,COinS_date=check_date(v.val,k,tCOinS_date);-- go test the date
 end
 elseif'year'==kthen-- if the parameter is |year= it should hold only a year value
 ifv.val:match("^[1-9]%d%d%d?%a?$")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'==kthen-- if the parameter is |pmc-embargo-date=
 good_date=check_date(v.val,k);-- go test the date
 iftrue==good_datethen-- 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
 iffalse==good_datethen-- 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
 returnanchor_year,embargo_date;-- and done
 end


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

 Temporary function to test |year= for acceptable values:
 	YYY, YYYY, year-only ranges, their circa forms, with or without CITEREF disambiguators.

 When |year= holds some form of date that is not one of these year-only dates, emit a maintenance message.

 This function necessary because many non-cs1|2 templates have a |year= parameter so cirrus searches are more-or-
 less useless

 ]]

 localfunctionyear_check(year)
 year=year:gsub('c%. *','');-- remove circa annotation (if present) before testing <year>

 for_,indexinipairs({'y-y','y4-y2','y'})do-- spin through these indexes into patterns_t
 ifmw.ustring.match(year,patterns_t[index][1])then
 return;-- if a match then |year= holds a valid 'year'
 end
 end

 set_message('maint_year');-- if here, |year= value is not an accepted value; add a maint cat
 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 numeric 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

 ]]

 localfunctionyear_date_check(year_string,year_origin,date_string,date_origin,error_list)
 localyear;
 localdate1;
 localdate2;
 localresult=1;-- result of the test; assume that the test passes

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

 ifdate_string:match('%d%d%d%d%-%d%d%-%d%d')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)');
 ifyear~=date1then
 result=0;-- years don't match
 elseifyear_string:match('%d%d%d%d%a')then
 result=2;-- years match; but because disambiguated, don't add to maint cat
 end

 elseifdate_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?)");
 ifyear~=date1andyear~=date2then
 result=0;
 end

 elseifmw.ustring.match(date_string,"%d%d%d%d[%-–]%d%d")then-- YYYY-YY date ranges
 localcentury;
 date1,century,date2=mw.ustring.match(date_string,"((%d%d)%d%d)[%-–]+(%d%d)");
 date2=century..date2;-- convert YY to YYYY
 ifyear~=date1andyear~=date2then
 result=0;
 end

 elseifdate_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?)");
 ifyear~=date1then
 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

 if0==resultthen-- year / date mismatch
 table.insert(error_list,substitute(cfg.messages['mismatch'],{year_origin,date_origin}));-- add error message to error_list sequence table
 elseif1==resultthen-- 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_t[pattern_idx][1]

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

 ]]

 localre_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
 --		},
 }


 localfunctionreformatter(date,pattern_idx,format_param,mon_len)
 ifnotin_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_t then not a reformattable date
 end

 if'ymd'==format_paramandin_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

 ifin_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_paramthen-- 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

 localc1,c2,c3,c4,c5,c6,c7;-- these hold the captures specified in patterns_t[pattern_idx][1]
 c1,c2,c3,c4,c5,c6,c7=mw.ustring.match(date,patterns_t[pattern_idx][1]);-- get the captures

 localt={-- table that holds k/v pairs of date parts from the captures and patterns_t[pattern_idx][2..]
 [patterns_t[pattern_idx][2]]=c1;-- at minimum there is always one capture with a matching indicator letter
 [patterns_t[pattern_idx][3]or'x']=c2;-- patterns_t can have a variable number of captures; each capture requires an indicator letter;
 [patterns_t[pattern_idx][4]or'x']=c3;-- where there is no capture, there is no indicator letter so n in patterns_t[pattern_idx][n] will be nil;
 [patterns_t[pattern_idx][5]or'x']=c4;-- the 'x' here spoofs an indicator letter to prevent 'table index is nil' error
 [patterns_t[pattern_idx][6]or'x']=c5;
 [patterns_t[pattern_idx][7]or'x']=c6;
 [patterns_t[pattern_idx][8]or'x']=c7;
 };

 ift.athen-- if this date has an anchor year capture (all convertable date formats except ymd)
 ift.y2then-- 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

 iftonumber(t.m)then-- if raw month is a number (converting from ymd)
 if's'==mon_lenthen-- 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_paramthen-- 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?
 if1582>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);
 elseifmon_lenthen-- if mon_len is set to either 'short' or 'long'
 for_,moninipairs({'m','m2'})do-- because there can be two month names, check both 
 ift[mon]then
 t[mon]=get_month_number(t[mon]);-- get the month number for this month (is length agnostic)
 if0==t[mon]thenreturn;end-- seasons and named dates can't be converted
 t[mon]=(('s'==mon_len)andcfg.date_names['inv_local_short'][t[mon]])orcfg.date_names['inv_local_long'][t[mon]];-- fetch month name according to length
 end
 end
 end

 localnew_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]]
 );

 returnnew_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().

 ]]

 localfunctionreformat_dates(date_parameters_list,format)
 localall=false;-- set to false to skip access- and archive-dates
 locallen_p='l';-- default publication date length shall be long
 locallen_a='l';-- default access-/archive-date length shall be long
 localresult=false;
 localnew_date;

 ifformat: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
 elseifformat: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_pthen-- because allowed by MOS:DATEUNIFY (sort of) range dates and My dates not reformatted
 format='ymd';-- override {{use xxx dates}}
 elseif(notis_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

 forparam_name,param_valinpairs(date_parameters_list)do-- for each date-holding parameter in the list
 ifis_set(param_val.val)then-- if the parameter has a value
 ifnot(notallandin_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
 forpattern_idx,patterninpairs(patterns_t)do
 ifmw.ustring.match(param_val.val,pattern[1])then
 ifallandin_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')orformat,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

 ifnew_datethen-- 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
 break;
 end
 end-- if
 end-- for
 end-- if
 end-- if
 end-- for
 returnresult;-- 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.

 ]]

 localfunctiondate_hyphen_to_dash(date_parameters_list)
 localresult=false;
 localn;
 forparam_name,param_valinpairs(date_parameters_list)do-- for each date-holding parameter in the list
 ifis_set(param_val.val)and
 notmw.ustring.match(param_val.val,patterns_t.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
 if0~=nthen
 date_parameters_list[param_name].val=param_val.val;-- update the list
 result=true;
 end
 end
 end
 returnresult;-- so we know if any hyphens were replaced
 end


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

 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.

 ]]

 localfunctiondate_name_xlate(date_parameters_list,xlt_dig)
 localxlate;
 localmode;-- long or short month names
 localmodified=false;
 localdate;

 localsources_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
 }

 localfunctionis_xlateable(month)-- local function to get local date name that replaces existing English-language date name
 for_,date_names_tinipairs(sources_t)do-- for each sequence table in date_names_t
 ifdate_names_t[1][month]then-- if date name is English month (long or short), quarter, season or named and
 ifdate_names_t[2][date_names_t[1][month]]then-- if there is a matching local date name
 returndate_names_t[2][date_names_t[1][month]];-- return the local date name
 end
 end
 end
 end

 forparam_name,param_valinpairs(date_parameters_list)do-- for each date-holding parameter in the list
 ifis_set(param_val.val)then-- if the parameter has a value
 date=param_val.val;
 formonthinmw.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 <month>; returns translation or nil

 ifxlatethen
 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

 ifxlt_digthen-- 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

 returnmodified;
 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.

 ]]

 localfunctionset_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.

 ]]

 localfunctionarchive_date_check(archive_date,archive_url_timestamp,df)
 localarchive_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_tinipairs({{'dMy','dmy-all'},{'Mdy','mdy-all'}})do-- is |archive-date= format dmy or mdy?
 ifarchive_date:match(patterns_t[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

 localdates_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()
 localarchive_url_date=archive_url_timestamp:gsub('(%d%d%d%d)(%d%d)(%d%d)%d*','%1-%2-%3');-- make ymd format date from timestamp

 ifdates_t['archive-date'].val==archive_url_datethen-- 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,dforarchive_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('err_archive_date_url_ts_mismatch',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,
 date_hyphen_to_dash=date_hyphen_to_dash,
 date_name_xlate=date_name_xlate,
 dates=dates,
 reformat_dates=reformat_dates,
 set_selected_modules=set_selected_modules,
 year_check=year_check,
 year_date_check=year_date_check,
 }