Module:Citation/CS1/Date validation/sandbox

--[[
History of changes since last sync: 2024-03-23

2024-07-12: maint cat for |year= value more precise that a year; see Help_talk:Citation_Style_1#year_parameter

]]


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

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


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

File-scope variables are declared here

]]

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


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

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

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

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

]=]

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

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

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


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

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

]]

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


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

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

returns 0 when <param> is not |date=

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

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

]]

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


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

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

returns 0 when <param> is not |date=

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

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

]]

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


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

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

returns 0 when <param> is not |date=

]]

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


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

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

]]

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


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

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

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

]]

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

 year = tonumber (year) or lang_object:parseFormattedNumber (year);   -- convert to number for the comparison
 if year and (100 > year) then            -- years less than 100 not supported
  return false;
 end
 
 if 'pmc-embargo-date' == param then           -- special case for |pmc-embargo-date=
  return year and (year <= tonumber(os.date("%Y"))+2) or false;   -- years more than two years in the future are not accepted
 end 
 return year and (year <= year_limit) or false;
end


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

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

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

]]

local function is_valid_date (year, month, day, param)
local days_in_month = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
local month_length;
 if not is_valid_year (year, param) then          -- no farther into the future than next year except |pmc-embargo-date= no more than two years in the future
  return false;
 end
 
 month = tonumber (month);             -- required for YYYY-MM-DD dates
 
 if (2 == month) then              -- if February
  month_length = 28;              -- then 28 days unless
  if 1582 > tonumber(year) then           -- Julian calendar
   if 0 == (year%4) then            -- is a leap year?
    month_length = 29;            -- if leap year then 29 days in February
   end
  else                 -- Gregorian calendar
   if (0 == (year%4) and (0 ~= (year%100) or 0 == (year%400))) then -- is a leap year?
    month_length = 29;            -- if leap year then 29 days in February
   end
  end
 else
  month_length = days_in_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. 
This function looks in cfg.date_names{} to see if both month names are listed in the long subtable or both are
listed in the short subtable.  When both have the same style (both are listed in the same table), returns true; false else

]]

local function is_valid_month_range_style (month1, month2)
 if (cfg.date_names.en.long[month1] and cfg.date_names.en.long[month2]) or     -- are both English names listed in the long subtable?
  (cfg.date_names.en.short[month1] and cfg.date_names.en.short[month2]) or    -- are both English names listed in the short subtable?
  (cfg.date_names['local'].long[month1] and cfg.date_names['local'].long[month2]) or  -- are both local names listed in the long subtable?
  (cfg.date_names['local'].short[month1] and cfg.date_names['local'].short[month2]) then -- are both local names listed in the short subtable?
   return true;
 end
 return false;                -- 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

]]

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

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

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


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

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

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

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

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

]]

local function make_COinS_date (input, tCOinS_date)
 local date;                 -- one date or first date in a range
 local date2 = '';               -- end of range date
 input.year = tonumber (input.year) or lang_object:parseFormattedNumber (input.year); -- language-aware tonumber()
 input.year2 = tonumber (input.year2) or lang_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
 if 20 < tonumber (input.month) then           -- if season, quarter, or proper-name date
  date = input.year;              -- &rft.date gets year only
  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', input.year, input.year2)   -- assemble the date range
  end

  local season = {[24] = 'winter', [21] = 'spring', [22] = 'summer', [23] = 'fall', [33] = '1', [34] = '2', [35] = '3', [36] = '4', [98] = 'Easter', [99] = 'Christmas'}; -- seasons lowercase, no autumn; proper-names use title case
  if 0 == input.month2 then            -- single season, quarter, or proper-name date
   if 40 < tonumber(input.month) then
    tCOinS_date.rftchron = season[input.month];      -- proper-name date; used in journal metadata only
   elseif 30 < 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
   if input.year ~= input.year2 then         -- season year – season year range or season year–year
    if 0 ~= input.month2 then
     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
 if 0 ~= input.day then
  date = string.format ('%s-%.2d-%.2d', input.year, tonumber(input.month), tonumber(input.day)); -- whole date
 elseif 0 ~= input.month then
  date = string.format ('%s-%.2d', input.year, tonumber(input.month)); -- year and month
 else
  date = string.format ('%s', input.year);        -- just year
 end

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


--[[--------------------------< P A T T E R N S _ 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()

]]

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

                    -- these date formats cannot be converted, per se, but month name can be rendered short or long
                    -- month/season year - month/season year; separated by spaced endash
 ['My-My'] = {'^(%D-) +(%d%d%d%d) +[%-–] +(%D-) +((%d%d%d%d)%a?)$', 'm', 'y', 'm2', 'a', 'y2'},
                    -- month/season range year; months separated by endash
 ['M-My'] = {'^(%D-)[%-–](%D-) +((%d%d%d%d)%a?)$', 'm', 'm2', 'a', 'y'},
                    -- month/season year or proper-name year; quarter year when First Quarter YYYY etc.
 ['My'] = {'^([^%d–]-) +((%d%d%d%d)%a?)$', 'm', 'a', 'y'},     -- this way because endash is a member of %D; %D- will match January–March 2019 when it shouldn't

                    -- these date formats cannot be converted
 ['Sy4-y2'] = {'^(%D-) +((%d%d)%d%d)[%-–]((%d%d)%a?)$'},      -- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
 ['Sy-y'] = {'^(%D-) +(%d%d%d%d)[%-–]((%d%d%d%d)%a?)$'},      -- special case Winter/Summer year-year; year separated with unspaced endash
 ['y-y'] = {'^(%d%d%d%d?)[%-–]((%d%d%d%d?)%a?)$'},       -- year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
 ['y4-y2'] = {'^((%d%d)%d%d)[%-–]((%d%d)%a?)$'},        -- year range: YYYY–YY; separated by unspaced endash
 ['y'] = {'^((%d%d%d%d?)%a?)$'},            -- year; here accept either YYY or YYYY
 }


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

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

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

]]

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


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

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

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

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

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

]]

local function check_date (date_string, param, tCOinS_date)
 local year;                 -- assume that year2, months, and days are not used;
 local year2 = 0;               -- second year in a year range
 local month = 0;
 local month2 = 0;               -- second month in a month range
 local day = 0;
 local day2 = 0;                -- second day in a day range
 local anchor_year;
 local coins_date;

 if date_string:match (patterns_t['ymd'][1]) then       -- year-initial numerical year month day format
  year, month, day = date_string:match (patterns_t['ymd'][1]);
  if 12 < tonumber(month) or 1 > tonumber(month) or 1582 > tonumber(year) or 0 == tonumber(day) then return false; end -- month or day number not valid or not Gregorian calendar
  anchor_year = year;
 
 elseif mw.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);
  if 0 == month then return false; end         -- return false if month text isn't one of the twelve months
    
 elseif mw.ustring.match(date_string, patterns_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]);
  if tonumber(day) >= tonumber(day2) then return false; end    -- date range order is left to right: earlier to later; dates may not be the same;
  month = get_month_number (month);
  if 0 == month then return false; end         -- return false if month text isn't one of the twelve months
  month2=month;               -- for metadata
  year2 = year;

 elseif mw.ustring.match(date_string, patterns_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);
  if 0 == month then return false; end         -- return false if month text isn't one of the twelve months

--[[ NOT supported at en.wiki
 elseif mw.ustring.match(date_string, patterns_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 ]]

 elseif mw.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]);
  if tonumber(day) >= tonumber(day2) then return false; end    -- date range order is left to right: earlier to later; dates may not be the same;
  month = get_month_number (month);
  if 0 == month then return false; end         -- return false if month text isn't one of the twelve months
  month2 = month;               -- for metadata
  year2 = year;

 elseif mw.ustring.match(date_string, patterns_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 (not is_valid_month_season_range(month, month2)) or not is_valid_year(year) then return false; end -- date range order is left to right: earlier to later;
  month = get_month_number (month);          -- for metadata
  month2 = get_month_number (month2);
  year2 = year;

 elseif mw.ustring.match(date_string, patterns_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 (not is_valid_month_season_range(month, month2, param)) or not is_valid_year(year) then return false; end
  month = get_month_number (month);          -- for metadata
  month2 = get_month_number (month2);
  year2 = year;

 elseif mw.ustring.match(date_string, patterns_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]);
  if tonumber(year2) <= tonumber(year) then return false; end    -- must be sequential years, left to right, earlier to later
  if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end  -- year2 no more than one year in the future; months same style
  month = get_month_number (month);          -- for metadata
  month2 = get_month_number (month2);
  if 0 == month or 0 == month2 then return false; end      -- both must be valid

 elseif mw.ustring.match(date_string, patterns_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]);
  if tonumber(year2) <= tonumber(year) then return false; end    -- must be sequential years, left to right, earlier to later
  if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end  -- year2 no more than one year in the future; months same style
  month = get_month_number (month);          -- for metadata
  month2 = get_month_number(month2);
  if 0 == month or 0 == month2 then return false; end      -- both must be valid

 elseif mw.ustring.match(date_string, patterns_t['Sy4-y2'][1]) then   -- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
  local century;
  month, year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns_t['Sy4-y2'][1]);
  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, param);

 elseif mw.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
   return false;              -- not Summer or Winter; abandon
  end
  anchor_year = year .. '–' .. anchor_year;        -- assemble anchor_year from both years
  if 1 ~= tonumber(year2) - tonumber(year) then return false; end   -- must be sequential years, left to right, earlier to later
  if not is_valid_year(year2) then return false; end      -- no year farther in the future than next year

 elseif mw.ustring.match(date_string, patterns_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
  if tonumber(year) >= tonumber(year2) then return false; end    -- left to right, earlier to later, not the same
  if not is_valid_year(year2) then return false; end      -- no year farther in the future than next year
  if 0 ~= get_month_number(month) and 0 ~= get_month_number(month2) and is_valid_month_range_style(month, month2) then  -- both must be month year, same month style
   month = get_month_number(month);
   month2 = get_month_number(month2);
  elseif 0 ~= get_season_number(month, param) and 0 ~= get_season_number(month2, param) then -- both must be season year, not mixed
   month = get_season_number(month, param);
   month2 = get_season_number(month2, param);
  else
    return false;
  end

 elseif mw.ustring.match(date_string, patterns_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 (not is_valid_month_season_range(month, month2, param)) or (not is_valid_year(year)) then return false; end
  if 0 ~= get_month_number(month) then         -- determined to be a valid range so just check this one to know if month or season
   month = get_month_number(month);
   month2 = get_month_number(month2);
   if 0 == month or 0 == month2 then return false; end
  else
   month = get_season_number(month, param);
   month2 = get_season_number(month2, param);
  end
  year2 = year;
  
 elseif mw.ustring.match(date_string, patterns_t['My'][1]) then    -- month/season/quarter/proper-name year
  month, anchor_year, year = mw.ustring.match(date_string, patterns_t['My'][1]);
  if not is_valid_year(year) then return false; end
  month = get_element_number(month, param);        -- get month season quarter proper-name number or nil
  if not month then return false; end          -- not valid whatever it is

 elseif mw.ustring.match(date_string, patterns_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
  if tonumber(year) >= tonumber(year2) then return false; end    -- left to right, earlier to later, not the same
  if not is_valid_year(year2) then return false; end      -- no year farther in the future than next year

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

  if in_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

 elseif mw.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]);
  if false == is_valid_year(year) then
   return false;
  end

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

 if param ~= 'date' then              -- CITEREF disambiguation only allowed in |date=; |year= & |publication-date= promote to date
  if anchor_year:match ('%l$') then
   return false;
  end
 end

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

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

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

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

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

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

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


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

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

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

]]

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

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


--[[--------------------------< 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

]]

local function year_check (year)
 year = year:gsub ('c%. *', '');            -- remove circa annotation (if present) before testing <year>
 
 for _, index in ipairs ({'y-y', 'y4-y2', 'y'}) do       -- spin through these indexes into patterns_t
  if mw.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

]]

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

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

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

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

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

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


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

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

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

]]

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


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

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

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

 local t = {                 -- 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;
  };

 if t.a then                 -- if this date has an anchor year capture (all convertable date formats except ymd)
  if t.y2 then               -- for year range date formats              
   t.y2 = t.a;               -- use the anchor year capture when reassembling the date
  else                 -- here for single date formats (except ymd)
   t.y = t.a;               -- use the anchor year capture when reassembling the date
  end
 end

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

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

 return new_date;
end


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

Reformats existing dates into the format specified by format.

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

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

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

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

]]

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

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


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

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

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

]]

local function date_hyphen_to_dash (date_parameters_list)
 local result = false;
 local n;
 for param_name, param_val in pairs(date_parameters_list) do     -- for each date-holding parameter in the list
  if is_set (param_val.val) and
   not mw.ustring.match (param_val.val, patterns_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
    if 0 ~= n then
     date_parameters_list[param_name].val = param_val.val;  -- update the list
     result = true;
    end
  end
 end
 return result;                -- so we know if any hyphens were replaced
end


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

]]

local function date_name_xlate (date_parameters_list, xlt_dig)
 local xlate;
 local mode;                 -- long or short month names
 local modified = false;
 local date;
 
 local sources_t = {
  {cfg.date_names.en.long, cfg.date_names.inv_local_long},    -- for translating long English month names to long local month names
  {cfg.date_names.en.short, cfg.date_names.inv_local_short},    -- short month names
  {cfg.date_names.en.quarter, cfg.date_names.inv_local_quarter},   -- quarter date names
  {cfg.date_names.en.season, cfg.date_names.inv_local_season},   -- season date nam
  {cfg.date_names.en.named, cfg.date_names.inv_local_named},    -- named dates
  }

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

 for param_name, param_val in pairs(date_parameters_list) do     -- for each date-holding parameter in the list
  if is_set(param_val.val) then           -- if the parameter has a value
   date = param_val.val;
   for month in mw.ustring.gmatch (date, '[%a ]+') do     -- iterate through all date names in the date (single date or date range)
    month = mw.text.trim (month);         -- this because quarterly dates contain whitespace
    xlate = is_xlateable (month);         -- get translate <month>; returns translation or nil
    
    if xlate then  
     date = mw.ustring.gsub (date, month, xlate);    -- replace the English with the translation
     date_parameters_list[param_name].val = date;    -- save the translated date
     modified = true;
    end
   end

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


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

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

]]

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

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


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

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

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

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

]]

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

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