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模块:Citation/CS1/Date validation

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local p = {}

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

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

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

]]

local function is_valid_accessdate (accessdate)
local lang = mw.getContentLanguage();
local good1, good2;
local access_ts, tomorrow_ts; -- to hold unix time stamps representing the dates

accessdate = accessdate:gsub("年", "-");
accessdate = accessdate:gsub("月", "-");
accessdate = accessdate:gsub("日", "-");
accessdate = accessdate:gsub("-$", "");
good1, access_ts = pcall( lang.formatDate, lang, 'U', accessdate ); -- convert accessdate value to unix timesatmp
good2, tomorrow_ts = pcall( lang.formatDate, lang, 'U', 'today + 2 days' ); -- today midnight + 2 days is one second more than all day tomorrow

if good1 and good2 then
access_ts = tonumber (access_ts); -- convert to numbers for the comparison
tomorrow_ts = tonumber (tomorrow_ts);
else
return false; -- one or both failed to convert to unix time stamp
end

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

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

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

]]

local function get_month_number (month)
local long_months = {['January']=1, ['February']=2, ['March']=3, ['April']=4, ['May']=5, ['June']=6, ['July']=7, ['August']=8, ['September']=9, ['October']=10, ['November']=11, ['December']=12};
local short_months = {['Jan']=1, ['Feb']=2, ['Mar']=3, ['Apr']=4, ['May']=5, ['Jun']=6, ['Jul']=7, ['Aug']=8, ['Sep']=9, ['Oct']=10, ['Nov']=11, ['Dec']=12};
local zh_months = {['1月']=1, ['2月']=2, ['3月']=3, ['4月']=4, ['5月']=5, ['6月']=6, ['7月']=7, ['8月']=8, ['9月']=9, ['10月']=10, ['11月']=11, ['12月']=12}; -- LOCAL
local temp;
temp=long_months[month];
if temp then return temp; end -- if month is the long-form name
temp=short_months[month];
if temp then return temp; end -- if month is the short-form name
temp=zh_months[month]; -- LOCAL
if temp then return temp; end -- if month is in Chinese -- LOCAL
return 0; -- misspelled, improper case, or not a month name
end

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

returns a number according to the sequence of seasons in a year: 1 for Winter, etc. Capitalization and spelling must be correct. If not a valid season, returns 0

]]

local function get_season_number (season)
local season_list = {['Winter']=21, ['Spring']=22, ['Summer']=23, ['Fall']=24, ['Autumn']=24}; -- make sure these numbers do not overlap month numbers
local temp;
temp=season_list[season];
if temp then return temp; end -- if season is a valid name return its number
return 0; -- misspelled, improper case, or not a season name
end

--[[--------------------------< I S _ P R O P E R _ N A M E >--------------------------------------------------

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

]]

local function is_proper_name (name)
local name_list = {['Christmas']=31}
local temp;
temp=name_list[name];
if temp then return temp; end -- if name is a valid name return its number
return 0; -- misspelled, improper case, or not a proper name
end

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

--returns true if month or season is valid (properly spelled, capitalized, abbreviated)

]]

local function is_valid_month_or_season (month_season)
if 0 == get_month_number (month_season) then -- if month text isn't one of the twelve months, might be a season
if 0 == get_season_number (month_season) then -- not a month, is it a season?
return false; -- return false not a month or one of the five seasons
end
end
return true;
end

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

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

]]

local function is_valid_year(year)
if not is_set(year_limit) then
year_limit = tonumber(os.date("%Y"))+1; -- global variable so we only have to fetch it once
end
return tonumber(year) <= year_limit; -- false if year is in the future more than one year
end

--[[--------------------------< I S _ V A L I D _ D A T E >----------------------------------------------------
Returns true if day is less than or equal to the number of days in month and year is no farther into the future
than next year; else returns false.

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

]]

local function is_valid_date (year, month, day)
local days_in_month = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
local month_length;
if not is_valid_year(year) then -- no farther into the future than next year
return false;
end

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

if (2==month) then -- if February
month_length = 28; -- then 28 days unless
if 1582 > tonumber(year) then -- Julian calendar
if 0==(year%4) then
month_length = 29;
end
else -- Gregorian calendar
if (0==(year%4) and (0~=(year%100) or 0==(year%400))) then -- is a leap year?
month_length = 29; -- if leap year then 29 days in February
end
end
else
month_length=days_in_month[month];
end

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

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

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

Returns true when style for both months is the same

]]

local function is_valid_month_range_style (month1, month2)
local len1 = month1:len();
local len2 = month2:len();
if len1 == len2 then
return true; -- both months are short form so return true
elseif 'May' == month1 or 'May'== month2 then
return true; -- both months are long form so return true
elseif 3 == len1 or 3 == len2 then
return false; -- months are mixed form so return false
else
return true; -- both months are long form so return true
end
end


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

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

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

Similarly, seasons are also left to right, earliest to latest in time. There is an oddity with seasons: winter is assigned a value of 1, spring 2, ...,
fall and autumn 4. Because winter can follow fall/autumn at the end of a calender year, a special test is made to see if |date=Fall-Winter yyyy (4-1) is the date.

]]

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

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

if 0 ~= range_start_number then -- is start of range a season?
if range_start_number < range_end_number then -- range_start is a season
return true; -- return true when range_end is also a season and follows start season; else false
end
if 24 == range_start_number and 21 == range_end_number then -- special case when season range is Fall-Winter or Autumn-Winter
return true;
end
end
return false; -- range_start is not a month or a season; or range_start is a season and range_end is not; or improper season sequence
end

local range_end_number = get_month_number (range_end); -- get end month number
if range_start_number < range_end_number then -- range_start is a month; does range_start precede range_end?
if is_valid_month_range_style (range_start, range_end) then -- do months have the same style?
return true; -- proper order and same style
end
end
return false; -- range_start month number is greater than or equal to range end number; or range end isn't a month
end


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

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

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

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

The input table has:
year, year2 – always present; if before 1582, ignore months and days if present
month, month2 – 0 if not provided, 1-12 for months, 21-24 for seasons; 31– proper name dates
day, day2 – 0 if not provided, 1-31 for days

the output table receives:
rftdate: an IS8601 formatted date
rftchron: a free-form version of the date, usually without year which is in rftdate (season ranges and propername dates)
rftssn: one of four season keywords: winter, spring, summer, fall (lowercase)

]]

local function make_COinS_date (input, tCOinS_date)
local date; -- one date or first date in a range
local date2 = ''; -- end of range date

if 1582 > tonumber(input.year) or 20 < tonumber(input.month) then -- Julian calendar or season so &rft.date gets year only
date = input.year;
if 0 ~= input.year2 and input.year ~= input.year2 then -- if a range, only the second year portion when not the same as range start year
date = string.format ('%.4d/%.4d', tonumber(input.year), tonumber(input.year2)) -- assemble the date range
end
if 20 < tonumber(input.month) then -- if season or propername date
local season = {[21]='winter', [22]='spring', [23]='summer', [24]='fall', [31]='Christmas'}; -- seasons lowercase, no autumn; proper names use title case
if 0 == input.month2 then -- single season date
if 30 <tonumber(input.month) then
tCOinS_date.rftchron = season[input.month]; -- proper name dates
else
tCOinS_date.rftssn = season[input.month]; -- seasons
end
else -- season range with a second season specified
if input.year ~= input.year2 then -- season year – season year range or season year–year
tCOinS_date.rftssn = season[input.month]; -- start of range season; keep this?
if 0~= month2 then
tCOinS_date.rftchron = string.format ('%s %s – %s %s', season[input.month], input.year, season[input.month2], input.year2);
end
else -- season–season year range
tCOinS_date.rftssn = season[input.month]; -- start of range season; keep this?
tCOinS_date.rftchron = season[input.month] .. '–' .. season[input.month2]; -- season–season year range
end
end
end
tCOinS_date.rftdate = date;
return; -- done
end

if 0 ~= input.day then
date = string.format ('%s-%.2d-%.2d', input.year, tonumber(input.month), tonumber(input.day)); -- whole date
elseif 0 ~= input.month then
date = string.format ('%s-%.2d', input.year, tonumber(input.month)); -- year and month
else
date = string.format ('%s', input.year); -- just year
end

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

tCOinS_date.rftdate = date .. date2; -- date2 has the '/' separator
return;
end


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

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

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

Inputs:
date_string - date string from date-holding parameters (date, year, accessdate, embargo, archivedate, etc.)

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

]]

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

if date_string:match("^%d%d%d%d%-%d%d%-%d%d$") then -- year-initial numerical year month day format
year, month, day=string.match(date_string, "(%d%d%d%d)%-(%d%d)%-(%d%d)");
if 12 < tonumber(month) or 1 > tonumber(month) or 1583 > tonumber(year) then return false; end -- month number not valid or not Gregorian calendar
anchor_year = year;

elseif date_string:match("^%a+ +[1-9]%d?, +[1-9]%d%d%d%a?$") then -- month-initial: month day, year
month, day, anchor_year, year=string.match(date_string, "(%a+)%s*(%d%d?),%s*((%d%d%d%d)%a?)");
month = get_month_number (month);
if 0 == month then return false; end -- return false if month text isn't one of the twelve months

elseif date_string:match("^%a+ +[1-9]%d?–[1-9]%d?, +[1-9]%d%d%d%a?$") then -- month-initial day range: month day–day, year; days are separated by endash
month, day, day2, anchor_year, year=string.match(date_string, "(%a+) +(%d%d?)–(%d%d?), +((%d%d%d%d)%a?)");
if tonumber(day) >= tonumber(day2) then return false; end -- date range order is left to right: earlier to later; dates may not be the same;
month = get_month_number (month);
if 0 == month then return false; end -- return false if month text isn't one of the twelve months
month2=month; -- for metadata
year2=year;

elseif date_string:match("^[1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then -- day-initial: day month year
day, month, anchor_year, year=string.match(date_string, "(%d%d*)%s*(%a+)%s*((%d%d%d%d)%a?)");
month = get_month_number (month);
if 0 == month then return false; end -- return false if month text isn't one of the twelve months

elseif date_string:match("^[1-9]%d?–[1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then -- day-range-initial: day–day month year; days are separated by endash
day, day2, month, anchor_year, year=string.match(date_string, "(%d%d?)–(%d%d?) +(%a+) +((%d%d%d%d)%a?)");
if tonumber(day) >= tonumber(day2) then return false; end -- date range order is left to right: earlier to later; dates may not be the same;
month = get_month_number (month);
if 0 == month then return false; end -- return false if month text isn't one of the twelve months
month2=month; -- for metadata
year2=year;

elseif date_string:match("^[1-9]%d? +%a+ – [1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then -- day initial month-day-range: day month - day month year; uses spaced endash
day, month, day2, month2, anchor_year, year=date_string:match("(%d%d?) +(%a+) – (%d%d?) +(%a+) +((%d%d%d%d)%a?)");
if (not is_valid_month_season_range(month, month2)) or not is_valid_year(year) then return false; end -- date range order is left to right: earlier to later;
month = get_month_number (month); -- for metadata
month2 = get_month_number (month2);
year2=year;

elseif date_string:match("^%a+ +[1-9]%d? – %a+ +[1-9]%d?, +[1-9]%d%d%d?%a?$") then -- month initial month-day-range: month day – month day, year; uses spaced endash
month, day, month2, day2, anchor_year, year=date_string:match("(%a+) +(%d%d?) – (%a+) +(%d%d?), +((%d%d%d%d)%a?)");
if (not is_valid_month_season_range(month, month2)) or not is_valid_year(year) then return false; end
month = get_month_number (month); -- for metadata
month2 = get_month_number (month2);
year2=year;

elseif date_string:match("^[1-9]%d? +%a+ +[1-9]%d%d%d – [1-9]%d? +%a+ +[1-9]%d%d%d%a?$") then -- day initial month-day-year-range: day month year - day month year; uses spaced endash
day, month, year, day2, month2, anchor_year, year2=date_string:match("(%d%d?) +(%a+) +(%d%d%d%d?) – (%d%d?) +(%a+) +((%d%d%d%d?)%a?)");
if tonumber(year2) <= tonumber(year) then return false; end -- must be sequential years, left to right, earlier to later
if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end -- year2 no more than one year in the future; months same style
month = get_month_number (month); -- for metadata
month2 = get_month_number (month2);

elseif date_string:match("^%a+ +[1-9]%d?, +[1-9]%d%d%d – %a+ +[1-9]%d?, +[1-9]%d%d%d%a?$") then -- month initial month-day-year-range: month day, year – month day, year; uses spaced endash
month, day, year, month2, day2, anchor_year, year2=date_string:match("(%a+) +(%d%d?), +(%d%d%d%d) – (%a+) +(%d%d?), +((%d%d%d%d)%a?)");
if tonumber(year2) <= tonumber(year) then return false; end -- must be sequential years, left to right, earlier to later
if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end -- year2 no more than one year in the future; months same style
month = get_month_number (month); -- for metadata
month2 = get_month_number (month2);

elseif date_string:match("^%a+ +[1-9]%d%d%d–%d%d%a?$") then -- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
local century;
month, year, century, anchor_year, year2=date_string:match("(%a+) +((%d%d)%d%d)–((%d%d)%a?)");
if 'Winter' ~= month and 'Summer' ~= month then return false end; -- 'month' can only be Winter or Summer
anchor_year=year..'–'..anchor_year; -- assemble anchor_year from both years
year2 = century..year2; -- add the century to year2 for comparisons
if 1 ~= tonumber(year2) - tonumber(year) then return false; end -- must be sequential years, left to right, earlier to later
if not is_valid_year(year2) then return false; end -- no year farther in the future than next year
month = get_season_number (month);

elseif date_string:match("^%a+ +[1-9]%d%d%d–[1-9]%d%d%d%a?$") then -- special case Winter/Summer year-year; year separated with unspaced endash
month, year, anchor_year, year2=date_string:match("(%a+) +(%d%d%d%d)–((%d%d%d%d)%a?)");
if 'Winter' ~= month and 'Summer' ~= month then return false end; -- 'month' can only be Winter or Summer
anchor_year=year..'–'..anchor_year; -- assemble anchor_year from both years
if 1 ~= tonumber(year2) - tonumber(year) then return false; end -- must be sequential years, left to right, earlier to later
if not is_valid_year(year2) then return false; end -- no year farther in the future than next year
month = get_season_number (month); -- for metadata

elseif date_string:match("^%a+ +[1-9]%d%d%d% – %a+ +[1-9]%d%d%d%a?$") then -- month/season year - month/season year; separated by spaced endash
month, year, month2, anchor_year, year2=date_string:match("(%a+) +(%d%d%d%d) – (%a+) +((%d%d%d%d)%a?)");
anchor_year=year..'–'..anchor_year; -- assemble anchor_year from both years
if tonumber(year) >= tonumber(year2) then return false; end -- left to right, earlier to later, not the same
if not is_valid_year(year2) then return false; end -- no year farther in the future than next year
if 0 ~= get_month_number(month) and 0 ~= get_month_number(month2) and is_valid_month_range_style(month, month2) then -- both must be month year, same month style
month = get_month_number(month);
month2 = get_month_number(month2);
elseif 0 ~= get_season_number(month) and 0 ~= get_season_number(month2) then -- both must be or season year, not mixed
month = get_season_number(month);
month2 = get_season_number(month2);
else
return false;
end

elseif date_string:match ("^%a+–%a+ +[1-9]%d%d%d%a?$") then -- month/season range year; months separated by endash
month, month2, anchor_year, year=date_string:match ("(%a+)–(%a+)%s*((%d%d%d%d)%a?)");
if (not is_valid_month_season_range(month, month2)) or (not is_valid_year(year)) then return false; end
if 0 ~= get_month_number(month) then -- determined to be a valid range so just check this one to know if month or season
month = get_month_number(month);
month2 = get_month_number(month2);
else
month = get_season_number(month);
month2 = get_season_number(month2);
end
year2=year;

elseif date_string:match("^%a+ +%d%d%d%d%a?$") then -- month/season year or proper-name year
month, anchor_year, year=date_string:match("(%a+)%s*((%d%d%d%d)%a?)");
if not is_valid_year(year) then return false; end
if not is_valid_month_or_season (month) and 0 == is_proper_name (month) then return false; end
if 0 ~= get_month_number(month) then -- determined to be a valid range so just check this one to know if month or season
month = get_month_number(month);
elseif 0 ~= get_season_number(month) then
month = get_season_number(month);
else
month = is_proper_name (month); -- must be proper name; not supported in COinS
end

elseif date_string:match("^[1-9]%d%d%d?–[1-9]%d%d%d?%a?$") then -- Year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
year, anchor_year, year2=date_string:match("(%d%d%d%d?)–((%d%d%d%d?)%a?)");
anchor_year=year..'–'..anchor_year; -- assemble anchor year from both years
if tonumber(year) >= tonumber(year2) then return false; end -- left to right, earlier to later, not the same
if not is_valid_year(year2) then return false; end -- no year farther in the future than next year

elseif date_string:match("^[1-9]%d%d%d–%d%d%a?$") then -- Year range: YYYY–YY; separated by unspaced endash
local century;
year, century, anchor_year, year2=date_string:match("((%d%d)%d%d)–((%d%d)%a?)");
anchor_year=year..'–'..anchor_year; -- assemble anchor year from both years
if 13 > tonumber(year2) then return false; end -- don't allow 2003-05 which might be May 2003
year2 = century..year2; -- add the century to year2 for comparisons
if tonumber(year) >= tonumber(year2) then return false; end -- left to right, earlier to later, not the same
if not is_valid_year(year2) then return false; end -- no year farther in the future than next year

elseif date_string:match("^[1-9]%d%d%d?%a?$") then -- year; here accept either YYY or YYYY
anchor_year, year=date_string:match("((%d%d%d%d?)%a?)");
if false == is_valid_year(year) then
return false;
end

-- LOCAL: do not use mw.ustring: it allows full-width characters for %d.
elseif date_string:match("^[1-9]%d%d%d年[1-9]%d?月[1-9]%d?日$") then -- zh: year month day
year, month, day=date_string:match("(%d%d%d%d)年(%d%d*月)(%d%d*)日");
month = get_month_number (month);
if 0 == month then return false; end
anchor_year = year;

elseif date_string:match("^[1-9]%d%d%d年[1-9]%d?月$") then -- zh: year month
year, month=date_string:match("(%d%d%d%d)年(%d%d*月)");
month = get_month_number (month);
if 0 == month then return false; end
anchor_year = year;

elseif date_string:match("^[1-9]%d%d%d?年$") then -- zh: year; here accept either YYY or YYYY
year=date_string:match("(%d%d%d%d?)年");
if false == is_valid_year(year) then
return false;
end
anchor_year = year;

elseif date_string:match("^%d%d%d%d%-%d%d$") then -- numerical year month format
year, month=date_string:match("(%d%d%d%d)%-(%d%d)");
month=tonumber(month);
if 12 < month or 1 > month or 1583 > tonumber(year) then return false; end -- month number not valid or not Gregorian calendar
anchor_year = year;
-- END LOCAL

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

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

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

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

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

if false == result then return false; end

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

return true, anchor_year; -- format is good and date string represents a real date
end


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

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

Unlike most error messages created in this module, only one error message is created by this function. Because all of the date holding parameters are processed serially,
a single error message is created as the dates are tested.

]]

local function dates(date_parameters_list, tCOinS_date)
local anchor_year; -- will return as nil if the date being tested is not |date=
local COinS_date; -- will return as nil if the date being tested is not |date=
local error_message = "";
local good_date = false;

for k, v in pairs(date_parameters_list) do -- for each date-holding parameter in the list
if is_set(v) then -- if the parameter has a value
if v:match("^c%. [1-9]%d%d%d?%a?$") then -- special case for c. year or with or without CITEREF disambiguator - only |date= and |year=
local year = v:match("c%. ([1-9]%d%d%d?)%a?"); -- get the year portion so it can be tested
if 'date'==k then
anchor_year, COinS_date = v:match("((c%. [1-9]%d%d%d?)%a?)"); -- anchor year and COinS_date only from |date= parameter
good_date = is_valid_year(year);
elseif 'year'==k then
good_date = is_valid_year(year);
end
elseif 'date'==k then -- if the parameter is |date=
if v:match("^n%.d%.%a?") then -- if |date=n.d. with or without a CITEREF disambiguator
good_date, anchor_year, COinS_date = true, v:match("((n%.d%.)%a?)"); --"n.d."; no error when date parameter is set to no date
elseif v:match("^nd%a?$") then -- if |date=nd with or without a CITEREF disambiguator
good_date, anchor_year, COinS_date = true, v:match("((nd)%a?)"); --"nd"; no error when date parameter is set to no date
else
good_date, anchor_year, COinS_date = check_date (v, tCOinS_date); -- go test the date
end
elseif 'access-date'==k then -- if the parameter is |date=
good_date = check_date (v); -- go test the date
if true == good_date then -- if the date is a valid date
good_date = is_valid_accessdate (v); -- is Wikipedia start date < accessdate < tomorrow's date?
end
else -- any other date-holding parameter
good_date = check_date (v); -- go test the date
end
if false==good_date then -- assemble one error message so we don't add the tracking category multiple times
if is_set(error_message) then -- once we've added the first portion of the error message ...
error_message=error_message .. ", "; -- ... add a comma space separator
end
error_message=error_message .. "&#124;" .. k .. "="; -- add the failed parameter
end
end
end
return anchor_year, error_message; -- and done
end


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

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

]]

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

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

if date_string:match ('%d%d%d%d%-%d%d%-%d%d') and year_string:match ('%d%d%d%d%a') then --special case where date and year 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 formats of date with two three- or four-digit years
date1, date2 = date_string:match ("(%d%d%d%d?).-(%d%d%d%d?)");
if year ~= date1 and year ~= date2 then
result = 0;
end

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

elseif date_string:match ("%d%d%d%d?") then -- any of the standard formats of date with one year
date1 = date_string:match ("(%d%d%d%d?)");
if year ~= date1 then
result = 0;
end
end
return result;
end

return {dates = dates, year_date_check = year_date_check} -- return exported functions