----------------------------< 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  
--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  
--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  
--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  
--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 '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