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

]]



local has_accept_as_written, is_set, in_array, set_message, select_one,			-- functions in Module:Citation/CS1/Utilities

		substitute, make_wikilink;



local z;																		-- table of tables defined in Module:Citation/CS1/Utilities



local cfg;																		-- table of configuration tables that are defined in Module:Citation/CS1/Configuration





--[[--------------------------< P A G E   S C O P E   V A R I A B L E S >--------------------------------------



declare variables here that have page-wide scope that are not brought in from other modules; that are created here and used here



]]



local auto_link_urls = {};														-- holds identifier URLs for those identifiers that can auto-link |title=





--============================<< H E L P E R   F U N C T I O N S >>============================================



--[[--------------------------< W I K I D A T A _ A R T I C L E _ N A M E _ G E T >----------------------------



as an aid to internationalizing identifier-label wikilinks, gets identifier article names from Wikidata.



returns :<lang code>:<article title> when <q> has an <article title> for <lang code>; nil else



for identifiers that do not have q, returns nil



for wikis that do not have mw.wikibase installed, returns nil



]]



local function wikidata_article_name_get (q)

	if not is_set (q) or (q and not mw.wikibase) then							-- when no q number or when a q number but mw.wikibase not installed on this wiki

		return nil;																-- abandon

	end



	local wd_article;

	local this_wiki_code = cfg.this_wiki_code;									-- Wikipedia subdomain; 'en' for en.wikipedia.org



	wd_article = mw.wikibase.getSitelink (q, this_wiki_code .. 'wiki');			-- fetch article title from WD; nil when no title available at this wiki



	if wd_article then

		wd_article = table.concat ({':', this_wiki_code, ':', wd_article});		-- interwiki-style link without brackets if taken from WD; leading colon required

	end



	return wd_article;															-- article title from WD; nil else

end





--[[--------------------------< L I N K _ L A B E L _ M A K E >------------------------------------------------



common function to create identifier link label from handler table or from Wikidata



returns the first available of

	1. redirect from local wiki's handler table (if enabled)

	2. Wikidata (if there is a Wikidata entry for this identifier in the local wiki's language)

	3. label specified in the local wiki's handler table

	

]]



local function link_label_make (handler)

	local wd_article;

	

	if not (cfg.use_identifier_redirects and is_set (handler.redirect)) then	-- redirect has priority so if enabled and available don't fetch from Wikidata because expensive

		wd_article = wikidata_article_name_get (handler.q);						-- if Wikidata has an article title for this wiki, get it;

	end

	

	return (cfg.use_identifier_redirects and is_set (handler.redirect) and handler.redirect) or wd_article or handler.link;

end





--[[--------------------------< E X T E R N A L _ L I N K _ I D >----------------------------------------------



Formats a wiki-style external link



]]



local function external_link_id (options)

	local url_string = options.id;

	local ext_link;

	local this_wiki_code = cfg.this_wiki_code;									-- Wikipedia subdomain; 'en' for en.wikipedia.org

	local wd_article;															-- article title from Wikidata

	

	if options.encode == true or options.encode == nil then

		url_string = mw.uri.encode (url_string, 'PATH');

	end



	if options.auto_link and is_set (options.access) then

		auto_link_urlsoptions.auto_link = table.concat ({options.prefix, url_string, options.suffix});

	end



	ext_link = mw.ustring.format ('[%s%s%s %s]', options.prefix, url_string, options.suffix or "", mw.text.nowiki (options.id));

	if is_set (options.access) then

		ext_link = substitute (cfg.presentation'ext-link-access-signal'], {cfg.presentationoptions.access].class, cfg.presentationoptions.access].title, ext_link});	-- add the free-to-read / paywall lock

	end



	return table.concat	({

		make_wikilink (link_label_make (options), options.label),				-- redirect, Wikidata link, or locally specified link (in that order)

		options.separator or '&nbsp;',

		ext_link

		});

end





--[[--------------------------< I N T E R N A L _ L I N K _ I D >----------------------------------------------



Formats a wiki-style internal link



TODO: Does not currently need to support options.access, options.encode, auto-linking and COinS (as in external_link_id),

but may be needed in the future for :m:Interwiki_map custom-prefixes like :arxiv:, :bibcode:, :DOI:, :hdl:, :ISSN:,

:JSTOR:, :Openlibrary:, :PMID:, :RFC:.



]]



local function internal_link_id (options)

	local id = mw.ustring.gsub (options.id, '%d', cfg.date_names.local_digits);	-- translate 'local' digits to Western 0-9



	return table.concat (

		{

		make_wikilink (link_label_make (options), options.label),				-- wiki-link the identifier label

		options.separator or '&nbsp;',											-- add the separator

		make_wikilink (

			table.concat (

				{

				options.prefix,

				id,																-- translated to Western digits

				options.suffix or ''

				}),

			substitute (cfg.presentation'bdi'], {'', mw.text.nowiki (options.id)})	-- bdi tags to prevent Latin script identifiers from being reversed at RTL language wikis

			);																	-- nowiki because MediaWiki still has magic links for ISBN and the like; TODO: is it really required?

		});

end





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



Determines if a PMC identifier's online version is embargoed. Compares the date in |pmc-embargo-date= against

today's date.  If embargo date is in the future, returns the content of |pmc-embargo-date=; otherwise, returns

an empty string because the embargo has expired or because |pmc-embargo-date= was not set in this cite.



]]



local function is_embargoed (embargo)

	if is_set (embargo) then

		local lang = mw.getContentLanguage();

		local good1, embargo_date, todays_date;

		good1, embargo_date = pcall (lang.formatDate, lang, 'U', embargo);

		todays_date = lang:formatDate ('U');

	

		if good1 then															-- if embargo date is a good date

			if tonumber (embargo_date) >= tonumber (todays_date) then			-- is embargo date is in the future?

				return embargo;													-- still embargoed

			else

				set_message ('maint_pmc_embargo');								-- embargo has expired; add main cat

				return '';														-- unset because embargo has expired

			end

		end

	end

	return '';																	-- |pmc-embargo-date= not set return empty string

end





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



for biorxiv, returns true if:

	2019-12-11T00:00Z <= biorxiv_date < today + 2 days

for medrxiv, returns true if:

	2020-01-01T00:00Z <= medrxiv_date < today + 2 days

	

The dated form of biorxiv identifier has a start date of 2019-12-11.  The Unix timestamp for that date is {{#time:U|2019-12-11}} = 1576022400

The medrxiv identifier has a start date of 2020-01-01.  The Unix timestamp for that date is {{#time:U|2020-01-01}} = 1577836800



<rxiv_date> is the date provided in those |biorxiv= parameter values that are dated and in |medrxiv= parameter values at time 00:00:00 UTC

<today> is the current date at time 00:00:00 UTC plus 48 hours

	if today's date is 2023-01-01T00:00:00 then

		adding 24 hours gives 2023-01-02T00:00:00 – one second more than today

		adding 24 hours gives 2023-01-03T00:00:00 – one second more than tomorrow



inputs:

	<y>, <m>, <d> – year, month, day parts of the date from the birxiv or medrxiv identifier

	<select> 'b' for biorxiv, 'm' for medrxiv; defaults to 'b'



]=]



local function is_valid_rxiv_date (y, m, d, select)

	if 0 == tonumber (m) and 12 < tonumber (m) then								-- <m> must be a number 1–12

		return false;

	end

	if 0 == tonumber (d) and 31 < tonumber (d) then								-- <d> must be a number 1–31; TODO: account for month length and leap yer?

		return false;

	end

	

	local rxiv_date = table.concat ({y, m, d}, '-');							-- make ymd date string

	local good1, good2;

	local rxiv_ts, tomorrow_ts;													-- to hold Unix timestamps representing the dates

	local lang_object = mw.getContentLanguage();



	good1, rxiv_ts = pcall (lang_object.formatDate, lang_object, 'U', rxiv_date);		-- convert rxiv_date 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 tonumber() may not understand

		rxiv_ts = tonumber (rxiv_ts) or lang_object:parseFormattedNumber (rxiv_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 timestamp

	end



	local limit_ts = ((select and ('m' == select)) and 1577836800) or 1576022400;	-- choose the appropriate limit timesatmp



	return ((limit_ts <= rxiv_ts) and (rxiv_ts < tomorrow_ts))					-- limit_ts <= rxiv_date < tomorrow's date

end





--[[--------------------------< IS _ V A L I D _ I S X N >-----------------------------------------------------



ISBN-10 and ISSN validator code calculates checksum across all ISBN/ISSN digits including the check digit.

ISBN-13 is checked in isbn().



If the number is valid the result will be 0. Before calling this function, ISBN/ISSN must be checked for length

and stripped of dashes, spaces and other non-ISxN characters.



]]



local function is_valid_isxn (isxn_str, len)

	local temp = 0;

	isxn_str = { isxn_str:byte(1, len) };										-- make a table of byte values '0' → 0x30 .. '9' → 0x39, 'X' → 0x58

	len = len + 1;																-- adjust to be a loop counter

	for i, v in ipairs (isxn_str) do											-- loop through all of the bytes and calculate the checksum

		if v == string.byte ("X" ) then											-- if checkdigit is X (compares the byte value of 'X' which is 0x58)

			temp = temp + 10 * (len - i);										-- it represents 10 decimal

		else

			temp = temp + tonumber (string.char (v) )*(len-i);

		end

	end

	return temp % 11 == 0;														-- returns true if calculation result is zero

end





--[[--------------------------< IS _ V A L I D _ I S X N _ 1 3 >-----------------------------------------------



ISBN-13 and ISMN validator code calculates checksum across all 13 ISBN/ISMN digits including the check digit.

If the number is valid, the result will be 0. Before calling this function, ISBN-13/ISMN must be checked for length

and stripped of dashes, spaces and other non-ISxN-13 characters.



]]



local function is_valid_isxn_13 (isxn_str)

	local temp=0;

	

	isxn_str = { isxn_str:byte(1, 13) };										-- make a table of byte values '0' → 0x30 .. '9' → 0x39

	for i, v in ipairs (isxn_str) do

		temp = temp + (3 - 2*(i % 2)) * tonumber (string.char (v) );			-- multiply odd index digits by 1, even index digits by 3 and sum; includes check digit

	end

	return temp % 10 == 0;														-- sum modulo 10 is zero when ISBN-13/ISMN is correct

end





--[[--------------------------< N O R M A L I Z E _ L C C N >--------------------------------------------------



LCCN normalization (https://www.loc.gov/marc/lccn-namespace.html#normalization)

1. Remove all blanks.

2. If there is a forward slash (/) in the string, remove it, and remove all characters to the right of the forward slash.

3. If there is a hyphen in the string:

	a. Remove it.

	b. Inspect the substring following (to the right of) the (removed) hyphen. Then (and assuming that steps 1 and 2 have been carried out):

		1. All these characters should be digits, and there should be six or less. (not done in this function)

		2. If the length of the substring is less than 6, left-fill the substring with zeroes until the length is six.



Returns a normalized LCCN for lccn() to validate.  There is no error checking (step 3.b.1) performed in this function.



]]



local function normalize_lccn (lccn)

	lccn = lccn:gsub ("%s", "");												-- 1. strip whitespace



	if nil ~= string.find (lccn, '/') then

		lccn = lccn:match ("(.-)/");											-- 2. remove forward slash and all character to the right of it

	end



	local prefix

	local suffix

	prefix, suffix = lccn:match ("(.+)%-(.+)");									-- 3.a remove hyphen by splitting the string into prefix and suffix



	if nil ~= suffix then														-- if there was a hyphen

		suffix = string.rep("0", 6-string.len (suffix)) .. suffix;				-- 3.b.2 left fill the suffix with 0s if suffix length less than 6

		lccn = prefix..suffix;													-- reassemble the LCCN

	end

	

	return lccn;

	end





--============================<< I D E N T I F I E R   F U N C T I O N S >>====================================



--[[--------------------------< A R X I V >--------------------------------------------------------------------



See: https://arxiv.org/help/arxiv_identifier



format and error check arXiv identifier.  There are three valid forms of the identifier:

the first form, valid only between date codes 9107 and 0703, is:

	arXiv:<archive>.<class>/<date code><number><version>

where:

	<archive> is a string of alpha characters - may be hyphenated; no other punctuation

	<class> is a string of alpha characters - may be hyphenated; no other punctuation; not the same as |class= parameter which is not supported in this form

	<date code> is four digits in the form YYMM where YY is the last two digits of the four-digit year and MM is the month number January = 01

		first digit of YY for this form can only 9 and 0

	<number> is a three-digit number

	<version> is a 1 or more digit number preceded with a lowercase v; no spaces (undocumented)

	

the second form, valid from April 2007 through December 2014 is:

	arXiv:<date code>.<number><version>

where:

	<date code> is four digits in the form YYMM where YY is the last two digits of the four-digit year and MM is the month number January = 01

	<number> is a four-digit number

	<version> is a 1 or more digit number preceded with a lowercase v; no spaces



the third form, valid from January 2015 is:

	arXiv:<date code>.<number><version>

where:

	<date code> and <version> are as defined for 0704-1412

	<number> is a five-digit number



]]



local function arxiv (options)

	local id = options.id;

	local class = options.Class;												-- TODO: lowercase?

	local handler = options.handler;

	local year, month, version;

	local err_msg = false;														-- assume no error message

	local text;																	-- output text

	

	if id:match("^%a[%a%.%-]+/[90]%d[01]%d%d%d%d$") or id:match("^%a[%a%.%-]+/[90]%d[01]%d%d%d%dv%d+$") then	-- test for the 9107-0703 format with or without version

		year, month = id:match("^%a[%a%.%-]+/([90]%d)([01]%d)%d%d%d[v%d]*$");

		year = tonumber (year);

		month = tonumber (month);

		if ((not (90 < year or 8 > year)) or (1 > month or 12 < month)) or		-- if invalid year or invalid month

			((91 == year and 7 > month) or (7 == year and 3 < month)) then		-- if years ok, are starting and ending months ok?

				err_msg = true;													-- flag for error message

		end



	elseif id:match("^%d%d[01]%d%.%d%d%d%d$") or id:match("^%d%d[01]%d%.%d%d%d%dv%d+$") then	-- test for the 0704-1412 with or without version

		year, month = id:match("^(%d%d)([01]%d)%.%d%d%d%d[v%d]*$");

		year = tonumber (year);

		month = tonumber (month);

		if ((7 > year) or (14 < year) or (1 > month or 12 < month)) or			-- is year invalid or is month invalid? (doesn't test for future years)

			((7 == year) and (4 > month)) then									-- when year is 07, is month invalid (before April)?

				err_msg = true;													-- flag for error message

		end



	elseif id:match("^%d%d[01]%d%.%d%d%d%d%d$") or id:match("^%d%d[01]%d%.%d%d%d%d%dv%d+$") then	-- test for the 1501- format with or without version

		year, month = id:match("^(%d%d)([01]%d)%.%d%d%d%d%d[v%d]*$");

		year = tonumber (year);

		month = tonumber (month);

		if ((15 > year) or (1 > month or 12 < month)) then						-- is year invalid or is month invalid? (doesn't test for future years)

			err_msg = true;														-- flag for error message

		end



	else

		err_msg = true;															-- not a recognized format; flag for error message

	end



	if err_msg then

		options.coins_list_t'ARXIV' = nil;									-- when error, unset so not included in COinS

	end

	

	local err_msg_t = {};

	if err_msg then

		set_message ('err_bad_arxiv');

	end



	text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = handler.access});



	if is_set (class) then

		if id:match ('^%d+') then

			text = table.concat ({text, ' [[https://arxiv.org/archive/', class, ' ', class, ']]'});	-- external link within square brackets, not wikilink

		else

			set_message ('err_class_ignored');

		end

	end



	return text;

end





--[[--------------------------< B I B C O D E >--------------------------------------------------------------------



Validates (sort of) and formats a bibcode ID.



Format for bibcodes is specified here: https://adsabs.harvard.edu/abs_doc/help_pages/data.html#bibcodes



But, this: 2015arXiv151206696F is apparently valid so apparently, the only things that really matter are length, 19 characters

and first four digits must be a year.  This function makes these tests:

	length must be 19 characters

	characters in position

		1–4 must be digits and must represent a year in the range of 1000 – next year

		5 must be a letter

		6–8 must be letter, digit, ampersand, or dot (ampersand cannot directly precede a dot; &. )

		9–18 must be letter, digit, or dot

		19 must be a letter or dot



]]



local function bibcode (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;

	local ignore_invalid = options.accept;

	local err_type;

	local err_msg = '';

	local year;



	local text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode,

		access = access});

	

	if 19 ~= id:len() then

		err_type = cfg.err_msg_supl.length;

	else

		year = id:match ("^(%d%d%d%d)[%a][%w&%.][%w&%.][%w&%.][%w.]+[%a%.]$");

		if not year then														-- if nil then no pattern match

			err_type = cfg.err_msg_supl.value;									-- so value error

		else

			local next_year = tonumber (os.date ('%Y')) + 1;					-- get the current year as a number and add one for next year

			year = tonumber (year);												-- convert year portion of bibcode to a number

			if (1000 > year) or (year > next_year) then

				err_type = cfg.err_msg_supl.year;								-- year out of bounds

			end

			if id:find('&%.') then

				err_type = cfg.err_msg_supl.journal;							-- journal abbreviation must not have '&.' (if it does it's missing a letter)

			end

			if id:match ('.........%.tmp%.') then								-- temporary bibcodes when positions 10–14 are '.tmp.'

				set_message ('maint_bibcode');

			end

		end

	end



	if is_set (err_type) and not ignore_invalid then							-- if there was an error detected and accept-as-written markup not used

		set_message ('err_bad_bibcode', {err_type});

		options.coins_list_t'BIBCODE' = nil;									-- when error, unset so not included in COinS

	end



	return text;

end





--[[--------------------------< B I O R X I V >-----------------------------------------------------------------



Format bioRxiv ID and do simple error checking.  Before 2019-12-11, biorXiv IDs were 10.1101/ followed by exactly

6 digits.  After 2019-12-11, biorXiv IDs retained the six-digit identifier but prefixed that with a yyyy.mm.dd. 

date and suffixed with an optional version identifier.



The bioRxiv ID is the string of characters:

	https://doi.org/10.1101/078733 -> 10.1101/078733

or a date followed by a six-digit number followed by an optional version indicator 'v' and one or more digits:

	https://www.biorxiv.org/content/10.1101/2019.12.11.123456v2 -> 10.1101/2019.12.11.123456v2

	

see https://www.biorxiv.org/about-biorxiv



]]



local function biorxiv (options)

	local id = options.id;

	local handler = options.handler;

	local err_msg = true;														-- flag; assume that there will be an error

	

	local patterns = {

		'^10%.1101/%d%d%d%d%d%d$',												-- simple 6-digit identifier (before 2019-12-11)

		'^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%dv%d+$',				-- y.m.d. date + 6-digit identifier + version (after 2019-12-11)

		'^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d$',					-- y.m.d. date + 6-digit identifier (after 2019-12-11)

		}

	

	for _, pattern in ipairs (patterns) do										-- spin through the patterns looking for a match

		if id:match (pattern) then

			local y, m, d = id:match (pattern);									-- found a match, attempt to get year, month and date from the identifier



			if m then															-- m is nil when id is the six-digit form

				if not is_valid_rxiv_date (y, m, d, 'b') then					-- validate the encoded date; 'b' for biorxiv limit

					break;														-- date fail; break out early so we don't unset the error message

				end

			end

			err_msg = nil;														-- we found a match so unset the error message

			break;																-- and done

		end

	end																			-- err_cat remains set here when no match



	if err_msg then

		options.coins_list_t'BIORXIV' = nil;									-- when error, unset so not included in COinS

		set_message ('err_bad_biorxiv');										-- and set the error message

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator,

			encode = handler.encode, access = handler.access});

end





--[[--------------------------< C I T E S E E R X >------------------------------------------------------------



CiteSeerX use their own notion of "doi" (not to be confused with the identifiers resolved via doi.org).



The description of the structure of this identifier can be found at Help_talk:Citation_Style_1/Archive_26#CiteSeerX_id_structure



]]



local function citeseerx (options)

	local id = options.id;

	local handler = options.handler;

	local matched;



	local text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode,

		access = handler.access});

	

	matched = id:match ("^10%.1%.1%.[1-9]%d?%d?%d?%.[1-9]%d?%d?%d?$");

	if not matched then

		set_message ('err_bad_citeseerx' );

		options.coins_list_t'CITESEERX' = nil;								-- when error, unset so not included in COinS

	end



	return text;

end





--[[--------------------------< D O I >------------------------------------------------------------------------



Formats a DOI and checks for DOI errors.



DOI names contain two parts: prefix and suffix separated by a forward slash.

	Prefix: directory indicator '10.' followed by a registrant code

	Suffix: character string of any length chosen by the registrant



This function checks a DOI name for: prefix/suffix.  If the DOI name contains spaces or endashes, or, if it ends

with a period or a comma, this function will emit a bad_doi error message.



DOI names are case-insensitive and can incorporate any printable Unicode characters so the test for spaces, endash,

and terminal punctuation may not be technically correct but it appears, that in practice these characters are rarely

if ever used in DOI names.



https://www.doi.org/doi_handbook/2_Numbering.html				-- 2.2 Syntax of a DOI name

https://www.doi.org/doi_handbook/2_Numbering.html#2.2.2			-- 2.2.2 DOI prefix



]]



local function doi (options)

	local id = options.id;

	local inactive = options.DoiBroken

	local access = options.access;

	local ignore_invalid = options.accept;

	local handler = options.handler;

	local err_flag;



	local text;

	if is_set (inactive) then

		local inactive_year = inactive:match("%d%d%d%d");						-- try to get the year portion from the inactive date

		local inactive_month, good;



		if is_set (inactive_year) then

			if 4 < inactive:len() then											-- inactive date has more than just a year (could be anything)

				local lang_obj = mw.getContentLanguage();						-- get a language object for this wiki

				good, inactive_month = pcall (lang_obj.formatDate, lang_obj, 'F', inactive);	-- try to get the month name from the inactive date

				if not good then

					inactive_month = nil;										-- something went wrong so make sure this is unset

				end

			end

		end																		-- otherwise, |doi-broken-date= has something but it isn't a date

		

		if is_set (inactive_year) and is_set (inactive_month) then

			set_message ('maint_doi_inactive_dated', {inactive_year, inactive_month, ' '});

		elseif is_set (inactive_year) then

			set_message ('maint_doi_inactive_dated', {inactive_year, '', ''});

		else

			set_message ('maint_doi_inactive');

		end

		inactive = " (" .. cfg.messages'inactive' .. ' ' .. inactive .. ')';

	end



	local registrant = mw.ustring.match (id, '^10%.([^/]+)/[^%s–]-[^%.,]$');	-- registrant set when DOI has the proper basic form



	local registrant_err_patterns = {											-- these patterns are for code ranges that are not supported 

		'^[^1-3]%d%d%d%d%.%d+$',												-- 5 digits with subcode (0xxxx, 40000+); accepts: 10000–39999

		'^[^1-6]%d%d%d%d$',														-- 5 digits without subcode (0xxxx, 60000+); accepts: 10000–69999

		'^[^1-9]%d%d%d%.%d+$',												-- 4 digits with subcode (0xxx); accepts: 1000–9999

		'^[^1-9]%d%d%d$',														-- 4 digits without subcode (0xxx); accepts: 1000–9999

		'^%d%d%d%d%d%d+',														-- 6 or more digits

		'^%d%d?%d?$',															-- less than 4 digits without subcode (3 digits with subcode is legitimate)

		'^%d%d?%.[%d%.]+',														-- 1 or 2 digits with subcode

		'^5555$',																-- test registrant will never resolve

		'[^%d%.]',																-- any character that isn't a digit or a dot

		}



	if not ignore_invalid then

		if registrant then														-- when DOI has proper form

			for i, pattern in ipairs (registrant_err_patterns) do				-- spin through error patterns

				if registrant:match (pattern) then								-- to validate registrant codes

					err_flag = set_message ('err_bad_doi');						-- when found, mark this DOI as bad

					break;														-- and done

				end

			end

		else

			err_flag = set_message ('err_bad_doi');								-- invalid directory or malformed

		end

	else

		set_message ('maint_doi_ignore');

	end



	if err_flag then

		options.coins_list_t'DOI' = nil;										-- when error, unset so not included in COinS

	else

		if not access and cfg.known_free_doi_registrants_tregistrant then		-- |doi-access=free not set and <registrant> is known to be free

			set_message ('maint_doi_unflagged_free');							-- set a maint cat

		end

	end

	

	text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = access,

		auto_link = not (err_flag or is_set (inactive) or ignore_invalid) and 'doi' or nil -- do not auto-link when |doi-broken-date= has a value or when there is a DOI error or (to play it safe, after all, auto-linking is not essential) when invalid DOIs are ignored

		}) .. (inactive or '');



	return text;

end





--[[--------------------------< H D L >------------------------------------------------------------------------



Formats an HDL with minor error checking.



HDL names contain two parts: prefix and suffix separated by a forward slash.

	Prefix: character string using any character in the UCS-2 character set except '/'

	Suffix: character string of any length using any character in the UCS-2 character set chosen by the registrant



This function checks a HDL name for: prefix/suffix.  If the HDL name contains spaces, endashes, or, if it ends

with a period or a comma, this function will emit a bad_hdl error message.



HDL names are case-insensitive and can incorporate any printable Unicode characters so the test for endashes and

terminal punctuation may not be technically correct but it appears, that in practice these characters are rarely

if ever used in HDLs.



Query string parameters are named here: https://www.handle.net/proxy_servlet.html.  query strings are not displayed

but since '?' is an allowed character in an HDL, '?' followed by one of the query parameters is the only way we

have to detect the query string so that it isn't URL-encoded with the rest of the identifier.



]]



local function hdl (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;

	local query_params = {														-- list of known query parameters from https://www.handle.net/proxy_servlet.html

		'noredirect',

		'ignore_aliases',

		'auth',

		'cert',

		'index',

		'type',

		'urlappend',

		'locatt',

		'action',

		}

	

	local hdl, suffix, param = id:match ('(.-)(%?(%a+).+)$');					-- look for query string

	local found;



	if hdl then																	-- when there are query strings, this is the handle identifier portion

		for _, q in ipairs (query_params) do									-- spin through the list of query parameters

			if param:match ('^' .. q) then										-- if the query string begins with one of the parameters

				found = true;													-- announce a find

				break;															-- and stop looking

			end

		end

	end



	if found then

		id = hdl;																-- found so replace id with the handle portion; this will be URL-encoded, suffix will not

	else

		suffix = '';															-- make sure suffix is empty string for concatenation else

	end



	local text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, suffix = suffix, separator = handler.separator, encode = handler.encode, access = access})



	if nil == id:match("^[^%s–]-/[^%s–]-[^%.,]$") then							-- HDL must contain a forward slash, must not contain spaces, endashes, and must not end with period or comma

		set_message ('err_bad_hdl' );

		options.coins_list_t'HDL' = nil;										-- when error, unset so not included in COinS

	end



	return text;

end





--[[--------------------------< I S B N >----------------------------------------------------------------------



Determines whether an ISBN string is valid



]]



local function isbn (options)

	local isbn_str = options.id;

	local ignore_invalid = options.accept;

	local handler = options.handler;



	local function return_result (check, err_type)								-- local function to handle the various returns

		local ISBN = internal_link_id ({link = handler.link, label = handler.label, redirect = handler.redirect,

						prefix = handler.prefix, id = isbn_str, separator = handler.separator});

		if ignore_invalid then													-- if ignoring ISBN errors

			set_message ('maint_isbn_ignore');									-- add a maint category even when there is no error

		else																	-- here when not ignoring

			if not check then													-- and there is an error

				options.coins_list_t'ISBN' = nil;								-- when error, unset so not included in COinS

				set_message ('err_bad_isbn', err_type);							-- set an error message

				return ISBN;										 			-- return id text

			end

		end

		return ISBN;															-- return id text

	end



	if nil ~= isbn_str:match ('[^%s-0-9X]') then

		return return_result (false, cfg.err_msg_supl.char);					-- fail if isbn_str contains anything but digits, hyphens, or the uppercase X

	end



	local id = isbn_str:gsub ('[%s-]', '');										-- remove hyphens and whitespace



	local len = id:len();

 

	if len ~= 10 and len ~= 13 then

		return return_result (false, cfg.err_msg_supl.length);					-- fail if incorrect length

	end



	if len == 10 then

		if id:match ('^%d*X?$') == nil then										-- fail if isbn_str has 'X' anywhere but last position

			return return_result (false, cfg.err_msg_supl.form);									

		end

		if not is_valid_isxn (id, 10) then										-- test isbn-10 for numerical validity

			return return_result (false, cfg.err_msg_supl.check);				-- fail if isbn-10 is not numerically valid

		end

		if id:find ('^63[01]') then												-- 630xxxxxxx and 631xxxxxxx are (apparently) not valid isbn group ids but are used by amazon as numeric identifiers (asin)

			return return_result (false, cfg.err_msg_supl.group);				-- fail if isbn-10 begins with 630/1

		end

		return return_result (true, cfg.err_msg_supl.check);					-- pass if isbn-10 is numerically valid

	else

		if id:match ('^%d+$') == nil then

			return return_result (false, cfg.err_msg_supl.char);				-- fail if ISBN-13 is not all digits

		end

		if id:match ('^97[89]%d*$') == nil then

			return return_result (false, cfg.err_msg_supl.prefix);				-- fail when ISBN-13 does not begin with 978 or 979

		end

		if id:match ('^9790') then

			return return_result (false, cfg.err_msg_supl.group);				-- group identifier '0' is reserved to ISMN

		end

		return return_result (is_valid_isxn_13 (id), cfg.err_msg_supl.check);

	end

end





--[[--------------------------< A S I N >----------------------------------------------------------------------



Formats a link to Amazon.  Do simple error checking: ASIN must be mix of 10 numeric or uppercase alpha

characters.  If a mix, first character must be uppercase alpha; if all numeric, ASINs must be 10-digit

ISBN. If 10-digit ISBN, add a maintenance category so a bot or AWB script can replace |asin= with |isbn=.

Error message if not 10 characters, if not ISBN-10, if mixed and first character is a digit.



|asin=630....... and |asin=631....... are (apparently) not a legitimate ISBN though it checksums as one; these

do not cause this function to emit the maint_asin message



This function is positioned here because it calls isbn()



]]



local function asin (options)

	local id = options.id;

	local domain = options.ASINTLD;

	

	local err_flag;



	if not id:match("^[%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u]$") then

		err_flag = set_message ('err_bad_asin');								-- ASIN is not a mix of 10 uppercase alpha and numeric characters

	else

		if id:match("^%d%d%d%d%d%d%d%d%d[%dX]$") then							-- if 10-digit numeric (or 9 digits with terminal X)

			if is_valid_isxn (id, 10) then										-- see if ASIN value is or validates as ISBN-10

				if not id:find ('^63[01]') then									-- 630xxxxxxx and 631xxxxxxx are (apparently) not a valid isbn prefixes but are used by amazon as a numeric identifier

					err_flag = set_message ('err_bad_asin');					-- ASIN has ISBN-10 form but begins with something other than 630/1 so probably an isbn 

				end

			elseif not is_set (err_flag) then

				err_flag = set_message ('err_bad_asin');						-- ASIN is not ISBN-10

			end

		elseif not id:match("^%u[%d%u]+$") then

			err_flag = set_message ('err_bad_asin');							-- asin doesn't begin with uppercase alpha

		end

	end

	if (not is_set (domain)) or in_array (domain, {'us'}) then					-- default: United States

		domain = "com";

	elseif in_array (domain, {'jp', 'uk'}) then									-- Japan, United Kingdom

		domain = "co." .. domain;

	elseif in_array (domain, {'z.cn'}) then 									-- China

		domain = "cn";

	elseif in_array (domain, {'au', 'br', 'mx', 'sg', 'tr'}) then				-- Australia, Brazil, Mexico, Singapore, Turkey

		domain = "com." .. domain;

	elseif not in_array (domain, {'ae', 'ca', 'cn', 'de', 'es', 'fr', 'in', 'it', 'nl', 'pl', 'sa', 'se', 'co.jp', 'co.uk', 'com', 'com.au', 'com.br', 'com.mx', 'com.sg', 'com.tr'}) then -- Arabic Emirates, Canada, China, Germany, Spain, France, Indonesia, Italy, Netherlands, Poland, Saudi Arabia, Sweden (as of 2021-03 Austria (.at), Liechtenstein (.li) and Switzerland (.ch) still redirect to the German site (.de) with special settings, so don't maintain local ASINs for them)

		err_flag = set_message ('err_bad_asin_tld');							-- unsupported asin-tld value

	end

	local handler = options.handler;



	if not is_set (err_flag) then

		options.coins_list_t'ASIN' = handler.prefix .. domain .. "/dp/" .. id;	-- asin for coins

	else

		options.coins_list_t'ASIN' = nil;										-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix .. domain .. "/dp/",

		id = id, encode = handler.encode, separator = handler.separator})

end





--[[--------------------------< I S M N >----------------------------------------------------------------------



Determines whether an ISMN string is valid.  Similar to ISBN-13, ISMN is 13 digits beginning 979-0-... and uses the

same check digit calculations.  See https://www.ismn-international.org/download/Web_ISMN_Users_Manual_2008-6.pdf

section 2, pages 9–12.



ismn value not made part of COinS metadata because we don't have a url or isn't a COinS-defined identifier (rft.xxx)

or an identifier registered at info-uri.info (info:)



]]



local function ismn (options)

	local id = options.id;

	local handler = options.handler;

	local text;

	local valid_ismn = true;

	local id_copy;



	id_copy = id;																-- save a copy because this testing is destructive

	id = id:gsub ('[%s-]', '');													-- remove hyphens and white space



	if 13 ~= id:len() or id:match ("^9790%d*$" ) == nil then					-- ISMN must be 13 digits and begin with 9790

		valid_ismn = false;

	else

		valid_ismn=is_valid_isxn_13 (id);										-- validate ISMN

	end



	--	text = internal_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,		-- use this (or external version) when there is some place to link to

	--		prefix = handler.prefix, id = id_copy, separator = handler.separator, encode = handler.encode})



	text = table.concat (														-- because no place to link to yet

		{

		make_wikilink (link_label_make (handler), handler.label),

		handler.separator,

		id_copy

		});



	if false == valid_ismn then

		options.coins_list_t'ISMN' = nil;										-- when error, unset so not included in COinS; not really necessary here because ismn not made part of COinS

		set_message ('err_bad_ismn');											-- create an error message if the ISMN is invalid

	end 

	

	return text;

end





--[[--------------------------< I S S N >----------------------------------------------------------------------



Validate and format an ISSN.  This code fixes the case where an editor has included an ISSN in the citation but

has separated the two groups of four digits with a space.  When that condition occurred, the resulting link looked

like this:



	|issn=0819 4327 gives: [https://www.worldcat.org/issn/0819 4327 0819 4327]	-- can't have spaces in an external link

	

This code now prevents that by inserting a hyphen at the ISSN midpoint.  It also validates the ISSN for length

and makes sure that the checkdigit agrees with the calculated value.  Incorrect length (8 digits), characters

other than 0-9 and X, or checkdigit / calculated value mismatch will all cause a check ISSN error message.  The

ISSN is always displayed with a hyphen, even if the ISSN was given as a single group of 8 digits.



]]



local function issn (options)

	local id = options.id;

	local handler = options.handler;

	local ignore_invalid = options.accept;



	local issn_copy = id;														-- save a copy of unadulterated ISSN; use this version for display if ISSN does not validate

	local text;

	local valid_issn = true;



	id = id:gsub ('[%s-]', '');													-- remove hyphens and whitespace



	if 8 ~= id:len() or nil == id:match ("^%d*X?$" ) then						-- validate the ISSN: 8 digits long, containing only 0-9 or X in the last position

		valid_issn = false;														-- wrong length or improper character

	else

		valid_issn = is_valid_isxn (id, 8);										-- validate ISSN

	end



	if true == valid_issn then

		id = string.sub (id, 1, 4 ) .. "-" .. string.sub (id, 5 );				-- if valid, display correctly formatted version

	else

		id = issn_copy;															-- if not valid, show the invalid ISSN with error message

	end



	text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode})



	if ignore_invalid then

		set_message ('maint_issn_ignore');

	else

		if false == valid_issn then

			options.coins_list_t'ISSN' = nil;									-- when error, unset so not included in COinS

			set_message ('err_bad_issn', (options.hkey == 'EISSN') and 'e' or '');	-- create an error message if the ISSN is invalid

		end 

	end

	

	return text;

end





--[[--------------------------< J F M >-----------------------------------------------------------------------



A numerical identifier in the form nn.nnnn.nn



]]



local function jfm (options)

	local id = options.id;

	local handler = options.handler;

	local id_num;



	id_num = id:match ('^[Jj][Ff][Mm](.*)$');									-- identifier with jfm prefix; extract identifier



	if is_set (id_num) then

		set_message ('maint_jfm_format');

	else																		-- plain number without JFM prefix

		id_num = id;															-- if here id does not have prefix

	end



	if id_num and id_num:match('^%d%d%.%d%d%d%d%.%d%d$') then

		id = id_num;															-- jfm matches pattern

	else

		set_message ('err_bad_jfm' );											-- set an error message

		options.coins_list_t'JFM' = nil;										-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode});

end





--[[--------------------------< J S T O R >--------------------------------------------------------------------



Format a JSTOR with some error checking



]]



local function jstor (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;



	if id:find ('[Jj][Ss][Tt][Oo][Rr]') or id:find ('^https?://') or id:find ('%s') then

		set_message ('err_bad_jstor');											-- set an error message

		options.coins_list_t'JSTOR' = nil;									-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = access});

end





--[[--------------------------< L C C N >----------------------------------------------------------------------



Format LCCN link and do simple error checking.  LCCN is a character string 8-12 characters long. The length of

the LCCN dictates the character type of the first 1-3 characters; the rightmost eight are always digits.

https://oclc-research.github.io/infoURI-Frozen/info-uri.info/info:lccn/reg.html



length = 8 then all digits

length = 9 then lccn[1] is lowercase alpha

length = 10 then lccn[1] and lccn[2] are both lowercase alpha or both digits

length = 11 then lccn[1] is lower case alpha, lccn[2] and lccn[3] are both lowercase alpha or both digits

length = 12 then lccn[1] and lccn[2] are both lowercase alpha



]]



local function lccn (options)

	local lccn = options.id;

	local handler = options.handler;

	local err_flag;																-- presume that LCCN is valid

	local id = lccn;															-- local copy of the LCCN



	id = normalize_lccn (id);													-- get canonical form (no whitespace, hyphens, forward slashes)

	local len = id:len();														-- get the length of the LCCN



	if 8 == len then

		if id:match("[^%d]") then												-- if LCCN has anything but digits (nil if only digits)

			err_flag = set_message ('err_bad_lccn');							-- set an error message

		end

	elseif 9 == len then														-- LCCN should be adddddddd

		if nil == id:match("%l%d%d%d%d%d%d%d%d") then							-- does it match our pattern?

			err_flag = set_message ('err_bad_lccn');							-- set an error message

		end

	elseif 10 == len then														-- LCCN should be aadddddddd or dddddddddd

		if id:match("[^%d]") then												-- if LCCN has anything but digits (nil if only digits) ...

			if nil == id:match("^%l%l%d%d%d%d%d%d%d%d") then					-- ... see if it matches our pattern

				err_flag = set_message ('err_bad_lccn');						-- no match, set an error message

			end

		end

	elseif 11 == len then														-- LCCN should be aaadddddddd or adddddddddd

		if not (id:match("^%l%l%l%d%d%d%d%d%d%d%d") or id:match("^%l%d%d%d%d%d%d%d%d%d%d")) then	-- see if it matches one of our patterns

			err_flag = set_message ('err_bad_lccn');							-- no match, set an error message

		end

	elseif 12 == len then														-- LCCN should be aadddddddddd

		if not id:match("^%l%l%d%d%d%d%d%d%d%d%d%d") then						-- see if it matches our pattern

			err_flag = set_message ('err_bad_lccn');							-- no match, set an error message

		end

	else

		err_flag = set_message ('err_bad_lccn');								-- wrong length, set an error message

	end



	if not is_set (err_flag) and nil ~= lccn:find ('%s') then

		err_flag = set_message ('err_bad_lccn');								-- lccn contains a space, set an error message

	end



	if is_set (err_flag) then

		options.coins_list_t'LCCN' = nil;										-- when error, unset so not included in COinS

	end



	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = lccn, separator = handler.separator, encode = handler.encode});

end





--[[--------------------------< M E D R X I V >-----------------------------------------------------------------



Format medRxiv ID and do simple error checking.  Similar to later bioRxiv IDs, medRxiv IDs are prefixed with a

yyyy.mm.dd. date and suffixed with an optional version identifier.  Ealiest date accepted is 2020.01.01



The medRxiv ID is a date followed by an eight-digit number followed by an optional version indicator 'v' and one or more digits:

	https://www.medrxiv.org/content/10.1101/2020.11.16.20232009v2 -> 10.1101/2020.11.16.20232009v2



]]



local function medrxiv (options)

	local id = options.id;

	local handler = options.handler;

	local err_msg_flag = true;													-- flag; assume that there will be an error



	local patterns = {

		'%d%d%d%d%d%d%d%d$',													-- simple 8-digit identifier; these should be relatively rare

		'^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d%d%dv%d+$',			-- y.m.d. date + 8-digit identifier + version (2020-01-01 and later)

		'^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d%d%d$',				-- y.m.d. date + 8-digit identifier (2020-01-01 and later)

		}

	

	for _, pattern in ipairs (patterns) do										-- spin through the patterns looking for a match

		if id:match (pattern) then

			local y, m, d = id:match (pattern);									-- found a match, attempt to get year, month and date from the identifier



			if m then															-- m is nil when id is the 8-digit form

				if not is_valid_rxiv_date (y, m, d, 'b') then					-- validate the encoded date; 'b' for medrxiv limit

					break;														-- date fail; break out early so we don't unset the error message

				end

			end

			err_msg_flag = nil;													-- we found a match so unset the error message

			break;																-- and done

		end

	end																			-- <err_msg_flag> remains set here when no match



	if err_msg_flag then

		options.coins_list_t'MEDRXIV' = nil;									-- when error, unset so not included in COinS

		set_message ('err_bad_medrxiv');										-- and set the error message

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator,

			encode = handler.encode, access = handler.access});

end





--[[--------------------------< M R >--------------------------------------------------------------------------



A seven digit number; if not seven digits, zero-fill leading digits to make seven digits.



]]



local function mr (options)

	local id = options.id;

	local handler = options.handler;

	local id_num;

	local id_len;



	id_num = id:match ('^[Mm][Rr](%d+)$');										-- identifier with mr prefix



	if is_set (id_num) then

		set_message ('maint_mr_format');										-- add maint cat

	else																		-- plain number without mr prefix

		id_num = id:match ('^%d+$');											-- if here id is all digits

	end



	id_len = id_num and id_num:len() or 0;

	if (7 >= id_len) and (0 ~= id_len) then

		id = string.rep ('0', 7-id_len) .. id_num;								-- zero-fill leading digits

	else

		set_message ('err_bad_mr');												-- set an error message

		options.coins_list_t'MR' = nil;										-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode});

end





--[[--------------------------< O C L C >----------------------------------------------------------------------



Validate and format an OCLC ID.  https://www.oclc.org/batchload/controlnumber.en.html {{dead link}}

archived at: https://web.archive.org/web/20161228233804/https://www.oclc.org/batchload/controlnumber.en.html



]]



local function oclc (options)

	local id = options.id;

	local handler = options.handler;

	local number;



	if id:match('^ocm%d%d%d%d%d%d%d%d$') then									-- ocm prefix and 8 digits; 001 field (12 characters)

		number = id:match('ocm(%d+)');											-- get the number

	elseif id:match('^ocn%d%d%d%d%d%d%d%d%d$') then								-- ocn prefix and 9 digits; 001 field (12 characters)

		number = id:match('ocn(%d+)');											-- get the number

	elseif id:match('^on%d%d%d%d%d%d%d%d%d%d+$') then							-- on prefix and 10 or more digits; 001 field (12 characters)

		number = id:match('^on(%d%d%d%d%d%d%d%d%d%d+)$');						-- get the number

	elseif id:match('^%(OCoLC%)[1-9]%d*$') then									-- (OCoLC) prefix and variable number digits; no leading zeros; 035 field

		number = id:match('%(OCoLC%)([1-9]%d*)');								-- get the number

		if 9 < number:len() then

			number = nil;														-- constrain to 1 to 9 digits; change this when OCLC issues 10-digit numbers

		end

	elseif id:match('^%d+$') then												-- no prefix

		number = id;															-- get the number

		if tonumber (id) > handler.id_limit then

			number = nil;														-- unset when id value exceeds the limit

		end

	end



	if number then																-- proper format

		id = number;															-- exclude prefix, if any, from external link

	else

		set_message ('err_bad_oclc')											-- add an error message if the id is malformed

		options.coins_list_t'OCLC' = nil;										-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode});

end





--[[--------------------------< O P E N L I B R A R Y >--------------------------------------------------------



Formats an OpenLibrary link, and checks for associated errors.



]]



local function openlibrary (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;

	local ident, code = id:gsub('^OL', ''):match("^(%d+([AMW]))$");				-- strip optional OL prefix followed immediately by digits followed by 'A', 'M', or 'W';

	local err_flag;

	local prefix = {															-- these are appended to the handler.prefix according to code

		'A'='authors/OL',

		'M'='books/OL',

		'W'='works/OL',

		'X'='OL'																-- not a code; spoof when 'code' in id is invalid

		};



	if not ident then

		code = 'X';																-- no code or id completely invalid

		ident = id;																-- copy id to ident so that we display the flawed identifier

		err_flag = set_message ('err_bad_ol');

	end



	if not is_set (err_flag) then

		options.coins_list_t'OL' = handler.prefix .. prefixcode .. ident;	-- experiment for ol coins

	else

		options.coins_list_t'OL' = nil;										-- when error, unset so not included in COinS

	end



	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix .. prefixcode],

		id = ident, separator = handler.separator, encode = handler.encode,

		access = access});

end





--[[--------------------------< O S T I >----------------------------------------------------------------------



Format OSTI and do simple error checking. OSTIs are sequential numbers beginning at 1 and counting up.  This

code checks the OSTI to see that it contains only digits and is less than test_limit specified in the configuration;

the value in test_limit will need to be updated periodically as more OSTIs are issued.



NB. 1018 is the lowest OSTI number found in the wild (so far) and resolving OK on the OSTI site



]]



local function osti (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;



	if id:match("[^%d]") then													-- if OSTI has anything but digits

		set_message ('err_bad_osti');											-- set an error message

		options.coins_list_t'OSTI' = nil;										-- when error, unset so not included in COinS

	else																		-- OSTI is only digits

		local id_num = tonumber (id);											-- convert id to a number for range testing

		if 1018 > id_num or handler.id_limit < id_num then						-- if OSTI is outside test limit boundaries

			set_message ('err_bad_osti');										-- set an error message

			options.coins_list_t'OSTI' = nil;									-- when error, unset so not included in COinS

		end

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = access});

end





--[[--------------------------< P M C >------------------------------------------------------------------------



Format a PMC, do simple error checking, and check for embargoed articles.



The embargo parameter takes a date for a value. If the embargo date is in the future the PMC identifier will not

be linked to the article.  If the embargo date is today or in the past, or if it is empty or omitted, then the

PMC identifier is linked to the article through the link at cfg.id_handlers['PMC'].prefix.



PMC embargo date testing is done in function is_embargoed () which is called earlier because when the citation

has |pmc=<value> but does not have a |url= then |title= is linked with the PMC link.  Function is_embargoed ()

returns the embargo date if the PMC article is still embargoed, otherwise it returns an empty string.



PMCs are sequential numbers beginning at 1 and counting up.  This code checks the PMC to see that it contains only digits and is less

than test_limit; the value in local variable test_limit will need to be updated periodically as more PMCs are issued.



]]



local function pmc (options)

	local id = options.id;

	local embargo = options.Embargo;											-- TODO: lowercase?

	local handler = options.handler;

	local err_flag;

	local id_num;

	local text;



	id_num = id:match ('^[Pp][Mm][Cc](%d+)$');									-- identifier with PMC prefix



	if is_set (id_num) then

		set_message ('maint_pmc_format');

	else																		-- plain number without PMC prefix

		id_num = id:match ('^%d+$');											-- if here id is all digits

	end



	if is_set (id_num) then														-- id_num has a value so test it

		id_num = tonumber (id_num);												-- convert id_num to a number for range testing

		if 1 > id_num or handler.id_limit < id_num then							-- if PMC is outside test limit boundaries

			err_flag = set_message ('err_bad_pmc');								-- set an error message

		else

			id = tostring (id_num);												-- make sure id is a string

		end

	else																		-- when id format incorrect

		err_flag = set_message ('err_bad_pmc');									-- set an error message

	end

	

	if is_set (embargo) and is_set (is_embargoed (embargo)) then				-- is PMC is still embargoed?

		text = table.concat (													-- still embargoed so no external link

			{

			make_wikilink (link_label_make (handler), handler.label),

			handler.separator,

			id,

			});

	else

		text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,	-- no embargo date or embargo has expired, ok to link to article

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = handler.access,

			auto_link = not err_flag and 'pmc' or nil							-- do not auto-link when PMC has error

			});

	end



	if err_flag then

		options.coins_list_t'PMC' = nil;										-- when error, unset so not included in COinS

	end



	return text;

end





--[[--------------------------< P M I D >----------------------------------------------------------------------



Format PMID and do simple error checking.  PMIDs are sequential numbers beginning at 1 and counting up.  This

code checks the PMID to see that it contains only digits and is less than test_limit; the value in local variable

test_limit will need to be updated periodically as more PMIDs are issued.



]]



local function pmid (options)

	local id = options.id;

	local handler = options.handler;



	if id:match("[^%d]") then													-- if PMID has anything but digits

		set_message ('err_bad_pmid');											-- set an error message

		options.coins_list_t'PMID' = nil;										-- when error, unset so not included in COinS

	else																		-- PMID is only digits

		local id_num = tonumber (id);											-- convert id to a number for range testing

		if 1 > id_num or handler.id_limit < id_num then							-- if PMID is outside test limit boundaries

			set_message ('err_bad_pmid');										-- set an error message

			options.coins_list_t'PMID' = nil;									-- when error, unset so not included in COinS

		end

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode});

end





--[[--------------------------< R F C >------------------------------------------------------------------------



Format RFC and do simple error checking. RFCs are sequential numbers beginning at 1 and counting up.  This

code checks the RFC to see that it contains only digits and is less than test_limit specified in the configuration;

the value in test_limit will need to be updated periodically as more RFCs are issued.



An index of all RFCs is here: https://tools.ietf.org/rfc/



]]



local function rfc (options)

	local id = options.id;

	local handler = options.handler;



	if id:match("[^%d]") then													-- if RFC has anything but digits

		set_message ('err_bad_rfc');											-- set an error message

		options.coins_list_t'RFC' = nil;										-- when error, unset so not included in COinS

	else																		-- RFC is only digits

		local id_num = tonumber (id);											-- convert id to a number for range testing

		if 1 > id_num or handler.id_limit < id_num then							-- if RFC is outside test limit boundaries

			set_message ('err_bad_rfc');										-- set an error message

			options.coins_list_t'RFC' = nil;									-- when error, unset so not included in COinS

		end

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = handler.access});

end





--[[--------------------------< S 2 C I D >--------------------------------------------------------------------



Format an S2CID, do simple error checking



S2CIDs are sequential numbers beginning at 1 and counting up.  This code checks the S2CID to see that it is only

digits and is less than test_limit; the value in local variable test_limit will need to be updated periodically

as more S2CIDs are issued.



]]



local function s2cid (options)

	local id = options.id;

	local access = options.access;

	local handler = options.handler;

	local id_num;

	local text;

	

	id_num = id:match ('^[1-9]%d*$');											-- id must be all digits; must not begin with 0; no open access flag



 	if is_set (id_num) then														-- id_num has a value so test it

		id_num = tonumber (id_num);												-- convert id_num to a number for range testing

		if handler.id_limit < id_num then										-- if S2CID is outside test limit boundaries

			set_message ('err_bad_s2cid');										-- set an error message

			options.coins_list_t'S2CID' = nil;								-- when error, unset so not included in COinS

		end

	else																		-- when id format incorrect

		set_message ('err_bad_s2cid');											-- set an error message

		options.coins_list_t'S2CID' = nil;									-- when error, unset so not included in COinS

	end



	text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = access});



	return text;

end





--[[--------------------------< S B N >------------------------------------------------------------------------



9-digit form of ISBN-10; uses same check-digit validation when SBN is prefixed with an additional '0' to make 10 digits



sbn value not made part of COinS metadata because we don't have a url or isn't a COinS-defined identifier (rft.xxx)

or an identifier registered at info-uri.info (info:)



]]



local function sbn (options)

	local id = options.id;

	local ignore_invalid = options.accept;

	local handler = options.handler;

	local function return_result (check, err_type)								-- local function to handle the various returns

		local SBN = internal_link_id ({link = handler.link, label = handler.label, redirect = handler.redirect,

						prefix = handler.prefix, id = id, separator = handler.separator});

		if not ignore_invalid then												-- if not ignoring SBN errors

			if not check then

				options.coins_list_t'SBN' = nil;								-- when error, unset so not included in COinS; not really necessary here because sbn not made part of COinS

				set_message ('err_bad_sbn', {err_type});						-- display an error message

				return SBN; 

			end

		else

			set_message ('maint_isbn_ignore');									-- add a maint category even when there is no error (ToDo: Possibly switch to separate message for SBNs only)

		end

		return SBN;

	end



	if id:match ('[^%s-0-9X]') then

		return return_result (false, cfg.err_msg_supl.char);					-- fail if SBN contains anything but digits, hyphens, or the uppercase X

	end



	local ident = id:gsub ('[%s-]', '');										-- remove hyphens and whitespace; they interfere with the rest of the tests



	if  9 ~= ident:len() then

		return return_result (false, cfg.err_msg_supl.length);					-- fail if incorrect length

	end



	if ident:match ('^%d*X?$') == nil then

		return return_result (false, cfg.err_msg_supl.form);					-- fail if SBN has 'X' anywhere but last position

	end



	return return_result (is_valid_isxn ('0' .. ident, 10), cfg.err_msg_supl.check);

end





--[[--------------------------< S S R N >----------------------------------------------------------------------



Format an SSRN, do simple error checking



SSRNs are sequential numbers beginning at 100? and counting up.  This code checks the SSRN to see that it is

only digits and is greater than 99 and less than test_limit; the value in local variable test_limit will need

to be updated periodically as more SSRNs are issued.



]]



local function ssrn (options)

	local id = options.id;

	local handler = options.handler;

	local id_num;

	local text;

	

	id_num = id:match ('^%d+$');												-- id must be all digits



	if is_set (id_num) then														-- id_num has a value so test it

		id_num = tonumber (id_num);												-- convert id_num to a number for range testing

		if 100 > id_num or handler.id_limit < id_num then						-- if SSRN is outside test limit boundaries

			set_message ('err_bad_ssrn');										-- set an error message

			options.coins_list_t'SSRN' = nil;									-- when error, unset so not included in COinS

		end

	else																		-- when id format incorrect

		set_message ('err_bad_ssrn');											-- set an error message

		options.coins_list_t'SSRN' = nil;										-- when error, unset so not included in COinS

	end

	

	text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode, access = options.access});



	return text;

end





--[[--------------------------< U S E N E T _ I D >------------------------------------------------------------



Validate and format a usenet message id.  Simple error checking, looks for 'id-left@id-right' not enclosed in

'<' and/or '>' angle brackets.



]]



local function usenet_id (options)

	local id = options.id;

	local handler = options.handler;



	local text = external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

		prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode})

 

	if not id:match('^.+@.+$') or not id:match('^[^<].*[^>]$') then				-- doesn't have '@' or has one or first or last character is '< or '>'

		set_message ('err_bad_usenet_id')										-- add an error message if the message id is invalid

		options.coins_list_t'USENETID' = nil;									-- when error, unset so not included in COinS

	end 

	

	return text;

end





--[[--------------------------< Z B L >-----------------------------------------------------------------------



A numerical identifier in the form nnnn.nnnnn - leading zeros in the first quartet optional



format described here: http://emis.mi.sanu.ac.rs/ZMATH/zmath/en/help/search/



temporary format is apparently eight digits.  Anything else is an error



]]



local function zbl (options)

	local id = options.id;

	local handler = options.handler;



	if id:match('^%d%d%d%d%d%d%d%d$') then										-- is this identifier using temporary format?

		set_message ('maint_zbl');												-- yes, add maint cat

	elseif not id:match('^%d?%d?%d?%d%.%d%d%d%d%d$') then						-- not temporary, is it normal format?

		set_message ('err_bad_zbl');											-- no, set an error message

		options.coins_list_t'ZBL' = nil;										-- when error, unset so not included in COinS

	end

	

	return external_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,

			prefix = handler.prefix, id = id, separator = handler.separator, encode = handler.encode});

end





--============================<< I N T E R F A C E   F U N C T I O N S >>==========================================



--[[--------------------------< E X T R A C T _ I D S >------------------------------------------------------------



Populates ID table from arguments using configuration settings. Loops through cfg.id_handlers and searches args for

any of the parameters listed in each cfg.id_handlers['...'].parameters.  If found, adds the parameter and value to

the identifier list.  Emits redundant error message if more than one alias exists in args



]]



local function extract_ids (args)

	local id_list = {};															-- list of identifiers found in args

	for k, v in pairs (cfg.id_handlers) do										-- k is uppercase identifier name as index to cfg.id_handlers; e.g. cfg.id_handlers['ISBN'], v is a table

		v = select_one (args, v.parameters, 'err_redundant_parameters' );		-- v.parameters is a table of aliases for k; here we pick one from args if present

		if is_set (v) then id_listk = v; end									-- if found in args, add identifier to our list

	end

	return id_list;

end





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



Fetches custom id access levels from arguments using configuration settings. Parameters which have a predefined access

level (e.g. arxiv) do not use this function as they are directly rendered as free without using an additional parameter.



returns a table of k/v pairs where k is same as the identifier's key in cfg.id_handlers and v is the assigned (valid) keyword



access-level values must match the case used in cfg.keywords_lists['id-access'] (lowercase unless there is some special reason for something else)



]]



local function extract_id_access_levels (args, id_list)

	local id_accesses_list = {};

	for k, v in pairs (cfg.id_handlers) do

		local access_param = v.custom_access;									-- name of identifier's access-level parameter

		if is_set (access_param) then

			local access_level = argsaccess_param];							-- get the assigned value if there is one

			if is_set (access_level) then

				if not in_array (access_level, cfg.keywords_lists'id-access']) then	-- exact match required

					set_message ('err_invalid_param_val', {access_param, access_level});	

					access_level = nil;											-- invalid so unset

				end

				if not is_set (id_listk]) then									-- identifier access-level must have a matching identifier

					set_message ('err_param_access_requires_param', {k:lower()});	-- parameter name is uppercase in cfg.id_handlers (k); lowercase for error message

				end

				id_accesses_listk = cfg.keywords_xlateaccess_level];			-- get translated keyword

			end

		end

	end

	return id_accesses_list;

end





--[[--------------------------< B U I L D _ I D _ L I S T >----------------------------------------------------



render the identifiers into a sorted sequence table



<ID_list_coins_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value

<options_t> is a table of various k/v option pairs provided in the call to new_build_id_list();

	modified by	this function and passed to all identifier rendering functions

<access_levels_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value (if valid)



returns a sequence table of sorted (by hkey - 'handler' key) rendered identifier strings



]]



local function build_id_list (ID_list_coins_t, options_t, access_levels_t)

	local ID_list_t = {};

	local accept;

	local func_map = {															--function map points to functions associated with hkey identifier

		'ARXIV' = arxiv,

		'ASIN' = asin,

		'BIBCODE' = bibcode,

		'BIORXIV' = biorxiv,

		'CITESEERX' = citeseerx,

		'DOI' = doi,

		'EISSN' = issn,

		'HDL' = hdl,

		'ISBN' = isbn,

		'ISMN' = ismn,

		'ISSN' = issn,

		'JFM' = jfm,

		'JSTOR' = jstor,

		'LCCN' = lccn,

		'MEDRXIV' = medrxiv,

		'MR' = mr,

		'OCLC' = oclc,

		'OL' = openlibrary,

		'OSTI' = osti,

		'PMC' = pmc,

		'PMID' = pmid,

		'RFC'  = rfc,

		'S2CID' = s2cid,

		'SBN' = sbn,

		'SSRN' = ssrn,

		'USENETID' = usenet_id,

		'ZBL' = zbl,

		}



	for hkey, v in pairs (ID_list_coins_t) do

		v, accept = has_accept_as_written (v);									-- remove accept-as-written markup if present; accept is boolean true when markup removed; false else

																				-- every function gets the options table with value v and accept boolean

		options_t.hkey = hkey;													-- ~/Configuration handler key

		options_t.id = v;														-- add that identifier value to the options table

		options_t.accept = accept;												-- add the accept boolean flag

		options_t.access = access_levels_thkey];								-- add the access level for those that have an |<identifier-access= parameter

		options_t.handler = cfg.id_handlershkey];

		options_t.coins_list_t = ID_list_coins_t;								-- pointer to ID_list_coins_t; for |asin= and |ol=; also to keep erroneous values out of the citation's metadata

		options_t.coins_list_thkey = v;										-- id value without accept-as-written markup for metadata

		

		if options_t.handler.access and not in_array (options_t.handler.access, cfg.keywords_lists'id-access']) then

			error (cfg.messages'unknown_ID_access' .. options_t.handler.access);	-- here when handler access key set to a value not listed in list of allowed id access keywords

		end



		if func_maphkey then

			local id_text = func_maphkey (options_t);							-- call the function to get identifier text and any error message

			table.insert (ID_list_t, {hkey, id_text});							-- add identifier text to the output sequence table

		else

			error (cfg.messages'unknown_ID_key' .. hkey);						-- here when func_map doesn't have a function for hkey

		end

	end



	local function comp (a, b)													-- used by following table.sort()

		return a1]:lower() < b1]:lower();										-- sort by hkey

	end



	table.sort (ID_list_t, comp);												-- sequence table of tables sort	

	for k, v in ipairs (ID_list_t) do											-- convert sequence table of tables to simple sequence table of strings

		ID_list_tk = v2];													-- v[2] is the identifier rendering from the call to the various functions in func_map{}

	end

	

	return ID_list_t;

end





--[[--------------------------< O P T I O N S _ C H E C K >----------------------------------------------------



check that certain option parameters have their associated identifier parameters with values



<ID_list_coins_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value

<ID_support_t> is a sequence table of tables created in citation0() where each subtable has four elements:

	[1] is the support parameter's assigned value; empty string if not set

	[2] is a text string same as key in cfg.id_handlers

	[3] is cfg.error_conditions key used to create error message

	[4] is original ID support parameter name used to create error message

	

returns nothing; on error emits an appropriate error message



]]



local function options_check (ID_list_coins_t, ID_support_t)

	for _, v in ipairs (ID_support_t) do

		if is_set (v1]) and not ID_list_coins_tv2]] then						-- when support parameter has a value but matching identifier parameter is missing or empty

			set_message (v3], (v4]));											-- emit the appropriate error message

		end

	end

end





--[[--------------------------< I D E N T I F I E R _ L I S T S _ G E T >--------------------------------------



Creates two identifier lists: a k/v table of identifiers and their values to be used locally and for use in the

COinS metadata, and a sequence table of the rendered identifier strings that will be included in the rendered

citation.



]]



local function identifier_lists_get (args_t, options_t, ID_support_t)

	local ID_list_coins_t = extract_ids (args_t);										-- get a table of identifiers and their values for use locally and for use in COinS

	options_check (ID_list_coins_t, ID_support_t);										-- ID support parameters must have matching identifier parameters 

	local ID_access_levels_t = extract_id_access_levels (args_t, ID_list_coins_t);		-- get a table of identifier access levels

	local ID_list_t = build_id_list (ID_list_coins_t, options_t, ID_access_levels_t);	-- get a sequence table of rendered identifier strings



	return ID_list_t, ID_list_coins_t;											-- return the tables

end





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



Sets local cfg table and 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)

	cfg = cfg_table_ptr;



	has_accept_as_written = utilities_page_ptr.has_accept_as_written;			-- import functions from select 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;

	select_one = utilities_page_ptr.select_one;

	substitute = utilities_page_ptr.substitute;

	make_wikilink = utilities_page_ptr.make_wikilink;



	z = utilities_page_ptr.z;													-- table of tables in Module:Citation/CS1/Utilities

end





--[[--------------------------< E X P O R T E D   F U N C T I O N S >------------------------------------------

]]



return {

	auto_link_urls = auto_link_urls,											-- table of identifier URLs to be used when auto-linking |title=

	

	identifier_lists_get = identifier_lists_get,								-- experiment to replace individual calls to build_id_list(), extract_ids, extract_id_access_levels

	is_embargoed = is_embargoed;

	set_selected_modules = set_selected_modules;

	}