# Module:Citation/CS1/Identifiers

----------------------------< 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_urls[options.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.presentation[options.access].class, cfg.presentation[options.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  

--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 = 1576022400  
The medrxiv identifier has a start date of 2020-01-01. The Unix timestamp for that date is = 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 of the forward slash.  
3. If there is a hyphen in the string:  
a. Remove it.  
b. Inspect the substring following (to the 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, -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 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 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 >>====================================  

--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, ' [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 function is_extended_free (registrant, suffix) -- local function to check those few registrants that are mixed; identifiable by the doi suffix <incipit>  
if cfg.extended_registrants_t[registrant] then -- if this registrant has known free-to-read extentions  
for _, incipit in ipairs (cfg.extended_registrants_t[registrant]) do -- loop through the registrant's incipits  
if mw.ustring.find (suffix, '^' .. incipit) then -- if found  
return true;  
end  
end  
end  
end  

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 suffix;  
local registrant, suffix = mw.ustring.match (id, '^10%.([^/]+)/([^%s–]-[^%.,])$'); -- registrant and suffix 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+$', -- 5 digits with subcode (0xxxx, 40000+); accepts: 10000–39999  
'^[^1-7]%d%d%d%d$', -- 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_t[registrant] or is_extended_free (registrant, suffix)) 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  

--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  

--issn=0819 4327 gives: 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  
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 .. prefix[code] .. 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 .. prefix[code],  
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-@id-' 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_list[k] = 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 = args[access_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_list[k]) 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_list[k] = cfg.keywords_xlate[access_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_t[hkey]; -- add the access level for those that have an |<identifier-access= parameter  
options_t.handler = cfg.id_handlers[hkey];  
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_t[hkey] = 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_map[hkey] then  
local id_text = func_map[hkey] (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 a[1]:lower < b[1]: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_t[k] = v[2]; -- 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 (v[1]) and not ID_list_coins_t[v[2]] then -- when support parameter has a value but matching identifier parameter is missing or empty  
set_message (v[3], (v[4])); -- 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;  
}