Module:Citation/CS1/Identifiers: Difference between revisions

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    ]]
    ]]


    local function set_cfg (cfg_table_ptr)
    local function set_cfg (cfg_table_ptr, utilities_page_ptr)
    cfg = cfg_table_ptr;
    cfg = cfg_table_ptr;
    utilities = require ('Module:Citation/CS1/Utilities');
    -- utilities = require ('Module:Citation/CS1/Utilities');
    utilities = utilities_page_ptr;
    is_set = utilities.is_set ; -- functions in Module:Citation/CS1/Utilities
    is_set = utilities.is_set ; -- functions in Module:Citation/CS1/Utilities
    in_array = utilities.in_array;
    in_array = utilities.in_array;

    Revision as of 16:37, 15 December 2015

    Documentation for this module may be created at Module:Citation/CS1/Identifiers/doc

    local utilities = '';
    
    local identifiers = {};
    
    --[[--------------------------< F O R W A R D   D E C L A R A T I O N S >--------------------------------------
    ]]
    
    local is_set, in_array, set_error, select_one, add_maint_cat;
    --local is_set = utilities.is_set	;												-- functions in Module:Citation/CS1/Utilities
    --local in_array = utilities.in_array;
    --local set_error = utilities.set_error;
    --local select_one = utilities.select_one;
    --local add_maint_cat = utilities.add_maint_cat;
    
    local z ={};																	-- tables in Module:Citation/CS1/Utilities
    
    local cfg;			-- table of configuration tables that are defined in Module:Citation/CS1/Configuration
    
    --[[--------------------------< 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;
    	if options.encode == true or options.encode == nil then
    		url_string = mw.uri.encode( url_string );
    	end
    	return mw.ustring.format( '[[%s|%s]]%s[%s%s%s %s]',
    		options.link, options.label, options.separator or "&nbsp;",
    		options.prefix, url_string, options.suffix or "",
    		mw.text.nowiki(options.id)
    	);
    end
    
    
    --[[--------------------------< I N T E R N A L _ L I N K _ I D >----------------------------------------------
    
    Formats a wiki style internal link
    
    ]]
    
    local function internal_link_id(options)
    	return mw.ustring.format( '[[%s|%s]]%s[[%s%s%s|%s]]',
    		options.link, options.label, options.separator or "&nbsp;",
    		options.prefix, options.id, options.suffix or "",
    		mw.text.nowiki(options.id)
    	);
    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 check_isbn().
    
    If the number is valid the result will be 0. Before calling this function, issbn/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
    
    
    --[[--------------------------< C H E C K _ I S B N >------------------------------------------------------------
    
    Determines whether an ISBN string is valid
    
    ]]
    
    local function check_isbn( isbn_str )
    	if nil ~= isbn_str:match("[^%s-0-9X]") then return false; end		-- fail if isbn_str contains anything but digits, hyphens, or the uppercase X
    	isbn_str = isbn_str:gsub( "-", "" ):gsub( " ", "" );	-- remove hyphens and spaces
    	local len = isbn_str:len();
     
    	if len ~= 10 and len ~= 13 then
    		return false;
    	end
    
    	if len == 10 then
    		if isbn_str:match( "^%d*X?$" ) == nil then return false; end
    		return is_valid_isxn(isbn_str, 10);
    	else
    		local temp = 0;
    		if isbn_str:match( "^97[89]%d*$" ) == nil then return false; end		-- isbn13 begins with 978 or 979; ismn begins with 979
    		return is_valid_isxn_13 (isbn_str);
    	end
    end
    
    
    --[[--------------------------< I S M N >----------------------------------------------------------------------
    
    Determines whether an ISMN string is valid.  Similar to isbn-13, ismn is 13 digits begining 979-0-... and uses the
    same check digit calculations.  See http://www.ismn-international.org/download/Web_ISMN_Users_Manual_2008-6.pdf
    section 2, pages 9–12.
    
    ]]
    
    local function ismn (id)
    	local handler = cfg.id_handlers['ISMN'];
    	local text;
    	local valid_ismn = true;
    
    	id=id:gsub( "[%s-–]", "" );													-- strip spaces, hyphens, and endashes from the ismn
    
    	if 13 ~= id:len() or id:match( "^9790%d*$" ) == nil then					-- ismn must be 13 digits and begin 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,		-- use this (or external version) when there is some place to link to
    --		prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode})
     
    	text="[[" .. handler.link .. "|" .. handler.label .. "]]" .. handler.separator .. id;		-- because no place to link to yet
    
    	if false == valid_ismn then
    		text = text .. ' ' .. set_error( 'bad_ismn' )							-- add an error message if the issn 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: [http://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(id)
    	local issn_copy = id;		-- save a copy of unadulterated issn; use this version for display if issn does not validate
    	local handler = cfg.id_handlers['ISSN'];
    	local text;
    	local valid_issn = true;
    
    	id=id:gsub( "[%s-–]", "" );									-- strip spaces, hyphens, and endashes from the issn
    
    	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, use the show the invalid issn with error message
    	end
    	
    	text = external_link_id({link = handler.link, label = handler.label,
    		prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode})
     
    	if false == valid_issn then
    		text = text .. ' ' .. set_error( 'bad_issn' )			-- add an error message if the issn is invalid
    	end 
    	
    	return text
    end
    
    
    --[[--------------------------< A M A Z O 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 isbn10, if mixed and first character is a digit.
    
    ]]
    
    local function amazon(id, domain)
    	local err_cat = ""
    
    	if not id:match("^[%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u]$") then
    		err_cat =  ' ' .. set_error ('bad_asin');								-- asin is not a mix of 10 uppercase alpha and numeric characters
    	else
    		if id:match("^%d%d%d%d%d%d%d%d%d[%dX]$") then								-- if 10-digit numeric (or 9 digits with terminal X)
    			if check_isbn( id ) then												-- see if asin value is isbn10
    				add_maint_cat ('ASIN');
    			elseif not is_set (err_cat) then
    				err_cat =  ' ' .. set_error ('bad_asin');						-- asin is not isbn10
    			end
    		elseif not id:match("^%u[%d%u]+$") then
    			err_cat =  ' ' .. set_error ('bad_asin');							-- asin doesn't begin with uppercase alpha
    		end
    	end
    	if not is_set(domain) then 
    		domain = "com";
    	elseif in_array (domain, {'jp', 'uk'}) then			-- Japan, United Kingdom
    		domain = "co." .. domain;
    	elseif in_array (domain, {'au', 'br', 'mx'}) then	-- Australia, Brazil, Mexico
    		domain = "com." .. domain;
    	end
    	local handler = cfg.id_handlers['ASIN'];
    	return external_link_id({link=handler.link,
    		label=handler.label, prefix=handler.prefix .. domain .. "/dp/",
    		id=id, encode=handler.encode, separator = handler.separator}) .. err_cat;
    end
    
    
    --[[--------------------------< A R X I V >--------------------------------------------------------------------
    
    See: http://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 9108 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
    	<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 (id, class)
    	local handler = cfg.id_handlers['ARXIV'];
    	local year, month, version;
    	local err_cat = '';
    	local 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 9108-0703 format w/ & w/o version
    		year, month = id:match("^%a[%a%.%-]+/([90]%d)([01]%d)%d%d%d[v%d]*$");
    		year = tonumber(year);
    		month = tonumber(month);
    		if ((not (90 < year or 8 > year)) or (1 > month or 12 < month)) or		-- if invalid year or invalid month
    			((91 == year and 7 > month) or (7 == year and 3 < month)) then		-- if years ok, are starting and ending months ok?
    				err_cat = ' ' .. set_error( 'bad_arxiv' );						-- set error message
    		end
    	elseif id:match("^%d%d[01]%d%.%d%d%d%d$") or id:match("^%d%d[01]%d%.%d%d%d%dv%d+$") then	-- test for the 0704-1412 w/ & w/o version
    		year, month = id:match("^(%d%d)([01]%d)%.%d%d%d%d[v%d]*$");
    		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 --or									-- when year is 07, is month invalid (before April)?
    				err_cat = ' ' .. set_error( 'bad_arxiv' );						-- set 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 w/ & w/o 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_cat = ' ' .. set_error( 'bad_arxiv' );							-- set error message
    		end
    	else
    		err_cat = ' ' .. set_error( 'bad_arxiv' );								-- arXiv id doesn't match any format
    	end
    
    	text = external_link_id({link = handler.link, label = handler.label,
    			prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode}) .. err_cat;
    
    	if is_set (class) then
    		class = ' [[' .. '//arxiv.org/archive/' .. class .. ' ' .. class .. ']]';	-- external link within square brackets, not wikilink
    	else
    		class = '';																-- empty string for concatenation
    	end
    	
    	return text .. class;
    end
    
    
    --[[--------------------------< N O R M A L I Z E _ L C C N >--------------------------------------------------
    
    lccn normalization (http://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
    
    
    --[[--------------------------< 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.
    http://info-uri.info/registry/OAIHandler?verb=GetRecord&metadataPrefix=reg&identifier=info:lccn/
    
    length = 8 then all digits
    length = 9 then lccn[1] is lower case alpha
    length = 10 then lccn[1] and lccn[2] are both lower case alpha or both digits
    length = 11 then lccn[1] is lower case alpha, lccn[2] and lccn[3] are both lower case alpha or both digits
    length = 12 then lccn[1] and lccn[2] are both lower case alpha
    
    ]]
    
    local function lccn(lccn)
    	local handler = cfg.id_handlers['LCCN'];
    	local err_cat =  '';								-- 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_cat = ' ' .. set_error( '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_cat = ' ' .. set_error( '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_cat = ' ' .. set_error( '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_cat = ' ' .. set_error( '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_cat = ' ' .. set_error( 'bad_lccn' );	-- no match, set an error message
    		end
    	else
    		err_cat = ' ' .. set_error( 'bad_lccn' );		-- wrong length, set an error message
    	end
    
    	if not is_set (err_cat) and nil ~= lccn:find ('%s') then
    		err_cat = ' ' .. set_error( 'bad_lccn' );		-- lccn contains a space, set an error message
    	end
    
    	return external_link_id({link = handler.link, label = handler.label,
    			prefix=handler.prefix,id=lccn,separator=handler.separator, encode=handler.encode}) .. err_cat;
    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(id)
    	local test_limit = 30000000;						-- update this value as PMIDs approach
    	local handler = cfg.id_handlers['PMID'];
    	local err_cat =  '';								-- presume that PMID is valid
    	
    	if id:match("[^%d]") then							-- if PMID has anything but digits
    		err_cat = ' ' .. set_error( 'bad_pmid' );		-- set an error message
    	else												-- PMID is only digits
    		local id_num = tonumber(id);					-- convert id to a number for range testing
    		if 1 > id_num or test_limit < id_num then		-- if PMID is outside test limit boundaries
    			err_cat = ' ' .. set_error( 'bad_pmid' );	-- set an error message
    		end
    	end
    	
    	return external_link_id({link = handler.link, label = handler.label,
    			prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode}) .. err_cat;
    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 |embargo= against today's date.  If embargo date is
    in the future, returns the content of |embargo=; otherwise, returns and empty string because the embargo has expired or because
    |embargo= was not set in this cite.
    
    ]]
    
    local function is_embargoed (embargo)
    	if is_set (embargo) then
    		local lang = mw.getContentLanguage();
    		local good1, embargo_date, good2, todays_date;
    		good1, embargo_date = pcall( lang.formatDate, lang, 'U', embargo );
    		good2, todays_date = pcall( lang.formatDate, lang, 'U' );
    	
    		if good1 and good2 then													-- if embargo date and today's date are good dates
    			if tonumber( embargo_date ) >= tonumber( todays_date ) then			-- is embargo date is in the future?
    				return embargo;													-- still embargoed
    			else
    				add_maint_cat ('embargo')
    				return '';														-- unset because embargo has expired
    			end
    		end
    	end
    	return '';																	-- |embargo= not set return empty string
    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(id, embargo)
    	local test_limit = 5000000;							-- update this value as PMCs approach
    	local handler = cfg.id_handlers['PMC'];
    	local err_cat =  '';								-- presume that PMC is valid
    	
    	local text;
    
    	if id:match("[^%d]") then							-- if PMC has anything but digits
    		err_cat = ' ' .. set_error( 'bad_pmc' );			-- set an error message
    	else												-- PMC is only digits
    		local id_num = tonumber(id);					-- convert id to a number for range testing
    		if 1 > id_num or test_limit < id_num then		-- if PMC is outside test limit boundaries
    			err_cat = ' ' .. set_error( 'bad_pmc' );		-- set an error message
    		end
    	end
    	
    	if is_set (embargo) then													-- is PMC is still embargoed?
    		text="[[" .. handler.link .. "|" .. handler.label .. "]]:" .. handler.separator .. id .. err_cat;	-- still embargoed so no external link
    	else
    		text = external_link_id({link = handler.link, label = handler.label,			-- no embargo date or embargo has expired, ok to link to article
    			prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode}) .. err_cat;
    	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.
    
    ]]
    
    local function doi(id, inactive)
    	local cat = ""
    	local handler = cfg.id_handlers['DOI'];
    	
    	local text;
    	if is_set(inactive) then
    		local inactive_year = inactive:match("%d%d%d%d") or '';		-- try to get the year portion from the inactive date
    		text = "[[" .. handler.link .. "|" .. handler.label .. "]]:" .. id;
    		if is_set(inactive_year) then
    			table.insert( z.error_categories, "Pages with DOIs inactive since " .. inactive_year );
    		else
    			table.insert( z.error_categories, "Pages with inactive DOIs" );	-- when inactive doesn't contain a recognizable year
    		end
    		inactive = " (" .. cfg.messages['inactive'] .. " " .. inactive .. ")" 
    	else 
    		text = external_link_id({link = handler.link, label = handler.label,
    			prefix=handler.prefix,id=id,separator=handler.separator, encode=handler.encode})
    		inactive = "" 
    	end
    
    	if nil == id:match("^10%.[^%s–]-/[^%s–]-[^%.,]$") then	-- doi must begin with '10.', must contain a fwd slash, must not contain spaces or endashes, and must not end with period or comma
    		cat = ' ' .. set_error( 'bad_doi' );
    	end
    	return text .. inactive .. cat 
    end
    
    
    --[[--------------------------< O P E N L I B R A R Y >--------------------------------------------------------
    
    Formats an OpenLibrary link, and checks for associated errors.
    
    ]]
    
    local function openlibrary(id)
    	local code = id:match("^%d+([AMW])$");										-- only digits followed by 'A', 'M', or 'W'
    	local handler = cfg.id_handlers['OL'];
    
    	if ( code == "A" ) then
    		return external_link_id({link=handler.link, label=handler.label,
    			prefix=handler.prefix .. 'authors/OL',
    			id=id, separator=handler.separator,	encode = handler.encode})
    	elseif ( code == "M" ) then
    		return external_link_id({link=handler.link, label=handler.label,
    			prefix=handler.prefix .. 'books/OL',
    			id=id, separator=handler.separator,	encode = handler.encode})
    	elseif ( code == "W" ) then
    		return external_link_id({link=handler.link, label=handler.label,
    			prefix=handler.prefix .. 'works/OL',
    			id=id, separator=handler.separator,	encode = handler.encode})
    	else
    		return external_link_id({link=handler.link, label=handler.label,
    			prefix=handler.prefix .. 'OL',
    			id=id, separator=handler.separator,	encode = handler.encode}) .. ' ' .. set_error( 'bad_ol' );
    	end
    end
    
    
    --[[--------------------------< M E S S A G E _ 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 message_id (id)
    	local handler = cfg.id_handlers['USENETID'];
    
    	local text = external_link_id({link = handler.link, label = handler.label,
    		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 '>'
    		text = text .. ' ' .. set_error( 'bad_message_id' )						-- add an error message if the message id is invalid
    	end 
    	
    	return text
    end
    
    
    --[[--------------------------< B U I L D _ I D _ L I S T >--------------------------------------------------------
    
    Takes a table of IDs created by extract_ids() and turns it into a table of formatted ID outputs.
    
    inputs:
    	id_list – table of identifiers built by extract_ids()
    	options – table of various template parameter values used to modify some manually handled identifiers
    
    ]]
    
    local function build_id_list( id_list, options )
    	local new_list, handler = {};
    
    	local function fallback(k) return { __index = function(t,i) return cfg.id_handlers[k][i] end } end;
    	
    	for k, v in pairs( id_list ) do												-- k is uc identifier name as index to cfg.id_handlers; e.g. cfg.id_handlers['ISBN'], v is a table
    		-- fallback to read-only cfg
    		handler = setmetatable( { ['id'] = v }, fallback(k) );
    		
    		if handler.mode == 'external' then
    			table.insert( new_list, {handler.label, external_link_id( handler ) } );
    		elseif handler.mode == 'internal' then
    			table.insert( new_list, {handler.label, internal_link_id( handler ) } );
    		elseif handler.mode ~= 'manual' then
    			error( cfg.messages['unknown_ID_mode'] );
    		elseif k == 'DOI' then
    			table.insert( new_list, {handler.label, doi( v, options.DoiBroken ) } );
    		elseif k == 'ARXIV' then
    			table.insert( new_list, {handler.label, arxiv( v, options.Class ) } ); 
    		elseif k == 'ASIN' then
    			table.insert( new_list, {handler.label, amazon( v, options.ASINTLD ) } ); 
    		elseif k == 'LCCN' then
    			table.insert( new_list, {handler.label, lccn( v ) } );
    		elseif k == 'OL' or k == 'OLA' then
    			table.insert( new_list, {handler.label, openlibrary( v ) } );
    		elseif k == 'PMC' then
    			table.insert( new_list, {handler.label, pmc( v, options.Embargo ) } );
    		elseif k == 'PMID' then
    			table.insert( new_list, {handler.label, pmid( v ) } );
    		elseif k == 'ISMN' then
    			table.insert( new_list, {handler.label, ismn( v ) } );
    		elseif k == 'ISSN' then
    			table.insert( new_list, {handler.label, issn( v ) } );
    		elseif k == 'ISBN' then
    			local ISBN = internal_link_id( handler );
    			if not check_isbn( v ) and not is_set(options.IgnoreISBN) then
    				ISBN = ISBN .. set_error( 'bad_isbn', {}, false, " ", "" );
    			end
    			table.insert( new_list, {handler.label, ISBN } );				
    		elseif k == 'USENETID' then
    			table.insert( new_list, {handler.label, message_id( v ) } );
    		else
    			error( cfg.messages['unknown_manual_ID'] );
    		end
    	end
    	
    	local function comp( a, b )	-- used in following table.sort()
    		return a[1] < b[1];
    	end
    	
    	table.sort( new_list, comp );
    	for k, v in ipairs( new_list ) do
    		new_list[k] = v[2];
    	end
    	
    	return new_list;
    end
    
    
    --[[--------------------------< 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 is 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 uc identifier name as index to cfg.id_handlers; e.g. cfg.id_handlers['ISBN'], v is a table
    		v = select_one( args, v.parameters, '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
    
    
    --[[--------------------------< S E T _ C F G >----------------------------------------------------------------
    
    Sets local cfg table to same as that used by the other modules
    
    ]]
    
    local function set_cfg (cfg_table_ptr, utilities_page_ptr)
    	cfg = cfg_table_ptr;
    --	utilities = require ('Module:Citation/CS1/Utilities');
    	utilities = utilities_page_ptr;
    	is_set = utilities.is_set	;												-- functions in Module:Citation/CS1/Utilities
    	in_array = utilities.in_array;
    	set_error = utilities.set_error;
    	select_one = utilities.select_one;
    	add_maint_cat = utilities.add_maint_cat;
    
    end
    
    
    
    return {
    	build_id_list = build_id_list,
    	extract_ids = extract_ids,
    	is_embargoed = is_embargoed;
    	set_cfg = set_cfg;
    	}