--[[



This code is derived from the ISXN validation code at Module:Citation/CS1.  It allows validating ISBN,

ISMN, and ISSN without invoking a citation template.



]]



local p = {}





--[[--------------------------< E R R _ M S G _ S U P L _ T >--------------------------------------------------



error message supplements for check_isbn(); adapted from a similarly named table at Module:Citation/CS1/Configuration



]]



local err_msg_supl_t = {

	'char' = 'invalid character',

	'check' = 'checksum',

	'form' = 'invalid form',

	'group' = 'invalid group id',

	'length' = 'length',

	'prefix' = 'invalid prefix',

	}





--[[--------------------------< 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.  Implements an ISBN validity check for {{ISBN}}, {{ISBNT}}, {{SBN}}, and

{{Format ISBN}}.



]]



local function check_isbn (isbn_str, frame)

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

		if not check then														-- <check> false when there is an error

			local template = ((frame.args.template_name and '' ~= frame.args.template_name) and frame.args.template_name) or nil;	-- get template name

			if not template then

				return '<span class="error" style="font-size:100%">&nbsp;calling template requires template_name parameter</span>';

			end



			local out_t = {'<span class="error" style="font-size:100%">'};		-- open the error message span

			table.insert (out_t, '&nbsp;Parameter error in {{[[Template:');		-- open 'template' markup; open wikilink with Template namespace

			table.insert (out_t, template);										-- template name wikilink

			table.insert (out_t, '|');											-- its pipe

			table.insert (out_t, template);										-- wikilink label

			table.insert (out_t, ']]}}:&nbsp;');								-- close wikilink; close 'template' markup

			table.insert (out_t, err_type);										-- type of isbn error

			table.insert (out_t, '</span>')										-- close the error message span

			if 0 == mw.title.getCurrentTitle().namespace then					-- categorize only when this template is used in mainspace

				local category = table.concat ({'[[Category:Pages with ISBN errors]]'});

				table.insert (out_t, category);

			end

			return table.concat (out_t);										-- make a big string and done

		end

	return '';																	-- no error, return an empty string

	end



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

		return return_result (false, err_msg_supl_t.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, err_msg_supl_t.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, err_msg_supl_t.form);									

		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, err_msg_supl_t.group);					-- fail if isbn-10 begins with 630/1

		end

		return return_result (is_valid_isxn (id, 10), err_msg_supl_t.check);	-- pass if isbn-10 is numerically valid (checksum)

	else

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

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

		end

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

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

		end

		if id:match ('^9790') then

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

		end

		return return_result (is_valid_isxn_13 (id), err_msg_supl_t.check);		-- pass if isbn-10 is numerically valid (checksum)

	end

end





--[[--------------------------< C H E C K _ 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 check_ismn (id, error_string)

	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



	return valid_ismn and '' or error_string

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.



]]



local function check_issn(id, error_string)

	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;



	if not id:match ('^%d%d%d%d%-%d%d%d[%dX]$') then

		return error_string;

	end

	

	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



	return valid_issn and '' or error_string

end





------------------------------< E N T R Y   P O I N T S >--------------------------------------------------====



function p.check_isbn(frame)

	return check_isbn(frame.args1 or frame:getParent().args1], frame)

end



function p.check_ismn(frame)

	return check_ismn(frame.args1 or frame:getParent().args1], frame.args'error' or frame:getParent().args'error' or 'error')

end



function p.check_issn(frame)

	return check_issn(frame.args1 or frame:getParent().args1], frame.args'error' or frame:getParent().args'error' or 'error')

end



return p