Module:String
--[[
 
 This module is intended to provide access to basic string functions.
 
 Most of the functions provided here can be invoked with named parameters,
 unnamed parameters, or a mixture.  If named parameters are used, Mediawiki will
 automatically remove any leading or trailing whitespace from the parameter.
 Depending on the intended use, it may be advantageous to either preserve or
 remove such whitespace.
 
 Global options
     ignore_errors: If set to 'true' or 1, any error condition will result in
         an empty string being returned rather than an error message.
 
     error_category: If an error occurs, specifies the name of a category to
         include with the error message.  The default category is
         [Category:Errors reported by Module String].
 
     no_category: If set to 'true' or 1, no category will be added if an error
         is generated.
 
 Unit tests for this module are available at Module:String/tests.
 ]]
 
 local str = {}
 
 --[[
 len
 
 This function returns the length of the target string.
 
 Usage:
 {{#invoke:String|len|target_string|}}
 OR
 {{#invoke:String|len|s=target_string}}
 
 Parameters
     s: The string whose length to report
 
 If invoked using named parameters, Mediawiki will automatically remove any leading or
 trailing whitespace from the target string.
 ]]
 function str.len( frame )
 	local new_args = str._getParameters( frame.args, {'s'} )
 	local s = new_args['s'] or ''
 	return mw.ustring.len( s )
 end
 
 --[[
 sub
 
 This function returns a substring of the target string at specified indices.
 
 Usage:
 {{#invoke:String|sub|target_string|start_index|end_index}}
 OR
 {{#invoke:String|sub|s=target_string|i=start_index|j=end_index}}
 
 Parameters
     s: The string to return a subset of
     i: The fist index of the substring to return, defaults to 1.
     j: The last index of the string to return, defaults to the last character.
 
 The first character of the string is assigned an index of 1.  If either i or j
 is a negative value, it is interpreted the same as selecting a character by
 counting from the end of the string.  Hence, a value of -1 is the same as
 selecting the last character of the string.
 
 If the requested indices are out of range for the given string, an error is
 reported.
 ]]
 function str.sub( frame )
 	local new_args = str._getParameters( frame.args, { 's', 'i', 'j' } )
 	local s = new_args['s'] or ''
 	local i = tonumber( new_args['i'] ) or 1
 	local j = tonumber( new_args['j'] ) or -1
 
 	local len = mw.ustring.len( s )
 
 	-- Convert negatives for range checking
 	if i &lt; 0 then
 		i = len + i + 1
 	end
 	if j &lt; 0 then
 		j = len + j + 1
 	end
 
 	if i &gt; len or j &gt; len or i &lt; 1 or j &lt; 1 then
 		return str._error( 'String subset index out of range' )
 	end
 	if j &lt; i then
 		return str._error( 'String subset indices out of order' )
 	end
 
 	return mw.ustring.sub( s, i, j )
 end
 
 --[[
 This function implements that features of {{str sub old}} and is kept in order
 to maintain these older templates.
 ]]
 function str.sublength( frame )
 	local i = tonumber( frame.args.i ) or 0
 	local len = tonumber( frame.args.len )
 	return mw.ustring.sub( frame.args.s, i + 1, len and ( i + len ) )
 end
 
 --[[
 _match
 
 This function returns a substring from the source string that matches a
 specified pattern. It is exported for use in other modules
 
 Usage:
 strmatch = require(&quot;Module:String&quot;)._match
 sresult = strmatch( s, pattern, start, match, plain, nomatch )
 
 Parameters
     s: The string to search
     pattern: The pattern or string to find within the string
     start: The index within the source string to start the search.  The first
         character of the string has index 1.  Defaults to 1.
     match: In some cases it may be possible to make multiple matches on a single
         string.  This specifies which match to return, where the first match is
         match= 1.  If a negative number is specified then a match is returned
         counting from the last match.  Hence match = -1 is the same as requesting
         the last match.  Defaults to 1.
     plain: A flag indicating that the pattern should be understood as plain
         text.  Defaults to false.
     nomatch: If no match is found, output the &quot;nomatch&quot; value rather than an error.
 
 For information on constructing Lua patterns, a form of [regular expression], see:
 
 * http://www.lua.org/manual/5.1/manual.html#5.4.1
 * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
 * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Ustring_patterns
 
 ]]
 -- This sub-routine is exported for use in other modules
 function str._match( s, pattern, start, match_index, plain_flag, nomatch )
 	if s == '' then
 		return str._error( 'Target string is empty' )
 	end
 	if pattern == '' then
 		return str._error( 'Pattern string is empty' )
 	end
 	start = tonumber(start) or 1
 	if math.abs(start) &lt; 1 or math.abs(start) &gt; mw.ustring.len( s ) then
 		return str._error( 'Requested start is out of range' )
 	end
 	if match_index == 0 then
 		return str._error( 'Match index is out of range' )
 	end
 	if plain_flag then
 		pattern = str._escapePattern( pattern )
 	end
 
 	local result
 	if match_index == 1 then
 		-- Find first match is simple case
 		result = mw.ustring.match( s, pattern, start )
 	else
 		if start &gt; 1 then
 			s = mw.ustring.sub( s, start )
 		end
 
 		local iterator = mw.ustring.gmatch(s, pattern)
 		if match_index &gt; 0 then
 			-- Forward search
 			for w in iterator do
 				match_index = match_index - 1
 				if match_index == 0 then
 					result = w
 					break
 				end
 			end
 		else
 			-- Reverse search
 			local result_table = {}
 			local count = 1
 			for w in iterator do
 				result_table[count] = w
 				count = count + 1
 			end
 
 			result = result_table[ count + match_index ]
 		end
 	end
 
 	if result == nil then
 		if nomatch == nil then
 			return str._error( 'Match not found' )
 		else
 			return nomatch
 		end
 	else
 		return result
 	end
 end
 
 --[[
 match
 
 This function returns a substring from the source string that matches a
 specified pattern.
 
 Usage:
 {{#invoke:String|match|source_string|pattern_string|start_index|match_number|plain_flag|nomatch_output}}
 OR
 {{#invoke:String|match|s=source_string|pattern=pattern_string|start=start_index
     |match=match_number|plain=plain_flag|nomatch=nomatch_output}}
 
 Parameters
     s: The string to search
     pattern: The pattern or string to find within the string
     start: The index within the source string to start the search.  The first
         character of the string has index 1.  Defaults to 1.
     match: In some cases it may be possible to make multiple matches on a single
         string.  This specifies which match to return, where the first match is
         match= 1.  If a negative number is specified then a match is returned
         counting from the last match.  Hence match = -1 is the same as requesting
         the last match.  Defaults to 1.
     plain: A flag indicating that the pattern should be understood as plain
         text.  Defaults to false.
     nomatch: If no match is found, output the &quot;nomatch&quot; value rather than an error.
 
 If invoked using named parameters, Mediawiki will automatically remove any leading or
 trailing whitespace from each string.  In some circumstances this is desirable, in
 other cases one may want to preserve the whitespace.
 
 If the match_number or start_index are out of range for the string being queried, then
 this function generates an error.  An error is also generated if no match is found.
 If one adds the parameter ignore_errors=true, then the error will be suppressed and
 an empty string will be returned on any failure.
 
 For information on constructing Lua patterns, a form of [regular expression], see:
 
 * http://www.lua.org/manual/5.1/manual.html#5.4.1
 * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
 * http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Ustring_patterns
 
 ]]
 -- This is the entry point for #invoke:String|match
 function str.match( frame )
 	local new_args = str._getParameters( frame.args, {'s', 'pattern', 'start', 'match', 'plain', 'nomatch'} )
 	local s = new_args['s'] or ''
 	local start = tonumber( new_args['start'] ) or 1
 	local plain_flag = str._getBoolean( new_args['plain'] or false )
 	local pattern = new_args['pattern'] or ''
 	local match_index = math.floor( tonumber(new_args['match']) or 1 )
 	local nomatch = new_args['nomatch']
 
 	return str._match( s, pattern, start, match_index, plain_flag, nomatch )
 end
 
 --[[
 pos
 
 This function returns a single character from the target string at position pos.
 
 Usage:
 {{#invoke:String|pos|target_string|index_value}}
 OR
 {{#invoke:String|pos|target=target_string|pos=index_value}}
 
 Parameters
     target: The string to search
     pos: The index for the character to return
 
 If invoked using named parameters, Mediawiki will automatically remove any leading or
 trailing whitespace from the target string.  In some circumstances this is desirable, in
 other cases one may want to preserve the whitespace.
 
 The first character has an index value of 1.
 
 If one requests a negative value, this function will select a character by counting backwards
 from the end of the string.  In other words pos = -1 is the same as asking for the last character.
 
 A requested value of zero, or a value greater than the length of the string returns an error.
 ]]
 function str.pos( frame )
 	local new_args = str._getParameters( frame.args, {'target', 'pos'} )
 	local target_str = new_args['target'] or ''
 	local pos = tonumber( new_args['pos'] ) or 0
 
 	if pos == 0 or math.abs(pos) &gt; mw.ustring.len( target_str ) then
 		return str._error( 'String index out of range' )
 	end
 
 	return mw.ustring.sub( target_str, pos, pos )
 end
 
 --[[
 str_find
 
 This function duplicates the behavior of {{str_find}}, including all of its quirks.
 This is provided in order to support existing templates, but is NOT RECOMMENDED for
 new code and templates.  New code is recommended to use the &quot;find&quot; function instead.
 
 Returns the first index in &quot;source&quot; that is a match to &quot;target&quot;.  Indexing is 1-based,
 and the function returns -1 if the &quot;target&quot; string is not present in &quot;source&quot;.
 
 Important Note: If the &quot;target&quot; string is empty / missing, this function returns a
 value of &quot;1&quot;, which is generally unexpected behavior, and must be accounted for
 separatetly.
 ]]
 function str.str_find( frame )
 	local new_args = str._getParameters( frame.args, {'source', 'target'} )
 	local source_str = new_args['source'] or ''
 	local target_str = new_args['target'] or ''
 
 	if target_str == '' then
 		return 1
 	end
 
 	local start = mw.ustring.find( source_str, target_str, 1, true )
 	if start == nil then
 		start = -1
 	end
 
 	return start
 end
 
 --[[
 find
 
 This function allows one to search for a target string or pattern within another
 string.
 
 Usage:
 {{#invoke:String|find|source_str|target_string|start_index|plain_flag}}
 OR
 {{#invoke:String|find|source=source_str|target=target_str|start=start_index|plain=plain_flag}}
 
 Parameters
     source: The string to search
     target: The string or pattern to find within source
     start: The index within the source string to start the search, defaults to 1
     plain: Boolean flag indicating that target should be understood as plain
         text and not as a Lua style regular expression, defaults to true
 
 If invoked using named parameters, Mediawiki will automatically remove any leading or
 trailing whitespace from the parameter.  In some circumstances this is desirable, in
 other cases one may want to preserve the whitespace.
 
 This function returns the first index &gt;= &quot;start&quot; where &quot;target&quot; can be found
 within &quot;source&quot;.  Indices are 1-based.  If &quot;target&quot; is not found, then this
 function returns 0.  If either &quot;source&quot; or &quot;target&quot; are missing / empty, this
 function also returns 0.
 
 This function should be safe for UTF-8 strings.
 ]]
 function str.find( frame )
 	local new_args = str._getParameters( frame.args, {'source', 'target', 'start', 'plain' } )
 	local source_str = new_args['source'] or ''
 	local pattern = new_args['target'] or ''
 	local start_pos = tonumber(new_args['start']) or 1
 	local plain = new_args['plain'] or true
 
 	if source_str == '' or pattern == '' then
 		return 0
 	end
 
 	plain = str._getBoolean( plain )
 
 	local start = mw.ustring.find( source_str, pattern, start_pos, plain )
 	if start == nil then
 		start = 0
 	end
 
 	return start
 end
 
 --[[
 replace
 
 This function allows one to replace a target string or pattern within another
 string.
 
 Usage:
 {{#invoke:String|replace|source_str|pattern_string|replace_string|replacement_count|plain_flag}}
 OR
 {{#invoke:String|replace|source=source_string|pattern=pattern_string|replace=replace_string|
    count=replacement_count|plain=plain_flag}}
 
 Parameters
     source: The string to search
     pattern: The string or pattern to find within source
     replace: The replacement text
     count: The number of occurences to replace, defaults to all.
     plain: Boolean flag indicating that pattern should be understood as plain
         text and not as a Lua style regular expression, defaults to true
 ]]
 function str.replace( frame )
 	local new_args = str._getParameters( frame.args, {'source', 'pattern', 'replace', 'count', 'plain' } )
 	local source_str = new_args['source'] or ''
 	local pattern = new_args['pattern'] or ''
 	local replace = new_args['replace'] or ''
 	local count = tonumber( new_args['count'] )
 	local plain = new_args['plain'] or true
 
 	if source_str == '' or pattern == '' then
 		return source_str
 	end
 	plain = str._getBoolean( plain )
 
 	if plain then
 		pattern = str._escapePattern( pattern )
 		replace = mw.ustring.gsub( replace, &quot;%%&quot;, &quot;%%%%&quot; ) --Only need to escape replacement sequences.
 	end
 
 	local result
 
 	if count ~= nil then
 		result = mw.ustring.gsub( source_str, pattern, replace, count )
 	else
 		result = mw.ustring.gsub( source_str, pattern, replace )
 	end
 
 	return result
 end
 
 --[[
     simple function to pipe string.rep to templates.
 ]]
 function str.rep( frame )
 	local repetitions = tonumber( frame.args[2] )
 	if not repetitions then
 		return str._error( 'function rep expects a number as second parameter, received &quot;' .. ( frame.args[2] or '' ) .. '&quot;' )
 	end
 	return string.rep( frame.args[1] or '', repetitions )
 end
 
 --[[
 escapePattern
 
 This function escapes special characters from a Lua string pattern. See [1]
 for details on how patterns work.
 
 [1] https://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
 
 Usage:
 {{#invoke:String|escapePattern|pattern_string}}
 
 Parameters
     pattern_string: The pattern string to escape.
 ]]
 function str.escapePattern( frame )
 	local pattern_str = frame.args[1]
 	if not pattern_str then
 		return str._error( 'No pattern string specified' )
 	end
 	local result = str._escapePattern( pattern_str )
 	return result
 end
 
 --[[
 count
 This function counts the number of occurrences of one string in another.
 ]]
 function str.count(frame)
 	local args = str._getParameters(frame.args, {'source', 'pattern', 'plain'})
 	local source = args.source or ''
 	local pattern = args.pattern or ''
 	local plain = str._getBoolean(args.plain or true)
 	if plain then
 		pattern = str._escapePattern(pattern)
 	end
 	local _, count = mw.ustring.gsub(source, pattern, '')
 	return count
 end
 
 --[[
 endswith
 This function determines whether a string ends with another string.
 ]]
 function str.endswith(frame)
 	local args = str._getParameters(frame.args, {'source', 'pattern'})
 	local source = args.source or ''
 	local pattern = args.pattern or ''
 	if pattern == '' then
 		-- All strings end with the empty string.
 		return &quot;yes&quot;
 	end
 	if mw.ustring.sub(source, -mw.ustring.len(pattern), -1) == pattern then
 		return &quot;yes&quot;
 	else
 		return &quot;&quot;
 	end
 end
 
 --[[
 join
 
 Join all non empty arguments together; the first argument is the separator.
 Usage:
 {{#invoke:String|join|sep|one|two|three}}
 ]]
 function str.join(frame)
 	local args = {}
 	local sep
 	for _, v in ipairs( frame.args ) do
 		if sep then
 			if v ~= '' then
 				table.insert(args, v)
 			end
 		else
 			sep = v
 		end
 	end
 	return table.concat( args, sep or '' )
 end
 
 --[[
 Helper function that populates the argument list given that user may need to use a mix of
 named and unnamed parameters.  This is relevant because named parameters are not
 identical to unnamed parameters due to string trimming, and when dealing with strings
 we sometimes want to either preserve or remove that whitespace depending on the application.
 ]]
 function str._getParameters( frame_args, arg_list )
 	local new_args = {}
 	local index = 1
 	local value
 
 	for _, arg in ipairs( arg_list ) do
 		value = frame_args[arg]
 		if value == nil then
 			value = frame_args[index]
 			index = index + 1
 		end
 		new_args[arg] = value
 	end
 
 	return new_args
 end
 
 --[[
 Helper function to handle error messages.
 ]]
 function str._error( error_str )
 	local frame = mw.getCurrentFrame()
 	local error_category = frame.args.error_category or 'Errors reported by Module String'
 	local ignore_errors = frame.args.ignore_errors or false
 	local no_category = frame.args.no_category or false
 
 	if str._getBoolean(ignore_errors) then
 		return ''
 	end
 
 	local error_str = '&lt;strong class=&quot;error&quot;&gt;String Module Error: ' .. error_str .. '&lt;/strong&gt;'
 	if error_category ~= '' and not str._getBoolean( no_category ) then
 		error_str = '[[Category:' .. error_category .. ']]' .. error_str
 	end
 
 	return error_str
 end
 
 --[[
 Helper Function to interpret boolean strings
 ]]
 function str._getBoolean( boolean_str )
 	local boolean_value
 
 	if type( boolean_str ) == 'string' then
 		boolean_str = boolean_str:lower()
 		if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0'
 				or boolean_str == '' then
 			boolean_value = false
 		else
 			boolean_value = true
 		end
 	elseif type( boolean_str ) == 'boolean' then
 		boolean_value = boolean_str
 	else
 		error( 'No boolean value found' )
 	end
 	return boolean_value
 end
 
 --[[
 Helper function that escapes all pattern characters so that they will be treated
 as plain text.
 ]]
 function str._escapePattern( pattern_str )
 	return mw.ustring.gsub( pattern_str, &quot;([%(%)%.%%%+%-%*%?%[%^%$%]])&quot;, &quot;%%%1&quot; )
 end