Module:String: Difference between revisions

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--[[
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 = {}
local str = {}


--[====[
--[[
len
len


Line 9: Line 33:
{{#invoke:String|len|target_string|}}
{{#invoke:String|len|target_string|}}
OR
OR
{{#invoke:String|pos|s=target_string}}
{{#invoke:String|len|s=target_string}}


Parameters
Parameters
Line 15: Line 39:


If invoked using named parameters, Mediawiki will automatically remove any leading or
If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the target string.
trailing whitespace from the target string.
]====]
]]
function str.len( frame )
function str.len( frame )
    local new_args = str._getParameters( frame.args, {'s'} );
local new_args = str._getParameters( frame.args, {'s'} )
    local s = new_args['s'] or '';
local s = new_args['s'] or ''
    return mw.ustring.len( s )
return mw.ustring.len( s )
end
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 )
function str.sub( frame )
    return mw.ustring.sub( frame.args.s, tonumber( frame.args.i ), tonumber( frame.args.j ) )
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 < 0 then
i = len + i + 1
end
if j < 0 then
j = len + j + 1
end
 
if i > len or j > len or i < 1 or j < 1 then
return str._error( 'String subset index out of range' )
end
if j < i then
return str._error( 'String subset indices out of order' )
end
 
return mw.ustring.sub( s, i, j )
end
end


--[[
This function implements that features of {{str sub old}} and is kept in order
to maintain these older templates.
]]
function str.sublength( frame )
function str.sublength( frame )
    local i = tonumber( frame.args.i ) or 0
local i = tonumber( frame.args.i ) or 0
    local len = tonumber( frame.args.len )
local len = tonumber( frame.args.len )
    return mw.ustring.sub( frame.args.s, i + 1, len and ( i + 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("Module:String")._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 "nomatch" 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) < 1 or math.abs(start) > 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 > 1 then
s = mw.ustring.sub( s, start )
end
 
local iterator = mw.ustring.gmatch(s, pattern)
if match_index > 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
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 "nomatch" 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 )
function str.match( frame )
    return mw.ustring.match( frame.args.s, frame.args.pattern, tonumber( frame.args.i ) )
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
end


--[====[
--[[
pos
pos


Line 52: Line 269:


If invoked using named parameters, Mediawiki will automatically remove any leading or
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  
trailing whitespace from the target string.  In some circumstances this is desirable, in
other cases one may want to preserve the whitespace.
other cases one may want to preserve the whitespace.


The first character has an index value of 1.
The first character has an index value of 1.


If one requests a negative value, this function will select a character by counting backwards  
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.
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.
A requested value of zero, or a value greater than the length of the string returns an error.
]====]
]]
function str.pos( frame )
function str.pos( frame )
    local new_args = str._getParameters( frame.args, {'target', 'pos'} );
local new_args = str._getParameters( frame.args, {'target', 'pos'} )
    local target_str = new_args['target'] or '';
local target_str = new_args['target'] or ''
    local pos = tonumber( new_args['pos'] ) or 0;
local pos = tonumber( new_args['pos'] ) or 0


    if pos == 0 or math.abs(pos) > mw.ustring.len( target_str ) then
if pos == 0 or math.abs(pos) > mw.ustring.len( target_str ) then
        return '<strong class="error">String index out of range</strong>';
return str._error( 'String index out of range' )
    end  
end
   
 
    return mw.ustring.sub( target_str, pos, pos );
return mw.ustring.sub( target_str, pos, pos )
end
end


--[====[
--[[
str_find
str_find


This function duplicates the behavior of {{str_find}}, including all of its quirks.
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  
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 "find" function instead.
new code and templates.  New code is recommended to use the "find" function instead.


Line 87: Line 304:
value of "1", which is generally unexpected behavior, and must be accounted for
value of "1", which is generally unexpected behavior, and must be accounted for
separatetly.
separatetly.
]====]
]]
function str.str_find( frame )
function str.str_find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target'} );
local new_args = str._getParameters( frame.args, {'source', 'target'} )
    local source_str = new_args['source'] or '';
local source_str = new_args['source'] or ''
    local target_str = new_args['target'] or '';
local target_str = new_args['target'] or ''


    if target_str == '' then
if target_str == '' then
        return 1;
return 1
    end  
end
   
 
    local start = mw.ustring.find( source_str, target_str, 1, true )
local start = mw.ustring.find( source_str, target_str, 1, true )
    if start == nil then
if start == nil then
        start = -1
start = -1
    end
end
   
 
    return start
return start
end
end


--[====[
--[[
find
find


Line 124: Line 341:


If invoked using named parameters, Mediawiki will automatically remove any leading or
If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the parameter.  In some circumstances this is desirable, in  
trailing whitespace from the parameter.  In some circumstances this is desirable, in
other cases one may want to preserve the whitespace.
other cases one may want to preserve the whitespace.


This function returns the first index >= "start" where "target" can be found  
This function returns the first index >= "start" where "target" can be found
within "source".  Indices are 1-based.  If "target" is not found, then this  
within "source".  Indices are 1-based.  If "target" is not found, then this
function returns 0.  If either "source" or "target" are missing / empty, this
function returns 0.  If either "source" or "target" are missing / empty, this
function also returns 0.
function also returns 0.


This function should be safe for UTF-8 strings.
This function should be safe for UTF-8 strings.
]====]
]]
function str.find( frame )
function str.find( frame )
    local new_args = str._getParameters( frame.args, {'source', 'target', 'start', 'plain' } );
local new_args = str._getParameters( frame.args, {'source', 'target', 'start', 'plain' } )
    local source_str = new_args['source'] or '';
local source_str = new_args['source'] or ''
    local pattern = new_args['target'] or '';
local pattern = new_args['target'] or ''
    local start_pos = tonumber(new_args['start']) or 1;
local start_pos = tonumber(new_args['start']) or 1
    local plain = new_args['plain'] or true;
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 source_str == '' or pattern == '' then
    if start == nil then
return 0
        start = 0
end
    end
 
   
plain = str._getBoolean( plain )
    return start
 
local start = mw.ustring.find( source_str, pattern, start_pos, plain )
if start == nil then
start = 0
end
 
return start
end
end


--[====[
--[[
replace
replace


Line 173: Line 390:
     count: The number of occurences to replace, defaults to all.
     count: The number of occurences to replace, defaults to all.
     plain: Boolean flag indicating that pattern should be understood as plain
     plain: Boolean flag indicating that pattern should be understood as plain
         text and not as a Lua style regular expression, defaults to true  
         text and not as a Lua style regular expression, defaults to true
]====]
]]
function str.replace( frame )
function str.replace( frame )
    local new_args = str._getParameters( frame.args, {'source', 'pattern', 'replace', 'count', 'plain' } );
local new_args = str._getParameters( frame.args, {'source', 'pattern', 'replace', 'count', 'plain' } )
    local source_str = new_args['source'] or '';
local source_str = new_args['source'] or ''
    local pattern = new_args['pattern'] or '';
local pattern = new_args['pattern'] or ''
    local replace = new_args['replace'] or '';
local replace = new_args['replace'] or ''
    local count = tonumber( new_args['count'] );
local count = tonumber( new_args['count'] )
    local plain = new_args['plain'] or true;
local plain = new_args['plain'] or true
       
    if source_str == '' or pattern == '' then
        return source_str;
    end   
    plain = str._getBoolean( plain );


    if plain then
if source_str == '' or pattern == '' then
        pattern = str._escapePattern( pattern );
return source_str
        replace = str._escapePattern( replace );
end
    end
plain = str._getBoolean( plain )
   
    local result;


    if count ~= nil then
if plain then
        result = mw.ustring.gsub( source_str, pattern, replace, count );
pattern = str._escapePattern( pattern )
    else
replace = mw.ustring.gsub( replace, "%%", "%%%%" ) --Only need to escape replacement sequences.
        result = mw.ustring.gsub( source_str, pattern, replace );
end
    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


     return result;
--[[
     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 "' .. ( frame.args[2] or '' ) .. '"' )
end
return string.rep( frame.args[1] or '', repetitions )
end
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 "yes"
end
if mw.ustring.sub(source, -mw.ustring.len(pattern), -1) == pattern then
return "yes"
else
return ""
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
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
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
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.
we sometimes want to either preserve or remove that whitespace depending on the application.
]====]
]]
function str._getParameters( frame_args, arg_list )
function str._getParameters( frame_args, arg_list )
    local new_args = {};
local new_args = {}
    local index = 1;
local index = 1
    local value;
local value
   
 
    for i,arg in ipairs( arg_list ) do
for _, arg in ipairs( arg_list ) do
        value = frame_args[arg]
value = frame_args[arg]
        if value == nil then
if value == nil then
            value = frame_args[index];
value = frame_args[index]
            index = index + 1;
index = index + 1
        end
end
        new_args[arg] = value;
new_args[arg] = value
    end
end
   
 
    return new_args;
return new_args
end      
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 = '<strong class="error">String Module Error: ' .. error_str .. '</strong>'
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
Helper Function to interpret boolean strings
]====]
]]
function str._getBoolean( boolean_str )
function str._getBoolean( boolean_str )
    local boolean_value;
local boolean_value
   
 
    if type( boolean_str ) == 'string' then
if type( boolean_str ) == 'string' then
        boolean_str = boolean_str:lower();
boolean_str = boolean_str:lower()
        if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0' then
if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0'
            boolean_value = false;
or boolean_str == '' then
        else
boolean_value = false
            boolean_value = true;
else
        end  
boolean_value = true
    elseif type( boolean_str ) == 'boolean' then
end
        boolean_value = boolean_str;
elseif type( boolean_str ) == 'boolean' then
    else
boolean_value = boolean_str
        error( 'No boolean value found' );
else
    end  
error( 'No boolean value found' )
    return boolean_value
end
return boolean_value
end
end


--[====[
--[[
Helper function that escapes all pattern characters so that they will be treated  
Helper function that escapes all pattern characters so that they will be treated
as plain text.
as plain text.
]====]
]]
function str._escapePattern( pattern_str )
function str._escapePattern( pattern_str )
    return mw.ustring.gsub( pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" );
return mw.ustring.gsub( pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" )
end
end


return str
return str

Latest revision as of 14:06, 12 December 2022

Documentation for this module may be created at Module:String/doc

--[[

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 < 0 then
		i = len + i + 1
	end
	if j < 0 then
		j = len + j + 1
	end

	if i > len or j > len or i < 1 or j < 1 then
		return str._error( 'String subset index out of range' )
	end
	if j < 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("Module:String")._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 "nomatch" 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) < 1 or math.abs(start) > 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 > 1 then
			s = mw.ustring.sub( s, start )
		end

		local iterator = mw.ustring.gmatch(s, pattern)
		if match_index > 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 "nomatch" 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) > 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 "find" function instead.

Returns the first index in "source" that is a match to "target".  Indexing is 1-based,
and the function returns -1 if the "target" string is not present in "source".

Important Note: If the "target" string is empty / missing, this function returns a
value of "1", 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 >= "start" where "target" can be found
within "source".  Indices are 1-based.  If "target" is not found, then this
function returns 0.  If either "source" or "target" 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, "%%", "%%%%" ) --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 "' .. ( frame.args[2] or '' ) .. '"' )
	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 "yes"
	end
	if mw.ustring.sub(source, -mw.ustring.len(pattern), -1) == pattern then
		return "yes"
	else
		return ""
	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 = '<strong class="error">String Module Error: ' .. error_str .. '</strong>'
	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, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" )
end

return str