--[[  
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:  
OR  
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
local new_args = str._getParameters( .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:  
OR  
Parameters
s: The string to return a subset of
i: The first 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
local new_args = str._getParameters( .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 and is kept in order
to maintain these older templates.  
function str.sublength
local i = tonumber( .args.i ) or 0
local len = tonumber( .args.len )
return mw.ustring.sub( .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:  
OR  
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
local new_args = str._getParameters( .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:  
OR  
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.