--[[  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 orremove 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 = {}--[[lenThis 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 reportIf invoked using named parameters, Mediawiki will automatically remove any leading ortrailing 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--[[subThis 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 jis 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 orderto 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--[[matchThis 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|pos|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 ortrailing 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, thenthis 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]]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'];        if s == '' then        return str._error( 'Target string is empty' );    end    if pattern == '' then        return str._error( 'Pattern string is empty' );    end    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;    endend--[[posThis 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 returnIf invoked using named parameters, Mediawiki will automatically remove any leading ortrailing 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_findThis 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 avalue of "1", which is generally unexpected behavior, and must be accounted forseparatetly.]]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 startend--[[findThis function allows one to search for a target string or pattern within anotherstring.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 trueIf invoked using named parameters, Mediawiki will automatically remove any leading ortrailing 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, thisfunction 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 startend--[[replaceThis function allows one to replace a target string or pattern within anotherstring.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--[[Helper function that populates the argument list given that user may need to use a mix ofnamed and unnamed parameters.  This is relevant because named parameters are notidentical to unnamed parameters due to string trimming, and when dealing with stringswe 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 i,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_valueend--[[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" );endreturn str