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( frame )
 local new_args = str._getParameters;
 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 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;
 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
end

--
This function implements that features of 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.

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:

]]
function str.match( frame )
 local new_args = str._getParameters;
 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)  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
 else
 if start > 1 then
 s = mw.ustring.sub;
 end
 
 local iterator = mw.ustring.gmatch;
 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

--
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.

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;
 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;
end

--
str_find

This function duplicates the behavior of , 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;
 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
 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:
OR

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; 
 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
 if start == nil then
 start = 0
 end
 
 return start
end

--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; 
 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; --Only need to escape replacement sequences.
 end
 
 local result;

 if count ~= nil then
 result = mw.ustring.gsub;
 else
 result = mw.ustring.gsub;
 end 

 return result;
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
 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 = '';
 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