Module:String: Difference between revisions

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(separate annotations for str.match from those for str._match)
 
wm>GVarnum-WMF
m (1 revision imported from meta:Module:String)
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--[[
--[[


This module is intended to provide access to basic string functions.
This module is intended to provide access to basic string functions.


Most of the functions provided here can be invoked with named parameters,
Most of the functions provided here can be invoked with named parameters,  
unnamed parameters, or a mixture.  If named parameters are used, Mediawiki will
unnamed parameters, or a mixture.  If named parameters are used, Mediawiki will  
automatically remove any leading or trailing whitespace from the parameter.
automatically remove any leading or trailing whitespace from the parameter.
Depending on the intended use, it may be advantageous to either preserve or
Depending on the intended use, it may be advantageous to either preserve or
remove such whitespace.
remove such whitespace.


Global options
Global options
     ignore_errors: If set to 'true' or 1, any error condition will result in
     ignore_errors: If set to 'true' or 1, any error condition will result in  
         an empty string being returned rather than an error message.
         an empty string being returned rather than an error message.
 
       
     error_category: If an error occurs, specifies the name of a category to
     error_category: If an error occurs, specifies the name of a category to  
         include with the error message.  The default category is
         include with the error message.  The default category is
         [Category:Errors reported by Module String].
         [Category:Errors reported by Module String].
 
       
     no_category: If set to 'true' or 1, no category will be added if an error
     no_category: If set to 'true' or 1, no category will be added if an error
         is generated.
         is generated.
 
       
Unit tests for this module are available at Module:String/tests.
Unit tests for this module are available at Module:String/tests.
]]
]]
Line 39: 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


Line 61: Line 61:
     i: The fist index of the substring to return, defaults to 1.
     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.
     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
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
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
counting from the end of the string.  Hence, a value of -1 is the same as  
selecting the last character of the string.
selecting the last character of the string.


If the requested indices are out of range for the given string, an error is
If the requested indices are out of range for the given string, an error is  
reported.
reported.
]]
]]
function str.sub( frame )
function str.sub( frame )
local new_args = str._getParameters( frame.args, { 's', 'i', 'j' } )
    local new_args = str._getParameters( frame.args, { 's', 'i', 'j' } );
local s = new_args['s'] or ''
    local s = new_args['s'] or '';
local i = tonumber( new_args['i'] ) or 1
    local i = tonumber( new_args['i'] ) or 1;
local j = tonumber( new_args['j'] ) or -1
    local j = tonumber( new_args['j'] ) or -1;
 
   
local len = mw.ustring.len( s )
    local len = mw.ustring.len( s );


-- Convert negatives for range checking
    -- Convert negatives for range checking
if i < 0 then
    if i < 0 then
i = len + i + 1
        i = len + i + 1;
end
    end
if j < 0 then
    if j < 0 then
j = len + j + 1
        j = len + j + 1;
end
    end
 
   
if i > len or j > len or i < 1 or j < 1 then
    if i > len or j > len or i < 1 or j < 1 then
return str._error( 'String subset index out of range' )
        return str._error( 'String subset index out of range' );
end
    end
if j < i then
    if j < i then
return str._error( 'String subset indices out of order' )
        return str._error( 'String subset indices out of order' );
end
    end
 
   
return mw.ustring.sub( s, i, j )
    return mw.ustring.sub( s, i, j )
end
end


--[[
--[[
This function implements that features of {{str sub old}} and is kept in order
This function implements that features of {{subr|s|skip|max}} and
to maintain these older templates.
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


--[[
Uses only numbered paramameters to preserve spaces (caller may trim
_match
whitespaces by passing the parameter explicitly by numbering the
parameters).


This function returns a substring from the source string that matches a
Accepts negative values as relative to strng length.
specified pattern. It is exported for use in other modules


Usage:
No error is returned if attempting to read past end of string or
strmatch = require("Module:String")._match
before start of string.
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


Currently does not parse and replace placeholders for nowiki tags.
]]
]]
-- This sub-routine is exported for use in other modules
function str.sublength( frame )
function str._match( s, pattern, start, match_index, plain_flag, nomatch )
    local s = frame.args[1] or '';
if s == '' then
    local skip = tonumber( frame.args[2] ) or 0;
return str._error( 'Target string is empty' )
    local max = tonumber( frame.args[3] ) or 0;
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
    local len = mw.ustring.len( s );
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)
    -- convert negative values of max and skip as relative to string length
if match_index > 0 then
    if max < 0 then
-- Forward search
        max = len + max
for w in iterator do
    end
match_index = match_index - 1
    if skip < 0 then
if match_index == 0 then
        skip = len + skip
result = w
    end
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 ]
    -- check boundaries to reduce the requested max
end
    if skip < 0 then        -- if before start of string
end
        max = max + skip
        skip = 0            -- skip can't underflow now
    end
    if max > len - skip then -- if past end of string
        max = len - skip    -- max can't overflow now
    end
    if max <= 0 then
        return '' -- nothing left to return
    end


if result == nil then
    return mw.ustring.sub( s, skip + 1, skip + max )
if nomatch == nil then
return str._error( 'Match not found' )
else
return nomatch
end
else
return result
end
end
end


Line 202: Line 144:
match
match


This function returns a substring from the source string that matches a
This function returns a substring from the source string that matches a  
specified pattern.
specified pattern.


Line 208: Line 150:
{{#invoke:String|match|source_string|pattern_string|start_index|match_number|plain_flag|nomatch_output}}
{{#invoke:String|match|source_string|pattern_string|start_index|match_number|plain_flag|nomatch_output}}
OR
OR
{{#invoke:String|match|s=source_string|pattern=pattern_string|start=start_index
{{#invoke:String|pos|s=source_string|pattern=pattern_string|start=start_index
     |match=match_number|plain=plain_flag|nomatch=nomatch_output}}
     |match=match_number|plain=plain_flag|nomatch=nomatch_output}}


Line 216: Line 158:
     start: The index within the source string to start the search.  The first
     start: The index within the source string to start the search.  The first
         character of the string has index 1.  Defaults to 1.
         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
     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
         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
         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
         counting from the last match.  Hence match = -1 is the same as requesting
         the last match.  Defaults to 1.
         the last match.  Defaults to 1.
Line 226: Line 168:


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 each string.  In some circumstances this is desirable, in
trailing whitespace from each 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.


If the match_number or start_index are out of range for the string being queried, then
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.
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
If one adds the parameter ignore_errors=true, then the error will be suppressed and  
an empty string will be returned on any failure.
an empty string will be returned on any failure.


Line 241: Line 183:


]]
]]
-- This is the entry point for #invoke:String|match
function str.match( frame )
function str.match( frame )
local new_args = str._getParameters( frame.args, {'s', 'pattern', 'start', 'match', 'plain', 'nomatch'} )
    local new_args = str._getParameters( frame.args, {'s', 'pattern', 'start', 'match', 'plain', 'nomatch'} );
local s = new_args['s'] or ''
    local s = new_args['s'] or '';
local start = tonumber( new_args['start'] ) or 1
    local start = tonumber( new_args['start'] ) or 1;
local plain_flag = str._getBoolean( new_args['plain'] or false )
    local plain_flag = str._getBoolean( new_args['plain'] or false );
local pattern = new_args['pattern'] or ''
    local pattern = new_args['pattern'] or '';
local match_index = math.floor( tonumber(new_args['match']) or 1 )
    local match_index = math.floor( tonumber(new_args['match']) or 1 );
local nomatch = new_args['nomatch']
    local nomatch = new_args['nomatch'];
 
   
return 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
    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


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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.


Line 280: Line 277:
]]
]]
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 str._error( 'String index out of range' )
        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


Line 295: Line 292:


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 306: Line 303:
]]
]]
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


Line 341: Line 338:


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.
Line 352: Line 349:
]]
]]
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
    if source_str == '' or pattern == '' then
return 0
        return 0;
end
    end  
 
   
plain = str._getBoolean( plain )
    plain = str._getBoolean( plain );
 
local start = mw.ustring.find( source_str, pattern, start_pos, plain )
if start == nil then
start = 0
end


return start
    local start = mw.ustring.find( source_str, pattern, start_pos, plain )
    if start == nil then
        start = 0
    end
   
    return start
end
end


Line 390: Line 387:
     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 source_str == '' or pattern == '' then
    if plain then
return source_str
        pattern = str._escapePattern( pattern );
end
        replace = mw.ustring.gsub( replace, "%%", "%%%%" ); --Only need to escape replacement sequences.
plain = str._getBoolean( plain )
    end
   
    local result;


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


local result
    return 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
end


--[[
--[[  
     simple function to pipe string.rep to templates.
     simple function to pipe string.rep to templates.
]]
]]
function str.rep( frame )
function str.rep( frame )
local repetitions = tonumber( frame.args[2] )
    local repetitions = tonumber( frame.args[2] )
if not repetitions then
    if not repetitions then  
return str._error( 'function rep expects a number as second parameter, received "' .. ( frame.args[2] or '' ) .. '"' )
        return str._error( 'function rep expects a number as second parameter, received "' .. ( frame.args[2] or '' ) .. '"' )
end
    end
return string.rep( frame.args[1] or '', repetitions )
    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
end


Line 519: Line 437:
]]
]]
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 _, arg in ipairs( arg_list ) do
    for i,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      


--[[
--[[
Line 539: Line 457:
]]
]]
function str._error( error_str )
function str._error( error_str )
local frame = mw.getCurrentFrame()
    local frame = mw.getCurrentFrame();
local error_category = frame.args.error_category or 'Errors reported by Module String'
    local error_category = frame.args.error_category or 'Errors reported by Module String';
local ignore_errors = frame.args.ignore_errors or false
    local ignore_errors = frame.args.ignore_errors or false;
local no_category = frame.args.no_category or false
    local no_category = frame.args.no_category or false;
 
   
if str._getBoolean(ignore_errors) then
    if str._getBoolean(ignore_errors) then
return ''
        return '';
end
    end
 
   
local error_str = '<strong class="error">String Module Error: ' .. error_str .. '</strong>'
    local error_str = '<strong class="error">String Module Error: ' .. error_str .. '</strong>';
if error_category ~= '' and not str._getBoolean( no_category ) then
    if error_category ~= '' and not str._getBoolean( no_category ) then
error_str = '[[Category:' .. error_category .. ']]' .. error_str
        error_str = '[[Category:' .. error_category .. ']]' .. error_str;
end
    end      
 
   
return error_str
    return error_str;
end
end


Line 560: Line 478:
]]
]]
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'
        if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0'  
or boolean_str == '' then
                or boolean_str == '' then
boolean_value = false
            boolean_value = false;
else
        else
boolean_value = true
            boolean_value = true;
end
        end  
elseif type( boolean_str ) == 'boolean' then
    elseif type( boolean_str ) == 'boolean' then
boolean_value = boolean_str
        boolean_value = boolean_str;
else
    else
error( 'No boolean value found' )
        error( 'No boolean value found' );
end
    end  
return boolean_value
    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

Revision as of 18:59, 9 December 2021

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 {{subr|s|skip|max}} and
is kept in order to maintain these older templates.

Uses only numbered paramameters to preserve spaces (caller may trim
whitespaces by passing the parameter explicitly by numbering the
parameters).

Accepts negative values as relative to strng length.

No error is returned if attempting to read past end of string or
before start of string.

Currently does not parse and replace placeholders for nowiki tags.
]]
function str.sublength( frame )
    local s = frame.args[1] or '';
    local skip = tonumber( frame.args[2] ) or 0;
    local max = tonumber( frame.args[3] ) or 0;

    local len = mw.ustring.len( s );

    -- convert negative values of max and skip as relative to string length
    if max < 0 then
        max = len + max
    end
    if skip < 0 then
        skip = len + skip
    end

    -- check boundaries to reduce the requested max
    if skip < 0 then         -- if before start of string
        max = max + skip
        skip = 0             -- skip can't underflow now
    end
    if max > len - skip then -- if past end of string
        max = len - skip     -- max can't overflow now
    end
    if max <= 0 then
        return '' -- nothing left to return
    end

    return mw.ustring.sub( s, skip + 1, skip + max )
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|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 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

]]
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;
    end
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

--[[
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 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_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