Module:String

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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 = {}

--[[
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