-- This module is intended to replace the functionality of Template:Formatnum and related templates. 

local p = {}



function p.main(frame)

    local args = frame:getParent().args

    local prec    = args.prec or ''

    local sep     = args.sep or ''

    local number  = args1 or args.number or ''

    local lang    = args2 or args.lang or ''

    -- validate the language parameter within MediaWiki's caller frame

    if lang == "arabic-indic" then -- only for back-compatibility ("arabic-indic" is not a SupportedLanguage)

        lang = "fa" -- better support than "ks"

    elseif lang == '' or not mw.language.isSupportedLanguage(lang) then

        -- Note that 'SupportedLanguages' are not necessarily 'BuiltinValidCodes', and so they are not necessarily

        -- 'KnownLanguages' (with a language name defined at least in the default localisation of the local wiki).

        -- But they all are ValidLanguageCodes (suitable as Wiki subpages or identifiers: no slash, colon, HTML tags, or entities)

        -- In addition, they do not contain any capital letter in order to be unique in page titles (restriction inexistant in BCP47),

        -- but they may violate the standard format of BCP47 language tags for specific needs in MediaWiki.

        -- Empty/unspecified and unsupported languages are treated here in Commons using the user's language,

        -- instead of the local 'ContentLanguage' of the Wiki.

        lang = frame:callParserFunction( "int", "lang" ) -- get user's chosen language

    end

    return p.formatNum(number, lang, prec, sep ~= '')

end



local digit = { -- substitution of decimal digits for languages not supported by mw.language:formatNum() in core Lua libraries for MediaWiki

    "ml-old" = { '൦', '൧', '൨', '൩', '൪', '൫', '൬', '൭', '൮', '൯' },

    "mn"     = { '᠐', '᠑', '᠒', '᠓', '᠔', '᠕', '᠖', '᠗', '᠘', '᠙'},

    "ta"     = { '௦', '௧', '௨', '௩', '௪', '௫', '௬', '௭', '௮', '௯'},

    "te"     = { '౦', '౧', '౨', '౩', '౪', '౫', '౬', '౭', '౮', '౯'},

    "th"     = { '๐', '๑', '๒', '๓', '๔', '๕', '๖', '๗', '๘', '๙'}

}



function p.formatNum(number, lang, prec, compact)



    -- Do not alter the specified value when it is not a valid number, return it as is

    local value = tonumber(number)

    if value == nil then

        return number

    end

    -- Basic ASCII-only formatting (without paddings)

    number = tostring(value)



    -- Check the presence of an exponent (incorrectly managed in mw.language:FormatNum() and even forgotten due to an internal bug, e.g. in Hindi)

    local exponent

    local pos = string.find(number, '[Ee]')

    if pos ~= nil then

        exponent = string.sub(number, pos + 1, string.len(number))

        number = string.sub(number, 1, pos - 1)

    else

        exponent = ''

    end



    -- Check the minimum precision requested

    prec = tonumber(prec) -- nil if not specified as a true number

    if prec ~= nil then

        prec = math.floor(prec)

        if prec < 0 then

            prec = nil -- discard an incorrect precision (not a positive integer)

        elseif prec > 14 then

            prec = 14 -- maximum precision supported by tostring(number)

        end

    end



    -- Preprocess the minimum precision in the ASCII string

    local dot

    if (prec or 0) > 0 then

        pos = string.find(number, '.', 1, true) -- plain search, no regexp

        if pos ~= nil then

            prec = pos + prec - string.len(number) -- effective number of trailing decimals to add or remove

            dot = '' -- already present

        else

            dot = '.' -- must be added

        end

    else

        dot = '' -- don't add dot

        prec = 0 -- don't alter the precision

    end



    if lang ~= nil and mw.language.isKnownLanguageTag(lang) == true then

        -- Convert number to localized digits, decimal separator, and group separators

        local language = mw.getLanguage(lang)

        if compact then

            number = language:formatNum(tonumber(number), { noCommafy = 'y' }) -- caveat: can load localized resources for up to 20 languages

        else

            number = language:formatNum(tonumber(number)) -- caveat: can load localized resources for up to 20 languages

        end

        -- Postprocessing the precision

        if prec > 0 then

            local zero = language:formatNum(0)

            number = number .. dot .. mw.ustring.rep(zero, prec)

        elseif prec < 0 then

            -- TODO: rounding of last decimal; here only truncate decimals in excess

            number = mw.ustring.sub(number, 1, mw.ustring.len(number) + prec)

        end



        -- Append the localized base-10 exponent without grouping separators (there's no reliable way to detect a localized leading symbol 'E')

        if exponent ~= '' then

            number = number .. 'E' .. language:formatNum(tonumber(exponent),{noCommafy=true})

        end

    else -- not localized, ASCII only

        -- Postprocessing the precision

        if prec > 0 then

            number = number .. dot .. mw.string.rep('0', prec)

        elseif prec < 0 then

            -- TODO: rounding of last decimal; here only truncate decimals in excess

            number = mw.string.sub(number, 1, mw.string.len(number) + prec)

        end



        -- Append the base-10 exponent

        if exponent ~= '' then

            number = number .. 'E' .. exponent

        end

    end



    -- Special cases for substitution of ASCII digits (missing support in Lua core libraries for some languages)

    if digitlang then

        for i, v in ipairs(digitlang]) do

            number = mw.ustring.gsub(number, tostring(i - 1), v)

        end

    end



    return number

end



return p