Format a number in Lua

util.lua

Util.format_num = function(amount, decimal, prefix, neg_prefix)
    local str_amount,  formatted, famount, remain

    decimal = decimal or 2  -- default 2 decimal places
    neg_prefix = neg_prefix or "-" -- default negative sign

    famount = math.abs(Util.round(amount,decimal))
    famount = math.floor(famount)

    remain = Util.round(math.abs(amount) - famount, decimal)

    -- comma to separate the thousands
    formatted = Util.comma_value(famount)

    -- attach the decimal portion
    if (decimal > 0) then
        remain = string.sub(tostring(remain),3)
        formatted = formatted .. "." .. remain ..
                string.rep("0", decimal - string.len(remain))
    end

    -- attach prefix string e.g '$'
    formatted = (prefix or "") .. formatted

    -- if value is negative then format accordingly
    if (amount<0) then
        if (neg_prefix=="()") then
            formatted = "("..formatted ..")"
        else
            formatted = neg_prefix .. formatted
        end
    end

    return formatted
end