function trim(s)
    return (s:gsub("^%s*(.-)%s*$", "%1"))
end

function split_fmt(f)
    if not type(f) == "string" then
        io.stderr:write("ERROR!  Argument '" .. format .. "' is not a string.")
        return nil
    end

    local ret = {}
    local curr = ""
    local in_spec = false
    for char in string.gmatch(f, ".") do
        if in_spec then
            if string.match(char, '[cdEefgiouXx]') then
                curr = curr .. char
                table.insert(ret, curr)
                in_spec = false
                curr = ""
            elseif string.match(char, '[qs]') then
                if string.match(curr, '^%%%-?[0-9]*$') then
                    curr = curr .. char
                    table.insert(ret, curr)
                    in_spec = false
                    curr = ""
                else
                    io.stderr:write("Invalid format:  '" .. curr .. char .. "'\n")
                    return nil
                end
            elseif string.match(char, '[0-9%.%-]') then
                curr = curr .. char
            elseif string.match(char, '%%') then
                if string.match(curr, '^%%') then
                    curr = curr .. char
                    table.insert(ret, curr)
                    in_spec = false
                    curr = ""
                else
                    io.stderr:write("Invalid format:  '" .. curr .. char .. "'\n")
                    return nil
                end
            else
                io.stderr:write("Invalid format:  '" .. curr .. char .. "'\n")
                return nil
            end
        else
            if char == '%' then
                in_spec = true
                if curr ~= "" then
                    table.insert(ret, curr)
                end
                curr = char
            else
                curr = curr .. char
            end
        end
    end
    if curr ~= "" then
        table.insert(ret, curr)
    end
    return ret
end

function table_length(t)
    local count = 0
    for _ in pairs(t) do
        count = count + 1
    end
    return count
end

function count_formats(formats)
    if type(formats) ~= 'table' then
        io.stderr:write("ERROR!  formats is not a table.\n")
        return nil
    end

    local count = 0
    for i,v in ipairs(formats) do
        if string.match(v, '^%%') and not string.match(v, '%%$') then
            count = count + 1
        end
    end
    return count
end

function is_fmt_spec(str)
    return string.match(str, "^%%")
end


function conky_printf(format, ...)
    formats = split_fmt(format)
    values = {...}

    if count_formats(formats) ~= table_length(values) then
        io.stderr:write("ERROR!  Number of format specifiers to printf doesn't match the number of values passed.\n")
        return nil
    end

    local parsed_values = {}
    for i,v in ipairs(values) do
        parsed_values[i] = conky_parse(v)
    end
    for i,fs in ipairs(formats) do
        if is_fmt_spec(fs) then -- we have a format specifier
            if string.match(fs, '[cdEefgiouXx]$') then -- we have a numeric format specifier, convert value to number
                parsed_values[i] = tonumber(trim((parsed_values[i])))
            end
        end
    end
    local formatted_output = ""
    local idx = 1
    for i,fs in ipairs(formats) do
        if is_fmt_spec(fs) then
            if not string.match(fs, '%%$') then
                formatted_output = formatted_output .. string.format(fs, parsed_values[idx])
                idx = idx + 1
            else
                formatted_output = formatted_output .. '%'
            end
        else
            formatted_output = formatted_output .. fs
        end
    end
    return formatted_output
end