local function reverse_resolve(ip, ns, retrans, timeout)
    local r, err = resolver:new{
        nameservers = ns,
        retrans = retrans,  -- 5 retransmissions on receive timeout
        timeout = timeout,  -- 1 sec
    }
    if not r then
        ngx.log(ngx.ERR, "failed to instantiate the resolver: ".. err .. ", client_ip: " .. ip)
        return
    end
    local answers, err = r:reverse_query(ip)
    if not answers then
        ngx.log(ngx.ERR, "failed to query the DNS server: " .. err .. ", client_ip: " .. ip)
        return
    end
    if answers.errcode then
        ngx.log(ngx.ERR, "server returned error code: " .. answers.errcode ..
                ": " .. answers.errstr .. ", client_ip: " .. ip)
        return
    end
    if not answers[1] or not answers[1].ptrdname then
        ngx.log(ngx.ERR, "ptrdname entry not exist, client_ip: " .. ip)
        return
    end
    local ip_host = answers[1].ptrdname
    ip_host = string.gsub(ip_host, "google.com", "googlebot.com") -- bring to single form
    local suff = string.sub(ip_host, -13)
    if suff == "googlebot.com" then
        return true
    end
    return nil, "not googlebot"
end

local function is_googlebot(ip, ns, retrans, timeout)
    local res = string.find(string.lower(ngx.var.http_user_agent or ""), "googlebot")
    if not res then
        -- not found googlebot in user agent
        return nil, "not googlebot"
    end
    return reverse_resolve(ip, ns, retrans, timeout)
end

local function has_referer()
    local referer = ngx.var.http_referer or ""
    if referer == "" then
        return
    end
    return referer
end

local function diff_ms(start)
    return math.ceil(ngx.now() - start)
end

--local remote_addr = ngx.var.proxy_add_x_forwarded_for
local remote_addr = ngx.var.http_cf_connecting_ip or "127.0.0.1"
--local remote_addr = ngx.var.arg_ip or "127.0.0.1" --TEST

local diff = -1
local wl, err = redis_get_wl(red, remote_addr)
if not wl or wl == ngx.null then
    -- redis error or not found in WL
    local bl, err = redis_get_bl(red, remote_addr)
    if not bl or bl == ngx.null then
        --redis error or not found in BL
    local start_at = ngx.now()
        local ip2loc = ip2location.new(ip2loc_db, ip2location.IP2LOCATION_FILE_IO)

    local proxy, iso = is_proxy(ip2loc, remote_addr)
        ip2loc:close()
    local diff = diff_ms(start_at)
    --local proxy = "1"
        if not proxy or proxy == "DCH" then
            -- seems to be not proxy or DCH(googlebot fall here)
            local googlebot, err = is_googlebot(remote_addr, resolver_ns, resolver_retrans, resolver_timeout)

        if not googlebot and proxy == "DCH" then
        redis_add_bl(red, remote_addr, bl_proxy_ttl)
        redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
        ngx.log(ngx.NOTICE, "BL: proxy: " .. proxy .. ", iso_code: " .. iso .. ", ttl: " .. bl_proxy_ttl .. ", client_ip: " .. remote_addr .. ", p.t: " .. diff)
        return ngx.exit(ngx.HTTP_NOT_FOUND)
        end

            if not googlebot then
                -- not googlebot
                local referer = has_referer()
                if not referer then
                    -- no referer 404 add to BL
                    redis_add_bl(red, remote_addr, bl_ttl)
                    redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
                    ngx.log(ngx.NOTICE, "BL: no referer, ttl: " .. bl_ttl .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)
                    return ngx.exit(ngx.HTTP_NOT_FOUND)
                end

                -- has referer add to WL
                redis_add_wl(red, remote_addr, wl_ttl)
                redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
                ngx.log(ngx.NOTICE, "WL: has referer, ttl: " .. wl_ttl .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)
                return
            end

            -- googlebot here add to WL
            redis_add_wl(red, remote_addr, wl_googlebot_ttl)
            redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
            ngx.log(ngx.NOTICE, "WL: googlebot detected, ttl: " .. wl_googlebot_ttl .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)
            return
        end

        -- seems to be proxy 404 add to BL
        redis_add_bl(red, remote_addr, bl_proxy_ttl)
        redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
        ngx.log(ngx.NOTICE, "BL: proxy: " .. proxy .. ", iso_code: " .. iso .. ", ttl: " .. bl_proxy_ttl .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)
        return ngx.exit(ngx.HTTP_NOT_FOUND)
    end

    -- exist in BL send 404
    redis_set_keepalive(red, redis_pool_size, redis_pool_timeout)
    ngx.log(ngx.NOTICE, "BL" .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)
    return ngx.exit(ngx.HTTP_NOT_FOUND)
end
ngx.log(ngx.NOTICE, "WL" .. ", client_ip: " .. remote_addr  .. ", p.t: " .. diff)