#!/opt/lnxall_app/bin/lua

-- Created by jiaqiang.ye@lnxall.com
-- Network 4G service for Debian-based gateways
-- 2023/12/01

-- Load external modules
local uci = require 'uci'
local bit32 = require 'bit32'
local posix = require 'posix'
local ulog = require 'ubuslog'
local invoker = require 'invoker'
local modem4g = require 'modem4g'

local g_modem = nil -- from modem4g.getmodem
local plat4gOps = {} -- Platform dependent 4G operations
-- global CONSTANT variables
local g_netuci = "/opt/lnxall_app/bin/netuci"
local g_recount = 0
local gfmt = string.format
local CHECK_INTERVAL = 180 -- check-interval for 4G network connection
local PING_ADDRS = { [1] = 'emsmqtt.lnxall.com', [2] = 'smc.lnxall.com',
        [3] = 'emsiot.lnxall.com', [4] = 'mqtt.lnxall.com' }

local g_metrics, g_metric_idx = { 100, 50 }, 1
local g_resolved = {} -- host to IPv4 address mapping
local g_backcfg = "/opt/lnxall_app/platspec/etc-config-network"

-- global varibales
local g_usbid = nil   -- USB ID of 4G network modem
local g_netdev = nil  -- name of USB network device
local g_4ginfo = {}   -- Array of supported USB modem
local g_dns = { [1] = '8.8.8.8', [2] = '114.114.114.114' }

g_4ginfo['2c7c:6005'] = { ['ttyindex'] = 2, ['script'] = 'ec200.gcom', -- EC200A
        ['bringup'] = 'AT+QCFG="usbnet",1\r\n', }
g_4ginfo['2c7c:6002'] = { ['ttyindex'] = 1, ['script'] = 'ec200.gcom', -- EC200N
        ['bringup'] = 'AT+QCFG="usbnet",1\r\n', }
g_4ginfo['2c7c:0904'] = { ['ttyindex'] = 0, ['script'] = 'ec800g.gcom', -- EC800G
        ['bringup'] = 'AT+QCFG="usbnet",1\r\n', }
g_4ginfo['2c7c:6026'] = { ['ttyindex'] = 2, ['script'] = 'ec200.gcom' } -- EC200T
g_4ginfo['2c7c:0901'] = { ['ttyindex'] = 0, ['script'] = 'ec200u.gcom' } -- EC200U
g_4ginfo['2c7c:0125'] = { ['ttyindex'] = 2, ['script'] = 'ec2x.gcom' } -- 全球通模组
g_4ginfo['1782:4e00'] = { ['ttyindex'] = 1, ['script'] = 'air720.gcom',
        ['bringup'] = "AT+SETUSB=2\r\n", } -- Air724UG
g_4ginfo['19d1:0001'] = { ['ttyindex'] = 0, ['script'] = 'air780.gcom'} --Air780.gcom
g_4ginfo['2cb7:0a0a'] = { ['ttyindex'] = 0, ['script'] = 'mc661.gcom'} -- MC661
g_4ginfo['2cb7:0a0b'] = { ['ttyindex'] = 0, ['script'] = 'mc661.gcom'} -- MC661
g_4ginfo['2cb7:0a0c'] = { ['ttyindex'] = 0, ['script'] = 'mc661.gcom'} -- MC661

local function netdev_exists(iface)
        if type(iface) ~= "string" or #iface == 0 then
                return false -- invalid method argument
        end
        local rval = invoker.invoke(invoker.NOSTDIO,
                "ip", "link", "show", "dev", iface)
        return rval == 0
end

local function nslookup(hostn)
        local pid, pfd = invoker.invoke(invoker.NOWAIT + invoker.NOSTDIO + invoker.OUTPUT, "nslookup", hostn)
        if not pid then return nil end

        local swait = invoker.uptimsec()
        local nwait, exited = swait, false
        swait = swait + 4000
        while nwait < swait do
                if invoker.waitpid(pid, true) then
                        exited = true
                        break
                end
                invoker.msleep(250)
                nwait = invoker.uptimsec()
        end

        if not exited then
                invoker.kill(pid, 9)
                invoker.waitpid(pid, false)
        end

        local output = invoker.readfd(pfd, 8192)
        if type(pfd) == "number" then
                invoker.closefd(pfd); pfd = nil
        end
        if type(output) ~= "string" then return nil end

        local iptab, ipn, ans = {}, 0, false
        for line in string.gmatch(output, "[^\r\n]+") do
                if not ans then
                        if string.find(line, "answer:", 1, true) then ans = true end
                else
                        local ipv4 = string.match(line, "Address:%s+([%d%.]+)")
                        if ipv4 and invoker.isipv4(ipv4) then
                                ipn = ipn + 1
                                iptab[ipn] = ipv4
                        end
                end
        end

        if ipn == 0 then return nil end
        return iptab
end

local function has_ipv4(ndev)
        local okay, output = invoker.invoke(invoker.OUTPUT, "ip", "addr", "show", "dev", ndev)
        if okay ~= 0 or type(output) ~= "string" then return false end

        local ipaddr = string.match(output, "inet%s+([%d%.]+)/")
        if not ipaddr then return false end
        return ipaddr
end

local function find_4g_netdev()
        local okay, output = invoker.invoke(invoker.OUTPUT, "ip", "link", "show")
        if okay ~= 0 or type(output) ~= "string" then
                return nil
        end
        for mdev in string.gmatch(output, "enp[^:\r\n]+:") do
                local nlen = string.len(mdev)
                if nlen >= 9 then return mdev:sub(1, nlen - 1) end
        end
        return nil
end

local function network_disabled(which)
        if type(which) ~= "string" then which = 'wwan' end
        local nuci = uci.cursor('/etc/config')
        local iface = nuci:get('network', which)
        if iface == nil then
                -- no configuration found. default to true
                nuci:close(); nuci = nil
                return false
        end

        local dev = nuci:get('network', which, 'device')
        local dis = nuci:get('network', which, 'disabled')
        nuci:close(); nuci = nil
        if dev == nil or dis == "1" or dis == 1 then return true end
        return false
end

local function fetch_ttyusb(idx)
        local jdx, kdx = 0, 0
        while jdx < 32 do
                local ndev = gfmt("/sys/bus/usb-serial/drivers/option1/ttyUSB%d", jdx)
                if posix.access(ndev) == 0 then
                        ndev = gfmt("/dev/ttyUSB%d", jdx)
                        local info = posix.stat(ndev)
                        if type(info) == "table" and info["type"] == "character device" then
                                if kdx >= idx then return ndev end
                                kdx = kdx + 1
                        end
                end
                jdx = jdx + 1
        end
        jdx = 0
        kdx = 0
        while jdx < 32 do
                local ndev = find_device_path (gfmt ("ttyACM%d", jdx))
                if not ndev then break end
                local vpid = get_vid_pid (ndev)
                if vpid == g_usbid then
                        if posix.access(ndev) == 0 then
                                ndev = gfmt("/dev/ttyACM%d", jdx)
                                local info = posix.stat(ndev)
                                if type(info) == "table" and info["type"] == "character device" then
                                        if kdx >= idx then return ndev end
                                        kdx = kdx + 1
                                end
                        end
                end
                jdx = jdx + 1
        end
        return nil
end

local function update_sim_iccid(usbdev)
        local outfile = modem4g.ICCID_FILE
        if posix.access(outfile) == 0 then return true end
        if not usbdev then
                if not g_usbid then return false end
                local i4g = g_4ginfo[g_usbid]
                usbdev = fetch_ttyusb(i4g.ttyindex)
        end
        if posix.access(usbdev) ~= 0 then return false end

        invoker.invoke(invoker.NOSTDIO, "stty", "-F", usbdev, "raw", "cs8", "-echo")
        local usbfd = posix.open(usbdev, posix.O_RDWR + posix.O_NONBLOCK + posix.O_NOCTTY)
        if type(usbfd) ~= "number" or usbfd < 0 then return false end
        while true do
                local ldat = posix.read(usbfd, 1024)
                if type(ldat) ~= "string" or #ldat == 0 then break end
        end

        local restab = {}
        posix.write(usbfd, "AT\r\n"); invoker.msleep(400)
        posix.write(usbfd, "AT+QCFG=\"nat\"\r\n"); invoker.msleep(400)
        posix.write(usbfd, "AT+ICCID\r\n"); invoker.msleep(400)
        posix.write(usbfd, "AT+QICCID\r\n"); invoker.msleep(400)
        posix.write(usbfd, "AT+CCID\r\n"); invoker.msleep(400)
        while true do
                local ldat = posix.read(usbfd, 1024)
                if type(ldat) == "string" and #ldat > 0 then
                        restab[#restab + 1] = ldat
                else
                        break
                end
        end
        local output = #restab > 0 and table.concat(restab) or nil
        if type(output) ~= "string" then
                posix.close(usbfd)
                return false
        end
        local iccid = string.match(output, "ICCID:%s+([%d%a]+)")
        if iccid == nil then iccid = string.match(output, "CCID:%s+([%d%a]+)") end
        if iccid then
                local filp = io.open(outfile, "wb")
                if filp then
                        filp:write(gfmt("ICCID: %s\n", iccid))
                        filp:close(); filp = nil
                end
        end

        -- check for nat configuration
        if string.find(output, 'QCFG: "nat"', 1, true) and
                not string.find(output, 'QCFG: "nat",1', 1, true) then
                posix.write(usbfd, "AT+QCFG=\"nat\",1\r\n"); invoker.msleep(300)
                posix.write(usbfd, "AT+CFUN=1,1\r\n"); invoker.msleep(1500)
        end

        posix.close(usbfd)
        return iccid
end

local function get_vid_pid(device_path) -- get the Vendor and Product ID from the real device path
    local vid, pid
    local path = device_path
    repeat
        local uevent_file = io.open(path .. "/uevent")  -- make sure the V and P id is saved in uevent, of course uedvadm also will get the information from uevent file
        if uevent_file then
            for line in uevent_file:lines() do
                local key, value = line:match("(%a+)=(.+)")
                if key == "PRODUCT" then
                    vid, pid = value:match("(%x+)%/(%x+)%/(%x+)")
                    if vid and pid then
                        vid = string.format("%04x", tonumber(vid, 16))
                        pid = string.format("%04x", tonumber(pid, 16))
                        return vid .. ":" .. pid
                    end
                end
            end
            uevent_file:close()
        end
        path = path:match("(.+)/[^/]+") -- if not found, next step is to check the parent directory.
    until not path or path == ""
    return nil, nil
end

local function find_device_path(device_name)
    local device_path
    -- unfortunately, this method is strong depends on kernel version. As far as I know it can't work on 2.4 kernel.
    for class in io.popen("ls " .. "/sys/class/"):lines() do
        local path = "/sys/class/" .. class .. "/" .. device_name

        if io.open(path) then
            local link = io.popen("readlink -f " .. path):read("*line") --  get the link path
            if link then
                while link:match("%.%./") do
                    link = link:gsub("/[^/]+/%.%./", "/") -- get the real path
                end
                device_path = link
                break
            end
        end
    end
    return device_path
end

local function check_resolv()
        local has_sr = ""
        if posix.access('/lib/systemd/systemd-resolved') == 0 then
                local conts, restart = {}, false
                local syscfg = '/etc/systemd/resolved.conf'

                conts[#conts + 1] = "# Generated by deb4gnet.lua\n[Resolve]\n"
                conts[#conts + 1] = string.format("DNS=%s %s\n", g_dns[1], g_dns[2])
                conts[#conts + 1] = "DNSSEC=no\n"
                conts[#conts + 1] = "Cache=yes\n"
                conts[#conts + 1] = "LLMNR=false\n"
                conts = table.concat(conts)

                local sfile, sdat = io.open(syscfg, "rb"), nil
                if sfile then
                        sdat = sfile:read("*a")
                        sfile:close(); sfile = nil
                end

                if sdat ~= conts then
                        restart = true
                        sfile = io.open(syscfg, "wb")
                        if sfile then
                                sfile:write(conts)
                                sfile:close(); sfile = nil
                        end
                end

                if not restart then
                        local _, output = invoker.invoke(invoker.OUTPUT, "systemctl", "status", "systemd-resolved")
                        if type(output) ~= "string" then output = "" end
                        if not string.find(output, "Active: active (running)", 1, true) then
                                restart = true
                        end
                end

                if restart then
                        io.stdout:write("Restarting systemd-resolved service...\n")
                        io.stdout:flush()
                        invoker.invoke(0, "systemctl", "enable", "systemd-resolved")
                        invoker.invoke(0, "systemctl", "restart", "systemd-resolved")
                end
                has_sr = "nameserver 127.0.0.53\n"
        end

        local content = gfmt("# Generated by deb4gnet.lua\n%snameserver %s\nnameserver %s\noptions timeout:12 attempts:3\n",
                has_sr, g_dns[1], g_dns[2])
        local rfile = "/etc/resolv.conf"
        local resolv, cont = io.open(rfile, "rb"), nil
        if resolv then
                cont = resolv:read('*a')
                resolv:close(); resolv = nil
        end
        if cont == content then return true end
        -- if cont then io.stdout:write("Warning: old DNS settings:\n" .. cont) end
        ulog.log(ulog.LOG_INFO, "Network4g: updating resolv.conf...")
        resolv = io.open(rfile, "wb")
        if resolv then
                resolv:write(content)
                resolv:close(); resolv = nil
                posix.sync()
                return true
        end
        return false
end

local function systemd_restart(initp, name)
        if posix.access(initp) == 0 then
                return invoker.invoke(invoker.NOSTDIO, "systemctl", "restart", name) == 0
        end
        return false
end

local function wwan_cannot_up()
        local file = io.open("/tmp/4g_modem_tty","r")
        local usbdev
        if file then
                local tty_usb = file:read("*all")
                usbdev = string.sub(tty_usb, 1,12)
        end
        file:close();file = nil
        local usbfd = posix.open(usbdev, posix.O_RDWR + posix.O_NONBLOCK + posix.O_NOCTTY)
        if type(usbfd) ~= "number" or usbfd < 0 then
                io.stderr:write(gfmt("failed to open %s for restart NetworkManager\n",usbdev))
                io.stderr:flush()
                return false
        end

    posix.write(usbfd, "AT+CEREG?\r\n"); invoker.msleep(400)
    local ldat = posix.read(usbfd,1024)
    if type(ldat) ~= "string" or #ldat <= 0 or not string.match(ldat,"0,1") then return false end

    posix.write(usbfd, "AT+CPIN?\r\n"); invoker.msleep(400)
    ldat = posix.read(usbfd,1024)
    if type(ldat) ~= "string" or #ldat <= 0 or not string.match(ldat,"READY") then return false end
        posix.close(usbfd)

    local result =  os.execute("nmcli con up wwan")
        if result == 0 then return false end
    return true
end

local function net4g_reload(iface, metric)
        local okay, output = invoker.invoke(invoker.OUTPUT,
                "nmcli", "-m", "tabular", "-t", "con", "show")
        if okay ~= 0 or type(output) ~= "string" then output = "" end

        local ndels = 0
        for line in string.gmatch(output, "[^\r\n]+") do
                local con = string.match(line, "^([^:]+)")
                if con and con ~= 'wwan' then
                        local cinfo = nil
                        okay, cinfo = invoker.invoke(invoker.OUTPUT + 0x70000,
                                "nmcli", "con", "show", con)
                        if okay == 0 and type(cinfo) == "string" and string.find(cinfo, iface, 1, true) then
                                ndels = ndels + 1
                                invoker.invoke(invoker.NOSTDIO, "nmcli", "con", "down", con)
                                invoker.invoke(invoker.NOSTDIO, "nmcli", "con", "delete", con)
                                io.stderr:write(gfmt("Delete NetworkManager connection: %s\n", con))
                                io.stderr:flush()
                        end
                end
        end

        local wuci, doc = uci.cursor('/etc/config'), false
        local ndev = wuci:get('network', 'wwan', 'device')
        if metric then
                metric = tostring(metric)
                local oldm = wuci:get('network', 'wwan', 'metric')
                if metric ~= oldm then
                        if type(oldm) ~= "string" then oldm = "nil" end
                        io.stdout:write(gfmt("Update wwan metric from %s to %s\n",
                                oldm, metric))
                        io.stdout:flush()

                        doc = true
                        wuci:delete('network', 'wwan', 'metric')
                        wuci:delete('network', 'wwan', 'metric')
                        wuci:set('network', 'wwan', 'metric', metric)
                end
        end
        if ndev ~= iface then
                if ndev == nil then
                        -- recheck whether wwan section exists
                        ndev = wuci:get('network', 'wwan')
                end
                if ndev == nil then
                        -- configuration section might be missing, force copy of network-configuration
                        local r = invoker.invoke(invoker.NOSTDIO, "cp", "-v", "-f", g_backcfg, "/etc/config/network")
                        if type(r) ~= "number" then r = 10 end
                        io.stderr:write(gfmt("Error, restoring network configuration from '%s': %d\n", g_backcfg, r))
                        io.stderr:flush()
                else
                        doc = true
                        wuci:delete('network', 'wwan', 'device')
                        wuci:delete('network', 'wwan', 'device')
                        wuci:set('network', 'wwan', 'device', iface)
                end
        end
        if doc then wuci:commit('network') end
        invoker.invoke(invoker.NOSTDIO, "lua", g_netuci)
        invoker.msleep(5000)
        if wwan_cannot_up() then
                io.stdout:write("restart NetworkManager")
                io.stdout:flush()
                invoker.invoke(invoker.NOSTDIO, "systemctl", "restart", "NetworkManager")
                invoker.msleep(3000)
                systemd_restart("/etc/systemd/system/multi-user.target.wants/bdhcpd.service", "bdhcpd")
                systemd_restart("/etc/systemd/system/multi-user.target.wants/lnxhostapd.service", "lnxhostapd")
        end
        return true
end

local function network_connect(iface)
        -- kill dhclient application first
        local i4g = g_4ginfo[g_usbid]

        local dftdev = gfmt('/dev/ttyUSB%d', i4g.ttyindex)
        update_sim_iccid(dftdev)
        -- check for /dev/ttyUSBx device
        local devn = fetch_ttyusb(i4g.ttyindex) or dftdev
        local devi = posix.stat(devn)
        if type(devi) ~= "table" or devi["type"] ~= "character device" then
                io.stderr:write(gfmt("Error, ttyUSB device not found: %s\n", devn))
                io.stderr:flush()
                return false
        end

        -- miscellaneous operations for 4G modem
        if g_modem then g_modem.update(g_modem, devn, false) end

        if i4g.script then -- we need to execute comgt script
                invoker.invoke(invoker.NOSTDIO, "ip", "addr", "flush", iface)
                -- invoke comgt to establish network connection
                local okay = invoker.invoke(invoker.NOSTDIO, 'comgt', '-d', devn, '-s',
                        gfmt('/opt/lnxall_app/etc/gcom/%s', i4g.script))
                if okay ~= 0 then
                        io.stderr:write(gfmt("Error, comgt has returned %d\n",
                                type(okay) == "number" and okay or 1))
                        io.stderr:flush()
                end
        elseif i4g.bringup then
                local tfd = posix.open(devn, posix.O_RDWR + posix.O_NONBLOCK + posix.O_NOCTTY)
                if type(tfd) == "number" and tfd >= 0 then
                        posix.write(tfd, i4g['bringup'])
                        posix.close(tfd)
                end
        end

        local count = 0
        invoker.msleep(5000) -- delay 3 seconds before continue
        -- wait for `iface network to show up
        while true do
                count = count + 1
                if count >= 10 then break end
                if netdev_exists(iface) then break end
                invoker.msleep(1000)
        end

        invoker.msleep(1000) -- again, delay one second
        -- check again for the existence of `iface
        if not netdev_exists(iface) then
                io.stderr:write(gfmt("Error, network device not found: %s\n", iface))
                io.stderr:flush()
                return false
        end

        local midx = nil
        if invoker.uptime() >= 90 then
                midx = g_metric_idx
                midx = midx + 1
                if midx > 3 then midx = 1 end
                g_metric_idx = midx
                midx = g_metrics[midx]
        end

        net4g_reload(iface, midx)
        return true
end

-- initialize working environment
local function n4g_init(initcnt)
        -- Enumerate output from `lsusb,
        -- and determine the 4G modem USB ID
        local okay, outbuf = invoker.invoke(invoker.OUTPUT, "lsusb")
        if okay ~= 0 or type(outbuf) ~= "string" or string.len(outbuf) == 0 then
                io.stderr:write("Error, failed to invoke `lsusb!\n")
                io.stderr:flush()
                return false
        end

        -- process line by line
        for output in string.gmatch(outbuf, "([^\r\n]+)") do
                local usbid = string.match(output, "(%x%x%x%x:%x%x%x%x)")
                if usbid and g_4ginfo[usbid] then
                        g_usbid = usbid
                        break
                end
        end

        if not g_usbid then
                if (initcnt % 32) == 0 then
                        io.stderr:write("Warning, no 4G network modem found!\n")
                        io.stderr:flush()
                end
                return false
        end

        -- write USBID to `/sys/bus/usb-serial/drivers/option1/new_id
        local opt = string.gsub(g_usbid, ":", " ") .. " ff\n"
        local new_id = "/sys/bus/usb-serial/drivers/option1/new_id"
        local oldpt = invoker.readfile(new_id)
        if opt ~= oldpt then
                local opth = io.open(new_id, "wb")
                if opth then opth:write(opt); opth:close(); opth = nil end
                invoker.waitsec(4)
        end
        opt, new_id, oldpt = nil, nil, nil -- remove local variables

        local nowtim = invoker.uptime()
        while nowtim < 65 do -- do not check 4G network in such a haste
                check_resolv() -- update resolv.conf before wait
                invoker.waitsec(65 - nowtim)
                nowtim = invoker.uptime()
        end
        check_resolv()

        local ttydev = fetch_ttyusb(g_4ginfo[g_usbid]["ttyindex"])
        if ttydev then
                -- write /tmp/4g_modem_tty with the control path of ttyUSB device
                local fhdl = io.open("/tmp/4g_modem_tty", "wb")
                if fhdl then
                        fhdl:write(gfmt("%s\n", ttydev))
                        fhdl:close(); fhdl = nil
                end
        end

        -- check network device
        g_netdev = plat4gOps.netdev()
        if type(g_netdev) ~= "string" or not netdev_exists(g_netdev) then
                g_netdev = nil
                local info4g = g_4ginfo[g_usbid]
                if ttydev and info4g['bringup'] then
                        local tfd = posix.open(ttydev, posix.O_RDWR + posix.O_NONBLOCK + posix.O_NOCTTY)
                        if type(tfd) == "number" and tfd >= 0 then
                                posix.write(tfd, info4g['bringup'])
                                posix.close(tfd)
                        end
                end
                g_modem = modem4g.getmodem(g_usbid)
                if g_modem then g_modem.init(g_modem, ttydev) end
                if (initcnt % 0x5) == 0 then
                        plat4gOps.poweron(false)
                elseif (initcnt % 0x5) == 1 then
                        plat4gOps.poweron(true)
                elseif (initcnt % 0x5) == 2 then
                        network_connect('wwan0')
                end
                io.stderr:write("Error, cannot determine 4G network device.\n")
                io.stderr:flush()
                return false
        end
        g_modem = modem4g.getmodem(g_usbid)
        if g_modem then g_modem.init(g_modem, ttydev) end

        local fc = '/etc/force_connect.txt'
        if invoker.uptime() < 240 and posix.access(fc) ~= 0 then
                network_connect(g_netdev)
                local filp = io.open(fc, "wb")
                if filp then
                        filp:write(gfmt("%s: Forcing network reconnect.\n", os.date()))
                        filp:close(); filp = nil
                end
                invoker.waitsec(15)
        elseif not has_ipv4(g_netdev) then
                invoker.invoke(invoker.NOSTDIO, "nmcli", "con", "del", "wwan")
                invoker.invoke(invoker.NOSTDIO, "lua", g_netuci)
        end
        return true
end

local function network_okay(iface)
        local cmds = { "ping", "-c3", "-w12" }
        local cmdidx = 0x1 + #cmds
        if type(iface) == "string" then
                cmds[cmdidx] = "-I"
                cmds[cmdidx + 0x1] = iface
                cmdidx = cmdidx + 0x2
        end
        for _, hname in pairs(PING_ADDRS) do
                local hipv4 = nil
                if invoker.isipv4(hname) then
                        hipv4 = hname
                else
                        hipv4 = g_resolved[hname]
                        if not hipv4 then
                                local ips = nslookup(hname)
                                if ips then
                                        hipv4 = ips[1]
                                        io.stdout:write(gfmt("DNS resolved: %s => %s\n", hname, hipv4))
                                        io.stdout:flush()
                                        g_resolved[hname] = hipv4
                                end
                        end
                end
                if hipv4 then
                        cmds[cmdidx] = hipv4
                        local okay, output = invoker.invoke(invoker.OUTPUT + invoker.NOSTDIO, cmds)
                        if type(output) == "string" and
                                string.find(output, 'packet loss', 1, true) and
                                not string.find(output, '100% packet loss', 1, true) then
                                return hname
                        end
                        if okay == 0 then return hname end
                        if invoker.tcpcheck(hipv4, 80, 1500) then return hname end
                        if invoker.tcpcheck(hipv4, 3883, 1500) then return hname end
                end
        end
        return false
end

local function reset_4g_modem(sdely)
        local resettag = '/tmp/.4g_modem_reset'
        if posix.access(resettag) == 0 then return false end

        local i4g = g_4ginfo[g_usbid]
        local dftdev = gfmt('/dev/ttyUSB%d', i4g.ttyindex)
        local devn = fetch_ttyusb(i4g.ttyindex) or dftdev
        local devi = posix.stat(devn)
        if type(devi) ~= "table" or devi["type"] ~= "character device" then
                io.stderr:write(gfmt("Error, ttyUSB device not found: %s\n", devn))
                io.stderr:flush()
                return false
        end

        local usbfd = posix.open(devn, bit32.bor(posix.O_WRONLY, posix.O_TRUNC,
                posix.O_NONBLOCK, posix.O_NOCTTY))
        if type(usbfd) ~= "number" or usbfd < 0 then
                io.stderr:write(gfmt("Error, failed to open %s for reset\n", devn))
                io.stderr:flush()
                return false
        end

        posix.write(usbfd, "AT+RESET\r\n"); invoker.msleep(300); posix.close(usbfd)
        local tagf = io.open(resettag, "wb")
        if tagf then
                tagf:write(gfmt("%s: 4G modem reset via %s\n", os.date(), devn))
                tagf:close(); tagf = nil
        end
        invoker.waitsec(sdelay)
        return true
end

local function watch_resolv(delay)
        local flags = bit32.bor(invoker.IN_CREATE, invoker.IN_DELETE_SELF,
                invoker.IN_MODIFY, invoker.IN_CLOSE_WRITE)
        local rfile = '/etc/resolv.conf'
        rfile = invoker.realpath(rfile)
        if not posix.access(rfile) then check_resolv() end

        local changed, errmsg = invoker.watchfile(flags, delay * 1000, nil, rfile)
        if changed == nil then
                if type(errmsg) ~= "string" then errmsg = "unknown watchfile error" end
                io.stderr:write(errmsg); io.stderr:write("\n"); io.stderr:flush()
                invoker.waitsec(delay)
                return false
        end
        if changed and changed > 0 then
                invoker.msleep(1500) -- delay 1.5 second to avoid modifying by too many processes
                check_resolv()
        end
        return true
end

local function isat_time(hour)
        local nowt = os.date("*t")
        return nowt["hour"] == hour
end

local function mainloop()
        local dcnt = 0 -- disconnect count
        local nowtim = invoker.uptime()
        local nextim = nowtim + CHECK_INTERVAL
        update_sim_iccid()
        while true do
                check_resolv() -- check resolv.conf before continue
                local phost = network_okay()
                if phost then
                        io.stdout:write(gfmt("%s: Network ping okay: %s\n", os.date(), phost))
                        io.stdout:flush()
                        if dcnt > 0 then dcnt = 0 end
                        if posix.access(modem4g.ICCID_FILE) ~= 0 then update_sim_iccid() end
                        if g_modem then g_modem.update(g_modem, nil, true) end
                elseif not network_disabled() then
                        if isat_time(23) and dcnt >= 4 and posix.access(modem4g.ICCID_FILE) == 0 then -- it is 23 at midnight, safe to reboot
                                ulog.log(ulog.LOG_ERR, gfmt("reboot due to 4G network failure: %d.", dcnt))
                                invoker.invoke(invoker.NOSTDIO, "reboot"); invoker.waitsec(5)
                        end

                        if not reset_4g_modem(10) and bit32.band(dcnt, 0x1) == 0x1 then
                                plat4gOps.poweron(false); invoker.waitsec(3)
                                plat4gOps.poweron(true); invoker.waitsec(12)
                        end
                        dcnt = dcnt + 1 -- increment disconnected

                        g_netdev = plat4gOps.netdev()
                        if not netdev_exists(g_netdev) then
                                ulog.log(ulog.LOG_ERR, gfmt("Error, no 4G net device found: %d", dcnt))
                        else
                                local midx = math.floor(dcnt % 2) + 1
                                ulog.log(ulog.LOG_ERR, gfmt("reconnect 4G network, count: %d", dcnt))
                                network_connect(g_netdev)
                        end
                end

                check_resolv() -- check resolv.conf again
                nowtim = invoker.uptime()
                -- delay until next checking time
                while nowtim < nextim do
                        watch_resolv(nextim - nowtim)
                        nowtim = invoker.uptime()
                end
                -- increment next checking time
                nextim = nextim + CHECK_INTERVAL
                if nextim <= nowtim then nextim = nextim + CHECK_INTERVAL end
        end
end

local function check_platform()
        local bname = invoker.readfile('/tmp/sysinfo/board_name', invoker.TRIMEND)
        if bname == 'WLOSANY_X86_V3' then
                invoker.invoke(invoker.NOSTDIO, "modprobe", "option")
                plat4gOps['init'] = function () return true end
                plat4gOps['poweron'] = function (ison) return true end
                plat4gOps['netdev'] = function ()
                        local ndev = "enp0s20f0u7"
                        -- if netdev_exists(ndev) then return ndev end
                        local okay, output = invoker.invoke(invoker.OUTPUT, "ip", "link", "show")
                        if okay == 0 and type(output) == "string" then
                                for line in string.gmatch(output, "[^\r\n]+") do
                                        local mdev = string.match(line, "^%d+: ([^:]+):")
                                        if mdev and #mdev >= 8 and mdev:sub(1, 3) == "enp" then
                                                ndev = mdev
                                                break
                                        end
                                end
                        end
                        return ndev
                end
                return true
        end
        if bname == 'WLOSANY_BAU-B30-003' or bname == 'WLOSANY_WooLink2004' then
                plat4gOps['init'] = function ()
                        -- TODO: add 4G modem poweron operation here
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        -- TODO: add 4G modem power on/off operation here
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_RK3568_FORLINX' then
                plat4gOps['init'] = function ()
                        local gpfx = "/sys/class/gpio/gpio101"
                        local direct = gfmt("%s/direction", gpfx)
                        local output = invoker.readfile(direct, invoker.TRIMEND)
                        if output ~= "out" then
                                invoker.invoke(0, "/bin/sh", "-c", "echo 101 > /sys/class/gpio/export")
                                invoker.invoke(0, "/bin/sh", "-c", gfmt("echo out > %s", direct))
                        end
                        -- power on 4G module
                        invoker.invoke(0, "/bin/sh", "-c", gfmt("echo 1 > %s/value", gpfx))
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        local cmd = gfmt("echo %s > /sys/class/gpio/gpio101value", ison and "1" or "0")
                        invoker.invoke(0, "/bin/sh", "-c", cmd)
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_RK3568' or bname == 'WLOSANY_RK3568_XDDL' then
                plat4gOps['init'] = function ()
                        local gpfx = "/sys/class/gpio/gpio74"
                        local direct = gfmt("%s/direction", gpfx)
                        local output = invoker.readfile(direct, invoker.TRIMEND)
                        if output ~= "out" then
                                invoker.invoke(0, "/bin/sh", "-c", "echo 74 > /sys/class/gpio/export")
                                invoker.invoke(0, "/bin/sh", "-c", gfmt("echo out > %s", direct))
                        end
                        -- power on 4G module
                        invoker.invoke(0, "/bin/sh", "-c", gfmt("echo 1 > %s/value", gpfx))
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        local cmd = gfmt("echo %s > /sys/class/gpio/gpio74/value", ison and "1" or "0")
                        invoker.invoke(0, "/bin/sh", "-c", cmd)
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_VM1220T' then
                plat4gOps['init'] = function ()
                        local gpfx = "/sys/class/gpio/gpio342"
                        local direct = gfmt("%s/direction", gpfx)
                        local output = invoker.readfile(direct, invoker.TRIMEND)
                        if output ~= "out" then
                                invoker.invoke(0, "/bin/sh", "-c", "echo 342 > /sys/class/gpio/export")
                                invoker.invoke(0, "/bin/sh", "-c", gfmt("echo out > %s", direct))
                        end
                        -- power on 4G module
                        invoker.invoke(0, "/bin/sh", "-c", gfmt("echo 0 > %s/value", gpfx))
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        local cmd = gfmt("echo %s > /sys/class/gpio/gpio342/value", ison and "0" or "1")
                        invoker.invoke(0, "/bin/sh", "-c", cmd)
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_RK3588' then
                plat4gOps['init'] = function ()
                        local gpfx = "/sys/class/gpio/gpio120"
                        local direct = gfmt("%s/direction", gpfx)
                        local output = invoker.readfile(direct, invoker.TRIMEND)
                        if output ~= "out" then
                                invoker.invoke(0, "/bin/sh", "-c", "echo 120 > /sys/class/gpio/export")
                                invoker.invoke(0, "/bin/sh", "-c", gfmt("echo out > %s", direct))
                        end
                        -- power on 4G module
                        invoker.invoke(0, "/bin/sh", "-c", gfmt("echo 1 > %s/value", gpfx))
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        local cmd = gfmt("echo %s > /sys/class/gpio/gpio120/value", ison and "1" or "0")
                        invoker.invoke(0, "/bin/sh", "-c", cmd)
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_LC100' then
                plat4gOps['init'] = function ()
                        local gpfx = "/sys/class/gpio/gpio132"
                        local direct = gfmt("%s/direction", gpfx)
                        local output = invoker.readfile(direct, invoker.TRIMEND)
                        if output ~= "out" then
                                invoker.invoke(0, "/bin/sh", "-c", "echo 132 > /sys/class/gpio/export")
                                invoker.invoke(0, "/bin/sh", "-c", gfmt("echo out > %s", direct))
                        end
                        -- power on 4G module
                        invoker.invoke(0, "/bin/sh", "-c", gfmt("echo 1 > %s/value", gpfx))
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        local cmd = gfmt("echo %s > /sys/class/gpio/gpio132/value", ison and "1" or "0")
                        invoker.invoke(0, "/bin/sh", "-c", cmd)
                        return true
                end
                plat4gOps['netdev'] = function () return 'usb0' end
                return true
        end

        if bname == 'WLOSANY_EM1000' then
                plat4gOps['init'] = function ()
                        invoker.invoke(0, 'gpioset', '0', '25=0') -- power on 4G module
                        return true
                end
                plat4gOps['poweron'] = function (ison)
                        invoker.invoke(0, 'gpioset', '0', gfmt("25=%s", ison and "0" or "1"))
                        return true
                end
                plat4gOps['netdev'] = function ()
                        if netdev_exists('modem0') then return 'modem0' end
                        return netdev_exists('eth0') and 'eth0' or 'usb0'
                end
                return true
        end

        io.stderr:write("Error, unsupported board_name for DEBIAN 4GNET.\n")
        io.stderr:flush()
        return false
end

local function preinit(pname, dns1, dns2)
        posix.unlink(modem4g.ICCID_FILE)
        if posix.access("/usr/lib/systemd/system/ModemManager.service") == 0 then
                invoker.invoke(invoker.NOSTDIO, "systemctl", "stop", "ModemManager")
                invoker.invoke(invoker.NOSTDIO, "systemctl", "disable", "ModemManager")
        end
        -- setup PATH environment variable
        posix.setenv('PATH', '/opt/lnxall_app/bin:/usr/bin:/usr/sbin:/bin:/sbin', true)
        posix.chdir("/")
        ulog.reinit(pname)
        invoker.setname(pname)

        if type(dns1) == "string" and invoker.isipv4(dns1) then g_dns[1] = dns1 end
        if type(dns2) == "string" and invoker.isipv4(dns2) then g_dns[2] = dns2 end

        -- wait until we have correct board_name
        while not check_platform() do invoker.msleep(5000) end

        check_resolv()
        local count = 0
        plat4gOps.init() -- initialize 4G module
        while network_disabled() do
                watch_resolv(30)
                if (invoker.uptime() - count) >= 30 then
                        check_resolv()
                        count = invoker.uptime()
                end
        end

        count = 0 -- reset to zero
        while not n4g_init(count) do
                watch_resolv(15)
                count = count + 1
        end
        return true
end

preinit('DEBIAN_4GNET', arg[1], arg[2])
ulog.log(ulog.LOG_INFO, "4G modem found, entering loop...")
mainloop() -- application hangs in the function
os.exit(2)