package xnet

import (
	"errors"
	"net/netip"
	"sync"
	"time"

	"github.com/soypat/lneto"
	"github.com/soypat/lneto/arp"
	"github.com/soypat/lneto/dhcpv4"
	"github.com/soypat/lneto/dns"
	"github.com/soypat/lneto/ethernet"
	"github.com/soypat/lneto/internet"
	"github.com/soypat/lneto/ntp"
	"github.com/soypat/lneto/tcp"
)

const (
	minTCPBuffer = 256
)

type StackAsync struct {
	mu       sync.Mutex
	hostname string
	clientID string
	link     internet.StackEthernet
	ip       internet.StackIP
	arp      arp.Handler
	udps     internet.StackPorts
	tcps     internet.StackPorts

	dhcpUDP     internet.StackUDPPort
	dhcp        dhcpv4.Client
	dhcpResults DHCPResults

	dnsUDP  internet.StackUDPPort
	dns     dns.Client
	ednsopt dns.Resource
	lookup  dns.Message
	dnssv   netip.Addr

	ntpUDP internet.StackUDPPort
	ntp    ntp.Client

	sysprec int8 // NTP system precision.

	prng uint32

	totalsent uint64
	totalrecv uint64
}

type StackConfig struct {
	StaticAddress   netip.Addr
	DNSServer       netip.Addr
	NTPServer       netip.Addr
	Hostname        string
	MaxTCPConns     int
	RandSeed        int64
	HardwareAddress [6]byte
	MTU             uint16
}

func (s *StackAsync) Hostname() string {
	return s.hostname
}

func (s *StackAsync) Demux(carrierData []byte, etherOff int) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.totalrecv += uint64(len(carrierData) - etherOff)
	return s.link.Demux(carrierData, etherOff)
}

func (s *StackAsync) Encapsulate(carrierData []byte, etherOff int) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	n, err := s.link.Encapsulate(carrierData, etherOff)
	s.totalsent += uint64(n)
	return n, err
}

func (s *StackAsync) MTU() int {
	return s.link.MTU()
}

func (s *StackAsync) Reset(cfg StackConfig) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	mac := cfg.HardwareAddress
	mtu := cfg.MTU
	addr := cfg.StaticAddress
	s.prng = uint32(cfg.RandSeed)
	if s.prng == 0 {
		return errors.New("zero random seed")
	}
	s.hostname = cfg.Hostname
	if !addr.IsValid() {
		addr = netip.AddrFrom4([4]byte{}) // If static not set DHCP will be performed and address will be zero.
	} else if addr.Is6() {
		return errors.New("IPv6 unsupported as of yet")
	}
	const linkNodes = 2 // ARP and IP nodes
	err := s.link.Reset6(mac, ethernet.BroadcastAddr(), int(mtu), linkNodes)
	if err != nil {
		return err
	}
	const ipNodes = 2 // UDP, TCP ports.
	err = s.ip.Reset(addr, ipNodes)
	if err != nil {
		return err
	}
	err = s.resetARP()
	if err != nil {
		return err
	}
	const udpMaintenanceConns = 3 // DHCP, DNS, NTP.
	err = s.udps.ResetUDP(udpMaintenanceConns)
	if err != nil {
		return err
	}

	// Enable TCP if connections present.
	if cfg.MaxTCPConns > 0 {
		err = s.tcps.ResetTCP(cfg.MaxTCPConns)
		if err != nil {
			return err
		}
		err = s.ip.Register(&s.tcps)
		if err != nil {
			return err
		}
	}

	// Now setup stacks.
	err = s.link.Register(&s.ip) // IPv4 | IPv6
	if err != nil {
		return err
	}
	err = s.link.Register(&s.arp) // ARP.
	if err != nil {
		return err
	}
	err = s.ip.Register(&s.udps)
	if err != nil {
		return err
	}
	var timebuf [32]time.Time
	s.sysprec = ntp.CalculateSystemPrecision(time.Now, timebuf[:])
	if s.clientID == "" {
		s.clientID = "lneto-" + s.hostname
	}
	s.totalrecv = 0
	s.totalsent = 0
	return nil
}

var errInvalidIPAddr = errors.New("invaldi IP address")

func (s *StackAsync) resetARP() error {
	mac := s.link.HardwareAddr6()
	addr := s.ip.Addr()
	if !addr.IsValid() {
		return errInvalidIPAddr
	}
	proto := ethernet.TypeIPv4
	if addr.Is6() {
		proto = ethernet.TypeIPv6
	}
	return s.arp.Reset(arp.HandlerConfig{
		HardwareAddr: mac[:],
		ProtocolAddr: addr.AsSlice(),
		MaxQueries:   3,
		MaxPending:   3,
		HardwareType: 1,
		ProtocolType: proto,
	})
}

// Prand32 generates a pseudo random 32-bit unsigned integer from the internal state and advances the seed.
func (s *StackAsync) Prand32() uint32 {
	/* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */
	seed := s.prng
	seed ^= seed << 13
	seed ^= seed >> 17
	seed ^= seed << 5
	s.prng = seed
	return seed
}

func (s *StackAsync) SetIPAddr(addr netip.Addr) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	err := s.ip.SetAddr(addr)
	if err != nil {
		return err
	}
	return s.resetARP()
}

func (s *StackAsync) Addr() netip.Addr {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.ip.Addr()
}

func (s *StackAsync) SetHardwareAddress(hw [6]byte) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.link.SetHardwareAddr6(hw)
	return s.resetARP()
}

func (s *StackAsync) HardwareAddress() (hw [6]byte) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.link.HardwareAddr6()
}

func (s *StackAsync) SetGateway6(gwhw [6]byte) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.link.SetGateway6(gwhw)
}

func (s *StackAsync) Gateway6() [6]byte {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.link.Gateway6()
}

func (s *StackAsync) DialTCP(conn *tcp.Conn, localPort uint16, addrp netip.AddrPort) (err error) {
	err = conn.OpenActive(localPort, addrp, tcp.Value(s.Prand32()))
	if err != nil {
		return err
	}
	err = s.tcps.Register(conn)
	if err != nil {
		conn.Abort()
		return err
	}
	return nil
}

func (s *StackAsync) ListenTCP(conn *tcp.Conn, localPort uint16) (err error) {
	err = conn.OpenListen(localPort, tcp.Value(s.Prand32()))
	if err != nil {
		return err
	}
	err = s.tcps.Register(conn)
	if err != nil {
		conn.Abort()
		return err
	}
	return nil
}

var errNoDNSServer = errors.New("no DNS server- did DHCP complete? You can set a predetermined DNS server in Stack configuration")

func (s *StackAsync) StartLookupIP(host string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !s.dnssv.IsValid() {
		return errNoDNSServer
	}
	name, err := dns.NewName(host)
	if err != nil {
		return err
	}

	s.ednsopt.SetEDNS0(uint16(s.link.MTU())-100, 0, 0, nil)
	rand := s.Prand32()
	err = s.dns.StartResolve(uint16(rand>>1)+1024, uint16(rand), dns.ResolveConfig{
		Questions: []dns.Question{
			{
				Name:  name,
				Type:  dns.TypeA,
				Class: dns.ClassINET,
			},
		},
		Additional: []dns.Resource{
			s.ednsopt,
		},
		EnableRecursion: true,
	})
	if err != nil {
		return err
	}
	dns4 := s.dnssv.As4()
	s.dnsUDP.SetStackNode(&s.dns, dns4[:], dns.ServerPort)
	err = s.udps.Register(&s.dnsUDP)
	return err
}

var errDNSNotDone = errors.New("DNS not done")

func (s *StackAsync) ResultLookupIP(host string) ([]netip.Addr, bool, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	done, err := s.dns.MessageCopyTo(&s.lookup)
	if err != nil {
		return nil, done, err
	} else if !done {
		return nil, done, errDNSNotDone
	}

	var addrs []netip.Addr
	ans := s.lookup.Answers
	for i := range ans {
		data := ans[i].RawData()
		if len(data) == 4 {
			addrs = append(addrs, netip.AddrFrom4([4]byte(data)))
		} else if len(data) == 16 {
			addrs = append(addrs, netip.AddrFrom16([16]byte(data)))
		} else {
			return addrs, done, errors.New("bogus IP")
		}
	}
	return addrs, done, nil
}

func (s *StackAsync) StartDHCPv4Request(request [4]byte) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.dhcp.Reset()
	xid := s.Prand32()
	err := s.dhcp.BeginRequest(xid, dhcpv4.RequestConfig{
		RequestedAddr:      request,
		ClientHardwareAddr: s.link.HardwareAddr6(),
		Hostname:           s.hostname,
		ClientID:           s.clientID,
	})
	if err != nil {
		return err
	}

	s.dhcpUDP.SetStackNode(&s.dhcp, nil, dhcpv4.DefaultServerPort)
	err = s.udps.Register(&s.dhcpUDP)
	if err != nil {
		return err
	}
	return err
}

func (s *StackAsync) StartNTP(addr netip.Addr) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.ntp.Reset(s.sysprec, time.Now)

	addr4 := addr.As4()
	s.ntpUDP.SetStackNode(&s.ntp, addr4[:], ntp.ServerPort)
	err := s.udps.Register(&s.ntpUDP)
	return err
}

// ResultNTPOffset returns the result of the NTP protocol such that the following code returns the corrected time.
// If the bool is false then the NTP has not yet completed.
//
//	nowCorrected := time.Now().Add(resultNTP)
func (s *StackAsync) ResultNTPOffset() (time.Duration, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.ntp.Offset(), s.ntp.IsDone()
}

func (s *StackAsync) StartResolveHardwareAddress6(ip netip.Addr) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !ip.Is4() {
		return errors.New("unsupported or invalid IP address")
	}
	addr := ip.As4()
	return s.arp.StartQuery(addr[:])
}

// ResultResolveHardwareAddress6
func (s *StackAsync) ResultResolveHardwareAddress6(ip netip.Addr) (hw [6]byte, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !ip.Is4() {
		return hw, errors.New("unsupported or invalid IP address")
	}
	addr := ip.As4()
	hwslice, err := s.arp.QueryResult(addr[:])
	if err != nil {
		return hw, err
	} else if len(hwslice) != 6 {
		panic("unreachable slice hw length")
	}
	return [6]byte(hwslice), nil
}

type DHCPResults struct {
	DNSServers    []netip.Addr
	Router        netip.Addr
	AssignedAddr  netip.Addr
	ServerAddr    netip.Addr
	BroadcastAddr netip.Addr
	Gateway       netip.Addr
	Subnet        netip.Prefix
	TRebind       uint32 // [seconds]
	TRenewal      uint32
	TLease        uint32 // IP lease time [seconds].
}

func (s *StackAsync) ResultDHCP() (*DHCPResults, error) {
	err := s.populateDHCPResults()
	if err != nil {
		return nil, err
	}
	return &s.dhcpResults, nil
}

type Statistics struct {
	// Total amount of bytes sent over encapsulate.
	TotalSent uint64
	// Total amount of bytes received over demux.
	TotalReceived uint64
}

func (s *StackAsync) ReadStatistics(stats *Statistics) {
	stats.TotalReceived = s.totalrecv
	stats.TotalSent = s.totalsent
}

// AssimilateDHCPResults sets the stack's following parameters:
//   - IPv4 address.
//   - DNS server.
func (stack *StackAsync) AssimilateDHCPResults(results *DHCPResults) error {
	stack.mu.Lock()
	defer stack.mu.Unlock()
	if results.AssignedAddr.IsValid() {
		err := stack.ip.SetAddr(results.AssignedAddr)
		if err != nil {
			return err
		}
	}
	if len(results.DNSServers) > 0 {
		if !results.DNSServers[0].IsValid() || !results.DNSServers[0].Is4() {
			return errors.New("bad DNS server address, IPv6 or invalid")
		}
		stack.dnssv = results.DNSServers[0]
	}
	return nil
}

func (s *StackAsync) populateDHCPResults() error {
	if !s.dhcp.State().HasIP() {
		return errors.New("DHCP not completed")
	}
	router4, ok := s.dhcp.RouterAddr()
	if !ok {
		return errors.New("no DHCP router address")
	}
	assigned4, ok := s.dhcp.AssignedAddr()
	if !ok {
		return errors.New("no DHCP assigned address")
	}
	router := netip.AddrFrom4(router4)
	s.dhcpResults = DHCPResults{
		Router:        router,
		Subnet:        s.dhcp.SubnetPrefix(),
		AssignedAddr:  netip.AddrFrom4(assigned4),
		ServerAddr:    addr4(s.dhcp.ServerAddr()),
		BroadcastAddr: addr4(s.dhcp.BroadcastAddr()),
		Gateway:       addr4(s.dhcp.GatewayAddr()),
		TRebind:       s.dhcp.RebindingSeconds(),
		TRenewal:      s.dhcp.RenewalSeconds(),
		TLease:        s.dhcp.IPLeaseSeconds(),
		DNSServers:    s.dhcpResults.DNSServers[:0], // reuse field capacity.
	}
	s.dhcpResults.DNSServers = s.dhcp.AppendDNSServers(s.dhcpResults.DNSServers)
	return nil
}

func addr4(addr [4]byte, ok bool) netip.Addr {
	if !ok {
		return netip.Addr{}
	}
	return netip.AddrFrom4(addr)
}

func hash(b []byte) uint16 {
	var csum lneto.CRC791
	csum.Write(b)
	return csum.Sum16()
}