package haza

import "context"
import "errors"
import "fmt"
import "net"
import "runtime"
import "sync"
import "sync/atomic"
import "unsafe"

import "golang.org/x/sys/unix"

type DhcpServer struct {
	Named

	Ctx              context.Context
	CtxCancel        context.CancelFunc

	wg sync.WaitGroup
	stop_req atomic.Bool

	ext_mtx          sync.Mutex
	ext_svcs         []Service
	ext_closed       bool

	conns_mtx sync.Mutex
	conns map[string]DhcpConn
	conns_by_fd map[int]DhcpConn

	p int // epoll
	efd int // eventfd


	log              Logger
}

func finalize_dhcp_server(s *DhcpServer) {
	var dc DhcpConn

	for _, dc = range s.conns_by_fd {

		// the internal udp sockets wasn't addded to epoll.
		// something liek the following isn't needed.
		//dc.ForEachUdpSockFd(func (fd int) {
		//	unix.EpollCtl(s.p, unix.EPOLL_CTL_DEL, fd, nil)
		//})

		unix.EpollCtl(s.p, unix.EPOLL_CTL_DEL, dc.Fd(), nil)
		delete(s.conns_by_fd, dc.Fd())
		delete(s.conns, dc.Iface())
		dc.Close()
	}

	if s.efd >= 0 {
		if s.p >= 0 { unix.EpollCtl(s.p, unix.EPOLL_CTL_DEL, s.efd, nil) }
		unix.Close(s.efd)
		s.efd = -1
	}

	if s.p >= 0 {
		unix.Close(s.p)
		s.p = -1
	}
}

func NewDhcpServer(ctx context.Context, name string, logger Logger) (*DhcpServer, error) {
	var s *DhcpServer
	var p int
	var efd int
	var err error

	p, err = unix.EpollCreate1(0)
	if err != nil {
		return nil, fmt.Errorf("unable to create epoll - %s", err.Error())
	}

     efd, err = unix.Eventfd(0, unix.EFD_CLOEXEC)
	if err != nil {
		unix.Close(p)
		return nil, err
	}

	err = unix.EpollCtl(p, unix.EPOLL_CTL_ADD, efd,
		&unix.EpollEvent{
			Events: unix.EPOLLIN | unix.EPOLLERR | unix.EPOLLHUP,
			Fd: int32(efd),
		},
	)
	if err != nil {
		unix.Close(efd)
		unix.Close(p)
		return nil, err
	}

	s = &DhcpServer{}
	s.Ctx, s.CtxCancel = context.WithCancel(ctx)
	s.name = name
	s.log = logger
	s.stop_req.Store(false)
     s.ext_svcs = make([]Service, 0, 1)
	s.ext_closed = false
	s.efd = efd
	s.p = p
	s.conns = make(map[string]DhcpConn, 0)
	s.conns_by_fd = make(map[int]DhcpConn, 0)

	runtime.SetFinalizer(s, finalize_dhcp_server)
	return s, nil
}

func (s *DhcpServer) AddListener4(iface string, addr *net.UDPAddr) error {
	var conn DhcpConn
	var ok bool
	var err error

	s.conns_mtx.Lock()
	defer s.conns_mtx.Unlock()

	conn, ok = s.conns[iface]
	if ok {
		err = conn.AddAddr(addr)
		if err != nil { return err }
	} else {
		conn, err = NewDhcp4Conn(iface, addr)
		if err != nil { return err }
fmt.Printf ("ADDING dhcp4... %d\n", conn.Fd())
		err = unix.EpollCtl(s.p, unix.EPOLL_CTL_ADD, conn.Fd(),
			&unix.EpollEvent{
				Events: unix.EPOLLIN | unix.EPOLLERR | unix.EPOLLHUP,
				Fd: int32(conn.Fd()),
			},
		)
		if err != nil {
			conn.Close()
			return err
		}

		s.conns[iface] = conn // this isn't needed??? or this must be a slice...
		s.conns_by_fd[conn.Fd()] = conn
	}

	return nil
}

func (s *DhcpServer) RunTask(wg *sync.WaitGroup) {
//	var l_wg sync.WaitGroup

	defer wg.Done()

/*
	for i = 0; i < 10; i++ { // TODO: configured number of handlersz...
		l_wg.Add(1)
		go s.run_handlers(&l_wg)
	}
*/
fmt.Printf ("beginning of recv loop\n")
	s.run_recv_loop()
fmt.Printf ("end of recv loop\n")

//	l_wg.Wait()
	finalize_dhcp_server(s)
}

func (s *DhcpServer) ReqStop() {
	if s.stop_req.CompareAndSwap(false, true) {
		var v uint64
		// eventfd needs an 8-byte integer.
		v = 1
		unix.Write(s.efd, (*[8]byte)(unsafe.Pointer(&v))[:])
	}
}

func (s *DhcpServer) StartService(data interface{}) {
	s.wg.Add(1)
	go s.RunTask(&s.wg)
}

func (s *DhcpServer) StartExtService(svc Service, data interface{}) {
	s.ext_mtx.Lock()
	if s.ext_closed {
		// don't start it if it's already closed
		s.ext_mtx.Unlock()
		return
	}
	s.ext_svcs = append(s.ext_svcs, svc)
	s.ext_mtx.Unlock()
	s.wg.Add(1)
	go svc.RunTask(&s.wg)
}

func (s *DhcpServer) StopServices() {
	var ext_svc Service
	s.ReqStop()
	s.ext_mtx.Lock()
	for _, ext_svc = range s.ext_svcs {
		ext_svc.StopServices()
	}
	s.ext_closed = true
	s.ext_mtx.Unlock()
}

func (s *DhcpServer) FixServices() {
	s.log.Rotate()
}

func (s *DhcpServer) WaitForTermination() {
	s.wg.Wait()
	s.log.Write("", LOG_INFO, "End of service")
}

func (s *DhcpServer) WriteLog(id string, level LogLevel, fmtstr string, args ...interface{}) {
	s.log.Write(id, level, fmtstr, args...)
}

func get_offsets(frame []byte) (int, int, int, int, int, error) {
	var eth_off int
	var ip_off int
	var ihl int
	var udp_off int
	var udp_len int
	var dhcp_off int
	var dhcp_end int

	if len(frame) < 14 {
		return 0, 0, 0, 0, 0, fmt.Errorf("frame too short for Ethernet header")
	}
	eth_off = 0
	ip_off = eth_off + 14

	if len(frame) < ip_off + 20 {
		return 0, 0, 0, 0, 0, fmt.Errorf("frame too short for IPv4 header")
	}

	ihl = int(frame[ip_off] & 0x0F) * 4 // the lower first 4 bits of the first bytes * 4
	if len(frame) < ip_off + ihl {
		return 0, 0, 0, 0, 0, fmt.Errorf("invalid IHL %d", ihl)
	}

	udp_off = ip_off + ihl
	if len(frame) < udp_off + 8 {
		return 0, 0, 0, 0, 0, fmt.Errorf("frame too short for UDP header")
	}

	udp_len = int(frame[udp_off + 4]) << 8 | int(frame[udp_off + 5])
	if udp_len < 8 {
		return 0, 0, 0, 0, 0, fmt.Errorf("invalid UDP length %d", udp_len)
	}
	if len(frame) < udp_off + udp_len {
		return 0, 0, 0, 0, 0, fmt.Errorf("frame too short for UDP length %d", udp_len)
	}

	dhcp_off = udp_off + 8
	dhcp_end = udp_off + udp_len

	return eth_off, ip_off, udp_off, dhcp_off, dhcp_end, nil
}

func (s *DhcpServer) run_recv_loop() error {
	var buf [1500]byte
	var nevts int
	var i int
	var evts [128]unix.EpollEvent
	var err error

epoll_loop:
	for {
		nevts, err = unix.EpollWait(s.p, evts[:], -1)
		if err != nil {
			if errors.Is(err, unix.EINTR) { continue }
			s.log.Write("", LOG_ERROR, "event multiplexer error - %s", err.Error())
			break epoll_loop
		}

		for i = 0; i < nevts ; i++ {
			if (evts[i].Events & (unix.EPOLLHUP | unix.EPOLLERR)) != 0 {
				s.log.Write("", LOG_ERROR, "event HUP or ERR detected on fd %d - %s", i)
				break epoll_loop
			}

			if int(evts[i].Fd) == s.efd {
				if ((evts[i].Events & unix.EPOLLIN) != 0) {
					unix.Read(s.efd, buf[:])
				}
				break epoll_loop
			} else {
				if (evts[i].Events & unix.EPOLLIN) != 0 {
					var n int
					var from unix.Sockaddr

					n, from, err = unix.Recvfrom(int(evts[i].Fd), buf[:], 0)
					fmt.Printf("%d %v [% x] %v\n", n, sockaddrToString(from), buf[:n], err)
					if n > 0 {
						var spos int
						var epos int
						_, _, _, spos, epos, err = get_offsets(buf[:n])
						if err != nil {
							fmt.Printf ("PACKET -> %s\n", err.Error())
						} else {
							//fmt.Printf (">>%d [%s]<<\n", epos - spos, string(buf[spos: epos]))
							if string(buf[spos:epos]) == "quit\n" {
								break epoll_loop
							}


							var pkt Dhcp4Pkt
							pkt.Decode(buf[spos:epos])
							fmt.Printf("%+v\n", pkt)
						}
					}

					if err != nil {
						s.log.Write("", LOG_ERROR, "Failed to read packet on fd %d - %s", i, err.Error())
						break epoll_loop
					}
				}
			}
		}
	}

	// if there are subtasks wait here for termination and close the dockets
	return nil
}