package yggdrasil

import "net"
import "time"
import "fmt"

import "golang.org/x/net/ipv6"

type multicast struct {
	core      *Core
	sock      *ipv6.PacketConn
	groupAddr string
  interfaces []net.Interface
}

func (m *multicast) init(core *Core) {
	m.core = core
	m.groupAddr = "[ff02::114]:9001"
  // Ask the system for network interfaces
  allifaces, err := net.Interfaces()
  if err != nil {
    panic(err)
  }
  // Work out which interfaces to announce on
  for _, iface := range allifaces {
    if iface.Flags & net.FlagUp == 0 {
      // Ignore interfaces that are down
      continue
    }
    if iface.Flags & net.FlagMulticast == 0 {
      // Ignore non-multicast interfaces
      continue
    }
    if iface.Flags & net.FlagPointToPoint != 0 {
      // Ignore point-to-point interfaces
      continue
    }
    for _, expr := range m.core.ifceExpr {
      m.core.log.Println(expr)
      if expr.MatchString(iface.Name) {
        m.core.log.Println(iface.Name, "matched", expr)
        m.interfaces = append(m.interfaces, iface)
      }
    }
  }
  m.core.log.Println("Found", len(m.interfaces), "multicast interfaces")
}

func (m *multicast) Start() {
	if len(m.core.ifceExpr) == 0 {
		m.core.log.Println("Not starting multicast discovery")
	} else {
    m.core.log.Println("Starting multicast discovery...")
  	addr, err := net.ResolveUDPAddr("udp", m.groupAddr)
  	if err != nil {
  		panic(err)
  	}
  	listenString := fmt.Sprintf("[::]:%v", addr.Port)
  	conn, err := net.ListenPacket("udp6", listenString)
  	if err != nil {
  		panic(err)
  	}
  	//defer conn.Close() // Let it close on its own when the application exits
  	m.sock = ipv6.NewPacketConn(conn)
  	if err = m.sock.SetControlMessage(ipv6.FlagDst, true); err != nil {
  		// Windows can't set this flag, so we need to handle it in other ways
  		//panic(err)
  	}

  	go m.listen()
  	go m.announce()
  }
}

func (m *multicast) announce() {
	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
	if err != nil {
		panic(err)
	}
	var anAddr net.TCPAddr
	myAddr := m.core.DEBUG_getGlobalTCPAddr()
	anAddr.Port = myAddr.Port
	destAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
	if err != nil {
		panic(err)
	}
	for {
		for _, iface := range m.interfaces {

			m.sock.JoinGroup(&iface, groupAddr)
			//err := n.sock.JoinGroup(&iface, groupAddr)
			//if err != nil { panic(err) }
			addrs, err := iface.Addrs()
			if err != nil {
				panic(err)
			}
			for _, addr := range addrs {
				addrIP, _, _ := net.ParseCIDR(addr.String())
				if addrIP.To4() != nil {
					continue
				} // IPv6 only
				if !addrIP.IsLinkLocalUnicast() {
					continue
				}
				anAddr.IP = addrIP
				anAddr.Zone = iface.Name
				destAddr.Zone = iface.Name
				msg := []byte(anAddr.String())
				m.sock.WriteTo(msg, nil, destAddr)
				break
			}
			time.Sleep(time.Second)
		}
		time.Sleep(time.Second)
	}
}

func (m *multicast) listen() {
	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
	if err != nil {
		panic(err)
	}
	bs := make([]byte, 2048)
	for {
		nBytes, rcm, fromAddr, err := m.sock.ReadFrom(bs)
		if err != nil {
			panic(err)
		}
		//if rcm == nil { continue } // wat
		//fmt.Println("DEBUG:", "packet from:", fromAddr.String())
		if rcm != nil {
			// Windows can't set the flag needed to return a non-nil value here
			// So only make these checks if we get something useful back
			// TODO? Skip them always, I'm not sure if they're really needed...
			if !rcm.Dst.IsLinkLocalMulticast() {
				continue
			}
			if !rcm.Dst.Equal(groupAddr.IP) {
				continue
			}
		}
		anAddr := string(bs[:nBytes])
		addr, err := net.ResolveTCPAddr("tcp6", anAddr)
		if err != nil {
			panic(err)
			continue
		} // Panic for testing, remove later
		from := fromAddr.(*net.UDPAddr)
		//fmt.Println("DEBUG:", "heard:", addr.IP.String(), "from:", from.IP.String())
		if addr.IP.String() != from.IP.String() {
			continue
		}
		addr.Zone = from.Zone
		saddr := addr.String()
		//if _, isIn := n.peers[saddr]; isIn { continue }
		//n.peers[saddr] = struct{}{}
		m.core.DEBUG_addTCPConn(saddr)
		//fmt.Println("DEBUG:", "added multicast peer:", saddr)
	}
}