package multicast

import (
	"context"
	"fmt"
	"net"
	"regexp"
	"time"

	"github.com/Arceliar/phony"
	"github.com/gologme/log"

	"github.com/yggdrasil-network/yggdrasil-go/src/config"
	"github.com/yggdrasil-network/yggdrasil-go/src/core"
	"golang.org/x/net/ipv6"
)

// Multicast represents the multicast advertisement and discovery mechanism used
// by Yggdrasil to find peers on the same subnet. When a beacon is received on a
// configured multicast interface, Yggdrasil will attempt to peer with that node
// automatically.
type Multicast struct {
	phony.Inbox
	core        *core.Core
	config      *config.NodeState
	log         *log.Logger
	sock        *ipv6.PacketConn
	groupAddr   string
	listeners   map[string]*listenerInfo
	listenPort  uint16
	isOpen      bool
	_interfaces map[string]interfaceInfo
}

type interfaceInfo struct {
	iface net.Interface
	addrs []net.Addr
}

type listenerInfo struct {
	listener *core.TcpListener
	time     time.Time
	interval time.Duration
}

// Init prepares the multicast interface for use.
func (m *Multicast) Init(core *core.Core, state *config.NodeState, log *log.Logger, options interface{}) error {
	m.core = core
	m.config = state
	m.log = log
	m.listeners = make(map[string]*listenerInfo)
	m._interfaces = make(map[string]interfaceInfo)
	current := m.config.GetCurrent()
	m.listenPort = current.LinkLocalTCPPort
	m.groupAddr = "[ff02::114]:9001"
	return nil
}

// Start starts the multicast interface. This launches goroutines which will
// listen for multicast beacons from other hosts and will advertise multicast
// beacons out to the network.
func (m *Multicast) Start() error {
	var err error
	phony.Block(m, func() {
		err = m._start()
	})
	m.log.Debugln("Started multicast module")
	return err
}

func (m *Multicast) _start() error {
	if m.isOpen {
		return fmt.Errorf("multicast module is already started")
	}
	if len(m.config.GetCurrent().MulticastInterfaces) == 0 {
		return nil
	}
	m.log.Infoln("Starting multicast module")
	addr, err := net.ResolveUDPAddr("udp", m.groupAddr)
	if err != nil {
		return err
	}
	listenString := fmt.Sprintf("[::]:%v", addr.Port)
	lc := net.ListenConfig{
		Control: m.multicastReuse,
	}
	conn, err := lc.ListenPacket(context.Background(), "udp6", listenString)
	if err != nil {
		return err
	}
	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
	}

	m.isOpen = true
	go m.listen()
	m.Act(nil, m._multicastStarted)
	m.Act(nil, m._announce)

	return nil
}

// IsStarted returns true if the module has been started.
func (m *Multicast) IsStarted() bool {
	var isOpen bool
	phony.Block(m, func() {
		isOpen = m.isOpen
	})
	return isOpen
}

// Stop stops the multicast module.
func (m *Multicast) Stop() error {
	var err error
	phony.Block(m, func() {
		err = m._stop()
	})
	m.log.Debugln("Stopped multicast module")
	return err
}

func (m *Multicast) _stop() error {
	m.log.Infoln("Stopping multicast module")
	m.isOpen = false
	if m.sock != nil {
		m.sock.Close()
	}
	return nil
}

func (m *Multicast) _updateInterfaces() {
	interfaces := make(map[string]interfaceInfo)
	intfs := m.getAllowedInterfaces()
	for _, intf := range intfs {
		addrs, err := intf.Addrs()
		if err != nil {
			m.log.Warnf("Failed up get addresses for interface %s: %s", intf.Name, err)
			continue
		}
		interfaces[intf.Name] = interfaceInfo{
			iface: intf,
			addrs: addrs,
		}
	}
	m._interfaces = interfaces
}

func (m *Multicast) Interfaces() map[string]net.Interface {
	interfaces := make(map[string]net.Interface)
	phony.Block(m, func() {
		for _, info := range m._interfaces {
			interfaces[info.iface.Name] = info.iface
		}
	})
	return interfaces
}

// getAllowedInterfaces returns the currently known/enabled multicast interfaces.
func (m *Multicast) getAllowedInterfaces() map[string]net.Interface {
	interfaces := make(map[string]net.Interface)
	// Get interface expressions from config
	current := m.config.GetCurrent()
	exprs := current.MulticastInterfaces
	// Ask the system for network interfaces
	allifaces, err := net.Interfaces()
	if err != nil {
		// Don't panic, since this may be from e.g. too many open files (from too much connection spam)
		// TODO? log something
		return nil
	}
	// 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 exprs {
			// Compile each regular expression
			e, err := regexp.Compile(expr)
			if err != nil {
				panic(err)
			}
			// Does the interface match the regular expression? Store it if so
			if e.MatchString(iface.Name) {
				interfaces[iface.Name] = iface
			}
		}
	}
	return interfaces
}

func (m *Multicast) _announce() {
	if !m.isOpen {
		return
	}
	m._updateInterfaces()
	groupAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
	if err != nil {
		panic(err)
	}
	destAddr, err := net.ResolveUDPAddr("udp6", m.groupAddr)
	if err != nil {
		panic(err)
	}
	// There might be interfaces that we configured listeners for but are no
	// longer up - if that's the case then we should stop the listeners
	for name, info := range m.listeners {
		// Prepare our stop function!
		stop := func() {
			info.listener.Stop()
			delete(m.listeners, name)
			m.log.Debugln("No longer multicasting on", name)
		}
		// If the interface is no longer visible on the system then stop the
		// listener, as another one will be started further down
		if _, ok := m._interfaces[name]; !ok {
			stop()
			continue
		}
		// It's possible that the link-local listener address has changed so if
		// that is the case then we should clean up the interface listener
		found := false
		listenaddr, err := net.ResolveTCPAddr("tcp6", info.listener.Listener.Addr().String())
		if err != nil {
			stop()
			continue
		}
		// Find the interface that matches the listener
		if info, ok := m._interfaces[name]; ok {
			for _, addr := range info.addrs {
				if ip, _, err := net.ParseCIDR(addr.String()); err == nil {
					// Does the interface address match our listener address?
					if ip.Equal(listenaddr.IP) {
						found = true
						break
					}
				}
			}
		}
		// If the address has not been found on the adapter then we should stop
		// and clean up the TCP listener. A new one will be created below if a
		// suitable link-local address is found
		if !found {
			stop()
		}
	}
	// Now that we have a list of valid interfaces from the operating system,
	// we can start checking if we can send multicasts on them
	for _, info := range m._interfaces {
		iface := info.iface
		for _, addr := range info.addrs {
			addrIP, _, _ := net.ParseCIDR(addr.String())
			// Ignore IPv4 addresses
			if addrIP.To4() != nil {
				continue
			}
			// Ignore non-link-local addresses
			if !addrIP.IsLinkLocalUnicast() {
				continue
			}
			// Join the multicast group
			m.sock.JoinGroup(&iface, groupAddr)
			// Try and see if we already have a TCP listener for this interface
			var info *listenerInfo
			if nfo, ok := m.listeners[iface.Name]; !ok || nfo.listener.Listener == nil {
				// No listener was found - let's create one
				listenaddr := fmt.Sprintf("[%s%%%s]:%d", addrIP, iface.Name, m.listenPort)
				var metric uint8 // TODO parse this from config
				if li, err := m.core.ListenTCP(listenaddr, metric); err == nil {
					m.log.Debugln("Started multicasting on", iface.Name)
					// Store the listener so that we can stop it later if needed
					info = &listenerInfo{listener: li, time: time.Now()}
					m.listeners[iface.Name] = info
				} else {
					m.log.Warnln("Not multicasting on", iface.Name, "due to error:", err)
				}
			} else {
				// An existing listener was found
				info = m.listeners[iface.Name]
			}
			// Make sure nothing above failed for some reason
			if info == nil {
				continue
			}
			if time.Since(info.time) < info.interval {
				continue
			}
			// Get the listener details and construct the multicast beacon
			lladdr := info.listener.Listener.Addr().String()
			if a, err := net.ResolveTCPAddr("tcp6", lladdr); err == nil {
				a.Zone = ""
				destAddr.Zone = iface.Name
				msg := []byte(a.String())
				m.sock.WriteTo(msg, nil, destAddr)
			}
			if info.interval.Seconds() < 15 {
				info.interval += time.Second
			}
			break
		}
	}
	time.AfterFunc(time.Second, func() {
		m.Act(nil, m._announce)
	})
}

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 {
			if !m.IsStarted() {
				return
			}
			panic(err)
		}
		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 {
			continue
		}
		from := fromAddr.(*net.UDPAddr)
		if addr.IP.String() != from.IP.String() {
			continue
		}
		var interfaces map[string]interfaceInfo
		phony.Block(m, func() {
			interfaces = m._interfaces
		})
		if _, ok := interfaces[from.Zone]; ok {
			addr.Zone = ""
			if err := m.core.CallPeer("tcp://"+addr.String(), from.Zone); err != nil {
				m.log.Debugln("Call from multicast failed:", err)
			}
		}
	}
}