package tuntap

import (
	"bytes"
	"errors"
	"time"

	"github.com/Arceliar/phony"
	"github.com/yggdrasil-network/yggdrasil-go/src/address"
	"github.com/yggdrasil-network/yggdrasil-go/src/crypto"
	"github.com/yggdrasil-network/yggdrasil-go/src/util"
	"github.com/yggdrasil-network/yggdrasil-go/src/yggdrasil"
	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv6"
)

const tunConnTimeout = 2 * time.Minute

type tunConn struct {
	phony.Inbox
	tun   *TunAdapter
	conn  *yggdrasil.Conn
	addr  address.Address
	snet  address.Subnet
	stop  chan struct{}
	alive *time.Timer // From calling time.AfterFunc
}

func (s *tunConn) close() {
	s.tun.mutex.Lock()
	defer s.tun.mutex.Unlock()
	s._close_nomutex()
}

func (s *tunConn) _close_nomutex() {
	s.conn.Close()
	delete(s.tun.addrToConn, s.addr)
	delete(s.tun.subnetToConn, s.snet)
	func() {
		defer func() { recover() }()
		close(s.stop) // Closes reader/writer goroutines
	}()
}

func (s *tunConn) _read(bs []byte) (err error) {
	select {
	case <-s.stop:
		err = errors.New("session was already closed")
		util.PutBytes(bs)
		return
	default:
	}
	if len(bs) == 0 {
		err = errors.New("read packet with 0 size")
		util.PutBytes(bs)
		return
	}
	ipv4 := len(bs) > 20 && bs[0]&0xf0 == 0x40
	ipv6 := len(bs) > 40 && bs[0]&0xf0 == 0x60
	isCGA := true
	// Check source addresses
	switch {
	case ipv6 && bs[8] == 0x02 && bytes.Equal(s.addr[:16], bs[8:24]): // source
	case ipv6 && bs[8] == 0x03 && bytes.Equal(s.snet[:8], bs[8:16]): // source
	default:
		isCGA = false
	}
	// Check destiantion addresses
	switch {
	case ipv6 && bs[24] == 0x02 && bytes.Equal(s.tun.addr[:16], bs[24:40]): // destination
	case ipv6 && bs[24] == 0x03 && bytes.Equal(s.tun.subnet[:8], bs[24:32]): // destination
	default:
		isCGA = false
	}
	// Decide how to handle the packet
	var skip bool
	switch {
	case isCGA: // Allowed
	case s.tun.ckr.isEnabled() && (ipv4 || ipv6):
		var srcAddr address.Address
		var dstAddr address.Address
		var addrlen int
		if ipv4 {
			copy(srcAddr[:], bs[12:16])
			copy(dstAddr[:], bs[16:20])
			addrlen = 4
		}
		if ipv6 {
			copy(srcAddr[:], bs[8:24])
			copy(dstAddr[:], bs[24:40])
			addrlen = 16
		}
		if !s.tun.ckr.isValidLocalAddress(dstAddr, addrlen) {
			// The destination address isn't in our CKR allowed range
			skip = true
		} else if key, err := s.tun.ckr.getPublicKeyForAddress(srcAddr, addrlen); err == nil {
			srcNodeID := crypto.GetNodeID(&key)
			if s.conn.RemoteAddr() == *srcNodeID {
				// This is the one allowed CKR case, where source and destination addresses are both good
			} else {
				// The CKR key associated with this address doesn't match the sender's NodeID
				skip = true
			}
		} else {
			// We have no CKR route for this source address
			skip = true
		}
	default:
		skip = true
	}
	if skip {
		err = errors.New("address not allowed")
		util.PutBytes(bs)
		return
	}
	s.tun.writer.writeFrom(s, bs)
	s.stillAlive()
	return
}

func (s *tunConn) _write(bs []byte) (err error) {
	select {
	case <-s.stop:
		err = errors.New("session was already closed")
		util.PutBytes(bs)
		return
	default:
	}
	v4 := len(bs) > 20 && bs[0]&0xf0 == 0x40
	v6 := len(bs) > 40 && bs[0]&0xf0 == 0x60
	isCGA := true
	// Check source addresses
	switch {
	case v6 && bs[8] == 0x02 && bytes.Equal(s.tun.addr[:16], bs[8:24]): // source
	case v6 && bs[8] == 0x03 && bytes.Equal(s.tun.subnet[:8], bs[8:16]): // source
	default:
		isCGA = false
	}
	// Check destiantion addresses
	switch {
	case v6 && bs[24] == 0x02 && bytes.Equal(s.addr[:16], bs[24:40]): // destination
	case v6 && bs[24] == 0x03 && bytes.Equal(s.snet[:8], bs[24:32]): // destination
	default:
		isCGA = false
	}
	// Decide how to handle the packet
	var skip bool
	switch {
	case isCGA: // Allowed
	case s.tun.ckr.isEnabled() && (v4 || v6):
		var srcAddr address.Address
		var dstAddr address.Address
		var addrlen int
		if v4 {
			copy(srcAddr[:], bs[12:16])
			copy(dstAddr[:], bs[16:20])
			addrlen = 4
		}
		if v6 {
			copy(srcAddr[:], bs[8:24])
			copy(dstAddr[:], bs[24:40])
			addrlen = 16
		}
		if !s.tun.ckr.isValidLocalAddress(srcAddr, addrlen) {
			// The source address isn't in our CKR allowed range
			skip = true
		} else if key, err := s.tun.ckr.getPublicKeyForAddress(dstAddr, addrlen); err == nil {
			dstNodeID := crypto.GetNodeID(&key)
			if s.conn.RemoteAddr() == *dstNodeID {
				// This is the one allowed CKR case, where source and destination addresses are both good
			} else {
				// The CKR key associated with this address doesn't match the sender's NodeID
				skip = true
			}
		} else {
			// We have no CKR route for this destination address... why do we have the packet in the first place?
			skip = true
		}
	default:
		skip = true
	}
	if skip {
		err = errors.New("address not allowed")
		util.PutBytes(bs)
		return
	}
	msg := yggdrasil.FlowKeyMessage{
		FlowKey: util.GetFlowKey(bs),
		Message: bs,
	}
	s.conn.WriteFrom(s, msg, func(err error) {
		if err == nil {
			// No point in wasting resources to send back an error if there was none
			return
		}
		s.RecvFrom(s.conn, func() {
			if e, eok := err.(yggdrasil.ConnError); !eok {
				if e.Closed() {
					s.tun.log.Debugln(s.conn.String(), "TUN/TAP generic write debug:", err)
				} else {
					s.tun.log.Errorln(s.conn.String(), "TUN/TAP generic write error:", err)
				}
			} else if e.PacketTooBig() {
				// TODO: This currently isn't aware of IPv4 for CKR
				ptb := &icmp.PacketTooBig{
					MTU:  int(e.PacketMaximumSize()),
					Data: bs[:900],
				}
				if packet, err := CreateICMPv6(bs[8:24], bs[24:40], ipv6.ICMPTypePacketTooBig, 0, ptb); err == nil {
					s.tun.writer.writeFrom(s, packet)
				}
			} else {
				if e.Closed() {
					s.tun.log.Debugln(s.conn.String(), "TUN/TAP conn write debug:", err)
				} else {
					s.tun.log.Errorln(s.conn.String(), "TUN/TAP conn write error:", err)
				}
			}
		})
	})
	s.stillAlive()
	return
}

func (s *tunConn) stillAlive() {
	if s.alive != nil {
		s.alive.Stop()
	}
	s.alive = time.AfterFunc(tunConnTimeout, s.close)
}