package tuntap

import (
	"bytes"
	"net"
	"time"

	"github.com/songgao/packets/ethernet"
	"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/Arceliar/phony"
)

type tunWriter struct {
	phony.Inbox
	tun *TunAdapter
}

func (w *tunWriter) writeFrom(from phony.Actor, b []byte) {
	w.Act(from, func() {
		w._write(b)
	})
}

// write is pretty loose with the memory safety rules, e.g. it assumes it can read w.tun.iface.IsTap() safely
func (w *tunWriter) _write(b []byte) {
	var written int
	var err error
	n := len(b)
	if n == 0 {
		return
	}
	if w.tun.iface.IsTAP() {
		sendndp := func(dstAddr address.Address) {
			neigh, known := w.tun.icmpv6.getNeighbor(dstAddr)
			known = known && (time.Since(neigh.lastsolicitation).Seconds() < 30)
			if !known {
				w.tun.icmpv6.Solicit(dstAddr)
			}
		}
		peermac := net.HardwareAddr{0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
		var dstAddr address.Address
		var peerknown bool
		if b[0]&0xf0 == 0x40 {
			dstAddr = w.tun.addr
		} else if b[0]&0xf0 == 0x60 {
			if !bytes.Equal(w.tun.addr[:16], dstAddr[:16]) && !bytes.Equal(w.tun.subnet[:8], dstAddr[:8]) {
				dstAddr = w.tun.addr
			}
		}
		if neighbor, ok := w.tun.icmpv6.getNeighbor(dstAddr); ok && neighbor.learned {
			// If we've learned the MAC of a 300::/7 address, for example, or a CKR
			// address, use the MAC address of that
			peermac = neighbor.mac
			peerknown = true
		} else if neighbor, ok := w.tun.icmpv6.getNeighbor(w.tun.addr); ok && neighbor.learned {
			// Otherwise send directly to the MAC address of the host if that's
			// known instead
			peermac = neighbor.mac
			peerknown = true
		} else {
			// Nothing has been discovered, try to discover the destination
			sendndp(w.tun.addr)
		}
		if peerknown {
			var proto ethernet.Ethertype
			switch {
			case b[0]&0xf0 == 0x60:
				proto = ethernet.IPv6
			case b[0]&0xf0 == 0x40:
				proto = ethernet.IPv4
			}
			var frame ethernet.Frame
			frame.Prepare(
				peermac[:6],            // Destination MAC address
				w.tun.icmpv6.mymac[:6], // Source MAC address
				ethernet.NotTagged,     // VLAN tagging
				proto,                  // Ethertype
				len(b))                 // Payload length
			copy(frame[tun_ETHER_HEADER_LENGTH:], b[:n])
			n += tun_ETHER_HEADER_LENGTH
			written, err = w.tun.iface.Write(frame[:n])
		} else {
			w.tun.log.Errorln("TUN/TAP iface write error: no peer MAC known for", net.IP(dstAddr[:]).String(), "- dropping packet")
		}
	} else {
		written, err = w.tun.iface.Write(b[:n])
		util.PutBytes(b)
	}
	if err != nil {
		w.tun.Act(w, func() {
			if !w.tun.isOpen {
				w.tun.log.Errorln("TUN/TAP iface write error:", err)
			}
		})
	}
	if written != n {
		w.tun.log.Errorln("TUN/TAP iface write mismatch:", written, "bytes written vs", n, "bytes given")
	}
}

type tunReader struct {
	phony.Inbox
	tun *TunAdapter
}

func (r *tunReader) _read() {
	// Get a slice to store the packet in
	recvd := util.ResizeBytes(util.GetBytes(), 65535+tun_ETHER_HEADER_LENGTH)
	// Wait for a packet to be delivered to us through the TUN/TAP adapter
	n, err := r.tun.iface.Read(recvd)
	if n <= 0 {
		util.PutBytes(recvd)
	} else {
		r.tun.handlePacketFrom(r, recvd[:n], err)
	}
	if err == nil {
		// Now read again
		r.Act(nil, r._read)
	}
}

func (tun *TunAdapter) handlePacketFrom(from phony.Actor, packet []byte, err error) {
	tun.Act(from, func() {
		tun._handlePacket(packet, err)
	})
}

// does the work of reading a packet and sending it to the correct tunConn
func (tun *TunAdapter) _handlePacket(recvd []byte, err error) {
	if err != nil {
		tun.log.Errorln("TUN/TAP iface read error:", err)
		return
	}
	// If it's a TAP adapter, update the buffer slice so that we no longer
	// include the ethernet headers
	offset := 0
	if tun.iface.IsTAP() {
		// Set our offset to beyond the ethernet headers
		offset = tun_ETHER_HEADER_LENGTH
		// Check first of all that we can go beyond the ethernet headers
		if len(recvd) <= offset {
			return
		}
	}
	// Offset the buffer from now on so that we can ignore ethernet frames if
	// they are present
	bs := recvd[offset:]
	// Check if the packet is long enough to detect if it's an ICMP packet or not
	if len(bs) < 7 {
		tun.log.Traceln("TUN/TAP iface read undersized unknown packet, length:", len(bs))
		return
	}
	// If we detect an ICMP packet then hand it to the ICMPv6 module
	if bs[6] == 58 {
		// Found an ICMPv6 packet - we need to make sure to give ICMPv6 the full
		// Ethernet frame rather than just the IPv6 packet as this is needed for
		// NDP to work correctly
		if err := tun.icmpv6.ParsePacket(recvd); err == nil {
			// We acted on the packet in the ICMPv6 module so don't forward or do
			// anything else with it
			return
		}
	}
	if offset != 0 {
		// Shift forward to avoid leaking bytes off the front of the slice when we eventually store it
		bs = append(recvd[:0], bs...)
	}
	// From the IP header, work out what our source and destination addresses
	// and node IDs are. We will need these in order to work out where to send
	// the packet
	var dstAddr address.Address
	var dstSnet address.Subnet
	var addrlen int
	n := len(bs)
	// Check the IP protocol - if it doesn't match then we drop the packet and
	// do nothing with it
	if bs[0]&0xf0 == 0x60 {
		// Check if we have a fully-sized IPv6 header
		if len(bs) < 40 {
			tun.log.Traceln("TUN/TAP iface read undersized ipv6 packet, length:", len(bs))
			return
		}
		// Check the packet size
		if n-tun_IPv6_HEADER_LENGTH != 256*int(bs[4])+int(bs[5]) {
			return
		}
		// IPv6 address
		addrlen = 16
		copy(dstAddr[:addrlen], bs[24:])
		copy(dstSnet[:addrlen/2], bs[24:])
	} else if bs[0]&0xf0 == 0x40 {
		// Check if we have a fully-sized IPv4 header
		if len(bs) < 20 {
			tun.log.Traceln("TUN/TAP iface read undersized ipv6 packet, length:", len(bs))
			return
		}
		// Check the packet size
		if n != 256*int(bs[2])+int(bs[3]) {
			return
		}
		// IPv4 address
		addrlen = 4
		copy(dstAddr[:addrlen], bs[16:])
	} else {
		// Unknown address length or protocol, so drop the packet and ignore it
		tun.log.Traceln("Unknown packet type, dropping")
		return
	}
	if tun.ckr.isEnabled() {
		if addrlen != 16 || (!dstAddr.IsValid() && !dstSnet.IsValid()) {
			if key, err := tun.ckr.getPublicKeyForAddress(dstAddr, addrlen); err == nil {
				// A public key was found, get the node ID for the search
				dstNodeID := crypto.GetNodeID(&key)
				dstAddr = *address.AddrForNodeID(dstNodeID)
				dstSnet = *address.SubnetForNodeID(dstNodeID)
				addrlen = 16
			}
		}
	}
	if addrlen != 16 || (!dstAddr.IsValid() && !dstSnet.IsValid()) {
		// Couldn't find this node's ygg IP
		return
	}
	// Do we have an active connection for this node address?
	var dstNodeID, dstNodeIDMask *crypto.NodeID
	session, isIn := tun.addrToConn[dstAddr]
	if !isIn || session == nil {
		session, isIn = tun.subnetToConn[dstSnet]
		if !isIn || session == nil {
			// Neither an address nor a subnet mapping matched, therefore populate
			// the node ID and mask to commence a search
			if dstAddr.IsValid() {
				dstNodeID, dstNodeIDMask = dstAddr.GetNodeIDandMask()
			} else {
				dstNodeID, dstNodeIDMask = dstSnet.GetNodeIDandMask()
			}
		}
	}
	// If we don't have a connection then we should open one
	if !isIn || session == nil {
		// Check we haven't been given empty node ID, really this shouldn't ever
		// happen but just to be sure...
		if dstNodeID == nil || dstNodeIDMask == nil {
			panic("Given empty dstNodeID and dstNodeIDMask - this shouldn't happen")
		}
		_, known := tun.dials[*dstNodeID]
		tun.dials[*dstNodeID] = append(tun.dials[*dstNodeID], bs)
		for len(tun.dials[*dstNodeID]) > 32 {
			util.PutBytes(tun.dials[*dstNodeID][0])
			tun.dials[*dstNodeID] = tun.dials[*dstNodeID][1:]
		}
		if !known {
			go func() {
				conn, err := tun.dialer.DialByNodeIDandMask(dstNodeID, dstNodeIDMask)
				tun.Act(nil, func() {
					packets := tun.dials[*dstNodeID]
					delete(tun.dials, *dstNodeID)
					if err != nil {
						return
					}
					// We've been given a connection so prepare the session wrapper
					var tc *tunConn
					if tc, err = tun._wrap(conn); err != nil {
						// Something went wrong when storing the connection, typically that
						// something already exists for this address or subnet
						tun.log.Debugln("TUN/TAP iface wrap:", err)
						return
					}
					for _, packet := range packets {
						tc.writeFrom(nil, packet)
					}
				})
				return
			}()
		}
	}
	// If we have a connection now, try writing to it
	if isIn && session != nil {
		session.writeFrom(tun, bs)
	}
}