package tuntap

import (
	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv6"
)

const TUN_OFFSET_BYTES = 4

func (tun *TunAdapter) read() {
	var buf [TUN_OFFSET_BYTES + 65535]byte
	for {
		n, err := tun.iface.Read(buf[:], TUN_OFFSET_BYTES)
		if n <= TUN_OFFSET_BYTES || err != nil {
			tun.log.Errorln("Error reading TUN:", err)
			ferr := tun.iface.Flush()
			if ferr != nil {
				tun.log.Errorln("Unable to flush packets:", ferr)
			}
			return
		}
		begin := TUN_OFFSET_BYTES
		end := begin + n
		bs := buf[begin:end]
		if _, err := tun.core.Write(bs); err != nil {
			tun.log.Errorln("Unable to send packet:", err)
		}
	}
}

func (tun *TunAdapter) write() {
	var buf [TUN_OFFSET_BYTES + 65535]byte
	for {
		bs := buf[TUN_OFFSET_BYTES:]
		n, err := tun.core.Read(bs)
		if err != nil {
			tun.log.Errorln("Exiting tun writer due to core read error:", err)
			return
		}
		if n > int(tun.MTU()) {
			ptb := &icmp.PacketTooBig{
				MTU:  int(tun.mtu),
				Data: bs[:40],
			}
			if packet, err := CreateICMPv6(bs[8:24], bs[24:40], ipv6.ICMPTypePacketTooBig, 0, ptb); err == nil {
				_, _ = tun.core.Write(packet)
			}
			continue
		}
		bs = buf[:TUN_OFFSET_BYTES+n]
		if _, err = tun.iface.Write(bs, TUN_OFFSET_BYTES); err != nil {
			tun.Act(nil, func() {
				if !tun.isOpen {
					tun.log.Errorln("TUN iface write error:", err)
				}
			})
		}
	}
}