package main

import (
	"bytes"
	"crypto/rand"
	"encoding/binary"
	"fmt"
	"net"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/nonoo/kappanhang/log"
)

var conn *net.UDPConn
var localSID uint32
var remoteSID uint32
var sendSeq uint16
var authSendSeq uint16
var authID [6]byte
var randIDByteForPktSeven [1]byte
var expectedPkt7ReplySeq uint16

func send(d []byte) {
	_, err := conn.Write(d)
	if err != nil {
		log.Fatal(err)
	}
}

func read() ([]byte, error) {
	err := conn.SetReadDeadline(time.Now().Add(time.Second))
	if err != nil {
		log.Fatal(err)
	}

	b := make([]byte, 1500)
	n, _, err := conn.ReadFromUDP(b)
	if err != nil {
		if err, ok := err.(net.Error); ok && !err.Timeout() {
			log.Fatal(err)
		}
	}
	return b[:n], err
}

func setupCloseHandler() {
	c := make(chan os.Signal)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-c
		log.Print("disconnecting")
		sendDisconnect()
		os.Exit(0)
	}()
}

func sendPkt7(replyID []byte) {
	// Example request from PC:  0x15, 0x00, 0x00, 0x00, 0x07, 0x00, 0x09, 0x00, 0xbe, 0xd9, 0xf2, 0x63, 0xe4, 0x35, 0xdd, 0x72, 0x00, 0x78, 0x40, 0xf6, 0x02
	// Example reply from radio: 0x00, 0x00, 0x00, 0x00, 0x07, 0x00, 0x09, 0x00, 0xe4, 0x35, 0xdd, 0x72, 0xbe, 0xd9, 0xf2, 0x63, 0x01, 0x78, 0x40, 0xf6, 0x02
	var replyFlag byte
	if replyID == nil {
		replyID = make([]byte, 4)
		var randID [2]byte
		_, err := rand.Read(randID[:])
		if err != nil {
			log.Fatal(err)
		}
		replyID[0] = randID[0]
		replyID[1] = randID[1]
		replyID[2] = randIDByteForPktSeven[0]
		replyID[3] = 0x03
	} else {
		replyFlag = 0x01
	}

	expectedPkt7ReplySeq = sendSeq

	send([]byte{0x15, 0x00, 0x00, 0x00, 0x07, 0x00, byte(sendSeq), byte(sendSeq >> 8),
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID),
		replyFlag, replyID[0], replyID[1], replyID[2], replyID[3]})
}

func sendPkt3() {
	send([]byte{0x10, 0x00, 0x00, 0x00, 0x03, 0x00, byte(sendSeq), byte(sendSeq >> 8),
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID)})
}

func sendPkt6() {
	send([]byte{0x10, 0x00, 0x00, 0x00, 0x06, 0x00, 0x01, 0x00,
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID)})
}

func sendPktLogin() {
	var randID [2]byte
	_, err := rand.Read(randID[:])
	if err != nil {
		log.Fatal(err)
	}
	send([]byte{0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID),
		0x00, 0x00, 0x00, 0x70, 0x01, 0x00, 0x00, byte(authSendSeq),
		byte(authSendSeq >> 8), 0x00, randID[0], randID[1], 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x2b, 0x3f, 0x55, 0x5c, 0x00, 0x00, 0x00, 0x00, // username: beer
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x2b, 0x3f, 0x55, 0x5c, 0x3f, 0x25, 0x77, 0x58, // pass: beerbeer
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x69, 0x63, 0x6f, 0x6d, 0x2d, 0x70, 0x63, 0x00, // icom-pc
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})
}

func sendPktReauth() {
	// Example request from PC:  0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0d, 0x00,
	//                           0xbb, 0x41, 0x3f, 0x2b, 0xe6, 0xb2, 0x7b, 0x7b,
	//                           0x00, 0x00, 0x00, 0x30, 0x01, 0x05, 0x00, 0x02,
	//                           0x00, 0x00, 0x5d, 0x37, 0x12, 0x82, 0x3b, 0xde,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
	// Example reply from radio: 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0e, 0x00,
	//                           0xe6, 0xb2, 0x7b, 0x7b, 0xbb, 0x41, 0x3f, 0x2b,
	//                           0x00, 0x00, 0x00, 0x30, 0x02, 0x05, 0x00, 0x02,
	//                           0x00, 0x00, 0x5d, 0x37, 0x12, 0x82, 0x3b, 0xde,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	//                           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
	send([]byte{0x40, 0x00, 0x00, 0x00, 0x00, 0x00, byte(sendSeq), byte(sendSeq >> 8),
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID),
		0x00, 0x00, 0x00, 0x30, 0x01, 0x05, 0x00, byte(authSendSeq),
		byte(authSendSeq >> 8), 0x00, authID[0], authID[1], authID[2], authID[3], authID[4], authID[5],
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})
}

func sendDisconnect() {
	send([]byte{0x40, 0x00, 0x00, 0x00, 0x00, 0x00, byte(sendSeq), byte(sendSeq >> 8),
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID),
		0x00, 0x00, 0x00, 0x30, 0x01, 0x01, 0x00, byte(authSendSeq),
		byte(authSendSeq >> 8), 0x00, authID[0], authID[1], authID[2], authID[3], authID[4], authID[5],
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})
	send([]byte{0x10, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00,
		byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID),
		byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID)})
}

func main() {
	log.Init()
	parseArgs()
	setupCloseHandler()

	hostPort := fmt.Sprint(connectAddress, ":", connectPort)
	log.Print("connecting to ", hostPort)
	raddr, err := net.ResolveUDPAddr("udp", hostPort)
	if err != nil {
		log.Fatal(err)
	}
	conn, err = net.DialUDP("udp", nil, raddr)
	if err != nil {
		log.Fatal(err)
	}

	// Constructing the local session ID by combining the local IP address and port.
	laddr := conn.LocalAddr().(*net.UDPAddr)
	localSID = binary.BigEndian.Uint32(laddr.IP[len(laddr.IP)-4:])<<16 | uint32(laddr.Port&0xffff)
	log.Debugf("using session id %.8x", localSID)

	sendPkt3()
	sendSeq = 1
	sendPkt7(nil)
	sendSeq = 0
	sendPkt3()

	for {
		// Expecting a Pkt4 answer.
		// Example answer from radio: 0x10, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x8c, 0x7d, 0x45, 0x7a, 0x1d, 0xf6, 0xe9, 0x0b
		r, _ := read()
		if bytes.Equal(r[:8], []byte{0x10, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00}) {
			remoteSID = binary.BigEndian.Uint32(r[8:12])
			break
		}
	}

	log.Debugf("got remote session id %.8x", remoteSID)

	sendSeq = 1
	authSendSeq = 1
	sendPkt6()
	sendPktLogin()
	authSendSeq++

	var lastPingAt time.Time
	var lastReauthAt time.Time
	var lastStatusLog time.Time
	var errCount int

	_, err = rand.Read(randIDByteForPktSeven[:])
	if err != nil {
		log.Fatal(err)
	}

	for {
		r, err := read()
		if err != nil {
			errCount++
			if errCount > 5 {
				log.Fatal("timeout")
			}
			log.Error("stream break detected")
		}
		errCount = 0

		// Example success auth packet: 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
		//                              0xe6, 0xb2, 0x7b, 0x7b, 0xbb, 0x41, 0x3f, 0x2b,
		//                              0x00, 0x00, 0x00, 0x50, 0x02, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x5d, 0x37, 0x12, 0x82, 0x3b, 0xde,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x46, 0x54, 0x54, 0x48, 0x00, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		//                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
		if len(r) == 96 && bytes.Equal(r[:8], []byte{0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00}) {
			if bytes.Equal(r[48:52], []byte{0xff, 0xff, 0xff, 0xfe}) {
				log.Fatal("invalid user/password")
			} else {
				copy(authID[:], r[26:32])
				log.Print("auth ok")
			}
		}
		if len(r) == 21 && bytes.Equal(r[1:6], []byte{0x00, 0x00, 0x00, 0x07, 0x00}) {
			if r[16] == 0x00 { // This is a pkt7 request from the radio.
				// Replying to the radio.
				// Example request from radio: 0x00, 0x00, 0x00, 0x00, 0x07, 0x00, 0x1c, 0x0e, 0xe4, 0x35, 0xdd, 0x72, 0xbe, 0xd9, 0xf2, 0x63, 0x00, 0x57, 0x2b, 0x12, 0x00
				// Example answer from PC:     0x15, 0x00, 0x00, 0x00, 0x07, 0x00, 0x1c, 0x0e, 0xbe, 0xd9, 0xf2, 0x63, 0xe4, 0x35, 0xdd, 0x72, 0x01, 0x57, 0x2b, 0x12, 0x00
				sendPkt7(r[17:21])
			} else {
				gotSeq := binary.LittleEndian.Uint16(r[6:8])
				if expectedPkt7ReplySeq != gotSeq {
					var missingPkts int
					if gotSeq > expectedPkt7ReplySeq {
						missingPkts = int(gotSeq) - int(expectedPkt7ReplySeq)
					} else {
						missingPkts = int(gotSeq) + 65536 - int(expectedPkt7ReplySeq)
					}
					if missingPkts < 1000 {
						log.Error("lost ", missingPkts, " packets ", gotSeq, " ", expectedPkt7ReplySeq)
					}
				}
			}
		}
		if len(r) == 16 && bytes.Equal(r[:6], []byte{0x10, 0x00, 0x00, 0x00, 0x00, 0x00}) {
			// Replying to the radio.
			// Example request from radio: 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x13, 0x00, 0xe4, 0x35, 0xdd, 0x72, 0xbe, 0xd9, 0xf2, 0x63
			// Example answer from PC:     0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x13, 0x00, 0xbe, 0xd9, 0xf2, 0x63, 0xe4, 0x35, 0xdd, 0x72
			gotSeq := binary.LittleEndian.Uint16(r[6:8])
			send([]byte{0x10, 0x00, 0x00, 0x00, 0x00, 0x00, byte(gotSeq), byte(gotSeq >> 8), byte(localSID >> 24), byte(localSID >> 16), byte(localSID >> 8), byte(localSID), byte(remoteSID >> 24), byte(remoteSID >> 16), byte(remoteSID >> 8), byte(remoteSID)})
		}

		if time.Since(lastPingAt) >= 100*time.Millisecond {
			sendPkt7(nil)
			sendPkt3()
			sendSeq++
			lastPingAt = time.Now()

			if time.Since(lastReauthAt) >= 60*time.Second {
				sendPktReauth()
				authSendSeq++
				lastReauthAt = time.Now()
			}

			if time.Since(lastStatusLog) >= 10*time.Second {
				log.Print("still connected")
				lastStatusLog = time.Now()
			}
		}
	}
}