package cat

// icomnet.go — the NETWORK transport for the Icom backend. It talks the Icom IP
// remote protocol (the LAN server built into the IC-7610, the one the Icom
// Remote Utility speaks) directly, and presents the tunnelled CI-V byte stream
// as a plain civTransport (Read/Write). So the entire IcomController surface —
// freq/mode, receive-DSP, TX, scope, RIT, CW — runs unchanged over the network;
// only the transport differs. OpsLog thus replaces BOTH the Remote Utility and
// RS-BA1.
//
// The protocol (framing, passcode table, packet offsets, power-on) was
// reimplemented from the public wfview protocol and verified byte-for-byte
// against real Remote-Utility captures. No GPLv3 code is copied.
//
// Three UDP streams exist on the rig (control 50001 / CI-V 50002 / audio 50003);
// this transport uses control + CI-V (audio is not needed for CAT). Connect:
//   control: areYouThere→iAmHere→areYouReady→iAmReady → login → token → conninfo
//   civ:     areYouThere→…→iAmReady → openClose(open) → power-on
// then CI-V flows in data packets. A pump goroutine keeps both streams alive
// (ping replies + idle keepalives) and feeds received CI-V bytes to Read.

import (
	"encoding/binary"
	"fmt"
	"io"
	"net"
	"strings"
	"sync"
	"time"
)

var icnLE = binary.LittleEndian
var icnBE = binary.BigEndian

// NewIcomNet builds an (unconnected) Icom backend whose transport is the network
// stream. host is the rig's IP/hostname; user/pass are the rig's Network User1
// credentials. Reuses the whole IcomSerial controller — only `open` differs.
func NewIcomNet(host, user, pass string, civAddr int, digitalDefault string) *IcomSerial {
	if civAddr <= 0 || civAddr > 0xFF {
		civAddr = 0x98 // IC-7610
	}
	if digitalDefault == "" {
		digitalDefault = "FT8"
	}
	b := &IcomSerial{
		portName:   host,
		rigAddr:    byte(civAddr),
		digital:    strings.ToUpper(digitalDefault),
		model:      "Icom",
		scopeFixed: true,
	}
	b.open = func() (civTransport, error) {
		if strings.TrimSpace(host) == "" {
			return nil, fmt.Errorf("no rig host configured")
		}
		return dialIcomNet(host, user, pass, "OpsLog", b.rigAddr)
	}
	return b
}

// icomNet is the connected network transport. It satisfies civTransport.
type icomNet struct {
	ctrl *net.UDPConn // control stream (50001)
	civ  *net.UDPConn // CI-V stream (50002)

	cID, cRemote uint32 // control stream ids
	vID, vRemote uint32 // civ stream ids

	// Tracked-packet sequence + CI-V data sequence. Written only by Write (on the
	// CAT goroutine) and during dial — never by the pump — so no lock is needed.
	vTracked uint16
	vCivSeq  uint16

	rx       chan []byte   // CI-V byte chunks from civPump → Read
	leftover []byte        // partial chunk not yet returned by Read (Read-only)
	readTO   time.Duration // Read timeout (SetReadTimeout)

	// sentBuf keeps recently-sent tracked civ packets (by outer seq) so we can
	// answer the rig's UDP retransmit requests. Written by Write (CAT goroutine),
	// read by the pumps → guarded by sentMu.
	sentMu  sync.Mutex
	sentBuf map[uint16][]byte

	done      chan struct{}
	closeOnce sync.Once
}

func (n *icomNet) SetReadTimeout(d time.Duration) error { n.readTO = d; return nil }
func (n *icomNet) SetDTR(bool) error                    { return nil } // n/a on the network
func (n *icomNet) SetRTS(bool) error                    { return nil }

// Read returns tunnelled CI-V bytes, mimicking a serial port: (0,nil) on
// timeout, (n,nil) with data, (0,err) when the link is closed.
func (n *icomNet) Read(p []byte) (int, error) {
	if len(n.leftover) > 0 {
		k := copy(p, n.leftover)
		n.leftover = n.leftover[k:]
		return k, nil
	}
	to := n.readTO
	if to <= 0 {
		to = 60 * time.Millisecond
	}
	select {
	case f, ok := <-n.rx:
		if !ok {
			return 0, io.EOF
		}
		k := copy(p, f)
		if k < len(f) {
			n.leftover = append(n.leftover[:0], f[k:]...)
		}
		return k, nil
	case <-time.After(to):
		return 0, nil // timeout, no data
	case <-n.done:
		return 0, io.EOF
	}
}

// Write wraps raw CI-V bytes (FE FE … FD) in a data packet and sends them.
func (n *icomNet) Write(p []byte) (int, error) {
	if icnTrace {
		debugLog.Printf("icom net TX: % X", p)
	}
	seq := n.vTracked
	pkt := icnCivData(seq, n.vID, n.vRemote, n.vCivSeq, p)
	n.vTracked++
	n.vCivSeq++
	n.sentMu.Lock()
	n.sentBuf[seq] = pkt
	delete(n.sentBuf, seq-256) // keep the buffer bounded (~last 256 packets)
	n.sentMu.Unlock()
	if _, err := n.civ.Write(pkt); err != nil {
		return 0, err
	}
	return len(p), nil
}

// icnTrace toggles verbose CI-V request/reply logging for diagnosing the
// network transport (temporary).
var icnTrace = true

func (n *icomNet) Close() error {
	n.closeOnce.Do(func() {
		close(n.done)
		// Best-effort clean teardown.
		_, _ = n.civ.Write(icnOpenClose(n.vTracked, n.vID, n.vRemote, n.vCivSeq, 0x00)) // close
		_, _ = n.civ.Write(icnCtrl(0x05, 0, n.vID, n.vRemote))                          // disconnect
		_, _ = n.ctrl.Write(icnCtrl(0x05, 0, n.cID, n.cRemote))
		_ = n.civ.Close()
		_ = n.ctrl.Close()
	})
	return nil
}

// ctrlPump keeps the control stream (50001) alive: replies to the rig's pings
// and sends idle keepalives. Its own goroutine so it never throttles civPump.
func (n *icomNet) ctrlPump() {
	buf := make([]byte, 4096)
	lastIdle := time.Now()
	for {
		select {
		case <-n.done:
			return
		default:
		}
		_ = n.ctrl.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
		if k, err := n.ctrl.Read(buf); err == nil && k >= 16 {
			switch icnLE.Uint16(buf[4:]) {
			case 0x07: // ping
				_, _ = n.ctrl.Write(icnPingReply(buf[:k], n.cID, n.cRemote))
			case 0x01: // retransmit request
				if k >= 8 {
					n.resend(icnLE.Uint16(buf[6:]))
				}
			}
		}
		if time.Since(lastIdle) > 150*time.Millisecond {
			_, _ = n.ctrl.Write(icnCtrl(0x00, 0, n.cID, n.cRemote))
			lastIdle = time.Now()
		}
	}
}

// civPump owns the CI-V stream (50002): drains it as fast as packets arrive
// (its own goroutine — not throttled by the control reads), replies to pings,
// answers retransmit requests, skips scope frames, and feeds control CI-V bytes
// to Read via n.rx.
func (n *icomNet) civPump() {
	buf := make([]byte, 8192)
	lastIdle := time.Now()
	for {
		select {
		case <-n.done:
			return
		default:
		}
		_ = n.civ.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
		if k, err := n.civ.Read(buf); err == nil && k >= 16 {
			switch typ := icnLE.Uint16(buf[4:]); {
			case typ == 0x07: // ping
				_, _ = n.civ.Write(icnPingReply(buf[:k], n.vID, n.vRemote))
			case typ == 0x01: // retransmit request — resend that seq
				if k >= 8 {
					n.resend(icnLE.Uint16(buf[6:]))
				}
			case typ == 0x00 && k > 0x15 && buf[0x10] == 0xc1: // CI-V data
				civBytes := buf[0x15:k]
				// Skip scope (0x27) frames: over the network the rig streams the
				// panadapter continuously as large frames that would crowd control
				// replies out of rx. (Network scope is handled separately.)
				if !(len(civBytes) >= 5 && civBytes[4] == 0x27) {
					if icnTrace {
						debugLog.Printf("icom net RX: % X", civBytes)
					}
					cp := append([]byte(nil), civBytes...)
					select {
					case n.rx <- cp:
					case <-n.done:
						return
					default: // buffer full — drop oldest, enqueue newest
						select {
						case <-n.rx:
						default:
						}
						select {
						case n.rx <- cp:
						default:
						}
					}
				}
			}
		}
		if time.Since(lastIdle) > 150*time.Millisecond {
			_, _ = n.civ.Write(icnCtrl(0x00, 0, n.vID, n.vRemote))
			lastIdle = time.Now()
		}
	}
}

// resend re-transmits a previously-sent tracked CI-V packet the rig asks for
// (its UDP retransmit mechanism). Without this the rig drops the whole session
// after a few seconds when a packet is lost under load.
func (n *icomNet) resend(seq uint16) {
	n.sentMu.Lock()
	pkt := n.sentBuf[seq]
	n.sentMu.Unlock()
	if pkt != nil {
		_, _ = n.civ.Write(pkt)
	}
}

// ------------------------- connect -------------------------

func dialIcomNet(host, user, pass, compName string, rigAddr byte) (*icomNet, error) {
	debugLog.Printf("icom net: connecting to %s (user %q, comp %q, rig addr 0x%02X)", host, user, compName, rigAddr)
	// ---- control stream (50001): handshake → login → token → conninfo ----
	craddr, err := net.ResolveUDPAddr("udp4", net.JoinHostPort(host, "50001"))
	if err != nil {
		return nil, err
	}
	ctrl, err := net.DialUDP("udp4", nil, craddr)
	if err != nil {
		return nil, fmt.Errorf("dial control: %w", err)
	}
	cID := icnLocalID(ctrl)
	cRemote, err := icnHandshake(ctrl, cID)
	if err != nil {
		_ = ctrl.Close()
		debugLog.Printf("icom net: control handshake FAILED (rig unreachable at %s:50001?): %v", host, err)
		return nil, fmt.Errorf("control handshake: %w", err)
	}
	debugLog.Printf("icom net: control link up (rig id 0x%08X) — logging in", cRemote)

	var cTracked, cInner uint16 = 1, 1
	tokReq := uint16(0x0c77)
	_, _ = ctrl.Write(icnLogin(cTracked, cInner, tokReq, cID, cRemote, 0, user, pass, compName))
	cTracked++
	cInner++

	var token uint32
	buf := make([]byte, 2048)
	deadline := time.Now().Add(5 * time.Second)
	for token == 0 && time.Now().Before(deadline) {
		p, ok := icnRecv(ctrl, 200, buf)
		if !ok {
			continue
		}
		length := icnLE.Uint32(p[0:])
		typ := icnLE.Uint16(p[4:])
		if typ == 0x00 && length == 0x60 && len(p) >= 0x34 { // login response
			token = icnLE.Uint32(p[0x1c:])
			if e := icnLE.Uint32(p[0x30:]); e != 0 || token == 0 {
				_ = ctrl.Close()
				debugLog.Printf("icom net: LOGIN REJECTED (err=0x%08X) — wrong Network User1 ID/Password", e)
				return nil, fmt.Errorf("login rejected — check the rig's Network User1 ID/Password")
			}
			_, _ = ctrl.Write(icnToken(cTracked, cInner, tokReq, cID, cRemote, token))
			cTracked++
			cInner++
			debugLog.Printf("icom net: LOGIN OK, token 0x%08X", token)
		} else if typ == 0x07 {
			_, _ = ctrl.Write(icnPingReply(p, cID, cRemote))
		}
	}
	if token == 0 {
		_ = ctrl.Close()
		debugLog.Printf("icom net: login TIMED OUT (no token in 5s) — check host/credentials")
		return nil, fmt.Errorf("login timed out (no token) — check host/credentials")
	}

	// Learn the rig's MAC from its conninfo push (144B) to echo in our conninfo.
	var rigMAC []byte
	macEnd := time.Now().Add(1200 * time.Millisecond)
	for time.Now().Before(macEnd) {
		p, ok := icnRecv(ctrl, 150, buf)
		if !ok {
			continue
		}
		if len(p) >= 0x30 && icnLE.Uint32(p[0:]) == 0x90 { // 144-byte conninfo push
			rigMAC = append([]byte(nil), p[0x2a:0x30]...)
		}
		if icnLE.Uint16(p[4:]) == 0x07 {
			_, _ = ctrl.Write(icnPingReply(p, cID, cRemote))
		}
		if rigMAC != nil {
			break
		}
	}
	if rigMAC == nil {
		rigMAC = make([]byte, 6)
	}

	_, _ = ctrl.Write(icnConnInfo(cTracked, cInner, tokReq, cID, cRemote, token, user, rigMAC, 50002, 50003))
	cTracked++
	cInner++
	drainEnd := time.Now().Add(500 * time.Millisecond)
	for time.Now().Before(drainEnd) {
		if p, ok := icnRecv(ctrl, 100, buf); ok && icnLE.Uint16(p[4:]) == 0x07 {
			_, _ = ctrl.Write(icnPingReply(p, cID, cRemote))
		}
	}

	// ---- CI-V stream (50002): bind LOCAL :50002 (the announced civport) ----
	vraddr, err := net.ResolveUDPAddr("udp4", net.JoinHostPort(host, "50002"))
	if err != nil {
		_ = ctrl.Close()
		return nil, err
	}
	debugLog.Printf("icom net: conninfo sent (rig mac % X) — opening CI-V stream", rigMAC)
	civ, err := net.DialUDP("udp4", &net.UDPAddr{Port: 50002}, vraddr)
	if err != nil {
		_ = ctrl.Close()
		debugLog.Printf("icom net: cannot bind local :50002 — the Icom Remote Utility is probably still running: %v", err)
		return nil, fmt.Errorf("dial CI-V (local :50002 — is the Icom Remote Utility still running?): %w", err)
	}
	vID := icnLocalID(civ)
	vRemote, err := icnHandshake(civ, vID)
	if err != nil {
		_ = civ.Close()
		_ = ctrl.Close()
		debugLog.Printf("icom net: CI-V handshake FAILED: %v", err)
		return nil, fmt.Errorf("CI-V handshake: %w", err)
	}
	debugLog.Printf("icom net: CI-V link up — sending power-on, waiting for the rig to boot (~15s)")

	// Bigger receive buffers so a burst of scope/CI-V packets doesn't overflow
	// (dropped packets → the rig's retransmit requests → session drop).
	_ = ctrl.SetReadBuffer(1 << 20)
	_ = civ.SetReadBuffer(1 << 20)

	n := &icomNet{
		ctrl: ctrl, civ: civ,
		cID: cID, cRemote: cRemote, vID: vID, vRemote: vRemote,
		vTracked: 1, vCivSeq: 1,
		rx:      make(chan []byte, 256),
		sentBuf: make(map[uint16][]byte),
		done:    make(chan struct{}),
	}
	// openClose(open) starts the CI-V data flow.
	ocPkt := icnOpenClose(n.vTracked, vID, vRemote, n.vCivSeq, 0x04)
	n.sentBuf[n.vTracked] = ocPkt
	_, _ = civ.Write(ocPkt)
	n.vTracked++
	n.vCivSeq++
	// Power-on (the rig may be in standby — it NG's every command until on):
	// an FE wake preamble then FE FE <rig> E0 18 01 FD. Harmless if already on.
	po := make([]byte, 0, 32)
	for i := 0; i < 25; i++ {
		po = append(po, 0xFE)
	}
	po = append(po, 0xFE, 0xFE, rigAddr, 0xE0, 0x18, 0x01, 0xFD)
	poPkt := icnCivData(n.vTracked, vID, vRemote, n.vCivSeq, po)
	n.sentBuf[n.vTracked] = poPkt
	_, _ = civ.Write(poPkt)
	n.vTracked++
	n.vCivSeq++

	// Wait for the rig to finish booting: a rig woken from standby NG's/ignores
	// commands for ~10-15 s. Poll read-freq (keeping both streams alive) until it
	// answers, so Connect only returns a READY link — otherwise the manager's
	// read-timeouts would flap the connection during boot. Give up after 25 s and
	// return anyway (the rig may already be on and just quiet).
	if n.waitReady(rigAddr, 25*time.Second) {
		debugLog.Printf("icom net: rig is READY (answered read-freq) — connection up ✓")
	} else {
		debugLog.Printf("icom net: boot wait timed out (25s, no freq reply) — proceeding anyway")
	}

	go n.ctrlPump()
	go n.civPump()
	return n, nil
}

// waitReady polls read-freq until the rig replies (booted) or timeout, replying
// to pings and sending idle keepalives so the session stays up. Runs before the
// pump goroutine starts, so it owns the socket reads.
func (n *icomNet) waitReady(rigAddr byte, timeout time.Duration) bool {
	cbuf := make([]byte, 4096)
	vbuf := make([]byte, 4096)
	readFreq := []byte{0xFE, 0xFE, rigAddr, 0xE0, 0x03, 0xFD}
	end := time.Now().Add(timeout)
	var lastPoll, lastIdle time.Time
	for time.Now().Before(end) {
		if p, ok := icnRecv(n.ctrl, 25, cbuf); ok && icnLE.Uint16(p[4:]) == 0x07 {
			_, _ = n.ctrl.Write(icnPingReply(p, n.cID, n.cRemote))
		}
		if p, ok := icnRecv(n.civ, 25, vbuf); ok {
			typ := icnLE.Uint16(p[4:])
			if typ == 0x07 {
				_, _ = n.civ.Write(icnPingReply(p, n.vID, n.vRemote))
			} else if typ == 0x00 && len(p) > 0x15 && p[0x10] == 0xc1 {
				f := p[0x15:]
				// A frequency reply from the rig: FE FE E0 <rig> 03 …
				if len(f) >= 6 && f[0] == 0xFE && f[1] == 0xFE && f[3] == rigAddr && f[4] == 0x03 {
					return true
				}
			}
		}
		if time.Since(lastIdle) > 180*time.Millisecond {
			_, _ = n.ctrl.Write(icnCtrl(0x00, 0, n.cID, n.cRemote))
			_, _ = n.civ.Write(icnCtrl(0x00, 0, n.vID, n.vRemote))
			lastIdle = time.Now()
		}
		if time.Since(lastPoll) > 1000*time.Millisecond {
			_, _ = n.civ.Write(icnCivData(n.vTracked, n.vID, n.vRemote, n.vCivSeq, readFreq))
			n.vTracked++
			n.vCivSeq++
			lastPoll = time.Now()
		}
	}
	return false
}

// icnHandshake: areYouThere(seq0) → iAmHere → areYouReady(seq1) → iAmReady.
func icnHandshake(c *net.UDPConn, myID uint32) (uint32, error) {
	buf := make([]byte, 2048)
	_, _ = c.Write(icnCtrl(0x03, 0, myID, 0))
	var remoteID uint32
	deadline := time.Now().Add(4 * time.Second)
	lastTry := time.Now()
	for time.Now().Before(deadline) {
		p, ok := icnRecv(c, 200, buf)
		if !ok {
			if remoteID == 0 && time.Since(lastTry) > 500*time.Millisecond {
				_, _ = c.Write(icnCtrl(0x03, 0, myID, 0))
				lastTry = time.Now()
			}
			continue
		}
		typ := icnLE.Uint16(p[4:])
		sentid := icnLE.Uint32(p[8:])
		switch typ {
		case 0x04: // iAmHere
			remoteID = sentid
			_, _ = c.Write(icnCtrl(0x06, 1, myID, remoteID))
		case 0x06: // iAmReady
			if remoteID != 0 {
				return remoteID, nil
			}
		case 0x07: // ping
			_, _ = c.Write(icnPingReply(p, myID, remoteID))
		}
	}
	return 0, fmt.Errorf("handshake timeout")
}

func icnRecv(c *net.UDPConn, ms int, buf []byte) ([]byte, bool) {
	_ = c.SetReadDeadline(time.Now().Add(time.Duration(ms) * time.Millisecond))
	k, err := c.Read(buf)
	if err != nil || k < 16 {
		return nil, false
	}
	return buf[:k], true
}

func icnLocalID(c *net.UDPConn) uint32 {
	a := c.LocalAddr().(*net.UDPAddr)
	ip := a.IP.To4()
	if ip == nil {
		ip = []byte{192, 168, 0, 1}
	}
	return uint32(ip[0])<<24 | uint32(ip[1])<<16 | uint32(uint16(a.Port))
}

// ------------------------- packet builders -------------------------
// (offsets verified vs wfview structs + real captures)

func icnCtrl(typ, seq uint16, sentid, rcvdid uint32) []byte {
	b := make([]byte, 16)
	icnLE.PutUint32(b[0:], 0x10)
	icnLE.PutUint16(b[4:], typ)
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	return b
}

func icnPingReply(pkt []byte, myID, remoteID uint32) []byte {
	r := append([]byte(nil), pkt...)
	if len(r) >= 17 {
		icnLE.PutUint32(r[8:], myID)
		icnLE.PutUint32(r[12:], remoteID)
		r[16] = 0x01
	}
	return r
}

func icnLogin(seq, innerSeq, tokReq uint16, sentid, rcvdid, token uint32, user, pass, name string) []byte {
	b := make([]byte, 0x80)
	icnLE.PutUint32(b[0:], 0x80)
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	icnBE.PutUint32(b[0x10:], 0x80-0x10)
	b[0x14] = 0x01
	b[0x15] = 0x00
	icnBE.PutUint16(b[0x16:], innerSeq)
	icnLE.PutUint16(b[0x1a:], tokReq)
	icnLE.PutUint32(b[0x1c:], token)
	copy(b[0x40:0x50], icnPasscode(user))
	copy(b[0x50:0x60], icnPasscode(pass))
	nm := name
	if len(nm) > 16 {
		nm = nm[:16]
	}
	copy(b[0x60:0x70], []byte(nm))
	return b
}

func icnToken(seq, innerSeq, tokReq uint16, sentid, rcvdid, token uint32) []byte {
	b := make([]byte, 0x40)
	icnLE.PutUint32(b[0:], 0x40)
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	icnBE.PutUint32(b[0x10:], 0x40-0x10)
	b[0x14] = 0x01
	b[0x15] = 0x02
	icnBE.PutUint16(b[0x16:], innerSeq)
	icnLE.PutUint16(b[0x1a:], tokReq)
	icnLE.PutUint32(b[0x1c:], token)
	return b
}

func icnConnInfo(seq, innerSeq, tokReq uint16, sentid, rcvdid, token uint32, user string, rigMAC []byte, civPort, audioPort uint16) []byte {
	b := make([]byte, 0x90)
	icnLE.PutUint32(b[0:], 0x90)
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	icnBE.PutUint32(b[0x10:], 0x90-0x10)
	b[0x14] = 0x01
	b[0x15] = 0x03 // requesttype = conninfo / open streams
	icnBE.PutUint16(b[0x16:], innerSeq)
	icnLE.PutUint16(b[0x1a:], tokReq)
	icnLE.PutUint32(b[0x1c:], token)
	icnLE.PutUint16(b[0x27:], 0x8010) // commoncap
	copy(b[0x2a:0x30], rigMAC)
	copy(b[0x40:0x60], []byte("IC-7610"))
	copy(b[0x60:0x70], icnPasscode(user))
	b[0x70] = 0x00 // rxenable (audio off — CI-V only)
	b[0x71] = 0x00 // txenable
	b[0x72] = 0x10 // rxcodec
	b[0x73] = 0x04 // txcodec
	icnBE.PutUint32(b[0x74:], 16000)
	icnBE.PutUint32(b[0x78:], 8000)
	icnBE.PutUint32(b[0x7c:], uint32(civPort))
	icnBE.PutUint32(b[0x80:], uint32(audioPort))
	icnBE.PutUint32(b[0x84:], 100)
	b[0x88] = 0x00
	return b
}

func icnOpenClose(seq uint16, sentid, rcvdid uint32, civSeq uint16, magic byte) []byte {
	b := make([]byte, 0x16)
	icnLE.PutUint32(b[0:], 0x16)
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	icnLE.PutUint16(b[0x10:], 0x01c0)
	icnBE.PutUint16(b[0x13:], civSeq)
	b[0x15] = magic
	return b
}

func icnCivData(seq uint16, sentid, rcvdid uint32, civSeq uint16, civ []byte) []byte {
	nn := 0x15 + len(civ)
	b := make([]byte, nn)
	icnLE.PutUint32(b[0:], uint32(nn))
	icnLE.PutUint16(b[6:], seq)
	icnLE.PutUint32(b[8:], sentid)
	icnLE.PutUint32(b[12:], rcvdid)
	b[0x10] = 0xc1
	icnLE.PutUint16(b[0x11:], uint16(len(civ)))
	icnBE.PutUint16(b[0x13:], civSeq)
	copy(b[0x15:], civ)
	return b
}

// icnPasscodeSeq — Icom's obfuscation table (values at index 0x20..0x7e).
// VERIFIED: user "f6bgc" → 3F 65 50 25 55 (matches the capture).
var icnPasscodeSeq = [256]byte{
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0x47, 0x5d, 0x4c, 0x42, 0x66, 0x20, 0x23, 0x46, 0x4e, 0x57, 0x45, 0x3d, 0x67, 0x76, 0x60, 0x41, 0x62, 0x39, 0x59, 0x2d, 0x68, 0x7e,
	0x7c, 0x65, 0x7d, 0x49, 0x29, 0x72, 0x73, 0x78, 0x21, 0x6e, 0x5a, 0x5e, 0x4a, 0x3e, 0x71, 0x2c, 0x2a, 0x54, 0x3c, 0x3a, 0x63, 0x4f,
	0x43, 0x75, 0x27, 0x79, 0x5b, 0x35, 0x70, 0x48, 0x6b, 0x56, 0x6f, 0x34, 0x32, 0x6c, 0x30, 0x61, 0x6d, 0x7b, 0x2f, 0x4b, 0x64, 0x38,
	0x2b, 0x2e, 0x50, 0x40, 0x3f, 0x55, 0x33, 0x37, 0x25, 0x77, 0x24, 0x26, 0x74, 0x6a, 0x28, 0x53, 0x4d, 0x69, 0x22, 0x5c, 0x44, 0x31,
	0x36, 0x58, 0x3b, 0x7a, 0x51, 0x5f, 0x52,
}

func icnPasscode(s string) []byte {
	out := make([]byte, 0, len(s))
	for i := 0; i < len(s) && i < 16; i++ {
		p := int(s[i]) + i
		if p > 126 {
			p = 32 + p%127
		}
		out = append(out, icnPasscodeSeq[p])
	}
	return out
}