// Package cluster provides a multi-server DX cluster client (telnet) —
// connects concurrently to several AR-Cluster / CC-Cluster / DXSpider
// nodes, logs in with the operator's callsign, optionally sends an init
// command list, and streams DX spots back to the UI via a callback.
//
// Spot parsing is tolerant of the dozens of slight format variations
// between cluster flavours (the prompt, the trailing locator, the time
// format). Anything that doesn't match the spot regex is treated as
// banner/chat noise and ignored, not surfaced as an error.
package cluster

import (
	"bufio"
	"fmt"
	"net"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"
)

// ServerConfig is the persisted shape of one cluster node. Mirrors the
// columns of the cluster_servers table; the frontend SettingsPanel
// pushes one of these per row.
type ServerConfig struct {
	ID            int64  `json:"id"`
	Name          string `json:"name"`
	Host          string `json:"host"`
	Port          int    `json:"port"`
	LoginOverride string `json:"login_override"`
	Password      string `json:"password,omitempty"`
	InitCommands  string `json:"init_commands"` // newline-separated, sent post-login
	Enabled       bool   `json:"enabled"`
	SortOrder     int    `json:"sort_order"`
}

// Spot is a single DX spot as parsed from the cluster stream.
// Country/Continent are filled by the caller (app.go) before the spot
// is emitted to the UI, so the table never has empty country cells
// flickering in for a few hundred ms.
type Spot struct {
	SourceID    int64     `json:"source_id"`              // ID of the cluster server this came from
	SourceName  string    `json:"source_name"`            // display name (handy in the UI when multiple servers)
	Spotter     string    `json:"spotter"`                // DE field
	DXCall      string    `json:"dx_call"`                // the DX station heard
	FreqKHz     float64   `json:"freq_khz"`
	FreqHz      int64     `json:"freq_hz"`
	Band        string    `json:"band,omitempty"`
	Comment     string    `json:"comment,omitempty"`
	Locator     string    `json:"locator,omitempty"`      // spotter grid (optional)
	TimeUTC     string    `json:"time_utc,omitempty"`
	Country     string    `json:"country,omitempty"`      // DXCC entity name (cty.dat)
	Continent   string    `json:"continent,omitempty"`    // 2-letter continent
	ReceivedAt  time.Time `json:"received_at"`
	Raw         string    `json:"raw"`
}

// State enumerates the per-server lifecycle.
type State string

const (
	StateDisconnected State = "disconnected"
	StateConnecting   State = "connecting"
	StateConnected    State = "connected"
	StateReconnecting State = "reconnecting"
	StateError        State = "error"
)

// ServerStatus is one row of the runtime status table — one entry per
// active session.
type ServerStatus struct {
	ServerID    int64     `json:"server_id"`
	Name        string    `json:"name"`
	Host        string    `json:"host"`
	Port        int       `json:"port"`
	State       State     `json:"state"`
	Login       string    `json:"login,omitempty"`
	Error       string    `json:"error,omitempty"`
	ConnectedAt time.Time `json:"connected_at,omitempty"`
	SpotsCount  int       `json:"spots_count,omitempty"`
	Retries     int       `json:"retries,omitempty"`
}

// session is one telnet connection bound to a single server config.
// Internal — callers use Manager. The onStatus callback is fire-and-
// forget: it tells the manager something changed; the frontend fetches
// the new aggregate via Status() rather than receiving per-server diffs.
type session struct {
	cfg      ServerConfig
	login    string
	onSpot   func(Spot)
	onStatus func()

	mu        sync.RWMutex
	status    ServerStatus
	conn      net.Conn
	stopCh    chan struct{}
	doneCh    chan struct{}
	stopped   bool // guards against double-stop on the same session
	spotsCnt  int
}

// Manager owns N sessions, one per enabled server. Safe for concurrent
// use from any goroutine; I/O is on per-session background goroutines.
type Manager struct {
	mu       sync.RWMutex
	sessions map[int64]*session
	onSpot   func(Spot)
	onStatus func()
}

// NewManager builds an empty manager. emitSpot is called for each parsed
// spot (with the source server filled in). emitStatusChanged is called
// whenever ANY server's status changes — the frontend then re-fetches
// the aggregate Status() via a Wails binding.
func NewManager(emitSpot func(Spot), emitStatusChanged func()) *Manager {
	return &Manager{
		sessions: make(map[int64]*session),
		onSpot:   emitSpot,
		onStatus: emitStatusChanged,
	}
}

// Status returns a snapshot of every running session's status.
func (m *Manager) Status() []ServerStatus {
	m.mu.RLock()
	defer m.mu.RUnlock()
	out := make([]ServerStatus, 0, len(m.sessions))
	for _, s := range m.sessions {
		out = append(out, s.snapshot())
	}
	return out
}

// StartServer launches a session for cfg. login is the resolved callsign
// to send (empty = anonymous). If a session for the same ID is already
// running it is restarted with the new config.
func (m *Manager) StartServer(cfg ServerConfig, login string) {
	m.StopServer(cfg.ID)
	if !cfg.Enabled || cfg.Host == "" {
		return
	}
	s := &session{
		cfg:      cfg,
		login:    login,
		onSpot:   m.onSpot,
		onStatus: m.emitStatus,
		stopCh:   make(chan struct{}),
		doneCh:   make(chan struct{}),
		status: ServerStatus{
			ServerID: cfg.ID, Name: cfg.Name, Host: cfg.Host, Port: cfg.Port,
			Login: login, State: StateConnecting,
		},
	}
	m.mu.Lock()
	m.sessions[cfg.ID] = s
	m.mu.Unlock()
	s.emitStatus()
	go s.run()
}

// StopServer terminates the session for the given ID (if any) and waits
// for its goroutine to exit.
func (m *Manager) StopServer(id int64) {
	m.mu.Lock()
	s, ok := m.sessions[id]
	if ok {
		delete(m.sessions, id)
	}
	remaining := len(m.sessions)
	m.mu.Unlock()
	fmt.Printf("cluster.StopServer id=%d found=%v remaining=%d\n", id, ok, remaining)
	if !ok {
		return
	}
	s.stop()
	fmt.Printf("cluster.StopServer id=%d stopped successfully\n", id)
	m.emitStatus()
}

// StopAll closes every running session.
func (m *Manager) StopAll() {
	m.mu.Lock()
	all := make([]*session, 0, len(m.sessions))
	for _, s := range m.sessions {
		all = append(all, s)
	}
	m.sessions = make(map[int64]*session)
	m.mu.Unlock()
	for _, s := range all {
		s.stop()
	}
	m.emitStatus()
}

// SendCommand writes raw text (a CRLF is appended) to the session for
// the given server ID. Used for "show last 30", "set/skimmer", etc.
func (m *Manager) SendCommand(serverID int64, cmd string) error {
	m.mu.RLock()
	s, ok := m.sessions[serverID]
	m.mu.RUnlock()
	if !ok {
		return fmt.Errorf("no active session for server %d", serverID)
	}
	return s.send(cmd)
}

func (m *Manager) emitStatus() {
	if m.onStatus != nil {
		m.onStatus()
	}
}

// ---------- session ----------

func (s *session) snapshot() ServerStatus {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.status
}

func (s *session) emitStatus() {
	if s.onStatus != nil {
		s.onStatus()
	}
}

func (s *session) send(cmd string) error {
	s.mu.RLock()
	conn := s.conn
	s.mu.RUnlock()
	if conn == nil {
		return fmt.Errorf("session %q not connected", s.cfg.Name)
	}
	_ = conn.SetWriteDeadline(time.Now().Add(5 * time.Second))
	_, err := conn.Write([]byte(strings.TrimRight(cmd, "\r\n") + "\r\n"))
	return err
}

func (s *session) stop() {
	// Critical: do NOT nil out s.stopCh — the supervisor goroutine reads
	// `<-s.stopCh` in its select. Setting the field to nil would make
	// `<-nil` block forever, leaving the supervisor stuck on its backoff
	// timer and then re-dialing → a "deleted" cluster keeps spotting.
	// We just close() the channel and let the goroutine see the broadcast.
	s.mu.Lock()
	if s.stopped {
		s.mu.Unlock()
		return
	}
	s.stopped = true
	stop, done := s.stopCh, s.doneCh
	conn := s.conn
	s.mu.Unlock()
	if conn != nil {
		_ = conn.Close()
	}
	if stop != nil {
		close(stop)
	}
	if done != nil {
		<-done
	}
}

// run is the per-session supervisor: keeps trying to connect until
// Stop is called. Backoff caps at 60s, resets after a 30s healthy link.
func (s *session) run() {
	defer close(s.doneCh)
	backoff := []time.Duration{2, 5, 10, 30, 60}
	attempt := 0
	for {
		select {
		case <-s.stopCh:
			return
		default:
		}
		connectedAt, err := s.runOnce()
		select {
		case <-s.stopCh:
			return
		default:
		}
		if !connectedAt.IsZero() && time.Since(connectedAt) > 30*time.Second {
			attempt = 0
		}
		idx := attempt
		if idx >= len(backoff) {
			idx = len(backoff) - 1
		}
		delay := backoff[idx] * time.Second
		attempt++

		s.mu.Lock()
		s.status.State = StateReconnecting
		if err != nil {
			s.status.Error = err.Error()
		}
		s.status.Retries = attempt
		s.mu.Unlock()
		s.emitStatus()

		select {
		case <-s.stopCh:
			return
		case <-time.After(delay):
		}
	}
}

// runOnce dials, optionally logs in, sends init commands, parses spots.
// Returns the moment we marked the link "connected" (zero if dial failed)
// and the error that ended the session (nil if stopCh).
func (s *session) runOnce() (time.Time, error) {
	addr := fmt.Sprintf("%s:%d", s.cfg.Host, s.cfg.Port)
	conn, err := net.DialTimeout("tcp", addr, 10*time.Second)
	if err != nil {
		return time.Time{}, fmt.Errorf("dial %s: %w", addr, err)
	}
	s.mu.Lock()
	s.conn = conn
	s.mu.Unlock()
	defer func() {
		s.mu.Lock()
		if s.conn == conn {
			s.conn = nil
		}
		s.mu.Unlock()
		_ = conn.Close()
	}()

	// Login: send on first prompt OR blindly after 1.5s. Many DXSpider
	// nodes accept the callsign without re-prompting.
	loginSent := false
	if s.login != "" {
		go func() {
			select {
			case <-s.stopCh:
				return
			case <-time.After(1500 * time.Millisecond):
				if !loginSent {
					_, _ = conn.Write([]byte(s.login + "\r\n"))
				}
			}
		}()
	}

	// Init commands: fire 1s after login goes through. Each command on
	// its own line; blank lines and "//" comments are skipped.
	initFired := false
	fireInitCommands := func() {
		if initFired || strings.TrimSpace(s.cfg.InitCommands) == "" {
			return
		}
		initFired = true
		go func() {
			time.Sleep(1 * time.Second)
			for _, line := range strings.Split(s.cfg.InitCommands, "\n") {
				line = strings.TrimRight(line, "\r")
				line = strings.TrimSpace(line)
				if line == "" || strings.HasPrefix(line, "//") {
					continue
				}
				select {
				case <-s.stopCh:
					return
				default:
				}
				_, _ = conn.Write([]byte(line + "\r\n"))
				time.Sleep(500 * time.Millisecond)
			}
		}()
	}

	var connectedAt time.Time
	rd := bufio.NewReader(conn)
	for {
		select {
		case <-s.stopCh:
			return connectedAt, nil
		default:
		}

		_ = conn.SetReadDeadline(time.Now().Add(120 * time.Second))
		line, err := rd.ReadString('\n')
		if err != nil {
			return connectedAt, fmt.Errorf("read: %w", err)
		}
		line = strings.TrimRight(line, "\r\n")
		if line == "" {
			continue
		}

		// Login on explicit prompt.
		if !loginSent && s.login != "" && isLoginPrompt(line) {
			_, _ = conn.Write([]byte(s.login + "\r\n"))
			loginSent = true
			continue
		}
		// Password on prompt (rare).
		if loginSent && s.cfg.Password != "" && isPasswordPrompt(line) {
			_, _ = conn.Write([]byte(s.cfg.Password + "\r\n"))
			continue
		}

		// Mark connected once we've sent login OR seen a welcome banner.
		if s.snapshot().State != StateConnected && (loginSent || isWelcome(line)) {
			connectedAt = time.Now()
			s.mu.Lock()
			s.status.State = StateConnected
			s.status.ConnectedAt = connectedAt
			s.status.Error = ""
			s.mu.Unlock()
			s.emitStatus()
			fireInitCommands()
		}

		if spot, ok := parseSpot(line); ok {
			spot.SourceID = s.cfg.ID
			spot.SourceName = s.cfg.Name
			s.mu.Lock()
			s.spotsCnt++
			s.status.SpotsCount = s.spotsCnt
			s.mu.Unlock()
			if s.onSpot != nil {
				s.onSpot(spot)
			}
		}
	}
}

// ---------- parsing ----------

// spotRE matches "DX de SPOTTER: FREQ DXCALL COMMENT TIME [LOC]".
var spotRE = regexp.MustCompile(
	`^\s*DX\s+de\s+([A-Z0-9/#\-]+):?\s+(\d+\.?\d*)\s+([A-Z0-9/]+)\s+(.*?)\s+(\d{4}Z?)(?:\s+([A-R]{2}\d{2}(?:[A-X]{2})?))?\s*$`,
)

func parseSpot(line string) (Spot, bool) {
	m := spotRE.FindStringSubmatch(line)
	if m == nil {
		return Spot{}, false
	}
	freqKHz, err := strconv.ParseFloat(m[2], 64)
	if err != nil {
		return Spot{}, false
	}
	freqHz := int64(freqKHz*1000 + 0.5)
	return Spot{
		Spotter:    strings.ToUpper(m[1]),
		FreqKHz:    freqKHz,
		FreqHz:     freqHz,
		Band:       bandFromHz(freqHz),
		DXCall:     strings.ToUpper(m[3]),
		Comment:    strings.TrimSpace(m[4]),
		TimeUTC:    m[5],
		Locator:    strings.ToUpper(m[6]),
		ReceivedAt: time.Now(),
		Raw:        line,
	}, true
}

func isLoginPrompt(s string) bool {
	low := strings.ToLower(s)
	return strings.Contains(low, "login:") ||
		strings.Contains(low, "please enter your call") ||
		strings.Contains(low, "your call:") ||
		strings.HasSuffix(strings.TrimSpace(low), "callsign:")
}

func isPasswordPrompt(s string) bool {
	low := strings.ToLower(s)
	return strings.Contains(low, "password:") || strings.Contains(low, "pwd:")
}

func isWelcome(s string) bool {
	low := strings.ToLower(s)
	return strings.Contains(low, "welcome") ||
		strings.Contains(low, "logged in") ||
		strings.Contains(low, "started")
}

func bandFromHz(hz int64) string {
	mhz := float64(hz) / 1_000_000
	switch {
	case mhz >= 1.8 && mhz <= 2.0:
		return "160m"
	case mhz >= 3.5 && mhz <= 4.0:
		return "80m"
	case mhz >= 5.3 && mhz <= 5.5:
		return "60m"
	case mhz >= 7.0 && mhz <= 7.3:
		return "40m"
	case mhz >= 10.1 && mhz <= 10.15:
		return "30m"
	case mhz >= 14.0 && mhz <= 14.35:
		return "20m"
	case mhz >= 18.068 && mhz <= 18.168:
		return "17m"
	case mhz >= 21.0 && mhz <= 21.45:
		return "15m"
	case mhz >= 24.89 && mhz <= 24.99:
		return "12m"
	case mhz >= 28.0 && mhz <= 29.7:
		return "10m"
	case mhz >= 50.0 && mhz <= 54.0:
		return "6m"
	case mhz >= 70.0 && mhz <= 70.5:
		return "4m"
	case mhz >= 144.0 && mhz <= 148.0:
		return "2m"
	case mhz >= 222.0 && mhz <= 225.0:
		return "1.25m"
	case mhz >= 420.0 && mhz <= 450.0:
		return "70cm"
	case mhz >= 902.0 && mhz <= 928.0:
		return "33cm"
	case mhz >= 1240.0 && mhz <= 1300.0:
		return "23cm"
	}
	return ""
}