// Package cat drives the transceiver via swappable backends (OmniRig, Flex…)
// and pushes state changes to the UI through an injected emitter callback.
//
// The poll loop runs on an OS-thread-locked goroutine so COM-based backends
// (OmniRig) work correctly — COM is thread-affine on Windows and must be
// initialised, used and uninitialised from the same OS thread.
package cat

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

// Backend abstracts a specific transceiver-control library. All methods run
// on the dedicated CAT goroutine spawned by Manager — implementations can
// assume single-threaded access and can safely manage thread-bound resources
// (e.g. COM objects in OmniRig).
type Backend interface {
	Name() string // "omnirig" | "flex" | …
	Connect() error
	Disconnect()
	ReadState() (RigState, error)
	SetFrequency(hz int64) error
	// SetMode receives an ADIF mode string (SSB, CW, FT8, RTTY, AM, FM…).
	// Implementations decide USB vs LSB (typically by current freq) and
	// generic vs specific digital modes (most rigs just have DATA).
	SetMode(mode string) error
}

// RigState is the snapshot exchanged with the frontend.
//
// FreqHz follows the ADIF FREQ convention: it is the TX frequency. When the
// rig is in split, FreqHz is the inactive VFO (where the operator transmits)
// and RxFreqHz is the active VFO (where they listen). When not split,
// RxFreqHz is 0 — the UI shouldn't show a redundant RX field.
type RigState struct {
	Enabled   bool      `json:"enabled"`               // user toggled CAT on
	Connected bool      `json:"connected"`             // backend says rig is online
	Backend   string    `json:"backend,omitempty"`     // active backend name
	RigNum    int       `json:"rig_num,omitempty"`     // OmniRig slot 1 or 2 (when applicable)
	Rig       string    `json:"rig,omitempty"`         // rig model (best-effort)
	FreqHz    int64     `json:"freq_hz,omitempty"`     // TX freq (= active VFO when not split)
	RxFreqHz  int64     `json:"freq_rx_hz,omitempty"`  // RX freq, only set when Split
	Split     bool      `json:"split,omitempty"`       // rig is in split mode
	Mode      string    `json:"mode,omitempty"`        // ADIF mode (SSB/CW/DATA/AM/FM/RTTY)
	Band      string    `json:"band,omitempty"`        // computed from FreqHz
	Vfo       string    `json:"vfo,omitempty"`         // "A" | "B" | "AA" | "AB" | "BA" | "BB"
	Error     string    `json:"error,omitempty"`       // last connect/poll error if any
	UpdatedAt time.Time `json:"updated_at,omitempty"`
}

// Manager owns the active backend and runs the polling loop.
type Manager struct {
	mu      sync.RWMutex
	state   RigState
	emit    func(RigState)
	backend Backend

	// Set when running. nil when stopped.
	stopCh chan struct{}
	doneCh chan struct{}
	cmdCh  chan func() // marshall arbitrary work onto the CAT goroutine

	pollEvery time.Duration
	cmdDelay  time.Duration // pause after each command (some rigs need it)
}

func NewManager(emit func(RigState)) *Manager {
	return &Manager{emit: emit, pollEvery: 250 * time.Millisecond}
}

// SetPollInterval changes the polling cadence. Caps at 50ms…2s to avoid
// either hammering the rig or feeling laggy.
func (m *Manager) SetPollInterval(d time.Duration) {
	if d < 50*time.Millisecond {
		d = 50 * time.Millisecond
	}
	if d > 2*time.Second {
		d = 2 * time.Second
	}
	m.mu.Lock()
	m.pollEvery = d
	m.mu.Unlock()
}

// SetCommandDelay sets a pause inserted after each CAT command. Some older
// Kenwood/Yaesu rigs drop bytes if commands arrive too fast back to back.
// Capped at 0…500ms — beyond that, fix your rig.
func (m *Manager) SetCommandDelay(d time.Duration) {
	if d < 0 {
		d = 0
	}
	if d > 500*time.Millisecond {
		d = 500 * time.Millisecond
	}
	m.mu.Lock()
	m.cmdDelay = d
	m.mu.Unlock()
}

// State returns a copy of the latest known state.
func (m *Manager) State() RigState {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.state
}

// Start spins up the CAT goroutine with the given backend. If a backend is
// already running it is stopped first. Errors during Connect are surfaced as
// state.Error rather than returned, so the UI can keep retrying via the
// poll loop on next reconnect attempt.
func (m *Manager) Start(b Backend) {
	m.Stop()
	m.mu.Lock()
	m.stopCh = make(chan struct{})
	m.doneCh = make(chan struct{})
	m.cmdCh = make(chan func(), 4)
	m.backend = b
	stop := m.stopCh
	done := m.doneCh
	cmds := m.cmdCh
	poll := m.pollEvery
	m.state = RigState{Enabled: true, Backend: b.Name()}
	m.mu.Unlock()
	m.emitState()

	go m.run(b, stop, done, cmds, poll)
}

// Stop signals the CAT goroutine to disconnect and waits for it to exit.
func (m *Manager) Stop() {
	m.mu.Lock()
	stop := m.stopCh
	done := m.doneCh
	m.stopCh = nil
	m.doneCh = nil
	m.cmdCh = nil
	m.backend = nil
	m.mu.Unlock()
	if stop != nil {
		close(stop)
	}
	if done != nil {
		<-done
	}
	m.mu.Lock()
	m.state = RigState{Enabled: false}
	m.mu.Unlock()
	m.emitState()
}

// SetFrequency dispatches a SetFreq call to the CAT goroutine.
func (m *Manager) SetFrequency(hz int64) error {
	return m.exec(func(b Backend) error { return b.SetFrequency(hz) })
}

// SetMode dispatches a SetMode call to the CAT goroutine.
func (m *Manager) SetMode(mode string) error {
	return m.exec(func(b Backend) error { return b.SetMode(mode) })
}

// exec marshals a backend operation onto the CAT goroutine. Returns the
// operation's error or a "busy"/"not running" error if dispatch failed.
func (m *Manager) exec(fn func(Backend) error) error {
	m.mu.RLock()
	cmds := m.cmdCh
	b := m.backend
	m.mu.RUnlock()
	if cmds == nil || b == nil {
		return fmt.Errorf("cat not running")
	}
	errCh := make(chan error, 1)
	select {
	case cmds <- func() { errCh <- fn(b) }:
	case <-time.After(500 * time.Millisecond):
		return fmt.Errorf("cat busy")
	}
	return <-errCh
}

// run is the CAT goroutine. Owns the backend lifecycle.
func (m *Manager) run(b Backend, stop, done chan struct{}, cmds chan func(), pollEvery time.Duration) {
	// Lock to a single OS thread — required for COM. Cheap for non-COM backends.
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	defer close(done)

	if err := b.Connect(); err != nil {
		m.update(RigState{
			Enabled: true, Backend: b.Name(), Connected: false,
			Error: err.Error(), UpdatedAt: time.Now(),
		})
		// Stay idle until Stop is called — let the user fix config and re-Start.
		for {
			select {
			case <-stop:
				return
			case fn := <-cmds:
				fn()
			}
		}
	}
	defer b.Disconnect()

	ticker := time.NewTicker(pollEvery)
	defer ticker.Stop()

	for {
		select {
		case <-stop:
			return
		case fn := <-cmds:
			fn()
			m.applyCommandDelay()
		case <-ticker.C:
			ns, err := b.ReadState()
			if err != nil {
				m.update(RigState{
					Enabled: true, Backend: b.Name(), Connected: false,
					Error: err.Error(), UpdatedAt: time.Now(),
				})
				continue
			}
			ns.Enabled = true
			ns.Backend = b.Name()
			ns.UpdatedAt = time.Now()
			if ns.FreqHz != 0 && ns.Band == "" {
				ns.Band = BandFromHz(ns.FreqHz)
			}
			m.update(ns)
		}
	}
}

func (m *Manager) applyCommandDelay() {
	m.mu.RLock()
	d := m.cmdDelay
	m.mu.RUnlock()
	if d > 0 {
		time.Sleep(d)
	}
}

// update stores the new state and emits an event ONLY if something changed
// that the UI cares about — avoids flooding the event bus 4x per second.
func (m *Manager) update(ns RigState) {
	m.mu.Lock()
	changed := !stateUserEqual(m.state, ns)
	m.state = ns
	m.mu.Unlock()
	if changed {
		m.emitState()
	}
}

func (m *Manager) emitState() {
	if m.emit == nil {
		return
	}
	m.emit(m.State())
}

func stateUserEqual(a, b RigState) bool {
	return a.Enabled == b.Enabled &&
		a.Connected == b.Connected &&
		a.Backend == b.Backend &&
		a.RigNum == b.RigNum &&
		a.Rig == b.Rig &&
		a.FreqHz == b.FreqHz &&
		a.RxFreqHz == b.RxFreqHz &&
		a.Split == b.Split &&
		a.Mode == b.Mode &&
		a.Vfo == b.Vfo &&
		a.Band == b.Band &&
		a.Error == b.Error
}

// BandFromHz returns the ADIF band tag covering the given frequency, or "".
// Ranges follow IARU/ITU plans. 60m is treated as a single block for
// simplicity — channelised access varies by region.
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 ""
}