package mk2driver

import (
	"errors"
	"fmt"
	"io"
	"math"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/sirupsen/logrus"
)

var mk2log = logrus.WithField("ctx", "inverter-gui-mk2driver")

type scaling struct {
	scale     float64
	offset    float64
	signed    bool
	supported bool
}

//nolint:deadcode,varcheck
const (
	ramVarVMains = iota
	ramVarIMains
	ramVarVInverter
	ramVarIInverter
	ramVarVBat
	ramVarIBat
	ramVarVBatRipple
	ramVarInverterPeriod
	ramVarMainPeriod
	ramVarIACLoad
	ramVarVirSwitchPos
	ramVarIgnACInState
	ramVarMultiFuncRelay
	ramVarChargeState
	ramVarInverterPower1
	ramVarInverterPower2
	ramVarOutPower

	ramVarMaxOffset = 14
)

const (
	infoFrameHeader   = 0x20
	frameHeader       = 0xff
	bootupFrameHeader = 0x0
	frameLengthLEDBit = 0x80
	frameLEDBytes     = 2
)

const (
	acL1InfoFrame  = 0x08
	dcInfoFrame    = 0x0C
	interfaceFrame = 0x48 // H
	setTargetFrame = 0x41
	infoReqFrame   = 0x46 //F
	ledFrame       = 0x4C
	stateFrame     = 0x53 // S
	vFrame         = 0x56
	winmonFrame    = 0x57
)

const (
	panelStateVariant2Flags = 0x80

	interfacePanelDetectFlag = 0x01
	interfaceStandbyFlag     = 0x02

	panelCurrentLimitUnknown = 0x8000
	panelCurrentLimitMax     = 0x7FFF
)

// info frame types
const (
	infoReqAddrDC   = 0x00
	infoReqAddrACL1 = 0x01
)

// winmon frame commands
const (
	commandSetState      = 0x0E
	commandReadRAMVar    = 0x30
	commandReadSetting   = 0x31
	commandWriteRAMVar   = 0x32
	commandWriteSetting  = 0x33
	commandWriteData     = 0x34
	commandReadSelected  = 0x35
	commandGetRAMVarInfo = 0x36
	commandWriteViaID    = 0x37
	commandWriteRAMViaID = 0x38

	commandUnsupportedResponse     = 0x80
	commandReadRAMResponse         = 0x85
	commandReadSettingResponse     = 0x86
	commandWriteRAMResponse        = 0x87
	commandWriteSettingResponse    = 0x88
	commandSetStateResponse        = 0x89
	commandReadSelectedResponse    = 0x8A
	commandWriteViaIDResponse      = 0x8B
	commandWriteRAMViaIDResponse   = 0x8C
	commandGetRAMVarInfoResponse   = 0x8E
	commandWriteNotAllowedResponse = 0x9B
)

const writeResponseTimeout = 3 * time.Second

var (
	errCommandUnsupported = errors.New("command is not supported by this device firmware")
	errWriteRejected      = errors.New("write command rejected by device access level")
)

type winmonResponse struct {
	command byte
	data    []byte
}

type mk2Ser struct {
	info       *Mk2Info
	p          io.ReadWriter
	scales     []scaling
	scaleCount int
	run        chan struct{}
	frameLock  bool
	infochan   chan *Mk2Info
	commandMu  sync.Mutex
	pollPaused atomic.Bool
	writeAck   chan byte
	winmonAck  chan winmonResponse
	stateAck   chan struct{}
	ifaceAck   chan byte
	wg         sync.WaitGroup

	diagMu       sync.Mutex
	traceLimit   int
	traces       []ProtocolTrace
	lastFrameAt  time.Time
	recentErrors []string

	commandTimeouts atomic.Uint64
	commandFailures atomic.Uint64
	checksumErrors  atomic.Uint64
}

var _ ProtocolControl = (*mk2Ser)(nil)
var _ MetadataControl = (*mk2Ser)(nil)
var _ SnapshotControl = (*mk2Ser)(nil)
var _ DiagnosticsControl = (*mk2Ser)(nil)

func parseFrameLength(raw byte) (payloadLength byte, hasLEDStatus bool) {
	if raw&frameLengthLEDBit != 0 {
		return raw &^ frameLengthLEDBit, true
	}
	return raw, false
}

func (m *mk2Ser) beginCommand() {
	m.commandMu.Lock()
	m.pollPaused.Store(true)
}

func (m *mk2Ser) endCommand() {
	m.pollPaused.Store(false)
	m.commandMu.Unlock()
}

func (m *mk2Ser) sendMonitoringCommand(data []byte) {
	if m.pollPaused.Load() {
		if len(data) > 0 {
			mk2log.WithField("command", fmt.Sprintf("0x%02x", data[0])).Debug("Skipping monitoring command during control transaction")
		}
		return
	}
	m.sendCommand(data)
}

func NewMk2Connection(dev io.ReadWriter) (Mk2, error) {
	mk2 := &mk2Ser{}
	mk2.p = dev
	mk2.info = &Mk2Info{}
	mk2.scaleCount = 0
	mk2.frameLock = false
	mk2.scales = make([]scaling, 0, ramVarMaxOffset)
	mk2.writeAck = make(chan byte, 4)
	mk2.winmonAck = make(chan winmonResponse, 32)
	mk2.stateAck = make(chan struct{}, 1)
	mk2.ifaceAck = make(chan byte, 1)
	mk2.traceLimit = 200
	mk2.traces = make([]ProtocolTrace, 0, mk2.traceLimit)
	mk2.recentErrors = make([]string, 0, 20)
	mk2.setTarget()
	mk2.run = make(chan struct{})
	mk2.infochan = make(chan *Mk2Info)
	mk2.wg.Add(1)
	mk2log.Info("MK2 connection initialized")
	go mk2.frameLocker()
	return mk2, nil
}

// Locks to incoming frame.
func (m *mk2Ser) frameLocker() {
	frame := make([]byte, 256)
	ledStatus := make([]byte, frameLEDBytes)
	var frameLengthRaw byte
	for {
		select {
		case <-m.run:
			m.wg.Done()
			return
		default:
		}
		if m.frameLock {
			frameLengthRaw = m.readByte()
			frameLength, hasLEDStatus := parseFrameLength(frameLengthRaw)
			frameLengthOffset := int(frameLength) + 1
			if frameLengthOffset > len(frame) {
				m.addError(fmt.Errorf("Read Length Error: frame length %d exceeds buffer", frameLengthOffset))
				m.frameLock = false
				continue
			}
			l, err := io.ReadFull(m.p, frame[:frameLengthOffset])
			if err != nil {
				m.addError(fmt.Errorf("Read Error: %v", err))
				m.frameLock = false
			} else if l != frameLengthOffset {
				m.addError(errors.New("Read Length Error"))
				m.frameLock = false
			} else {
				var appendedLED []byte
				if hasLEDStatus {
					if _, err = io.ReadFull(m.p, ledStatus); err != nil {
						m.addError(fmt.Errorf("Read LED status error: %v", err))
						m.frameLock = false
						continue
					}
					appendedLED = ledStatus
				}
				m.handleFrame(frameLength, frame[:frameLengthOffset], appendedLED)
			}
		} else {
			tmp := m.readByte()
			frameLength, hasLEDStatus := parseFrameLength(frameLengthRaw)
			frameLengthOffset := int(frameLength)
			if tmp == frameHeader || tmp == infoFrameHeader {
				if frameLengthOffset > len(frame) {
					frameLengthRaw = tmp
					continue
				}
				l, err := io.ReadFull(m.p, frame[:frameLengthOffset])
				if err != nil {
					m.addError(fmt.Errorf("Read Error: %v", err))
					time.Sleep(1 * time.Second)
				} else if l != frameLengthOffset {
					m.addError(errors.New("Read Length Error"))
				} else {
					if hasLEDStatus {
						if _, err = io.ReadFull(m.p, ledStatus); err != nil {
							m.addError(fmt.Errorf("Read LED status error: %v", err))
							frameLengthRaw = tmp
							continue
						}
					}
					if checkChecksum(frameLength, tmp, frame[:frameLengthOffset]) {
						m.frameLock = true
						mk2log.Info("Frame lock acquired")
					}
				}
			}
			frameLengthRaw = tmp
		}
	}
}

// Close Mk2
func (m *mk2Ser) Close() {
	mk2log.Info("Closing MK2 connection")
	close(m.run)
	m.wg.Wait()
	mk2log.Info("MK2 connection closed")
}

func (m *mk2Ser) C() chan *Mk2Info {
	return m.infochan
}

func (m *mk2Ser) RegisterMetadata(kind RegisterKind, id uint16) (RegisterMetadata, bool) {
	return lookupRegisterMetadata(kind, id)
}

func (m *mk2Ser) ListRegisterMetadata() []RegisterMetadata {
	return listRegisterMetadata()
}

func (m *mk2Ser) ReadRegister(kind RegisterKind, id uint16) (int16, error) {
	m.beginCommand()
	defer m.endCommand()
	return m.readRegisterLocked(kind, id)
}

func (m *mk2Ser) WriteRegister(kind RegisterKind, id uint16, value int16, opts TransactionOptions) (RegisterTransactionResult, error) {
	options := normalizeTransactionOptions(opts)
	commandTimeout := resolveCommandTimeout(options)
	start := time.Now()
	result := RegisterTransactionResult{
		Kind:        kind,
		ID:          id,
		TargetValue: value,
		Timeout:     commandTimeout,
	}

	if meta, ok := lookupRegisterMetadata(kind, id); ok {
		if !meta.Writable {
			return result, fmt.Errorf("register %s:%d (%s) is marked read-only", kind, id, meta.Name)
		}
		if err := validateValueAgainstMetadata(meta, value); err != nil {
			return result, err
		}
	}

	m.beginCommand()
	defer m.endCommand()

	if options.ReadBeforeWrite {
		prev, err := m.readRegisterLockedWithTimeout(kind, id, commandTimeout)
		if err != nil {
			result.Duration = time.Since(start)
			return result, fmt.Errorf("could not read current value for %s:%d: %w", kind, id, err)
		}
		result.PreviousValue = int16Ptr(prev)
	}

	var lastErr error
	maxAttempts := options.Retries + 1
	for attempt := 1; attempt <= maxAttempts; attempt++ {
		result.Attempts = attempt

		err := m.writeRegisterLockedWithTimeout(kind, id, value, commandTimeout)
		if err != nil {
			lastErr = err
			if attempt < maxAttempts {
				delay := retryDelayForAttempt(options, attempt)
				if delay > 0 {
					time.Sleep(delay)
				}
				continue
			}
			break
		}

		if !options.VerifyAfterWrite {
			result.Duration = time.Since(start)
			return result, nil
		}

		verified, err := m.readRegisterLockedWithTimeout(kind, id, commandTimeout)
		if err != nil {
			lastErr = fmt.Errorf("verification read failed for %s:%d: %w", kind, id, err)
			if attempt < maxAttempts {
				delay := retryDelayForAttempt(options, attempt)
				if delay > 0 {
					time.Sleep(delay)
				}
				continue
			}
			break
		}
		result.VerifiedValue = int16Ptr(verified)
		if verified != value {
			lastErr = fmt.Errorf("verification mismatch for %s:%d expected %d got %d", kind, id, value, verified)
			if attempt < maxAttempts {
				delay := retryDelayForAttempt(options, attempt)
				if delay > 0 {
					time.Sleep(delay)
				}
				continue
			}
			break
		}

		result.Duration = time.Since(start)
		return result, nil
	}

	if lastErr == nil {
		lastErr = fmt.Errorf("transaction failed for %s:%d", kind, id)
	}
	result.Duration = time.Since(start)
	return result, lastErr
}

func (m *mk2Ser) CaptureSnapshot(addresses []RegisterAddress) (RegisterSnapshot, error) {
	if len(addresses) == 0 {
		addresses = defaultWritableRegisterAddresses()
	}
	snapshotTime := time.Now().UTC()
	snapshot := RegisterSnapshot{
		CapturedAt: snapshotTime,
		Entries:    make([]RegisterSnapshotEntry, 0, len(addresses)),
	}
	for _, address := range addresses {
		value, err := m.ReadRegister(address.Kind, address.ID)
		if err != nil {
			return snapshot, fmt.Errorf("capture snapshot read failed for %s:%d: %w", address.Kind, address.ID, err)
		}
		meta, ok := m.RegisterMetadata(address.Kind, address.ID)
		entry := RegisterSnapshotEntry{
			Kind:       address.Kind,
			ID:         address.ID,
			Value:      value,
			CapturedAt: snapshotTime,
		}
		if ok {
			entry.Name = meta.Name
			entry.Writable = meta.Writable
			entry.Safety = meta.SafetyClass
		}
		snapshot.Entries = append(snapshot.Entries, entry)
	}
	return snapshot, nil
}

func (m *mk2Ser) DiffSnapshot(snapshot RegisterSnapshot) ([]SnapshotDiff, error) {
	diffs := make([]SnapshotDiff, 0, len(snapshot.Entries))
	for _, entry := range snapshot.Entries {
		current, err := m.ReadRegister(entry.Kind, entry.ID)
		if err != nil {
			return diffs, fmt.Errorf("snapshot diff read failed for %s:%d: %w", entry.Kind, entry.ID, err)
		}
		meta, ok := m.RegisterMetadata(entry.Kind, entry.ID)
		name := entry.Name
		writable := entry.Writable
		safety := entry.Safety
		if ok {
			name = meta.Name
			writable = meta.Writable
			safety = meta.SafetyClass
		}
		diff := SnapshotDiff{
			Kind:      entry.Kind,
			ID:        entry.ID,
			Name:      name,
			Current:   current,
			Target:    entry.Value,
			Changed:   current != entry.Value,
			Writable:  writable,
			Safety:    safety,
			DiffValue: int32(entry.Value) - int32(current),
		}
		diffs = append(diffs, diff)
	}
	return diffs, nil
}

func (m *mk2Ser) RestoreSnapshot(snapshot RegisterSnapshot, opts TransactionOptions) (SnapshotRestoreResult, error) {
	restoreResult := SnapshotRestoreResult{
		Applied: make([]RegisterTransactionResult, 0, len(snapshot.Entries)),
	}
	diffs, err := m.DiffSnapshot(snapshot)
	if err != nil {
		return restoreResult, err
	}
	for _, diff := range diffs {
		if !diff.Changed || !diff.Writable {
			continue
		}
		txResult, txErr := m.WriteRegister(diff.Kind, diff.ID, diff.Target, opts)
		if txErr == nil {
			restoreResult.Applied = append(restoreResult.Applied, txResult)
			continue
		}

		restoreResult.RolledBack = true
		rollbackErrs := m.rollbackAppliedTransactions(restoreResult.Applied, opts)
		restoreResult.RollbackErrors = append(restoreResult.RollbackErrors, rollbackErrs...)
		return restoreResult, fmt.Errorf("restore failed for %s:%d: %w", diff.Kind, diff.ID, txErr)
	}
	return restoreResult, nil
}

func (m *mk2Ser) rollbackAppliedTransactions(applied []RegisterTransactionResult, opts TransactionOptions) []string {
	errs := make([]string, 0)
	rollbackOpts := normalizeTransactionOptions(TransactionOptions{
		Retries:          1,
		RetryDelay:       opts.RetryDelay,
		BackoffFactor:    opts.BackoffFactor,
		VerifyAfterWrite: true,
		TimeoutClass:     opts.TimeoutClass,
		CommandTimeout:   opts.CommandTimeout,
	})
	for i := len(applied) - 1; i >= 0; i-- {
		tx := applied[i]
		if tx.PreviousValue == nil {
			continue
		}
		if _, err := m.WriteRegister(tx.Kind, tx.ID, *tx.PreviousValue, rollbackOpts); err != nil {
			errs = append(errs, fmt.Sprintf("rollback failed for %s:%d: %v", tx.Kind, tx.ID, err))
		}
	}
	return errs
}

func (m *mk2Ser) DriverDiagnostics(limit int) DriverDiagnostics {
	m.diagMu.Lock()
	defer m.diagMu.Unlock()

	traceLimit := limit
	if traceLimit <= 0 || traceLimit > len(m.traces) {
		traceLimit = len(m.traces)
	}
	traces := make([]ProtocolTrace, traceLimit)
	if traceLimit > 0 {
		copy(traces, m.traces[len(m.traces)-traceLimit:])
	}
	recentErrors := append([]string(nil), m.recentErrors...)

	diag := DriverDiagnostics{
		GeneratedAt:      time.Now().UTC(),
		CommandTimeouts:  m.commandTimeouts.Load(),
		CommandFailures:  m.commandFailures.Load(),
		ChecksumFailures: m.checksumErrors.Load(),
		RecentErrors:     recentErrors,
		Traces:           traces,
	}
	if !m.lastFrameAt.IsZero() {
		last := m.lastFrameAt
		diag.LastFrameAt = &last
	}
	diag.HealthScore = calculateDriverHealthScore(diag)
	return diag
}

func (m *mk2Ser) readRegisterLocked(kind RegisterKind, id uint16) (int16, error) {
	return m.readRegisterLockedWithTimeout(kind, id, writeResponseTimeout)
}

func (m *mk2Ser) readRegisterLockedWithTimeout(kind RegisterKind, id uint16, timeout time.Duration) (int16, error) {
	switch kind {
	case RegisterKindRAMVar:
		return m.readValueByIDWithTimeout(commandReadRAMVar, commandReadRAMResponse, id, timeout)
	case RegisterKindSetting:
		return m.readValueByIDWithTimeout(commandReadSetting, commandReadSettingResponse, id, timeout)
	default:
		return 0, fmt.Errorf("unsupported register kind %q", kind)
	}
}

func (m *mk2Ser) writeRegisterLocked(kind RegisterKind, id uint16, value int16) error {
	return m.writeRegisterLockedWithTimeout(kind, id, value, writeResponseTimeout)
}

func (m *mk2Ser) writeRegisterLockedWithTimeout(kind RegisterKind, id uint16, value int16, timeout time.Duration) error {
	switch kind {
	case RegisterKindRAMVar:
		err := m.writeByIDOnlyWithTimeout(commandWriteRAMViaID, commandWriteRAMViaIDResponse, id, value, timeout)
		if err != nil && !errors.Is(err, errWriteRejected) {
			mk2log.WithFields(logrus.Fields{
				"id":    id,
				"value": value,
			}).WithError(err).Warn("WriteRegister RAM by-id failed, trying legacy write path")
			err = m.writeBySelectionWithTimeout(commandWriteRAMVar, commandWriteRAMResponse, id, value, timeout)
		}
		return err
	case RegisterKindSetting:
		err := m.writeByIDOnlyWithTimeout(commandWriteViaID, commandWriteViaIDResponse, id, value, timeout)
		if err != nil && !errors.Is(err, errWriteRejected) {
			mk2log.WithFields(logrus.Fields{
				"id":    id,
				"value": value,
			}).WithError(err).Warn("WriteRegister setting by-id failed, trying legacy write path")
			err = m.writeBySelectionWithTimeout(commandWriteSetting, commandWriteSettingResponse, id, value, timeout)
		}
		return err
	default:
		return fmt.Errorf("unsupported register kind %q", kind)
	}
}

func (m *mk2Ser) WriteRAMVar(id uint16, value int16) error {
	mk2log.WithFields(logrus.Fields{
		"id":    id,
		"value": value,
	}).Info("WriteRAMVar requested")

	m.beginCommand()
	defer m.endCommand()

	err := m.writeByIDOnly(commandWriteRAMViaID, commandWriteRAMViaIDResponse, id, value)
	if err != nil {
		if errors.Is(err, errWriteRejected) {
			mk2log.WithError(err).WithField("id", id).Error("WriteRAMVar failed")
			return err
		}
		mk2log.WithFields(logrus.Fields{
			"id":    id,
			"value": value,
		}).WithError(err).Warn("WriteRAMVar by-id command failed, falling back to legacy write sequence")
		err = m.writeBySelection(commandWriteRAMVar, commandWriteRAMResponse, id, value)
	}
	if err != nil {
		mk2log.WithError(err).WithField("id", id).Error("WriteRAMVar failed")
		return err
	}
	mk2log.WithField("id", id).Info("WriteRAMVar applied")
	return nil
}

func (m *mk2Ser) WriteSetting(id uint16, value int16) error {
	mk2log.WithFields(logrus.Fields{
		"id":    id,
		"value": value,
	}).Info("WriteSetting requested")

	m.beginCommand()
	defer m.endCommand()

	err := m.writeByIDOnly(commandWriteViaID, commandWriteViaIDResponse, id, value)
	if err != nil {
		if errors.Is(err, errWriteRejected) {
			mk2log.WithError(err).WithField("id", id).Error("WriteSetting failed")
			return err
		}
		mk2log.WithFields(logrus.Fields{
			"id":    id,
			"value": value,
		}).WithError(err).Warn("WriteSetting by-id command failed, falling back to legacy write sequence")
		err = m.writeBySelection(commandWriteSetting, commandWriteSettingResponse, id, value)
	}
	if err != nil {
		mk2log.WithError(err).WithField("id", id).Error("WriteSetting failed")
		return err
	}
	mk2log.WithField("id", id).Info("WriteSetting applied")
	return nil
}

func (m *mk2Ser) WriteSettingByID(id uint16, value int16) error {
	m.beginCommand()
	defer m.endCommand()
	return m.writeByIDOnly(commandWriteViaID, commandWriteViaIDResponse, id, value)
}

func (m *mk2Ser) WriteRAMVarByID(id uint16, value int16) error {
	m.beginCommand()
	defer m.endCommand()
	return m.writeByIDOnly(commandWriteRAMViaID, commandWriteRAMViaIDResponse, id, value)
}

func (m *mk2Ser) WriteSettingBySelection(id uint16, value int16) error {
	m.beginCommand()
	defer m.endCommand()
	return m.writeBySelection(commandWriteSetting, commandWriteSettingResponse, id, value)
}

func (m *mk2Ser) WriteRAMVarBySelection(id uint16, value int16) error {
	m.beginCommand()
	defer m.endCommand()
	return m.writeBySelection(commandWriteRAMVar, commandWriteRAMResponse, id, value)
}

func (m *mk2Ser) WriteSelectedData(value int16) error {
	m.beginCommand()
	defer m.endCommand()

	m.clearWriteResponses()
	raw := uint16(value)
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandWriteData,
		byte(raw),
		byte(raw >> 8),
	})
	_, err := m.waitForAnyWriteResponseWithTimeout([]byte{
		commandWriteRAMResponse,
		commandWriteSettingResponse,
		commandWriteViaIDResponse,
		commandWriteRAMViaIDResponse,
	}, writeResponseTimeout)
	return err
}

func (m *mk2Ser) GetDeviceState() (DeviceState, error) {
	m.beginCommand()
	defer m.endCommand()

	m.clearWinmonResponses()
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandSetState,
		0x00,
	})
	resp, err := m.waitForWinmonResponse(commandSetStateResponse)
	if err != nil {
		return 0, err
	}
	return decodeDeviceStateResponse(resp)
}

func (m *mk2Ser) SetDeviceState(state DeviceState) error {
	if !validDeviceState(state) {
		return fmt.Errorf("invalid device state: 0x%02x", byte(state))
	}

	m.beginCommand()
	defer m.endCommand()

	m.clearWinmonResponses()
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandSetState,
		0x00,
		byte(state),
	})

	resp, err := m.waitForWinmonResponse(commandSetStateResponse)
	if err != nil {
		return err
	}
	ackState, err := decodeDeviceStateResponse(resp)
	if err != nil {
		return err
	}
	if ackState != state {
		return fmt.Errorf("device acknowledged state %s (0x%02x), expected %s (0x%02x)", formatDeviceState(ackState), byte(ackState), formatDeviceState(state), byte(state))
	}
	return nil
}

func (m *mk2Ser) ReadRAMVarByID(id uint16) (int16, error) {
	m.beginCommand()
	defer m.endCommand()
	return m.readValueByID(commandReadRAMVar, commandReadRAMResponse, id)
}

func (m *mk2Ser) ReadSettingByID(id uint16) (int16, error) {
	m.beginCommand()
	defer m.endCommand()
	return m.readValueByID(commandReadSetting, commandReadSettingResponse, id)
}

func (m *mk2Ser) SelectRAMVar(id uint16) error {
	m.beginCommand()
	defer m.endCommand()
	_, err := m.readValueByID(commandReadRAMVar, commandReadRAMResponse, id)
	return err
}

func (m *mk2Ser) SelectSetting(id uint16) error {
	m.beginCommand()
	defer m.endCommand()
	_, err := m.readValueByID(commandReadSetting, commandReadSettingResponse, id)
	return err
}

func (m *mk2Ser) ReadSelected() (int16, error) {
	m.beginCommand()
	defer m.endCommand()

	m.clearWinmonResponses()
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandReadSelected,
	})
	resp, err := m.waitForWinmonResponse(commandReadSelectedResponse)
	if err != nil {
		return 0, err
	}
	return decodeInt16Response(resp)
}

func (m *mk2Ser) ReadRAMVarInfo(id uint16) (RAMVarInfo, error) {
	m.beginCommand()
	defer m.endCommand()

	m.clearWinmonResponses()
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandGetRAMVarInfo,
		byte(id),
		byte(id >> 8),
	})
	resp, err := m.waitForWinmonResponse(commandGetRAMVarInfoResponse)
	if err != nil {
		return RAMVarInfo{}, err
	}
	return decodeRAMVarInfoResponse(id, resp)
}

func (m *mk2Ser) SetPanelState(switchState PanelSwitchState, currentLimitA *float64) error {
	if !validPanelSwitchState(switchState) {
		return fmt.Errorf("invalid panel switch state: %d", switchState)
	}

	currentLimitRaw, err := encodePanelCurrentLimit(currentLimitA)
	if err != nil {
		return err
	}

	m.beginCommand()
	defer m.endCommand()

	logEntry := mk2log.WithField("switch_state", switchState)
	if currentLimitA != nil {
		logEntry = logEntry.WithField("current_limit_a", *currentLimitA)
	}
	logEntry.Info("SetPanelState requested")

	m.clearStateResponses()
	m.sendCommandLocked([]byte{
		stateFrame,
		byte(switchState),
		byte(currentLimitRaw),
		byte(currentLimitRaw >> 8),
		0x01,
		panelStateVariant2Flags,
	})

	err = m.waitForStateResponse()
	if err != nil {
		logEntry.WithError(err).Error("SetPanelState failed")
		return err
	}
	logEntry.Info("SetPanelState acknowledged")
	return nil
}

func (m *mk2Ser) SetStandby(enabled bool) error {
	lineState := byte(interfacePanelDetectFlag)
	if enabled {
		lineState |= interfaceStandbyFlag
	}

	m.beginCommand()
	defer m.endCommand()
	logEntry := mk2log.WithField("standby_enabled", enabled)
	logEntry.Info("SetStandby requested")

	m.clearInterfaceResponses()
	m.sendCommandLocked([]byte{
		interfaceFrame,
		lineState,
	})

	err := m.waitForInterfaceResponse(enabled)
	if err != nil {
		logEntry.WithError(err).Error("SetStandby failed")
		return err
	}
	logEntry.Info("SetStandby acknowledged")
	return nil
}

func validPanelSwitchState(switchState PanelSwitchState) bool {
	switch switchState {
	case PanelSwitchChargerOnly, PanelSwitchInverterOnly, PanelSwitchOn, PanelSwitchOff:
		return true
	default:
		return false
	}
}

func validDeviceState(state DeviceState) bool {
	switch state {
	case DeviceStateChargerOnly, DeviceStateInverterOnly, DeviceStateOn, DeviceStateOff:
		return true
	default:
		return false
	}
}

func formatDeviceState(state DeviceState) string {
	if name, ok := DeviceStateNames[state]; ok {
		return name
	}
	return "unknown"
}

func encodePanelCurrentLimit(currentLimitA *float64) (uint16, error) {
	if currentLimitA == nil {
		return panelCurrentLimitUnknown, nil
	}
	if *currentLimitA < 0 {
		return 0, fmt.Errorf("current_limit must be >= 0, got %.3f", *currentLimitA)
	}

	raw := math.Round(*currentLimitA * 10)
	if raw > panelCurrentLimitMax {
		return 0, fmt.Errorf("current_limit %.3f A is above MK2 maximum %.1f A", *currentLimitA, panelCurrentLimitMax/10.0)
	}
	return uint16(raw), nil
}

func (m *mk2Ser) writeByIDOnly(writeCommand, expectedResponse byte, id uint16, value int16) error {
	return m.writeByIDOnlyWithTimeout(writeCommand, expectedResponse, id, value, writeResponseTimeout)
}

func (m *mk2Ser) writeByIDOnlyWithTimeout(writeCommand, expectedResponse byte, id uint16, value int16, timeout time.Duration) error {
	m.clearWriteResponses()
	rawValue := uint16(value)
	m.sendCommandLocked([]byte{
		winmonFrame,
		writeCommand,
		byte(id),
		byte(id >> 8),
		byte(rawValue),
		byte(rawValue >> 8),
	})
	return m.waitForWriteResponseWithTimeout(expectedResponse, timeout)
}

func (m *mk2Ser) writeBySelection(selectCommand, expectedResponse byte, id uint16, value int16) error {
	return m.writeBySelectionWithTimeout(selectCommand, expectedResponse, id, value, writeResponseTimeout)
}

func (m *mk2Ser) writeBySelectionWithTimeout(selectCommand, expectedResponse byte, id uint16, value int16, timeout time.Duration) error {
	m.clearWriteResponses()
	rawValue := uint16(value)
	m.sendCommandLocked([]byte{
		winmonFrame,
		selectCommand,
		byte(id),
		byte(id >> 8),
	})
	m.sendCommandLocked([]byte{
		winmonFrame,
		commandWriteData,
		byte(rawValue),
		byte(rawValue >> 8),
	})

	return m.waitForWriteResponseWithTimeout(expectedResponse, timeout)
}

func (m *mk2Ser) readValueByID(readCommand, expectedResponse byte, id uint16) (int16, error) {
	return m.readValueByIDWithTimeout(readCommand, expectedResponse, id, writeResponseTimeout)
}

func (m *mk2Ser) readValueByIDWithTimeout(readCommand, expectedResponse byte, id uint16, timeout time.Duration) (int16, error) {
	m.clearWinmonResponses()
	m.sendCommandLocked([]byte{
		winmonFrame,
		readCommand,
		byte(id),
		byte(id >> 8),
	})

	resp, err := m.waitForWinmonResponseWithTimeout(expectedResponse, timeout)
	if err != nil {
		return 0, err
	}
	return decodeInt16Response(resp)
}

func decodeInt16Response(resp winmonResponse) (int16, error) {
	if len(resp.data) < 2 {
		return 0, fmt.Errorf("invalid response 0x%02x payload length %d", resp.command, len(resp.data))
	}
	return int16(uint16(resp.data[0]) | uint16(resp.data[1])<<8), nil
}

func decodeDeviceStateResponse(resp winmonResponse) (DeviceState, error) {
	if len(resp.data) < 1 {
		return 0, fmt.Errorf("invalid device state response payload length %d", len(resp.data))
	}

	var raw byte
	if len(resp.data) >= 2 {
		raw = resp.data[1]
	} else {
		raw = resp.data[0]
	}
	state := DeviceState(raw)
	if !validDeviceState(state) {
		return state, fmt.Errorf("unsupported device state 0x%02x", raw)
	}
	return state, nil
}

func decodeRAMVarInfoResponse(id uint16, resp winmonResponse) (RAMVarInfo, error) {
	info := RAMVarInfo{
		ID: id,
	}
	if len(resp.data) < 4 {
		return info, nil
	}

	scl := int16(resp.data[1])<<8 + int16(resp.data[0])
	var ofs int16
	if len(resp.data) == 4 {
		ofs = int16(uint16(resp.data[3])<<8 + uint16(resp.data[2]))
	} else {
		ofs = int16(uint16(resp.data[4])<<8 + uint16(resp.data[3]))
	}

	info.Supported = true
	info.Scale = scl
	info.Offset = ofs
	info.Signed = scl < 0
	scale := int16Abs(scl)
	if scale >= 0x4000 {
		info.Factor = 1 / (0x8000 - float64(scale))
	} else {
		info.Factor = float64(scale)
	}

	return info, nil
}

func (m *mk2Ser) clearWriteResponses() {
	if m.writeAck == nil {
		m.writeAck = make(chan byte, 4)
		return
	}
	for {
		select {
		case <-m.writeAck:
		default:
			return
		}
	}
}

func (m *mk2Ser) waitForWriteResponse(expectedResponse byte) error {
	return m.waitForWriteResponseWithTimeout(expectedResponse, writeResponseTimeout)
}

func (m *mk2Ser) waitForWriteResponseWithTimeout(expectedResponse byte, timeout time.Duration) error {
	if m.writeAck == nil {
		return errors.New("write response channel is not initialized")
	}

	select {
	case response := <-m.writeAck:
		mk2log.WithFields(logrus.Fields{
			"expected_response": fmt.Sprintf("0x%02x", expectedResponse),
			"received_response": fmt.Sprintf("0x%02x", response),
		}).Debug("Received write acknowledgement")
		switch response {
		case expectedResponse:
			return nil
		case commandUnsupportedResponse:
			m.noteCommandFailure(fmt.Errorf("received unsupported response 0x%02x", response))
			return errCommandUnsupported
		case commandWriteNotAllowedResponse:
			m.noteCommandFailure(fmt.Errorf("received write rejected response 0x%02x", response))
			return errWriteRejected
		default:
			err := fmt.Errorf("unexpected write response 0x%02x", response)
			m.noteCommandFailure(err)
			return err
		}
	case <-time.After(timeout):
		err := fmt.Errorf("timed out waiting for write response after %s", timeout)
		mk2log.WithField("expected_response", fmt.Sprintf("0x%02x", expectedResponse)).WithError(err).Error("Timed out waiting for write acknowledgement")
		m.noteCommandTimeout(err)
		return err
	}
}

func (m *mk2Ser) waitForAnyWriteResponseWithTimeout(expectedResponses []byte, timeout time.Duration) (byte, error) {
	if m.writeAck == nil {
		return 0, errors.New("write response channel is not initialized")
	}
	expected := make(map[byte]struct{}, len(expectedResponses))
	for _, response := range expectedResponses {
		expected[response] = struct{}{}
	}

	select {
	case response := <-m.writeAck:
		if _, ok := expected[response]; ok {
			return response, nil
		}
		switch response {
		case commandUnsupportedResponse:
			err := fmt.Errorf("received unsupported write response 0x%02x", response)
			m.noteCommandFailure(err)
			return response, errCommandUnsupported
		case commandWriteNotAllowedResponse:
			err := fmt.Errorf("received write rejected response 0x%02x", response)
			m.noteCommandFailure(err)
			return response, errWriteRejected
		default:
			err := fmt.Errorf("unexpected write response 0x%02x", response)
			m.noteCommandFailure(err)
			return response, err
		}
	case <-time.After(timeout):
		err := fmt.Errorf("timed out waiting for write response after %s", timeout)
		m.noteCommandTimeout(err)
		return 0, err
	}
}

func (m *mk2Ser) pushWriteResponse(response byte) {
	if m.writeAck == nil {
		return
	}

	select {
	case m.writeAck <- response:
	default:
	}
}

func (m *mk2Ser) clearWinmonResponses() {
	if m.winmonAck == nil {
		m.winmonAck = make(chan winmonResponse, 32)
		return
	}
	for {
		select {
		case <-m.winmonAck:
		default:
			return
		}
	}
}

func (m *mk2Ser) waitForWinmonResponse(expectedResponse byte) (winmonResponse, error) {
	return m.waitForWinmonResponseWithTimeout(expectedResponse, writeResponseTimeout)
}

func (m *mk2Ser) waitForWinmonResponseWithTimeout(expectedResponse byte, timeout time.Duration) (winmonResponse, error) {
	if m.winmonAck == nil {
		return winmonResponse{}, errors.New("winmon response channel is not initialized")
	}

	timeoutChan := time.After(timeout)
	for {
		select {
		case response := <-m.winmonAck:
			mk2log.WithFields(logrus.Fields{
				"expected_response": fmt.Sprintf("0x%02x", expectedResponse),
				"received_response": fmt.Sprintf("0x%02x", response.command),
				"response_len":      len(response.data),
			}).Debug("Received winmon response")

			switch response.command {
			case expectedResponse:
				return response, nil
			case commandUnsupportedResponse:
				m.noteCommandFailure(fmt.Errorf("received unsupported winmon response 0x%02x", response.command))
				return winmonResponse{}, errCommandUnsupported
			case commandWriteNotAllowedResponse:
				m.noteCommandFailure(fmt.Errorf("received write rejected winmon response 0x%02x", response.command))
				return winmonResponse{}, errWriteRejected
			default:
				mk2log.WithFields(logrus.Fields{
					"expected_response": fmt.Sprintf("0x%02x", expectedResponse),
					"received_response": fmt.Sprintf("0x%02x", response.command),
				}).Debug("Ignoring unrelated winmon response while waiting")
			}
		case <-timeoutChan:
			err := fmt.Errorf("timed out waiting for winmon response 0x%02x after %s", expectedResponse, timeout)
			m.noteCommandTimeout(err)
			return winmonResponse{}, err
		}
	}
}

func (m *mk2Ser) pushWinmonResponse(command byte, data []byte) {
	if m.winmonAck == nil {
		return
	}
	payloadCopy := make([]byte, len(data))
	copy(payloadCopy, data)

	select {
	case m.winmonAck <- winmonResponse{command: command, data: payloadCopy}:
	default:
	}
}

func (m *mk2Ser) clearStateResponses() {
	if m.stateAck == nil {
		m.stateAck = make(chan struct{}, 1)
		return
	}
	for {
		select {
		case <-m.stateAck:
		default:
			return
		}
	}
}

func (m *mk2Ser) waitForStateResponse() error {
	return m.waitForStateResponseWithTimeout(writeResponseTimeout)
}

func (m *mk2Ser) waitForStateResponseWithTimeout(timeout time.Duration) error {
	if m.stateAck == nil {
		return errors.New("panel state response channel is not initialized")
	}

	select {
	case <-m.stateAck:
		mk2log.Debug("Received panel state acknowledgement")
		return nil
	case <-time.After(timeout):
		err := fmt.Errorf("timed out waiting for panel state response after %s", timeout)
		mk2log.WithError(err).Error("Timed out waiting for panel state acknowledgement")
		m.noteCommandTimeout(err)
		return err
	}
}

func (m *mk2Ser) pushStateResponse() {
	if m.stateAck == nil {
		return
	}

	select {
	case m.stateAck <- struct{}{}:
	default:
	}
}

func (m *mk2Ser) clearInterfaceResponses() {
	if m.ifaceAck == nil {
		m.ifaceAck = make(chan byte, 1)
		return
	}
	for {
		select {
		case <-m.ifaceAck:
		default:
			return
		}
	}
}

func (m *mk2Ser) waitForInterfaceResponse(expectedStandby bool) error {
	return m.waitForInterfaceResponseWithTimeout(expectedStandby, writeResponseTimeout)
}

func (m *mk2Ser) waitForInterfaceResponseWithTimeout(expectedStandby bool, timeout time.Duration) error {
	if m.ifaceAck == nil {
		return errors.New("interface response channel is not initialized")
	}

	select {
	case lineState := <-m.ifaceAck:
		standbyEnabled := lineState&interfaceStandbyFlag != 0
		mk2log.WithFields(logrus.Fields{
			"line_state":       fmt.Sprintf("0x%02x", lineState),
			"expected_standby": expectedStandby,
			"actual_standby":   standbyEnabled,
		}).Debug("Received standby interface acknowledgement")
		if standbyEnabled != expectedStandby {
			err := fmt.Errorf("unexpected standby line state 0x%02x", lineState)
			m.noteCommandFailure(err)
			return err
		}
		return nil
	case <-time.After(timeout):
		err := fmt.Errorf("timed out waiting for standby response after %s", timeout)
		mk2log.WithField("expected_standby", expectedStandby).WithError(err).Error("Timed out waiting for standby acknowledgement")
		m.noteCommandTimeout(err)
		return err
	}
}

func (m *mk2Ser) pushInterfaceResponse(lineState byte) {
	if m.ifaceAck == nil {
		return
	}

	select {
	case m.ifaceAck <- lineState:
	default:
	}
}

func (m *mk2Ser) readByte() byte {
	buffer := make([]byte, 1)
	_, err := io.ReadFull(m.p, buffer)
	if err != nil {
		m.addError(fmt.Errorf("Read error: %v", err))
		return 0
	}
	return buffer[0]
}

// Adds error to error slice.
func (m *mk2Ser) addError(err error) {
	mk2log.Errorf("Mk2 serial slice error: %q", err.Error())
	if m.info.Errors == nil {
		m.info.Errors = make([]error, 0)
	}
	m.info.Errors = append(m.info.Errors, err)
	m.info.Valid = false
	m.recordError(err)
}

func (m *mk2Ser) noteCommandTimeout(err error) {
	m.commandTimeouts.Add(1)
	m.commandFailures.Add(1)
	m.recordError(err)
}

func (m *mk2Ser) noteCommandFailure(err error) {
	m.commandFailures.Add(1)
	m.recordError(err)
}

// Updates report.
func (m *mk2Ser) updateReport() {
	m.info.Timestamp = time.Now()
	mk2log.WithFields(logrus.Fields{
		"in_voltage":   m.info.InVoltage,
		"in_current":   m.info.InCurrent,
		"out_voltage":  m.info.OutVoltage,
		"out_current":  m.info.OutCurrent,
		"bat_voltage":  m.info.BatVoltage,
		"bat_current":  m.info.BatCurrent,
		"charge_state": m.info.ChargeState,
		"valid":        m.info.Valid,
	}).Debug("Publishing MK2 status update")
	select {
	case m.infochan <- m.info:
	default:
		mk2log.Warn("Dropping MK2 status update; consumer channel is full")
	}
	m.info = &Mk2Info{}
}

// Checks for valid frame and chooses decoding.
func (m *mk2Ser) handleFrame(l byte, frame []byte, appendedLED []byte) {
	mk2log.Debugf("[handleFrame] frame %#v", frame)
	if len(frame) == 0 {
		mk2log.Warn("[handleFrame] empty frame")
		return
	}
	if checkChecksum(l, frame[0], frame[1:]) {
		m.markFrameSeen()
		m.recordRXTrace(frame)
		switch frame[0] {
		case bootupFrameHeader:
			if m.pollPaused.Load() {
				mk2log.Debug("Skipping setTarget during active control transaction")
				return
			}
			m.setTarget()
		case frameHeader:
			if len(frame) < 2 {
				mk2log.Warnf("[handleFrame] truncated frameHeader frame: %#v", frame)
				return
			}
			switch frame[1] {
			case interfaceFrame:
				if len(frame) > 2 {
					m.pushInterfaceResponse(frame[2])
				}
			case stateFrame:
				if len(appendedLED) == frameLEDBytes {
					m.setLEDState(appendedLED[0], appendedLED[1])
				}
				m.pushStateResponse()
			case vFrame:
				if len(frame) < 6 {
					mk2log.Warnf("[handleFrame] truncated version frame: %#v", frame)
					return
				}
				m.versionDecode(frame[2:])
			case winmonFrame:
				if len(frame) < 3 {
					mk2log.Warnf("[handleFrame] truncated winmon frame: %#v", frame)
					return
				}
				winmonCommand := frame[2]
				var winmonData []byte
				if len(frame) > 3 {
					winmonData = frame[3 : len(frame)-1]
				}
				m.pushWinmonResponse(winmonCommand, winmonData)
				switch frame[2] {
				case commandGetRAMVarInfoResponse:
					if !m.pollPaused.Load() {
						m.scaleDecode(frame[2:])
					}
				case commandReadRAMResponse:
					if !m.pollPaused.Load() {
						m.stateDecode(frame[2:])
					}
				case commandReadSettingResponse, commandReadSelectedResponse:
					// Responses are consumed by synchronous protocol command methods.
				case commandSetStateResponse, commandWriteRAMResponse, commandWriteSettingResponse, commandWriteViaIDResponse, commandWriteRAMViaIDResponse, commandUnsupportedResponse, commandWriteNotAllowedResponse:
					m.pushWriteResponse(frame[2])
				default:
					mk2log.Warnf("[handleFrame] invalid winmonFrame %v", frame[2:])
				}

			case ledFrame:
				if len(frame) < 4 {
					mk2log.Warnf("[handleFrame] truncated LED frame: %#v", frame)
					return
				}
				m.ledDecode(frame[2:])
			default:
				mk2log.Warnf("[handleFrame] invalid frameHeader %v", frame[1])
			}

		case infoFrameHeader:
			if len(frame) < 6 {
				mk2log.Warnf("[handleFrame] truncated info frame: %#v", frame)
				return
			}
			switch frame[5] {
			case dcInfoFrame:
				m.dcDecode(frame[1:])
			case acL1InfoFrame:
				m.acDecode(frame[1:])
			default:
				mk2log.Warnf("[handleFrame] invalid infoFrameHeader %v", frame[5])
			}
		default:
			mk2log.Warnf("[handleFrame] Invalid frame %v", frame[0])
		}
	} else {
		m.checksumErrors.Add(1)
		mk2log.Errorf("[handleFrame] Invalid incoming frame checksum: %x", frame)
		m.frameLock = false
		m.recordError(fmt.Errorf("invalid incoming frame checksum"))
	}
}

// Set the target VBus device.
func (m *mk2Ser) setTarget() {
	cmd := make([]byte, 3)
	cmd[0] = setTargetFrame
	cmd[1] = 0x01
	cmd[2] = 0x00
	m.sendCommand(cmd)
}

// Request the scaling factor for entry 'in'.
func (m *mk2Ser) reqScaleFactor(in byte) {
	cmd := make([]byte, 4)
	cmd[0] = winmonFrame
	cmd[1] = commandGetRAMVarInfo
	cmd[2] = in
	m.sendMonitoringCommand(cmd)
}

func int16Abs(in int16) uint16 {
	if in < 0 {
		return uint16(-in)
	}
	return uint16(in)
}

// Decode the scale factor frame.
func (m *mk2Ser) scaleDecode(frame []byte) {
	tmp := scaling{}
	mk2log.Debugf("Scale frame(%d): 0x%x", len(frame), frame)
	if len(frame) < 6 {
		tmp.supported = false
		mk2log.Warnf("Skiping scaling factors for: %d", m.scaleCount)
	} else {
		tmp.supported = true
		var scl int16
		var ofs int16
		if len(frame) == 6 {
			scl = int16(frame[2])<<8 + int16(frame[1])
			ofs = int16(uint16(frame[4])<<8 + uint16(frame[3]))
		} else {
			scl = int16(frame[2])<<8 + int16(frame[1])
			ofs = int16(uint16(frame[5])<<8 + uint16(frame[4]))
		}
		if scl < 0 {
			tmp.signed = true
		}
		tmp.offset = float64(ofs)
		scale := int16Abs(scl)
		if scale >= 0x4000 {
			tmp.scale = 1 / (0x8000 - float64(scale))
		} else {
			tmp.scale = float64(scale)
		}
	}
	mk2log.Debugf("scalecount %v: %#v \n", m.scaleCount, tmp)
	m.scales = append(m.scales, tmp)
	m.scaleCount++
	if m.scaleCount < ramVarMaxOffset {
		m.reqScaleFactor(byte(m.scaleCount))
	} else {
		mk2log.Info("Monitoring starting.")
	}
}

// Decode the version number
func (m *mk2Ser) versionDecode(frame []byte) {
	mk2log.Debugf("versiondecode %v", frame)
	m.info.Version = 0
	m.info.Valid = true
	for i := 0; i < 4; i++ {
		m.info.Version += uint32(frame[i]) << uint(i) * 8
	}

	if m.scaleCount < ramVarMaxOffset {
		mk2log.WithField("version", m.info.Version).Info("Get scaling factors")
		m.reqScaleFactor(byte(m.scaleCount))
	} else {
		// Send DC status request
		cmd := make([]byte, 2)
		cmd[0] = infoReqFrame
		cmd[1] = infoReqAddrDC
		m.sendMonitoringCommand(cmd)
	}
}

// Decode with correct signedness and apply scale
func (m *mk2Ser) applyScaleAndSign(data []byte, scale int) float64 {
	var value float64
	if !m.scales[scale].supported {
		return 0
	}
	if m.scales[scale].signed {
		value = getSigned(data)
	} else {
		value = getUnsigned16(data)
	}
	return m.applyScale(value, scale)
}

// Apply scaling to float
func (m *mk2Ser) applyScale(value float64, scale int) float64 {
	if !m.scales[scale].supported {
		return value
	}
	return m.scales[scale].scale * (value + m.scales[scale].offset)
}

// Convert bytes->int16->float
func getSigned(data []byte) float64 {
	return float64(int16(data[0]) + int16(data[1])<<8)
}

// Convert bytes->int16->float
func getUnsigned16(data []byte) float64 {
	return float64(uint16(data[0]) + uint16(data[1])<<8)
}

// Convert bytes->uint32->float
func getUnsigned(data []byte) float64 {
	return float64(uint32(data[0]) + uint32(data[1])<<8 + uint32(data[2])<<16)
}

// Decodes DC frame.
func (m *mk2Ser) dcDecode(frame []byte) {
	m.info.BatVoltage = m.applyScaleAndSign(frame[5:7], ramVarVBat)

	usedC := m.applyScale(getUnsigned(frame[7:10]), ramVarIBat)
	chargeC := m.applyScale(getUnsigned(frame[10:13]), ramVarIBat)
	m.info.BatCurrent = usedC - chargeC

	m.info.OutFrequency = m.calcFreq(frame[13], ramVarInverterPeriod)
	mk2log.Debugf("dcDecode %#v", m.info)

	// Send L1 status request
	cmd := make([]byte, 2)
	cmd[0] = infoReqFrame
	cmd[1] = infoReqAddrACL1
	m.sendMonitoringCommand(cmd)
}

// Decodes AC frame.
func (m *mk2Ser) acDecode(frame []byte) {
	m.info.InVoltage = m.applyScale(getSigned(frame[5:7]), ramVarVMains)
	m.info.InCurrent = m.applyScale(getSigned(frame[7:9]), ramVarIMains)
	m.info.OutVoltage = m.applyScale(getSigned(frame[9:11]), ramVarVInverter)
	m.info.OutCurrent = m.applyScale(getSigned(frame[11:13]), ramVarIInverter)
	m.info.InFrequency = m.calcFreq(frame[13], ramVarMainPeriod)

	mk2log.Debugf("acDecode %#v", m.info)

	// Send status request
	cmd := make([]byte, 1)
	cmd[0] = ledFrame
	m.sendMonitoringCommand(cmd)
}

func (m *mk2Ser) calcFreq(data byte, scaleIndex int) float64 {
	if data == 0xff || data == 0x00 {
		return 0
	}
	return 10 / (m.applyScale(float64(data), scaleIndex))
}

// Decode charge state of battery.
func (m *mk2Ser) stateDecode(frame []byte) {
	m.info.ChargeState = m.applyScaleAndSign(frame[1:3], ramVarChargeState)
	mk2log.Debugf("battery state decode %#v", m.info)
	m.updateReport()
}

// Decode the LED state frame.
func (m *mk2Ser) ledDecode(frame []byte) {
	if len(frame) < 2 {
		mk2log.Warnf("Skipping LED decode for short frame: %#v", frame)
		return
	}
	m.setLEDState(frame[0], frame[1])
	// Send charge state request
	cmd := make([]byte, 4)
	cmd[0] = winmonFrame
	cmd[1] = commandReadRAMVar
	cmd[2] = ramVarChargeState
	m.sendMonitoringCommand(cmd)
}

func (m *mk2Ser) setLEDState(ledsOn, ledsBlink byte) {
	m.info.LEDs = getLEDs(ledsOn, ledsBlink)
}

// Adds active LEDs to list.
func getLEDs(ledsOn, ledsBlink byte) map[Led]LEDstate {

	leds := map[Led]LEDstate{}
	for i := 0; i < 8; i++ {
		on := (ledsOn >> uint(i)) & 1
		blink := (ledsBlink >> uint(i)) & 1
		if on == 1 {
			leds[Led(i)] = LedOn
		} else if blink == 1 {
			leds[Led(i)] = LedBlink
		} else {
			leds[Led(i)] = LedOff
		}
	}
	return leds
}

// Adds header and trailing crc for frame to send.
func (m *mk2Ser) sendCommand(data []byte) {
	m.commandMu.Lock()
	defer m.commandMu.Unlock()
	m.sendCommandLocked(data)
}

func (m *mk2Ser) sendCommandLocked(data []byte) {
	l := len(data)
	dataOut := make([]byte, l+3)
	dataOut[0] = byte(l + 1)
	dataOut[1] = frameHeader
	cr := -dataOut[0] - dataOut[1]
	for i := 0; i < len(data); i++ {
		cr = cr - data[i]
		dataOut[i+2] = data[i]
	}
	dataOut[l+2] = cr

	mk2log.Debugf("sendCommand %#v", dataOut)
	m.recordTXTrace(dataOut, data)
	_, err := m.p.Write(dataOut)
	if err != nil {
		mk2log.WithError(err).Error("Failed to send MK2 command")
		m.addError(fmt.Errorf("Write error: %v", err))
		m.noteCommandFailure(err)
	}
}

func (m *mk2Ser) markFrameSeen() {
	m.diagMu.Lock()
	m.lastFrameAt = time.Now().UTC()
	m.diagMu.Unlock()
}

func (m *mk2Ser) recordError(err error) {
	if err == nil {
		return
	}
	m.diagMu.Lock()
	defer m.diagMu.Unlock()
	m.recentErrors = append(m.recentErrors, err.Error())
	if len(m.recentErrors) > 20 {
		m.recentErrors = m.recentErrors[len(m.recentErrors)-20:]
	}
}

func (m *mk2Ser) recordTXTrace(fullFrame []byte, payload []byte) {
	command := ""
	frame := ""
	if len(payload) > 0 {
		frame = fmt.Sprintf("0x%02x", payload[0])
		command = decodeTraceCommandName(payload)
	}
	m.appendTrace(ProtocolTrace{
		Timestamp: time.Now().UTC(),
		Direction: TraceDirectionTX,
		Frame:     frame,
		Command:   command,
		BytesHex:  strings.ToUpper(fmt.Sprintf("%X", fullFrame)),
	})
}

func (m *mk2Ser) recordRXTrace(frame []byte) {
	command := ""
	frameName := ""
	if len(frame) > 0 {
		frameName = fmt.Sprintf("0x%02x", frame[0])
		command = decodeTraceCommandName(frame)
	}
	m.appendTrace(ProtocolTrace{
		Timestamp: time.Now().UTC(),
		Direction: TraceDirectionRX,
		Frame:     frameName,
		Command:   command,
		BytesHex:  strings.ToUpper(fmt.Sprintf("%X", frame)),
	})
}

func decodeTraceCommandName(frame []byte) string {
	if len(frame) == 0 {
		return ""
	}
	switch frame[0] {
	case winmonFrame:
		if len(frame) < 2 {
			return "winmon"
		}
		return fmt.Sprintf("winmon:0x%02x", frame[1])
	case stateFrame:
		return "panel_state"
	case interfaceFrame:
		return "interface"
	case infoReqFrame:
		return "info_request"
	case ledFrame:
		return "led_status"
	case vFrame:
		return "version"
	case setTargetFrame:
		return "set_target"
	default:
		if frame[0] == frameHeader && len(frame) > 1 && frame[1] == winmonFrame && len(frame) > 2 {
			return fmt.Sprintf("winmon:0x%02x", frame[2])
		}
		return ""
	}
}

func (m *mk2Ser) appendTrace(trace ProtocolTrace) {
	m.diagMu.Lock()
	defer m.diagMu.Unlock()
	m.traces = append(m.traces, trace)
	limit := m.traceLimit
	if limit <= 0 {
		limit = 200
	}
	if len(m.traces) > limit {
		m.traces = m.traces[len(m.traces)-limit:]
	}
}

func calculateDriverHealthScore(diag DriverDiagnostics) int {
	score := 100
	score -= int(diag.CommandTimeouts) * 5
	score -= int(diag.CommandFailures) * 2
	score -= int(diag.ChecksumFailures) * 3
	if diag.LastFrameAt == nil {
		score -= 10
	} else if time.Since(diag.LastFrameAt.UTC()) > 30*time.Second {
		score -= 10
	}
	if score < 0 {
		return 0
	}
	if score > 100 {
		return 100
	}
	return score
}

// Checks the frame crc.
func checkChecksum(l, t byte, d []byte) bool {
	cr := (uint16(l) + uint16(t)) % 256
	for i := 0; i < len(d); i++ {
		cr = (cr + uint16(d[i])) % 256
	}
	return cr == 0
}