// Package dispenser provides a queue-based client (single owner of port).
package dispenser

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"time"

	log "github.com/sirupsen/logrus"
	"github.com/tarm/serial"
)

type cmdType int

const (
	cmdStatus cmdType = iota
	cmdToEncoder
	cmdOutOfMouth
	cmdReset
	cmdDeliveryClearance
)

type cmdReq struct {
	typ    cmdType
	ctx    context.Context
	respCh chan cmdResp
}

type cmdResp struct {
	deliveryPending bool
	status          []byte
	err             error
}

type sequenceTiming struct {
	now  func() time.Time
	wait func(context.Context, time.Duration) error
}

const (
	sequencePollInterval     = time.Second
	sequenceShakeAfter       = 3 * time.Second
	sequenceResetWait        = 2 * time.Second
	sequenceTimeout          = 32 * time.Second
	sequenceUncertainWait    = 4 * time.Second
	sequenceMaxShakes        = 3
	deliveryClearanceTimeout = 6 * time.Second
	deliveryMinimumWait      = 2 * time.Second
)

type Client struct {
	port serialTransport

	reqCh chan cmdReq
	done  chan struct{}

	// Owned exclusively by the serial worker.
	deliveryPending bool
	deliveryStarted time.Time

	sequenceTiming sequenceTiming

	// status cache
	mu          sync.RWMutex
	lastStatus  []byte
	lastStatusT time.Time
	statusTTL   time.Duration

	// published "stock/cardwell" cache + callback
	lastStockMu sync.RWMutex
	lastStock   string
	onStock     func(string)
}

// NewClient starts the worker that owns the serial port.
func NewClient(port *serial.Port, queueSize int) *Client {
	if queueSize <= 0 {
		queueSize = 16
	}
	c := &Client{
		port:  port,
		reqCh: make(chan cmdReq, queueSize),
		done:  make(chan struct{}),
		sequenceTiming: sequenceTiming{
			now:  time.Now,
			wait: waitForSequence,
		},
		statusTTL: defaultStatusTTL,
	}
	go c.loop()
	return c
}

func waitForSequence(ctx context.Context, duration time.Duration) error {
	timer := time.NewTimer(duration)
	defer timer.Stop()

	select {
	case <-timer.C:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (c *Client) Close() {
	select {
	case <-c.done:
		return
	default:
		close(c.done)
	}
}

// SetStatusTTL sets the duration for which cached status is considered fresh.
func (c *Client) SetStatusTTL(d time.Duration) {
	c.mu.Lock()
	c.statusTTL = d
	c.mu.Unlock()
}

// OnStockUpdate registers a callback called whenever polling (or status reads) produce a stock status string.
func (c *Client) OnStockUpdate(fn func(string)) {
	c.lastStockMu.Lock()
	c.onStock = fn
	c.lastStockMu.Unlock()
}

// LastStock returns the most recently computed stock/card-well status string.
func (c *Client) LastStock() string {
	c.lastStockMu.RLock()
	defer c.lastStockMu.RUnlock()
	return c.lastStock
}

func (c *Client) setStock(statusBytes []byte) {
	stock := stockTake(statusBytes)

	c.lastStockMu.Lock()
	c.lastStock = stock
	fn := c.onStock
	c.lastStockMu.Unlock()

	// call outside lock
	if fn != nil {
		fn(stock)
	}
}

// StartPolling performs a periodic status refresh.
// It will NOT interrupt commands: it enqueues only when queue is idle.
func (c *Client) StartPolling(interval time.Duration) {
	if interval <= 0 {
		return
	}
	go func() {
		t := time.NewTicker(interval)
		defer t.Stop()

		for {
			select {
			case <-c.done:
				return
			case <-t.C:
				// enqueue only if idle to avoid delaying real commands
				if len(c.reqCh) != 0 {
					continue
				}
				ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
				_, err := c.CheckStatus(ctx)
				if err != nil {
					log.Debugf("dispenser polling: %v", err)
				}
				cancel()
			}
		}
	}()
}

func (c *Client) loop() {
	for {
		select {
		case <-c.done:
			return
		case req := <-c.reqCh:
			c.handle(req)
		}
	}
}

func (c *Client) handle(req cmdReq) {
	select {
	case <-req.ctx.Done():
		req.respCh <- cmdResp{err: req.ctx.Err()}
		return
	default:
	}

	switch req.typ {
	case cmdStatus:
		st, err := c.readWorkerStatus(req.ctx)
		req.respCh <- cmdResp{status: st, err: err, deliveryPending: c.deliveryPending}

	case cmdDeliveryClearance:
		st, err := c.waitWorkerDeliveryClearance(req.ctx)
		req.respCh <- cmdResp{status: st, err: err, deliveryPending: c.deliveryPending}

	case cmdToEncoder:
		if c.deliveryPending {
			if _, err := c.waitWorkerDeliveryClearance(req.ctx); err != nil {
				req.respCh <- cmdResp{err: err}
				return
			}
		}
		err := cardToEncoderPosition(req.ctx, c.port)
		log.Infof("FC7 dispatch finished; dispatched=%t error=%v", err == nil, err)
		c.invalidateStatusCache()
		req.respCh <- cmdResp{err: err}

	case cmdReset:
		err := resetDispenser(req.ctx, c.port)
		log.Infof("RS dispatch finished; dispatched=%t error=%v", err == nil, err)
		c.invalidateStatusCache()
		req.respCh <- cmdResp{err: err}

	case cmdOutOfMouth:
		attempted, err := cardOutOfMouth(req.ctx, c.port)
		log.Infof("FC0 dispatch finished; ENQ_attempted=%t error=%v", attempted, err)
		if attempted {
			c.deliveryPending = true
			c.deliveryStarted = c.now()
			log.Info("delivery ENQ attempted; awaiting mechanical clearance")
		}
		// A movement command makes any previously cached position unreliable.
		c.invalidateStatusCache()
		req.respCh <- cmdResp{err: err}

	default:
		req.respCh <- cmdResp{err: fmt.Errorf("unknown command")}
	}
}

// deliveryClearance deliberately does not apply encoder-success precedence.
func deliveryClearance(status []byte) (bool, error) {
	class, err := classifyPreparationStatus(status)
	if err != nil {
		return false, err
	}
	if class == positionWellEmpty {
		return false, ErrCardWellEmpty
	}
	if isPreparationMoving(status) || status[1] == 0x34 {
		return false, nil
	}
	return status[3] == 0x30 || status[3] == 0x34, nil
}

func (c *Client) now() time.Time {
	if c.sequenceTiming.now != nil {
		return c.sequenceTiming.now()
	}
	return time.Now()
}

// readWorkerStatus is called only by the serial worker and always reads fresh AP.
func (c *Client) readWorkerStatus(ctx context.Context) ([]byte, error) {
	st, err := checkDispenserStatus(ctx, c.port)
	if err != nil {
		return st, err
	}
	if err := ctx.Err(); err != nil {
		return st, err
	}
	if c.deliveryPending {
		class, _ := classifyPreparationStatus(st)
		log.Infof("delivery clearance AP; class=%s elapsed=%s raw status: % X", class, c.now().Sub(c.deliveryStarted), st)
		clear, clearanceErr := deliveryClearance(st)
		if clearanceErr != nil {
			log.Warnf("delivery clearance failed: %v; %s raw status: % X", clearanceErr, statusDescription(st), st)
		} else if clear && c.now().Sub(c.deliveryStarted) >= deliveryMinimumWait {
			c.deliveryPending = false
			log.Infof("previous delivery cleared after %s; FC7 permitted", c.now().Sub(c.deliveryStarted))
		}
	}
	if len(st) == 4 {
		c.mu.Lock()
		c.lastStatus = append([]byte(nil), st...)
		c.lastStatusT = time.Now()
		c.mu.Unlock()
		c.setStock(st)
	}
	return st, nil
}

func (c *Client) do(ctx context.Context, typ cmdType) ([]byte, error) {
	r := c.doResponse(ctx, typ)
	return r.status, r.err
}

func (c *Client) doResponse(ctx context.Context, typ cmdType) cmdResp {
	rch := make(chan cmdResp, 1)
	req := cmdReq{typ: typ, ctx: ctx, respCh: rch}

	select {
	case c.reqCh <- req:
	case <-ctx.Done():
		return cmdResp{err: ctx.Err()}
	}

	select {
	case r := <-rch:
		return r
	case <-ctx.Done():
		return cmdResp{err: ctx.Err()}
	}
}

// CheckStatus returns cached status if fresh, otherwise enqueues a device status read.
func (c *Client) CheckStatus(ctx context.Context) ([]byte, error) {
	c.mu.RLock()
	ttl := c.statusTTL
	st := append([]byte(nil), c.lastStatus...)
	ts := c.lastStatusT
	c.mu.RUnlock()

	if len(st) == 4 && time.Since(ts) <= ttl {
		// even when returning cached, keep stock in sync
		c.setStock(st)
		return st, nil
	}
	return c.do(ctx, cmdStatus)
}

func (c *Client) invalidateStatusCache() {
	c.mu.Lock()
	c.lastStatus = nil
	c.lastStatusT = time.Time{}
	c.mu.Unlock()
}

func (c *Client) ToEncoder(ctx context.Context) error {
	_, err := c.do(ctx, cmdToEncoder)
	return err
}

// Reset dispatches RS through the port owner; acceptance does not imply mechanical completion.
func (c *Client) Reset(ctx context.Context) error {
	_, err := c.do(ctx, cmdReset)
	return err
}

func (c *Client) OutOfMouth(ctx context.Context) error {
	_, err := c.do(ctx, cmdOutOfMouth)
	return err
}

// --------------------
// Public sequences updated to use Client (queue)
// --------------------

// DispenserPrepare checks status; if empty => ok; else ensure at encoder.
func (c *Client) DispenserPrepare(ctx context.Context) (string, error) {
	const funcName = "DispenserPrepare"
	stockStatus := ""

	status, err := c.CheckStatus(ctx)
	if err != nil {
		return stockStatus, fmt.Errorf("[%s] check status: %w", funcName, err)
	}

	logStatus(status)
	stockStatus = stockTake(status)
	c.setStock(status)

	if isCardWellEmpty(status) {
		return stockStatus, nil
	}
	if isAtEncoderPosition(status) {
		return stockStatus, nil
	}

	if err := c.ToEncoder(ctx); err != nil {
		return stockStatus, fmt.Errorf("[%s] to encoder: %w", funcName, err)
	}

	time.Sleep(delay)
	status, err = c.CheckStatus(ctx)
	if err != nil {
		return stockStatus, fmt.Errorf("[%s] re-check status: %w", funcName, err)
	}
	logStatus(status)
	stockStatus = stockTake(status)
	c.setStock(status)

	return stockStatus, nil
}

func (c *Client) readSequenceStatus(ctx context.Context, operation string) ([]byte, string, error) {
	response := c.doResponse(ctx, cmdStatus)
	if err := ctx.Err(); err != nil {
		return nil, "", err
	}
	if response.deliveryPending {
		return c.waitForDeliveryClearance(ctx, operation)
	}
	status := usableObservation(response.status, response.err, operation)

	stockStatus := ""
	if len(status) == 4 {
		stockStatus = stockTake(status)
		c.setStock(status)
		logStatus(status)
	}
	return status, stockStatus, nil
}

// waitWorkerDeliveryClearance runs only inside the serial worker.
// An unusable observation never becomes a fabricated physical position.
func (c *Client) waitWorkerDeliveryClearance(parent context.Context) ([]byte, error) {
	ctx, cancel := context.WithTimeout(parent, deliveryClearanceTimeout)
	defer cancel()
	deadline := c.now().Add(deliveryClearanceTimeout)
	var latest []byte
	for {
		if err := parent.Err(); err != nil {
			return nil, err
		}
		if !c.now().Before(deadline) || ctx.Err() != nil {
			class, err := classifyPreparationStatus(latest)
			if err == nil && class == positionWellEmpty {
				return latest, ErrCardWellEmpty
			}
			if err == nil && (isPreparationMoving(latest) || latest[1] == 0x34) {
				return latest, context.DeadlineExceeded
			}
			c.deliveryPending = false
			log.Warn("delivery clearance assumed after bounded observation fallback")
			return latest, nil
		}
		st, err := c.readWorkerStatus(ctx)
		if parent.Err() != nil {
			return nil, parent.Err()
		}
		latest = usableObservation(st, err, "delivery clearance")
		if latest != nil && latest[3] == 0x38 {
			return latest, ErrCardWellEmpty
		}
		if !c.deliveryPending {
			return latest, nil
		}
		remaining := deadline.Sub(c.now())
		if remaining <= 0 || ctx.Err() != nil {
			continue
		}
		wait := sequencePollInterval
		if remaining < wait {
			wait = remaining
		}
		if err := c.sequenceTiming.wait(ctx, wait); err != nil && parent.Err() != nil {
			return nil, parent.Err()
		}
	}
}

// usableObservation preserves strict validation while discarding unusable telemetry.
func usableObservation(status []byte, err error, operation string) []byte {
	if err == nil {
		_, err = classifyPreparationStatus(status)
	}
	if err != nil {
		log.Warnf("[%s] unusable AP observation; raw status: % X error=%v", operation, status, err)
		return nil
	}
	return status
}

// waitForDeliveryClearance uses a worker request; no worker recursively enqueues.
func (c *Client) waitForDeliveryClearance(ctx context.Context, operation string) ([]byte, string, error) {
	r := c.doResponse(ctx, cmdDeliveryClearance)
	stock := ""
	if len(r.status) == 4 {
		stock = stockTake(r.status)
	}
	if r.err != nil {
		return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, r.err)
	}
	return r.status, stock, nil
}

func (c *Client) prepareCardAtEncoder(parent context.Context, operation string) (stock string, resultErr error) {
	status, stock, err := c.waitForDeliveryClearance(parent, operation)
	if err != nil {
		return stock, err
	}
	status = usableObservation(status, nil, operation)
	started := c.now()
	deadline := started.Add(sequenceTimeout)
	ctx, cancel := context.WithTimeoutCause(parent, sequenceTimeout, ErrPreparationExhausted)
	defer cancel()
	shakes := 0
	stage := "initial status"
	var lastFC7, uncertainSince time.Time
	var previous preparationClass
	defer func() {
		log.Infof("[%s] preparation finished; stage=%s shakes=%d elapsed=%s raw status: % X error=%v", operation, stage, shakes, c.now().Sub(started), status, resultErr)
	}()
	checkDeadline := func() error {
		if err := parent.Err(); err != nil {
			return err
		}
		if !c.now().Before(deadline) || errors.Is(context.Cause(ctx), ErrPreparationExhausted) {
			return ErrPreparationExhausted
		}
		return ctx.Err()
	}
	// Only observation exhaustion can grant a deadline handoff. Command and
	// reset-settle failures never pass through this policy.
	observationResult := func(err error) error {
		if parent.Err() != nil {
			return parent.Err()
		}
		if !errors.Is(err, ErrPreparationExhausted) || lastFC7.IsZero() {
			return err
		}
		class, _ := classifyPreparationStatus(status)
		switch class {
		case positionWellEmpty:
			return ErrCardWellEmpty
		case positionNoCard:
			return err
		default:
			stage = "observation deadline encoder handoff"
			return nil
		}
	}
	wait := func(duration time.Duration) error {
		if err := checkDeadline(); err != nil {
			return err
		}
		if remaining := deadline.Sub(c.now()); remaining < duration {
			duration = remaining
		}
		if err := c.sequenceTiming.wait(ctx, duration); err != nil {
			if deadlineErr := checkDeadline(); deadlineErr != nil {
				return deadlineErr
			}
			return err
		}
		return checkDeadline()
	}
	sendFC7 := func() error {
		stage = "FC7 dispatch"
		if err := checkDeadline(); err != nil {
			return err
		}
		err := c.ToEncoder(ctx)
		if deadlineErr := checkDeadline(); deadlineErr != nil {
			return deadlineErr
		}
		if err != nil {
			return fmt.Errorf("[%s] FC7 dispatch: %w", operation, err)
		}
		lastFC7 = c.now()
		log.Infof("[%s] FC7 dispatched; shake=%d elapsed=%s", operation, shakes, lastFC7.Sub(started))
		return nil
	}
	for {
		if err := checkDeadline(); err != nil {
			return stock, observationResult(err)
		}
		class, _ := classifyPreparationStatus(status)
		// No class means unusable telemetry, sharing the uncertainty timer.

		log.Infof("[%s] fresh AP; class=%s previous=%s elapsed=%s shake=%d raw status: % X", operation, class, previous, c.now().Sub(started), shakes, status)
		previous = class
		switch class {
		case encoderConfirmed:
			stage = "encoder sensor handoff"
			return stock, observationResult(checkDeadline())
		case positionWellEmpty:
			stage = "empty"
			return stock, ErrCardWellEmpty
		}
		if lastFC7.IsZero() {
			if err := sendFC7(); err != nil {
				return stock, err
			}
		} else if class == positionNoCard && c.now().Sub(lastFC7) >= sequenceShakeAfter {
			uncertainSince = time.Time{}
			if shakes == sequenceMaxShakes {
				stage = "three shakes exhausted"
				return stock, ErrPreparationExhausted
			}
			shakes++
			stage = "RS dispatch"
			if err := checkDeadline(); err != nil {
				return stock, err
			}
			err := c.Reset(ctx)
			if deadlineErr := checkDeadline(); deadlineErr != nil {
				return stock, deadlineErr
			}
			if err != nil {
				return stock, fmt.Errorf("[%s] RS dispatch: %w", operation, err)
			}
			stage = "reset settling"
			log.Infof("[%s] RS dispatched; shake=%d settling=%s", operation, shakes, sequenceResetWait)
			if err := wait(sequenceResetWait); err != nil {
				return stock, err
			}
			log.Infof("[%s] reset settle wait completed; shake=%d", operation, shakes)
			if err := sendFC7(); err != nil {
				return stock, err
			}
		} else {
			if class == positionUncertain || class == "" {
				if uncertainSince.IsZero() {
					uncertainSince = c.now()
				}
				if c.now().Sub(uncertainSince) >= sequenceUncertainWait {
					stage = "uncertain position handoff"
					return stock, observationResult(checkDeadline())
				}
			} else {
				uncertainSince = time.Time{}
			}
			stage = "polling"
			if err := wait(sequencePollInterval); err != nil {
				return stock, observationResult(err)
			}
		}
		stage = "fresh AP"
		if err := checkDeadline(); err != nil {
			return stock, observationResult(err)
		}
		status, stock, err = c.readSequenceStatus(ctx, operation)
		if deadlineErr := checkDeadline(); deadlineErr != nil {
			return stock, observationResult(deadlineErr)
		}
		if err != nil {
			return stock, err
		}
	}
}

// PrepareCurrentCard grants one encoder opportunity after bounded physical preparation.
func (c *Client) PrepareCurrentCard(ctx context.Context) (string, error) {
	return c.prepareCardAtEncoder(ctx, "PrepareCurrentCard")
}

// DeliverCurrentCard presents the encoded card and confirms command acceptance.
func (c *Client) DeliverCurrentCard(ctx context.Context) (string, error) {
	const operation = "DeliverCurrentCard"

	if err := c.OutOfMouth(ctx); err != nil {
		return "", fmt.Errorf("[%s] out of mouth: %w", operation, err)
	}
	return "", nil
}

// BeginPrepareNextCard waits for worker-owned clearance and dispatches one FC7.
// It does not wait for encoder readiness.
func (c *Client) BeginPrepareNextCard(ctx context.Context) error {
	if err := c.ToEncoder(ctx); err != nil {
		return fmt.Errorf("[BeginPrepareNextCard] to encoder: %w", err)
	}
	return nil
}

// PrepareNextCard runs the same bounded physical preparation for a later issuance attempt.
func (c *Client) PrepareNextCard(ctx context.Context) (string, error) {
	return c.prepareCardAtEncoder(ctx, "PrepareNextCard")
}