// 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
)

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

var errDeliveryPending = errors.New("next-card preparation deferred: previous delivery is not clear")

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
	sequenceRetryAfter   = 6 * time.Second
	sequenceResetWait    = 2 * time.Second
	sequenceTimeout      = 16 * 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 cmdToEncoder:
		if c.deliveryPending {
			// Stay inside port ownership: never enqueue a request from the worker.
			st, err := c.readWorkerStatus(req.ctx)
			if err == nil {
				_, err = deliveryClearance(st)
			}
			if err == nil && c.deliveryPending {
				err = errDeliveryPending
				log.Debugf("next-card preparation deferred; raw status: % X", st)
			}
			if err != nil {
				req.respCh <- cmdResp{err: err}
				return
			}
		}
		err := cardToEncoderPosition(req.ctx, c.port)
		c.invalidateStatusCache()
		req.respCh <- cmdResp{err: err}

	case cmdReset:
		err := resetDispenser(req.ctx, c.port)
		c.invalidateStatusCache()
		req.respCh <- cmdResp{err: err}

	case cmdOutOfMouth:
		attempted, err := cardOutOfMouth(req.ctx, c.port)
		if attempted {
			c.deliveryPending = true
			c.deliveryStarted = time.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) {
	if err := validateDispenserStatusData(status); err != nil {
		return false, err
	}
	if isCardWellEmpty(status) {
		return false, ErrCardWellEmpty
	}
	if isPreparationMoving(status) {
		return false, nil
	}
	if err := dispenserStatusError(status); err != nil {
		return false, err
	}
	return status[0] == 0x30 && status[1] == 0x30 && status[3] == 0x30, nil
}

// 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 c.deliveryPending {
		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.deliveryPending = false
			log.Infof("previous delivery cleared after %s; FC7 permitted", time.Since(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)
	status, err := response.status, response.err
	if err == nil && response.deliveryPending {
		err = errDeliveryPending
	}
	if err != nil {
		if ctxErr := ctx.Err(); ctxErr != nil {
			return nil, "", fmt.Errorf("[%s] read status: %w", operation, ctxErr)
		}
		return nil, "", fmt.Errorf("[%s] read status: %w", operation, err)
	}

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

func preparationStatus(operation string, status []byte, allowCombinedFailure bool) (bool, error) {
	// A confirmed read sensor takes precedence over every other diagnostic.
	if isAtEncoderPosition(status) {
		if hasPreparationDiagnostics(status) {
			log.Warnf(
				"[%s] card confirmed at encoder with dispenser diagnostics: %s raw status: % X",
				operation,
				statusDescription(status),
				status,
			)
		}
		return true, nil
	}
	if err := validateDispenserStatusData(status); err != nil {
		return false, fmt.Errorf("[%s] %w", operation, err)
	}
	if isCardWellEmpty(status) {
		return false, fmt.Errorf("[%s] %w", operation, ErrCardWellEmpty)
	}
	if isPreparationMoving(status) {
		return false, nil
	}

	// Some dispenser firmware briefly reports 0x32 ("Preparing card fails")
	// while the card is still travelling to the encoder. Treat that one
	// diagnostic as transient during an active preparation sequence and let
	// pollForEncoderPosition decide encoder success or timeout. Do not mask
	// independent hard errors reported in the other status bytes.
	// Combined command rejection is also recoverable before the one retry.
	if status[0] == 0x32 || (status[0] == 0x36 && allowCombinedFailure) {
		statusWithoutPrepareFailure := append([]byte(nil), status...)
		statusWithoutPrepareFailure[0] = 0x30
		if err := dispenserStatusError(statusWithoutPrepareFailure); err != nil {
			return false, fmt.Errorf("[%s] %w", operation, err)
		}

		log.Warnf(
			"[%s] transient preparation failure (%s); waiting for encoder position, raw status: % X",
			operation,
			statusDescription(status),
			status,
		)
		return false, nil
	}

	if err := dispenserStatusError(status); err != nil {
		return false, fmt.Errorf("[%s] %w", operation, err)
	}
	return false, nil
}

func (c *Client) pollForEncoderPosition(ctx context.Context, operation string) (stockStatus string, resultErr error) {
	started := c.sequenceTiming.now()
	recoveryAt := started.Add(sequenceRetryAfter)
	deadline := started.Add(sequenceTimeout)
	ctx, cancel := context.WithTimeout(ctx, sequenceTimeout)
	defer cancel()
	retried := false
	resetAttempted := false
	retryAfterReset := false
	consecutiveFailures := 0
	stage := "initial polling"
	var lastStatus []byte
	defer func() {
		if resultErr != nil {
			log.Warnf("[%s] card preparation failed; stage=%s reset_attempted=%t raw status: % X: %v", operation, stage, resetAttempted, lastStatus, resultErr)
		}
	}()

	checkDeadline := func() error {
		if err := ctx.Err(); err != nil {
			return fmt.Errorf("[%s] %s: %w", operation, stage, err)
		}
		if !c.sequenceTiming.now().Before(deadline) {
			return fmt.Errorf("[%s] %s: timed out after %s", operation, stage, sequenceTimeout)
		}
		return nil
	}

	for {
		if err := checkDeadline(); err != nil {
			return stockStatus, err
		}
		status, currentStockStatus, err := c.readSequenceStatus(ctx, operation)
		stockStatus = currentStockStatus
		lastStatus = status
		if err != nil {
			return stockStatus, err
		}
		if err := checkDeadline(); err != nil {
			return stockStatus, err
		}
		ready, err := preparationStatus(operation, status, !retried || retryAfterReset)
		if err != nil {
			return stockStatus, err
		}
		if ready {
			if resetAttempted {
				log.Infof("[%s] card preparation recovered after reset", operation)
			}
			return stockStatus, nil
		}

		moving := isPreparationMoving(status)
		prepareFailed := status[0] == 0x32 || status[0] == 0x36
		if prepareFailed && !moving {
			consecutiveFailures++
		} else {
			consecutiveFailures = 0
		}
		if !moving && retryAfterReset {
			stage = "post-reset FC7"
			if err := checkDeadline(); err != nil {
				return stockStatus, err
			}
			log.Infof("[%s] reset settle wait completed; retrying card preparation", operation)
			if err := c.ToEncoder(ctx); err != nil {
				return stockStatus, fmt.Errorf("[%s] post-reset retry command: %w", operation, err)
			}
			retryAfterReset = false
			stage = "polling after reset and retry"
		} else if !moving && !retried && !c.sequenceTiming.now().Before(recoveryAt) {
			if prepareFailed && consecutiveFailures >= 2 {
				stage = "RS recovery"
				if err := checkDeadline(); err != nil {
					return stockStatus, err
				}
				retried = true
				resetAttempted = true
				log.Warnf("[%s] persistent prepare failure; resetting dispenser, raw status: % X", operation, status)
				if err := c.Reset(ctx); err != nil {
					return stockStatus, fmt.Errorf("[%s] reset command: %w", operation, err)
				}
				stage = "reset settle"
				if err := checkDeadline(); err != nil {
					return stockStatus, err
				}
				log.Infof("[%s] reset dispatched; waiting for mechanical settling", operation)
				wait := sequenceResetWait
				if remaining := deadline.Sub(c.sequenceTiming.now()); remaining < wait {
					wait = remaining
				}
				if err := c.sequenceTiming.wait(ctx, wait); err != nil {
					return stockStatus, fmt.Errorf("[%s] reset settle: %w", operation, err)
				}
				retryAfterReset = true
				stage = "post-reset status"
				continue // Always read fresh physical status before the retry.
			}
			if !prepareFailed {
				stage = "FC7 retry"
				if err := checkDeadline(); err != nil {
					return stockStatus, err
				}
				retried = true
				if err := c.ToEncoder(ctx); err != nil {
					return stockStatus, fmt.Errorf("[%s] retry command: %w", operation, err)
				}
			}
		}

		if err := checkDeadline(); err != nil {
			return stockStatus, err
		}
		wait := sequencePollInterval
		if remaining := deadline.Sub(c.sequenceTiming.now()); remaining < wait {
			wait = remaining
		}
		if err := c.sequenceTiming.wait(ctx, wait); err != nil {
			return stockStatus, fmt.Errorf("[%s] %s: %w", operation, stage, err)
		}
	}
}

// waitForDeliveryClearance reuses the first clear AP as the initial preparation sample.
// Its bounded window is separate from recovery, which starts after initial FC7.
func (c *Client) waitForDeliveryClearance(ctx context.Context, operation string) (status []byte, stock string, resultErr error) {
	ctx, cancel := context.WithTimeout(ctx, sequenceTimeout)
	defer cancel()
	deadline := c.sequenceTiming.now().Add(sequenceTimeout)
	var lastStatus []byte
	defer func() {
		if resultErr != nil {
			log.Warnf("[%s] delivery clearance stopped: %v; %s raw status: % X", operation, resultErr, statusDescription(lastStatus), lastStatus)
		}
	}()
	for {
		if err := ctx.Err(); err != nil {
			return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, err)
		}
		if !c.sequenceTiming.now().Before(deadline) {
			return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, context.DeadlineExceeded)
		}
		r := c.doResponse(ctx, cmdStatus)
		if len(r.status) > 0 {
			lastStatus = r.status
		}
		if r.err != nil {
			return nil, stock, fmt.Errorf("[%s] delivery clearance status: %w", operation, r.err)
		}
		if len(r.status) == 4 {
			stock = stockTake(r.status)
			c.setStock(r.status)
		}
		if err := ctx.Err(); err != nil {
			return nil, stock, err
		}
		if !c.sequenceTiming.now().Before(deadline) {
			return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, context.DeadlineExceeded)
		}
		if !r.deliveryPending {
			return r.status, stock, nil
		}
		if _, err := deliveryClearance(r.status); err != nil {
			return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, err)
		}
		wait := sequencePollInterval
		if remaining := deadline.Sub(c.sequenceTiming.now()); remaining < wait {
			wait = remaining
		}
		if err := c.sequenceTiming.wait(ctx, wait); err != nil {
			return nil, stock, fmt.Errorf("[%s] delivery clearance: %w", operation, err)
		}
	}
}

func (c *Client) prepareCardAtEncoder(ctx context.Context, operation string) (string, error) {
	status, stockStatus, err := c.waitForDeliveryClearance(ctx, operation)
	if err != nil {
		return stockStatus, err
	}
	ready, err := preparationStatus(operation, status, true)
	if err != nil {
		return stockStatus, err
	}
	if ready {
		return stockStatus, nil
	}

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

// PrepareCurrentCard authoritatively places the card to be encoded at the encoder.
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 starts moving the next card to the encoder without waiting for 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 places a new card at the encoder for a later issuance attempt.
func (c *Client) PrepareNextCard(ctx context.Context) (string, error) {
	return c.prepareCardAtEncoder(ctx, "PrepareNextCard")
}