// --------------------
// Queue-based client (single owner of port)
// --------------------
package dispenser

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

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

type cmdType int

const (
	cmdStatus cmdType = iota
	cmdToEncoder
	cmdOutOfMouth
)

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

type cmdResp struct {
	status []byte
	err    error
}

type Client struct {
	port *serial.Port

	reqCh chan cmdReq
	done  chan struct{}

	// 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{}),
		statusTTL: defaultStatusTTL,
	}
	go c.loop()
	return c
}

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

// Optional: tune cache TTL (how "fresh" cached status must be)
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 := checkDispenserStatus(c.port)
		if err == nil && len(st) == 4 {
			c.mu.Lock()
			c.lastStatus = append([]byte(nil), st...)
			c.lastStatusT = time.Now()
			c.mu.Unlock()

			// publish stock/cardwell
			c.setStock(st)
		}
		req.respCh <- cmdResp{status: st, err: err}

	case cmdToEncoder:
		err := cardToEncoderPosition(c.port)
		req.respCh <- cmdResp{err: err}

	case cmdOutOfMouth:
		err := cardOutOfMouth(c.port)
		req.respCh <- cmdResp{err: err}

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

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

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

	select {
	case r := <-rch:
		return r.status, r.err
	case <-ctx.Done():
		return nil, 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) ToEncoder(ctx context.Context) error {
	_, err := c.do(ctx, cmdToEncoder)
	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: check 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) DispenserStart(ctx context.Context) (string, error) {
	const funcName = "DispenserStart"
	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, fmt.Errorf(stockStatus)
	}
	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) DispenserFinal(ctx context.Context) (string, error) {
	const funcName = "DispenserFinal"
	stockStatus := ""

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

	time.Sleep(delay)
	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)

	time.Sleep(delay)
	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
}