package devicecheck

import (
	"context"
	"database/sql"
	"encoding/json"
	"log"
	"strings"
	"sync"
	"time"

	"git.piskot.si/SeminarM2/lambdaiot-core/internal/mqtt"
)

// Checker periodically pings devices via MQTT and updates their status
// based on responses received on the subscribed topic.
type Checker struct {
	DB       *sql.DB
	MQTT     *mqtt.Client
	Topic    string
	Interval time.Duration
	Timeout  time.Duration

	mu      sync.Mutex
	waiters map[string]chan struct{}
}

// New constructs a Checker with sane defaults for interval and timeout when zero.
func New(db *sql.DB, mq *mqtt.Client, topic string, interval, timeout time.Duration) *Checker {
	if interval == 0 {
		interval = time.Minute
	}
	if timeout == 0 {
		timeout = 10 * time.Second
	}
	if topic == "" {
		topic = "lambdaiot"
	}
	return &Checker{
		DB:       db,
		MQTT:     mq,
		Topic:    topic,
		Interval: interval,
		Timeout:  timeout,
		waiters:  make(map[string]chan struct{}),
	}
}

// Start launches the periodic checker until the context is canceled.
func (c *Checker) Start(ctx context.Context) {
	if c != nil {
		log.Printf("devicecheck: starting (topic=%s interval=%s timeout=%s)", c.Topic, c.Interval, c.Timeout)
	}
	go c.loop(ctx)
}

// HandleMessage attempts to parse a device state/check response message and
// signals any waiter for the given device. Expected JSON payload shape:
//
//	{
//	  "type": "device_check_response" | "device_state",
//	  "device_id": "uuid",
//	  "status": "ok" | "lost" | "pending"
//	}
func (c *Checker) HandleMessage(payload []byte) {
	if c == nil {
		return
	}
	var msg struct {
		Type     string `json:"type"`
		DeviceID string `json:"device_id"`
		Status   string `json:"status"`
	}
	if err := json.Unmarshal(payload, &msg); err != nil {
		return
	}
	id := strings.ToLower(strings.TrimSpace(msg.DeviceID))
	if id == "" {
		return
	}

	msgType := strings.ToLower(strings.TrimSpace(msg.Type))
	if msgType != "device_check_response" && msgType != "device_state" && !strings.EqualFold(msg.Status, "ok") {
		return
	}

	// Notify waiter if present for valid response/state
	c.mu.Lock()
	ch := c.waiters[id]
	c.mu.Unlock()
	if ch != nil {
		select {
		case ch <- struct{}{}:
		default:
		}
	}

	// Update status to ok on explicit ok or check response/state
	_ = c.updateStatus(id, 1) // 1 = ok
}

func (c *Checker) loop(ctx context.Context) {
	ticker := time.NewTicker(c.Interval)
	defer ticker.Stop()

	// Run immediately
	c.runOnce()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			c.runOnce()
		}
	}
}

func (c *Checker) runOnce() {
	if c == nil || c.DB == nil || c.MQTT == nil {
		return
	}

	rows, err := c.DB.Query("SELECT BIN_TO_UUID(id) FROM devices WHERE status_id NOT IN (3, 4)") // skip lost/disabled
	if err != nil {
		log.Printf("devicecheck: query devices failed: %v", err)
		return
	}
	defer rows.Close()

	var ids []string
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			log.Printf("devicecheck: scan id failed: %v", err)
			return
		}
		ids = append(ids, strings.ToLower(id))
	}
	if err := rows.Err(); err != nil {
		log.Printf("devicecheck: rows error: %v", err)
		return
	}
	if len(ids) == 0 {
		log.Printf("devicecheck: no devices found to check")
		return
	}

	var wg sync.WaitGroup
	for _, id := range ids {
		wg.Add(1)
		go func(deviceID string) {
			defer wg.Done()
			c.checkDevice(deviceID)
		}(id)
	}
	wg.Wait()
}

func (c *Checker) checkDevice(deviceID string) {
	if c == nil || c.DB == nil || c.MQTT == nil {
		return
	}

	ch := make(chan struct{}, 1)
	c.mu.Lock()
	c.waiters[deviceID] = ch
	c.mu.Unlock()

	payload := struct {
		Type        string `json:"type"`
		DeviceID    string `json:"device_id"`
		RequestedAt string `json:"requested_at"`
	}{
		Type:        "device_check_request",
		DeviceID:    deviceID,
		RequestedAt: time.Now().UTC().Format(time.RFC3339),
	}

	body, err := json.Marshal(payload)
	if err == nil {
		log.Printf("devicecheck: publish request for %s", deviceID)
		if err := c.MQTT.Publish(c.Topic, body); err != nil {
			log.Printf("devicecheck: publish failed for %s: %v", deviceID, err)
		}
	}

	if err := c.updateStatus(deviceID, 2); err != nil { // 2 = pending
		log.Printf("devicecheck: set pending failed for %s: %v", deviceID, err)
	}

	select {
	case <-ch:
		if err := c.updateStatus(deviceID, 1); err != nil { // ok
			log.Printf("devicecheck: set ok failed for %s: %v", deviceID, err)
		}
	case <-time.After(c.Interval):
		if err := c.updateStatus(deviceID, 3); err != nil { // lost
			log.Printf("devicecheck: set lost failed for %s: %v", deviceID, err)
		}
	}

	c.mu.Lock()
	delete(c.waiters, deviceID)
	c.mu.Unlock()
}

func (c *Checker) updateStatus(deviceID string, statusID int) error {
	if c == nil || c.DB == nil {
		return nil
	}
	log.Printf("devicecheck: update status request %s -> %d", deviceID, statusID)
	res, err := c.DB.Exec("UPDATE devices SET status_id = ?, updated_at = NOW(6) WHERE id = UUID_TO_BIN(?)", statusID, deviceID)
	if err != nil {
		log.Printf("devicecheck: update status failed for %s -> %d: %v", deviceID, statusID, err)
		return err
	}
	rows, err := res.RowsAffected()
	if err != nil {
		log.Printf("devicecheck: rows affected failed for %s -> %d: %v", deviceID, statusID, err)
		return err
	}
	if rows == 0 {
		log.Printf("devicecheck: no rows updated for %s -> %d", deviceID, statusID)
	}
	return nil
}