package service

import (
	"context"
	"log"
	"sync"
	"time"

	"accounting-app/internal/cache"
)

// SyncScheduler handles scheduled synchronization of exchange rates
// It uses ExchangeRateServiceV2 to fetch rates from YunAPI and update Redis cache
type SyncScheduler struct {
	service  *ExchangeRateServiceV2
	interval time.Duration
	stopChan chan struct{}
	mu       sync.Mutex
	running  bool
}

// NewSyncScheduler creates a new SyncScheduler instance
// interval specifies the time between sync operations (default: 10 minutes)
func NewSyncScheduler(service *ExchangeRateServiceV2, interval time.Duration) *SyncScheduler {
	if interval <= 0 {
		interval = 10 * time.Minute // Default to 10 minutes
	}

	return &SyncScheduler{
		service:  service,
		interval: interval,
		stopChan: make(chan struct{}),
		running:  false,
	}
}

// Start begins the scheduled synchronization of exchange rates
// It performs an initial sync immediately, then syncs every interval
// This method blocks until Stop() is called or context is cancelled
// Requirements: 3.1 (sync on start), 3.2 (10-minute interval)
func (s *SyncScheduler) Start(ctx context.Context) {
	s.mu.Lock()
	if s.running {
		s.mu.Unlock()
		log.Println("[SyncScheduler] Scheduler is already running")
		return
	}
	s.running = true
	s.stopChan = make(chan struct{}) // Reset stop channel
	s.mu.Unlock()

	log.Printf("[SyncScheduler] Starting exchange rate sync scheduler with interval: %v", s.interval)

	// Perform initial sync immediately (Requirement 3.1)
	s.performSync(ctx)

	// Create ticker for periodic sync
	ticker := time.NewTicker(s.interval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			s.performSync(ctx)
		case <-s.stopChan:
			log.Println("[SyncScheduler] Scheduler stopped by Stop() call")
			s.mu.Lock()
			s.running = false
			s.mu.Unlock()
			return
		case <-ctx.Done():
			log.Println("[SyncScheduler] Scheduler stopped due to context cancellation")
			s.mu.Lock()
			s.running = false
			s.mu.Unlock()
			return
		}
	}
}

// Stop gracefully stops the scheduler
// It signals the scheduler to stop and waits for it to finish
func (s *SyncScheduler) Stop() {
	s.mu.Lock()
	defer s.mu.Unlock()

	if !s.running {
		log.Println("[SyncScheduler] Scheduler is not running")
		return
	}

	log.Println("[SyncScheduler] Stopping scheduler...")
	close(s.stopChan)
}

// IsRunning returns whether the scheduler is currently running
func (s *SyncScheduler) IsRunning() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.running
}

// GetInterval returns the sync interval
func (s *SyncScheduler) GetInterval() time.Duration {
	return s.interval
}

// performSync executes a single sync operation
// It fetches rates from YunAPI, updates Redis cache, and records sync status
// Requirements: 3.4 (record sync time and status)
func (s *SyncScheduler) performSync(ctx context.Context) {
	log.Println("[SyncScheduler] Starting exchange rate sync...")
	startTime := time.Now()

	// Get the API client and cache from the service
	client := s.service.GetClient()
	rateCache := s.service.GetCache()

	// Fetch rates from YunAPI (uses exponential backoff retry internally)
	rates, err := client.FetchRates()
	if err != nil {
		log.Printf("[SyncScheduler] Failed to fetch rates: %v", err)
		s.updateSyncStatus(ctx, rateCache, false, 0, err.Error())
		return
	}

	// Update Redis cache with fetched rates
	if err := rateCache.SetAll(ctx, rates); err != nil {
		log.Printf("[SyncScheduler] Failed to update cache: %v", err)
		s.updateSyncStatus(ctx, rateCache, false, 0, err.Error())
		return
	}

	// Update sync status to success
	s.updateSyncStatus(ctx, rateCache, true, len(rates), "")

	elapsed := time.Since(startTime)
	log.Printf("[SyncScheduler] Sync completed successfully: %d rates updated in %v", len(rates), elapsed)
}

// updateSyncStatus updates the sync status in Redis cache
// Requirements: 3.4 (record sync time and status)
func (s *SyncScheduler) updateSyncStatus(ctx context.Context, rateCache *cache.ExchangeRateCache, success bool, ratesCount int, errorMsg string) {
	status := &cache.SyncStatus{
		LastSyncTime: time.Now(),
		NextSyncTime: time.Now().Add(s.interval),
		RatesCount:   ratesCount,
	}

	if success {
		status.LastSyncStatus = "success"
	} else {
		status.LastSyncStatus = "failed"
		status.ErrorMessage = errorMsg
	}

	if err := rateCache.SetSyncStatus(ctx, status); err != nil {
		log.Printf("[SyncScheduler] Warning: failed to update sync status: %v", err)
	}
}

// ForceSync triggers an immediate sync operation outside of the regular schedule
// This can be used for manual refresh requests
func (s *SyncScheduler) ForceSync(ctx context.Context) error {
	log.Println("[SyncScheduler] Force sync triggered")
	s.performSync(ctx)
	return nil
}