import { IEventBus } from '../types/CalendarTypes';
import { CoreEvents } from '../constants/CoreEvents';
import { OperationQueue } from '../storage/OperationQueue';
import { IQueueOperation } from '../storage/IndexedDBService';
import { IndexedDBService } from '../storage/IndexedDBService';
import { ApiEventRepository } from '../repositories/ApiEventRepository';

/**
 * SyncManager - Background sync worker
 * Processes operation queue and syncs with API when online
 *
 * Features:
 * - Monitors online/offline status
 * - Processes queue with FIFO order
 * - Exponential backoff retry logic
 * - Updates syncStatus in IndexedDB after successful sync
 * - Emits sync events for UI feedback
 */
export class SyncManager {
  private eventBus: IEventBus;
  private queue: OperationQueue;
  private indexedDB: IndexedDBService;
  private apiRepository: ApiEventRepository;

  private isOnline: boolean = navigator.onLine;
  private isSyncing: boolean = false;
  private syncInterval: number = 5000; // 5 seconds
  private maxRetries: number = 5;
  private intervalId: number | null = null;

  constructor(
    eventBus: IEventBus,
    queue: OperationQueue,
    indexedDB: IndexedDBService,
    apiRepository: ApiEventRepository
  ) {
    this.eventBus = eventBus;
    this.queue = queue;
    this.indexedDB = indexedDB;
    this.apiRepository = apiRepository;

    this.setupNetworkListeners();
  }

  /**
   * Setup online/offline event listeners
   */
  private setupNetworkListeners(): void {
    window.addEventListener('online', () => {
      this.isOnline = true;
      this.eventBus.emit(CoreEvents.OFFLINE_MODE_CHANGED, {
        isOnline: true
      });
      console.log('SyncManager: Network online - starting sync');
      this.startSync();
    });

    window.addEventListener('offline', () => {
      this.isOnline = false;
      this.eventBus.emit(CoreEvents.OFFLINE_MODE_CHANGED, {
        isOnline: false
      });
      console.log('SyncManager: Network offline - pausing sync');
      this.stopSync();
    });
  }

  /**
   * Start background sync worker
   */
  public startSync(): void {
    if (this.intervalId) {
      return; // Already running
    }

    console.log('SyncManager: Starting background sync');

    // Process immediately
    this.processQueue();

    // Then poll every syncInterval
    this.intervalId = window.setInterval(() => {
      this.processQueue();
    }, this.syncInterval);
  }

  /**
   * Stop background sync worker
   */
  public stopSync(): void {
    if (this.intervalId) {
      window.clearInterval(this.intervalId);
      this.intervalId = null;
      console.log('SyncManager: Stopped background sync');
    }
  }

  /**
   * Process operation queue
   * Sends pending operations to API
   */
  private async processQueue(): Promise<void> {
    // Don't sync if offline
    if (!this.isOnline) {
      return;
    }

    // Don't start new sync if already syncing
    if (this.isSyncing) {
      return;
    }

    // Check if queue is empty
    if (await this.queue.isEmpty()) {
      return;
    }

    this.isSyncing = true;

    try {
      const operations = await this.queue.getAll();

      this.eventBus.emit(CoreEvents.SYNC_STARTED, {
        operationCount: operations.length
      });

      // Process operations one by one (FIFO)
      for (const operation of operations) {
        await this.processOperation(operation);
      }

      this.eventBus.emit(CoreEvents.SYNC_COMPLETED, {
        operationCount: operations.length
      });

    } catch (error) {
      console.error('SyncManager: Queue processing error:', error);
      this.eventBus.emit(CoreEvents.SYNC_FAILED, {
        error: error instanceof Error ? error.message : 'Unknown error'
      });
    } finally {
      this.isSyncing = false;
    }
  }

  /**
   * Process a single operation
   */
  private async processOperation(operation: IQueueOperation): Promise<void> {
    // Check if max retries exceeded
    if (operation.retryCount >= this.maxRetries) {
      console.error(`SyncManager: Max retries exceeded for operation ${operation.id}`, operation);
      await this.queue.remove(operation.id);
      await this.markEventAsError(operation.eventId);
      return;
    }

    try {
      // Send to API based on operation type
      switch (operation.type) {
        case 'create':
          await this.apiRepository.sendCreate(operation.data as any);
          break;

        case 'update':
          await this.apiRepository.sendUpdate(operation.eventId, operation.data);
          break;

        case 'delete':
          await this.apiRepository.sendDelete(operation.eventId);
          break;

        default:
          console.error(`SyncManager: Unknown operation type ${operation.type}`);
          await this.queue.remove(operation.id);
          return;
      }

      // Success - remove from queue and mark as synced
      await this.queue.remove(operation.id);
      await this.markEventAsSynced(operation.eventId);

      console.log(`SyncManager: Successfully synced operation ${operation.id}`);

    } catch (error) {
      console.error(`SyncManager: Failed to sync operation ${operation.id}:`, error);

      // Increment retry count
      await this.queue.incrementRetryCount(operation.id);

      // Calculate backoff delay
      const backoffDelay = this.calculateBackoff(operation.retryCount + 1);

      this.eventBus.emit(CoreEvents.SYNC_RETRY, {
        operationId: operation.id,
        retryCount: operation.retryCount + 1,
        nextRetryIn: backoffDelay
      });
    }
  }

  /**
   * Mark event as synced in IndexedDB
   */
  private async markEventAsSynced(eventId: string): Promise<void> {
    try {
      const event = await this.indexedDB.getEvent(eventId);
      if (event) {
        event.syncStatus = 'synced';
        await this.indexedDB.saveEvent(event);
      }
    } catch (error) {
      console.error(`SyncManager: Failed to mark event ${eventId} as synced:`, error);
    }
  }

  /**
   * Mark event as error in IndexedDB
   */
  private async markEventAsError(eventId: string): Promise<void> {
    try {
      const event = await this.indexedDB.getEvent(eventId);
      if (event) {
        event.syncStatus = 'error';
        await this.indexedDB.saveEvent(event);
      }
    } catch (error) {
      console.error(`SyncManager: Failed to mark event ${eventId} as error:`, error);
    }
  }

  /**
   * Calculate exponential backoff delay
   * @param retryCount Current retry count
   * @returns Delay in milliseconds
   */
  private calculateBackoff(retryCount: number): number {
    // Exponential backoff: 2^retryCount * 1000ms
    // Retry 1: 2s, Retry 2: 4s, Retry 3: 8s, Retry 4: 16s, Retry 5: 32s
    const baseDelay = 1000;
    const exponentialDelay = Math.pow(2, retryCount) * baseDelay;
    const maxDelay = 60000; // Max 1 minute
    return Math.min(exponentialDelay, maxDelay);
  }

  /**
   * Manually trigger sync (for testing or manual sync button)
   */
  public async triggerManualSync(): Promise<void> {
    console.log('SyncManager: Manual sync triggered');
    await this.processQueue();
  }

  /**
   * Get current sync status
   */
  public getSyncStatus(): {
    isOnline: boolean;
    isSyncing: boolean;
    isRunning: boolean;
  } {
    return {
      isOnline: this.isOnline,
      isSyncing: this.isSyncing,
      isRunning: this.intervalId !== null
    };
  }

  /**
   * Cleanup - stop sync and remove listeners
   */
  public destroy(): void {
    this.stopSync();
    // Note: We don't remove window event listeners as they're global
  }
}