import { IEventBus } from '../types/CalendarTypes';
import { CoreEvents } from '../constants/CoreEvents';
import { IAuditEntry } from '../types/AuditTypes';
import { AuditService } from '../storage/audit/AuditService';
import { IApiRepository } from '../repositories/IApiRepository';

/**
 * SyncManager - Background sync worker
 * Syncs audit entries with backend API when online
 *
 * NEW ARCHITECTURE:
 * - Listens to AUDIT_LOGGED events (triggered after AuditService saves)
 * - Polls AuditService for pending audit entries
 * - Syncs audit entries to backend API
 * - Marks audit entries as synced when successful
 *
 * EVENT CHAIN:
 * Entity change → ENTITY_SAVED/DELETED → AuditService → AUDIT_LOGGED → SyncManager
 *
 * Features:
 * - Monitors online/offline status
 * - Processes pending audits 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 auditService: AuditService;
  private auditApiRepository: IApiRepository<IAuditEntry>;

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

  // Track retry counts per audit entry (in memory)
  private retryCounts: Map<string, number> = new Map();

  constructor(
    eventBus: IEventBus,
    auditService: AuditService,
    auditApiRepository: IApiRepository<IAuditEntry>
  ) {
    this.eventBus = eventBus;
    this.auditService = auditService;
    this.auditApiRepository = auditApiRepository;

    this.setupNetworkListeners();
    this.setupAuditListener();
    this.startSync();
    console.log('SyncManager initialized - listening for AUDIT_LOGGED events');
  }

  /**
   * Setup listener for AUDIT_LOGGED events
   * Triggers immediate sync attempt when new audit entry is saved
   */
  private setupAuditListener(): void {
    this.eventBus.on(CoreEvents.AUDIT_LOGGED, () => {
      // New audit entry saved - try to sync if online
      if (this.isOnline && !this.isSyncing) {
        this.processPendingAudits();
      }
    });
  }

  /**
   * 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.processPendingAudits();

    // Then poll every syncInterval
    this.intervalId = window.setInterval(() => {
      this.processPendingAudits();
    }, 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 pending audit entries
   * Fetches from AuditService and syncs to backend
   */
  private async processPendingAudits(): Promise<void> {
    // Don't sync if offline
    if (!this.isOnline) {
      return;
    }

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

    this.isSyncing = true;

    try {
      const pendingAudits = await this.auditService.getPendingAudits();

      if (pendingAudits.length === 0) {
        this.isSyncing = false;
        return;
      }

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

      // Process audits one by one (FIFO - oldest first by timestamp)
      const sortedAudits = pendingAudits.sort((a, b) => a.timestamp - b.timestamp);

      for (const audit of sortedAudits) {
        await this.processAuditEntry(audit);
      }

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

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

  /**
   * Process a single audit entry
   * Sends to backend API and marks as synced
   */
  private async processAuditEntry(audit: IAuditEntry): Promise<void> {
    const retryCount = this.retryCounts.get(audit.id) || 0;

    // Check if max retries exceeded
    if (retryCount >= this.maxRetries) {
      console.error(`SyncManager: Max retries exceeded for audit ${audit.id}`);
      await this.auditService.markAsError(audit.id);
      this.retryCounts.delete(audit.id);
      return;
    }

    try {
      // Send audit entry to backend
      await this.auditApiRepository.sendCreate(audit);

      // Success - mark as synced and clear retry count
      await this.auditService.markAsSynced(audit.id);
      this.retryCounts.delete(audit.id);

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

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

      // Increment retry count
      this.retryCounts.set(audit.id, retryCount + 1);

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

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

  /**
   * 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.processPendingAudits();
  }

  /**
   * 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();
    this.retryCounts.clear();
    // Note: We don't remove window event listeners as they're global
  }
}