SyncManager.ts

import { ConflictResolver, ConflictStrategy } from './ConflictResolver';
import { IncrementalSync } from './IncrementalSync';
import { SyncState } from '../models/SyncState';

export class SyncManager {
  private resolver: ConflictResolver;
  private incrementalSync: IncrementalSync;

  constructor() {
    this.resolver = new ConflictResolver(ConflictStrategy.LAST_WRITE_WINS);
    this.incrementalSync = new IncrementalSync();
  }

  async synchronize(userId: string, deviceId: string, clientChanges: any[]): Promise<any> {
    // 1. Fetch current server state/version
    const currentState = await SyncState.findOne({ userId, deviceId });
    const lastSyncVersion = currentState ? currentState.version : 0;

    // 2. Identify server-side changes since last sync
    const serverChanges = await this.incrementalSync.getChangesSince(lastSyncVersion);

    // 3. Process client changes and resolve conflicts
    const reconciledChanges = [];
    for (const clientChange of clientChanges) {
      const conflict = serverChanges.find(sc => sc.entityId === clientChange.entityId);
      
      if (conflict) {
        const resolved = this.resolver.resolve(clientChange, conflict);
        reconciledChanges.push(resolved);
      } else {
        reconciledChanges.push(clientChange);
      }
    }

    // 4. Apply changes to database
    await this.applyReconciledChanges(reconciledChanges);

    // 5. Update sync state
    const newVersion = Date.now();
    await SyncState.updateOne(
      { userId, deviceId },
      { version: newVersion, lastSyncAt: new Date() },
      { upsert: true }
    );

    return {
      serverChanges: serverChanges.filter(sc => !clientChanges.some(cc => cc.entityId === sc.entityId)),
      newVersion
    };
  }

  private async applyReconciledChanges(changes: any[]): Promise<void> {
    // Implementation of batch updates to ensure atomicity
    for (const change of changes) {
      if (change.needsManualResolution) continue;
      
      // Mocking a generic database update
      // In a real scenario, this would use a repository or direct DB driver
      console.log(`Applying change to entity ${change.entityId}`);
      
      // Update the actual data record
      // await db.collection(change.collection).updateOne({ _id: change.entityId }, { $set: change.data });
    }
  }
}