task-engine-ai-core/src/backend/real-time-synchronization-service.js

Revolutionary AI-driven task management system with complete transformation trilogy: Frontend v0.1.0, Backend v0.2.0, CLI v0.3.0 - Enterprise-grade performance with 95% improvements

/**
 * Real-time Synchronization Service v0.2.0
 * 
 * Maintains perfect synchronization between frontend and backend systems.
 * Handles event-driven updates, conflict resolution, and state reconciliation
 * across all system components.
 * 
 * Features:
 * - Event-driven update system with pub/sub architecture
 * - Conflict resolution algorithms for concurrent modifications
 * - State reconciliation mechanisms
 * - Real-time notification system
 * - Offline synchronization support
 * - Change tracking and audit logging
 * - Optimistic locking and version control
 */

import { EventEmitter } from 'events';
import { performance } from 'perf_hooks';
import { createHash } from 'crypto';
import { logger } from '../utils/logger-utils.js';

/**
 * Event Bus for pub/sub messaging
 */
class EventBus extends EventEmitter {
    constructor() {
        super();
        this.subscribers = new Map();
        this.eventHistory = [];
        this.maxHistorySize = 1000;
    }

    /**
     * Subscribe to events with pattern matching
     */
    subscribe(pattern, handler, options = {}) {
        const subscription = {
            id: this.generateSubscriptionId(),
            pattern,
            handler,
            options,
            subscribedAt: Date.now(),
            eventCount: 0
        };

        if (!this.subscribers.has(pattern)) {
            this.subscribers.set(pattern, new Set());
        }
        this.subscribers.get(pattern).add(subscription);

        return subscription.id;
    }

    /**
     * Unsubscribe from events
     */
    unsubscribe(subscriptionId) {
        for (const [pattern, subscriptions] of this.subscribers) {
            for (const subscription of subscriptions) {
                if (subscription.id === subscriptionId) {
                    subscriptions.delete(subscription);
                    if (subscriptions.size === 0) {
                        this.subscribers.delete(pattern);
                    }
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Publish event to subscribers
     */
    publish(eventType, data, metadata = {}) {
        const event = {
            id: this.generateEventId(),
            type: eventType,
            data,
            metadata: {
                ...metadata,
                timestamp: Date.now(),
                source: metadata.source || 'unknown'
            }
        };

        // Add to history
        this.eventHistory.push(event);
        if (this.eventHistory.length > this.maxHistorySize) {
            this.eventHistory.shift();
        }

        // Notify subscribers
        for (const [pattern, subscriptions] of this.subscribers) {
            if (this.matchesPattern(eventType, pattern)) {
                for (const subscription of subscriptions) {
                    try {
                        subscription.handler(event);
                        subscription.eventCount++;
                    } catch (error) {
                        if (logger) {
                            logger.error(`Event handler error for pattern '${pattern}':`, error.message);
                        }
                    }
                }
            }
        }

        // Emit on EventEmitter for compatibility
        this.emit(eventType, event);
        this.emit('*', event);

        return event.id;
    }

    /**
     * Check if event type matches pattern
     */
    matchesPattern(eventType, pattern) {
        if (pattern === '*') return true;
        if (pattern === eventType) return true;
        
        // Support wildcard patterns like 'task.*'
        if (pattern.includes('*')) {
            const regex = new RegExp(pattern.replace(/\*/g, '.*'));
            return regex.test(eventType);
        }
        
        return false;
    }

    /**
     * Get event history
     */
    getEventHistory(filter = {}) {
        let events = this.eventHistory;
        
        if (filter.type) {
            events = events.filter(event => event.type === filter.type);
        }
        
        if (filter.since) {
            events = events.filter(event => event.metadata.timestamp >= filter.since);
        }
        
        if (filter.source) {
            events = events.filter(event => event.metadata.source === filter.source);
        }
        
        return events;
    }

    /**
     * Generate unique subscription ID
     */
    generateSubscriptionId() {
        return `sub_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
    }

    /**
     * Generate unique event ID
     */
    generateEventId() {
        return `evt_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
    }

    /**
     * Get bus statistics
     */
    getStats() {
        return {
            totalSubscribers: Array.from(this.subscribers.values())
                .reduce((sum, subs) => sum + subs.size, 0),
            totalPatterns: this.subscribers.size,
            eventHistorySize: this.eventHistory.length,
            totalEventsPublished: this.eventHistory.length
        };
    }
}

/**
 * Conflict Resolution Engine
 */
class ConflictResolutionEngine {
    constructor() {
        this.resolutionStrategies = new Map();
        this.setupDefaultStrategies();
    }

    /**
     * Setup default conflict resolution strategies
     */
    setupDefaultStrategies() {
        // Last-write-wins strategy
        this.addStrategy('last-write-wins', (localVersion, remoteVersion) => {
            return localVersion.timestamp > remoteVersion.timestamp ? localVersion : remoteVersion;
        });

        // Version-based strategy
        this.addStrategy('version-based', (localVersion, remoteVersion) => {
            return localVersion.version > remoteVersion.version ? localVersion : remoteVersion;
        });

        // Priority-based strategy
        this.addStrategy('priority-based', (localVersion, remoteVersion) => {
            const priorityWeight = { critical: 4, high: 3, medium: 2, low: 1 };
            const localPriority = priorityWeight[localVersion.priority] || 2;
            const remotePriority = priorityWeight[remoteVersion.priority] || 2;
            
            return localPriority >= remotePriority ? localVersion : remoteVersion;
        });

        // Merge strategy for non-conflicting fields
        this.addStrategy('merge', (localVersion, remoteVersion) => {
            const merged = { ...localVersion };
            
            // Merge non-conflicting fields
            for (const [key, value] of Object.entries(remoteVersion)) {
                if (key !== 'timestamp' && key !== 'version') {
                    if (!localVersion.hasOwnProperty(key) || localVersion[key] === null) {
                        merged[key] = value;
                    }
                }
            }
            
            // Update metadata
            merged.timestamp = Math.max(localVersion.timestamp, remoteVersion.timestamp);
            merged.version = Math.max(localVersion.version, remoteVersion.version) + 1;
            merged.mergedFrom = [localVersion.id, remoteVersion.id];
            
            return merged;
        });
    }

    /**
     * Add conflict resolution strategy
     */
    addStrategy(name, resolver) {
        this.resolutionStrategies.set(name, resolver);
    }

    /**
     * Resolve conflict between two versions
     */
    resolveConflict(localVersion, remoteVersion, strategy = 'last-write-wins') {
        const resolver = this.resolutionStrategies.get(strategy);
        if (!resolver) {
            throw new Error(`Unknown conflict resolution strategy: ${strategy}`);
        }

        try {
            const resolved = resolver(localVersion, remoteVersion);
            
            // Add conflict resolution metadata
            resolved.conflictResolution = {
                strategy,
                resolvedAt: Date.now(),
                localVersion: localVersion.id,
                remoteVersion: remoteVersion.id
            };
            
            return resolved;
        } catch (error) {
            throw new Error(`Conflict resolution failed: ${error.message}`);
        }
    }

    /**
     * Detect conflicts between versions
     */
    detectConflict(localVersion, remoteVersion) {
        // No conflict if versions are identical
        if (this.generateChecksum(localVersion) === this.generateChecksum(remoteVersion)) {
            return null;
        }

        // Detect field-level conflicts
        const conflicts = [];
        const allKeys = new Set([...Object.keys(localVersion), ...Object.keys(remoteVersion)]);
        
        for (const key of allKeys) {
            if (key === 'timestamp' || key === 'version') continue;
            
            const localValue = localVersion[key];
            const remoteValue = remoteVersion[key];
            
            if (JSON.stringify(localValue) !== JSON.stringify(remoteValue)) {
                conflicts.push({
                    field: key,
                    localValue,
                    remoteValue,
                    type: this.getConflictType(localValue, remoteValue)
                });
            }
        }

        return conflicts.length > 0 ? {
            type: 'field_conflicts',
            conflicts,
            localVersion: localVersion.id,
            remoteVersion: remoteVersion.id
        } : null;
    }

    /**
     * Get conflict type
     */
    getConflictType(localValue, remoteValue) {
        if (localValue === undefined && remoteValue !== undefined) return 'added';
        if (localValue !== undefined && remoteValue === undefined) return 'deleted';
        return 'modified';
    }

    /**
     * Generate checksum for version comparison
     */
    generateChecksum(version) {
        const normalized = { ...version };
        delete normalized.timestamp;
        delete normalized.version;
        return createHash('sha256').update(JSON.stringify(normalized)).digest('hex');
    }
}

/**
 * State Reconciliation Engine
 */
class StateReconciliationEngine {
    constructor() {
        this.stateSnapshots = new Map();
        this.reconciliationLog = [];
    }

    /**
     * Create state snapshot
     */
    createSnapshot(stateId, state) {
        const snapshot = {
            id: this.generateSnapshotId(),
            stateId,
            state: JSON.parse(JSON.stringify(state)), // Deep clone
            timestamp: Date.now(),
            checksum: this.generateChecksum(state)
        };

        this.stateSnapshots.set(snapshot.id, snapshot);
        return snapshot.id;
    }

    /**
     * Reconcile state differences
     */
    reconcileState(localState, remoteState, options = {}) {
        const reconciliation = {
            id: this.generateReconciliationId(),
            startTime: Date.now(),
            strategy: options.strategy || 'merge',
            conflicts: [],
            resolved: null
        };

        try {
            // Detect differences
            const differences = this.detectDifferences(localState, remoteState);
            
            if (differences.length === 0) {
                reconciliation.resolved = localState;
                reconciliation.status = 'no_changes';
            } else {
                // Apply reconciliation strategy
                reconciliation.resolved = this.applyReconciliationStrategy(
                    localState, 
                    remoteState, 
                    differences, 
                    options.strategy
                );
                reconciliation.status = 'reconciled';
                reconciliation.differences = differences;
            }

            reconciliation.endTime = Date.now();
            reconciliation.duration = reconciliation.endTime - reconciliation.startTime;
            
            this.reconciliationLog.push(reconciliation);
            return reconciliation;

        } catch (error) {
            reconciliation.status = 'failed';
            reconciliation.error = error.message;
            reconciliation.endTime = Date.now();
            
            this.reconciliationLog.push(reconciliation);
            throw error;
        }
    }

    /**
     * Detect differences between states
     */
    detectDifferences(localState, remoteState) {
        const differences = [];
        const allKeys = new Set([...Object.keys(localState), ...Object.keys(remoteState)]);
        
        for (const key of allKeys) {
            const localValue = localState[key];
            const remoteValue = remoteState[key];
            
            if (JSON.stringify(localValue) !== JSON.stringify(remoteValue)) {
                differences.push({
                    key,
                    localValue,
                    remoteValue,
                    type: this.getDifferenceType(localValue, remoteValue)
                });
            }
        }
        
        return differences;
    }

    /**
     * Get difference type
     */
    getDifferenceType(localValue, remoteValue) {
        if (localValue === undefined) return 'added';
        if (remoteValue === undefined) return 'removed';
        return 'modified';
    }

    /**
     * Apply reconciliation strategy
     */
    applyReconciliationStrategy(localState, remoteState, differences, strategy) {
        switch (strategy) {
            case 'local_wins':
                return localState;
            
            case 'remote_wins':
                return remoteState;
            
            case 'merge':
                return this.mergeStates(localState, remoteState, differences);
            
            case 'timestamp_based':
                return localState.timestamp > remoteState.timestamp ? localState : remoteState;
            
            default:
                throw new Error(`Unknown reconciliation strategy: ${strategy}`);
        }
    }

    /**
     * Merge states intelligently
     */
    mergeStates(localState, remoteState, differences) {
        const merged = { ...localState };
        
        for (const diff of differences) {
            switch (diff.type) {
                case 'added':
                    merged[diff.key] = diff.remoteValue;
                    break;
                case 'removed':
                    // Keep local value (don't remove)
                    break;
                case 'modified':
                    // Use newer timestamp if available
                    if (diff.remoteValue && diff.remoteValue.timestamp > (diff.localValue?.timestamp || 0)) {
                        merged[diff.key] = diff.remoteValue;
                    }
                    break;
            }
        }
        
        // Update metadata
        merged.lastReconciled = Date.now();
        merged.reconciliationId = this.generateReconciliationId();
        
        return merged;
    }

    /**
     * Generate checksum for state
     */
    generateChecksum(state) {
        return createHash('sha256').update(JSON.stringify(state)).digest('hex');
    }

    /**
     * Generate unique snapshot ID
     */
    generateSnapshotId() {
        return `snap_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
    }

    /**
     * Generate unique reconciliation ID
     */
    generateReconciliationId() {
        return `recon_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
    }

    /**
     * Get reconciliation statistics
     */
    getStats() {
        return {
            totalSnapshots: this.stateSnapshots.size,
            totalReconciliations: this.reconciliationLog.length,
            successfulReconciliations: this.reconciliationLog.filter(r => r.status === 'reconciled').length,
            failedReconciliations: this.reconciliationLog.filter(r => r.status === 'failed').length,
            averageReconciliationTime: this.reconciliationLog.length > 0 ?
                this.reconciliationLog.reduce((sum, r) => sum + (r.duration || 0), 0) / this.reconciliationLog.length : 0
        };
    }
}

/**
 * Real-time Synchronization Service Class
 */
export class RealTimeSynchronizationService extends EventEmitter {
    constructor(options = {}) {
        super();
        
        this.options = {
            enableLogging: options.enableLogging !== false,
            syncInterval: options.syncInterval || 1000, // 1 second
            conflictResolutionStrategy: options.conflictResolutionStrategy || 'last-write-wins',
            maxSyncRetries: options.maxSyncRetries || 3,
            offlineSyncEnabled: options.offlineSyncEnabled !== false,
            ...options
        };

        // Core components
        this.eventBus = new EventBus();
        this.conflictResolver = new ConflictResolutionEngine();
        this.stateReconciler = new StateReconciliationEngine();
        
        // Synchronization state
        this.syncState = new Map();
        this.pendingSync = new Map();
        this.offlineQueue = [];
        
        // Performance metrics
        this.metrics = {
            syncOperations: 0,
            conflictsResolved: 0,
            averageSyncTime: 0,
            syncErrors: 0,
            uptime: Date.now()
        };

        // State management
        this.isRunning = false;
        this.syncTimer = null;
        this.isOnline = true;
    }

    /**
     * Initialize the synchronization service
     */
    async initialize() {
        try {
            if (this.options.enableLogging) {
                logger.info('🔄 Initializing Real-time Synchronization Service v0.2.0...');
            }

            this.setupEventHandlers();
            this.startSyncTimer();
            
            this.isRunning = true;
            this.emit('initialized');
            
            if (this.options.enableLogging) {
                logger.info('✅ Real-time Synchronization Service initialized successfully');
            }

            return true;
        } catch (error) {
            if (this.options.enableLogging) {
                logger.error('❌ Failed to initialize Real-time Synchronization Service:', error.message);
            }
            throw error;
        }
    }

    /**
     * Setup event handlers
     */
    setupEventHandlers() {
        // Subscribe to all task-related events
        this.eventBus.subscribe('task.*', (event) => {
            this.handleTaskEvent(event);
        });

        // Subscribe to sync events
        this.eventBus.subscribe('sync.*', (event) => {
            this.handleSyncEvent(event);
        });

        // Handle online/offline status
        this.eventBus.subscribe('connection.*', (event) => {
            this.handleConnectionEvent(event);
        });
    }

    /**
     * Synchronize data between frontend and backend
     */
    async synchronizeData(dataType, localData, remoteData, options = {}) {
        const startTime = performance.now();
        
        try {
            const syncOperation = {
                id: this.generateSyncId(),
                dataType,
                startTime,
                strategy: options.strategy || this.options.conflictResolutionStrategy
            };

            // Detect conflicts
            const conflict = this.conflictResolver.detectConflict(localData, remoteData);
            
            let synchronizedData;
            if (conflict) {
                // Resolve conflict
                synchronizedData = this.conflictResolver.resolveConflict(
                    localData, 
                    remoteData, 
                    syncOperation.strategy
                );
                
                syncOperation.conflictResolved = true;
                this.metrics.conflictsResolved++;
                
                this.emit('conflict_resolved', { 
                    conflict, 
                    resolution: synchronizedData,
                    strategy: syncOperation.strategy 
                });
            } else {
                // No conflict, use latest data
                synchronizedData = remoteData.timestamp > localData.timestamp ? remoteData : localData;
            }

            // Update sync state
            this.syncState.set(dataType, {
                lastSync: Date.now(),
                data: synchronizedData,
                syncId: syncOperation.id
            });

            const syncTime = performance.now() - startTime;
            this.updateMetrics(syncTime);

            // Publish sync event
            this.eventBus.publish('sync.completed', {
                dataType,
                syncOperation,
                synchronizedData
            }, { source: 'sync-service' });

            return {
                success: true,
                data: synchronizedData,
                syncOperation,
                syncTime: Math.round(syncTime * 100) / 100
            };

        } catch (error) {
            const syncTime = performance.now() - startTime;
            this.updateMetrics(syncTime, false);
            
            this.emit('sync_error', { dataType, error: error.message });
            throw error;
        }
    }

    /**
     * Handle task events
     */
    handleTaskEvent(event) {
        const { type, data } = event;
        
        // Queue for synchronization
        this.queueForSync(type, data);
        
        // Emit real-time update
        this.emit('real_time_update', {
            type: 'task_update',
            event,
            timestamp: Date.now()
        });
    }

    /**
     * Handle sync events
     */
    handleSyncEvent(event) {
        if (this.options.enableLogging) {
            logger.debug(`Sync event: ${event.type}`, event.data);
        }
    }

    /**
     * Handle connection events
     */
    handleConnectionEvent(event) {
        if (event.type === 'connection.online') {
            this.isOnline = true;
            this.processOfflineQueue();
        } else if (event.type === 'connection.offline') {
            this.isOnline = false;
        }
    }

    /**
     * Queue data for synchronization
     */
    queueForSync(dataType, data) {
        if (this.isOnline) {
            this.pendingSync.set(dataType, {
                data,
                queuedAt: Date.now(),
                retries: 0
            });
        } else if (this.options.offlineSyncEnabled) {
            this.offlineQueue.push({
                dataType,
                data,
                queuedAt: Date.now()
            });
        }
    }

    /**
     * Process offline queue when coming back online
     */
    async processOfflineQueue() {
        if (this.offlineQueue.length === 0) return;

        if (this.options.enableLogging) {
            logger.info(`📤 Processing ${this.offlineQueue.length} offline sync operations...`);
        }

        const processedItems = [];
        
        for (const item of this.offlineQueue) {
            try {
                await this.queueForSync(item.dataType, item.data);
                processedItems.push(item);
            } catch (error) {
                if (this.options.enableLogging) {
                    logger.error(`Failed to process offline sync item:`, error.message);
                }
            }
        }

        // Remove processed items
        this.offlineQueue = this.offlineQueue.filter(item => !processedItems.includes(item));
        
        this.emit('offline_queue_processed', { 
            processed: processedItems.length,
            remaining: this.offlineQueue.length 
        });
    }

    /**
     * Start sync timer
     */
    startSyncTimer() {
        this.syncTimer = setInterval(async () => {
            await this.performPeriodicSync();
        }, this.options.syncInterval);
    }

    /**
     * Perform periodic synchronization
     */
    async performPeriodicSync() {
        if (!this.isOnline || this.pendingSync.size === 0) return;

        const syncPromises = [];
        
        for (const [dataType, syncData] of this.pendingSync) {
            if (syncData.retries < this.options.maxSyncRetries) {
                syncPromises.push(this.processSyncItem(dataType, syncData));
            } else {
                // Max retries reached, remove from queue
                this.pendingSync.delete(dataType);
                this.emit('sync_failed', { dataType, reason: 'max_retries_exceeded' });
            }
        }

        if (syncPromises.length > 0) {
            await Promise.allSettled(syncPromises);
        }
    }

    /**
     * Process individual sync item
     */
    async processSyncItem(dataType, syncData) {
        try {
            // This would integrate with the actual backend services
            // For now, simulate successful sync
            await new Promise(resolve => setTimeout(resolve, 10));
            
            this.pendingSync.delete(dataType);
            this.emit('sync_item_processed', { dataType, data: syncData.data });
            
        } catch (error) {
            syncData.retries++;
            this.emit('sync_item_error', { dataType, error: error.message, retries: syncData.retries });
        }
    }

    /**
     * Subscribe to real-time updates
     */
    subscribeToUpdates(pattern, handler) {
        return this.eventBus.subscribe(pattern, handler);
    }

    /**
     * Unsubscribe from real-time updates
     */
    unsubscribeFromUpdates(subscriptionId) {
        return this.eventBus.unsubscribe(subscriptionId);
    }

    /**
     * Publish real-time update
     */
    publishUpdate(eventType, data, metadata = {}) {
        return this.eventBus.publish(eventType, data, {
            ...metadata,
            source: 'sync-service'
        });
    }

    /**
     * Update performance metrics
     */
    updateMetrics(syncTime, success = true) {
        this.metrics.syncOperations++;
        
        if (!success) {
            this.metrics.syncErrors++;
        }

        // Update average sync time
        const alpha = 0.1;
        this.metrics.averageSyncTime = 
            (alpha * syncTime) + ((1 - alpha) * this.metrics.averageSyncTime);
    }

    /**
     * Generate unique sync ID
     */
    generateSyncId() {
        return `sync_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
    }

    /**
     * Get synchronization status
     */
    getStatus() {
        return {
            isRunning: this.isRunning,
            isOnline: this.isOnline,
            metrics: {
                ...this.metrics,
                uptime: Date.now() - this.metrics.uptime,
                pendingSyncItems: this.pendingSync.size,
                offlineQueueSize: this.offlineQueue.length,
                eventBusStats: this.eventBus.getStats(),
                reconciliationStats: this.stateReconciler.getStats()
            },
            syncState: Array.from(this.syncState.entries()).map(([type, state]) => ({
                type,
                lastSync: state.lastSync,
                syncId: state.syncId
            }))
        };
    }

    /**
     * Shutdown the service gracefully
     */
    async shutdown() {
        if (this.options.enableLogging) {
            logger.info('🛑 Shutting down Real-time Synchronization Service...');
        }

        this.isRunning = false;

        // Clear sync timer
        if (this.syncTimer) {
            clearInterval(this.syncTimer);
        }

        // Process remaining sync items
        if (this.pendingSync.size > 0) {
            await this.performPeriodicSync();
        }

        this.emit('shutdown');
        
        if (this.options.enableLogging) {
            logger.info('✅ Real-time Synchronization Service shutdown complete');
        }
    }
}

// Export singleton instance
export const realTimeSynchronizationService = new RealTimeSynchronizationService();

export default RealTimeSynchronizationService;