Notification Analytics and Performance Optimization: A/B Testing, Metrics, and Tuning at Scale

interface NotificationAnalytics {  // Layer 1: Delivery Fundamentals  delivery: {    sent: number;    delivered: number;    failed: number;    bounced: number;    deliveryRate: number;    avgDeliveryTime: number;  };    // Layer 2: User Engagement  engagement: {    opened: number;    clicked: number;    dismissed: number;    actioned: number; // User took intended action    openRate: number;    clickThroughRate: number;    conversionRate: number; // Action completion rate  };    // Layer 3: Business Impact  businessImpact: {    revenueGenerated: number;    userRetention: number;    featureAdoption: number;    supportTicketReduction: number;    userLifetimeValue: number;  };    // Layer 4: System Performance  performance: {    processingLatency: number;    queueDepth: number;    resourceUtilization: number;    costPerNotification: number;    errorRates: Record<string, number>;  };}
class NotificationAnalyticsEngine {  private eventStore: EventStore;  private metricsAggregator: MetricsAggregator;  private cohortAnalyzer: CohortAnalyzer;
  async trackNotificationEvent(event: NotificationAnalyticsEvent): Promise<void> {    // Store raw event    await this.eventStore.store(event);        // Real-time aggregation for dashboards    await this.metricsAggregator.update(event);        // Cohort analysis for deeper insights    if (event.type === 'user_action') {      await this.cohortAnalyzer.processUserAction(event);    }        // Trigger anomaly detection    await this.checkForAnomalies(event);  }
  async generateInsights(    dateRange: DateRange,    segmentBy?: string[]  ): Promise<NotificationInsights> {    const baseMetrics = await this.getBaseMetrics(dateRange);    const segmentedAnalysis = segmentBy ?       await this.getSegmentedAnalysis(dateRange, segmentBy) : null;        const insights: NotificationInsights = {      summary: baseMetrics,      segments: segmentedAnalysis,      trends: await this.getTrendAnalysis(dateRange),      anomalies: await this.getAnomalies(dateRange),      recommendations: await this.generateRecommendations(baseMetrics)    };        return insights;  }
  private async generateRecommendations(    metrics: NotificationMetrics  ): Promise<OptimizationRecommendation[]> {    const recommendations: OptimizationRecommendation[] = [];        // Delivery optimization (thresholds vary by channel type)    const channelThresholds = {      email: 0.95,  // 95% delivery rate      push: 0.98,  // 98% delivery rate (higher threshold due to direct device delivery)      sms: 0.97  // 97% delivery rate    };
    const threshold = channelThresholds[metrics.channel] || 0.95;    if (metrics.delivery.deliveryRate < threshold) {      recommendations.push({        type: 'delivery',        priority: 'high',        description: `Low delivery rate detected for ${metrics.channel} (below ${threshold * 100}% threshold)`,        suggestedActions: [          'Review channel-specific authentication settings',          'Check sender reputation and certificates',          'Audit suppression and opt-out lists'        ],        expectedImpact: `Increase ${metrics.channel} delivery rate by 5-10%`      });    }        // Engagement optimization (platform-specific benchmarks)    const engagementBenchmarks = {      email: { open: 0.20, click: 0.025 },  // 20% open, 2.5% click      push: { open: 0.90, click: 0.05 },  // 90% delivery view, 5% click      sms: { open: 0.98, click: 0.08 }  // 98% read rate, 8% click    };
    const benchmark = engagementBenchmarks[metrics.channel] || engagementBenchmarks.email;    if (metrics.engagement.openRate < benchmark.open) {      const channelActions = {        email: ['A/B test subject lines', 'Review send time optimization', 'Analyze sender name impact'],        push: ['Test notification copy and timing', 'Optimize badge and icon usage', 'Review permission prompts'],        sms: ['Test message length and clarity', 'Optimize send timing', 'Review opt-in messaging']      };
      recommendations.push({        type: 'engagement',        priority: 'medium',        description: `Below-average ${metrics.channel} open rate (${(metrics.engagement.openRate * 100).toFixed(1)}% vs ${(benchmark.open * 100)}% benchmark)`,        suggestedActions: channelActions[metrics.channel] || channelActions.email,        expectedImpact: `Potential 15-25% improvement in ${metrics.channel} open rate`      });    }        // Performance optimization    if (metrics.performance.avgLatency > 5000) {      recommendations.push({        type: 'performance',        priority: 'high',         description: 'High processing latency',        suggestedActions: [          'Review template rendering performance',          'Optimize database queries',          'Consider implementing caching layer'        ],        expectedImpact: 'Reduce latency by 40-60%'      });    }        return recommendations;  }}

interface UserNotificationJourney {  userId: string;  journeyType: string; // 'onboarding', 'feature_adoption', 'retention'  startedAt: Date;  currentStep: number;  totalSteps: number;  events: NotificationJourneyEvent[];  outcome?: JourneyOutcome;  dropOffReason?: string;}
class NotificationJourneyTracker {  async trackJourneyEvent(    userId: string,    journeyType: string,    event: NotificationJourneyEvent  ): Promise<void> {    const journey = await this.getOrCreateJourney(userId, journeyType);        journey.events.push({      ...event,      timestamp: new Date(),      stepNumber: journey.currentStep    });        // Update journey state based on event    await this.updateJourneyState(journey, event);        // Check for journey completion or abandonment    await this.evaluateJourneyStatus(journey);        await this.saveJourney(journey);  }
  async analyzeJourneyPerformance(    journeyType: string,    dateRange: DateRange  ): Promise<JourneyAnalytics> {    const journeys = await this.getJourneys(journeyType, dateRange);        const stepConversionRates = this.calculateStepConversions(journeys);    const dropOffPoints = this.identifyDropOffPoints(journeys);    const timeToComplete = this.calculateCompletionTimes(journeys);        return {      totalJourneys: journeys.length,      completionRate: journeys.filter(j => j.outcome === 'completed').length / journeys.length,      stepConversionRates,      dropOffPoints,      averageTimeToComplete: timeToComplete.average,      medianTimeToComplete: timeToComplete.median,      recommendations: this.generateJourneyOptimizations(stepConversionRates, dropOffPoints)    };  }
  private generateJourneyOptimizations(    conversionRates: Record<number, number>,    dropOffPoints: DropOffAnalysis[]  ): JourneyOptimization[] {    const optimizations: JourneyOptimization[] = [];        // Find steps with low conversion rates    Object.entries(conversionRates).forEach(([step, rate]) => {      if (rate < 0.7) { // Less than 70% conversion        optimizations.push({          stepNumber: parseInt(step),          type: 'low_conversion',          currentRate: rate,          suggestions: [            'Simplify the required action',            'Improve notification copy clarity',            'Add progress indicators',            'Provide contextual help'          ]        });      }    });        // Analyze major drop-off points    dropOffPoints.forEach(dropOff => {      if (dropOff.dropOffRate > 0.3) { // More than 30% drop-off        optimizations.push({          stepNumber: dropOff.stepNumber,          type: 'high_dropoff',          currentRate: 1 - dropOff.dropOffRate,          suggestions: [            'Review notification timing',            'Check message relevance',             'Test different call-to-action phrases',            'Consider breaking step into smaller actions'          ]        });      }    });        return optimizations;  }}

interface NotificationExperiment {  id: string;  name: string;  type: ExperimentType; // 'subject_line', 'timing', 'content', 'frequency', 'channel'  status: ExperimentStatus;  hypothesis: string;  variants: ExperimentVariant[];  targetAudience: AudienceDefinition;  trafficAllocation: number; // Percentage of eligible users  primaryMetric: string;  secondaryMetrics: string[];  minimumDetectableEffect: number;  significanceLevel: number;  powerLevel: number;  startDate: Date;  endDate?: Date;  results?: ExperimentResults;}
class NotificationExperimentManager {  private statisticalEngine: StatisticalEngine;  private userSegmenter: UserSegmenter;  private safetyMonitor: SafetyMonitor;
  async createExperiment(    experimentConfig: ExperimentConfig  ): Promise<NotificationExperiment> {    // Calculate required sample size    const sampleSize = this.statisticalEngine.calculateSampleSize(      experimentConfig.minimumDetectableEffect,      experimentConfig.significanceLevel,      experimentConfig.powerLevel,      experimentConfig.baselineConversionRate    );        // Validate experiment safety    const safetyCheck = await this.safetyMonitor.validateExperiment(experimentConfig);    if (!safetyCheck.isSafe) {      throw new Error(`Experiment failed safety check: ${safetyCheck.reasons.join(', ')}`);    }        // Set up user segmentation    const audience = await this.userSegmenter.defineAudience(      experimentConfig.targetCriteria,      sampleSize    );        const experiment: NotificationExperiment = {      id: this.generateExperimentId(),      name: experimentConfig.name,      type: experimentConfig.type,      status: 'draft',      hypothesis: experimentConfig.hypothesis,      variants: experimentConfig.variants,      targetAudience: audience,      trafficAllocation: experimentConfig.trafficAllocation,      primaryMetric: experimentConfig.primaryMetric,      secondaryMetrics: experimentConfig.secondaryMetrics,      minimumDetectableEffect: experimentConfig.minimumDetectableEffect,      significanceLevel: experimentConfig.significanceLevel,      powerLevel: experimentConfig.powerLevel,      startDate: experimentConfig.startDate    };        await this.saveExperiment(experiment);    return experiment;  }
  async assignUserToExperiment(    userId: string,    experimentId: string  ): Promise<ExperimentAssignment> {    const experiment = await this.getExperiment(experimentId);        if (experiment.status !== 'running') {      return { variant: 'control', reason: 'experiment_not_running' };    }        // Check if user is in target audience    const isEligible = await this.userSegmenter.isUserEligible(      userId,      experiment.targetAudience    );        if (!isEligible) {      return { variant: 'control', reason: 'not_in_target_audience' };    }        // Check traffic allocation    const userHash = this.hashUserId(userId, experiment.id);    const trafficBucket = userHash % 100;        if (trafficBucket >= experiment.trafficAllocation) {      return { variant: 'control', reason: 'traffic_allocation' };    }        // Assign to variant based on hash    const variantIndex = Math.floor(      (userHash / 100) * experiment.variants.length    );    const assignedVariant = experiment.variants[variantIndex];        // Store assignment for consistency    await this.storeUserAssignment(userId, experimentId, assignedVariant.id);        return {      variant: assignedVariant.id,      experimentId,      assignedAt: new Date()    };  }
  async analyzeExperimentResults(    experimentId: string  ): Promise<ExperimentAnalysis> {    const experiment = await this.getExperiment(experimentId);    const rawData = await this.getExperimentData(experimentId);        // Statistical significance testing    const primaryResults = await this.statisticalEngine.performTest(      rawData,      experiment.primaryMetric,      experiment.significanceLevel    );        // Secondary metric analysis    const secondaryResults = await Promise.all(      experiment.secondaryMetrics.map(metric =>        this.statisticalEngine.performTest(rawData, metric, 0.05)      )    );        // Effect size calculation    const effectSize = this.statisticalEngine.calculateEffectSize(      primaryResults,      experiment.minimumDetectableEffect    );        // Business impact estimation    const businessImpact = await this.estimateBusinessImpact(      primaryResults,      experiment    );        return {      experiment,      primaryResults,      secondaryResults,      effectSize,      businessImpact,      recommendation: this.generateRecommendation(        primaryResults,        secondaryResults,        businessImpact      ),      confidenceLevel: primaryResults.confidenceLevel    };  }}

class ExperimentSafetyMonitor {  private alerting: AlertingService;  private metrics: MetricsService;
  async monitorExperimentSafety(experimentId: string): Promise<SafetyStatus> {    const experiment = await this.getExperiment(experimentId);    const safetyChecks = await Promise.all([      this.checkDeliveryRates(experiment),      this.checkEngagementMetrics(experiment),      this.checkUserComplaintsRate(experiment),      this.checkBusinessMetricImpact(experiment),      this.checkSystemPerformance(experiment)    ]);        const criticalIssues = safetyChecks.filter(check => check.severity === 'critical');    const warnings = safetyChecks.filter(check => check.severity === 'warning');        if (criticalIssues.length > 0) {      await this.triggerExperimentPause(experimentId, criticalIssues);      await this.alerting.sendCriticalAlert({        type: 'experiment_safety_violation',        experimentId,        issues: criticalIssues      });    }        return {      status: criticalIssues.length > 0 ? 'critical' :               warnings.length > 0 ? 'warning' : 'healthy',      checks: safetyChecks,      lastChecked: new Date()    };  }
  private async checkDeliveryRates(experiment: NotificationExperiment): Promise<SafetyCheck> {    const deliveryRates = await this.getVariantDeliveryRates(experiment.id);        for (const [variantId, rate] of Object.entries(deliveryRates)) {      if (rate < 0.90) { // Less than 90% delivery rate        return {          checkType: 'delivery_rate',          severity: 'critical',          message: `Variant ${variantId} has delivery rate of ${rate * 100}%`,          threshold: 0.90,          actualValue: rate,          recommendation: 'Pause experiment and investigate delivery issues'        };      }    }        return {      checkType: 'delivery_rate',      severity: 'healthy',      message: 'All variants have acceptable delivery rates'    };  }
  private async checkUserComplaintsRate(experiment: NotificationExperiment): Promise<SafetyCheck> {    const complaintRates = await this.getVariantComplaintRates(experiment.id);        for (const [variantId, rate] of Object.entries(complaintRates)) {      if (rate > 0.01) { // More than 1% complaint rate        return {          checkType: 'user_complaints',          severity: 'critical',          message: `Variant ${variantId} has complaint rate of ${rate * 100}%`,          threshold: 0.01,          actualValue: rate,          recommendation: 'Immediately pause experiment - high complaint rate indicates poor user experience'        };      }    }        return {      checkType: 'user_complaints',       severity: 'healthy',      message: 'Complaint rates within acceptable range'    };  }
  private async triggerExperimentPause(    experimentId: string,    reasons: SafetyCheck[]  ): Promise<void> {    await this.updateExperimentStatus(experimentId, 'paused_for_safety');        // Log the pause reason    await this.logExperimentEvent(experimentId, {      type: 'safety_pause',      timestamp: new Date(),      reasons: reasons.map(r => r.message),      autoResumeEligible: reasons.every(r => r.severity === 'warning')    });        // Notify experiment owners    await this.notifyExperimentOwners(experimentId, reasons);  }}

class OptimizedTemplateRenderer {  private templateCache: LRUCache<string, CompiledTemplate>;  private dataPreloader: DataPreloader;  private renderPool: WorkerPool;
  constructor() {    this.templateCache = new LRUCache({ max: 1000, ttl: 1000 * 60 * 60 }); // 1 hour    this.renderPool = new WorkerPool({      size: 10,      taskTimeout: 5000    });  }
  async renderTemplate(    templateId: string,    userData: any,    notificationData: any  ): Promise<RenderedContent> {    // Use compiled template cache    let template = this.templateCache.get(templateId);        if (!template) {      const templateSource = await this.getTemplateSource(templateId);      template = await this.compileTemplate(templateSource);      this.templateCache.set(templateId, template);    }        // Pre-load commonly needed data to prevent N+1 queries    const preloadedData = await this.dataPreloader.preloadForTemplate(      template.requiredData,      userData.userId    );        const renderContext = {      ...userData,      ...notificationData,      ...preloadedData    };        // Use worker pool for CPU-intensive rendering    const renderTask = {      templateId,      template: template.compiled,      context: renderContext    };        try {      const result = await this.renderPool.execute(renderTask);            // Track rendering performance      await this.trackRenderingMetrics(templateId, result.renderTime, true);            return result.content;    } catch (error) {      await this.trackRenderingMetrics(templateId, 0, false);            // Fallback to simple template      return await this.renderFallbackTemplate(templateId, renderContext);    }  }}
class DataPreloader {  private queryBatcher: QueryBatcher;  private dataCache: Cache;
  async preloadForTemplate(    requiredData: string[],    userId: string  ): Promise<Record<string, any>> {    const preloadPromises: Promise<any>[] = [];    const preloadedData: Record<string, any> = {};        if (requiredData.includes('user_projects')) {      preloadPromises.push(        this.queryBatcher.batch('user_projects', userId)          .then(data => preloadedData.projects = data)      );    }        if (requiredData.includes('user_activities')) {      preloadPromises.push(        this.queryBatcher.batch('user_activities', userId)          .then(data => preloadedData.recentActivities = data)      );    }        if (requiredData.includes('user_settings')) {      preloadPromises.push(        this.queryBatcher.batch('user_settings', userId)          .then(data => preloadedData.settings = data)      );    }        await Promise.all(preloadPromises);    return preloadedData;  }}
class QueryBatcher {  private batches: Map<string, BatchQuery> = new Map();  private batchTimeout = 50; // 50ms batch window    async batch<T>(queryType: string, param: any): Promise<T> {    return new Promise((resolve, reject) => {      if (!this.batches.has(queryType)) {        this.batches.set(queryType, {          params: [],          promises: [],          timeoutId: setTimeout(() => this.executeBatch(queryType), this.batchTimeout)        });      }            const batch = this.batches.get(queryType)!;      batch.params.push(param);      batch.promises.push({ resolve, reject });    });  }    private async executeBatch(queryType: string): Promise<void> {    const batch = this.batches.get(queryType);    if (!batch) return;        this.batches.delete(queryType);    clearTimeout(batch.timeoutId);        try {      const results = await this.executeQuery(queryType, batch.params);            batch.promises.forEach((promise, index) => {        promise.resolve(results[index]);      });    } catch (error) {      batch.promises.forEach(promise => {        promise.reject(error);      });    }  }}

class OptimizedNotificationQueries {  private readReplica: Database;  private writeDatabase: Database;  private queryCache: Redis;
  async getUserNotificationPreferences(    userId: string  ): Promise<NotificationPreferences> {    // Use read replica for preference lookups    const cacheKey = `prefs:${userId}`;        // Try cache first    const cached = await this.queryCache.get(cacheKey);    if (cached) {      return JSON.parse(cached);    }        // Single query to get all preferences    const preferences = await this.readReplica.query(`      SELECT         np.notification_type,        np.channel,        np.enabled,        np.frequency,        np.quiet_hours_start,        np.quiet_hours_end,        u.timezone,        u.locale      FROM notification_preferences np      JOIN users u ON u.id = np.user_id      WHERE np.user_id = $1    `, [userId]);        const structured = this.structurePreferences(preferences);        // Cache for 5 minutes    await this.queryCache.setex(cacheKey, 300, JSON.stringify(structured));        return structured;  }
  async getBatchUserData(userIds: string[]): Promise<Map<string, UserData>> {    // Batch query instead of N individual queries    const userData = await this.readReplica.query(`      SELECT         u.id,        u.email,        u.locale,        u.timezone,        u.email_enabled,        u.sms_enabled,        u.push_enabled,        array_agg(pt.token) as push_tokens,        array_agg(pt.platform) as push_platforms      FROM users u      LEFT JOIN push_tokens pt ON pt.user_id = u.id AND pt.is_active = true      WHERE u.id = ANY($1)      GROUP BY u.id, u.email, u.locale, u.timezone, u.email_enabled, u.sms_enabled, u.push_enabled    `, [userIds]);        const userMap = new Map<string, UserData>();        userData.forEach(row => {      userMap.set(row.id, {        id: row.id,        email: row.email,        locale: row.locale,        timezone: row.timezone,        emailEnabled: row.email_enabled,        smsEnabled: row.sms_enabled,        pushEnabled: row.push_enabled,        pushTokens: row.push_tokens?.filter(Boolean) || [],        pushPlatforms: row.push_platforms?.filter(Boolean) || []      });    });        return userMap;  }
  async getNotificationAnalytics(    dateRange: DateRange,    filters?: AnalyticsFilters  ): Promise<NotificationAnalytics> {    // Use materialized view for analytics queries    let query = `      SELECT         notification_type,        channel,        date_trunc('day', created_at) as date,        COUNT(*) as total_sent,        COUNT(*) FILTER (WHERE status = 'delivered') as delivered,        COUNT(*) FILTER (WHERE status = 'opened') as opened,        COUNT(*) FILTER (WHERE status = 'clicked') as clicked,        COUNT(*) FILTER (WHERE status = 'failed') as failed,        AVG(EXTRACT(EPOCH FROM (delivered_at - created_at))) as avg_delivery_time      FROM notification_metrics_daily      WHERE created_at >= $1 AND created_at <= $2    `;        const params = [dateRange.start, dateRange.end];        if (filters?.notificationType) {      query += ` AND notification_type = $${params.length + 1}`;      params.push(filters.notificationType);    }        if (filters?.channel) {      query += ` AND channel = $${params.length + 1}`;      params.push(filters.channel);    }        query += `      GROUP BY notification_type, channel, date_trunc('day', created_at)      ORDER BY date DESC    `;        const results = await this.readReplica.query(query, params);    return this.aggregateAnalytics(results);  }}

class OptimizedNotificationProcessor {  private processingQueue: Queue;  private batchProcessor: BatchProcessor;  private resourceMonitor: ResourceMonitor;
  constructor() {    this.batchProcessor = new BatchProcessor({      batchSize: 100,      batchTimeout: 1000, // 1 second      concurrency: 10    });  }
  async startProcessing(): Promise<void> {    // Dynamic concurrency based on system resources    this.processingQueue.process('notification', async (job) => {      const notifications = Array.isArray(job.data) ? job.data : [job.data];            // Group by similar processing requirements      const groupedNotifications = this.groupNotifications(notifications);            const processingPromises = Object.entries(groupedNotifications).map(        ([group, groupNotifications]) =>           this.processNotificationGroup(group, groupNotifications)      );            return await Promise.allSettled(processingPromises);    });        // Adjust processing concurrency based on system load    setInterval(async () => {      const systemLoad = await this.resourceMonitor.getCurrentLoad();      const optimalConcurrency = this.calculateOptimalConcurrency(systemLoad);            this.processingQueue.setConcurrency(optimalConcurrency);    }, 30000); // Every 30 seconds  }
  private async processNotificationGroup(    groupType: string,    notifications: NotificationEvent[]  ): Promise<BatchProcessingResult> {    switch (groupType) {      case 'email_batch':        return await this.processEmailBatch(notifications);      case 'push_batch':        return await this.processPushBatch(notifications);      case 'template_heavy':        return await this.processTemplateHeavyBatch(notifications);      default:        return await this.processIndividualNotifications(notifications);    }  }
  private async processEmailBatch(    notifications: NotificationEvent[]  ): Promise<BatchProcessingResult> {    // Batch similar email notifications    const templateGroups = this.groupByTemplate(notifications);        const batchPromises = Object.entries(templateGroups).map(      async ([templateId, templateNotifications]) => {        // Pre-render template once for the batch        const baseTemplate = await this.getTemplate(templateId);                // Batch user data lookup        const userIds = templateNotifications.map(n => n.userId);        const userData = await this.getBatchUserData(userIds);                // Process all notifications with pre-loaded data        const emailPromises = templateNotifications.map(notification =>           this.processEmailWithPreloadedData(notification, userData, baseTemplate)        );                return await Promise.allSettled(emailPromises);      }    );        const results = await Promise.all(batchPromises);        return {      processed: notifications.length,      successful: results.flat().filter(r => r.status === 'fulfilled').length,      failed: results.flat().filter(r => r.status === 'rejected').length,      processingTime: Date.now() - performance.now()    };  }
  private calculateOptimalConcurrency(systemLoad: SystemLoad): number {    const baseConcurrency = 10;        if (systemLoad.cpu > 0.8) {      return Math.max(2, baseConcurrency * 0.5);    } else if (systemLoad.cpu > 0.6) {      return Math.max(5, baseConcurrency * 0.7);    } else if (systemLoad.cpu < 0.3) {      return Math.min(20, baseConcurrency * 1.5);    }        return baseConcurrency;  }}

class CostOptimizedNotificationSystem {  private costTracker: CostTracker;  private resourceAllocator: ResourceAllocator;
  async processNotificationWithCostOptimization(    notification: NotificationEvent  ): Promise<void> {    const costAnalysis = await this.analyzeCost(notification);        // Choose processing strategy based on cost-benefit    if (costAnalysis.highValue && costAnalysis.lowCost) {      // Premium processing for high-value, low-cost notifications      await this.processPremium(notification);    } else if (costAnalysis.highValue && costAnalysis.highCost) {      // Optimized processing for high-value, high-cost notifications      await this.processOptimized(notification);    } else if (costAnalysis.lowValue && costAnalysis.lowCost) {      // Batch processing for low-value, low-cost notifications      await this.queueForBatchProcessing(notification);    } else {      // Evaluate if notification should be sent at all      const shouldSend = await this.evaluateROI(notification, costAnalysis);      if (shouldSend) {        await this.processEconomical(notification);      }    }  }
  private async analyzeCost(notification: NotificationEvent): Promise<CostAnalysis> {    const channels = await this.getTargetChannels(notification.userId, notification.type);        let totalCost = 0;    let estimatedValue = 0;        for (const channel of channels) {      const channelCost = await this.costTracker.getChannelCost(channel);      const channelValue = await this.estimateChannelValue(notification, channel);            totalCost += channelCost;      estimatedValue += channelValue;    }        return {      totalCost,      estimatedValue,      roi: estimatedValue / totalCost,      highValue: estimatedValue > 5.0, // $5 estimated value      lowCost: totalCost < 0.10,  // 10 cents      highCost: totalCost > 1.0  // $1    };  }
  private async evaluateROI(    notification: NotificationEvent,    costAnalysis: CostAnalysis  ): Promise<boolean> {    // Don't send notifications with negative ROI    if (costAnalysis.roi < 1.0) {      await this.trackSkippedNotification(notification, 'negative_roi');      return false;    }        // For marginal ROI, consider user engagement history    if (costAnalysis.roi < 1.5) {      const userEngagement = await this.getUserEngagementScore(notification.userId);      if (userEngagement < 0.1) { // Very low engagement        await this.trackSkippedNotification(notification, 'low_engagement_roi');        return false;      }    }        return true;  }}