Third-party Integration - 2/2

// Advanced webhook processing system that handles floods and ensures reliability
class WebhookProcessingEngine {
  private processors: Map<string, WebhookProcessor> = new Map();
  private incomingQueue: WebhookQueue;
  private processingQueue: WebhookQueue;
  private deadLetterQueue: WebhookQueue;
  private deduplicationCache: DeduplicationCache;
  private rateLimiter: WebhookRateLimiter;
  private retryManager: WebhookRetryManager;
  private metricsCollector: WebhookMetrics;

  constructor(config: WebhookEngineConfig) {
    this.incomingQueue = new WebhookQueue("incoming", config.queueConfig);
    this.processingQueue = new WebhookQueue("processing", config.queueConfig);
    this.deadLetterQueue = new WebhookQueue("dead-letter", config.queueConfig);
    this.deduplicationCache = new DeduplicationCache(config.cacheConfig);
    this.rateLimiter = new WebhookRateLimiter(config.rateLimitConfig);
    this.retryManager = new WebhookRetryManager(config.retryConfig);
    this.metricsCollector = new WebhookMetrics();

    this.initializeProcessors(config.processors);
    this.startProcessingWorkers(config.workerCount || 10);
    this.setupHealthMonitoring();
  }

  // Accept incoming webhook with immediate response
  async receiveWebhook(
    provider: string,
    signature: string,
    payload: any,
    headers: Record<string, string>
  ): Promise<WebhookReceiptResult> {
    const webhookId = this.generateWebhookId();
    const receivedAt = Date.now();

    try {
      // Immediate signature validation (fast path)
      const processor = this.processors.get(provider);
      if (!processor) {
        throw new WebhookError(
          `No processor found for provider: ${provider}`,
          "UNKNOWN_PROVIDER"
        );
      }

      // Basic signature validation
      const isValidSignature = await processor.validateSignature(
        signature,
        payload,
        headers
      );

      if (!isValidSignature) {
        await this.metricsCollector.recordRejected(
          provider,
          "INVALID_SIGNATURE"
        );
        throw new WebhookError(
          "Invalid webhook signature",
          "INVALID_SIGNATURE"
        );
      }

      // Apply rate limiting per provider
      const rateLimitResult = await this.rateLimiter.checkLimit(provider);
      if (!rateLimitResult.allowed) {
        await this.metricsCollector.recordRejected(provider, "RATE_LIMITED");
        throw new WebhookError("Rate limit exceeded", "RATE_LIMITED", 429, {
          retryAfter: rateLimitResult.retryAfter,
        });
      }

      // Create webhook record
      const webhook: IncomingWebhook = {
        id: webhookId,
        provider,
        signature,
        payload,
        headers,
        receivedAt,
        status: "received",
        attempts: 0,
        maxAttempts: this.getMaxAttempts(provider),
        nextRetryAt: null,
      };

      // Queue for processing (fast operation)
      await this.incomingQueue.enqueue(webhook);

      // Record metrics
      await this.metricsCollector.recordReceived(provider);

      console.log(`Webhook received: ${webhookId} from ${provider}`);

      return {
        webhookId,
        status: "accepted",
        message: "Webhook queued for processing",
      };
    } catch (error) {
      console.error(`Webhook reception failed: ${webhookId}`, error);

      return {
        webhookId,
        status: "rejected",
        message: error.message,
        error: error.code,
      };
    }
  }

  // Process webhooks with deduplication and retry logic
  private async processWebhook(webhook: IncomingWebhook): Promise<void> {
    const startTime = Date.now();
    let processingResult: WebhookProcessingResult;

    try {
      // Check for duplicate processing
      const deduplicationKey = this.generateDeduplicationKey(webhook);
      const isDuplicate = await this.deduplicationCache.isDuplicate(
        deduplicationKey
      );

      if (isDuplicate) {
        console.log(`Duplicate webhook detected: ${webhook.id}`);
        await this.metricsCollector.recordDuplicate(webhook.provider);
        return;
      }

      // Mark as processing to prevent duplicates
      await this.deduplicationCache.markProcessing(
        deduplicationKey,
        webhook.id
      );

      // Get processor for this provider
      const processor = this.processors.get(webhook.provider);
      if (!processor) {
        throw new WebhookError(
          `No processor found for provider: ${webhook.provider}`,
          "NO_PROCESSOR"
        );
      }

      // Parse webhook events
      const events = await processor.parseEvents(
        webhook.payload,
        webhook.headers
      );

      if (events.length === 0) {
        console.log(`No events found in webhook: ${webhook.id}`);
        await this.metricsCollector.recordProcessed(
          webhook.provider,
          0,
          Date.now() - startTime
        );
        return;
      }

      // Process each event in the webhook
      processingResult = await this.processWebhookEvents(webhook, events);

      // Record successful processing
      await this.metricsCollector.recordProcessed(
        webhook.provider,
        events.length,
        Date.now() - startTime
      );

      // Mark processing complete in cache
      await this.deduplicationCache.markCompleted(
        deduplicationKey,
        processingResult
      );

      console.log(
        `Webhook processed successfully: ${webhook.id} (${events.length} events)`
      );
    } catch (error) {
      const duration = Date.now() - startTime;

      console.error(`Webhook processing failed: ${webhook.id}`, error);

      // Determine if error is retryable
      const shouldRetry = this.shouldRetryWebhook(error, webhook);

      if (shouldRetry && webhook.attempts < webhook.maxAttempts) {
        // Calculate retry delay with exponential backoff
        const retryDelay = this.calculateRetryDelay(webhook.attempts);
        webhook.nextRetryAt = Date.now() + retryDelay;
        webhook.attempts++;
        webhook.lastError = error.message;

        // Requeue for retry
        await this.processingQueue.enqueueDelayed(webhook, retryDelay);

        await this.metricsCollector.recordRetry(
          webhook.provider,
          webhook.attempts
        );

        console.log(
          `Webhook queued for retry: ${webhook.id} (attempt ${webhook.attempts}/${webhook.maxAttempts})`
        );
      } else {
        // Max retries exceeded or non-retryable error
        webhook.status = "failed";
        webhook.lastError = error.message;

        await this.deadLetterQueue.enqueue(webhook);
        await this.metricsCollector.recordFailed(webhook.provider, duration);

        console.error(
          `Webhook moved to dead letter queue: ${webhook.id}`,
          error
        );
      }
    }
  }

  private async processWebhookEvents(
    webhook: IncomingWebhook,
    events: WebhookEvent[]
  ): Promise<WebhookProcessingResult> {
    const results: EventProcessingResult[] = [];
    const processor = this.processors.get(webhook.provider)!;

    for (const event of events) {
      try {
        // Process individual event with timeout
        const eventResult = await Promise.race([
          processor.processEvent(event, webhook),
          new Promise<never>((_, reject) =>
            setTimeout(
              () => reject(new Error("Event processing timeout")),
              30000 // 30 second timeout per event
            )
          ),
        ]);

        results.push({
          eventId: event.id,
          eventType: event.type,
          success: true,
          result: eventResult,
        });
      } catch (error) {
        console.error(
          `Event processing failed: ${webhook.id}/${event.id}`,
          error
        );

        results.push({
          eventId: event.id,
          eventType: event.type,
          success: false,
          error: error.message,
        });

        // If it's a critical event type, fail the entire webhook
        if (this.isCriticalEventType(event.type)) {
          throw new WebhookError(
            `Critical event processing failed: ${event.type}`,
            "CRITICAL_EVENT_FAILED",
            500,
            { eventId: event.id, originalError: error }
          );
        }
      }
    }

    const successfulEvents = results.filter((r) => r.success).length;
    const failedEvents = results.filter((r) => !r.success).length;

    return {
      webhookId: webhook.id,
      totalEvents: events.length,
      successfulEvents,
      failedEvents,
      results,
      processedAt: Date.now(),
    };
  }

  // Start processing workers
  private startProcessingWorkers(workerCount: number): void {
    for (let i = 0; i < workerCount; i++) {
      this.startProcessingWorker(`worker-${i}`);
    }
    console.log(`Started ${workerCount} webhook processing workers`);
  }

  private async startProcessingWorker(workerId: string): Promise<void> {
    console.log(`Starting webhook processing worker: ${workerId}`);

    // Process incoming webhooks
    const processIncoming = async () => {
      while (true) {
        try {
          const webhook = await this.incomingQueue.dequeue(5000); // 5 second timeout
          if (webhook) {
            webhook.status = "processing";
            await this.processWebhook(webhook);
          }
        } catch (error) {
          console.error(`Worker ${workerId} error processing incoming:`, error);
          await new Promise((resolve) => setTimeout(resolve, 1000)); // Brief pause on error
        }
      }
    };

    // Process retry webhooks
    const processRetries = async () => {
      while (true) {
        try {
          const webhook = await this.processingQueue.dequeueReady(5000);
          if (webhook) {
            webhook.status = "retrying";
            await this.processWebhook(webhook);
          }
        } catch (error) {
          console.error(`Worker ${workerId} error processing retries:`, error);
          await new Promise((resolve) => setTimeout(resolve, 1000));
        }
      }
    };

    // Run both processing loops concurrently
    Promise.all([processIncoming(), processRetries()]);
  }

  // Webhook replay for failed processing
  async replayWebhook(webhookId: string): Promise<WebhookReplayResult> {
    try {
      // Find webhook in dead letter queue
      const webhook = await this.deadLetterQueue.findById(webhookId);
      if (!webhook) {
        throw new WebhookError("Webhook not found", "WEBHOOK_NOT_FOUND");
      }

      // Reset webhook state for replay
      webhook.status = "received";
      webhook.attempts = 0;
      webhook.nextRetryAt = null;
      webhook.lastError = null;

      // Remove from dead letter queue
      await this.deadLetterQueue.remove(webhookId);

      // Requeue for processing
      await this.incomingQueue.enqueue(webhook);

      console.log(`Webhook queued for replay: ${webhookId}`);

      return {
        webhookId,
        status: "replaying",
        message: "Webhook queued for replay processing",
      };
    } catch (error) {
      return {
        webhookId,
        status: "replay_failed",
        message: error.message,
        error: error.code,
      };
    }
  }

  // Batch webhook operations
  async replayWebhookBatch(
    criteria: WebhookReplayCriteria
  ): Promise<BatchReplayResult> {
    const webhooks = await this.deadLetterQueue.findByCriteria(criteria);
    const results: WebhookReplayResult[] = [];

    for (const webhook of webhooks) {
      const result = await this.replayWebhook(webhook.id);
      results.push(result);
    }

    return {
      total: webhooks.length,
      successful: results.filter((r) => r.status === "replaying").length,
      failed: results.filter((r) => r.status === "replay_failed").length,
      results,
    };
  }

  // Webhook analytics and monitoring
  async getWebhookStatistics(
    timeRange: TimeRange,
    provider?: string
  ): Promise<WebhookStatistics> {
    return await this.metricsCollector.getStatistics(timeRange, provider);
  }

  async getWebhookHealth(): Promise<WebhookHealthStatus> {
    const queueStats = {
      incoming: await this.incomingQueue.getSize(),
      processing: await this.processingQueue.getSize(),
      deadLetter: await this.deadLetterQueue.getSize(),
    };

    const processingRates = await this.metricsCollector.getProcessingRates();
    const errorRates = await this.metricsCollector.getErrorRates();

    return {
      queues: queueStats,
      processingRates,
      errorRates,
      healthScore: this.calculateHealthScore(queueStats, errorRates),
      lastUpdated: Date.now(),
    };
  }

  // Initialize webhook processors for different providers
  private initializeProcessors(
    processorConfigs: WebhookProcessorConfig[]
  ): void {
    for (const config of processorConfigs) {
      let processor: WebhookProcessor;

      switch (config.provider) {
        case "stripe":
          processor = new StripeWebhookProcessor(config);
          break;
        case "paypal":
          processor = new PayPalWebhookProcessor(config);
          break;
        case "github":
          processor = new GitHubWebhookProcessor(config);
          break;
        case "sendgrid":
          processor = new SendGridWebhookProcessor(config);
          break;
        default:
          throw new Error(`Unsupported webhook provider: ${config.provider}`);
      }

      this.processors.set(config.provider, processor);
      console.log(`Initialized webhook processor: ${config.provider}`);
    }
  }

  // Utility methods
  private generateWebhookId(): string {
    return `wh_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
  }

  private generateDeduplicationKey(webhook: IncomingWebhook): string {
    // Create unique key based on provider, signature, and payload hash
    const payloadHash = this.hashPayload(webhook.payload);
    return `${webhook.provider}:${webhook.signature}:${payloadHash}`;
  }

  private hashPayload(payload: any): string {
    const crypto = require("crypto");
    return crypto
      .createHash("sha256")
      .update(JSON.stringify(payload))
      .digest("hex");
  }

  private shouldRetryWebhook(error: any, webhook: IncomingWebhook): boolean {
    // Determine if webhook should be retried based on error type
    const retryableErrors = [
      "TIMEOUT",
      "CONNECTION_ERROR",
      "SERVICE_UNAVAILABLE",
      "DATABASE_ERROR",
    ];

    const nonRetryableErrors = [
      "INVALID_SIGNATURE",
      "NO_PROCESSOR",
      "MALFORMED_PAYLOAD",
    ];

    if (nonRetryableErrors.includes(error.code)) {
      return false;
    }

    if (retryableErrors.includes(error.code) || error.status >= 500) {
      return true;
    }

    return false;
  }

  private calculateRetryDelay(attemptNumber: number): number {
    // Exponential backoff with jitter
    const baseDelay = 1000; // 1 second
    const maxDelay = 300000; // 5 minutes
    const exponentialDelay = baseDelay * Math.pow(2, attemptNumber);
    const jitter = Math.random() * 1000; // Up to 1 second jitter

    return Math.min(maxDelay, exponentialDelay + jitter);
  }

  private getMaxAttempts(provider: string): number {
    const maxAttemptsByProvider: Record<string, number> = {
      stripe: 5,
      paypal: 3,
      github: 7,
      sendgrid: 5,
    };

    return maxAttemptsByProvider[provider] || 5;
  }

  private isCriticalEventType(eventType: string): boolean {
    const criticalEvents = [
      "payment.completed",
      "payment.failed",
      "subscription.cancelled",
      "account.deleted",
    ];

    return criticalEvents.includes(eventType);
  }

  private calculateHealthScore(queueStats: any, errorRates: any): number {
    let score = 100;

    // Deduct points for queue backlog
    if (queueStats.incoming > 1000) score -= 20;
    if (queueStats.processing > 500) score -= 15;
    if (queueStats.deadLetter > 100) score -= 25;

    // Deduct points for high error rates
    if (errorRates.overall > 0.1) score -= 30; // 10% error rate
    if (errorRates.overall > 0.05) score -= 15; // 5% error rate

    return Math.max(0, Math.min(100, score));
  }

  private setupHealthMonitoring(): void {
    setInterval(async () => {
      try {
        const health = await this.getWebhookHealth();

        if (health.healthScore < 70) {
          console.warn("Webhook system health degraded:", health);
        }

        // Auto-scale workers if queues are backing up
        if (health.queues.incoming > 5000) {
          console.log("High webhook queue detected, consider scaling workers");
        }
      } catch (error) {
        console.error("Health monitoring error:", error);
      }
    }, 30000); // Every 30 seconds
  }
}

// Example Stripe webhook processor implementation
class StripeWebhookProcessor implements WebhookProcessor {
  constructor(private config: WebhookProcessorConfig) {}

  async validateSignature(
    signature: string,
    payload: any,
    headers: Record<string, string>
  ): Promise<boolean> {
    try {
      const stripe = require("stripe")(this.config.secretKey);
      const endpointSecret = this.config.webhookSecret;

      // Use Stripe's signature validation
      stripe.webhooks.constructEvent(payload, signature, endpointSecret);
      return true;
    } catch (error) {
      console.error("Stripe signature validation failed:", error.message);
      return false;
    }
  }

  async parseEvents(
    payload: any,
    headers: Record<string, string>
  ): Promise<WebhookEvent[]> {
    const stripeEvent = payload;

    return [
      {
        id: stripeEvent.id,
        type: stripeEvent.type,
        data: stripeEvent.data,
        createdAt: stripeEvent.created * 1000, // Convert to milliseconds
        metadata: {
          apiVersion: stripeEvent.api_version,
          livemode: stripeEvent.livemode,
        },
      },
    ];
  }

  async processEvent(
    event: WebhookEvent,
    webhook: IncomingWebhook
  ): Promise<EventProcessingResult> {
    console.log(`Processing Stripe event: ${event.type} (${event.id})`);

    try {
      switch (event.type) {
        case "payment_intent.succeeded":
          return await this.handlePaymentSuccess(event);

        case "payment_intent.payment_failed":
          return await this.handlePaymentFailed(event);

        case "customer.subscription.created":
          return await this.handleSubscriptionCreated(event);

        case "customer.subscription.deleted":
          return await this.handleSubscriptionCancelled(event);

        case "invoice.payment_succeeded":
          return await this.handleInvoicePaymentSuccess(event);

        case "invoice.payment_failed":
          return await this.handleInvoicePaymentFailed(event);

        default:
          console.log(`Unhandled Stripe event type: ${event.type}`);
          return {
            success: true,
            message: "Event type not handled, but acknowledged",
          };
      }
    } catch (error) {
      return {
        success: false,
        error: error.message,
        retryable: this.isRetryableError(error),
      };
    }
  }

  private async handlePaymentSuccess(
    event: WebhookEvent
  ): Promise<EventProcessingResult> {
    const paymentIntent = event.data.object;

    // Update payment status in database
    await this.updatePaymentStatus(
      paymentIntent.metadata?.orderId || paymentIntent.id,
      "completed",
      {
        stripePaymentIntentId: paymentIntent.id,
        amount: paymentIntent.amount,
        currency: paymentIntent.currency,
      }
    );

    // Send confirmation email
    await this.sendPaymentConfirmation(paymentIntent);

    // Update inventory
    await this.updateInventory(paymentIntent.metadata?.orderId);

    return {
      success: true,
      message: `Payment confirmed: ${paymentIntent.id}`,
      data: { paymentIntentId: paymentIntent.id },
    };
  }

  private async handlePaymentFailed(
    event: WebhookEvent
  ): Promise<EventProcessingResult> {
    const paymentIntent = event.data.object;

    // Update payment status in database
    await this.updatePaymentStatus(
      paymentIntent.metadata?.orderId || paymentIntent.id,
      "failed",
      {
        stripePaymentIntentId: paymentIntent.id,
        failureReason: paymentIntent.last_payment_error?.message,
      }
    );

    // Send failure notification
    await this.sendPaymentFailureNotification(paymentIntent);

    // Release inventory hold
    await this.releaseInventoryHold(paymentIntent.metadata?.orderId);

    return {
      success: true,
      message: `Payment failure processed: ${paymentIntent.id}`,
      data: { paymentIntentId: paymentIntent.id },
    };
  }

  private async handleSubscriptionCreated(
    event: WebhookEvent
  ): Promise<EventProcessingResult> {
    const subscription = event.data.object;

    // Create subscription record
    await this.createSubscription({
      stripeSubscriptionId: subscription.id,
      customerId: subscription.customer,
      status: subscription.status,
      currentPeriodStart: subscription.current_period_start * 1000,
      currentPeriodEnd: subscription.current_period_end * 1000,
      items: subscription.items.data,
    });

    // Send welcome email
    await this.sendSubscriptionWelcome(subscription);

    return {
      success: true,
      message: `Subscription created: ${subscription.id}`,
      data: { subscriptionId: subscription.id },
    };
  }

  // Placeholder methods for actual business logic
  private async updatePaymentStatus(
    orderId: string,
    status: string,
    metadata: any
  ): Promise<void> {
    // Implementation would update your database
    console.log(`Updating payment status: ${orderId} -> ${status}`);
  }

  private async sendPaymentConfirmation(paymentIntent: any): Promise<void> {
    // Implementation would send email via your email service
    console.log(`Sending payment confirmation for: ${paymentIntent.id}`);
  }

  private async updateInventory(orderId: string): Promise<void> {
    // Implementation would update inventory levels
    console.log(`Updating inventory for order: ${orderId}`);
  }

  private async sendPaymentFailureNotification(
    paymentIntent: any
  ): Promise<void> {
    // Implementation would notify customer of payment failure
    console.log(`Sending failure notification for: ${paymentIntent.id}`);
  }

  private async releaseInventoryHold(orderId: string): Promise<void> {
    // Implementation would release inventory hold
    console.log(`Releasing inventory hold for order: ${orderId}`);
  }

  private async createSubscription(subscriptionData: any): Promise<void> {
    // Implementation would create subscription record
    console.log(
      `Creating subscription: ${subscriptionData.stripeSubscriptionId}`
    );
  }

  private async sendSubscriptionWelcome(subscription: any): Promise<void> {
    // Implementation would send welcome email
    console.log(`Sending subscription welcome: ${subscription.id}`);
  }

  private isRetryableError(error: any): boolean {
    const retryableErrors = [
      "DATABASE_CONNECTION_ERROR",
      "EMAIL_SERVICE_ERROR",
      "INVENTORY_SERVICE_ERROR",
    ];

    return retryableErrors.includes(error.code) || error.status >= 500;
  }
}

// Supporting classes and interfaces
interface WebhookEngineConfig {
  queueConfig: any;
  cacheConfig: any;
  rateLimitConfig: any;
  retryConfig: any;
  processors: WebhookProcessorConfig[];
  workerCount?: number;
}

interface WebhookProcessorConfig {
  provider: string;
  secretKey: string;
  webhookSecret: string;
  maxEvents?: number;
}

interface WebhookProcessor {
  validateSignature(
    signature: string,
    payload: any,
    headers: Record<string, string>
  ): Promise<boolean>;
  parseEvents(
    payload: any,
    headers: Record<string, string>
  ): Promise<WebhookEvent[]>;
  processEvent(
    event: WebhookEvent,
    webhook: IncomingWebhook
  ): Promise<EventProcessingResult>;
}

interface IncomingWebhook {
  id: string;
  provider: string;
  signature: string;
  payload: any;
  headers: Record<string, string>;
  receivedAt: number;
  status: "received" | "processing" | "retrying" | "completed" | "failed";
  attempts: number;
  maxAttempts: number;
  nextRetryAt: number | null;
  lastError?: string;
}

interface WebhookEvent {
  id: string;
  type: string;
  data: any;
  createdAt: number;
  metadata?: any;
}

interface EventProcessingResult {
  success: boolean;
  message?: string;
  data?: any;
  error?: string;
  retryable?: boolean;
}

interface WebhookProcessingResult {
  webhookId: string;
  totalEvents: number;
  successfulEvents: number;
  failedEvents: number;
  results: EventProcessingResult[];
  processedAt: number;
}

interface WebhookReceiptResult {
  webhookId: string;
  status: "accepted" | "rejected";
  message: string;
  error?: string;
}

interface WebhookReplayResult {
  webhookId: string;
  status: "replaying" | "replay_failed";
  message: string;
  error?: string;
}

interface BatchReplayResult {
  total: number;
  successful: number;
  failed: number;
  results: WebhookReplayResult[];
}

interface WebhookReplayCriteria {
  provider?: string;
  dateRange?: { start: Date; end: Date };
  errorType?: string;
  limit?: number;
}

interface WebhookStatistics {
  totalReceived: number;
  totalProcessed: number;
  totalFailed: number;
  successRate: number;
  averageProcessingTime: number;
  byProvider: Record<string, any>;
}

interface WebhookHealthStatus {
  queues: {
    incoming: number;
    processing: number;
    deadLetter: number;
  };
  processingRates: any;
  errorRates: any;
  healthScore: number;
  lastUpdated: number;
}

interface TimeRange {
  start: Date;
  end: Date;
}

class WebhookError extends Error {
  constructor(
    message: string,
    public code: string,
    public status?: number,
    public metadata?: any
  ) {
    super(message);
    this.name = "WebhookError";
  }
}

// Placeholder classes that would need full implementation
class WebhookQueue {
  constructor(private name: string, private config: any) {}
  async enqueue(webhook: IncomingWebhook): Promise<void> {}
  async enqueueDelayed(
    webhook: IncomingWebhook,
    delayMs: number
  ): Promise<void> {}
  async dequeue(timeoutMs?: number): Promise<IncomingWebhook | null> {
    return null;
  }
  async dequeueReady(timeoutMs?: number): Promise<IncomingWebhook | null> {
    return null;
  }
  async findById(id: string): Promise<IncomingWebhook | null> {
    return null;
  }
  async findByCriteria(
    criteria: WebhookReplayCriteria
  ): Promise<IncomingWebhook[]> {
    return [];
  }
  async remove(id: string): Promise<void> {}
  async getSize(): Promise<number> {
    return 0;
  }
}

class DeduplicationCache {
  constructor(private config: any) {}
  async isDuplicate(key: string): Promise<boolean> {
    return false;
  }
  async markProcessing(key: string, webhookId: string): Promise<void> {}
  async markCompleted(
    key: string,
    result: WebhookProcessingResult
  ): Promise<void> {}
}

class WebhookRateLimiter {
  constructor(private config: any) {}
  async checkLimit(
    provider: string
  ): Promise<{ allowed: boolean; retryAfter?: number }> {
    return { allowed: true };
  }
}

class WebhookRetryManager {
  constructor(private config: any) {}
}

class WebhookMetrics {
  async recordReceived(provider: string): Promise<void> {}
  async recordRejected(provider: string, reason: string): Promise<void> {}
  async recordProcessed(
    provider: string,
    eventCount: number,
    duration: number
  ): Promise<void> {}
  async recordRetry(provider: string, attempt: number): Promise<void> {}
  async recordFailed(provider: string, duration: number): Promise<void> {}
  async recordDuplicate(provider: string): Promise<void> {}
  async getStatistics(
    timeRange: TimeRange,
    provider?: string
  ): Promise<WebhookStatistics> {
    return {} as WebhookStatistics;
  }
  async getProcessingRates(): Promise<any> {
    return {};
  }
  async getErrorRates(): Promise<any> {
    return {};
  }
}

// Advanced rate limiting and retry system that adapts to API behavior
class IntelligentAPIManager {
  private rateLimiters: Map<string, AdaptiveRateLimiter> = new Map();
  private retryStrategies: Map<string, RetryStrategy> = new Map();
  private circuitBreakers: Map<string, CircuitBreaker> = new Map();
  private apiMetrics: APIMetricsCollector;
  private healthMonitor: APIHealthMonitor;
  private backoffCalculator: BackoffCalculator;

  constructor(config: APIManagerConfig) {
    this.apiMetrics = new APIMetricsCollector();
    this.healthMonitor = new APIHealthMonitor();
    this.backoffCalculator = new BackoffCalculator();

    this.initializeAPIConfigs(config.apis);
    this.startHealthMonitoring();
    this.startRateLimitAdjustment();
  }

  private initializeAPIConfigs(apiConfigs: APIConfig[]): void {
    for (const config of apiConfigs) {
      // Initialize adaptive rate limiter
      const rateLimiter = new AdaptiveRateLimiter({
        name: config.name,
        initialLimit: config.rateLimit.initialLimit,
        windowMs: config.rateLimit.windowMs,
        maxLimit:
          config.rateLimit.maxLimit || config.rateLimit.initialLimit * 10,
        minLimit:
          config.rateLimit.minLimit ||
          Math.max(1, config.rateLimit.initialLimit / 10),
        adaptationFactor: config.rateLimit.adaptationFactor || 0.1,
      });

      // Initialize retry strategy
      const retryStrategy = new RetryStrategy({
        name: config.name,
        maxAttempts: config.retry.maxAttempts,
        baseDelayMs: config.retry.baseDelayMs,
        maxDelayMs: config.retry.maxDelayMs,
        backoffType: config.retry.backoffType,
        jitterFactor: config.retry.jitterFactor || 0.1,
        retryableStatusCodes: config.retry.retryableStatusCodes,
        retryableErrors: config.retry.retryableErrors,
      });

      // Initialize circuit breaker
      const circuitBreaker = new CircuitBreaker({
        name: config.name,
        failureThreshold: config.circuitBreaker.failureThreshold,
        recoveryTimeoutMs: config.circuitBreaker.recoveryTimeoutMs,
        halfOpenMaxCalls: config.circuitBreaker.halfOpenMaxCalls || 3,
        monitoringWindowMs: config.circuitBreaker.monitoringWindowMs || 60000,
      });

      this.rateLimiters.set(config.name, rateLimiter);
      this.retryStrategies.set(config.name, retryStrategy);
      this.circuitBreakers.set(config.name, circuitBreaker);

      console.log(`Initialized API management for: ${config.name}`);
    }
  }

  // Execute API request with intelligent rate limiting and retry
  async executeRequest<T>(
    apiName: string,
    requestConfig: APIRequestConfig
  ): Promise<APIExecutionResult<T>> {
    const startTime = Date.now();
    const requestId = this.generateRequestId();

    const rateLimiter = this.rateLimiters.get(apiName);
    const retryStrategy = this.retryStrategies.get(apiName);
    const circuitBreaker = this.circuitBreakers.get(apiName);

    if (!rateLimiter || !retryStrategy || !circuitBreaker) {
      throw new Error(`API configuration not found: ${apiName}`);
    }

    // Check circuit breaker state
    if (circuitBreaker.isOpen()) {
      const error = new APIError(
        `Circuit breaker open for API: ${apiName}`,
        "CIRCUIT_BREAKER_OPEN",
        503
      );

      await this.apiMetrics.recordRequest(apiName, requestId, {
        status: "circuit_breaker_open",
        duration: Date.now() - startTime,
        error: error.code,
      });

      throw error;
    }

    let attemptNumber = 0;
    let lastError: APIError;

    while (attemptNumber < retryStrategy.maxAttempts) {
      attemptNumber++;

      try {
        // Wait for rate limit availability
        await this.waitForRateLimit(rateLimiter, requestId);

        // Execute the actual request
        const result = await this.executeActualRequest<T>(
          apiName,
          requestConfig,
          requestId,
          attemptNumber
        );

        // Record success metrics
        await this.recordSuccessMetrics(
          apiName,
          requestId,
          startTime,
          attemptNumber
        );

        // Update circuit breaker
        circuitBreaker.recordSuccess();

        // Adjust rate limits based on success
        await this.adjustRateLimitsOnSuccess(rateLimiter, result);

        return {
          requestId,
          data: result.data,
          status: result.status,
          headers: result.headers,
          duration: Date.now() - startTime,
          attempts: attemptNumber,
          apiName,
        };
      } catch (error) {
        lastError = error as APIError;

        // Record error metrics
        await this.recordErrorMetrics(
          apiName,
          requestId,
          startTime,
          attemptNumber,
          lastError
        );

        // Update circuit breaker
        circuitBreaker.recordFailure();

        // Adjust rate limits based on error
        await this.adjustRateLimitsOnError(rateLimiter, lastError);

        // Check if error is retryable
        if (!this.shouldRetry(retryStrategy, lastError, attemptNumber)) {
          break;
        }

        // Calculate and wait for retry delay
        if (attemptNumber < retryStrategy.maxAttempts) {
          const retryDelay = await this.calculateRetryDelay(
            retryStrategy,
            lastError,
            attemptNumber
          );

          console.log(
            `Retrying API request: ${requestId} (attempt ${attemptNumber + 1}/${
              retryStrategy.maxAttempts
            }) after ${retryDelay}ms`
          );

          await new Promise((resolve) => setTimeout(resolve, retryDelay));
        }
      }
    }

    // All retries exhausted
    throw new APIError(
      `All retry attempts exhausted for API: ${apiName}`,
      "MAX_RETRIES_EXCEEDED",
      lastError?.status || 500,
      {
        originalError: lastError,
        attempts: attemptNumber,
        totalDuration: Date.now() - startTime,
      }
    );
  }

  private async waitForRateLimit(
    rateLimiter: AdaptiveRateLimiter,
    requestId: string
  ): Promise<void> {
    const waitTime = await rateLimiter.getWaitTime();

    if (waitTime > 0) {
      console.log(`Rate limit wait: ${requestId} waiting ${waitTime}ms`);
      await new Promise((resolve) => setTimeout(resolve, waitTime));
    }

    await rateLimiter.acquireToken();
  }

  private async executeActualRequest<T>(
    apiName: string,
    requestConfig: APIRequestConfig,
    requestId: string,
    attemptNumber: number
  ): Promise<RawAPIResponse<T>> {
    const requestStart = Date.now();

    try {
      // Add retry headers
      const headers = {
        ...requestConfig.headers,
        "X-Request-ID": requestId,
        "X-Retry-Attempt": attemptNumber.toString(),
      };

      // Execute request with timeout
      const timeoutPromise = new Promise<never>((_, reject) => {
        setTimeout(
          () => reject(new APIError("Request timeout", "TIMEOUT", 408)),
          requestConfig.timeoutMs || 30000
        );
      });

      const requestPromise = this.makeHTTPRequest<T>({
        ...requestConfig,
        headers,
      });

      const response = await Promise.race([requestPromise, timeoutPromise]);

      // Check for API-specific error conditions
      this.validateAPIResponse(response);

      return response;
    } catch (error) {
      const duration = Date.now() - requestStart;

      // Transform error to standardized format
      throw this.transformError(error, apiName, duration);
    }
  }

  private async calculateRetryDelay(
    strategy: RetryStrategy,
    error: APIError,
    attemptNumber: number
  ): Promise<number> {
    let delay: number;

    // Check if API provided Retry-After header
    if (error.retryAfter) {
      delay = error.retryAfter * 1000; // Convert seconds to milliseconds
    } else {
      // Use configured backoff strategy
      delay = this.backoffCalculator.calculateDelay(
        strategy.backoffType,
        strategy.baseDelayMs,
        attemptNumber,
        strategy.maxDelayMs
      );
    }

    // Add jitter to prevent thundering herd
    if (strategy.jitterFactor > 0) {
      const jitter = delay * strategy.jitterFactor * (Math.random() - 0.5) * 2;
      delay = Math.max(0, delay + jitter);
    }

    // Apply error-specific delay multipliers
    delay = this.applyErrorSpecificDelay(delay, error);

    return Math.min(delay, strategy.maxDelayMs);
  }

  private applyErrorSpecificDelay(baseDelay: number, error: APIError): number {
    const multipliers: Record<string, number> = {
      RATE_LIMITED: 2.0, // Wait longer for rate limit errors
      SERVER_ERROR: 1.5, // Wait a bit longer for server errors
      TIMEOUT: 1.2, // Slightly longer for timeouts
      CONNECTION_ERROR: 2.0, // Much longer for connection issues
    };

    const multiplier = multipliers[error.code] || 1.0;
    return baseDelay * multiplier;
  }

  private async adjustRateLimitsOnSuccess(
    rateLimiter: AdaptiveRateLimiter,
    response: RawAPIResponse<any>
  ): Promise<void> {
    // Check for rate limit headers
    const remaining = this.parseRateLimitHeader(response.headers, "remaining");
    const limit = this.parseRateLimitHeader(response.headers, "limit");
    const resetTime = this.parseRateLimitHeader(response.headers, "reset");

    if (remaining !== null && limit !== null) {
      const usagePercent = (limit - remaining) / limit;

      // If we're using less than 70% of available rate limit, we can increase
      if (usagePercent < 0.7) {
        await rateLimiter.adjustLimit("increase", {
          reason: "low_usage",
          currentUsage: usagePercent,
          responseTime: response.duration || 0,
        });
      }
    }

    // If response was fast, we might be able to increase rate limit
    const responseTime = response.duration || 0;
    if (responseTime < 1000) {
      // Less than 1 second
      await rateLimiter.adjustLimit("increase", {
        reason: "fast_response",
        responseTime,
      });
    }
  }

  private async adjustRateLimitsOnError(
    rateLimiter: AdaptiveRateLimiter,
    error: APIError
  ): Promise<void> {
    if (error.code === "RATE_LIMITED") {
      // Decrease rate limit aggressively on rate limit errors
      await rateLimiter.adjustLimit("decrease", {
        reason: "rate_limited",
        severity: "high",
        retryAfter: error.retryAfter,
      });
    } else if (error.status && error.status >= 500) {
      // Decrease rate limit moderately on server errors
      await rateLimiter.adjustLimit("decrease", {
        reason: "server_error",
        severity: "medium",
        status: error.status,
      });
    } else if (error.code === "TIMEOUT") {
      // Decrease rate limit on timeouts
      await rateLimiter.adjustLimit("decrease", {
        reason: "timeout",
        severity: "medium",
      });
    }
  }

  private parseRateLimitHeader(
    headers: Record<string, any>,
    type: "remaining" | "limit" | "reset"
  ): number | null {
    // Common rate limit header patterns
    const headerVariations: Record<string, string[]> = {
      remaining: [
        "x-ratelimit-remaining",
        "x-rate-limit-remaining",
        "ratelimit-remaining",
        "rate-limit-remaining",
      ],
      limit: [
        "x-ratelimit-limit",
        "x-rate-limit-limit",
        "ratelimit-limit",
        "rate-limit-limit",
      ],
      reset: [
        "x-ratelimit-reset",
        "x-rate-limit-reset",
        "ratelimit-reset",
        "rate-limit-reset",
      ],
    };

    for (const headerName of headerVariations[type]) {
      const value = headers[headerName] || headers[headerName.toLowerCase()];
      if (value !== undefined) {
        const parsed = parseInt(value, 10);
        return isNaN(parsed) ? null : parsed;
      }
    }

    return null;
  }

  // API health monitoring and adaptive adjustment
  private startHealthMonitoring(): void {
    setInterval(async () => {
      for (const [apiName, rateLimiter] of this.rateLimiters) {
        try {
          const metrics = await this.apiMetrics.getRecentMetrics(
            apiName,
            300000
          ); // Last 5 minutes
          const healthScore = this.calculateAPIHealthScore(metrics);

          await this.healthMonitor.recordHealth(apiName, healthScore, metrics);

          // Auto-adjust based on health
          if (healthScore < 0.7) {
            console.warn(`API health degraded for ${apiName}: ${healthScore}`);
            await rateLimiter.adjustLimit("decrease", {
              reason: "poor_health",
              healthScore,
            });
          } else if (healthScore > 0.9) {
            await rateLimiter.adjustLimit("increase", {
              reason: "good_health",
              healthScore,
            });
          }
        } catch (error) {
          console.error(`Health monitoring error for ${apiName}:`, error);
        }
      }
    }, 60000); // Every minute
  }

  private startRateLimitAdjustment(): void {
    setInterval(async () => {
      for (const [apiName, rateLimiter] of this.rateLimiters) {
        try {
          const stats = await rateLimiter.getStatistics();

          // Auto-adjust based on token utilization
          if (stats.utilizationRate < 0.5) {
            // Low utilization, can increase
            await rateLimiter.adjustLimit("increase", {
              reason: "low_utilization",
              utilizationRate: stats.utilizationRate,
            });
          } else if (stats.utilizationRate > 0.9) {
            // High utilization, might need to decrease
            const recentErrors = await this.apiMetrics.getErrorRate(
              apiName,
              60000
            );
            if (recentErrors > 0.1) {
              await rateLimiter.adjustLimit("decrease", {
                reason: "high_utilization_with_errors",
                utilizationRate: stats.utilizationRate,
                errorRate: recentErrors,
              });
            }
          }
        } catch (error) {
          console.error(`Rate limit adjustment error for ${apiName}:`, error);
        }
      }
    }, 30000); // Every 30 seconds
  }

  private calculateAPIHealthScore(metrics: APIMetrics): number {
    let score = 1.0;

    // Factor in error rate
    if (metrics.errorRate > 0.1) score *= 0.5; // 10% error rate
    else if (metrics.errorRate > 0.05) score *= 0.7; // 5% error rate
    else if (metrics.errorRate > 0.01) score *= 0.9; // 1% error rate

    // Factor in response time
    if (metrics.avgResponseTime > 10000) score *= 0.3; // 10+ seconds
    else if (metrics.avgResponseTime > 5000) score *= 0.6; // 5+ seconds
    else if (metrics.avgResponseTime > 2000) score *= 0.8; // 2+ seconds

    // Factor in timeout rate
    if (metrics.timeoutRate > 0.05) score *= 0.4; // 5% timeout rate
    else if (metrics.timeoutRate > 0.01) score *= 0.8; // 1% timeout rate

    return Math.max(0, Math.min(1, score));
  }

  // Batch request processing with intelligent concurrency
  async executeBatchRequests<T>(
    apiName: string,
    requests: APIRequestConfig[],
    options: BatchRequestOptions = {}
  ): Promise<BatchExecutionResult<T>> {
    const batchId = this.generateRequestId();
    const concurrency = options.concurrency || 5;
    const failFast = options.failFast || false;

    console.log(
      `Executing batch requests: ${batchId} (${requests.length} requests, concurrency: ${concurrency})`
    );

    const results: APIExecutionResult<T>[] = [];
    const errors: BatchRequestError[] = [];
    const executing: Promise<any>[] = [];

    for (let i = 0; i < requests.length; i++) {
      const request = requests[i];

      const promise = this.executeRequest<T>(apiName, {
        ...request,
        headers: {
          ...request.headers,
          "X-Batch-ID": batchId,
          "X-Batch-Index": i.toString(),
        },
      }).then(
        (result) => {
          results.push(result);
          return result;
        },
        (error) => {
          const batchError: BatchRequestError = {
            index: i,
            request,
            error,
          };
          errors.push(batchError);

          if (failFast) {
            throw error;
          }

          return batchError;
        }
      );

      executing.push(promise);

      // Control concurrency
      if (executing.length >= concurrency) {
        await Promise.race(executing);
        const finishedIndex = executing.findIndex((p) => p === promise);
        if (finishedIndex !== -1) {
          executing.splice(finishedIndex, 1);
        }
      }
    }

    // Wait for all remaining requests
    if (failFast) {
      await Promise.all(executing);
    } else {
      await Promise.allSettled(executing);
    }

    return {
      batchId,
      totalRequests: requests.length,
      successfulRequests: results.length,
      failedRequests: errors.length,
      results,
      errors,
      duration: Date.now() - parseInt(batchId.split("_")[1]),
    };
  }

  // Get API statistics and health
  async getAPIStatistics(
    apiName: string,
    timeRange?: TimeRange
  ): Promise<APIStatistics> {
    const rateLimiter = this.rateLimiters.get(apiName);
    const circuitBreaker = this.circuitBreakers.get(apiName);

    if (!rateLimiter || !circuitBreaker) {
      throw new Error(`API configuration not found: ${apiName}`);
    }

    const metrics = await this.apiMetrics.getMetrics(apiName, timeRange);
    const rateLimitStats = await rateLimiter.getStatistics();
    const circuitBreakerState = circuitBreaker.getState();
    const healthScore = this.calculateAPIHealthScore(metrics);

    return {
      apiName,
      healthScore,
      metrics,
      rateLimiting: rateLimitStats,
      circuitBreaker: circuitBreakerState,
      timeRange: timeRange || {
        start: new Date(Date.now() - 3600000), // Last hour
        end: new Date(),
      },
    };
  }

  // Utility methods
  private shouldRetry(
    strategy: RetryStrategy,
    error: APIError,
    attemptNumber: number
  ): boolean {
    if (attemptNumber >= strategy.maxAttempts) {
      return false;
    }

    // Check non-retryable status codes
    if (
      error.status &&
      strategy.nonRetryableStatusCodes?.includes(error.status)
    ) {
      return false;
    }

    // Check retryable status codes
    if (error.status && strategy.retryableStatusCodes?.includes(error.status)) {
      return true;
    }

    // Check retryable error codes
    if (strategy.retryableErrors?.includes(error.code)) {
      return true;
    }

    // Default retryable conditions
    return error.status
      ? error.status >= 500
      : ["TIMEOUT", "CONNECTION_ERROR"].includes(error.code);
  }

  private validateAPIResponse(response: RawAPIResponse<any>): void {
    // Basic response validation
    if (!response.status || response.status < 200 || response.status >= 400) {
      throw new APIError(
        `HTTP error: ${response.status}`,
        "HTTP_ERROR",
        response.status
      );
    }
  }

  private transformError(
    error: any,
    apiName: string,
    duration: number
  ): APIError {
    if (error instanceof APIError) {
      return error;
    }

    // Transform common error types
    if (error.code === "ENOTFOUND" || error.code === "ECONNREFUSED") {
      return new APIError("Connection error", "CONNECTION_ERROR", 0, {
        originalError: error,
        apiName,
        duration,
      });
    }

    if (error.code === "ETIMEDOUT") {
      return new APIError("Request timeout", "TIMEOUT", 408, {
        originalError: error,
        apiName,
        duration,
      });
    }

    // Handle HTTP errors
    if (error.response) {
      const status = error.response.status || 500;
      const retryAfter = this.parseRetryAfterHeader(error.response.headers);

      return new APIError(
        error.response.statusText || error.message,
        status === 429 ? "RATE_LIMITED" : "HTTP_ERROR",
        status,
        {
          originalError: error,
          apiName,
          duration,
          retryAfter,
          responseData: error.response.data,
        }
      );
    }

    return new APIError(
      error.message || "Unknown API error",
      "UNKNOWN_ERROR",
      500,
      { originalError: error, apiName, duration }
    );
  }

  private parseRetryAfterHeader(headers: Record<string, any>): number | null {
    const retryAfter = headers["retry-after"] || headers["Retry-After"];
    if (!retryAfter) return null;

    const parsed = parseInt(retryAfter, 10);
    return isNaN(parsed) ? null : parsed;
  }

  private async makeHTTPRequest<T>(
    config: APIRequestConfig
  ): Promise<RawAPIResponse<T>> {
    // This would use your HTTP client (axios, fetch, etc.)
    // Placeholder implementation
    throw new Error("HTTP request implementation needed");
  }

  private async recordSuccessMetrics(
    apiName: string,
    requestId: string,
    startTime: number,
    attempts: number
  ): Promise<void> {
    await this.apiMetrics.recordRequest(apiName, requestId, {
      status: "success",
      duration: Date.now() - startTime,
      attempts,
    });
  }

  private async recordErrorMetrics(
    apiName: string,
    requestId: string,
    startTime: number,
    attempts: number,
    error: APIError
  ): Promise<void> {
    await this.apiMetrics.recordRequest(apiName, requestId, {
      status: "error",
      duration: Date.now() - startTime,
      attempts,
      error: error.code,
      httpStatus: error.status,
    });
  }

  private generateRequestId(): string {
    return `req_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
  }
}

// Supporting classes for rate limiting and retry logic
class AdaptiveRateLimiter {
  private tokens: number;
  private lastRefillTime: number;
  private currentLimit: number;
  private statistics: RateLimitStatistics;

  constructor(private config: RateLimiterConfig) {
    this.tokens = config.initialLimit;
    this.currentLimit = config.initialLimit;
    this.lastRefillTime = Date.now();
    this.statistics = {
      tokensConsumed: 0,
      tokensRefilled: 0,
      waitTime: 0,
      adjustments: 0,
      utilizationRate: 0,
    };
  }

  async acquireToken(): Promise<void> {
    this.refillTokens();

    if (this.tokens <= 0) {
      throw new APIError("No tokens available", "RATE_LIMITED", 429);
    }

    this.tokens--;
    this.statistics.tokensConsumed++;
  }

  async getWaitTime(): Promise<number> {
    this.refillTokens();

    if (this.tokens > 0) {
      return 0;
    }

    // Calculate time until next token is available
    const timeSinceRefill = Date.now() - this.lastRefillTime;
    const timeUntilRefill =
      this.config.windowMs - (timeSinceRefill % this.config.windowMs);

    return timeUntilRefill;
  }

  async adjustLimit(
    direction: "increase" | "decrease",
    context: RateLimitAdjustmentContext
  ): Promise<void> {
    const factor = this.config.adaptationFactor;
    let adjustment: number;

    if (direction === "increase") {
      adjustment = Math.ceil(this.currentLimit * factor);
      this.currentLimit = Math.min(
        this.config.maxLimit,
        this.currentLimit + adjustment
      );
    } else {
      adjustment = Math.ceil(this.currentLimit * factor);
      this.currentLimit = Math.max(
        this.config.minLimit,
        this.currentLimit - adjustment
      );
    }

    console.log(
      `Rate limit adjusted for ${this.config.name}: ${this.currentLimit} (${direction} by ${adjustment}, reason: ${context.reason})`
    );

    this.statistics.adjustments++;
  }

  private refillTokens(): void {
    const now = Date.now();
    const timePassed = now - this.lastRefillTime;

    if (timePassed >= this.config.windowMs) {
      const periods = Math.floor(timePassed / this.config.windowMs);
      const tokensToAdd = periods * this.currentLimit;

      this.tokens = Math.min(this.currentLimit, this.tokens + tokensToAdd);
      this.lastRefillTime = now;
      this.statistics.tokensRefilled += tokensToAdd;
    }

    // Update utilization rate
    this.statistics.utilizationRate =
      (this.currentLimit - this.tokens) / this.currentLimit;
  }

  async getStatistics(): Promise<RateLimitStatistics> {
    return { ...this.statistics };
  }
}

class RetryStrategy {
  constructor(public config: RetryStrategyConfig) {}

  get maxAttempts(): number {
    return this.config.maxAttempts;
  }
  get baseDelayMs(): number {
    return this.config.baseDelayMs;
  }
  get maxDelayMs(): number {
    return this.config.maxDelayMs;
  }
  get backoffType(): string {
    return this.config.backoffType;
  }
  get jitterFactor(): number {
    return this.config.jitterFactor;
  }
  get retryableStatusCodes(): number[] | undefined {
    return this.config.retryableStatusCodes;
  }
  get nonRetryableStatusCodes(): number[] | undefined {
    return this.config.nonRetryableStatusCodes;
  }
  get retryableErrors(): string[] | undefined {
    return this.config.retryableErrors;
  }
}

class CircuitBreaker {
  private failures = 0;
  private successes = 0;
  private lastFailureTime = 0;
  private state: "CLOSED" | "OPEN" | "HALF_OPEN" = "CLOSED";
  private halfOpenCalls = 0;

  constructor(private config: CircuitBreakerConfig) {}

  isOpen(): boolean {
    if (this.state === "OPEN") {
      if (Date.now() - this.lastFailureTime > this.config.recoveryTimeoutMs) {
        this.state = "HALF_OPEN";
        this.halfOpenCalls = 0;
        return false;
      }
      return true;
    }

    if (this.state === "HALF_OPEN") {
      return this.halfOpenCalls >= this.config.halfOpenMaxCalls;
    }

    return false;
  }

  recordSuccess(): void {
    this.successes++;

    if (this.state === "HALF_OPEN") {
      this.halfOpenCalls++;
      if (this.halfOpenCalls >= this.config.halfOpenMaxCalls) {
        this.state = "CLOSED";
        this.failures = 0;
      }
    } else if (this.state === "CLOSED") {
      // Reset failure count on success
      this.failures = 0;
    }
  }

  recordFailure(): void {
    this.failures++;
    this.lastFailureTime = Date.now();

    if (this.state === "HALF_OPEN") {
      this.state = "OPEN";
    } else if (this.shouldTrip()) {
      this.state = "OPEN";
    }
  }

  private shouldTrip(): boolean {
    const totalCalls = this.failures + this.successes;
    if (totalCalls === 0) return false;

    const failureRate = this.failures / totalCalls;
    return failureRate >= this.config.failureThreshold;
  }

  getState(): CircuitBreakerState {
    return {
      state: this.state,
      failures: this.failures,
      successes: this.successes,
      failureRate:
        this.failures + this.successes === 0
          ? 0
          : this.failures / (this.failures + this.successes),
      lastFailureTime: this.lastFailureTime,
    };
  }
}

class BackoffCalculator {
  calculateDelay(
    backoffType: string,
    baseDelayMs: number,
    attemptNumber: number,
    maxDelayMs: number
  ): number {
    let delay: number;

    switch (backoffType) {
      case "linear":
        delay = baseDelayMs * attemptNumber;
        break;

      case "exponential":
        delay = baseDelayMs * Math.pow(2, attemptNumber - 1);
        break;

      case "polynomial":
        delay = baseDelayMs * Math.pow(attemptNumber, 2);
        break;

      case "fibonacci":
        delay = baseDelayMs * this.fibonacci(attemptNumber);
        break;

      default:
        delay = baseDelayMs;
    }

    return Math.min(delay, maxDelayMs);
  }

  private fibonacci(n: number): number {
    if (n <= 1) return 1;
    let a = 1,
      b = 1;
    for (let i = 2; i < n; i++) {
      [a, b] = [b, a + b];
    }
    return b;
  }
}

// Error class for API operations
class APIError extends Error {
  constructor(
    message: string,
    public code: string,
    public status?: number,
    public metadata?: any
  ) {
    super(message);
    this.name = "APIError";
  }

  get retryAfter(): number | null {
    return this.metadata?.retryAfter || null;
  }
}

// Supporting interfaces and types
interface APIManagerConfig {
  apis: APIConfig[];
}

interface APIConfig {
  name: string;
  baseUrl: string;
  rateLimit: {
    initialLimit: number;
    windowMs: number;
    maxLimit?: number;
    minLimit?: number;
    adaptationFactor?: number;
  };
  retry: {
    maxAttempts: number;
    baseDelayMs: number;
    maxDelayMs: number;
    backoffType: string;
    jitterFactor?: number;
    retryableStatusCodes?: number[];
    nonRetryableStatusCodes?: number[];
    retryableErrors?: string[];
  };
  circuitBreaker: {
    failureThreshold: number;
    recoveryTimeoutMs: number;
    halfOpenMaxCalls?: number;
    monitoringWindowMs?: number;
  };
}

interface RateLimiterConfig {
  name: string;
  initialLimit: number;
  windowMs: number;
  maxLimit: number;
  minLimit: number;
  adaptationFactor: number;
}

interface RetryStrategyConfig {
  name: string;
  maxAttempts: number;
  baseDelayMs: number;
  maxDelayMs: number;
  backoffType: string;
  jitterFactor: number;
  retryableStatusCodes?: number[];
  nonRetryableStatusCodes?: number[];
  retryableErrors?: string[];
}

interface CircuitBreakerConfig {
  name: string;
  failureThreshold: number;
  recoveryTimeoutMs: number;
  halfOpenMaxCalls: number;
  monitoringWindowMs: number;
}

interface APIRequestConfig {
  method: string;
  url: string;
  headers?: Record<string, string>;
  data?: any;
  params?: Record<string, any>;
  timeoutMs?: number;
}

interface APIExecutionResult<T> {
  requestId: string;
  data: T;
  status: number;
  headers: Record<string, any>;
  duration: number;
  attempts: number;
  apiName: string;
}

interface RawAPIResponse<T> {
  data: T;
  status: number;
  headers: Record<string, any>;
  duration?: number;
}

interface BatchRequestOptions {
  concurrency?: number;
  failFast?: boolean;
}

interface BatchExecutionResult<T> {
  batchId: string;
  totalRequests: number;
  successfulRequests: number;
  failedRequests: number;
  results: APIExecutionResult<T>[];
  errors: BatchRequestError[];
  duration: number;
}

interface BatchRequestError {
  index: number;
  request: APIRequestConfig;
  error: APIError;
}

interface RateLimitStatistics {
  tokensConsumed: number;
  tokensRefilled: number;
  waitTime: number;
  adjustments: number;
  utilizationRate: number;
}

interface RateLimitAdjustmentContext {
  reason: string;
  severity?: "low" | "medium" | "high";
  healthScore?: number;
  utilizationRate?: number;
  errorRate?: number;
  responseTime?: number;
  retryAfter?: number;
  status?: number;
  currentUsage?: number;
}

interface CircuitBreakerState {
  state: "CLOSED" | "OPEN" | "HALF_OPEN";
  failures: number;
  successes: number;
  failureRate: number;
  lastFailureTime: number;
}

interface APIMetrics {
  errorRate: number;
  avgResponseTime: number;
  timeoutRate: number;
  totalRequests: number;
  successfulRequests: number;
  failedRequests: number;
}

interface APIStatistics {
  apiName: string;
  healthScore: number;
  metrics: APIMetrics;
  rateLimiting: RateLimitStatistics;
  circuitBreaker: CircuitBreakerState;
  timeRange: TimeRange;
}

// Placeholder classes that would need full implementation
class APIMetricsCollector {
  async recordRequest(
    apiName: string,
    requestId: string,
    data: any
  ): Promise<void> {}
  async getRecentMetrics(
    apiName: string,
    timeWindowMs: number
  ): Promise<APIMetrics> {
    return {} as APIMetrics;
  }
  async getErrorRate(apiName: string, timeWindowMs: number): Promise<number> {
    return 0;
  }
  async getMetrics(
    apiName: string,
    timeRange?: TimeRange
  ): Promise<APIMetrics> {
    return {} as APIMetrics;
  }
}

class APIHealthMonitor {
  async recordHealth(
    apiName: string,
    healthScore: number,
    metrics: APIMetrics
  ): Promise<void> {}
}