Customer.io SDK Patterns

---
name: customerio-sdk-patterns
description: |
  Apply production-ready Customer.io SDK patterns.
  Use when implementing best practices, refactoring integrations,
  or optimizing Customer.io usage in your application.
  Trigger with phrases like "customer.io best practices", "customer.io patterns",
  "production customer.io", "customer.io architecture".
allowed-tools: Read, Write, Edit, Bash(npm:*), Bash(pip:*), Grep
version: 1.0.0
license: MIT
author: Jeremy Longshore <jeremy@intentsolutions.io>
---

# Customer.io SDK Patterns

## Overview
Production-ready patterns for Customer.io SDK usage including error handling, batching, and type safety.

## Prerequisites
- Customer.io SDK installed
- TypeScript project (recommended)
- Understanding of async/await patterns

## Instructions

### Pattern 1: Type-Safe Client
```typescript
// types/customerio.ts
export interface UserAttributes {
  email: string;
  first_name?: string;
  last_name?: string;
  created_at?: number;
  plan?: 'free' | 'pro' | 'enterprise';
  [key: string]: string | number | boolean | undefined;
}

export interface EventData {
  [key: string]: string | number | boolean | object;
}

export type EventName =
  | 'signed_up'
  | 'subscription_started'
  | 'subscription_cancelled'
  | 'feature_used'
  | 'email_verified';

// lib/customerio-client.ts
import { TrackClient, RegionUS } from '@customerio/track';
import type { UserAttributes, EventData, EventName } from '../types/customerio';

export class TypedCustomerIO {
  private client: TrackClient;

  constructor() {
    this.client = new TrackClient(
      process.env.CUSTOMERIO_SITE_ID!,
      process.env.CUSTOMERIO_API_KEY!,
      { region: RegionUS }
    );
  }

  async identify(userId: string, attributes: UserAttributes): Promise<void> {
    await this.client.identify(userId, {
      ...attributes,
      _updated_at: Math.floor(Date.now() / 1000)
    });
  }

  async track(userId: string, event: EventName, data?: EventData): Promise<void> {
    await this.client.track(userId, { name: event, data });
  }
}
```

### Pattern 2: Retry with Exponential Backoff
```typescript
// lib/customerio-resilient.ts
import { TrackClient } from '@customerio/track';

interface RetryConfig {
  maxRetries: number;
  baseDelay: number;
  maxDelay: number;
}

const defaultRetryConfig: RetryConfig = {
  maxRetries: 3,
  baseDelay: 1000,
  maxDelay: 10000
};

async function withRetry<T>(
  operation: () => Promise<T>,
  config: RetryConfig = defaultRetryConfig
): Promise<T> {
  let lastError: Error | undefined;

  for (let attempt = 0; attempt <= config.maxRetries; attempt++) {
    try {
      return await operation();
    } catch (error) {
      lastError = error as Error;

      if (attempt === config.maxRetries) break;

      // Don't retry on 4xx errors (client errors)
      if (error instanceof Error && error.message.includes('4')) {
        throw error;
      }

      const delay = Math.min(
        config.baseDelay * Math.pow(2, attempt),
        config.maxDelay
      );
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  }

  throw lastError;
}

export class ResilientCustomerIO {
  private client: TrackClient;

  constructor(siteId: string, apiKey: string) {
    this.client = new TrackClient(siteId, apiKey, { region: RegionUS });
  }

  async identify(userId: string, attributes: Record<string, any>) {
    return withRetry(() => this.client.identify(userId, attributes));
  }

  async track(userId: string, event: string, data?: Record<string, any>) {
    return withRetry(() => this.client.track(userId, { name: event, data }));
  }
}
```

### Pattern 3: Event Queue with Batching
```typescript
// lib/customerio-queue.ts
interface QueuedEvent {
  userId: string;
  event: string;
  data?: Record<string, any>;
  timestamp: number;
}

export class CustomerIOQueue {
  private queue: QueuedEvent[] = [];
  private flushInterval: NodeJS.Timer | null = null;
  private maxBatchSize = 100;
  private flushIntervalMs = 5000;

  constructor(private client: TrackClient) {
    this.startAutoFlush();
  }

  enqueue(userId: string, event: string, data?: Record<string, any>) {
    this.queue.push({
      userId,
      event,
      data,
      timestamp: Date.now()
    });

    if (this.queue.length >= this.maxBatchSize) {
      this.flush();
    }
  }

  async flush(): Promise<void> {
    if (this.queue.length === 0) return;

    const batch = this.queue.splice(0, this.maxBatchSize);

    await Promise.allSettled(
      batch.map(item =>
        this.client.track(item.userId, {
          name: item.event,
          data: { ...item.data, _queued_at: item.timestamp }
        })
      )
    );
  }

  private startAutoFlush() {
    this.flushInterval = setInterval(() => this.flush(), this.flushIntervalMs);
  }

  async shutdown(): Promise<void> {
    if (this.flushInterval) {
      clearInterval(this.flushInterval);
    }
    await this.flush();
  }
}
```

### Pattern 4: Singleton with Lazy Initialization
```typescript
// lib/customerio-singleton.ts
import { TrackClient, RegionUS } from '@customerio/track';

let instance: TrackClient | null = null;

export function getCustomerIO(): TrackClient {
  if (!instance) {
    if (!process.env.CUSTOMERIO_SITE_ID || !process.env.CUSTOMERIO_API_KEY) {
      throw new Error('Customer.io credentials not configured');
    }
    instance = new TrackClient(
      process.env.CUSTOMERIO_SITE_ID,
      process.env.CUSTOMERIO_API_KEY,
      { region: RegionUS }
    );
  }
  return instance;
}

// Usage
import { getCustomerIO } from './lib/customerio-singleton';
await getCustomerIO().identify('user-123', { email: 'user@example.com' });
```

## Output
- Type-safe Customer.io client
- Resilient error handling with retries
- Event batching for high-volume scenarios
- Singleton pattern for resource efficiency

## Error Handling
| Error | Cause | Solution |
|-------|-------|----------|
| Type mismatch | Invalid attribute type | Use TypeScript interfaces |
| Queue overflow | Too many events | Increase flush frequency or batch size |
| Retry exhausted | Persistent failure | Check network and credentials |

## Resources
- [Customer.io SDK GitHub](https://github.com/customerio/customerio-node)
- [API Rate Limits](https://customer.io/docs/api/track/#section/Limits)

## Next Steps
After implementing patterns, proceed to `customerio-primary-workflow` to implement messaging workflows.