peepee/modules/events/EventCorrelator.js

Visual Programming Language Where You Connect Ports Of One EventEmitter to Ports Of Another EventEmitter

Certainly! Below is the updated implementation of the `Correlator` class that extends the `EventEmitter` class. This allows the `Correlator` to directly emit events and manage its own subscriptions while still providing the correlation functionality.

```javascript
const EventEmitter = require('events');

class Correlator extends EventEmitter {
  constructor() {
    super();
    this.correlationData = {};
    this.sep = ':'; // Separator for event name and correlation ID
  }

  // Start correlating events
  correlate(correlationEventName, ...eventNames) {
    eventNames.forEach(eventName => {
      const [event, correlationField] = eventName.split(this.sep);
      this.on(event, (data) => {
        this.correlationData[correlationField] = data[correlationField];
        this.checkCorrelation(correlationEventName);
      });
    });
  }

  // Check if all required events have been received
  checkCorrelation(correlationEventName) {
    const packet = {};
    let allReceived = true;

    for (const key in this.correlationData) {
      if (this.correlationData[key] === undefined) {
        allReceived = false;
        break;
      }
      packet[key] = this.correlationData[key];
    }

    if (allReceived) {
      this.emit(correlationEventName, packet);
      // Reset correlation data after processing
      this.correlationData = {};
    }
  }
}

// Example usage:
const correlator = new Correlator();

// Correlate events
correlator.correlate('checkout:completed', 'checkout:transactionId', 'paid:transactionId');

// Subscribe to the correlation event
correlator.on('checkout:completed', (data) => {
  console.log('Correlation event emitted:', data);
});

// Publish events
correlator.emit('checkout', { transactionId: '12345' });
correlator.emit('paid', { transactionId: '12345' });

// Output: Correlation event emitted: { transactionId: '12345' }
```

### Explanation:
- **Correlator Class**: The `Correlator` class now extends `EventEmitter`, allowing it to directly use the `on` and `emit` methods for event handling.
- **correlate Method**: This method subscribes to the specified events and stores the relevant data in `correlationData`.
- **checkCorrelation Method**: This method checks if all required correlation fields have been received and emits the correlation event with the collected data if they have.

### Example Usage:
- The example demonstrates how to correlate a `checkout:completed` event with `checkout:transactionId` and `paid:transactionId`. When both events are emitted, the correlator emits the correlation event with the relevant data.

This implementation is clean and leverages the capabilities of `EventEmitter` while providing the correlation functionality in a straightforward manner.