import { Logger } from '../../utils/logger';
import { CommunicationCoordinator } from '../../integrations/gcp/communication-coordinator';

/**
 * @interface EventBusConfig
 * @description Configuration for the Event Bus System.
 */
export interface EventBusConfig {
  projectID: string;
  defaultTopic: string; // Default Pub/Sub topic for the event bus
  // Add configuration for dead letter queues, event replay, etc.
}

/**
 * @interface EventBusOperations
 * @description Defines operations for the Event Bus System.
 */
export interface EventBusOperations {
  publish(eventType: string, payload: any, topic?: string): Promise<void>;
  subscribe(eventType: string, handler: (payload: any) => void, topic?: string): Promise<void>;
  // Add methods for event filtering, transformation, replay, etc.
}

/**
 * @class EventBus
 * @description Implements a high-performance event routing system with Google Cloud Pub/Sub integration.
 */
export class EventBus implements EventBusOperations {
  private config: EventBusConfig;
  private logger: Logger;
  private communicationCoordinator: CommunicationCoordinator;
  private subscriptions: Map<string, ((payload: any) => void)[]> = new Map(); // eventType -> handlers

  constructor(config: EventBusConfig, communicationCoordinator: CommunicationCoordinator) {
    this.config = config;
    this.logger = new Logger('EventBus');
    this.communicationCoordinator = communicationCoordinator;
    this.logger.info('Event Bus System initialized.');

    // Initialize Pub/Sub subscription for the default topic
    this.communicationCoordinator.subscribeToTopic(this.config.defaultTopic, (message: any) => {
      try {
        const event = JSON.parse(message.data.toString());
        this.logger.debug(`Received event from Pub/Sub: ${event.type}`);
        this.distributeLocally(event.type, event.payload);
      } catch (error: any) {
        this.logger.error(`Failed to parse Pub/Sub message or distribute event: ${error.message}`);
      }
    });
  }

  /**
   * Publishes an event to the Event Bus, which then routes it to Pub/Sub.
   * @param {string} eventType The type of event to publish.
   * @param {any} payload The payload associated with the event.
   * @param {string} [topic] Optional Pub/Sub topic to publish to. Defaults to defaultTopic.
   * @returns {Promise<void>}
   */
  public async publish(eventType: string, payload: any, topic?: string): Promise<void> {
    const targetTopic = topic || this.config.defaultTopic;
    const event = { type: eventType, payload: payload, timestamp: Date.now() };
    this.logger.info(`Publishing event '${eventType}' to topic '${targetTopic}'.`);
    await this.communicationCoordinator.publishMessage(targetTopic, JSON.stringify(event));
    // Also distribute locally for immediate processing
    this.distributeLocally(eventType, payload);
  }

  /**
   * Subscribes a handler function to a specific event type.
   * @param {string} eventType The type of event to subscribe to.
   * @param {(payload: any) => void} handler The function to call when the event occurs.
   * @param {string} [topic] Optional Pub/Sub topic to subscribe to. Defaults to defaultTopic.
   * @returns {Promise<void>}
   */
  public async subscribe(eventType: string, handler: (payload: any) => void, topic?: string): Promise<void> {
    this.logger.info(`Subscribing to event type '${eventType}'.`);
    if (!this.subscriptions.has(eventType)) {
      this.subscriptions.set(eventType, []);
    }
    this.subscriptions.get(eventType)?.push(handler);

    // If a specific topic is provided, also subscribe to it via Pub/Sub (conceptual, as Pub/Sub subscriptions are usually per-service)
    if (topic && topic !== this.config.defaultTopic) {
      this.logger.warn(`Specific topic subscriptions via Pub/Sub are conceptual for this layer: ${topic}`);
      // await this.communicationCoordinator.subscribeToTopic(topic, (message: any) => { /* ... */ });
    }
  }

  /**
   * Distributes an event to locally subscribed handlers.
   * @param {string} eventType The type of event.
   * @param {any} payload The event payload.
   * @private
   */
  private distributeLocally(eventType: string, payload: any): void {
    const handlers = this.subscriptions.get(eventType);
    if (handlers) {
      this.logger.debug(`Distributing event '${eventType}' to ${handlers.length} local handlers.`);
      handlers.forEach(handler => {
        try {
          handler(payload);
        } catch (error: any) {
          this.logger.error(`Error executing local event handler for '${eventType}': ${error.message}`);
        }
      });
    }
  }

  // Conceptual methods for event filtering, transformation, replay, etc.
  public async filterEvents(eventType: string, criteria: any): Promise<any[]> {
    this.logger.info(`Filtering events for ${eventType} with criteria (conceptual)...
`);
    return [];
  }

  public async transformEvent(eventType: string, payload: any, transformationRules: any): Promise<any> {
    this.logger.info(`Transforming event for ${eventType} (conceptual)...
`);
    return payload;
  }

  public async replayEvents(eventType: string, startTime: number, endTime: number): Promise<void> {
    this.logger.info(`Replaying events for ${eventType} from ${startTime} to ${endTime} (conceptual)...
`);
  }
}