import { QueueWorker, type QueueJob, type QueueStore } from '@bytelyst/queue';
import type { EmitResult } from './memory.js';
import type {
  EventHandler,
  EventSubscription,
  PlatformEvent,
  PlatformEventName,
  PlatformEventPayload,
} from './types.js';

interface EventEnvelope<T extends PlatformEventName = PlatformEventName> {
  event: PlatformEvent<T>;
}

export interface DurableEventBusOptions {
  store: QueueStore;
  queueName?: string;
  workerId?: string;
  pollIntervalMs?: number;
  leaseMs?: number;
  backoffMs?: number;
  autoStart?: boolean;
}

export class DurableEventBus {
  private readonly handlers = new Map<
    string,
    Set<{ id: string; fn: EventHandler<PlatformEventName> }>
  >();
  private subscriptionCounter = 0;
  private readonly queueName: string;
  private readonly store: QueueStore;
  private readonly worker: QueueWorker<EventEnvelope, void>;
  private running = false;

  constructor(options: DurableEventBusOptions) {
    this.queueName = options.queueName ?? 'platform-events';
    this.store = options.store;
    this.worker = new QueueWorker<EventEnvelope, void>({
      queueName: this.queueName,
      store: this.store,
      workerId: options.workerId,
      pollIntervalMs: options.pollIntervalMs,
      leaseMs: options.leaseMs,
      backoffMs: options.backoffMs,
      handler: async job => {
        await this.dispatch(job);
      },
    });

    if (options.autoStart !== false) {
      this.start();
    }
  }

  on<T extends PlatformEventName>(eventType: T, handler: EventHandler<T>): EventSubscription {
    const id = `sub_${++this.subscriptionCounter}`;

    if (!this.handlers.has(eventType)) {
      this.handlers.set(eventType, new Set());
    }

    const entry = { id, fn: handler as EventHandler<PlatformEventName> };
    this.handlers.get(eventType)!.add(entry);

    return {
      id,
      eventType,
      unsubscribe: () => {
        this.handlers.get(eventType)?.delete(entry);
      },
    };
  }

  async emit<T extends PlatformEventName>(
    eventType: T,
    payload: PlatformEventPayload<T>,
    options?: { source?: string }
  ): Promise<EmitResult> {
    const event: PlatformEvent<T> = {
      id: crypto.randomUUID(),
      type: eventType,
      payload,
      timestamp: new Date().toISOString(),
      source: options?.source,
    };

    await this.store.enqueue<EventEnvelope>(this.queueName, {
      idempotencyKey: event.id,
      type: eventType,
      payload: { event },
      productId: extractProductId(payload),
      metadata: {
        source: options?.source,
      },
    });

    return {
      eventId: event.id,
      handlerCount: this.listenerCount(eventType),
      errors: [],
    };
  }

  start(): void {
    if (this.running) return;
    this.running = true;
    this.worker.start();
  }

  async stop(): Promise<void> {
    if (!this.running) return;
    this.running = false;
    await this.worker.stop();
  }

  clear(eventType?: PlatformEventName): void {
    if (eventType) {
      this.handlers.delete(eventType);
    } else {
      this.handlers.clear();
    }
  }

  listenerCount(eventType: PlatformEventName): number {
    return this.handlers.get(eventType)?.size ?? 0;
  }

  eventTypes(): PlatformEventName[] {
    return Array.from(this.handlers.entries())
      .filter(([, set]) => set.size > 0)
      .map(([type]) => type as PlatformEventName);
  }

  private async dispatch(job: QueueJob<EventEnvelope, void>): Promise<void> {
    const event = job.payload.event;
    const handlers = this.handlers.get(event.type);
    if (!handlers || handlers.size === 0) {
      return;
    }

    await Promise.allSettled(
      Array.from(handlers).map(async ({ fn }) => fn(event as PlatformEvent<PlatformEventName>))
    );
  }
}

function extractProductId(payload: unknown): string | undefined {
  if (!payload || typeof payload !== 'object') return undefined;
  const productId = (payload as { productId?: unknown }).productId;
  return typeof productId === 'string' ? productId : undefined;
}