import { randomUUID } from 'node:crypto';
import type { QueueWorkerOptions, WorkerContext } from './types.js';

export class QueueWorker<TPayload = unknown, TResult = unknown> {
  private readonly queueName: string;
  private readonly store: QueueWorkerOptions<TPayload, TResult>['store'];
  private readonly handler: QueueWorkerOptions<TPayload, TResult>['handler'];
  private readonly workerId: string;
  private readonly pollIntervalMs: number;
  private readonly leaseMs: number;
  private readonly backoffMs: number;
  private timer?: ReturnType<typeof setTimeout>;
  private running = false;
  private inflight?: Promise<void>;

  constructor(options: QueueWorkerOptions<TPayload, TResult>) {
    this.queueName = options.queueName;
    this.store = options.store;
    this.handler = options.handler;
    this.workerId = options.workerId || `worker_${randomUUID()}`;
    this.pollIntervalMs = options.pollIntervalMs ?? 200;
    this.leaseMs = options.leaseMs ?? 30_000;
    this.backoffMs = options.backoffMs ?? 1_000;
  }

  start(): void {
    if (this.running) return;
    this.running = true;
    this.schedule(0);
  }

  async stop(): Promise<void> {
    this.running = false;
    if (this.timer) {
      clearTimeout(this.timer);
      this.timer = undefined;
    }
    await this.inflight;
  }

  private schedule(delayMs: number): void {
    if (!this.running) return;
    this.timer = globalThis.setTimeout(() => {
      this.inflight = this.tick().finally(() => {
        this.inflight = undefined;
      });
    }, delayMs);
  }

  private async tick(): Promise<void> {
    const job = await this.store.claimNext<TPayload, TResult>(
      this.queueName,
      this.workerId,
      this.leaseMs
    );
    if (!job) {
      this.schedule(this.pollIntervalMs);
      return;
    }

    const context: WorkerContext<TPayload, TResult> = {
      patch: async patch => {
        await this.store.patch<TPayload, TResult>(this.queueName, job.id, patch);
      },
      heartbeat: async () => {
        await this.store.patch<TPayload, TResult>(this.queueName, job.id, {
          leaseOwner: this.workerId,
          leaseExpiresAt: new Date(Date.now() + this.leaseMs).toISOString(),
        });
      },
    };

    try {
      const result = await this.handler(job, context);
      await this.store.patch<TPayload, TResult>(this.queueName, job.id, {
        status: 'succeeded',
        result,
        completedAt: new Date().toISOString(),
        leaseOwner: undefined,
        leaseExpiresAt: undefined,
      });
    } catch (err: unknown) {
      const lastError = err instanceof Error ? err.message : String(err);
      const finalStatus = job.attempts >= job.maxAttempts ? 'dead_letter' : 'queued';
      await this.store.patch<TPayload, TResult>(this.queueName, job.id, {
        status: finalStatus,
        lastError,
        scheduledAt:
          finalStatus === 'queued'
            ? new Date(Date.now() + this.backoffMs * job.attempts).toISOString()
            : job.scheduledAt,
        completedAt: finalStatus === 'dead_letter' ? new Date().toISOString() : undefined,
        leaseOwner: undefined,
        leaseExpiresAt: undefined,
      });
    }

    this.schedule(0);
  }
}