export class QvacScheduler {
  constructor({ concurrency = 1 } = {}) {
    this.concurrency = Math.max(1, concurrency);
    this.running = 0;
    this.queue = [];
    this.completed = 0; this.failed = 0; this.totalDurationMs = 0; this.byLane = {};
  }

  run(task, { lane = 'background', signal } = {}) {
    return new Promise((resolve, reject) => {
      this.queue.push({ task, lane, signal, resolve, reject, enqueuedAt: Date.now() });
      this.queue.sort((a, b) => this.priority(b.lane) - this.priority(a.lane) || a.enqueuedAt - b.enqueuedAt);
      this.pump();
    });
  }

  priority(lane) { return { voice: 3, 'computer-use': 2, background: 1, maintenance: 0 }[lane] ?? 0; }

  pump() {
    while (this.running < this.concurrency && this.queue.length) {
      const job = this.queue.shift();
      if (job.signal?.aborted) { job.reject(new Error('QVAC job cancelled before start')); continue; }
      this.running += 1; const started = Date.now();
      Promise.resolve().then(() => job.task(job.signal)).then((value) => { this.completed += 1; job.resolve(value); }, (error) => { this.failed += 1; job.reject(error); }).finally(() => {
        this.totalDurationMs += Date.now() - started; this.byLane[job.lane] = (this.byLane[job.lane] || 0) + 1;
        this.running -= 1;
        this.pump();
      });
    }
  }

  cancelQueued(predicate = () => true) {
    const kept = [];
    for (const job of this.queue) {
      if (predicate(job)) job.reject(new Error('QVAC job cancelled'));
      else kept.push(job);
    }
    this.queue = kept;
  }

  status() { return { running: this.running, queued: this.queue.map((j) => j.lane) }; }
  metrics() { return { completed: this.completed, failed: this.failed, total_duration_ms: this.totalDurationMs, by_lane: { ...this.byLane } }; }
}