Queue System with Priority

class PriorityQueue {
  constructor(maxConcurrent = 3) {
    this.queue = [];
    this.running = 0;
    this.maxConcurrent = maxConcurrent;
    this.nextId = 1;
  }
  
  add(task, priority = 0) {
    const taskId = this.nextId++;
    const queueItem = {
      id: taskId,
      task,
      priority,
      addedAt: Date.now(),
      status: 'pending'
    };
    
    this.queue.push(queueItem);
    this.queue.sort((a, b) => {
      if (a.priority !== b.priority) {
        return b.priority - a.priority; // Higher priority first
      }
      return a.addedAt - b.addedAt; // Older first if same priority
    });
    
    this.process();
    return taskId;
  }
  
  async process() {
    if (this.running >= this.maxConcurrent || this.queue.length === 0) {
      return;
    }
    
    const nextItem = this.queue.shift();
    this.running++;
    nextItem.status = 'running';
    
    try {
      const result = await nextItem.task();
      nextItem.status = 'completed';
      nextItem.result = result;
      nextItem.completedAt = Date.now();
    } catch (error) {
      nextItem.status = 'failed';
      nextItem.error = error;
      nextItem.failedAt = Date.now();
    } finally {
      this.running--;
      this.process(); // Try to process next item
    }
  }
  
  getStatus(id) {
    const item = this.queue.find(item => item.id === id) ||
      this.completed.find(item => item.id === id);
    return item ? item.status : 'not_found';
  }
  
  setMaxConcurrent(max) {
    this.maxConcurrent = max;
    this.process();
  }
  
  clearPending() {
    this.queue = this.queue.filter(item => item.status === 'running');
  }
  
  getStats() {
    return {
      pending: this.queue.length,
      running: this.running,
      maxConcurrent: this.maxConcurrent,
      totalInQueue: this.queue.length + this.running
    };
  }
}

// Task Factory
function createTask(name, duration, shouldFail = false) {
  return async () => {
    console.log(`Starting task: ${name}`);
    await new Promise(resolve => setTimeout(resolve, duration));
    
    if (shouldFail) {
      throw new Error(`Task ${name} failed!`);
    }
    
    console.log(`Completed task: ${name}`);
    return `Result of ${name}`;
  };
}