CREATE TABLE resources (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  description TEXT,
  max_duration INT, -- 最大预订时长（分钟）
  min_advance INT, -- 最小提前预订时间（分钟）
  max_advance INT -- 最大提前预订时间（分钟）
);

CREATE TABLE bookings (
  id INT PRIMARY KEY,
  resource_id INT REFERENCES resources(id),
  user_id INT,
  start_time TIMESTAMP,
  end_time TIMESTAMP,
  status VARCHAR(20), -- 'confirmed', 'cancelled', 'pending'
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

def is_available(resource_id, desired_start, desired_end):
    # 检查资源是否存在
    resource = get_resource_by_id(resource_id)
    if not resource:
        return False
    
    # 检查预订时间是否在允许范围内
    now = datetime.now()
    min_start = now + timedelta(minutes=resource.min_advance)
    max_start = now + timedelta(minutes=resource.max_advance)
    
    if desired_start < min_start or desired_start > max_start:
        return False
    
    # 检查持续时间是否超过最大值
    duration = (desired_end - desired_start).total_seconds() / 60
    if duration > resource.max_duration:
        return False
    
    # 检查是否有时间冲突
    conflicting_bookings = session.query(Booking).filter(
        Booking.resource_id == resource_id,
        Booking.status == 'confirmed',
        or_(
            and_(Booking.start_time < desired_end, Booking.end_time > desired_start),
            and_(desired_start < Booking.end_time, desired_end > Booking.start_time)
        )
    ).count()
    
    return conflicting_bookings == 0

# 使用数据库事务和行锁
def make_booking(user_id, resource_id, start_time, end_time):
    with session.begin():
        # 加锁检查可用性
        resource = session.query(Resource).with_for_update().get(resource_id)
        if not is_available(resource_id, start_time, end_time):
            raise Exception("Resource not available")
        
        # 创建预订
        booking = Booking(
            user_id=user_id,
            resource_id=resource_id,
            start_time=start_time,
            end_time=end_time,
            status='confirmed'
        )
        session.add(booking)