#pragma once

#include <memory>

#include "envoy/common/exception.h"

#include "envoy/common/pure.h"

#include "source/common/common/assert.h"

namespace Envoy {

namespace Server {

// Struct for reporting usage for a particular resource.

struct ResourceUsage {

  // Fraction of (resource usage)/(resource limit).

  double resource_pressure_;

};

/**

 * Notifies caller of updated resource usage.

 */

class ResourceUpdateCallbacks {

public:

  /**

   * Called when the request for updated resource usage succeeds.

   * @param usage the updated resource usage

   */

  virtual void onSuccess(const ResourceUsage& usage) PURE;

  /**

   * Called when the request for updated resource usage fails.

   * @param error the exception caught when trying to get updated resource usage

   */

  virtual void onFailure(const EnvoyException& error) PURE;

};

class ResourceMonitor {

public:

  /**

   * Recalculate resource usage.

   * This must be non-blocking so if RPCs need to be made they should be

   * done asynchronously and invoke the callback when finished.

   */

  virtual void updateResourceUsage(ResourceUpdateCallbacks& callbacks) PURE;

};

using ResourceMonitorPtr = std::unique_ptr<ResourceMonitor>;

} // namespace Server

} // namespace Envoy