// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COBALT_SRC_PUBLIC_ACTIVITY_LISTENER_INTERFACE_H_
#define COBALT_SRC_PUBLIC_ACTIVITY_LISTENER_INTERFACE_H_

#include <functional>

namespace cobalt {

// The possible device states that Cobalt is prepared to handle.
enum ActivityState { ACTIVE, IDLE, UNKNOWN };

class ActivityListenerInterface {
 public:
  ActivityListenerInterface() = default;
  virtual ~ActivityListenerInterface() = default;

  // Triggers the listener to begin listening for changes in the device state.
  //
  // This method should be called only once and should be called before the ActivityState is read
  // directly.
  //
  // |callback| will be called when the device state changes and when device state is received for
  // the first time.
  virtual void Start(const std::function<void(ActivityState)>& callback) = 0;

  // Returns the current activity state of the device. Start() must be called before the
  // ActivityState value is read directly.
  //
  // Start() should be
  virtual ActivityState state() = 0;
};

}  // namespace cobalt

#endif  // COBALT_SRC_PUBLIC_ACTIVITY_LISTENER_INTERFACE_H_