// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_METRICS_METRICS_SCHEDULER_H_
#define COMPONENTS_METRICS_METRICS_SCHEDULER_H_

#include "base/functional/callback.h"
#include "base/time/time.h"
#include "base/timer/timer.h"

namespace metrics {

// Scheduler task to drive a MetricsService object's uploading.
class MetricsScheduler {
 public:
  // Creates MetricsScheduler object with the given |task_callback|
  // callback to call when a task should happen.
  MetricsScheduler(const base::RepeatingClosure& task_callback,
                   bool fast_startup);

  MetricsScheduler(const MetricsScheduler&) = delete;
  MetricsScheduler& operator=(const MetricsScheduler&) = delete;

  virtual ~MetricsScheduler();

  // Starts scheduling uploads. This in a no-op if the scheduler is already
  // running, so it is safe to call more than once.
  void Start();

  // Stops scheduling uploads.
  void Stop();

  // Sets `done_callback_`, a callback to run when the current task has finished
  // running. The task must currently be running to call this.
  void SetDoneCallback(base::OnceClosure done_callback);

  // Whether the scheduler is running.
  bool IsRunning() { return running_; }

  // Whether a callback is currently pending (i.e. TriggerTask() was run, but
  // not its matching TaskDone()).
  bool IsCallbackPending() { return callback_pending_; }

  // Returns the interval for the currently scheduled task.
  base::TimeDelta GetIntervalForTesting() { return interval_; }

  // Returns the initial delay before the task is run for the first time.
  static int GetInitialIntervalSeconds();

 protected:
  // Subclasses should provide task_callback with a wrapper to call this with.
  // This indicates the triggered task was completed/cancelled and the next
  // call can be scheduled.
  void TaskDone(base::TimeDelta next_interval);

  // Called by the Timer when it's time to run the task.
  virtual void TriggerTask();

  // Sets `interval_`.
  void SetInterval(base::TimeDelta interval) { interval_ = interval; }

 private:
  // Schedules a future call to TriggerTask if one isn't already pending.
  void ScheduleNextTask();

  // The method to call when task should happen.
  const base::RepeatingClosure task_callback_;

  // The method to call when the task has finished running.
  base::OnceClosure done_callback_;

  // Uses a one-shot timer rather than a repeating one because the task may be
  // async, and the length of the interval may change.
  base::OneShotTimer timer_;

  // The interval between being told an task is done and starting the next task.
  base::TimeDelta interval_;

  // Indicates that the scheduler is running (i.e., that Start has been called
  // more recently than Stop).
  bool running_;

  // Indicates that the last triggered task hasn't resolved yet.
  bool callback_pending_;
};

}  // namespace metrics

#endif  // COMPONENTS_METRICS_METRICS_SCHEDULER_H_