/*
 * Copyright (C) 2018 Open Source Robotics Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
*/

#ifndef GZ_MATH_STOPWATCH_HH_
#define GZ_MATH_STOPWATCH_HH_

#include <chrono>
#include <memory>
#include <gz/math/Export.hh>
#include <gz/math/config.hh>

namespace ignition
{
  namespace math
  {
    // Use a steady clock
    using clock = std::chrono::steady_clock;

    // Inline bracket to help doxygen filtering.
    inline namespace IGNITION_MATH_VERSION_NAMESPACE {
    //
    // Forward declarations.
    class StopwatchPrivate;

    //
    /// \class Stopwatch Stopwatch.hh ignition/math/Stopwatch.hh
    /// \brief The Stopwatch keeps track of time spent in the run state,
    /// accessed through ElapsedRunTime(), and time spent in the stop state,
    /// accessed through ElapsedStopTime(). Elapsed run time starts accumulating
    /// after the first call to Start(). Elapsed stop time starts
    /// accumulation after Start() has been called followed by Stop(). The
    /// stopwatch can be reset with the Reset() function.
    ///
    /// # Example usage
    ///
    /// ```{.cpp}
    /// gz::math::Stopwatch watch;
    /// watch.Start();
    ///
    /// // do something...
    ///
    /// std::cout << "Elapsed time is "
    /// << std::chrono::duration_cast<std::chrono::milliseconds>(
    ///   timeSys.ElapsedRunTime()).count() << " ms\n";
    /// watch.Stop();
    /// ```
    class IGNITION_MATH_VISIBLE Stopwatch
    {
      /// \brief Constructor.
      public: Stopwatch();

      /// \brief Copy constructor
      /// \param[in] _watch The stop watch to copy.
      public: Stopwatch(const Stopwatch &_watch);

      /// \brief Move constructor
      /// \param[in] _watch The stop watch to move.
      public: Stopwatch(Stopwatch &&_watch) noexcept;

      /// \brief Destructor.
      public: virtual ~Stopwatch();

      /// \brief Start the stopwatch.
      /// \param[in] _reset If true the stopwatch is reset first.
      /// \return True if the the stopwatch was started. This will return
      /// false if the stopwatch was already running.
      public: bool Start(const bool _reset = false);

      /// \brief Get the time when the stopwatch was started.
      /// \return The time when stopwatch was started, or
      /// std::chrono::steady_clock::time_point::min() if the stopwatch
      /// has not been started.
      public: clock::time_point StartTime() const;

      /// \brief Stop the stopwatch
      /// \return True if the stopwatch was stopped. This will return false
      /// if the stopwatch is not running.
      public: bool Stop();

      /// \brief Get the time when the stopwatch was last stopped.
      /// \return The time when stopwatch was last stopped, or
      /// std::chrono::steady_clock::time_point::min() if the stopwatch
      /// has never been stopped.
      public: clock::time_point StopTime() const;

      /// \brief Get whether the stopwatch is running.
      /// \return True if the stopwatch is running.
      public: bool Running() const;

      /// \brief Reset the stopwatch. This resets the start time, stop time,
      /// elapsed duration and elapsed stop duration.
      public: void Reset();

      /// \brief Get the amount of time that the stop watch has been
      /// running. This is the total amount of run time, spannning all start
      /// and stop calls. The Reset function or passing true to the Start
      /// function will reset this value.
      /// \return Total amount of elapsed run time.
      public: clock::duration ElapsedRunTime() const;

      /// \brief Get the amount of time that the stop watch has been
      /// stopped. This is the total amount of stop time, spannning all start
      /// and stop calls. The Reset function or passing true to the Start
      /// function will reset this value.
      /// \return Total amount of elapsed stop time.
      public: clock::duration ElapsedStopTime() const;

      /// \brief Equality operator.
      /// \param[in] _watch The watch to compare.
      /// \return True if this watch equals the provided watch.
      public: bool operator==(const Stopwatch &_watch) const;

      /// \brief Inequality operator.
      /// \param[in] _watch The watch to compare.
      /// \return True if this watch does not equal the provided watch.
      public: bool operator!=(const Stopwatch &_watch) const;

      /// \brief Copy assignment operator
      /// \param[in] _watch The stop watch to copy.
      /// \return Reference to this.
      public: Stopwatch &operator=(const Stopwatch &_watch);

      /// \brief Move assignment operator
      /// \param[in] _watch The stop watch to move.
      /// \return Reference to this.
      public: Stopwatch &operator=(Stopwatch &&_watch);

#ifdef _WIN32
// Disable warning C4251 which is triggered by
// std::unique_ptr
#pragma warning(push)
#pragma warning(disable: 4251)
#endif
      /// \brief Private data pointer.
      private: std::unique_ptr<StopwatchPrivate> dataPtr;
#ifdef _WIN32
#pragma warning(pop)
#endif
    };
  }
  }
}
#endif
