// Copyright 2019 The Dawn Authors
//
// 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.

#include <CoreServices/CoreServices.h>
#include <mach/mach.h>
#include <mach/mach_time.h>

#include "dawn/utils/Timer.h"

namespace utils {

class OSXTimer : public Timer {
  public:
    OSXTimer() : Timer(), mRunning(false), mSecondCoeff(0) {}

    ~OSXTimer() override = default;

    void Start() override {
        mStartTime = mach_absolute_time();
        // Cache secondCoeff
        GetSecondCoeff();
        mRunning = true;
    }

    void Stop() override {
        mStopTime = mach_absolute_time();
        mRunning = false;
    }

    double GetElapsedTime() const override {
        if (mRunning) {
            return mSecondCoeff * (mach_absolute_time() - mStartTime);
        } else {
            return mSecondCoeff * (mStopTime - mStartTime);
        }
    }

    double GetAbsoluteTime() override { return GetSecondCoeff() * mach_absolute_time(); }

  private:
    double GetSecondCoeff() {
        // If this is the first time we've run, get the timebase.
        if (mSecondCoeff == 0.0) {
            mach_timebase_info_data_t timebaseInfo;
            mach_timebase_info(&timebaseInfo);

            mSecondCoeff = timebaseInfo.numer * (1.0 / 1000000000) / timebaseInfo.denom;
        }

        return mSecondCoeff;
    }

    bool mRunning;
    uint64_t mStartTime;
    uint64_t mStopTime;
    double mSecondCoeff;
};

Timer* CreateTimer() {
    return new OSXTimer();
}

}  // namespace utils