/*

 * Copyright 2021 MusicScience37 (Kenta Kabashima)

 *

 * 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.

 */

/*!

 * \file

 * \brief Definition of determine_iterations function.

 */

#include "stat_bench/measurer/determine_iterations.h"

#include <algorithm>  // std::min, std::max

#include <vector>

#include "stat_bench/clock/duration.h"

#include "stat_bench/measurer/measure_once.h"

#include "stat_bench/measurer/measurement.h"

namespace stat_bench {

namespace measurer {

auto determine_iterations(bench_impl::IBenchmarkCase* bench_case,

    const BenchmarkCondition& cond, const MeasurementType& measurement_type,

    double min_sample_duration_sec) -> std::size_t {

    std::size_t iterations = 1;

    constexpr std::size_t trials = 10;

    for (std::size_t i = 0; i < trials; ++i) {

        constexpr std::size_t samples = 2;

        const auto data = measure_once(

            bench_case, cond, measurement_type, iterations, samples, 0);

        const double duration_sec = data.durations().at(0).at(1).seconds();

        if (duration_sec > min_sample_duration_sec) {

            break;

        }

        const double multiplier =

            std::min(

                min_sample_duration_sec / std::max(duration_sec, 1e-9), 10.0) *

            1.2;

        constexpr double max_iterations = 1e+6;

        iterations = static_cast<std::size_t>(std::min(

            max_iterations, static_cast<double>(iterations) * multiplier));

    }

    return iterations;

}

}  // namespace measurer

}  // namespace stat_bench