/*!
 * \file fft_length_test.cc
 * \brief  This file implements timing tests for the FFT.
 * \author Carles Fernandez-Prades, 2016. cfernandez(at)cttc.es
 *
 *
 * -------------------------------------------------------------------------
 *
 * Copyright (C) 2010-2016  (see AUTHORS file for a list of contributors)
 *
 * GNSS-SDR is a software defined Global Navigation
 *          Satellite Systems receiver
 *
 * This file is part of GNSS-SDR.
 *
 * GNSS-SDR is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * GNSS-SDR is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNSS-SDR. If not, see <http://www.gnu.org/licenses/>.
 *
 * -------------------------------------------------------------------------
 */

#include <algorithm>
#include <chrono>
#include <functional>
#include <random>
#include <boost/filesystem.hpp>
#include <gnuradio/fft/fft.h>


#if defined GNUPLOT_EXECUTABLE
  #include "gnuplot_i.h"
  const bool exists_gnuplot_fft_test_length = true;
#elif !defined GNUPLOT_EXECUTABLE
  const bool exists_gnuplot_fft_test_length = false;
#endif


DEFINE_int32(fft_iterations_test, 1000, "Number of averaged iterations in FFT length timing test");
DEFINE_bool(plot_fft_length_test, false, "Plots results of FFTLengthTest with gnuplot");

// Note from FFTW documentation: the standard FFTW distribution works most efficiently for arrays whose
// size can be factored into small primes (2, 3, 5, and 7), and otherwise it uses a slower general-purpose routine.

TEST(FFTLengthTest, MeasureExecutionTime)
{
    unsigned int fft_sizes [] = { 512, 1000, 1024, 1100, 1297, 1400, 1500, 1960, 2000, 2048, 2221, 2500, 3000, 3500, 4000,
            4096, 4200, 4500, 4725, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8192, 8500, 9000, 9500, 10000, 10368, 11000,
            12000, 15000, 16000, 16384, 27000, 32768, 50000, 65536 };

    std::chrono::time_point<std::chrono::system_clock> start, end;

    std::random_device r;
    std::default_random_engine e1(r());
    std::default_random_engine e2(r());
    std::uniform_real_distribution<float> uniform_dist(-1, 1);
    auto func = [] (float a, float b) { return gr_complex(a, b); }; // Helper lambda function that returns a gr_complex
    auto random_number1 = std::bind(uniform_dist, e1);
    auto random_number2 = std::bind(uniform_dist, e2);
    auto gen = std::bind(func, random_number1, random_number2); // Function that returns a random gr_complex

    std::vector<unsigned int> fft_sizes_v(fft_sizes, fft_sizes + sizeof(fft_sizes) / sizeof(unsigned int) );
    std::sort(fft_sizes_v.begin(), fft_sizes_v.end());
    std::vector<unsigned int>::const_iterator it;
    unsigned int d_fft_size;
    std::vector<double> execution_times;
    std::vector<unsigned int> powers_of_two;
    std::vector<double> execution_times_powers_of_two;

    EXPECT_NO_THROW(
            for(it = fft_sizes_v.cbegin(); it != fft_sizes_v.cend(); ++it)
                {
                    gr::fft::fft_complex* d_fft;
                    d_fft_size = *it;
                    d_fft = new gr::fft::fft_complex(d_fft_size, true);

                    std::generate_n( d_fft->get_inbuf(), d_fft_size, gen );

                    start = std::chrono::system_clock::now();
                    for(int k = 0; k < FLAGS_fft_iterations_test; k++)
                        {
                            d_fft->execute();
                        }
                    end = std::chrono::system_clock::now();
                    std::chrono::duration<double> elapsed_seconds = end - start;
                    double exec_time = elapsed_seconds.count() / static_cast<double>(FLAGS_fft_iterations_test);
                    execution_times.push_back(exec_time * 1e3);
                    std::cout << "FFT execution time for length=" << d_fft_size << " : " << exec_time << " [s]" << std::endl;
                    delete d_fft;

                    if( (d_fft_size & (d_fft_size - 1)) == 0 ) // if it is a power of two
                        {
                            powers_of_two.push_back(d_fft_size);
                            execution_times_powers_of_two.push_back(exec_time / 1e-3);
                        }

                }
    );

    if(FLAGS_plot_fft_length_test == true)
        {
            if(!exists_gnuplot_fft_test_length)
                {
                    std::cout << "WARNING: Although the flag plot_fft_length_test has been set to TRUE," << std::endl;
                    std::cout << "gnuplot has not been found in your system." << std::endl;
                    std::cout << "Test results will not be plotted." << std::endl;
                }
            else
                {
#if defined GNUPLOT_EXECUTABLE
                    try
                    {
                            std::string gnuplot_executable = std::string(GNUPLOT_EXECUTABLE);
                            boost::filesystem::path p(gnuplot_executable);
                            boost::filesystem::path dir = p.parent_path();
                            std::string gnuplot_path = dir.native();
                            Gnuplot::set_GNUPlotPath(gnuplot_path);

                            Gnuplot g1("linespoints");
                            g1.set_title("FFT execution times for different lengths");
                            g1.set_grid();
                            g1.set_xlabel("FFT length");
                            g1.set_ylabel("Execution time [ms]");
                            g1.plot_xy(fft_sizes_v, execution_times, "FFT execution time (averaged over " + std::to_string(FLAGS_fft_iterations_test) + " iterations)");
                            g1.set_style("points").plot_xy(powers_of_two, execution_times_powers_of_two, "Power of 2");
                            g1.showonscreen(); // window output

                            Gnuplot g2("linespoints");
                            g2.set_title("FFT execution times for different lengths (up to 2^{14}=16384)");
                            g2.set_grid();
                            g2.set_xlabel("FFT length");
                            g2.set_ylabel("Execution time [ms]");
                            g2.set_xrange(0, 16384);
                            g2.plot_xy(fft_sizes_v, execution_times, "FFT execution time (averaged over " + std::to_string(FLAGS_fft_iterations_test) + " iterations)");
                            g2.set_style("points").plot_xy(powers_of_two, execution_times_powers_of_two, "Power of 2");
                            g2.savetops("FFT_execution_times");
                            g2.showonscreen(); // window output
                    }
                    catch (GnuplotException ge)
                    {
                            std::cout << ge.what() << std::endl;
                    }
#endif
                }
        }
}