/*!
 * \file pcps_opencl_acquisition_cc.cc
 * \brief This class implements a Parallel Code Phase Search Acquisition
 * using OpenCL to offload some functions to the GPU.
 *
 *  Acquisition strategy (Kay Borre book + CFAR threshold).
 *  <ol>
 *  <li> Compute the input signal power estimation
 *  <li> Doppler serial search loop
 *  <li> Perform the FFT-based circular convolution (parallel time search)
 *  <li> Record the maximum peak and the associated synchronization parameters
 *  <li> Compute the test statistics and compare to the threshold
 *  <li> Declare positive or negative acquisition using a message queue
 *  </ol>
 *
 * Kay Borre book: K.Borre, D.M.Akos, N.Bertelsen, P.Rinder, and S.H.Jensen,
 * "A Software-Defined GPS and Galileo Receiver. A Single-Frequency
 * Approach", Birkha user, 2007. pp 81-84
 *
 * \authors <ul>
 *          <li> Javier Arribas, 2011. jarribas(at)cttc.es
 *          <li> Luis Esteve, 2012. luis(at)epsilon-formacion.com
 *          <li> Marc Molina, 2013. marc.molina.pena@gmail.com
 *          </ul>
 *
 * -------------------------------------------------------------------------
 *
 * Copyright (C) 2010-2012  (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 "pcps_opencl_acquisition_cc.h"
#include "gnss_signal_processing.h"
#include "control_message_factory.h"
#include "fft_base_kernels.h"
#include "fft_internal.h"
#include <gnuradio/io_signature.h>
#include <sstream>
#include <fstream>
#include <iostream>
#include <glog/log_severity.h>
#include <glog/logging.h>
#include <volk/volk.h>
#include <sys/time.h>

using google::LogMessage;

pcps_opencl_acquisition_cc_sptr pcps_make_opencl_acquisition_cc(
                                 unsigned int sampled_ms, unsigned int max_dwells,
                                 unsigned int doppler_max, long freq, long fs_in,
                                 int samples_per_ms, int samples_per_code,
                                 bool bit_transition_flag,
                                 gr::msg_queue::sptr queue, bool dump,
                                 std::string dump_filename)
{

    return pcps_opencl_acquisition_cc_sptr(
            new pcps_opencl_acquisition_cc(sampled_ms, max_dwells, doppler_max, freq, fs_in, samples_per_ms,
                                     samples_per_code, bit_transition_flag, queue, dump, dump_filename));
}

pcps_opencl_acquisition_cc::pcps_opencl_acquisition_cc(
                         unsigned int sampled_ms, unsigned int max_dwells,
                         unsigned int doppler_max, long freq, long fs_in,
                         int samples_per_ms, int samples_per_code,
                         bool bit_transition_flag,
                         gr::msg_queue::sptr queue, bool dump,
                         std::string dump_filename) :
    gr::block("pcps_opencl_acquisition_cc",
    gr::io_signature::make(1, 1, sizeof(gr_complex) * sampled_ms * samples_per_ms),
    gr::io_signature::make(0, 0, sizeof(gr_complex) * sampled_ms * samples_per_ms))
{
    d_sample_counter = 0;    // SAMPLE COUNTER
    d_active = false;
    d_state = 0;
    d_core_working = false;
    d_queue = queue;
    d_freq = freq;
    d_fs_in = fs_in;
    d_samples_per_ms = samples_per_ms;
    d_samples_per_code = samples_per_code;
    d_sampled_ms = sampled_ms;
    d_max_dwells = max_dwells;
    d_well_count = 0;
    d_doppler_max = doppler_max;
    d_fft_size = d_sampled_ms * d_samples_per_ms;
    d_fft_size_pow2 = pow(2, ceil(log2(2*d_fft_size)));
    d_mag = 0;
    d_input_power = 0.0;
    d_num_doppler_bins = 0;
    d_bit_transition_flag = bit_transition_flag;
    d_in_dwell_count = 0;
    d_cl_fft_batch_size = 1;

    d_in_buffer = new gr_complex*[d_max_dwells];

    //todo: do something if posix_memalign fails
    for (unsigned int i = 0; i < d_max_dwells; i++)
        {
            if (posix_memalign((void**)&d_in_buffer[i], 16,
                        d_fft_size * sizeof(gr_complex)) == 0){};

        }
    if (posix_memalign((void**)&d_magnitude, 16, d_fft_size * sizeof(float)) == 0){};
    if (posix_memalign((void**)&d_fft_codes, 16, d_fft_size_pow2 * sizeof(gr_complex)) == 0){};
    if (posix_memalign((void**)&d_zero_vector, 16, (d_fft_size_pow2-d_fft_size) * sizeof(gr_complex)) == 0){};

    for (unsigned int i = 0; i < (d_fft_size_pow2-d_fft_size); i++)
        {
            d_zero_vector[i] = gr_complex(0.0,0.0);
        }

    d_opencl = init_opencl_environment("math_kernel.cl");

    if (d_opencl != 0)
    {
        // Direct FFT
        d_fft_if = new gr::fft::fft_complex(d_fft_size, true);

        // Inverse FFT
        d_ifft = new gr::fft::fft_complex(d_fft_size, false);
    }

    // For dumping samples into a file
    d_dump = dump;
    d_dump_filename = dump_filename;

}

pcps_opencl_acquisition_cc::~pcps_opencl_acquisition_cc()
{
    if (d_num_doppler_bins > 0)
        {
            for (unsigned int i = 0; i < d_num_doppler_bins; i++)
                {
                    free(d_grid_doppler_wipeoffs[i]);
                }
            delete[] d_grid_doppler_wipeoffs;
        }

    for (unsigned int i = 0; i < d_max_dwells; i++)
        {
            free(d_in_buffer[i]);
        }
    delete[] d_in_buffer;

    free(d_fft_codes);
    free(d_magnitude);
    free(d_zero_vector);

    if (d_opencl == 0)
        {
            delete d_cl_queue;
            delete d_cl_buffer_in;
            delete d_cl_buffer_1;
            delete d_cl_buffer_2;
            delete d_cl_buffer_magnitude;
            delete d_cl_buffer_fft_codes;
            if(d_num_doppler_bins > 0)
                {
                    delete[] d_cl_buffer_grid_doppler_wipeoffs;
                }

            clFFT_DestroyPlan(d_cl_fft_plan);
        }
    else
        {
            delete d_ifft;
            delete d_fft_if;
        }

    if (d_dump)
        {
            d_dump_file.close();
        }
}

int pcps_opencl_acquisition_cc::init_opencl_environment(std::string kernel_filename)
{
    //get all platforms (drivers)
    std::vector<cl::Platform> all_platforms;
    cl::Platform::get(&all_platforms);

    if(all_platforms.size()==0)
    {
        std::cout << "No OpenCL platforms found. Check OpenCL installation!" << std::endl;
        return 1;
    }

    d_cl_platform = all_platforms[0]; //get default platform
    std::cout << "Using platform: " << d_cl_platform.getInfo<CL_PLATFORM_NAME>()
              << std::endl;

    //get default GPU device of the default platform
    std::vector<cl::Device> gpu_devices;
    d_cl_platform.getDevices(CL_DEVICE_TYPE_GPU, &gpu_devices);

    if(gpu_devices.size()==0)
    {
        std::cout << "No GPU devices found. Check OpenCL installation!" << std::endl;
        return 2;
    }

    d_cl_device = gpu_devices[0];

    std::vector<cl::Device> device;
    device.push_back(d_cl_device);
    std::cout << "Using device: " << d_cl_device.getInfo<CL_DEVICE_NAME>() << std::endl;

    cl::Context context(device);
    d_cl_context = context;

    // build the program from the source in the file
    std::ifstream kernel_file(kernel_filename, std::ifstream::in);
    std::string kernel_code(std::istreambuf_iterator<char>(kernel_file),
        (std::istreambuf_iterator<char>()));
    kernel_file.close();

    // std::cout << "Kernel code: \n" << kernel_code << std::endl;

    cl::Program::Sources sources;

    sources.push_back({kernel_code.c_str(),kernel_code.length()});

    cl::Program program(context,sources);
    if(program.build(device)!=CL_SUCCESS)
    {
        std::cout << " Error building: "
                  << program.getBuildInfo<CL_PROGRAM_BUILD_LOG>(device[0])
                  << std::endl;
        return 3;
    }
    d_cl_program = program;

    // create buffers on the device
    d_cl_buffer_in = new cl::Buffer(d_cl_context,CL_MEM_READ_WRITE,sizeof(gr_complex)*d_fft_size);
    d_cl_buffer_fft_codes = new cl::Buffer(d_cl_context,CL_MEM_READ_WRITE,sizeof(gr_complex)*d_fft_size_pow2);
    d_cl_buffer_1 = new cl::Buffer(d_cl_context,CL_MEM_READ_WRITE,sizeof(gr_complex)*d_fft_size_pow2);
    d_cl_buffer_2 = new cl::Buffer(d_cl_context,CL_MEM_READ_WRITE,sizeof(gr_complex)*d_fft_size_pow2);
    d_cl_buffer_magnitude = new cl::Buffer(d_cl_context,CL_MEM_READ_WRITE,sizeof(float)*d_fft_size);

    //create queue to which we will push commands for the device.
    d_cl_queue = new cl::CommandQueue(d_cl_context,d_cl_device);

    //create FFT plan
    cl_int err;
    clFFT_Dim3 dim = {d_fft_size_pow2, 1, 1};

    d_cl_fft_plan = clFFT_CreatePlan(d_cl_context(), dim, clFFT_1D,
                                     clFFT_InterleavedComplexFormat, &err);

    if (err != 0)
    {
        delete d_cl_queue;
        delete d_cl_buffer_in;
        delete d_cl_buffer_1;
        delete d_cl_buffer_2;
        delete d_cl_buffer_magnitude;
        delete d_cl_buffer_fft_codes;

        std::cout << "Error creating OpenCL FFT plan." << std::endl;
        return 4;
    }

    return 0;
}

void pcps_opencl_acquisition_cc::init()
{
    d_gnss_synchro->Acq_delay_samples = 0.0;
    d_gnss_synchro->Acq_doppler_hz = 0.0;
    d_gnss_synchro->Acq_samplestamp_samples = 0;
    d_mag = 0.0;
    d_input_power = 0.0;

    // Count the number of bins
    d_num_doppler_bins = 0;
    for (int doppler = (int)(-d_doppler_max);
         doppler <= (int)d_doppler_max;
         doppler += d_doppler_step)
    {
        d_num_doppler_bins++;
    }

    // Create the carrier Doppler wipeoff signals
    d_grid_doppler_wipeoffs = new gr_complex*[d_num_doppler_bins];
    if (d_opencl == 0)
        {
            d_cl_buffer_grid_doppler_wipeoffs = new cl::Buffer*[d_num_doppler_bins];
        }

    for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
        {
            if (posix_memalign((void**)&(d_grid_doppler_wipeoffs[doppler_index]), 16,
                               d_fft_size * sizeof(gr_complex)) == 0){};

            int doppler= -(int)d_doppler_max + d_doppler_step*doppler_index;
            complex_exp_gen_conj(d_grid_doppler_wipeoffs[doppler_index],
                                 d_freq + doppler, d_fs_in, d_fft_size);

            if (d_opencl == 0)
                {
                    d_cl_buffer_grid_doppler_wipeoffs[doppler_index] =
                            new cl::Buffer(d_cl_context, CL_MEM_READ_WRITE, sizeof(gr_complex)*d_fft_size);

                    d_cl_queue->enqueueWriteBuffer(*(d_cl_buffer_grid_doppler_wipeoffs[doppler_index]),
                                                   CL_TRUE, 0, sizeof(gr_complex)*d_fft_size,
                                                   d_grid_doppler_wipeoffs[doppler_index]);
                }
        }

    // zero padding in buffer_1 (FFT input)
    if (d_opencl == 0)
    {
        d_cl_queue->enqueueWriteBuffer(*d_cl_buffer_1, CL_TRUE, sizeof(gr_complex)*d_fft_size,
                                       sizeof(gr_complex)*(d_fft_size_pow2 - d_fft_size), d_zero_vector);
    }
}

void pcps_opencl_acquisition_cc::set_local_code(std::complex<float> * code)
{
    if(d_opencl == 0)
    {
        d_cl_queue->enqueueWriteBuffer(*d_cl_buffer_2, CL_TRUE, 0,
                                       sizeof(gr_complex)*d_fft_size, code);

        d_cl_queue->enqueueWriteBuffer(*d_cl_buffer_2, CL_TRUE, sizeof(gr_complex)*d_fft_size,
                                       sizeof(gr_complex)*(d_fft_size_pow2 - 2*d_fft_size),
                                       d_zero_vector);

        d_cl_queue->enqueueWriteBuffer(*d_cl_buffer_2, CL_TRUE, sizeof(gr_complex)
                                       *(d_fft_size_pow2 - d_fft_size),
                                       sizeof(gr_complex)*d_fft_size, code);

        clFFT_ExecuteInterleaved((*d_cl_queue)(), d_cl_fft_plan, d_cl_fft_batch_size,
                                  clFFT_Forward, (*d_cl_buffer_2)(), (*d_cl_buffer_2)(),
                                  0, NULL, NULL);

        //Conjucate the local code
        cl::Kernel kernel = cl::Kernel(d_cl_program, "conj_vector");
        kernel.setArg(0, *d_cl_buffer_2);         //input
        kernel.setArg(1, *d_cl_buffer_fft_codes); //output
        d_cl_queue->enqueueNDRangeKernel(kernel, cl::NullRange, cl::NDRange(d_fft_size_pow2), cl::NullRange);
    }
    else
    {
        memcpy(d_fft_if->get_inbuf(), code, sizeof(gr_complex)*d_fft_size);

        d_fft_if->execute(); // We need the FFT of local code

        //Conjugate the local code
        if (is_unaligned())
            {
                volk_32fc_conjugate_32fc_u(d_fft_codes, d_fft_if->get_outbuf(), d_fft_size);
            }
        else
            {
                volk_32fc_conjugate_32fc_a(d_fft_codes, d_fft_if->get_outbuf(), d_fft_size);
            }
    }
}

void pcps_opencl_acquisition_cc::acquisition_core_volk()
{
    // initialize acquisition algorithm
    int doppler;
    unsigned int indext = 0;
    float magt = 0.0;
    float fft_normalization_factor = (float)d_fft_size * (float)d_fft_size;
    gr_complex* in = d_in_buffer[d_well_count];
    unsigned long int samplestamp = d_sample_counter_buffer[d_well_count];

    d_input_power = 0.0;
    d_mag = 0.0;

    d_well_count++;

    DLOG(INFO) << "Channel: " << d_channel
            << " , doing acquisition of satellite: " << d_gnss_synchro->System << " "<< d_gnss_synchro->PRN
            << " ,sample stamp: " << d_sample_counter << ", threshold: "
            << d_threshold << ", doppler_max: " << d_doppler_max
            << ", doppler_step: " << d_doppler_step;

    // 1- Compute the input signal power estimation
    volk_32fc_magnitude_squared_32f_a(d_magnitude, in, d_fft_size);
    volk_32f_accumulator_s32f_a(&d_input_power, d_magnitude, d_fft_size);
    d_input_power /= (float)d_fft_size;

    // 2- Doppler frequency search loop
    for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
        {
            // doppler search steps

            doppler = -(int)d_doppler_max + d_doppler_step*doppler_index;


            volk_32fc_x2_multiply_32fc_a(d_fft_if->get_inbuf(), in,
                        d_grid_doppler_wipeoffs[doppler_index], d_fft_size);

            // 3- Perform the FFT-based convolution  (parallel time search)
            // Compute the FFT of the carrier wiped--off incoming signal
            d_fft_if->execute();

            // Multiply carrier wiped--off, Fourier transformed incoming signal
            // with the local FFT'd code reference using SIMD operations with VOLK library
            volk_32fc_x2_multiply_32fc_a(d_ifft->get_inbuf(),
                        d_fft_if->get_outbuf(), d_fft_codes, d_fft_size);

            // compute the inverse FFT
            d_ifft->execute();

            // Search maximum
            volk_32fc_magnitude_squared_32f_a(d_magnitude, d_ifft->get_outbuf(), d_fft_size);
            volk_32f_index_max_16u_a(&indext, d_magnitude, d_fft_size);

            // Normalize the maximum value to correct the scale factor introduced by FFTW
            magt = d_magnitude[indext] / (fft_normalization_factor * fft_normalization_factor);

            // 4- record the maximum peak and the associated synchronization parameters
            if (d_mag < magt)
                {
                    d_mag = magt;

                    // In case that d_bit_transition_flag = true, we compare the potentially
                    // new maximum test statistics (d_mag/d_input_power) with the value in
                    // d_test_statistics. When the second dwell is being processed, the value
                    // of d_mag/d_input_power could be lower than d_test_statistics (i.e,
                    // the maximum test statistics in the previous dwell is greater than
                    // current d_mag/d_input_power). Note that d_test_statistics is not
                    // restarted between consecutive dwells in multidwell operation.
                    if (d_test_statistics < (d_mag / d_input_power) || !d_bit_transition_flag)
                    {
                        d_gnss_synchro->Acq_delay_samples = (double)(indext % d_samples_per_code);
                        d_gnss_synchro->Acq_doppler_hz = (double)doppler;
                        d_gnss_synchro->Acq_samplestamp_samples = samplestamp;

                        // 5- Compute the test statistics and compare to the threshold
                        //d_test_statistics = 2 * d_fft_size * d_mag / d_input_power;
                        d_test_statistics = d_mag / d_input_power;
                    }
                }

            // Record results to file if required
            if (d_dump)
                {
                    std::stringstream filename;
                    std::streamsize n = 2 * sizeof(float) * (d_fft_size); // complex file write
                    filename.str("");
                    filename << "../data/test_statistics_" << d_gnss_synchro->System
                             <<"_" << d_gnss_synchro->Signal << "_sat_"
                             << d_gnss_synchro->PRN << "_doppler_" <<  doppler << ".dat";
                    d_dump_file.open(filename.str().c_str(), std::ios::out | std::ios::binary);
                    d_dump_file.write((char*)d_ifft->get_outbuf(), n); //write directly |abs(x)|^2 in this Doppler bin?
                    d_dump_file.close();
                }
        }

    if (!d_bit_transition_flag)
        {
            if (d_test_statistics > d_threshold)
                {
                    d_state = 2; // Positive acquisition
                }
            else if (d_well_count == d_max_dwells)
                {
                    d_state = 3; // Negative acquisition
                }
        }
    else
        {
            if (d_well_count == d_max_dwells) // d_max_dwells = 2
                {
                    if (d_test_statistics > d_threshold)
                        {
                            d_state = 2; // Positive acquisition
                        }
                    else
                        {
                            d_state = 3; // Negative acquisition
                        }
                }
        }

    d_core_working = false;
}

void pcps_opencl_acquisition_cc::acquisition_core_opencl()
{
    // initialize acquisition algorithm
    int doppler;
    unsigned int indext = 0;
    float magt = 0.0;
    float fft_normalization_factor = ((float)d_fft_size_pow2 * (float)d_fft_size); //This works, but I am not sure why.
    gr_complex* in = d_in_buffer[d_well_count];
    unsigned long int samplestamp = d_sample_counter_buffer[d_well_count];

    d_input_power = 0.0;
    d_mag = 0.0;

    // write input vector in buffer of OpenCL device
    d_cl_queue->enqueueWriteBuffer(*d_cl_buffer_in, CL_TRUE, 0, sizeof(gr_complex)*d_fft_size, in);

    d_well_count++;

//    struct timeval tv;
//    long long int begin = 0;
//    long long int end = 0;

//    gettimeofday(&tv, NULL);
//    begin = tv.tv_sec *1e6 + tv.tv_usec;

    DLOG(INFO) << "Channel: " << d_channel
            << " , doing acquisition of satellite: " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN
            << " ,sample stamp: " << d_sample_counter << ", threshold: "
            << d_threshold << ", doppler_max: " << d_doppler_max
            << ", doppler_step: " << d_doppler_step;

    // 1- Compute the input signal power estimation
    volk_32fc_magnitude_squared_32f_a(d_magnitude, in, d_fft_size);
    volk_32f_accumulator_s32f_a(&d_input_power, d_magnitude, d_fft_size);
    d_input_power /= (float)d_fft_size;

    cl::Kernel kernel;

    // 2- Doppler frequency search loop
    for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
        {
            // doppler search steps

            doppler = -(int)d_doppler_max + d_doppler_step*doppler_index;

            //Multiply input signal with doppler wipe-off
            kernel = cl::Kernel(d_cl_program, "mult_vectors");
            kernel.setArg(0, *d_cl_buffer_in); //input 1
            kernel.setArg(1, *d_cl_buffer_grid_doppler_wipeoffs[doppler_index]); //input 2
            kernel.setArg(2, *d_cl_buffer_1); //output
            d_cl_queue->enqueueNDRangeKernel(kernel,cl::NullRange, cl::NDRange(d_fft_size),
                                             cl::NullRange);

            // In the previous operation, we store the result in the first d_fft_size positions
            // of d_cl_buffer_1. The rest d_fft_size_pow2-d_fft_size already have zeros
            // (zero-padding is made in init() for optimization purposes).

            clFFT_ExecuteInterleaved((*d_cl_queue)(), d_cl_fft_plan, d_cl_fft_batch_size,
                                      clFFT_Forward,(*d_cl_buffer_1)(), (*d_cl_buffer_2)(),
                                      0, NULL, NULL);

            // Multiply carrier wiped--off, Fourier transformed incoming signal
            // with the local FFT'd code reference
            kernel = cl::Kernel(d_cl_program, "mult_vectors");
            kernel.setArg(0, *d_cl_buffer_2);         //input 1
            kernel.setArg(1, *d_cl_buffer_fft_codes); //input 2
            kernel.setArg(2, *d_cl_buffer_2);         //output
            d_cl_queue->enqueueNDRangeKernel(kernel, cl::NullRange, cl::NDRange(d_fft_size_pow2),
                                             cl::NullRange);

            // compute the inverse FFT
            clFFT_ExecuteInterleaved((*d_cl_queue)(), d_cl_fft_plan, d_cl_fft_batch_size,
                                      clFFT_Inverse, (*d_cl_buffer_2)(), (*d_cl_buffer_2)(),
                                      0, NULL, NULL);

            // Compute magnitude
            kernel = cl::Kernel(d_cl_program, "magnitude_squared");
            kernel.setArg(0, *d_cl_buffer_2);         //input 1
            kernel.setArg(1, *d_cl_buffer_magnitude); //output
            d_cl_queue->enqueueNDRangeKernel(kernel, cl::NullRange, cl::NDRange(d_fft_size),
                                             cl::NullRange);

            // This is the only function that blocks this thread until all previously enqueued
            // OpenCL commands are completed.
            d_cl_queue->enqueueReadBuffer(*d_cl_buffer_magnitude, CL_TRUE, 0,
                                          sizeof(float)*d_fft_size,d_magnitude);

            // Search maximum
            // @TODO: find an efficient way to search the maximum with OpenCL in the GPU.
            volk_32f_index_max_16u_a(&indext, d_magnitude, d_fft_size);

            // Normalize the maximum value to correct the scale factor introduced by FFTW
            magt = d_magnitude[indext] / (fft_normalization_factor * fft_normalization_factor);

            // 4- record the maximum peak and the associated synchronization parameters
            if (d_mag < magt)
                {
                    d_mag = magt;

                    // In case that d_bit_transition_flag = true, we compare the potentially
                    // new maximum test statistics (d_mag/d_input_power) with the value in
                    // d_test_statistics. When the second dwell is being processed, the value
                    // of d_mag/d_input_power could be lower than d_test_statistics (i.e,
                    // the maximum test statistics in the previous dwell is greater than
                    // current d_mag/d_input_power). Note that d_test_statistics is not
                    // restarted between consecutive dwells in multidwell operation.
                    if (d_test_statistics < (d_mag / d_input_power) || !d_bit_transition_flag)
                    {
                        d_gnss_synchro->Acq_delay_samples = (double)(indext % d_samples_per_code);
                        d_gnss_synchro->Acq_doppler_hz = (double)doppler;
                        d_gnss_synchro->Acq_samplestamp_samples = samplestamp;

                        // 5- Compute the test statistics and compare to the threshold
                        //d_test_statistics = 2 * d_fft_size * d_mag / d_input_power;
                        d_test_statistics = d_mag / d_input_power;
                    }
                }

            // Record results to file if required
            if (d_dump)
                {
                    std::stringstream filename;
                    std::streamsize n = 2 * sizeof(float) * (d_fft_size); // complex file write
                    filename.str("");
                    filename << "../data/test_statistics_" << d_gnss_synchro->System
                             << "_" << d_gnss_synchro->Signal << "_sat_"
                             << d_gnss_synchro->PRN << "_doppler_" <<  doppler << ".dat";
                    d_dump_file.open(filename.str().c_str(), std::ios::out | std::ios::binary);
                    d_dump_file.write((char*)d_ifft->get_outbuf(), n); //write directly |abs(x)|^2 in this Doppler bin?
                    d_dump_file.close();
                }
        }

//    gettimeofday(&tv, NULL);
//    end = tv.tv_sec *1e6 + tv.tv_usec;
//    std::cout << "Acq time = " << (end-begin) << " us" << std::endl;

    if (!d_bit_transition_flag)
        {
            if (d_test_statistics > d_threshold)
                {
                    d_state = 2; // Positive acquisition
                }
            else if (d_well_count == d_max_dwells)
                {
                    d_state = 3; // Negative acquisition
                }
        }
    else
        {
            if (d_well_count == d_max_dwells) // d_max_dwells = 2
                {
                    if (d_test_statistics > d_threshold)
                        {
                            d_state = 2; // Positive acquisition
                        }
                    else
                        {
                            d_state = 3; // Negative acquisition
                        }
                }
        }

    d_core_working = false;
}

int pcps_opencl_acquisition_cc::general_work(int noutput_items,
        gr_vector_int &ninput_items, gr_vector_const_void_star &input_items,
        gr_vector_void_star &output_items)
{

    int acquisition_message = -1; //0=STOP_CHANNEL 1=ACQ_SUCCEES 2=ACQ_FAIL

    switch (d_state)
    {
    case 0:
        {
            if (d_active)
                {
                    //restart acquisition variables
                    d_gnss_synchro->Acq_delay_samples = 0.0;
                    d_gnss_synchro->Acq_doppler_hz = 0.0;
                    d_gnss_synchro->Acq_samplestamp_samples = 0;
                    d_well_count = 0;
                    d_mag = 0.0;
                    d_input_power = 0.0;
                    d_test_statistics = 0.0;
                    d_in_dwell_count = 0;
                    d_sample_counter_buffer.clear();

                    d_state = 1;
                }

            d_sample_counter += d_fft_size * ninput_items[0]; // sample counter

            break;
        }

    case 1:
        {
            if (d_in_dwell_count < d_max_dwells)
                {
                    // Fill internal buffer with d_max_dwells signal blocks. This step ensures that
                    // consecutive signal blocks will be processed in multi-dwell operation. This is
                    // essential when d_bit_transition_flag = true.
                    unsigned int num_dwells = std::min((int)(d_max_dwells-d_in_dwell_count),ninput_items[0]);
                    for (unsigned int i = 0; i < num_dwells; i++)
                        {
                            memcpy(d_in_buffer[d_in_dwell_count++], (gr_complex*)input_items[i],
                                    sizeof(gr_complex)*d_fft_size);
                            d_sample_counter += d_fft_size;
                            d_sample_counter_buffer.push_back(d_sample_counter);
                        }

                    if (ninput_items[0] > (int)num_dwells)
                        {
                            d_sample_counter += d_fft_size * (ninput_items[0]-num_dwells);
                        }
                }
            else
                {
                    // We already have d_max_dwells consecutive blocks in the internal buffer,
                    // just skip input blocks.
                    d_sample_counter += d_fft_size * ninput_items[0];
                }

            // We create a new thread to process next block if the following
            // conditions are fulfilled:
            //   1. There are new blocks in d_in_buffer that have not been processed yet
            //      (d_well_count < d_in_dwell_count).
            //   2. No other acquisition_core thead is working (!d_core_working).
            //   3. d_state==1. We need to check again d_state because it can be modified at any
            //      moment by the external thread (may have changed since checked in the switch()).
            //      If the external thread has already declared positive (d_state=2) or negative
            //      (d_state=3) acquisition, we don't have to process next block!!
            if ((d_well_count < d_in_dwell_count) && !d_core_working && d_state==1)
                {
                    d_core_working = true;
                    if (d_opencl == 0)
                        {   // Use OpenCL implementation
                            boost::thread(&pcps_opencl_acquisition_cc::acquisition_core_opencl, this);
                        }
                    else
                        {   // Use Volk implementation
                            boost::thread(&pcps_opencl_acquisition_cc::acquisition_core_volk, this);
                        }
                }

            break;
        }

    case 2:
        {
            // Declare positive acquisition using a message queue
            DLOG(INFO) << "positive acquisition";
            DLOG(INFO) << "satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN;
            DLOG(INFO) << "sample_stamp " << d_sample_counter;
            DLOG(INFO) << "test statistics value " << d_test_statistics;
            DLOG(INFO) << "test statistics threshold " << d_threshold;
            DLOG(INFO) << "code phase " << d_gnss_synchro->Acq_delay_samples;
            DLOG(INFO) << "doppler " << d_gnss_synchro->Acq_doppler_hz;
            DLOG(INFO) << "magnitude " << d_mag;
            DLOG(INFO) << "input signal power " << d_input_power;

            d_active = false;
            d_state = 0;

            d_sample_counter += d_fft_size * ninput_items[0]; // sample counter

            acquisition_message = 1;
            d_channel_internal_queue->push(acquisition_message);

            break;
        }

    case 3:
        {
            // Declare negative acquisition using a message queue
            DLOG(INFO) << "negative acquisition";
            DLOG(INFO) << "satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN;
            DLOG(INFO) << "sample_stamp " << d_sample_counter;
            DLOG(INFO) << "test statistics value " << d_test_statistics;
            DLOG(INFO) << "test statistics threshold " << d_threshold;
            DLOG(INFO) << "code phase " << d_gnss_synchro->Acq_delay_samples;
            DLOG(INFO) << "doppler " << d_gnss_synchro->Acq_doppler_hz;
            DLOG(INFO) << "magnitude " << d_mag;
            DLOG(INFO) << "input signal power " << d_input_power;

            d_active = false;
            d_state = 0;

            d_sample_counter += d_fft_size * ninput_items[0]; // sample counter

            acquisition_message = 2;
            d_channel_internal_queue->push(acquisition_message);

            break;
        }
    }

    consume_each(ninput_items[0]);

    return 0;
}