/* -*- c++ -*- */
/*
 * Copyright 2004,2013 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */

#ifndef INCLUDED_GR_SIMPLE_CORRELATOR_IMPL_H
#define INCLUDED_GR_SIMPLE_CORRELATOR_IMPL_H

#include <gnuradio/digital/simple_correlator.h>

// To enable tracing to the debug logger, un-comment the following line
//#define	DEBUG_SIMPLE_CORRELATOR

namespace gr {
namespace digital {

class simple_correlator_impl : public simple_correlator
{
private:
    static constexpr int OVERSAMPLE = 8;
    enum state_t { ST_LOOKING, ST_UNDER_THRESHOLD, ST_LOCKED };

    int d_payload_bytesize;
    state_t d_state;
    unsigned int d_osi;            // over sample index [0,OVERSAMPLE-1]
    unsigned int d_transition_osi; // first index where Hamming dist < thresh
    unsigned int d_center_osi;     // center of bit
    unsigned long long int d_shift_reg[OVERSAMPLE];
    int d_bblen;             // length of bitbuf
    unsigned char* d_bitbuf; // demodulated bits
    unsigned char* d_pktbuf; // temp packet buf
    int d_bbi;               // bitbuf index

    static const int AVG_PERIOD = 512; // must be power of 2 (for freq offset correction)
    int d_avbi;
    float d_avgbuf[AVG_PERIOD];
    float d_avg;
    float d_accum;

    inline int slice(float x) { return x >= d_avg ? 1 : 0; }

    void update_avg(float x);

    void enter_locked();
    void enter_under_threshold();
    void enter_looking();

    static int add_index(int a, int b)
    {
        int t = a + b;
        if (t >= OVERSAMPLE)
            t -= OVERSAMPLE;
        assert(t >= 0 && t < OVERSAMPLE);
        return t;
    }

    static int sub_index(int a, int b)
    {
        int t = a - b;
        if (t < 0)
            t += OVERSAMPLE;
        assert(t >= 0 && t < OVERSAMPLE);
        return t;
    }

public:
    simple_correlator_impl(int payload_bytesize);
    ~simple_correlator_impl() override;

    int general_work(int noutput_items,
                     gr_vector_int& ninput_items,
                     gr_vector_const_void_star& input_items,
                     gr_vector_void_star& output_items) override;
};

} /* namespace digital */
} /* namespace gr */

#endif /* INCLUDED_GR_SIMPLE_CORRELATOR_IMPL_H */
