MIL-STD-188-110C/include/encoder/ModemController.h

#ifndef MODEM_CONTROLLER_H
#define MODEM_CONTROLLER_H

#include <cstdint>
#include <limits>
#include <memory>
#include <vector>

#include "bitstream.h"
#include "FECEncoder.h"
#include "Interleaver.h"
#include "MGDDecoder.h"
#include "PSKModulator.h"
#include "Scrambler.h"
#include "SymbolFormation.h"

/**
 * @brief Clamps an integer value to the range of int16_t.
 * @param x The value to be clamped.
 * @return The clamped value.
 */
constexpr int16_t clamp(int16_t x) {
    constexpr int16_t max_val = std::numeric_limits<int16_t>::max();
    constexpr int16_t min_val = std::numeric_limits<int16_t>::min();
    return (x > max_val) ? max_val : (x < min_val) ? min_val : x;
}

/**
 * @class ModemController
 * @brief Controls the modulation process for transmitting data using FEC encoding, interleaving, scrambling, and PSK modulation.
 */
class ModemController {
public:
    /**
     * @brief Constructs a ModemController object.
     * @param baud_rate The baud rate for the modem.
     * @param is_voice Indicates if the data being transmitted is voice.
     * @param is_frequency_hopping Indicates if frequency hopping is used.
     * @param interleave_setting The interleave setting to be used.
     * @param data The input data stream to be transmitted. The `is_voice` parameter controls whether the modem treats it as binary file data,
     *             or a binary stream from the MELPe (or other) voice codec.
     */
    ModemController(const size_t _baud_rate, const bool _is_voice, const bool _is_frequency_hopping, const size_t _interleave_setting, BitStream _data)
        : baud_rate(_baud_rate),
          is_voice(_is_voice),
          is_frequency_hopping(_is_frequency_hopping),
          interleave_setting(_interleave_setting),
          symbol_formation(baud_rate, interleave_setting, is_voice, is_frequency_hopping),
          scrambler(),
          fec_encoder(baud_rate, is_frequency_hopping),
          interleaver(baud_rate, interleave_setting, is_frequency_hopping),
          input_data(std::move(_data)),
          mgd_decoder(baud_rate, is_frequency_hopping),
          modulator(baud_rate, 48000, 0.5, is_frequency_hopping) {}

    /**
     * @brief Transmits the input data by processing it through different phases like FEC encoding, interleaving, symbol formation, scrambling, and modulation.
     * @return The scrambled data ready for modulation.
     * @note The modulated signal is generated internally but is intended to be handled externally.
     */
    std::vector<int16_t> transmit() {
        // Step 1: Append EOM Symbols
        BitStream eom_appended_data = appendEOMSymbols(input_data);

        std::vector<uint8_t> processed_data;
        if (baud_rate == 4800) {
            processed_data = splitTribitSymbols(eom_appended_data);
        } else {
            // Step 2: FEC Encoding
            BitStream fec_encoded_data = fec_encoder.encode(eom_appended_data);

            // Step 3: Interleaving
            processed_data = interleaver.interleaveStream(fec_encoded_data);
        }

        std::vector<uint8_t> mgd_decoded_data = mgd_decoder.mgdDecode(processed_data);

        // Step 4: Symbol Formation. This function injects the sync preamble symbols. Scrambling is built-in.
        std::vector<uint8_t> symbol_stream = symbol_formation.formSymbols(mgd_decoded_data);

        std::vector<int16_t> modulated_signal = modulator.modulate(symbol_stream);

        return modulated_signal;
    }

private:
    size_t baud_rate;                ///< The baud rate for the modem.
    bool is_voice;                   ///< Indicates if the data being transmitted is voice.
    bool is_frequency_hopping;       ///< Indicates if frequency hopping is used.
    BitStream input_data;            ///< The input data stream.
    size_t interleave_setting;       ///< The interleave setting to be used.
    size_t sample_rate;

    SymbolFormation symbol_formation; ///< Symbol formation instance to form symbols from data.
    Scrambler scrambler;              ///< Scrambler instance for scrambling the data.
    FECEncoder fec_encoder;           ///< FEC encoder instance for encoding the data.
    Interleaver interleaver;          ///< Interleaver instance for interleaving the data.
    PSKModulator modulator;           ///< PSK modulator instance for modulating the data.
    MGDDecoder mgd_decoder;           ///< MGD decoder

    /**
     * @brief Appends the EOM symbols to the input data and flushes the FEC encoder and interleaver.
     * @param input_data The input data to which the EOM symbols are appended.
     * @return The input data with EOM symbols and flush bits appended.
     * @details The EOM sequence (4B65A5B2 in hexadecimal) is appended to the data, followed by enough zero bits to flush
     *          the FEC encoder and interleaver matrices. The function calculates the number of flush bits required
     *          based on the FEC and interleaver settings.
     */
    BitStream appendEOMSymbols(const BitStream& input_data) const {
        BitStream eom_data = input_data;
        // Append the EOM sequence (4B65A5B2 in hexadecimal)
        BitStream eom_sequence({0x4B, 0x65, 0xA5, 0xB2}, 32);
        eom_data += eom_sequence;

        // Append additional zeros to flush the FEC encoder and interleaver
        size_t fec_flush_bits = 144; // FEC encoder flush bits
        size_t interleave_flush_bits = interleaver.getFlushBits();
        size_t total_flush_bits = fec_flush_bits + ((interleave_setting == 0) ? 0 : interleave_flush_bits);
        while ((eom_data.getMaxBitIndex() + total_flush_bits) % interleave_flush_bits)
            total_flush_bits++;
        
        size_t total_bytes = (total_flush_bits + 7) / 8; // Round up to ensure we have enough bytes to handle all bits.
        BitStream flush_bits(std::vector<uint8_t>(total_bytes, 0), total_flush_bits);
        eom_data += flush_bits;

        return eom_data;
    }

    std::vector<uint8_t> splitTribitSymbols(const BitStream& input_data) {
        std::vector<uint8_t> return_vector;
        size_t max_index = input_data.getMaxBitIndex();
        size_t current_index = 0;

        while (current_index + 2 < max_index) {
            uint8_t symbol = 0;
            for (int i = 0; i < 3; i++) {
                symbol = (symbol << 1) | input_data.getBitVal(current_index + i);
            }
            return_vector.push_back(symbol);
            current_index += 3;
        }

        return return_vector;
    }
};



#endif