comm_drv_n0183.cpp

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/**************************************************************************
 *   Copyright (C) 2022 David Register                                     *
 *   Copyright (C) 2022 - 2025  Alec Leamas                                *
 *                                                                         *
 *   This program 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 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program 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 this program; if not, see <https://www.gnu.org/licenses/>. *
 **************************************************************************/
 
// For compilers that support precompilation, includes "wx.h".
#include <wx/wxprec.h>
#ifndef WX_PRECOMP
#include <wx/wx.h>
#endif
 
#include "model/comm_drv_n0183.h"
 
static bool Is0183ChecksumOk(const std::string& sentence) {
  const size_t cs_start = sentence.find('*');
  if (cs_start == std::string::npos || cs_start > sentence.size() - 3)
    return false;  // Not found, or didn't have 2 characters following it.
 
  const std::string cs_str = sentence.substr(cs_start + 1, 2);
  const unsigned long checksum = strtol(cs_str.c_str(), nullptr, 16);
  if (checksum == 0L && cs_str != "00") return false;
 
  unsigned char calculated_checksum = 0;
  for (const char c : sentence.substr(1, cs_start - 1))
    calculated_checksum ^= static_cast<unsigned char>(c);
  return calculated_checksum == checksum;
}
 
static std::string GetPayloadSentence(const std::string& sentence) {
  size_t start_pos = sentence.find('$');
  if (start_pos == std::string::npos) start_pos = sentence.find('!');
  if (start_pos == std::string::npos) return "";
  if (sentence.size() < start_pos + 6) return "";
  return sentence.substr(start_pos);
}
 
CommDriverN0183::CommDriverN0183() : AbstractCommDriver(NavAddr::Bus::N0183) {}
 
CommDriverN0183::CommDriverN0183(NavAddr::Bus, const std::string& s)
    : AbstractCommDriver(NavAddr::Bus::N0183, s) {}
 
CommDriverN0183::~CommDriverN0183() = default;
 
void CommDriverN0183::SendToListener(const std::string& payload,
                                     DriverListener& listener,
                                     const ConnectionParams& params) {
  const std::string sentence = GetPayloadSentence(payload);
  if (sentence.empty()) return;
  assert(sentence[0] == '$' || sentence[0] == '!');
  assert(sentence.size() >= 6);
 
  const bool is_garbage =
      sentence.size() > 128 ||
      std::any_of(sentence.begin(), sentence.end(),
                  [](char c) { return !isprint(c) && c != '\n' && c != '\r'; });
  const bool has_checksum =
      sentence.find('*', sentence.size() - 6) != std::string::npos;
 
  NavMsg::State state;
  if (is_garbage)
    state = NavMsg::State::kCannotParse;
  else if (!params.SentencePassesFilter(sentence, FILTER_INPUT))
    state = NavMsg::State::kFiltered;
  else if (has_checksum && !Is0183ChecksumOk(sentence))
    state = NavMsg::State::kBadChecksum;
  else
    state = NavMsg::State::kOk;
 
  if (is_garbage) {
    auto msg = std::make_shared<const Nmea0183Msg>("TRASH", payload,
                                                   GetAddress(), state);
    listener.Notify(std::move(msg));
  } else {
    // We notify based on full message, including the Talker ID
    const std::string id = sentence.substr(1, 5);
    auto msg =
        std::make_shared<const Nmea0183Msg>(id, sentence, GetAddress(), state);
    listener.Notify(std::move(msg));
  }
}