#include <sys/ioctl.h>
#include <sys/poll.h>
#include <asm/termbits.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>

#include <iostream>
#include <vector>
#include <cstring>
#include <atomic>
#include <span>
#include <time.h>

/**
 * Вспомогательная функция для получения текущего времени в миллисекундах
 */
inline int64_t milliseconds() {
    timespec ts{};
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return static_cast<int64_t>(ts.tv_sec) * 1000 + static_cast<int64_t>(ts.tv_nsec) / 1000000;
}

constexpr int64_t SBUS_SEND_FRAME_INTERVAL = 50;
constexpr int64_t SBUS_RXLOSS_INTERVAL = 500;

class UDPServer {
public:
    int sockfd;
    sockaddr_in server_addr, client_addr;
    socklen_t client_len;

    UDPServer(uint16_t port) : client_len(sizeof(client_addr)) {
        // Создание UDP сокета
        sockfd = socket(AF_INET, SOCK_DGRAM, 0);
        if (sockfd < 0) {
            throw std::runtime_error("Failed to create socket");
        }

        // Настройка адреса сервера
        memset(&server_addr, 0, sizeof(server_addr));
        server_addr.sin_family = AF_INET;
        server_addr.sin_addr.s_addr = INADDR_ANY;
        server_addr.sin_port = htons(port);

        // Привязка сокета
        if (bind(sockfd, (sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
            close(sockfd);
            throw std::runtime_error("Failed to bind socket");
        }

        std::cout << "UDP server listening on port " << port << std::endl;
    }

    ~UDPServer() {
        if (sockfd >= 0) {
            close(sockfd);
        }
    }

    std::vector<uint16_t> receive() {
        std::vector<uint16_t> data(64);

        ssize_t received = recvfrom(sockfd,
                                   data.data(),
                                   data.size() * sizeof(uint16_t),
                                   MSG_DONTWAIT, // Неблокирующий режим
                                   (sockaddr*)&client_addr,
                                   &client_len);

        if (received > 0) {
            // Выводим информацию о отправителе и данные
            data.resize(received / 2);
            char client_ip[INET_ADDRSTRLEN];
            inet_ntop(AF_INET, &client_addr.sin_addr, client_ip, INET_ADDRSTRLEN);
            // std::cout << "Received data from " << client_ip << ":" << ntohs(client_addr.sin_port) << std::endl;

            // std::cout << "Data: ";
            // for (int i = 0; i < 4 && i < data.size(); ++i) {
            //     std::cout << data[i] << " ";
            // }
            // std::cout << "..." << std::endl;

            return data;
        }

        return {};
    }
};

struct SbusData {
    bool lost_frame = false;
    bool failsafe = false;
    bool ch17 = false, ch18 = false;
    static constexpr size_t NUM_CH = 18;
    static constexpr int16_t SBUS_CH_MIN = 173 + 20;
    static constexpr int16_t SBUS_CH_MAX = 1812 - 20;
    int16_t ch[NUM_CH];

    /* Message len */
    static constexpr int8_t BUF_LEN_ = 25;
    /* SBUS message defs */
    static constexpr int8_t NUM_SBUS_CH_ = 16;
    static constexpr uint8_t HEADER_ = 0x0F;
    static constexpr uint8_t FOOTER_ = 0x00;
    static constexpr uint8_t FOOTER2_ = 0x04;
    static constexpr uint8_t CH17_MASK_ = 0x01;
    static constexpr uint8_t CH18_MASK_ = 0x02;
    static constexpr uint8_t LOST_FRAME_MASK_ = 0x04;
    static constexpr uint8_t FAILSAFE_MASK_ = 0x08;
    uint8_t binaryBuffer[25];

    typedef struct sbusChannels_s {
        // 176 bits of data (11 bits per channel * 16 channels) = 22 bytes.
        unsigned int chan0 : 11;
        unsigned int chan1 : 11;
        unsigned int chan2 : 11;
        unsigned int chan3 : 11;
        unsigned int chan4 : 11;
        unsigned int chan5 : 11;
        unsigned int chan6 : 11;
        unsigned int chan7 : 11;
        unsigned int chan8 : 11;
        unsigned int chan9 : 11;
        unsigned int chan10 : 11;
        unsigned int chan11 : 11;
        unsigned int chan12 : 11;
        unsigned int chan13 : 11;
        unsigned int chan14 : 11;
        unsigned int chan15 : 11;
    } __attribute__((__packed__)) sbusChannels_t;
    static_assert(sizeof(sbusChannels_s) == 22);
    struct sbusFrame_s {
        uint8_t syncByte = HEADER_;
        sbusChannels_t channels{};
        uint8_t flags{};
        /**
         * The endByte is 0x00 on FrSky and some futaba RX's, on Some SBUS2 RX's the value indicates the telemetry byte that is sent after every 4th sbus frame.
         *
         * See https://github.com/cleanflight/cleanflight/issues/590#issuecomment-101027349
         * and
         * https://github.com/cleanflight/cleanflight/issues/590#issuecomment-101706023
         */
        uint8_t endByte = FOOTER_;
    } __attribute__ ((__packed__));
    static_assert(sizeof(sbusFrame_s) == sizeof(binaryBuffer));

    void fillDataBuf() {
        auto* dest = reinterpret_cast<sbusFrame_s*>(binaryBuffer);
        dest->syncByte = HEADER_;
        dest->channels.chan0 = std::min(std::max(ch[0], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan1 = std::min(std::max(ch[1], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan2 = std::min(std::max(ch[2], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan3 = std::min(std::max(ch[3], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan4 = std::min(std::max(ch[4], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan5 = std::min(std::max(ch[5], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan6 = std::min(std::max(ch[6], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan7 = std::min(std::max(ch[7], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan8 = std::min(std::max(ch[8], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan9 = std::min(std::max(ch[9], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan10 = std::min(std::max(ch[10], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan11 = std::min(std::max(ch[11], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan12 = std::min(std::max(ch[12], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan13 = std::min(std::max(ch[13], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan14 = std::min(std::max(ch[14], SBUS_CH_MIN), SBUS_CH_MAX);
        dest->channels.chan15 = std::min(std::max(ch[15], SBUS_CH_MIN), SBUS_CH_MAX);

        dest->flags = 0;
        if (ch[16] >= (SBUS_CH_MAX + SBUS_CH_MAX) / 2) { dest->flags |= CH17_MASK_; }
        if (ch[17] >= (SBUS_CH_MAX + SBUS_CH_MAX) / 2) { dest->flags |= CH18_MASK_; }

        dest->endByte = FOOTER_;
    }

};

class SerialPort {
    int fd;

public:
    SerialPort() : fd(-1) {}

    bool open(const std::string& port_path) {
        // Открытие последовательного порта
        fd = ::open(port_path.c_str(), O_RDWR | O_NOCTTY | O_SYNC);
        if (fd < 0) {
            std::cout << "Failed to open serial port " << port_path << ": " << std::strerror(errno) << std::endl;
            return false;
        }
        struct termios2 tio{};
        ioctl(fd, TCGETS2, &tio);
        // 8bit
        tio.c_cflag &= ~CSIZE;
        tio.c_cflag |= CS8;
        // even
        tio.c_cflag &= ~(PARODD | CMSPAR);
        tio.c_cflag |= PARENB;
        // 2 stop bits
        tio.c_cflag |= CSTOPB;
        // baud rate
        tio.c_ispeed = 100000;
        tio.c_ospeed = 100000;
        // other
        tio.c_iflag |= (INPCK|IGNBRK|IGNCR|ISTRIP);
        tio.c_cflag &= ~CBAUD;
        tio.c_cflag |= (BOTHER|CREAD|CLOCAL);

        if (ioctl(fd, TCSETS2, &tio) != 0) {
            std::cout << "Failed to set termios2 attributes: " << std::strerror(errno) << std::endl;
            close(fd);
            return false;
        }

        std::cout << "Serial port " << port_path << " opened and configured: 100000 baud, 8E2" << std::endl;
        return true;
    }

    ~SerialPort() {
        _close();
    }

    void _close() {
        if (fd >= 0) {
            ::close(fd);
            fd = -1;
        }
    }

    // Метод для получения файлового дескриптора порта
    int getDescriptor() const {
        return fd;
    }

    int drain() {
        int ret;
        do {
            ret = ioctl(fd, TCSBRK, 1);
        } while (ret < 0 && errno == EINTR);

        return ret;
    }

    // Метод для записи данных в порт
    bool writeBuffer(std::span<const uint8_t> data) {
        if (fd < 0) return false;

        ssize_t written = write(fd, data.data(), data.size());
        if (written < 0) {
            std::cout << "Failed to write to serial port " << strerror(errno) << std::endl;
            return false;
        }

        // Принудительная отправка данных
        if (drain() < 0) {
            std::cout << "Failed to flush data to serial port" << strerror(errno) << std::endl;
            return false;
        }
        return true;
    }
};

int main(int argc, char* argv[]) {
    // Парсим аргументы командной строки
    std::string serial_port = "/dev/ttyPS0";
    if (argc > 1) {
        serial_port = argv[1];
    }

    try {
        // Создание UDP сервера
        UDPServer udp_server(1066);

        // Открытие последовательного порта
        SerialPort serial;
        if (!serial.open(serial_port)) {
            return 1;
        }

        std::cout << "Ready to receive UDP packets and forward to serial port" << std::endl;
        std::cout << "Press Ctrl+C to exit" << std::endl;

        SbusData sb{};
        int64_t lastSbusWrite = 0;
        int64_t lastSbusRecv = 0;

        int packetCount = 0;
        int totalPacketCount = 0;
        int serialErrors = 0;
        int64_t lastStatisticsShow = milliseconds();
        int64_t _lastLoopNow = lastStatisticsShow;
        while (true) {
            pollfd udpFd{.fd = udp_server.sockfd, .events = POLLIN, .revents = 0};
            poll(&udpFd, 1, SBUS_SEND_FRAME_INTERVAL / 4);
            auto now = milliseconds();
            if (std::abs(now - _lastLoopNow) > SBUS_SEND_FRAME_INTERVAL) {
                std::cout << "Warning: Loop freeze, reset timers. now time:" << now << std::endl;
                lastSbusWrite = 0;
                lastSbusRecv = 0;
                lastStatisticsShow = 0;
            }
            _lastLoopNow = now;

            if (udpFd.revents & POLLIN) {
                // Прием UDP пакета
                std::vector<uint16_t> data = udp_server.receive();
                lastSbusRecv = now;

                if (!data.empty()) {
                    packetCount++;

                    for (int i = 0; i < SbusData::NUM_CH; ++i) {
                        auto item = i < data.size() ? static_cast<double>(data[i]) : 1500.0;
                        item -= 1000.0;
                        item = std::min(item, 1000.0);
                        item = std::max(item, 0.0);
                        item *= (SbusData::SBUS_CH_MAX - SbusData::SBUS_CH_MIN) / 1000.0;
                        item += SbusData::SBUS_CH_MIN;

                        sb.ch[i] = static_cast<int16_t>(item);
                        if (sb.ch[i] < SbusData::SBUS_CH_MIN) {
                            sb.ch[i] = SbusData::SBUS_CH_MIN; // минимальное число
                        } else if (sb.ch[i] > SbusData::SBUS_CH_MAX) {
                            sb.ch[i] = SbusData::SBUS_CH_MAX; // максимальное число
                        }
                    }
                    sb.fillDataBuf();
                }
            }

            // std::cout << "from loop: current time " << now << std::endl;
            if (now - lastSbusWrite >= SBUS_SEND_FRAME_INTERVAL && now - lastSbusRecv <= SBUS_RXLOSS_INTERVAL) {
                lastSbusWrite = now;
                if (!serial.writeBuffer(sb.binaryBuffer)) {
                    serialErrors++;
                } else {
                    serialErrors = 0;
                }

                // после 50 ошибок дальше не будем пытаться что-то писать, ибо это бесполезно
                if (serialErrors >= 50) {
                    std::cout << "FATAL: 50 errors on serial port write operation, exit" << std::endl;
                    break;
                }
            }

            if (now - lastStatisticsShow >= 1000) {
                lastStatisticsShow = now;
                totalPacketCount += packetCount;
                std::cout << "Received " << totalPacketCount << " packets total, " << packetCount << " in last second" << std::endl;
                packetCount = 0;
            }
        }

    } catch (const std::exception& e) {
        std::cout << "Error: " << e.what() << std::endl;
        return 1;
    }

    std::cout << "Exiting..." << std::endl;
    return 0;
}