// gps.hpp — u-blox NMEA GPS reader over UART
// No external libs; uses POSIX termios + read().
//
// Hardware pins (THE TRUTH):
//   GPIO14/TXD0 → UBLOX_TX line  (/dev/serial0)
//   GPIO15/RXD0 → UBLOX_RX line
//   Default baud: 9600
//
// Enable UART: sudo raspi-config → Interfaces → Serial Port
//   "login shell over serial" = No, "serial port hardware" = Yes
#pragma once

#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>

#include <fcntl.h>
#include <termios.h>
#include <unistd.h>

namespace gps {

struct Fix {
    bool   valid = false;
    double lat   = 0.0; // degrees, positive=N
    double lon   = 0.0; // degrees, positive=E
    float  speed_knots = 0.0f;
    char   time[12]{}; // HHMMSS.ss (raw NMEA)
    char   date[7]{};  // DDMMYY
};

class Reader {
public:
    bool begin(const char *dev = "/dev/serial0", int baud = 9600);
    void end();

    // Read one NMEA sentence into buf (null-terminated). Returns false on error.
    bool readLine(char *buf, size_t cap);

    // Parse $GPRMC or $GNRMC from a sentence. Returns false if sentence is
    // not RMC or position is invalid.
    static bool parseRmc(const char *sentence, Fix &fix);

private:
    int fd_ = -1;
};

inline bool Reader::begin(const char *dev, int baud)
{
    fd_ = ::open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd_ < 0) return false;
    ::fcntl(fd_, F_SETFL, 0); // blocking

    termios t{};
    if (tcgetattr(fd_, &t) < 0) return false;

    speed_t spd;
    switch (baud) {
        case 4800:  spd = B4800;  break;
        case 9600:  spd = B9600;  break;
        case 19200: spd = B19200; break;
        case 38400: spd = B38400; break;
        case 57600: spd = B57600; break;
        default:    spd = B9600;
    }
    cfsetispeed(&t, spd);
    cfsetospeed(&t, spd);
    cfmakeraw(&t);
    t.c_cc[VMIN]  = 1;
    t.c_cc[VTIME] = 0;
    tcsetattr(fd_, TCSANOW, &t);
    return true;
}

inline void Reader::end()
{
    if (fd_ >= 0) { ::close(fd_); fd_ = -1; }
}

inline bool Reader::readLine(char *buf, size_t cap)
{
    size_t n = 0;
    char   c;
    // Wait for '$' (start of NMEA sentence)
    do {
        if (::read(fd_, &c, 1) != 1) return false;
    } while (c != '$');
    buf[n++] = '$';

    while (n < cap - 1) {
        if (::read(fd_, &c, 1) != 1) return false;
        buf[n++] = c;
        if (c == '\n') break;
    }
    buf[n] = '\0';
    return true;
}

// Parse $GPRMC or $GNRMC
// Format: $GNRMC,HHMMSS.ss,A,DDMM.MMMM,N,DDDMM.MMMM,E,spd,crs,DDMMYY,...
inline bool Reader::parseRmc(const char *sentence, Fix &fix)
{
    if (!sentence) return false;

    // Check sentence type
    if (std::strncmp(sentence, "$GPRMC", 6) != 0 &&
        std::strncmp(sentence, "$GNRMC", 6) != 0)
        return false;

    // Make a mutable copy
    char buf[128];
    std::strncpy(buf, sentence, sizeof(buf) - 1);
    buf[sizeof(buf) - 1] = '\0';

    // Tokenize on commas
    const char *fields[13]{};
    int         nf = 0;
    char       *p  = buf;
    while (*p && nf < 13) {
        fields[nf++] = p;
        char *next = std::strchr(p, ',');
        if (!next) break;
        *next = '\0';
        p     = next + 1;
    }
    if (nf < 10) return false;

    // field[2] = status ('A'=valid, 'V'=void)
    if (fields[2][0] != 'A') { fix.valid = false; return false; }

    // field[1] = time
    std::strncpy(fix.time, fields[1], sizeof(fix.time) - 1);

    // field[3] = lat DDMM.MMMM, field[4] = N/S
    double raw_lat = std::atof(fields[3]);
    int    lat_deg = (int)(raw_lat / 100.0);
    double lat_min = raw_lat - lat_deg * 100.0;
    fix.lat = lat_deg + lat_min / 60.0;
    if (fields[4][0] == 'S') fix.lat = -fix.lat;

    // field[5] = lon DDDMM.MMMM, field[6] = E/W
    double raw_lon = std::atof(fields[5]);
    int    lon_deg = (int)(raw_lon / 100.0);
    double lon_min = raw_lon - lon_deg * 100.0;
    fix.lon = lon_deg + lon_min / 60.0;
    if (fields[6][0] == 'W') fix.lon = -fix.lon;

    fix.speed_knots = (float)std::atof(fields[7]);

    // field[9] = date DDMMYY
    std::strncpy(fix.date, fields[9], sizeof(fix.date) - 1);

    fix.valid = true;
    return true;
}

} // namespace gps