#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 5005
#define BUF_SIZE 512

double nmea_to_decimal(const char *nmea, char direction) {
    double val = atof(nmea);
    int deg = (int)(val / 100);
    double min = val - deg * 100;
    double dec = deg + min / 60.0;
    if (direction == 'S' || direction == 'W') dec = -dec;
    return dec;
}

int main() {
    int sockfd;
    struct sockaddr_in server_addr, client_addr;
    char buffer[BUF_SIZE];

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) { perror("socket failed"); return 1; }

    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);

    if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind failed"); return 1;
    }

    printf("Listening on UDP port %d...\n", PORT);

    while (1) {
        socklen_t addr_len = sizeof(client_addr);
        int n = recvfrom(sockfd, buffer, BUF_SIZE - 1, 0, (struct sockaddr *)&client_addr, &addr_len);
        if (n < 0) { perror("recvfrom failed"); break; }
        buffer[n] = '\0';

        char *line = strtok(buffer, "\n");
        while (line != NULL) {
            if (strncmp(line, "$GPGGA", 6) == 0) {
                char *tokens[15];
                char *ptr = strtok(line, ",");
                int i = 0;
                while (ptr != NULL && i < 15) {
                    tokens[i++] = ptr;
                    ptr = strtok(NULL, ",");
                }

                if (i >= 7 && atoi(tokens[6]) > 0) { // fix quality > 0
                    double lat = nmea_to_decimal(tokens[2], tokens[3][0]);
                    double lon = nmea_to_decimal(tokens[4], tokens[5][0]);
                    double alt = atof(tokens[9]);
                    printf("Latitude: %.6f | Longitude: %.6f | Altitude: %.2f m | Fix: %s\n",
                        lat, lon, alt, tokens[6]);
                } else {
                    printf("No valid fix yet.\n");
                }
            }
            line = strtok(NULL, "\n");
        }
    }

    close(sockfd);
    return 0;
}