#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <stdlib.h>
 
#define I2C_DEVICE "/dev/i2c-1"
#define SLAVE_ADDR 0x50
#define DATA_ADDR 0x54
 
// Function to write a sequence to the I2C device
int i2c_write_sequence(int file, uint8_t *sequence, uint8_t length) {
    return write(file, sequence, length);
}
 
// Function to read data from the I2C device
int i2c_read(int file, uint8_t *data, uint8_t length) {
    return read(file, data, length);
}
 
  
int main() {
    int file;
 
    // Open the I2C device
    if ((file = open(I2C_DEVICE, O_RDWR)) < 0) {
        perror("Failed to open the I2C bus");
        return 1;
    }
 
    // Set the slave address for the length command
    if (ioctl(file, I2C_SLAVE, SLAVE_ADDR) < 0) {
        perror("Failed to set slave address");
        close(file);
        return 1;
    }
 
    // Step 1: Send command to read NMEA data length
    uint8_t length_command[] = {0x08, 0x00, 0x51, 0xAA, 0x04, 0x00, 0x00, 0x00};

    usleep(10000);
 
    if (i2c_write_sequence(file, length_command, sizeof(length_command)) < 0) {
        perror("Failed to send length command 1");
        close(file);
        return 1;
    }
 
    usleep(10000);
 
    // Switch to data address
    if (ioctl(file, I2C_SLAVE, DATA_ADDR) < 0) {
        perror("Failed to set slave address for data");
        close(file);
        return 1;
    }
 
    uint8_t length_data[4];
    if (i2c_read(file, length_data, 4) < 0) {
        perror("Failed to read NMEA length");
        close(file);
        return 1;
    }
 
    usleep(10000);
 

    // Calculate the NMEA data length
  uint8_t nmea_length = (length_data[3] << 24) | (length_data[2] << 16) | (length_data[1] << 8) | length_data[0];
    printf("NMEA Data Length: %d bytes\n", nmea_length);
 
    if (nmea_length <= 0 || nmea_length > 1024) {
        fprintf(stderr, "Invalid NMEA data length.\n");
        close(file);
        return 1;
    }
 
    // Step 2: Send command to read NMEA data
   uint8_t data_command[] = {0x00, 0x20, 0x51, 0xAA, nmea_length, 0x00, 0x00, 0x00};

   if (ioctl(file, I2C_SLAVE, SLAVE_ADDR) < 0) {
        perror("Failed to set slave address");
        close(file);
        return 1;
    }

   usleep(10000);
 
    if (i2c_write_sequence(file, data_command, sizeof(data_command)) < 0) {
        perror("Failed to send data command");
        close(file);
        return 1;
    }
 
    usleep(10000);
 
    // Allocate buffer for NMEA data
    uint8_t *nmea_data = malloc(nmea_length);
    if (!nmea_data) {
        perror("Memory allocation failed");
        close(file);
        return 1;
    }
 
       
    if (ioctl(file, I2C_SLAVE, DATA_ADDR) < 0) {
        perror("Failed to set slave address for data");
        close(file);
        return 1;
    }
 
    if (i2c_read(file, nmea_data, nmea_length) < 0) {
        perror("Failed to read NMEA data");
        free(nmea_data);
        close(file);
        return 1;
    }

    usleep(10000);
 
    printf("Raw NMEA Data:\n");
    for (int i = 0; i < nmea_length; i++) {
        printf("%c", nmea_data[i]);
    }
    printf("\n");
  
    free(nmea_data);
    close(file);
    return 0;
}