#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include <errno.h>
#include <sys/signal.h>
#include <sys/types.h>

#define SUCCESS 0
#define ERROR_ARGS 1
#define ERROR_DEV 2
#define ERROR_CONN 3

long getbaudrate(int rate) {
	switch (rate) {
		case 115200: return B115200;
		case 57600:  return B57600;
		case 38400:  return B38400;
		case 19200:  return B19200;
		case 9600:   return B9600;
		case 2400:   return B2400;
		case 1800:   return B1800;
		case 1200:   return B1200;
		case 600:    return B600;
		case 300:    return B300;
		case 200:    return B200;
		default:
			fprintf(stderr, "Unsupported baudrate %d\n", rate);
			exit(ERROR_ARGS);
	}
}

int main(int argc, char **argv) {
	if (argc != 3) {
		printf("Usage: %s device speed\n", argv[0]);
		exit(ERROR_ARGS);
	}
	
	long ratebyte = getbaudrate(atoi(argv[2]));
	
	int fd;
	
	fd = open(argv[1], O_RDWR | O_NOCTTY | O_NONBLOCK);
	
	if (fd < 0) {
		perror(argv[1]);
		exit(ERROR_DEV);
	}
	
	struct termios attr;

	tcgetattr(fd, &attr);
	attr.c_cflag |= CLOCAL | CS8 | ratebyte;
	tcflush(fd, TCIOFLUSH);
	tcsetattr(fd, TCSANOW, &attr);
	
	write(fd, "AT\r\n", 4);
	
	int state = 0;
	int endtime = time(NULL) + 2;
	
	while (time(NULL) < endtime) {
		usleep(100000);
		
		char buf;
		int count;
		count = read(fd, &buf, 1);
		
		if (count == 0 || (count == -1 && errno == EAGAIN))
			continue;
		
		if (count == -1) {
			perror(argv[1]);
			close(fd);
			exit(ERROR_DEV);
		}
		
		if (count == 1) {
			if (state == 0 && buf == 'O') {
				state = 1;
			} else if (state == 1 && buf == 'K') {
				close(fd);
				exit(SUCCESS);
			} else if (state == 1) {
				state = 0;
			}
		}
	}
	
	close(fd);
	exit(ERROR_CONN);
}