#include <stdio.h>
#include <string.h>

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

#include <signal.h>
#include <poll.h>
#include <errno.h>
#include <err.h>


int main(int argc, char *argv[])
{
    if (argc == 1) {
        fprintf(stderr, "usage: reader tty-device\r\n");
        return 1;
    }

    int fd;
    struct termios tty;
    memset(&tty, 0, sizeof(tty));

    fd = open(argv[1], O_RDWR);
    if (fd <= 0) {
        err(1, "open %s", argv[1]);
    }

    if (tcgetattr(fd, &tty) != 0) {
        err(1, "tcgetattr");
    }

    tty.c_cflag &= ~PARENB; // Clear parity bit, disabling parity (most common)
    tty.c_cflag &= ~CSTOPB; // Clear stop field, only one stop bit used in communication (most common)
    tty.c_cflag |= CS8; // 8 bits per byte (most common)
    tty.c_cflag &= ~CRTSCTS; // Disable RTS/CTS hardware flow control (most common)
    tty.c_cflag |= CREAD | CLOCAL; // Turn on READ & ignore ctrl lines (CLOCAL = 1)

    tty.c_lflag &= ~ICANON;
    tty.c_lflag &= ~ECHO; // Disable echo
    tty.c_lflag &= ~ECHOE; // Disable erasure
    tty.c_lflag &= ~ECHONL; // Disable new-line echo
    tty.c_lflag &= ~ISIG; // Disable interpretation of INTR, QUIT and SUSP
    tty.c_iflag &= ~(IXON | IXOFF | IXANY); // Turn off s/w flow ctrl
    tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL); // Disable any special handling of received bytes

    tty.c_oflag &= ~OPOST;
    tty.c_oflag &= ~ONLCR;

    tty.c_cc[VTIME] = 0; // non-blocking
    tty.c_cc[VMIN] = 0;

    cfsetispeed(&tty, B115200);
    cfsetospeed(&tty, B115200);

    if (tcsetattr(fd, TCSANOW, &tty) != 0) {
        err(1, "tcsetattr");
    }

    char data[100] = { 0 };

    if (write(fd, "test\n", 5) < 0) {
        err(1, "write");
    }

    while (1) {
        struct pollfd ufds;
        ufds.fd = fd;
        ufds.events = POLLIN;

        int rc = poll(&ufds, 1, 0);
        if (rc < 0) {
            err(1, "poll");
        }
        if (rc == 0) {
            // timeout
            continue;
        }
        if (ufds.revents & POLLIN) {
            ssize_t r = read(ufds.fd, data, sizeof(data));
            if (r == -1) {
                err(1, "read");
            }
            if (rc > 0) {
                printf("read %d bytes\n");
            }
        }
    }
}