/* SPDX-License-Identifier: GPL-2.0 */

#define _GNU_SOURCE 1
#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <termios.h>
#include <unistd.h>

#include <linux/if_ppp.h>

#define PPP_DEV "/dev/ppp"

int main(int argc, char *argv[]) {
	int tty_fd, ppp_ch_fd, ppp_unit_fd;
	int ppp_disc = N_PPP;
	int ch_idx;
	int unit = -1;
	int flags;
	struct termios termios;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s <tty>\n", argv[0]);
		return 1;
	}

	/* 1. tty */
	tty_fd = open(argv[1], O_RDWR);
	if (tty_fd < 0) {
		perror("open(tty_fd)");
		return 1;
	}

	/* set exclusive mode */
	if (ioctl(tty_fd, TIOCEXCL, 0) < 0 && errno != EIO) {
		perror("ioctl(tty_fd, TIOCEXCL)");
		return 1;
	}

	/* tty setting */
	if (tcgetattr(tty_fd, &termios) < 0) {
		perror("tcgetattr(tty_fd)");
		return 1;
	}
	/* now hardware flow control */
	termios.c_cflag &= ~CRTSCTS;
	/* increase speed */
	cfsetspeed(&termios, B460800);
	/* applay changed values */
	if (tcsetattr(tty_fd, TCSANOW, &termios) < 0) {
		perror("tcsetattr(tty_fd)");
		return 1;
	}

	/* set tty to ppp line discipline */
	if (ioctl(tty_fd, TIOCSETD, &ppp_disc)) {
		perror("ioctl(tty_fd, TIOCSETD)");
		return 1;
	}
	/* get channel index */
	if (ioctl(tty_fd, PPPIOCGCHAN, &ch_idx) < 0) {
		perror("ioctl(tty_fd, PPPIOCGCHAN)");
		return 1;
	}

	/* 2. ppp channel */
	ppp_ch_fd = open(PPP_DEV, O_RDWR);
	if (ppp_ch_fd < 0) {
		perror("open(ppp_ch_fd)");
		return 1;
	}
	/* connect attach tty to channel */
	if (ioctl(ppp_ch_fd, PPPIOCATTCHAN, &ch_idx) < 0) {
		perror("ioctl(ppp_ch_fd, PPPIOCATTCHAN)");
		return 1;
	}

	/* 3. ppp unit */
	ppp_unit_fd = open(PPP_DEV, O_RDWR);
	if (ppp_unit_fd < 0) {
		perror("open(ppp_unit_fd)");
		return 1;
	}
	if (ioctl(ppp_unit_fd, PPPIOCNEWUNIT, &unit) < 0) {
		perror("ioctl(ppp_unit_fd, PPPIOCNEWUNIT)");
		return 1;
	}
	/* connect ppp channel to ppp unit */
	if (ioctl(ppp_ch_fd, PPPIOCCONNECT, &unit) < 0) {
		perror("ioctl(ppp_ch_fd, PPPIOCATTCHAN)");
		return 1;
	}

	for (;;) {
		uint8_t buf[2048];
		long i;
		long len = read(ppp_unit_fd, buf, sizeof(buf));

		if (len < 0)
			break;

		printf("rx: len %ld", len);
		for (i = 0; i < len; i++) {
			switch (i % 16) {
			case 0:
				printf("\n");
				break;
			case 4:
			case 8:
			case 12:
				printf(" ");
				break;
			}
			printf("%02x", buf[i]);
		}
		printf("\n");
	}

	return 0;
}