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

#define _GNU_SOURCE 1

#include <libbasis/misc.h>
#include <libbasis/term.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <spawn.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <termios.h>
#include <unistd.h>

#include <linux/if_ppp.h>

#define PPP_DEV "/dev/ppp"

extern char **environ;

int main(int argc, char *argv[]) {
	const char *usage =
		"usage: pppdlite TTY [PROG...]\n"
		"\n"
		"Options:\n"
		"\n"
		"    -h          Print this help text.\n"
		"    -s BAUDRATE Configure the TTY to use this baudrate. (Default: 115200)\n"
		"\n"
		"Initialize and hold open a PPP connection on TTY with the baudrate\n"
		"BAUDRATE.\n"
		"If [PROG...] is specified it is executed once the connection is initialized\n"
		"with the environment variable PPPDLITE_IFNAME set to the interface name\n"
		"of the newly created network interface.";

	int tty_fd, ppp_ch_fd, ppp_unit_fd;
	int ppp_disc = N_PPP;
	int ch_idx;
	int unit = -1;
	const char *tty;
	speed_t speed = B115200;
	int opt, rv;

	while ((opt = getopt(argc, argv, "hs:")) > 0) {
		switch (opt) {
		case 'h':
			fprintf(stderr, "%s\n", usage);
			exit(0);
			break;
		case 's':
			if (term_speed_parse(optarg, &speed) < 0)
				errx(EXIT_FAIL_USAGE,
				     "fatal: unable to parse the command line: unknown argument to -s: %s\n%s",
				     optarg, usage);
			break;
		default:
			errx(EXIT_FAIL_USAGE,
			     "fatal: unable to parse the command line: unknown option: '%c'\n%s",
			     opt, usage);
			break;
		}
	}

	argv += optind;
	argc -= optind;

	if (argc < 1) {
		errx(EXIT_FAIL_USAGE,
		     "fatal: unable to parse the command line: not enough arguments\n%s",
		     usage);
	}

	tty = argv[0];

	argv += 1;
	argc -= 1;

	/* 1. tty */
	tty_fd = open(tty, O_RDWR|O_CLOEXEC);
	if (tty_fd < 0)
		err(EXIT_FAIL_USAGE, "fatal: unable to open %s", tty);

	/* set exclusive mode */
	if (ioctl(tty_fd, TIOCEXCL, 0) < 0 && errno != EIO)
		err(EXIT_FAIL_USAGE, "fatal: unable to open %s exclusively",
		    tty);

	/* tty setting */
	if (term_setconf_init() < 0 ||
	    term_setconf_raw(tty_fd, speed) < 0)
		err(EXIT_FAIL_MISC, "fatal: unable to configure the terminal");

	/* set tty to ppp line discipline */
	if (ioctl(tty_fd, TIOCSETD, &ppp_disc))
		err(EXIT_FAIL_MISC,
		    "fatal: unable to enable the PPP line discipline on %s",
		    tty);

	/* get channel index */
	if (ioctl(tty_fd, PPPIOCGCHAN, &ch_idx) < 0)
		err(EXIT_FAIL_MISC,
		    "fatal: unable to get a PPP channel index from %s", tty);

	/* 2. ppp channel */
	ppp_ch_fd = open(PPP_DEV, O_RDWR);
	if (ppp_ch_fd < 0)
		err(EXIT_FAIL_MISC, "fatal: unable to open %s", PPP_DEV);

	/* connect attach tty to channel */
	if (ioctl(ppp_ch_fd, PPPIOCATTCHAN, &ch_idx) < 0)
		err(EXIT_FAIL_MISC,
		    "fatal: unable to attach %s to the ppp channel", tty);

	/* 3. ppp unit */
	ppp_unit_fd = open(PPP_DEV, O_RDWR);
	if (ppp_unit_fd < 0)
		err(EXIT_FAIL_MISC, "fatal: unable to open %s", PPP_DEV);

	if (ioctl(ppp_unit_fd, PPPIOCNEWUNIT, &unit) < 0)
		err(EXIT_FAIL_MISC,
		    "fatal: unable to create a new PPP instance");

	/* connect ppp channel to ppp unit */
	if (ioctl(ppp_ch_fd, PPPIOCCONNECT, &unit) < 0)
		err(EXIT_FAIL_MISC,
		    "fatal: unable to connect the PPP channel to the PPP unit");

	if (argc) {
		char ifname[IFNAMSIZ];
		pid_t pid;
		int status;

		rv = snprintf(ifname, sizeof(ifname), "ppp%d", unit);
		if (rv < 0)
			err(EXIT_FAIL_MISC, "fatal: unable to set $PPPDLITE_IFNAME");
		if ((size_t)rv >= sizeof(ifname))
			errx(EXIT_FAIL_MISC, "fatal: unable to set $PPPDLITE_IFNAME: the name ppp%d is too long", unit);
		if (setenv("PPPDLITE_IFNAME", ifname, 1) < 0)
			err(EXIT_FAIL_MISC, "fatal: unable to set $PPPDLITE_IFNAME");

		errno = posix_spawnp(&pid, argv[0], NULL, NULL, argv, environ);
		if (errno)
			err(EXIT_FAIL_MISC, "fatal: unable to spawn %s", argv[0]);

		if (waitpid(pid, &status, 0) < 0)
			err(EXIT_FAIL_MISC, "fatal: unable to wait on a child process");

		if (WIFEXITED(status)) {
			if (WEXITSTATUS(status))
				errx(EXIT_FAIL_MISC, "fatal: unable to run %s: the subprocess returned %d",
				     argv[0], WEXITSTATUS(status));
		} else if (WIFSIGNALED(status)) {
			errx(EXIT_FAIL_MISC, "fatal: unable to run %s: the subprocess was killed by signal %d",
			     argv[0], WTERMSIG(status));
		} else {
			errx(EXIT_FAIL_MISC, "fatal: unable to run %s: the subprocess died with status %d",
			     argv[0], status);
		}
	}

	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;
}