/**
 * Copyright © 2015  Mattias Andrée <maandree@member.fsf.org>
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */
#include <unistd.h>
#include <errno.h>
#include <pwd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/file.h>

#include "daemonise.h"
#include "common.h"



/**
 * The size of the backlog on the socket.
 */
#ifndef SATD_BACKLOG
# define SATD_BACKLOG  5
#endif



COMMAND("satd")
USAGE("[-f]")



/**
 * Create the socket.
 * 
 * @param   address  Output parameter for the socket address.
 * @return           The file descriptor for the socket, -1 on error.
 */
static int
create_socket(struct sockaddr_un *address)
{
	int fd = -1, bound = 0;
	ssize_t len;
	char *dir;
	int saved_errno;

	/* Get socket address. */
	dir = getenv("XDG_RUNTIME_DIR"), dir = (dir ? dir : "/run");
	t (snprintf(NULL, 0, "%s/satd.socket%zn", dir, &len) == -1);
	if ((len < 0) || ((size_t)len >= sizeof(address->sun_path)))
		t ((errno = ENAMETOOLONG));
	sprintf(address->sun_path, "%s/satd.socket", dir);
	address->sun_family = AF_UNIX;

	/* Check that no living process owns the socket. */
	fd = open(address->sun_path, O_RDONLY);
	if (fd == -1) {
		t (errno != ENOENT);
		goto does_not_exist;
	} else {
		if (flock(fd, LOCK_EX | LOCK_NB) == -1) {
			t (errno != EWOULDBLOCK);
			fprintf(stderr, "%s: the daemon's socket file is already in use.\n", argv0);
			errno = 0;
			goto fail;
		}
		flock(fd, LOCK_UN);
		close(fd), fd = -1;
	}

	/* Create socket. */
	unlink(address->sun_path);
does_not_exist:
	t ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) == -1);
	t (fchmod(fd, S_IRWXU) == -1);
	t (fchown(fd, getuid(), getgid()) == -1);
	t (bind(fd, (struct sockaddr *)address, sizeof(*address)) == -1);
	/* EADDRINUSE just means that the file already exists, not that it is actually used. */
	bound = 1;

	/* Mark the socket as owned by a living process. */
	t (flock(fd, LOCK_SH));

	return fd;
fail:
	saved_errno = errno;
	if (fd >= 0)
		close(fd);
	if (bound)
		unlink(address->sun_path);
	errno = saved_errno;
	return -1;
}


/**
 * Construct the pathname for the hook script.
 * 
 * @param   env     The environment variable to use for the beginning
 *                  of the pathname, `NULL` for the home directory.
 * @param   suffix  The rest of the pathname.
 * @return          The pathname.
 * 
 * @throws  0  The environment variable is not set, or, if `env` is
 *             `NULL` the user is root or homeless.
 */
static char *
hookpath(const char *env, const char *suffix)
{
	const char *prefix = NULL;
	char *path;
	struct passwd *pwd;

	if (!env) {
		if (!getuid())
			goto try_next;
		pwd = getpwuid(getuid());
		prefix = pwd ? pwd->pw_dir : NULL;
	} else {
		prefix = getenv(env);
	}
	if (!prefix || !*prefix)
		goto try_next;

	path = malloc((strlen(prefix) + strlen(suffix) + 1) * sizeof(char));
	t (!path);
	stpcpy(stpcpy(path, prefix), suffix);

	return path;
fail:
	return NULL;
try_next:
	return errno = 0, NULL;
}


/**
 * Duplicate a file descriptor, and
 * open /dev/null to the old file descriptor.
 * However, if `old` is 3 or greater, it will
 * be closed rather than /dev/null.
 * 
 * @param   old  The old file descriptor.
 * @param   new  The new file descriptor.
 * @return       `new`, -1 on error.
 */
static int
dup2_and_null(int old, int new)
{
	int want, fd = -1;
	int saved_errno;

	if (old != new) {
		t (dup2(old, new) == -1);
		close(old), want = old;
		if (want < 3) {
			fd = open("/dev/null", O_RDWR);
			t (fd == -1);
			if (fd != want) {
				t (dup2(fd, want) == -1);
				close(fd), fd = -1;
			}
		}
	}

	return new;
fail:
	saved_errno = errno;
	if (fd >= 0)
		close(fd);
	errno = saved_errno;
	return -1;
}


/**
 * The sat daemon initialisation.
 * 
 * @param   argc  Any value in [0, 2] is accepted.
 * @param   argv  The name of the process, and -f if the process
 *                shall not be daemonised.
 * @return  0     The process was successful.
 * @return  1     The process failed queuing the job.
 * @return  2     User error, you do not know what you are doing.
 */
int
main(int argc, char *argv[])
{
	struct sockaddr_un address;
	int sock = -1, state = -1, foreground = 0;
	struct stat attr;
	char *path = NULL;
	char *dir;
	ssize_t len;

	/* Parse command line. */
	if (argc > 0)  argv0 = argv[0];
	if (argc > 2)  usage();
	if (argc == 2)
		if (!(foreground = !strcmp(argv[1], "-f")))
			usage();

	/* Get hook-script pathname. */
	if (!getenv("SAT_HOOK_PATH")) {
		int do_not_free = 0;
		path = hookpath("XDG_CONFIG_HOME", "/sat/hook");
		t (!path && errno);
		path = path ? path : hookpath("HOME", "/.config/sat/hook");
		t (!path && errno);
		path = path ? path : hookpath(NULL, "/.config/sat/hook");
		t (!path && errno);
		path = path ? path : (do_not_free = 1, "/etc/sat/hook");
		t (setenv("SAT_HOOK_PATH", path, 1));
		if (!do_not_free)
			free(path);
		path = NULL;
	}

	/* Open/create state file. */
	dir = getenv("XDG_RUNTIME_DIR"), dir = (dir ? dir : "/run");
	t (snprintf(NULL, 0, "%s/satd.state%zn", dir, &len) == -1);
	path = malloc(((size_t)len + 1) * sizeof(char));
	t (!path);
	sprintf(path, "%s/satd.state", dir);
	state = open(path, O_RDWR | O_CREAT /* but not O_EXCL */, S_IRWXU);
	t (state == -1);
	free(path), path = NULL;

	/* The state fill shall be on fd 4. */
	t (dup2_and_null(state, 4) == -1);
	state = 4;

	/* Create socket. */
	t (sock = create_socket(&address), sock == -1);

	/* Socket shall be on fd 3. */
	t (dup2_and_null(sock, 3) == -1);
	sock = 3;

	/* Listen for incoming conections. */
#if SOMAXCONN < SATD_BACKLOG
	t (listen(sock, SOMAXCONN));
#else
	t (listen(sock, SATD_BACKLOG));
#endif

	/* Daemonise. */
	t (foreground ? 0 : daemonise("satd", DAEMONISE_KEEP_FDS, sock, -1));
	if (foreground)
		close(5); /* Required to be closed by the next image. */

	/* Change to a process image without all this initialisation text. */
	execl(LIBEXEC "/" PACKAGE "/satd-diminished", argv0,
	      address.sun_path, getenv("SAT_HOOK_PATH"), NULL);

fail:
	if (errno)
		perror(argv0);
	free(path);
	if (sock >= 0) {
		unlink(address.sun_path);
		close(sock);
	}
	if (state >= 0)
		close(state);
	undaemonise();
	return 1;
}