/*
  Copyright (c) 2012-2014, Matthias Schiffer <mschiffer@universe-factory.net>
  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice,
       this list of conditions and the following disclaimer in the documentation
       and/or other materials provided with the distribution.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/**
   \file

   Initialization, main loop and cleanup
*/


#include "fastd.h"
#include "async.h"
#include "config.h"
#include "crypto.h"
#include "peer.h"
#include "peer_hashtable.h"
#include "poll.h"
#include <fastd_version.h>

#include <grp.h>
#include <signal.h>
#include <syslog.h>
#include <sys/resource.h>
#include <sys/wait.h>

#ifdef HAVE_LIBSODIUM
#include <sodium/core.h>
#endif

#ifdef ENABLE_OPENSSL
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#endif

#ifdef ENABLE_SYSTEMD
#include <sys/un.h>
#endif


/** The global context */
fastd_context_t ctx = {};


static volatile bool sighup = false;		/**< Is set to true when a SIGHUP is received */
static volatile bool terminate = false;		/**< Is set to true when a SIGTERM, SIGQUIT or SIGINT is received */
static volatile bool dump = false;		/**< Is set to true when a SIGUSR1 is received */
static volatile bool sigchld = false;		/**< Is set to true when a SIGCHLD is received */


/** Signal handler; just saves the signals to be handled later */
static void on_signal(int signo) {
	switch(signo) {
	case SIGHUP:
		sighup = true;
		break;

	case SIGUSR1:
		dump = true;
		break;

	case SIGCHLD:
		sigchld = true;
		break;

	case SIGTERM:
	case SIGQUIT:
	case SIGINT:
		terminate = true;
		break;

	default:
		return;
	}

#ifndef USE_EPOLL
	/* Avoids a race condition between pthread_sigmask() and poll() (FreeBSD doesn't have ppoll() ...) */
	fastd_async_enqueue(ASYNC_TYPE_NOP, NULL, 0);
#endif
}

/** Installs signal handlers */
static void init_signals(void) {
	sigset_t set;
	sigfillset(&set);
	/* block all signals */
	pthread_sigmask(SIG_SETMASK, &set, NULL);

	struct sigaction action = {};
	sigemptyset(&action.sa_mask);

	action.sa_handler = on_signal;
	if (sigaction(SIGHUP, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGUSR1, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGCHLD, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGTERM, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGQUIT, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGINT, &action, NULL))
		exit_errno("sigaction");

	action.sa_handler = SIG_IGN;
	if (sigaction(SIGPIPE, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGTTIN, &action, NULL))
		exit_errno("sigaction");
	if (sigaction(SIGTTOU, &action, NULL))
		exit_errno("sigaction");

}

/** Initializes log destinations */
static inline void init_log(void) {
	if (conf.log_syslog_level > LL_UNSPEC)
		openlog(conf.log_syslog_ident, LOG_PID, LOG_DAEMON);

	ctx.log_initialized = true;
}

/** Cleans up log destinations */
static inline void close_log(void) {
	closelog();
}


/** Initializes the configured sockets */
static void init_sockets(void) {
	ctx.socks = malloc(conf.n_bind_addrs * sizeof(fastd_socket_t));

	size_t i;
	fastd_bind_address_t *addr = conf.bind_addrs;
	for (i = 0; i < conf.n_bind_addrs; i++) {
		ctx.socks[i] = (fastd_socket_t){ .fd = -2, .addr = addr };

		if (addr == conf.bind_addr_default_v4)
			ctx.sock_default_v4 = &ctx.socks[i];

		if (addr == conf.bind_addr_default_v6)
			ctx.sock_default_v6 = &ctx.socks[i];

		addr = addr->next;
	}

	ctx.n_socks = conf.n_bind_addrs;
}

/** Closes fastd's sockets */
static void close_sockets(void) {
	size_t i;
	for (i = 0; i < ctx.n_socks; i++)
		fastd_socket_close(&ctx.socks[i]);

	free(ctx.socks);
}

/** Calls the on-pre-up command */
static inline void on_pre_up(void) {
	fastd_shell_command_exec(&conf.on_pre_up, NULL);
}

/** Calls the on-up command */
static inline void on_up(void) {
	fastd_shell_command_exec(&conf.on_up, NULL);
}

/** Calls the on-down command */
static inline void on_down(void) {
	fastd_shell_command_exec(&conf.on_down, NULL);
}

/** Calls the on-post-down command */
static inline void on_post_down(void) {
	fastd_shell_command_exec(&conf.on_post_down, NULL);
}

/**
   Initializes the peers

   Is called after each reconfiguration to remove old peers and add new ones.
*/
static void init_peers(void) {
	fastd_peer_config_t *peer_conf;
	for (peer_conf = conf.peers; peer_conf; peer_conf = peer_conf->next)
		conf.protocol->peer_configure(peer_conf);

	for (peer_conf = conf.peers; peer_conf; peer_conf = peer_conf->next) {
		bool enable = conf.protocol->peer_check(peer_conf);

		if (enable && !peer_conf->enabled)
			fastd_peer_add(peer_conf);

		peer_conf->enabled = enable;
	}

	size_t i;
	for (i = 0; i < VECTOR_LEN(ctx.peers);) {
		fastd_peer_t *peer = VECTOR_INDEX(ctx.peers, i);

		if (peer->config) {
			if (!peer->config->enabled) {
				pr_info("previously enabled peer %P disabled, deleting.", peer);
				fastd_peer_delete(peer);
				continue;
			}
		}
		else {
			if (!conf.protocol->peer_check_temporary(peer)) {
				fastd_peer_delete(peer);
				continue;
			}
		}

		i++;
	}
}

/** Removes all peers */
static void delete_peers(void) {
	while (VECTOR_LEN(ctx.peers))
		fastd_peer_delete(VECTOR_INDEX(ctx.peers, VECTOR_LEN(ctx.peers)-1));
}

/** Dumps statistics and the list of known peers to the logs */
static void dump_state(void) {
	pr_info("TX stats: %U packet(s), %U byte(s); dropped: %U packet(s), %U byte(s); error: %U packet(s), %U byte(s)",
		ctx.tx.packets, ctx.tx.bytes, ctx.tx_dropped.packets, ctx.tx_dropped.bytes, ctx.tx_error.packets, ctx.tx_error.bytes);
	pr_info("RX stats: %U packet(s), %U byte(s)", ctx.rx.packets, ctx.rx.bytes);

	pr_info("dumping peers:");

	size_t i;
	for (i = 0; i < VECTOR_LEN(ctx.peers); i++) {
		fastd_peer_t *peer = VECTOR_INDEX(ctx.peers, i);

		if (!fastd_peer_is_established(peer)) {
			pr_info("peer %P not connected, address: %I", peer, &peer->address);
			continue;
		}

		if (conf.mode == MODE_TAP) {
			unsigned eth_addresses = 0;
			size_t j;
			for (j = 0; j < VECTOR_LEN(ctx.eth_addrs); j++) {
				if (VECTOR_INDEX(ctx.eth_addrs, j).peer == peer)
					eth_addresses++;
			}

			pr_info("peer %P connected, address: %I, associated MAC addresses: %u", peer, &peer->address, eth_addresses);
		}
		else {
			pr_info("peer %P connected, address: %I", peer, &peer->address);
		}
	}

	pr_info("dump finished.");
}


/** Closes all open FDs except stdin, stdout and stderr */
void fastd_close_all_fds(void) {
	struct rlimit rl;
	int fd, maxfd;

	if (getrlimit(RLIMIT_NOFILE, &rl) > 0)
		maxfd = (int)rl.rlim_max;
	else
		maxfd = sysconf(_SC_OPEN_MAX);

	for (fd = 3; fd < maxfd; fd++) {
		if (close(fd) < 0) {
			if (errno != EBADF)
				pr_error_errno("close");
		}
	}
}


/** Writes the PID file */
static inline void write_pid(void) {
	if (!conf.pid_file)
		return;

	uid_t uid = geteuid();
	gid_t gid = getegid();

	if (conf.user || conf.group) {
		if (setegid(conf.gid) < 0)
			pr_debug_errno("setegid");
		if (seteuid(conf.uid) < 0)
			pr_debug_errno("seteuid");
	}

	int fd = open(conf.pid_file, O_WRONLY|O_CREAT|O_TRUNC, 0666);
	if (fd < 0) {
		pr_error_errno("can't write PID file: open");
		goto end;
	}

	if (dprintf(fd, "%u", (unsigned)getpid()) < 0)
		pr_error_errno("can't write PID file: dprintf");

	if (close(fd) < 0)
		pr_warn_errno("close");

 end:
	if (seteuid(uid) < 0)
		pr_debug_errno("seteuid");
	if (setegid(gid) < 0)
		pr_debug_errno("setegid");
}

/** Switches to the configured user */
static void set_user(void) {
	if (conf.user || conf.group) {
		if (setgid(conf.gid) < 0)
			exit_errno("setgid");

		if (setuid(conf.uid) < 0)
			exit_errno("setuid");

		pr_info("changed to UID %i, GID %i", (int)conf.uid, (int)conf.gid);
	}
}

/** Sets the configured user's supplementary groups */
static void set_groups(void) {
	if (conf.groups) {
		if (setgroups(conf.n_groups, conf.groups) < 0) {
			if (errno != EPERM)
				pr_debug_errno("setgroups");
		}
	}
	else if (conf.user || conf.group) {
		if (setgroups(1, &conf.gid) < 0) {
			if (errno != EPERM)
				pr_debug_errno("setgroups");
		}
	}
}

/** Switches the user and drops all capabilities */
static void drop_caps(void) {
	set_user();
	fastd_cap_drop();
}

/** Will double fork and wait for a status notification from the child before exiting in the original parent */
static int daemonize(void) {
	uint8_t status = 1;
	int pipefd[2];

	if (pipe(pipefd))
		exit_errno("pipe");

	pid_t fork1 = fork();

	if (fork1 < 0) {
		exit_errno("fork");
	}
	else if (fork1 > 0) {
		/* parent */
		if (close(pipefd[1]) < 0)
			exit_errno("close");

		if (waitpid(fork1, NULL, 0) < 0)
			exit_errno("waitpid");

		if (read(pipefd[0], &status, 1) < 0)
			exit_errno("read");

		exit(status);
	}
	else {
		/* child 1 */
		if (close(pipefd[0]) < 0)
			pr_error_errno("close");

		if (setsid() < 0)
			pr_error_errno("setsid");

		pid_t fork2 = fork();

		if (fork2 < 0) {
			exit_errno("fork");
		}
		else if (fork2 > 0) {
			/* still child 1 */
			_exit(0);
		}
		else {
			/* child 2 */
			return pipefd[1];
		}
	}
}

/** Sends a readiness notification on a notify socket */
static inline void notify_systemd(void) {
#ifdef ENABLE_SYSTEMD
	int fd;
	struct sockaddr_un sa = {};
	const char *notify_socket = getenv("NOTIFY_SOCKET");

	if (!notify_socket)
		return;

	if ((notify_socket[0] != '@' && notify_socket[0] != '/') || notify_socket[1] == 0)
		return;

	fd = socket(AF_UNIX, SOCK_DGRAM, 0);
	if (fd < 0)
		return;

	sa.sun_family = AF_UNIX;

	strncpy(sa.sun_path, notify_socket, sizeof(sa.sun_path));
	if (sa.sun_path[0] == '@')
		sa.sun_path[0] = 0;

	if (connect(fd, (struct sockaddr*)&sa, offsetof(struct sockaddr_un, sun_path) + strnlen(notify_socket, sizeof(sa.sun_path))) < 0) {
		pr_debug_errno("unable to connect to notify socket: connect");
		close(fd);
		return;
	}

	dprintf(fd, "READY=1\nMAINPID=%lu", (unsigned long) getpid());
	pr_debug("sent startup notification to systemd");

	close(fd);
#endif
}

/** Early initialization before reading the config */
static inline void init_early(void) {
	fastd_close_all_fds();

	fastd_random_bytes(&ctx.randseed, sizeof(ctx.randseed), false);

	fastd_cipher_init();
	fastd_mac_init();
}

/**
   Performs further initialization after the config has been loaded

   This also handles special run modes like \em generate-key and \em verify-config.
*/
static inline void init_config(int *status_fd) {
	if (conf.verify_config) {
		fastd_config_verify();
		exit(0);
	}

	if (conf.generate_key) {
		conf.protocol->generate_key();
		exit(0);
	}

	conf.protocol_config = conf.protocol->init();

	if (conf.show_key) {
		conf.protocol->show_key();
		exit(0);
	}

	init_signals();

	if (conf.daemon)
		*status_fd = daemonize();

	if (chdir("/"))
		pr_error("can't chdir to `/': %s", strerror(errno));

	/*
	  Initialize log here, as:
	   - we have already daemonized, so syslog will show the correct PID
	   - special run modes that should always log to stderr have been handled
	 */
	init_log();

	/* Init crypto libs here as fastd_config_check() initializes the methods and might need them */
#ifdef HAVE_LIBSODIUM
	sodium_init();
#endif

#ifdef ENABLE_OPENSSL
	ERR_load_crypto_strings();
	OpenSSL_add_all_algorithms();
	OPENSSL_config(NULL);
#endif

	fastd_config_check();
}

/** Initializes fastd */
static inline void init(int argc, char *argv[]) {
	int status_fd = -1;

	init_early();
	fastd_configure(argc, argv);
	init_config(&status_fd);

	fastd_update_time();
	ctx.next_maintenance = fastd_in_seconds(MAINTENANCE_INTERVAL);
	ctx.unknown_handshakes[0].timeout = ctx.now;

	VECTOR_ALLOC(ctx.eth_addrs, 0);
	VECTOR_ALLOC(ctx.peers, 0);
	VECTOR_ALLOC(ctx.async_pids, 0);

#ifdef WITH_VERIFY
	if (sem_init(&ctx.verify_limit, 0, VERIFY_LIMIT))
		exit_errno("sem_init");
#endif

	if (pthread_attr_init(&ctx.detached_thread))
		exit_errno("pthread_attr_init");
	if (pthread_attr_setdetachstate(&ctx.detached_thread, PTHREAD_CREATE_DETACHED))
		exit_errno("pthread_attr_setdetachstate");

	pr_info("fastd " FASTD_VERSION " starting");

	fastd_cap_init();

	init_sockets();
	fastd_async_init();
	fastd_poll_init();

	if (!fastd_socket_handle_binds())
		exit_error("unable to bind default socket");

	on_pre_up();

	fastd_tuntap_open();

	/* change groups before trying to write the PID file as they can be relevant for file access */
	set_groups();
	write_pid();

	fastd_peer_hashtable_init();

	notify_systemd();

	if (status_fd >= 0) {
		static const uint8_t STATUS = 0;
		if (write(status_fd, &STATUS, 1) < 0)
			exit_errno("status: write");
		if (close(status_fd))
			exit_errno("status: close");
	}

	if (conf.drop_caps == DROP_CAPS_EARLY)
		drop_caps();

	on_up();

	if (conf.drop_caps == DROP_CAPS_ON)
		drop_caps();
	else if (conf.drop_caps == DROP_CAPS_OFF)
		set_user();

	fastd_config_load_peer_dirs();
	init_peers();
}


/** Performs periodic maintenance tasks */
static inline void maintenance(void) {
	if (!fastd_timed_out(&ctx.next_maintenance))
		return;

	fastd_socket_handle_binds();
	fastd_peer_maintenance();

	ctx.next_maintenance.tv_sec += MAINTENANCE_INTERVAL;
}

/** Reaps zombies of asynchronous shell commands. */
static inline void reap_zombies(void) {
	size_t i;
	for (i = 0; i < VECTOR_LEN(ctx.async_pids);) {
		pid_t pid = VECTOR_INDEX(ctx.async_pids, i);
		if (waitpid(pid, NULL, WNOHANG) > 0) {
			pr_debug("child process %u finished", (unsigned)pid);
		}
		else {
			if (errno == ECHILD) {
				i++;
				continue;
			}
			else {
				pr_error_errno("waitpid");
			}
		}

		VECTOR_DELETE(ctx.async_pids, i);
	}
}

/** The \em real signal handlers */
static inline void handle_signals(void) {
	if (sighup) {
		sighup = false;

		pr_info("reconfigure triggered");

		fastd_config_load_peer_dirs();
		init_peers();
	}

	if (dump) {
		dump = false;
		dump_state();
	}

	if (sigchld) {
		sigchld = false;
		reap_zombies();
	}
}


/** A single iteration of fastd's main loop */
static inline void run(void) {
	fastd_peer_handle_handshake_queue();
	fastd_poll_handle();

	maintenance();
	handle_signals();
}

/**
   Performs cleanup of resources used by fastd

   Besides running the on-down scripts and closing the TUN/TAP interface, this
   also frees all memory allocatedby fastd to make debugging memory leaks with
   valgrind as easy as possible.
*/
static inline void cleanup(void) {
	pr_info("terminating fastd");

	on_down();

	delete_peers();

	fastd_tuntap_close();
	close_sockets();
	fastd_poll_free();

	on_post_down();

	fastd_peer_hashtable_free();

	pthread_attr_destroy(&ctx.detached_thread);

	VECTOR_FREE(ctx.async_pids);
	VECTOR_FREE(ctx.peers);
	VECTOR_FREE(ctx.eth_addrs);

	free(ctx.protocol_state);
	free(ctx.ifname);

#ifdef ENABLE_OPENSSL
	CONF_modules_free();
	EVP_cleanup();
	ERR_free_strings();
#endif

	close_log();
	fastd_config_release();
}


/** Main function */
int main(int argc, char *argv[]) {
	init(argc, argv);

	while (!terminate)
		run();

	cleanup();

	return 0;
}