/*
  Copyright (c) 2012, 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.
*/


#define _GNU_SOURCE

#include <alloca.h>
#include <errno.h>
#include <libgen.h>
#include <poll.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <arpa/inet.h>

#include <linux/rtnetlink.h>

#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_arp.h>

#include <netinet/in.h>

#include <netpacket/packet.h>

#include <sys/types.h>
#include <sys/stat.h>


#define ANNOUNCE_INTERVAL 10
#define ANNOUNCE_TIMEOUT (3*ANNOUNCE_INTERVAL)
#define ANNOUNCE_PRUNE (3*ANNOUNCE_TIMEOUT)

#define SYSFS_PATH_MAX 256
#define SYSFS_CLASS_NET "/sys/class/net"

#define FFD_MAGIC 0xffd
#define FFVISD_VERSION 0

#define FFD_PROTO 0xffd
#define FFD_PORT 0xffd


typedef struct __attribute__((__packed__)) _eth_addr_t {
	uint8_t address[ETH_ALEN];
} eth_addr_t;

typedef struct __attribute__((__packed__)) _ffvisd_ipv6_host_addr_t {
	uint8_t address[8];
} ffvisd_ipv6_host_addr_t;

typedef struct __attribute__((__packed__)) _ffvisd_packet_server_announce_t {
	uint16_t seqno;
	eth_addr_t eth_address;
	ffvisd_ipv6_host_addr_t address;
} ffvisd_packet_server_announce_t;

typedef struct __attribute__((__packed__)) _ffvisd_packet_announce_t {
	uint16_t magic;
	uint16_t version;
	uint16_t csum;
	uint16_t n_servers;
	ffvisd_packet_server_announce_t servers[];
} ffvisd_packet_announce_t;

typedef enum _ffvisd_iftype_t {
	IF_UNKNOWN = 0,
	IF_WIRED,
	IF_WIRELESS,
	IF_VIRTUAL,
	IF_BRIDGE,
	IF_MESH,
	IF_MAX
} ffvisd_iftype_t;

typedef struct _ffvisd_announce_t {
	struct _ffvisd_announce_t *next;

	struct timespec received;
	ffvisd_packet_server_announce_t announce;
} ffvisd_announce_t;

/*static const char *ffvisd_iftype_names[IF_MAX] = {
	[IF_UNKNOWN] = "unknown",
	[IF_WIRED] = "wired",
	[IF_WIRELESS] = "wireless",
	[IF_VIRTUAL] = "virtual",
	[IF_BRIDGE] = "bridge",
	[IF_MESH] = "mesh",
	};*/


typedef void (*iface_cb)(const char *ifname, unsigned ifindex, void *arg);


static const eth_addr_t eth_addr_unspec = {{0x00, 0x00, 0x00, 0x00, 0x00, 0x00}};

static const eth_addr_t ffd_addr = {{0x03, 0x00, 0x00, 0x00, 0x0f, 0xfd}};


static int sockfd;
static char *mesh = "bat0";

static struct timespec now;
static ffvisd_announce_t *announcements = NULL;


/* ones' complement add */
static inline u_int16_t add16(u_int16_t a, u_int16_t b) {
        a += b;
        return a + (a < b);
}

static inline bool is_eth_addr_unspec(const eth_addr_t *address) {
	const uint8_t *a = address->address;

	if (a[0]||a[1]||a[2]||a[3]||a[4]||a[5])
		return false;
	else
		return true;
}

static inline bool are_eth_addrs_equal(const eth_addr_t *address1, const eth_addr_t *address2) {
	const uint8_t *a = address1->address;
	const uint8_t *b = address2->address;

	return (a[0]==b[0] && a[1]==b[1] && a[2]==b[2] && a[3]==b[3] && a[4]==b[4] && a[5]==b[5]);
}

static inline bool are_ipv6_host_addrs_equal(const ffvisd_ipv6_host_addr_t *address1, const ffvisd_ipv6_host_addr_t *address2) {
	const uint8_t *a = address1->address;
	const uint8_t *b = address2->address;

	return (a[0]==b[0] && a[1]==b[1] && a[2]==b[2] && a[3]==b[3] && a[4]==b[4] && a[5]==b[5] && a[6]==b[6] && a[7]==b[7]);
}

/* returns (tp1 - tp2) in milliseconds  */
static inline int timespec_diff(const struct timespec *tp1, const struct timespec *tp2) {
	return ((tp1->tv_sec - tp2->tv_sec))*1000 + (tp1->tv_nsec - tp2->tv_nsec)/1e6;
}


static inline bool are_announcements_equal(const ffvisd_packet_server_announce_t *a1, const ffvisd_packet_server_announce_t *a2) {
	return (are_eth_addrs_equal(&a1->eth_address, &a2->eth_address) && are_ipv6_host_addrs_equal(&a1->address, &a2->address));
}

static inline bool is_announcement_local(const ffvisd_announce_t *a) {
	return (a->received.tv_sec == 0);
}

static inline bool is_announcement_valid(const ffvisd_announce_t *a) {
	if (is_announcement_local(a))
		return true;

	int diff = timespec_diff(&now, &a->received);
	return (diff < ANNOUNCE_TIMEOUT*1000);
}


static bool file_readv(const char *file, const char *format, va_list ap) {
	FILE *f = fopen(file, "r");
	if (!f)
		return false;

	int ret = vfscanf(f, format, ap);

	fclose(f);

	return (ret > 0);
}

static bool iface_file_read(const char *ifname, const char *file, const char *format, ...) {
	char filename[SYSFS_PATH_MAX];

	snprintf(filename, SYSFS_PATH_MAX, SYSFS_CLASS_NET"/%s/%s", ifname, file);

	va_list ap;
	va_start(ap, format);
	bool ret = file_readv(filename, format, ap);
	va_end(ap);

	return ret;
}

static bool iface_file_exists(const char *ifname, const char *file) {
	char filename[SYSFS_PATH_MAX];

	snprintf(filename, SYSFS_PATH_MAX, SYSFS_CLASS_NET"/%s/%s", ifname, file);

	struct stat st;
	return (stat(filename, &st) == 0);
}

static bool iface_is_mesh(const char *ifname) {
	return iface_file_exists(ifname, "mesh");
}

static char* iface_get_mesh(const char *ifname) {
	char *mesh = NULL;

	if (!iface_file_read(ifname, "batman_adv/mesh_iface", "%as", &mesh) || !strcmp(mesh, "none")) {
		free(mesh);
		return NULL;
	}

	return mesh;
}

static char* iface_get_bridge(const char *ifname) {
	char filename[SYSFS_PATH_MAX], filename2[SYSFS_PATH_MAX] = {0};

	snprintf(filename, SYSFS_PATH_MAX, SYSFS_CLASS_NET"/%s/brport/bridge", ifname);
	if (readlink(filename, filename2, sizeof(filename2)) < 0)
		return NULL;

	return strdup(basename(filename2));
}

static eth_addr_t iface_get_eth_address(const char *ifname) {
	eth_addr_t ret;
	uint8_t *a = ret.address;

	if (!iface_file_read(ifname, "address", "%x:%x:%x:%x:%x:%x", &a[0], &a[1], &a[2], &a[3], &a[4], &a[5]))
		return eth_addr_unspec;

	return ret;
}

static struct in6_addr iface_get_address(unsigned ifindex, int scope) {
	struct msg {
		struct nlmsghdr nh;
		struct ifaddrmsg addr;
		uint8_t attrbuf[16384];
	} msg;

	memset(&msg, 0, sizeof(msg));

	int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);

	msg.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifaddrmsg));
	msg.nh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ROOT;
	msg.nh.nlmsg_type = RTM_GETADDR;

	msg.addr.ifa_family = AF_INET6;

	if(write(rtnetlink_sk, &msg, msg.nh.nlmsg_len) <= 0) {
		fprintf(stderr, "error: write: %m\n");
		close(rtnetlink_sk);
		return in6addr_any;
	}

	int readlen = read(rtnetlink_sk, &msg, sizeof(msg));

	if (readlen <= 0) {
		fprintf(stderr, "error: read: %m\n");
		close(rtnetlink_sk);
		return in6addr_any;
	}

	close(rtnetlink_sk);

	struct msg *chunk;

	for (chunk = &msg; readlen > sizeof(struct nlmsghdr);) {
		int len = chunk->nh.nlmsg_len - sizeof(struct nlmsghdr);

		if (len < sizeof(struct ifaddrmsg) || readlen < len)
			return in6addr_any;

		if (!NLMSG_OK(&chunk->nh, readlen))
			return in6addr_any;

		if (chunk->nh.nlmsg_type == RTM_NEWADDR && chunk->addr.ifa_scope == scope && chunk->addr.ifa_index == ifindex) {
			struct rtattr *rta = (struct rtattr *)IFA_RTA(&chunk->addr);
			int rtattrlen = IFA_PAYLOAD(&chunk->nh);

			for (; RTA_OK(rta, rtattrlen); rta = RTA_NEXT(rta, rtattrlen)) {
				if(rta->rta_type == IFA_ADDRESS && rta->rta_len == RTA_LENGTH(16)) {
					struct in6_addr ret;
					memcpy(ret.s6_addr, RTA_DATA(rta), 16);
					return ret;
				}
			}
		}

		readlen -= NLMSG_ALIGN(chunk->nh.nlmsg_len);
		chunk = (struct msg*)((uint8_t*)chunk + NLMSG_ALIGN(chunk->nh.nlmsg_len));
	}

	return in6addr_any;
}

static void ffvisd_iface_foreach(iface_cb cb, void *arg) {
	struct if_nameindex *ifaces = if_nameindex();

	if (!ifaces) {
		fprintf(stderr, "error: if_nameindex: %m\n");
		return;
	}

	int i;
	for (i = 0; ifaces[i].if_name; i++)
		cb(ifaces[i].if_name, ifaces[i].if_index, arg);

	if_freenameindex(ifaces);
}


static void join_mcast(const char *ifname, unsigned ifindex, void *arg) {
	char *if_mesh = iface_get_mesh(ifname);

	if (if_mesh && !strcmp(if_mesh, mesh)) {
		struct packet_mreq mr;
		memset(&mr, 0, sizeof(mr));
		mr.mr_ifindex = ifindex;
		mr.mr_type = PACKET_MR_MULTICAST;
		mr.mr_alen = ETH_ALEN;
		memcpy(mr.mr_address, ffd_addr.address, ETH_ALEN);
		if (setsockopt(sockfd, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) && errno != EADDRINUSE)
			fprintf(stderr, "warning: setsockopt: %m\n");
	}

	free(if_mesh);
}

static void pr_announcement_packet(const ffvisd_packet_server_announce_t *announce) {
	const uint8_t *e = announce->eth_address.address, *a = announce->address.address;

	printf("seqno: %u, ether: %02x:%02x:%02x:%02x:%02x:%02x, address: fe80::%02x%02x:%02x%02x:%02x%02x:%02x%02x\n",
	       ntohs(announce->seqno),
	       e[0], e[1], e[2], e[3], e[4], e[5],
	       a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7]);
}

static void pr_announcement(const ffvisd_announce_t *announce) {
	if (is_announcement_local(announce)) {
		printf("local, ");
	}
	else {
		struct timespec tv;
		clock_gettime(CLOCK_MONOTONIC, &tv);
		printf("age: %.1fs, ", timespec_diff(&tv, &announce->received)/1000.0);
	}

	printf("valid: %s, ", is_announcement_valid(announce) ? "yes" : "no");

	pr_announcement_packet(&announce->announce);
}

static bool check_config() {
	if (!iface_is_mesh(mesh)) {
		fprintf(stderr, "error: configured interface is no mesh\n");
		return false;
	}

	return true;
}

static bool init_socket() {
	sockfd = socket(AF_PACKET, SOCK_DGRAM, htons(FFD_PROTO));
	if (sockfd < 0) {
		fprintf(stderr, "error: socket: %m\n");
		return false;
	}

	return true;
}

static bool init_announcements() {
	char *ifname = iface_get_bridge(mesh);

	if (!ifname)
		ifname = strdup(mesh);

	unsigned ifindex = if_nametoindex(ifname);

	if (!ifindex) {
		free(ifname);
		return false;
	}

	ffvisd_announce_t *announce = announcements = calloc(1, sizeof(ffvisd_announce_t));

	announce->announce.eth_address = iface_get_eth_address(ifname);
	if (is_eth_addr_unspec(&announce->announce.eth_address)) {
		free(ifname);
		return false;
	}

	struct in6_addr addr = iface_get_address(ifindex, RT_SCOPE_LINK);
	if (IN6_IS_ADDR_UNSPECIFIED(&addr)) {
		free(ifname);
		return false;
	}

	memcpy(announce->announce.address.address, addr.s6_addr+8, 8);

	free(ifname);

	return true;
}

static void maintenance() {
	clock_gettime(CLOCK_MONOTONIC, &now);

	ffvisd_announce_t **announce, **next;

	for(announce = &announcements; *announce; announce = next) {
		next = &(*announce)->next;

		if (is_announcement_local(*announce)) {
			(*announce)->announce.seqno = htons(ntohs((*announce)->announce.seqno)+1);
			continue;
		}

		int diff = timespec_diff(&now, &(*announce)->received);
		if (diff >= ANNOUNCE_PRUNE*1000) {
			ffvisd_announce_t *del = *announce;

			*announce = *next;
			next = announce;

			free(del);
		}
	}
}

static uint16_t do_checksum(void *data, unsigned n_words) {
	uint16_t ret = 0;
	uint16_t *words = data;

	while(n_words)
		ret = add16(ret, words[--n_words]);

	return ~ret;
}

static void send_announcement(const char *ifname, unsigned ifindex, void *arg) {
	char *if_mesh = iface_get_mesh(ifname);

	if (if_mesh && !strcmp(if_mesh, mesh)) {
		ffvisd_packet_announce_t *packet = arg;

		struct sockaddr_ll sa;
		memset(&sa, 0, sizeof(sa));

		sa.sll_family = AF_PACKET;
		sa.sll_protocol = htons(FFD_PROTO);
		sa.sll_ifindex = ifindex;
		sa.sll_halen = ETH_ALEN;
		memcpy(sa.sll_addr, ffd_addr.address, ETH_ALEN);

		unsigned len = sizeof(ffvisd_packet_announce_t) + ntohs(packet->n_servers)*sizeof(ffvisd_packet_server_announce_t);
		sendto(sockfd, packet, len > 46 ? len : 46, 0, (struct sockaddr*)&sa, sizeof(sa));
	}
	free(if_mesh);
}

static void send_announcements() {
	ffvisd_packet_announce_t *packet = alloca(sizeof(ffvisd_packet_announce_t) + 75*sizeof(ffvisd_packet_server_announce_t));

	memset(packet, 0, 46); /* minimum ethernet packet size is 46 bytes */

	packet->magic = htons(FFD_MAGIC);
	packet->version = htons(FFVISD_VERSION);
	packet->csum = 0;

	uint16_t n_servers = 0;
	ffvisd_announce_t *announce;
	for(announce = announcements; announce; announce = announce->next) {
		if (!is_announcement_valid(announce))
			continue;

		packet->servers[n_servers++] = announce->announce;
	}

	packet->n_servers = htons(n_servers);

	packet->csum = do_checksum(packet, (sizeof(ffvisd_packet_announce_t) + n_servers*sizeof(ffvisd_packet_server_announce_t))/2);

	ffvisd_iface_foreach(send_announcement, packet);
}

static void handle_announcement(const ffvisd_packet_server_announce_t *server) {
	ffvisd_announce_t *announce;
	for(announce = announcements; announce; announce = announce->next) {
		if (!are_announcements_equal(server, &announce->announce))
			continue;

		if (is_announcement_local(announce))
			return;

		uint16_t seqno_diff = ntohs(server->seqno) - ntohs(announce->announce.seqno);

		if (seqno_diff > 0 && seqno_diff < 0x8000) {
			announce->received = now;
			announce->announce = *server;
		}

		return;
	}

	/* no matching annouce was found */
	announce = calloc(1, sizeof(ffvisd_announce_t));
	announce->received = now;
	announce->announce = *server;

	announce->next = announcements;
	announcements = announce;
}

static void receive_announcement() {
	ffvisd_packet_announce_t *packet = alloca(sizeof(ffvisd_packet_announce_t) + 75*sizeof(ffvisd_packet_server_announce_t));

	int readlen = read(sockfd, packet, sizeof(ffvisd_packet_announce_t) + 75*sizeof(ffvisd_packet_server_announce_t));

	if (readlen < 0) {
		fprintf(stderr, "error: read: %m\n");
		return;
	}

	if (readlen < sizeof(ffvisd_packet_announce_t)) {
		fprintf(stderr, "warning: short read");
		return;
	}

	int n_servers = ntohs(packet->n_servers);

	if (readlen < sizeof(ffvisd_packet_announce_t) + n_servers*sizeof(ffvisd_packet_server_announce_t)) {
		fprintf(stderr, "warning: short read");
		return;
	}

	if (do_checksum(packet, (sizeof(ffvisd_packet_announce_t) + n_servers*sizeof(ffvisd_packet_server_announce_t))/2)) {
		fprintf(stderr, "warning: invalid checksum");
		return;
	}

	clock_gettime(CLOCK_MONOTONIC, &now);

	int i;
	for(i = 0; i < n_servers; i++)
		handle_announcement(&packet->servers[i]);
}

int main() {
	if (!check_config())
		return 1;

	if (!init_socket())
		return 1;

	if (!init_announcements())
		return 1;

	struct timespec next_announce;
	clock_gettime(CLOCK_MONOTONIC, &next_announce);

	while (true) {
		ffvisd_iface_foreach(join_mcast, NULL);

		maintenance();

		puts("Dumping announcements...");
		ffvisd_announce_t *announce;
		for(announce = announcements; announce; announce = announce->next)
			pr_announcement(announce);
		puts("");

		send_announcements();

		next_announce.tv_sec += ANNOUNCE_INTERVAL;

		while (true) {
			clock_gettime(CLOCK_MONOTONIC, &now);
			int timeout = timespec_diff(&next_announce, &now);

			if (timeout <= 0)
				break;

			struct pollfd fds[1];

			fds[0].fd = sockfd;
			fds[0].events = POLLIN;

			poll(fds, 1, timeout);

			if (fds[0].revents & POLLIN)
				receive_announcement();
		}
	}

	return 0;
}