// SPDX-License-Identifier: MIT
/*
Copyright (c) 2007, 2008 by Juliusz Chroboczek
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <sys/time.h>
#include <time.h>

#include <zebra.h>
#include "if.h"

#include "babel_main.h"
#include "babeld.h"
#include "util.h"
#include "babel_interface.h"
#include "neighbour.h"
#include "source.h"
#include "route.h"
#include "message.h"
#include "resend.h"
#include "babel_errors.h"

struct neighbour *neighs = NULL;

static struct neighbour *
find_neighbour_nocreate(const unsigned char *address, struct interface *ifp)
{
    struct neighbour *neigh;
    FOR_ALL_NEIGHBOURS(neigh) {
        if(memcmp(address, neigh->address, 16) == 0 && neigh->ifp == ifp)
            return neigh;
    }
    return NULL;
}

void flush_neighbour(struct neighbour *neigh)
{
    debugf(BABEL_DEBUG_COMMON,"Flushing neighbour %s (reach 0x%04x)",
           format_address(neigh->address), neigh->reach);
    flush_neighbour_routes(neigh);
    if(unicast_neighbour == neigh)
        flush_unicast(1);
    flush_resends(neigh);

    if(neighs == neigh) {
        neighs = neigh->next;
    } else {
        struct neighbour *previous = neighs;
        while(previous->next != neigh)
            previous = previous->next;
        previous->next = neigh->next;
    }
    free(neigh);
}

struct neighbour *
find_neighbour(const unsigned char *address, struct interface *ifp)
{
    struct neighbour *neigh;
    const struct timeval zero = {0, 0};

    neigh = find_neighbour_nocreate(address, ifp);
    if(neigh)
        return neigh;

    debugf(BABEL_DEBUG_COMMON,"Creating neighbour %s on %s.",
           format_address(address), ifp->name);

    neigh = malloc(sizeof(struct neighbour));
    if(neigh == NULL) {
        flog_err(EC_BABEL_MEMORY, "malloc(neighbour): %s",
		  safe_strerror(errno));
        return NULL;
    }

    neigh->hello_seqno = -1;
    memcpy(neigh->address, address, 16);
    neigh->reach = 0;
    neigh->txcost = INFINITY;
    neigh->ihu_time = babel_now;
    neigh->hello_time = zero;
    neigh->hello_interval = 0;
    neigh->ihu_interval = 0;
    neigh->hello_send_us = 0;
    neigh->hello_rtt_receive_time = zero;
    neigh->rtt = 0;
    neigh->rtt_time = zero;
    neigh->ifp = ifp;
    neigh->next = neighs;
    neighs = neigh;
    send_hello(ifp);
    return neigh;
}

/* Recompute a neighbour's rxcost.  Return true if anything changed. */
int update_neighbour(struct neighbour *neigh, int hello, int hello_interval)
{
    int missed_hellos;
    int rc = 0;

    if(hello < 0) {
        if(neigh->hello_interval == 0)
            return rc;
        missed_hellos =
            ((int)timeval_minus_msec(&babel_now, &neigh->hello_time) -
             neigh->hello_interval * 7) /
            (neigh->hello_interval * 10);
        if(missed_hellos <= 0)
            return rc;
        timeval_add_msec(&neigh->hello_time, &neigh->hello_time,
                          missed_hellos * neigh->hello_interval * 10);
    } else {
        if(neigh->hello_seqno >= 0 && neigh->reach > 0) {
            missed_hellos = seqno_minus(hello, neigh->hello_seqno) - 1;
            if(missed_hellos < -8) {
                /* Probably a neighbour that rebooted and lost its seqno.
                   Reboot the universe. */
                neigh->reach = 0;
                missed_hellos = 0;
                rc = 1;
            } else if(missed_hellos < 0) {
                if(hello_interval > neigh->hello_interval) {
                    /* This neighbour has increased its hello interval,
                       and we didn't notice. */
                    neigh->reach <<= -missed_hellos;
                    missed_hellos = 0;
                } else {
                    /* Late hello.  Probably due to the link layer buffering
                       packets during a link outage.  Ignore it, but reset
                       the expected seqno. */
                    neigh->hello_seqno = hello;
                    hello = -1;
                    missed_hellos = 0;
                }
                rc = 1;
            }
        } else {
            missed_hellos = 0;
        }
        neigh->hello_time = babel_now;
        neigh->hello_interval = hello_interval;
    }

    if(missed_hellos > 0) {
        neigh->reach >>= missed_hellos;
        neigh->hello_seqno = seqno_plus(neigh->hello_seqno, missed_hellos);
        rc = 1;
    }

    if(hello >= 0) {
        neigh->hello_seqno = hello;
        neigh->reach >>= 1;
        SET_FLAG(neigh->reach, 0x8000);
        if(CHECK_FLAG(neigh->reach, 0xFC00) != 0xFC00)
            rc = 1;
    }

    /* Make sure to give neighbours some feedback early after association */
    if(CHECK_FLAG(neigh->reach, 0xBF00) == 0x8000) {
        /* A new neighbour */
        send_hello(neigh->ifp);
    } else {
        /* Don't send hellos, in order to avoid a positive feedback loop. */
        int a = CHECK_FLAG(neigh->reach, 0xC000);
        int b = CHECK_FLAG(neigh->reach, 0x3000);
        if((a == 0xC000 && b == 0) || (a == 0 && b == 0x3000)) {
            /* Reachability is either 1100 or 0011 */
            send_self_update(neigh->ifp);
        }
    }

    if(CHECK_FLAG(neigh->reach, 0xFC00) == 0xC000) {
        /* This is a newish neighbour, let's request a full route dump.
           We ought to avoid this when the network is dense */
        send_unicast_request(neigh, NULL, 0);
        send_ihu(neigh, NULL);
    }
    return rc;
}

static int reset_txcost(struct neighbour *neigh)
{
    unsigned delay;

    delay = timeval_minus_msec(&babel_now, &neigh->ihu_time);

    if(neigh->ihu_interval > 0 && delay < neigh->ihu_interval * 10U * 3U)
        return 0;

    /* If we're losing a lot of packets, we probably lost an IHU too */
    if (delay >= 180000 || CHECK_FLAG(neigh->reach, 0xFFF0) == 0 ||
       (neigh->ihu_interval > 0 && delay >= neigh->ihu_interval * 10U * 10U)) {
        neigh->txcost = INFINITY;
        neigh->ihu_time = babel_now;
        return 1;
    }

    return 0;
}

unsigned neighbour_txcost(struct neighbour *neigh)
{
    return neigh->txcost;
}

unsigned check_neighbours(void)
{
    struct neighbour *neigh;
    int changed, rc;
    unsigned msecs = 50000;

    debugf(BABEL_DEBUG_COMMON,"Checking neighbours.");

    neigh = neighs;
    while(neigh) {
        changed = update_neighbour(neigh, -1, 0);

        if(neigh->reach == 0 ||
           neigh->hello_time.tv_sec > babel_now.tv_sec || /* clock stepped */
           timeval_minus_msec(&babel_now, &neigh->hello_time) > 300000) {
            struct neighbour *old = neigh;
            neigh = neigh->next;
            flush_neighbour(old);
            continue;
        }

        rc = reset_txcost(neigh);
        changed = changed || rc;

        update_neighbour_metric(neigh, changed);

        if(neigh->hello_interval > 0)
            msecs = MIN(msecs, neigh->hello_interval * 10U);
        if(neigh->ihu_interval > 0)
            msecs = MIN(msecs, neigh->ihu_interval * 10U);
        neigh = neigh->next;
    }

    return msecs;
}

unsigned neighbour_rxcost(struct neighbour *neigh)
{
    unsigned delay;
    unsigned short reach = neigh->reach;

    delay = timeval_minus_msec(&babel_now, &neigh->hello_time);

    if(CHECK_FLAG(reach, 0xFFF0) == 0 || delay >= 180000) {
        return INFINITY;
    } else if (CHECK_FLAG(babel_get_if_nfo(neigh->ifp)->flags, BABEL_IF_LQ)) {
        int sreach =
            (CHECK_FLAG(reach, 0x8000) >> 2) +
            (CHECK_FLAG(reach, 0x4000) >> 1) +
            CHECK_FLAG(reach, 0x3FFF);
        /* 0 <= sreach <= 0x7FFF */
        int cost = (0x8000 * babel_get_if_nfo(neigh->ifp)->cost) / (sreach + 1);
        /* cost >= interface->cost */
        if(delay >= 40000)
            cost = (cost * (delay - 20000) + 10000) / 20000;
        return MIN(cost, INFINITY);
    } else {
        /* To lose one hello is a misfortune, to lose two is carelessness. */
        if (CHECK_FLAG(reach, 0xC000) == 0xC000)
            return babel_get_if_nfo(neigh->ifp)->cost;
        else if (CHECK_FLAG(reach, 0xC000) == 0)
            return INFINITY;
        else if (CHECK_FLAG(reach, 0x2000))
            return babel_get_if_nfo(neigh->ifp)->cost;
        else
            return INFINITY;
    }
}

unsigned neighbour_rttcost(struct neighbour *neigh)
{
    struct interface *ifp = neigh->ifp;
    babel_interface_nfo *babel_ifp = babel_get_if_nfo(ifp);

    if(!babel_ifp->max_rtt_penalty || !valid_rtt(neigh))
        return 0;

    /* Function: linear behaviour between rtt_min and rtt_max. */
    if(neigh->rtt <= babel_ifp->rtt_min) {
        return 0;
    } else if(neigh->rtt <= babel_ifp->rtt_max) {
        unsigned long long tmp =
            (unsigned long long)babel_ifp->max_rtt_penalty *
            (neigh->rtt - babel_ifp->rtt_min) /
            (babel_ifp->rtt_max - babel_ifp->rtt_min);
        assert(CHECK_FLAG(tmp, 0x7FFFFFFF) == tmp);
        return tmp;
    } else {
        return babel_ifp->max_rtt_penalty;
    }
}

unsigned neighbour_cost(struct neighbour *neigh)
{
    unsigned a, b, cost;

    if(!if_up(neigh->ifp))
        return INFINITY;

    a = neighbour_txcost(neigh);

    if(a >= INFINITY)
        return INFINITY;

    b = neighbour_rxcost(neigh);
    if(b >= INFINITY)
        return INFINITY;

    if (!CHECK_FLAG(babel_get_if_nfo(neigh->ifp)->flags, BABEL_IF_LQ)
       || (a < 256 && b < 256)) {
        cost = a;
    } else {
        /* a = 256/alpha, b = 256/beta, where alpha and beta are the expected
           probabilities of a packet getting through in the direct and reverse
           directions. */
        a = MAX(a, 256);
        b = MAX(b, 256);
        /* 1/(alpha * beta), which is just plain ETX. */
        /* Since a and b are capped to 16 bits, overflow is impossible. */
        cost = (a * b + 128) >> 8;
    }

    cost += neighbour_rttcost(neigh);

    return MIN(cost, INFINITY);
}

int valid_rtt(struct neighbour *neigh)
{
    return (timeval_minus_msec(&babel_now, &neigh->rtt_time) < 180000) ? 1 : 0;
}