/*
 *  ircd-ratbox: A slightly useful ircd.
 *  m_nick.c: Sets a users nick.
 *
 *  Copyright (C) 1990 Jarkko Oikarinen and University of Oulu, Co Center
 *  Copyright (C) 1996-2002 Hybrid Development Team
 *  Copyright (C) 2002-2005 ircd-ratbox development team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
 *  USA
 *
 */

#include "stdinc.h"
#include "client.h"
#include "hash.h"
#include "match.h"
#include "ircd.h"
#include "numeric.h"
#include "s_conf.h"
#include "s_stats.h"
#include "s_user.h"
#include "hash.h"
#include "whowas.h"
#include "s_serv.h"
#include "send.h"
#include "channel.h"
#include "logger.h"
#include "msg.h"
#include "parse.h"
#include "modules.h"
#include "common.h"
#include "packet.h"
#include "scache.h"
#include "s_newconf.h"
#include "monitor.h"

/* Give all UID nicks the same TS. This ensures nick TS is always the same on
 * all servers for each nick-user pair, also if a user with a UID nick changes
 * their nick but is collided again (the server detecting the collision will
 * not propagate the nick change further). -- jilles
 */
#define SAVE_NICKTS 100

static int mr_nick(struct Client *, struct Client *, int, const char **);
static int m_nick(struct Client *, struct Client *, int, const char **);
static int mc_nick(struct Client *, struct Client *, int, const char **);
static int ms_nick(struct Client *, struct Client *, int, const char **);
static int ms_uid(struct Client *, struct Client *, int, const char **);
static int ms_euid(struct Client *, struct Client *, int, const char **);
static int ms_save(struct Client *, struct Client *, int, const char **);
static int can_save(struct Client *);
static void save_user(struct Client *, struct Client *, struct Client *);
static void bad_nickname(struct Client *, const char *);

struct Message nick_msgtab = {
    "NICK", 0, 0, 0, MFLG_SLOW,
    {{mr_nick, 0}, {m_nick, 0}, {mc_nick, 3}, {ms_nick, 0}, mg_ignore, {m_nick, 0}}
};
struct Message uid_msgtab = {
    "UID", 0, 0, 0, MFLG_SLOW,
    {mg_ignore, mg_ignore, mg_ignore, {ms_uid, 9}, mg_ignore, mg_ignore}
};
struct Message euid_msgtab = {
    "EUID", 0, 0, 0, MFLG_SLOW,
    {mg_ignore, mg_ignore, mg_ignore, {ms_euid, 12}, mg_ignore, mg_ignore}
};
struct Message save_msgtab = {
    "SAVE", 0, 0, 0, MFLG_SLOW,
    {mg_ignore, mg_ignore, mg_ignore, {ms_save, 3}, mg_ignore, mg_ignore}
};

mapi_clist_av1 nick_clist[] = { &nick_msgtab, &uid_msgtab, &euid_msgtab,
                                &save_msgtab, NULL
                              };

DECLARE_MODULE_AV1(nick, NULL, NULL, nick_clist, NULL, NULL, "$Revision: 3518 $");

static int change_remote_nick(struct Client *, struct Client *, time_t,
                              const char *, int);

static int clean_nick(const char *, int loc_client);
static int clean_username(const char *);
static int clean_host(const char *);
static int clean_uid(const char *uid);

static void set_initial_nick(struct Client *client_p, struct Client *source_p, char *nick);
static void change_local_nick(struct Client *client_p, struct Client *source_p, char *nick, int);
static int register_client(struct Client *client_p, struct Client *server,
                           const char *nick, time_t newts, int parc, const char *parv[]);

static int perform_nick_collides(struct Client *, struct Client *,
                                 struct Client *, int, const char **,
                                 time_t, const char *, const char *);
static int perform_nickchange_collides(struct Client *, struct Client *,
                                       struct Client *, int, const char **, time_t, const char *);

/* mr_nick()
 *       parv[1] = nickname
 */
static int
mr_nick(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;
    char nick[NICKLEN];

    if (strlen(client_p->id) == 3) {
        exit_client(client_p, client_p, client_p, "Mixing client and server protocol");
        return 0;
    }

    if(parc < 2 || EmptyString(parv[1])) {
        sendto_one(source_p, form_str(ERR_NONICKNAMEGIVEN),
                   me.name, EmptyString(source_p->name) ? "*" : source_p->name);
        return 0;
    }

    /* copy the nick and terminate it */
    rb_strlcpy(nick, parv[1], sizeof(nick));

    /* check the nickname is ok */
    if(!clean_nick(nick, 1)) {
        sendto_one(source_p, form_str(ERR_ERRONEUSNICKNAME),
                   me.name, EmptyString(source_p->name) ? "*" : source_p->name, parv[1]);
        return 0;
    }

    /* check if the nick is resv'd */
    if(find_nick_resv(nick)) {
        sendto_one(source_p, form_str(ERR_ERRONEUSNICKNAME),
                   me.name, EmptyString(source_p->name) ? "*" : source_p->name, nick);
        return 0;
    }

    if(irc_dictionary_find(nd_dict, nick)) {
        sendto_one(source_p, form_str(ERR_UNAVAILRESOURCE),
                   me.name, EmptyString(source_p->name) ? "*" : source_p->name, nick);
        return 0;
    }

    if((target_p = find_named_client(nick)) == NULL)
        set_initial_nick(client_p, source_p, nick);
    else if(source_p == target_p)
        strcpy(source_p->name, nick);
    else
        sendto_one(source_p, form_str(ERR_NICKNAMEINUSE), me.name, "*", nick);

    return 0;
}

/* m_nick()
 *     parv[1] = nickname
 */
static int
m_nick(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;
    char nick[NICKLEN];

    if(parc < 2 || EmptyString(parv[1])) {
        sendto_one(source_p, form_str(ERR_NONICKNAMEGIVEN), me.name, source_p->name);
        return 0;
    }

    /* mark end of grace period, to prevent nickflooding */
    if(!IsFloodDone(source_p))
        flood_endgrace(source_p);

    /* terminate nick to NICKLEN, we dont want clean_nick() to error! */
    rb_strlcpy(nick, parv[1], sizeof(nick));

    /* check the nickname is ok */
    if(!clean_nick(nick, 1)) {
        sendto_one(source_p, form_str(ERR_ERRONEUSNICKNAME), me.name, source_p->name, nick);
        return 0;
    }

    if(!IsExemptResv(source_p) && find_nick_resv(nick)) {
        sendto_one(source_p, form_str(ERR_ERRONEUSNICKNAME), me.name, source_p->name, nick);
        return 0;
    }

    if(irc_dictionary_find(nd_dict, nick)) {
        sendto_one(source_p, form_str(ERR_UNAVAILRESOURCE),
                   me.name, EmptyString(source_p->name) ? "*" : source_p->name, nick);
        return 0;
    }

    if((target_p = find_named_client(nick))) {
        /* If(target_p == source_p) the client is changing nicks between
         * equivalent nicknames ie: [nick] -> {nick}
         */
        if(target_p == source_p) {
            /* check the nick isnt exactly the same */
            if(strcmp(target_p->name, nick))
                change_local_nick(client_p, source_p, nick, 1);

        }

        /* drop unregged client */
        else if(IsUnknown(target_p)) {
            exit_client(NULL, target_p, &me, "Overridden");
            change_local_nick(client_p, source_p, nick, 1);
        } else
            sendto_one(source_p, form_str(ERR_NICKNAMEINUSE), me.name, source_p->name, nick);

        return 0;
    } else
        change_local_nick(client_p, source_p, nick, 1);

    return 0;
}

/* mc_nick()
 *
 * server -> server nick change
 *    parv[1] = nickname
 *    parv[2] = TS when nick change
 */
static int
mc_nick(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;
    time_t newts = 0;

    /* if nicks erroneous, or too long, kill */
    if(!clean_nick(parv[1], 0)) {
        bad_nickname(client_p, parv[1]);
        return 0;
    }

    newts = atol(parv[2]);
    target_p = find_named_client(parv[1]);

    /* if the nick doesnt exist, allow it and process like normal */
    if(target_p == NULL) {
        change_remote_nick(client_p, source_p, newts, parv[1], 1);
    } else if(IsUnknown(target_p)) {
        exit_client(NULL, target_p, &me, "Overridden");
        change_remote_nick(client_p, source_p, newts, parv[1], 1);
    } else if(target_p == source_p) {
        /* client changing case of nick */
        if(strcmp(target_p->name, parv[1]))
            change_remote_nick(client_p, source_p, newts, parv[1], 1);
    }
    /* we've got a collision! */
    else
        perform_nickchange_collides(source_p, client_p, target_p,
                                    parc, parv, newts, parv[1]);

    return 0;
}

static int
ms_nick(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    const char *nick, *server;

    nick = parc > 1 ? parv[1] : "?";
    server = parc > 7 ? parv[7] : "?";

    sendto_wallops_flags(UMODE_WALLOP, &me,
                         "Link %s cancelled, TS5 nickname %s on %s introduced (old server?)",
                         client_p->name, nick, server);
    sendto_server(NULL, NULL, CAP_TS6, NOCAPS,
                  ":%s WALLOPS :Link %s cancelled, TS5 nickname %s on %s introduced (old server?)",
                  me.id, client_p->name, nick, server);
    ilog(L_SERVER, "Link %s cancelled, TS5 nickname %s on %s introduced (old server?)",
         client_p->name, nick, server);

    exit_client(client_p, client_p, &me, "TS5 nickname introduced");

    return 0;
}

/* ms_uid()
 *     parv[1] - nickname
 *     parv[2] - hops
 *     parv[3] - TS
 *     parv[4] - umodes
 *     parv[5] - username
 *     parv[6] - hostname
 *     parv[7] - IP
 *     parv[8] - UID
 *     parv[9] - gecos
 */
static int
ms_uid(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;
    time_t newts = 0;
    char squitreason[120];

    newts = atol(parv[3]);

    if(parc != 10) {
        sendto_realops_snomask(SNO_GENERAL, L_ALL,
                               "Dropping server %s due to (invalid) command 'UID' "
                               "with %d arguments (expecting 10)", client_p->name, parc);
        ilog(L_SERVER, "Excess parameters (%d) for command 'UID' from %s.",
             parc, client_p->name);
        rb_snprintf(squitreason, sizeof squitreason,
                    "Excess parameters (%d) to %s command, expecting %d",
                    parc, "UID", 10);
        exit_client(client_p, client_p, client_p, squitreason);
        return 0;
    }

    /* if nicks erroneous, or too long, kill */
    if(!clean_nick(parv[1], 0)) {
        bad_nickname(client_p, parv[1]);
        return 0;
    }

    if(!clean_uid(parv[8])) {
        rb_snprintf(squitreason, sizeof squitreason,
                    "Invalid UID %s for nick %s on %s",
                    parv[8], parv[1], source_p->name);
        exit_client(client_p, client_p, client_p, squitreason);
        return 0;
    }

    if(!clean_username(parv[5]) || !clean_host(parv[6])) {
        ServerStats.is_kill++;
        sendto_realops_snomask(SNO_DEBUG, L_ALL,
                               "Bad user@host: %s@%s From: %s(via %s)",
                               parv[5], parv[6], source_p->name, client_p->name);
        sendto_one(client_p, ":%s KILL %s :%s (Bad user@host)", me.id, parv[8], me.name);
        return 0;
    }

    /* check length of clients gecos */
    if(strlen(parv[9]) > REALLEN) {
        char *s = LOCAL_COPY(parv[9]);
        sendto_realops_snomask(SNO_GENERAL, L_ALL, "Long realname from server %s for %s",
                               source_p->name, parv[1]);
        s[REALLEN] = '\0';
        parv[9] = s;
    }

    target_p = find_named_client(parv[1]);

    if(target_p == NULL) {
        register_client(client_p, source_p, parv[1], newts, parc, parv);
    } else if(IsUnknown(target_p)) {
        exit_client(NULL, target_p, &me, "Overridden");
        register_client(client_p, source_p, parv[1], newts, parc, parv);
    }
    /* we've got a collision! */
    else
        perform_nick_collides(source_p, client_p, target_p, parc, parv,
                              newts, parv[1], parv[8]);

    return 0;
}

/* ms_euid()
 *     parv[1] - nickname
 *     parv[2] - hops
 *     parv[3] - TS
 *     parv[4] - umodes
 *     parv[5] - username
 *     parv[6] - hostname
 *     parv[7] - IP
 *     parv[8] - UID
 *     parv[9] - realhost
 *     parv[10] - account
 *     parv[11] - gecos
 */
static int
ms_euid(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;
    time_t newts = 0;
    char squitreason[120];

    newts = atol(parv[3]);

    if(parc != 12) {
        sendto_realops_snomask(SNO_GENERAL, L_ALL,
                               "Dropping server %s due to (invalid) command 'EUID' "
                               "with %d arguments (expecting 12)", client_p->name, parc);
        ilog(L_SERVER, "Excess parameters (%d) for command 'EUID' from %s.",
             parc, client_p->name);
        rb_snprintf(squitreason, sizeof squitreason,
                    "Excess parameters (%d) to %s command, expecting %d",
                    parc, "EUID", 12);
        exit_client(client_p, client_p, client_p, squitreason);
        return 0;
    }

    /* if nicks erroneous, or too long, kill */
    if(!clean_nick(parv[1], 0)) {
        bad_nickname(client_p, parv[1]);
        return 0;
    }

    if(!clean_uid(parv[8])) {
        rb_snprintf(squitreason, sizeof squitreason,
                    "Invalid UID %s for nick %s on %s",
                    parv[8], parv[1], source_p->name);
        exit_client(client_p, client_p, client_p, squitreason);
        return 0;
    }

    if(!clean_username(parv[5]) || !clean_host(parv[6])) {
        ServerStats.is_kill++;
        sendto_realops_snomask(SNO_DEBUG, L_ALL,
                               "Bad user@host: %s@%s From: %s(via %s)",
                               parv[5], parv[6], source_p->name, client_p->name);
        sendto_one(client_p, ":%s KILL %s :%s (Bad user@host)", me.id, parv[8], me.name);
        return 0;
    }

    if(strcmp(parv[9], "*") && !clean_host(parv[9])) {
        ServerStats.is_kill++;
        sendto_realops_snomask(SNO_DEBUG, L_ALL,
                               "Bad realhost: %s From: %s(via %s)",
                               parv[9], source_p->name, client_p->name);
        sendto_one(client_p, ":%s KILL %s :%s (Bad user@host)", me.id, parv[8], me.name);
        return 0;
    }

    /* check length of clients gecos */
    if(strlen(parv[11]) > REALLEN) {
        char *s = LOCAL_COPY(parv[11]);
        sendto_realops_snomask(SNO_GENERAL, L_ALL, "Long realname from server %s for %s",
                               source_p->name, parv[1]);
        s[REALLEN] = '\0';
        parv[11] = s;
    }

    target_p = find_named_client(parv[1]);

    if(target_p == NULL) {
        register_client(client_p, source_p, parv[1], newts, parc, parv);
    } else if(IsUnknown(target_p)) {
        exit_client(NULL, target_p, &me, "Overridden");
        register_client(client_p, source_p, parv[1], newts, parc, parv);
    }
    /* we've got a collision! */
    else
        perform_nick_collides(source_p, client_p, target_p, parc, parv,
                              newts, parv[1], parv[8]);

    return 0;
}

/* ms_save()
 *   parv[1] - UID
 *   parv[2] - TS
 */
static int
ms_save(struct Client *client_p, struct Client *source_p, int parc, const char *parv[])
{
    struct Client *target_p;

    target_p = find_id(parv[1]);
    if (target_p == NULL)
        return 0;
    if (!IsPerson(target_p))
        sendto_realops_snomask(SNO_GENERAL, L_ALL,
                               "Ignored SAVE message for non-person %s from %s",
                               target_p->name, source_p->name);
    else if (IsDigit(target_p->name[0]))
        sendto_realops_snomask(SNO_DEBUG, L_ALL,
                               "Ignored noop SAVE message for %s from %s",
                               target_p->name, source_p->name);
    else if (target_p->tsinfo == atol(parv[2]))
        save_user(client_p, source_p, target_p);
    else
        sendto_realops_snomask(SNO_SKILL, L_ALL,
                               "Ignored SAVE message for %s from %s",
                               target_p->name, source_p->name);
    return 0;
}

/* clean_nick()
 *
 * input	- nickname to check
 * output	- 0 if erroneous, else 1
 * side effects -
 */
static int
clean_nick(const char *nick, int loc_client)
{
    int len = 0;

    /* nicks cant start with a digit or -, and must have a length */
    if(*nick == '-' || *nick == '\0')
        return 0;

    if(loc_client && IsDigit(*nick))
        return 0;

    for(; *nick; nick++) {
        len++;
        if(!IsNickChar(*nick))
            return 0;
    }

    /* nicklen is +1 */
    if(len >= NICKLEN)
        return 0;

    return 1;
}

/* clean_username()
 *
 * input	- username to check
 * output	- 0 if erroneous, else 0
 * side effects -
 */
static int
clean_username(const char *username)
{
    int len = 0;

    for(; *username; username++) {
        len++;

        if(!IsUserChar(*username))
            return 0;
    }

    if(len > USERLEN)
        return 0;

    return 1;
}

/* clean_host()
 *
 * input	- host to check
 * output	- 0 if erroneous, else 0
 * side effects -
 */
static int
clean_host(const char *host)
{
    int len = 0;

    for(; *host; host++) {
        len++;

        if(!IsHostChar(*host))
            return 0;
    }

    if(len > HOSTLEN)
        return 0;

    return 1;
}

static int
clean_uid(const char *uid)
{
    int len = 1;

    if(!IsDigit(*uid++))
        return 0;

    for(; *uid; uid++) {
        len++;

        if(!IsIdChar(*uid))
            return 0;
    }

    if(len != IDLEN - 1)
        return 0;

    return 1;
}

static void
set_initial_nick(struct Client *client_p, struct Client *source_p, char *nick)
{
    char buf[USERLEN + 1];
    char note[NICKLEN + 10];

    /* This had to be copied here to avoid problems.. */
    source_p->tsinfo = rb_current_time();
    if(source_p->name[0])
        del_from_client_hash(source_p->name, source_p);

    strcpy(source_p->name, nick);
    add_to_client_hash(nick, source_p);

    rb_snprintf(note, sizeof(note), "Nick: %s", nick);
    rb_note(client_p->localClient->F, note);

    if(source_p->flags & FLAGS_SENTUSER) {
        rb_strlcpy(buf, source_p->username, sizeof(buf));

        /* got user, heres nick. */
        register_local_user(client_p, source_p, buf);

    }
}

static void
change_local_nick(struct Client *client_p, struct Client *source_p,
                  char *nick, int dosend)
{
    struct Client *target_p;
    rb_dlink_node *ptr, *next_ptr;
    struct Channel *chptr;
    char note[NICKLEN + 10];
    int samenick;

    if (dosend) {
        chptr = find_bannickchange_channel(source_p);
        if (chptr != NULL) {
            sendto_one_numeric(source_p, ERR_BANNICKCHANGE,
                               form_str(ERR_BANNICKCHANGE),
                               nick, chptr->chname);
            return;
        }

        chptr = find_nonickchange_channel(source_p);
        if (chptr != NULL) {
            sendto_one_numeric(source_p, ERR_NONICK,
                               form_str(ERR_NONICK),
                               chptr->chname);
            return;
        }

        if((source_p->localClient->last_nick_change + ConfigFileEntry.max_nick_time) < rb_current_time())
            source_p->localClient->number_of_nick_changes = 0;

        source_p->localClient->last_nick_change = rb_current_time();
        source_p->localClient->number_of_nick_changes++;

        if(ConfigFileEntry.anti_nick_flood && !IsOper(source_p) &&
           source_p->localClient->number_of_nick_changes > ConfigFileEntry.max_nick_changes) {
            sendto_one(source_p, form_str(ERR_NICKTOOFAST),
                       me.name, source_p->name, source_p->name,
                       nick, ConfigFileEntry.max_nick_time);
            return;
        }
    }

    samenick = irccmp(source_p->name, nick) ? 0 : 1;

    /* dont reset TS if theyre just changing case of nick */
    if(!samenick) {
        /* force the TS to increase -- jilles */
        if (source_p->tsinfo >= rb_current_time())
            source_p->tsinfo++;
        else
            source_p->tsinfo = rb_current_time();
        monitor_signoff(source_p);
        /* we only do bancache for local users -- jilles */
        if(source_p->user)
            invalidate_bancache_user(source_p);
    }

    sendto_realops_snomask(SNO_NCHANGE, L_ALL,
                           "Nick change: From %s to %s [%s@%s]",
                           source_p->name, nick, source_p->username, source_p->host);

    /* send the nick change to the users channels */
    sendto_common_channels_local(source_p, NOCAPS, ":%s!%s@%s NICK :%s",
                                 source_p->name, source_p->username, source_p->host, nick);

    /* send the nick change to servers.. */
    if(source_p->user) {
        add_history(source_p, 1);

        if (dosend) {
            sendto_server(client_p, NULL, CAP_TS6, NOCAPS, ":%s NICK %s :%ld",
                          use_id(source_p), nick, (long) source_p->tsinfo);
        }
    }

    /* Finally, add to hash */
    del_from_client_hash(source_p->name, source_p);
    strcpy(source_p->name, nick);
    add_to_client_hash(nick, source_p);

    if(!samenick)
        monitor_signon(source_p);

    /* Make sure everyone that has this client on its accept list
     * loses that reference.
     */
    /* we used to call del_all_accepts() here, but theres no real reason
     * to clear a clients own list of accepted clients.  So just remove
     * them from everyone elses list --anfl
     */
    RB_DLINK_FOREACH_SAFE(ptr, next_ptr, source_p->on_allow_list.head) {
        target_p = ptr->data;

        rb_dlinkFindDestroy(source_p, &target_p->localClient->allow_list);
        rb_dlinkDestroy(ptr, &source_p->on_allow_list);
    }

    rb_snprintf(note, sizeof(note), "Nick: %s", nick);
    rb_note(client_p->localClient->F, note);

    return;
}

/*
 * change_remote_nick()
 */
static int
change_remote_nick(struct Client *client_p, struct Client *source_p,
                   time_t newts, const char *nick, int dosend)
{
    struct nd_entry *nd;
    int samenick = irccmp(source_p->name, nick) ? 0 : 1;

    /* client changing their nick - dont reset ts if its same */
    if(!samenick) {
        source_p->tsinfo = newts ? newts : rb_current_time();
        monitor_signoff(source_p);
    }

    sendto_common_channels_local(source_p, NOCAPS, ":%s!%s@%s NICK :%s",
                                 source_p->name, source_p->username, source_p->host, nick);

    if(source_p->user) {
        add_history(source_p, 1);
        if (dosend) {
            sendto_server(client_p, NULL, CAP_TS6, NOCAPS, ":%s NICK %s :%ld",
                          use_id(source_p), nick, (long) source_p->tsinfo);
        }
    }

    del_from_client_hash(source_p->name, source_p);

    /* invalidate nick delay when a remote client uses the nick.. */
    if((nd = irc_dictionary_retrieve(nd_dict, nick)))
        free_nd_entry(nd);

    strcpy(source_p->name, nick);
    add_to_client_hash(nick, source_p);

    if(!samenick)
        monitor_signon(source_p);

    /* remove all accepts pointing to the client */
    del_all_accepts(source_p);

    return 0;
}

static int
perform_nick_collides(struct Client *source_p, struct Client *client_p,
                      struct Client *target_p, int parc, const char *parv[],
                      time_t newts, const char *nick, const char *uid)
{
    int sameuser;
    int use_save;
    const char *action;

    use_save = ConfigFileEntry.collision_fnc && can_save(target_p) &&
               uid != NULL && can_save(source_p);
    action = use_save ? "saved" : "killed";

    /* if we dont have a ts, or their TS's are the same, kill both */
    if(!newts || !target_p->tsinfo || (newts == target_p->tsinfo)) {
        sendto_realops_snomask(SNO_SKILL, L_ALL,
                               "Nick collision on %s(%s <- %s)(both %s)",
                               target_p->name, target_p->from->name, client_p->name, action);

        if (use_save) {
            save_user(&me, &me, target_p);
            ServerStats.is_save++;
            sendto_one(client_p, ":%s SAVE %s %ld", me.id,
                       uid, (long)newts);
            register_client(client_p, source_p,
                            uid, SAVE_NICKTS, parc, parv);
        } else {
            sendto_one_numeric(target_p, ERR_NICKCOLLISION,
                               form_str(ERR_NICKCOLLISION), target_p->name);

            /* if the new client being introduced has a UID, we need to
             * issue a KILL for it..
             */
            if(uid)
                sendto_one(client_p, ":%s KILL %s :%s (Nick collision (new))",
                           me.id, uid, me.name);

            /* we then need to KILL the old client everywhere */
            kill_client_serv_butone(NULL, target_p, "%s (Nick collision (new))", me.name);
            ServerStats.is_kill++;

            target_p->flags |= FLAGS_KILLED;
            exit_client(client_p, target_p, &me, "Nick collision (new)");
        }
        return 0;
    }
    /* the timestamps are different */
    else {
        sameuser = (target_p->user) && !irccmp(target_p->username, parv[5])
                   && !irccmp(target_p->host, parv[6]);

        if((sameuser && newts < target_p->tsinfo) ||
           (!sameuser && newts > target_p->tsinfo)) {
            /* if we have a UID, then we need to issue a KILL,
             * otherwise we do nothing and hope that the other
             * client will collide it..
             */
            if (use_save) {
                sendto_one(client_p, ":%s SAVE %s %ld", me.id,
                           uid, (long)newts);
                register_client(client_p, source_p,
                                uid, SAVE_NICKTS, parc, parv);
            } else if(uid)
                sendto_one(client_p,
                           ":%s KILL %s :%s (Nick collision (new))",
                           me.id, uid, me.name);
            return 0;
        } else {
            if(sameuser)
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick collision on %s(%s <- %s)(older %s)",
                                       target_p->name, target_p->from->name,
                                       client_p->name, action);
            else
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick collision on %s(%s <- %s)(newer %s)",
                                       target_p->name, target_p->from->name,
                                       client_p->name, action);

            if (use_save) {
                ServerStats.is_save++;
                save_user(&me, &me, target_p);
            } else {
                ServerStats.is_kill++;
                sendto_one_numeric(target_p, ERR_NICKCOLLISION,
                                   form_str(ERR_NICKCOLLISION), target_p->name);

                /* now we just need to kill the existing client */
                kill_client_serv_butone(client_p, target_p,
                                        "%s (Nick collision (new))", me.name);

                target_p->flags |= FLAGS_KILLED;
                (void) exit_client(client_p, target_p, &me, "Nick collision");
            }

            register_client(client_p, source_p,
                            nick, newts, parc, parv);

            return 0;
        }
    }
}


static int
perform_nickchange_collides(struct Client *source_p, struct Client *client_p,
                            struct Client *target_p, int parc,
                            const char *parv[], time_t newts, const char *nick)
{
    int sameuser;
    int use_save;
    const char *action;

    use_save = ConfigFileEntry.collision_fnc && can_save(target_p) &&
               can_save(source_p);
    action = use_save ? "saved" : "killed";

    /* its a client changing nick and causing a collide */
    if(!newts || !target_p->tsinfo || (newts == target_p->tsinfo) || !source_p->user) {
        sendto_realops_snomask(SNO_SKILL, L_ALL,
                               "Nick change collision from %s to %s(%s <- %s)(both %s)",
                               source_p->name, target_p->name, target_p->from->name,
                               client_p->name, action);

        if (use_save) {
            ServerStats.is_save += 2;
            save_user(&me, &me, target_p);
            sendto_one(client_p, ":%s SAVE %s %ld", me.id,
                       source_p->id, (long)newts);
            /* don't send a redundant nick change */
            if (!IsDigit(source_p->name[0]))
                change_remote_nick(client_p, source_p, SAVE_NICKTS, source_p->id, 1);
        } else {
            ServerStats.is_kill++;
            sendto_one_numeric(target_p, ERR_NICKCOLLISION,
                               form_str(ERR_NICKCOLLISION), target_p->name);

            kill_client_serv_butone(NULL, source_p, "%s (Nick change collision)", me.name);

            ServerStats.is_kill++;

            kill_client_serv_butone(NULL, target_p, "%s (Nick change collision)", me.name);

            target_p->flags |= FLAGS_KILLED;
            exit_client(NULL, target_p, &me, "Nick collision(new)");
            source_p->flags |= FLAGS_KILLED;
            exit_client(client_p, source_p, &me, "Nick collision(old)");
        }
        return 0;
    } else {
        sameuser = !irccmp(target_p->username, source_p->username) &&
                   !irccmp(target_p->host, source_p->host);

        if((sameuser && newts < target_p->tsinfo) ||
           (!sameuser && newts > target_p->tsinfo)) {
            if(sameuser)
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick change collision from %s to %s(%s <- %s)(older %s)",
                                       source_p->name, target_p->name,
                                       target_p->from->name, client_p->name, action);
            else
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick change collision from %s to %s(%s <- %s)(newer %s)",
                                       source_p->name, target_p->name,
                                       target_p->from->name, client_p->name, action);

            if (use_save) {
                ServerStats.is_save++;
                /* can't broadcast a SAVE because the
                 * nickchange has happened at client_p
                 * but not in other directions -- jilles */
                sendto_one(client_p, ":%s SAVE %s %ld", me.id,
                           source_p->id, (long)newts);
                /* send a :<id> NICK <id> <ts> (!) */
                if (!IsDigit(source_p->name[0]))
                    change_remote_nick(client_p, source_p, SAVE_NICKTS, source_p->id, 1);
            } else {
                ServerStats.is_kill++;

                sendto_one_numeric(target_p, ERR_NICKCOLLISION,
                                   form_str(ERR_NICKCOLLISION), target_p->name);

                /* kill the client issuing the nickchange */
                kill_client_serv_butone(client_p, source_p,
                                        "%s (Nick change collision)", me.name);

                source_p->flags |= FLAGS_KILLED;

                if(sameuser)
                    exit_client(client_p, source_p, &me, "Nick collision(old)");
                else
                    exit_client(client_p, source_p, &me, "Nick collision(new)");
            }
            return 0;
        } else {
            if(sameuser)
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick collision on %s(%s <- %s)(older %s)",
                                       target_p->name, target_p->from->name,
                                       client_p->name, action);
            else
                sendto_realops_snomask(SNO_SKILL, L_ALL,
                                       "Nick collision on %s(%s <- %s)(newer %s)",
                                       target_p->name, target_p->from->name,
                                       client_p->name, action);

            if (use_save) {
                ServerStats.is_save++;
                save_user(&me, &me, target_p);
            } else {
                sendto_one_numeric(target_p, ERR_NICKCOLLISION,
                                   form_str(ERR_NICKCOLLISION), target_p->name);

                /* kill the client who existed before hand */
                kill_client_serv_butone(client_p, target_p, "%s (Nick collision)", me.name);

                ServerStats.is_kill++;

                target_p->flags |= FLAGS_KILLED;
                (void) exit_client(client_p, target_p, &me, "Nick collision");
            }
        }
    }

    change_remote_nick(client_p, source_p, newts, nick, 1);

    return 0;
}

static int
register_client(struct Client *client_p, struct Client *server,
                const char *nick, time_t newts, int parc, const char *parv[])
{
    struct Client *source_p;
    struct User *user;
    struct nd_entry *nd;
    const char *m;
    int flag;

    source_p = make_client(client_p);
    user = make_user(source_p);
    rb_dlinkAddTail(source_p, &source_p->node, &global_client_list);

    source_p->hopcount = atoi(parv[2]);
    source_p->tsinfo = newts;

    strcpy(source_p->name, nick);
    rb_strlcpy(source_p->username, parv[5], sizeof(source_p->username));
    rb_strlcpy(source_p->host, parv[6], sizeof(source_p->host));
    rb_strlcpy(source_p->orighost, source_p->host, sizeof(source_p->orighost));

    if(parc == 12) {
        rb_strlcpy(source_p->info, parv[11], sizeof(source_p->info));
        rb_strlcpy(source_p->sockhost, parv[7], sizeof(source_p->sockhost));
        rb_strlcpy(source_p->id, parv[8], sizeof(source_p->id));
        add_to_id_hash(source_p->id, source_p);
        if (strcmp(parv[9], "*")) {
            rb_strlcpy(source_p->orighost, parv[9], sizeof(source_p->orighost));
            if (irccmp(source_p->host, source_p->orighost))
                SetDynSpoof(source_p);
        }
        if (strcmp(parv[10], "*"))
            rb_strlcpy(source_p->user->suser, parv[10], sizeof(source_p->user->suser));
    } else if(parc == 10) {
        rb_strlcpy(source_p->info, parv[9], sizeof(source_p->info));
        rb_strlcpy(source_p->sockhost, parv[7], sizeof(source_p->sockhost));
        rb_strlcpy(source_p->id, parv[8], sizeof(source_p->id));
        add_to_id_hash(source_p->id, source_p);
    } else {
        s_assert(0);
    }

    /* remove any nd entries for this nick */
    if((nd = irc_dictionary_retrieve(nd_dict, nick)))
        free_nd_entry(nd);

    add_to_client_hash(nick, source_p);
    add_to_hostname_hash(source_p->orighost, source_p);
    monitor_signon(source_p);

    m = &parv[4][1];
    while(*m) {
        flag = user_modes[(unsigned char) *m];

        if(flag & UMODE_SERVICE) {
            int hit = 0;
            rb_dlink_node *ptr;

            RB_DLINK_FOREACH(ptr, service_list.head) {
                if(!irccmp((const char *) ptr->data, server->name)) {
                    hit++;
                    break;
                }
            }

            if(!hit) {
                m++;
                continue;
            }
        }

        /* increment +i count if theyre invis */
        if(!(source_p->umodes & UMODE_INVISIBLE) && (flag & UMODE_INVISIBLE))
            Count.invisi++;

        /* increment opered count if theyre opered */
        if(!(source_p->umodes & UMODE_OPER) && (flag & UMODE_OPER))
            Count.oper++;

        source_p->umodes |= flag;
        m++;
    }

    if(IsOper(source_p) && !IsService(source_p))
        rb_dlinkAddAlloc(source_p, &oper_list);

    SetRemoteClient(source_p);

    if(++Count.total > Count.max_tot)
        Count.max_tot = Count.total;

    source_p->servptr = server;

    rb_dlinkAdd(source_p, &source_p->lnode, &source_p->servptr->serv->users);

    call_hook(h_new_remote_user, source_p);

    return (introduce_client(client_p, source_p, user, nick, parc == 12));
}

/* Check if we can do SAVE. target_p can be a client to save or a
 * server introducing a client -- jilles */
static int
can_save(struct Client *target_p)
{
    struct Client *serv_p;

    if (MyClient(target_p))
        return 1;
    if (!has_id(target_p))
        return 0;
    serv_p = IsServer(target_p) ? target_p : target_p->servptr;
    while (serv_p != NULL && serv_p != &me) {
        if (!(serv_p->serv->caps & CAP_SAVE))
            return 0;
        serv_p = serv_p->servptr;
    }
    return serv_p == &me;
}

static void
save_user(struct Client *client_p, struct Client *source_p,
          struct Client *target_p)
{
    if (!MyConnect(target_p) && (!has_id(target_p) || !IsCapable(target_p->from, CAP_SAVE))) {
        /* This shouldn't happen */
        /* Note we only need SAVE support in this direction */
        sendto_realops_snomask(SNO_GENERAL, L_ALL,
                               "Killed %s!%s@%s for nick collision detected by %s (%s does not support SAVE)",
                               target_p->name, target_p->username, target_p->host, source_p->name, target_p->from->name);
        kill_client_serv_butone(NULL, target_p, "%s (Nick collision (no SAVE support))", me.name);
        ServerStats.is_kill++;

        target_p->flags |= FLAGS_KILLED;
        (void) exit_client(NULL, target_p, &me, "Nick collision (no SAVE support)");
        return;
    }
    sendto_server(client_p, NULL, CAP_SAVE|CAP_TS6, NOCAPS, ":%s SAVE %s %ld",
                  source_p->id, target_p->id, (long)target_p->tsinfo);
    sendto_server(client_p, NULL, CAP_TS6, CAP_SAVE, ":%s NICK %s :%ld",
                  target_p->id, target_p->id, (long)SAVE_NICKTS);
    if (!IsMe(client_p))
        sendto_realops_snomask(SNO_SKILL, L_ALL,
                               "Received SAVE message for %s from %s",
                               target_p->name, source_p->name);
    if (MyClient(target_p)) {
        sendto_one_numeric(target_p, RPL_SAVENICK,
                           form_str(RPL_SAVENICK), target_p->id);
        change_local_nick(target_p, target_p, target_p->id, 0);
        target_p->tsinfo = SAVE_NICKTS;
    } else
        change_remote_nick(target_p, target_p, SAVE_NICKTS, target_p->id, 0);
}

static void bad_nickname(struct Client *client_p, const char *nick)
{
    char squitreason[100];

    sendto_wallops_flags(UMODE_WALLOP, &me,
                         "Squitting %s because of bad nickname %s (NICKLEN mismatch?)",
                         client_p->name, nick);
    sendto_server(NULL, NULL, CAP_TS6, NOCAPS,
                  ":%s WALLOPS :Squitting %s because of bad nickname %s (NICKLEN mismatch?)",
                  me.id, client_p->name, nick);
    ilog(L_SERVER, "Link %s cancelled, bad nickname %s sent (NICKLEN mismatch?)",
         client_p->name, nick);

    rb_snprintf(squitreason, sizeof squitreason,
                "Bad nickname introduced [%s]", nick);
    exit_client(client_p, client_p, &me, squitreason);
}
