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<?php

/**
 * Handle merging and splitting of topics
 *
 * Simple Machines Forum (SMF)
 *
 * @package SMF
 * @author Simple Machines https://www.simplemachines.org
 * @copyright 2020 Simple Machines and individual contributors
 * @license https://www.simplemachines.org/about/smf/license.php BSD
 *
 * @version 2.1 RC2
 *
 * Original module by Mach8 - We'll never forget you.
 */

if (!defined('SMF'))
    die('No direct access...');

/**
 * splits a topic into two topics.
 * delegates to the other functions (based on the URL parameter 'sa').
 * loads the SplitTopics template.
 * requires the split_any permission.
 * is accessed with ?action=splittopics.
 */
function SplitTopics()
{
    global $topic, $sourcedir;

    // And... which topic were you splitting, again?
    if (empty($topic))
        fatal_lang_error('numbers_one_to_nine', false);

    // Are you allowed to split topics?
    isAllowedTo('split_any');

    // Load up the "dependencies" - the template, getMsgMemberID(), and sendNotifications().
    if (!isset($_REQUEST['xml']))
        loadTemplate('SplitTopics');
    require_once($sourcedir . '/Subs-Boards.php');
    require_once($sourcedir . '/Subs-Post.php');

    $subActions = array(
        'selectTopics' => 'SplitSelectTopics',
        'execute' => 'SplitExecute',
        'index' => 'SplitIndex',
        'splitSelection' => 'SplitSelectionExecute',
    );

    // ?action=splittopics;sa=LETSBREAKIT won't work, sorry.
    if (empty($_REQUEST['sa']) || !isset($subActions[$_REQUEST['sa']]))
        SplitIndex();

    else
        call_helper($subActions[$_REQUEST['sa']]);
}

/**
 * screen shown before the actual split.
 * is accessed with ?action=splittopics;sa=index.
 * default sub action for ?action=splittopics.
 * uses 'ask' sub template of the SplitTopics template.
 * redirects to SplitSelectTopics if the message given turns out to be
 * the first message of a topic.
 * shows the user three ways to split the current topic.
 */
function SplitIndex()
{
    global $txt, $topic, $context, $smcFunc, $modSettings;

    // Validate "at".
    if (empty($_GET['at']))
        fatal_lang_error('numbers_one_to_nine', false);
    $_GET['at'] = (int) $_GET['at'];

    // Retrieve the subject and stuff of the specific topic/message.
    $request = $smcFunc['db_query']('', '
        SELECT m.subject, t.num_replies, t.unapproved_posts, t.id_first_msg, t.approved
        FROM {db_prefix}messages AS m
            INNER JOIN {db_prefix}topics AS t ON (t.id_topic = {int:current_topic})
        WHERE m.id_msg = {int:split_at}' . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
            AND m.approved = 1') . '
            AND m.id_topic = {int:current_topic}
        LIMIT 1',
        array(
            'current_topic' => $topic,
            'split_at' => $_GET['at'],
        )
    );
    if ($smcFunc['db_num_rows']($request) == 0)
        fatal_lang_error('cant_find_messages');

    list ($_REQUEST['subname'], $num_replies, $unapproved_posts, $id_first_msg, $approved) = $smcFunc['db_fetch_row']($request);
    $smcFunc['db_free_result']($request);

    // If not approved validate they can see it.
    if ($modSettings['postmod_active'] && !$approved)
        isAllowedTo('approve_posts');

    // If this topic has unapproved posts, we need to count them too...
    if ($modSettings['postmod_active'] && allowedTo('approve_posts'))
        $num_replies += $unapproved_posts - ($approved ? 0 : 1);

    // Check if there is more than one message in the topic.  (there should be.)
    if ($num_replies < 1)
        fatal_lang_error('topic_one_post', false);

    // Check if this is the first message in the topic (if so, the first and second option won't be available)
    if ($id_first_msg == $_GET['at'])
        return SplitSelectTopics();

    // Basic template information....
    $context['message'] = array(
        'id' => $_GET['at'],
        'subject' => $_REQUEST['subname']
    );
    $context['sub_template'] = 'ask';
    $context['page_title'] = $txt['split'];
}

/**
 * do the actual split.
 * is accessed with ?action=splittopics;sa=execute.
 * uses the main SplitTopics template.
 * supports three ways of splitting:
 * (1) only one message is split off.
 * (2) all messages after and including a given message are split off.
 * (3) select topics to split (redirects to SplitSelectTopics()).
 * uses splitTopic function to do the actual splitting.
 */
function SplitExecute()
{
    global $txt, $topic, $context, $smcFunc;

    // Check the session to make sure they meant to do this.
    checkSession();

    // Clean up the subject.
    if (!isset($_POST['subname']) || $_POST['subname'] == '')
        $_POST['subname'] = $txt['new_topic'];

    // Redirect to the selector if they chose selective.
    if ($_POST['step2'] == 'selective')
        redirectexit ('action=splittopics;sa=selectTopics;subname=' . $_POST['subname'] . ';topic=' . $topic . '.0;start2=0');

    $_POST['at'] = (int) $_POST['at'];
    $messagesToBeSplit = array();

    if ($_POST['step2'] == 'afterthis')
    {
        // Fetch the message IDs of the topic that are at or after the message.
        $request = $smcFunc['db_query']('', '
            SELECT id_msg
            FROM {db_prefix}messages
            WHERE id_topic = {int:current_topic}
                AND id_msg >= {int:split_at}',
            array(
                'current_topic' => $topic,
                'split_at' => $_POST['at'],
            )
        );
        while ($row = $smcFunc['db_fetch_assoc']($request))
            $messagesToBeSplit[] = $row['id_msg'];

        $smcFunc['db_free_result']($request);
    }
    // Only the selected message has to be split. That should be easy.
    elseif ($_POST['step2'] == 'onlythis')
        $messagesToBeSplit[] = $_POST['at'];
    // There's another action?!
    else
        fatal_lang_error('no_access', false);

    $context['old_topic'] = $topic;
    $context['new_topic'] = splitTopic($topic, $messagesToBeSplit, $_POST['subname']);
    $context['page_title'] = $txt['split'];
}

/**
 * allows the user to select the messages to be split.
 * is accessed with ?action=splittopics;sa=selectTopics.
 * uses 'select' sub template of the SplitTopics template or (for
 * XMLhttp) the 'split' sub template of the Xml template.
 * supports XMLhttp for adding/removing a message to the selection.
 * uses a session variable to store the selected topics.
 * shows two independent page indexes for both the selected and
 * not-selected messages (;topic=1.x;start2=y).
 */
function SplitSelectTopics()
{
    global $txt, $scripturl, $topic, $context, $modSettings, $original_msgs, $smcFunc, $options;

    $context['page_title'] = $txt['split'] . ' - ' . $txt['select_split_posts'];

    // Haven't selected anything have we?
    $_SESSION['split_selection'][$topic] = empty($_SESSION['split_selection'][$topic]) ? array() : $_SESSION['split_selection'][$topic];

    // This is a special case for split topics from quick-moderation checkboxes
    if (isset($_REQUEST['subname_enc']))
        $_REQUEST['subname'] = urldecode($_REQUEST['subname_enc']);

    $context['not_selected'] = array(
        'num_messages' => 0,
        'start' => empty($_REQUEST['start']) ? 0 : (int) $_REQUEST['start'],
        'messages' => array(),
    );

    $context['selected'] = array(
        'num_messages' => 0,
        'start' => empty($_REQUEST['start2']) ? 0 : (int) $_REQUEST['start2'],
        'messages' => array(),
    );

    $context['topic'] = array(
        'id' => $topic,
        'subject' => urlencode($_REQUEST['subname']),
    );

    // Some stuff for our favorite template.
    $context['new_subject'] = $_REQUEST['subname'];

    // Using the "select" sub template.
    $context['sub_template'] = isset($_REQUEST['xml']) ? 'split' : 'select';

    // Are we using a custom messages per page?
    $context['messages_per_page'] = empty($modSettings['disableCustomPerPage']) && !empty($options['messages_per_page']) ? $options['messages_per_page'] : $modSettings['defaultMaxMessages'];

    // Get the message ID's from before the move.
    if (isset($_REQUEST['xml']))
    {
        $original_msgs = array(
            'not_selected' => array(),
            'selected' => array(),
        );
        $request = $smcFunc['db_query']('', '
            SELECT id_msg
            FROM {db_prefix}messages
            WHERE id_topic = {int:current_topic}' . (empty($_SESSION['split_selection'][$topic]) ? '' : '
                AND id_msg NOT IN ({array_int:no_split_msgs})') . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
                AND approved = {int:is_approved}') . '
                ' . (empty($options['view_newest_first']) ? '' : 'ORDER BY id_msg DESC') . '
                LIMIT {int:start}, {int:messages_per_page}',
            array(
                'current_topic' => $topic,
                'no_split_msgs' => empty($_SESSION['split_selection'][$topic]) ? array() : $_SESSION['split_selection'][$topic],
                'is_approved' => 1,
                'start' => $context['not_selected']['start'],
                'messages_per_page' => $context['messages_per_page'],
            )
        );
        // You can't split the last message off.
        if (empty($context['not_selected']['start']) && $smcFunc['db_num_rows']($request) <= 1 && $_REQUEST['move'] == 'down')
            $_REQUEST['move'] = '';
        while ($row = $smcFunc['db_fetch_assoc']($request))
            $original_msgs['not_selected'][] = $row['id_msg'];
        $smcFunc['db_free_result']($request);
        if (!empty($_SESSION['split_selection'][$topic]))
        {
            $request = $smcFunc['db_query']('', '
                SELECT id_msg
                FROM {db_prefix}messages
                WHERE id_topic = {int:current_topic}
                    AND id_msg IN ({array_int:split_msgs})' . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
                    AND approved = {int:is_approved}') . '
                ' . (empty($options['view_newest_first']) ? '' : 'ORDER BY id_msg DESC') . '
                LIMIT {int:start}, {int:messages_per_page}',
                array(
                    'current_topic' => $topic,
                    'split_msgs' => $_SESSION['split_selection'][$topic],
                    'is_approved' => 1,
                    'start' => $context['selected']['start'],
                    'messages_per_page' => $context['messages_per_page'],
                )
            );
            while ($row = $smcFunc['db_fetch_assoc']($request))
                $original_msgs['selected'][] = $row['id_msg'];

            $smcFunc['db_free_result']($request);
        }
    }

    // (De)select a message..
    if (!empty($_REQUEST['move']))
    {
        $_REQUEST['msg'] = (int) $_REQUEST['msg'];

        if ($_REQUEST['move'] == 'reset')
            $_SESSION['split_selection'][$topic] = array();
        elseif ($_REQUEST['move'] == 'up')
            $_SESSION['split_selection'][$topic] = array_diff($_SESSION['split_selection'][$topic], array($_REQUEST['msg']));
        else
            $_SESSION['split_selection'][$topic][] = $_REQUEST['msg'];
    }

    // Make sure the selection is still accurate.
    if (!empty($_SESSION['split_selection'][$topic]))
    {
        $request = $smcFunc['db_query']('', '
            SELECT id_msg
            FROM {db_prefix}messages
            WHERE id_topic = {int:current_topic}
                AND id_msg IN ({array_int:split_msgs})' . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
                AND approved = {int:is_approved}'),
            array(
                'current_topic' => $topic,
                'split_msgs' => $_SESSION['split_selection'][$topic],
                'is_approved' => 1,
            )
        );
        $_SESSION['split_selection'][$topic] = array();

        while ($row = $smcFunc['db_fetch_assoc']($request))
            $_SESSION['split_selection'][$topic][] = $row['id_msg'];

        $smcFunc['db_free_result']($request);
    }

    // Get the number of messages (not) selected to be split.
    $request = $smcFunc['db_query']('', '
        SELECT ' . (empty($_SESSION['split_selection'][$topic]) ? '0' : 'm.id_msg IN ({array_int:split_msgs})') . ' AS is_selected, COUNT(*) AS num_messages
        FROM {db_prefix}messages AS m
        WHERE m.id_topic = {int:current_topic}' . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
            AND approved = {int:is_approved}') . (empty($_SESSION['split_selection'][$topic]) ? '' : '
        GROUP BY is_selected'),
        array(
            'current_topic' => $topic,
            'split_msgs' => !empty($_SESSION['split_selection'][$topic]) ? $_SESSION['split_selection'][$topic] : array(),
            'is_approved' => 1,
        )
    );
    while ($row = $smcFunc['db_fetch_assoc']($request))
        $context[empty($row['is_selected']) || $row['is_selected'] == 'f' ? 'not_selected' : 'selected']['num_messages'] = $row['num_messages'];
    $smcFunc['db_free_result']($request);

    // Fix an oversized starting page (to make sure both pageindexes are properly set).
    if ($context['selected']['start'] >= $context['selected']['num_messages'])
        $context['selected']['start'] = $context['selected']['num_messages'] <= $context['messages_per_page'] ? 0 : ($context['selected']['num_messages'] - (($context['selected']['num_messages'] % $context['messages_per_page']) == 0 ? $context['messages_per_page'] : ($context['selected']['num_messages'] % $context['messages_per_page'])));

    // Build a page list of the not-selected topics...
    $context['not_selected']['page_index'] = constructPageIndex($scripturl . '?action=splittopics;sa=selectTopics;subname=' . strtr(urlencode($_REQUEST['subname']), array('%' => '%%')) . ';topic=' . $topic . '.%1$d;start2=' . $context['selected']['start'], $context['not_selected']['start'], $context['not_selected']['num_messages'], $context['messages_per_page'], true);
    // ...and one of the selected topics.
    $context['selected']['page_index'] = constructPageIndex($scripturl . '?action=splittopics;sa=selectTopics;subname=' . strtr(urlencode($_REQUEST['subname']), array('%' => '%%')) . ';topic=' . $topic . '.' . $context['not_selected']['start'] . ';start2=%1$d', $context['selected']['start'], $context['selected']['num_messages'], $context['messages_per_page'], true);

    // Get the messages and stick them into an array.
    $request = $smcFunc['db_query']('', '
        SELECT m.subject, COALESCE(mem.real_name, m.poster_name) AS real_name, m.poster_time, m.body, m.id_msg, m.smileys_enabled
        FROM {db_prefix}messages AS m
            LEFT JOIN {db_prefix}members AS mem ON (mem.id_member = m.id_member)
        WHERE m.id_topic = {int:current_topic}' . (empty($_SESSION['split_selection'][$topic]) ? '' : '
            AND id_msg NOT IN ({array_int:no_split_msgs})') . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
            AND approved = {int:is_approved}') . '
            ' . (empty($options['view_newest_first']) ? '' : 'ORDER BY m.id_msg DESC') . '
            LIMIT {int:start}, {int:messages_per_page}',
        array(
            'current_topic' => $topic,
            'no_split_msgs' => !empty($_SESSION['split_selection'][$topic]) ? $_SESSION['split_selection'][$topic] : array(),
            'is_approved' => 1,
            'start' => $context['not_selected']['start'],
            'messages_per_page' => $context['messages_per_page'],
        )
    );
    $context['messages'] = array();
    for ($counter = 0; $row = $smcFunc['db_fetch_assoc']($request); $counter++)
    {
        censorText($row['subject']);
        censorText($row['body']);

        $row['body'] = parse_bbc($row['body'], $row['smileys_enabled'], $row['id_msg']);

        $context['not_selected']['messages'][$row['id_msg']] = array(
            'id' => $row['id_msg'],
            'subject' => $row['subject'],
            'time' => timeformat($row['poster_time']),
            'timestamp' => forum_time(true, $row['poster_time']),
            'body' => $row['body'],
            'poster' => $row['real_name'],
        );
    }
    $smcFunc['db_free_result']($request);

    // Now get the selected messages.
    if (!empty($_SESSION['split_selection'][$topic]))
    {
        // Get the messages and stick them into an array.
        $request = $smcFunc['db_query']('', '
            SELECT m.subject, COALESCE(mem.real_name, m.poster_name) AS real_name,  m.poster_time, m.body, m.id_msg, m.smileys_enabled
            FROM {db_prefix}messages AS m
                LEFT JOIN {db_prefix}members AS mem ON (mem.id_member = m.id_member)
            WHERE m.id_topic = {int:current_topic}
                AND m.id_msg IN ({array_int:split_msgs})' . (!$modSettings['postmod_active'] || allowedTo('approve_posts') ? '' : '
                AND approved = {int:is_approved}') . '
            ' . (empty($options['view_newest_first']) ? '' : 'ORDER BY m.id_msg DESC') . '
            LIMIT {int:start}, {int:messages_per_page}',
            array(
                'current_topic' => $topic,
                'split_msgs' => $_SESSION['split_selection'][$topic],
                'is_approved' => 1,
                'start' => $context['selected']['start'],
                'messages_per_page' => $context['messages_per_page'],
            )
        );
        $context['messages'] = array();
        for ($counter = 0; $row = $smcFunc['db_fetch_assoc']($request); $counter++)
        {
            censorText($row['subject']);
            censorText($row['body']);

            $row['body'] = parse_bbc($row['body'], $row['smileys_enabled'], $row['id_msg']);

            $context['selected']['messages'][$row['id_msg']] = array(
                'id' => $row['id_msg'],
                'subject' => $row['subject'],
                'time' => timeformat($row['poster_time']),
                'timestamp' => forum_time(true, $row['poster_time']),
                'body' => $row['body'],
                'poster' => $row['real_name']
            );
        }
        $smcFunc['db_free_result']($request);
    }

    // The XMLhttp method only needs the stuff that changed, so let's compare.
    if (isset($_REQUEST['xml']))
    {
        $changes = array(
            'remove' => array(
                'not_selected' => array_diff($original_msgs['not_selected'], array_keys($context['not_selected']['messages'])),
                'selected' => array_diff($original_msgs['selected'], array_keys($context['selected']['messages'])),
            ),
            'insert' => array(
                'not_selected' => array_diff(array_keys($context['not_selected']['messages']), $original_msgs['not_selected']),
                'selected' => array_diff(array_keys($context['selected']['messages']), $original_msgs['selected']),
            ),
        );

        $context['changes'] = array();
        foreach ($changes as $change_type => $change_array)
            foreach ($change_array as $section => $msg_array)
            {
                if (empty($msg_array))
                    continue;

                foreach ($msg_array as $id_msg)
                {
                    $context['changes'][$change_type . $id_msg] = array(
                        'id' => $id_msg,
                        'type' => $change_type,
                        'section' => $section,
                    );
                    if ($change_type == 'insert')
                        $context['changes']['insert' . $id_msg]['insert_value'] = $context[$section]['messages'][$id_msg];
                }
            }
    }
}

/**
 * do the actual split of a selection of topics.
 * is accessed with ?action=splittopics;sa=splitSelection.
 * uses the main SplitTopics template.
 * uses splitTopic function to do the actual splitting.
 */
function SplitSelectionExecute()
{
    global $txt, $topic, $context;

    // Make sure the session id was passed with post.
    checkSession();

    // Default the subject in case it's blank.
    if (!isset($_POST['subname']) || $_POST['subname'] == '')
        $_POST['subname'] = $txt['new_topic'];

    // You must've selected some messages!  Can't split out none!
    if (empty($_SESSION['split_selection'][$topic]))
        fatal_lang_error('no_posts_selected', false);

    $context['old_topic'] = $topic;
    $context['new_topic'] = splitTopic($topic, $_SESSION['split_selection'][$topic], $_POST['subname']);
    $context['page_title'] = $txt['split'];
}

/**
 * general function to split off a topic.
 * creates a new topic and moves the messages with the IDs in
 * array messagesToBeSplit to the new topic.
 * the subject of the newly created topic is set to 'newSubject'.
 * marks the newly created message as read for the user splitting it.
 * updates the statistics to reflect a newly created topic.
 * logs the action in the moderation log.
 * a notification is sent to all users monitoring this topic.
 *
 * @param int $split1_ID_TOPIC The ID of the topic we're splitting
 * @param array $splitMessages The IDs of the messages being split
 * @param string $new_subject The subject of the new topic
 * @return int The ID of the new split topic.
 */
function splitTopic($split1_ID_TOPIC, $splitMessages, $new_subject)
{
    global $smcFunc, $txt, $sourcedir;

    // Nothing to split?
    if (empty($splitMessages))
        fatal_lang_error('no_posts_selected', false);

    // Get some board info.
    $request = $smcFunc['db_query']('', '
        SELECT id_board, approved
        FROM {db_prefix}topics
        WHERE id_topic = {int:id_topic}
        LIMIT 1',
        array(
            'id_topic' => $split1_ID_TOPIC,
        )
    );
    list ($id_board, $split1_approved) = $smcFunc['db_fetch_row']($request);
    $smcFunc['db_free_result']($request);

    // Find the new first and last not in the list. (old topic)
    $request = $smcFunc['db_query']('', '
        SELECT
            MIN(m.id_msg) AS myid_first_msg, MAX(m.id_msg) AS myid_last_msg, COUNT(*) AS message_count, m.approved
        FROM {db_prefix}messages AS m
            INNER JOIN {db_prefix}topics AS t ON (t.id_topic = {int:id_topic})
        WHERE m.id_msg NOT IN ({array_int:no_msg_list})
            AND m.id_topic = {int:id_topic}
        GROUP BY m.approved
        ORDER BY m.approved DESC
        LIMIT 2',
        array(
            'id_topic' => $split1_ID_TOPIC,
            'no_msg_list' => $splitMessages,
        )
    );
    // You can't select ALL the messages!
    if ($smcFunc['db_num_rows']($request) == 0)
        fatal_lang_error('selected_all_posts', false);

    $split1_first_msg = null;
    $split1_last_msg = null;

    while ($row = $smcFunc['db_fetch_assoc']($request))
    {
        // Get the right first and last message dependant on approved state...
        if (empty($split1_first_msg) || $row['myid_first_msg'] < $split1_first_msg)
            $split1_first_msg = $row['myid_first_msg'];
        if (empty($split1_last_msg) || $row['approved'])
            $split1_last_msg = $row['myid_last_msg'];

        // Get the counts correct...
        if ($row['approved'])
        {
            $split1_replies = $row['message_count'] - 1;
            $split1_unapprovedposts = 0;
        }
        else
        {
            if (!isset($split1_replies))
                $split1_replies = 0;
            // If the topic isn't approved then num replies must go up by one... as first post wouldn't be counted.
            elseif (!$split1_approved)
                $split1_replies++;

            $split1_unapprovedposts = $row['message_count'];
        }
    }
    $smcFunc['db_free_result']($request);
    $split1_firstMem = getMsgMemberID($split1_first_msg);
    $split1_lastMem = getMsgMemberID($split1_last_msg);

    // Find the first and last in the list. (new topic)
    $request = $smcFunc['db_query']('', '
        SELECT MIN(id_msg) AS myid_first_msg, MAX(id_msg) AS myid_last_msg, COUNT(*) AS message_count, approved
        FROM {db_prefix}messages
        WHERE id_msg IN ({array_int:msg_list})
            AND id_topic = {int:id_topic}
        GROUP BY id_topic, approved
        ORDER BY approved DESC
        LIMIT 2',
        array(
            'msg_list' => $splitMessages,
            'id_topic' => $split1_ID_TOPIC,
        )
    );
    while ($row = $smcFunc['db_fetch_assoc']($request))
    {
        // As before get the right first and last message dependant on approved state...
        if (empty($split2_first_msg) || $row['myid_first_msg'] < $split2_first_msg)
            $split2_first_msg = $row['myid_first_msg'];
        if (empty($split2_last_msg) || $row['approved'])
            $split2_last_msg = $row['myid_last_msg'];

        // Then do the counts again...
        if ($row['approved'])
        {
            $split2_approved = true;
            $split2_replies = $row['message_count'] - 1;
            $split2_unapprovedposts = 0;
        }
        else
        {
            // Should this one be approved??
            if ($split2_first_msg == $row['myid_first_msg'])
                $split2_approved = false;

            if (!isset($split2_replies))
                $split2_replies = 0;
            // As before, fix number of replies.
            elseif (!$split2_approved)
                $split2_replies++;

            $split2_unapprovedposts = $row['message_count'];
        }
    }
    $smcFunc['db_free_result']($request);
    $split2_firstMem = getMsgMemberID($split2_first_msg);
    $split2_lastMem = getMsgMemberID($split2_last_msg);

    // No database changes yet, so let's double check to see if everything makes at least a little sense.
    if ($split1_first_msg <= 0 || $split1_last_msg <= 0 || $split2_first_msg <= 0 || $split2_last_msg <= 0 || $split1_replies < 0 || $split2_replies < 0 || $split1_unapprovedposts < 0 || $split2_unapprovedposts < 0 || !isset($split1_approved) || !isset($split2_approved))
        fatal_lang_error('cant_find_messages');

    // You cannot split off the first message of a topic.
    if ($split1_first_msg > $split2_first_msg)
        fatal_lang_error('split_first_post', false);

    // We're off to insert the new topic!  Use 0 for now to avoid UNIQUE errors.
    $split2_ID_TOPIC = $smcFunc['db_insert']('',
        '{db_prefix}topics',
        array(
            'id_board' => 'int',
            'id_member_started' => 'int',
            'id_member_updated' => 'int',
            'id_first_msg' => 'int',
            'id_last_msg' => 'int',
            'num_replies' => 'int',
            'unapproved_posts' => 'int',
            'approved' => 'int',
            'is_sticky' => 'int',
        ),
        array(
            (int) $id_board, $split2_firstMem, $split2_lastMem, 0,
            0, $split2_replies, $split2_unapprovedposts, (int) $split2_approved, 0,
        ),
        array('id_topic'),
        1
    );
    if ($split2_ID_TOPIC <= 0)
        fatal_lang_error('cant_insert_topic');

    // Move the messages over to the other topic.
    $new_subject = strtr($smcFunc['htmltrim']($smcFunc['htmlspecialchars']($new_subject)), array("\r" => '', "\n" => '', "\t" => ''));
    // Check the subject length.
    if ($smcFunc['strlen']($new_subject) > 100)
        $new_subject = $smcFunc['substr']($new_subject, 0, 100);
    // Valid subject?
    if ($new_subject != '')
    {
        $smcFunc['db_query']('', '
            UPDATE {db_prefix}messages
            SET
                id_topic = {int:id_topic},
                subject = CASE WHEN id_msg = {int:split_first_msg} THEN {string:new_subject} ELSE {string:new_subject_replies} END
            WHERE id_msg IN ({array_int:split_msgs})',
            array(
                'split_msgs' => $splitMessages,
                'id_topic' => $split2_ID_TOPIC,
                'new_subject' => $new_subject,
                'split_first_msg' => $split2_first_msg,
                'new_subject_replies' => $txt['response_prefix'] . $new_subject,
            )
        );

        // Cache the new topics subject... we can do it now as all the subjects are the same!
        updateStats('subject', $split2_ID_TOPIC, $new_subject);
    }

    // Any associated reported posts better follow...
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}log_reported
        SET id_topic = {int:id_topic}
        WHERE id_msg IN ({array_int:split_msgs})',
        array(
            'split_msgs' => $splitMessages,
            'id_topic' => $split2_ID_TOPIC,
        )
    );

    // Mess with the old topic's first, last, and number of messages.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}topics
        SET
            num_replies = {int:num_replies},
            id_first_msg = {int:id_first_msg},
            id_last_msg = {int:id_last_msg},
            id_member_started = {int:id_member_started},
            id_member_updated = {int:id_member_updated},
            unapproved_posts = {int:unapproved_posts}
        WHERE id_topic = {int:id_topic}',
        array(
            'num_replies' => $split1_replies,
            'id_first_msg' => $split1_first_msg,
            'id_last_msg' => $split1_last_msg,
            'id_member_started' => $split1_firstMem,
            'id_member_updated' => $split1_lastMem,
            'unapproved_posts' => $split1_unapprovedposts,
            'id_topic' => $split1_ID_TOPIC,
        )
    );

    // Now, put the first/last message back to what they should be.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}topics
        SET
            id_first_msg = {int:id_first_msg},
            id_last_msg = {int:id_last_msg}
        WHERE id_topic = {int:id_topic}',
        array(
            'id_first_msg' => $split2_first_msg,
            'id_last_msg' => $split2_last_msg,
            'id_topic' => $split2_ID_TOPIC,
        )
    );

    // If the new topic isn't approved ensure the first message flags this just in case.
    if (!$split2_approved)
        $smcFunc['db_query']('', '
            UPDATE {db_prefix}messages
            SET approved = {int:approved}
            WHERE id_msg = {int:id_msg}
                AND id_topic = {int:id_topic}',
            array(
                'approved' => 0,
                'id_msg' => $split2_first_msg,
                'id_topic' => $split2_ID_TOPIC,
            )
        );

    // The board has more topics now (Or more unapproved ones!).
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}boards
        SET ' . ($split2_approved ? '
            num_topics = num_topics + 1' : '
            unapproved_topics = unapproved_topics + 1') . '
        WHERE id_board = {int:id_board}',
        array(
            'id_board' => $id_board,
        )
    );

    // Copy log topic entries.
    // @todo This should really be chunked.
    $request = $smcFunc['db_query']('', '
        SELECT id_member, id_msg, unwatched
        FROM {db_prefix}log_topics
        WHERE id_topic = {int:id_topic}',
        array(
            'id_topic' => (int) $split1_ID_TOPIC,
        )
    );
    if ($smcFunc['db_num_rows']($request) > 0)
    {
        $replaceEntries = array();
        while ($row = $smcFunc['db_fetch_assoc']($request))
            $replaceEntries[] = array($row['id_member'], $split2_ID_TOPIC, $row['id_msg'], $row['unwatched']);

        $smcFunc['db_insert']('ignore',
            '{db_prefix}log_topics',
            array('id_member' => 'int', 'id_topic' => 'int', 'id_msg' => 'int', 'unwatched' => 'int'),
            $replaceEntries,
            array('id_member', 'id_topic')
        );
        unset($replaceEntries);
    }
    $smcFunc['db_free_result']($request);

    // Housekeeping.
    updateStats('topic');
    updateLastMessages($id_board);

    logAction('split', array('topic' => $split1_ID_TOPIC, 'new_topic' => $split2_ID_TOPIC, 'board' => $id_board));

    // Notify people that this topic has been split?
    sendNotifications($split1_ID_TOPIC, 'split');

    // If there's a search index that needs updating, update it...
    require_once($sourcedir . '/Search.php');
    $searchAPI = findSearchAPI();
    if (is_callable(array($searchAPI, 'topicSplit')))
        $searchAPI->topicSplit($split2_ID_TOPIC, $splitMessages);

    // Maybe we want to let an external CMS know about this split
    $split1 = array(
        'num_replies' => $split1_replies,
        'id_first_msg' => $split1_first_msg,
        'id_last_msg' => $split1_last_msg,
        'id_member_started' => $split1_firstMem,
        'id_member_updated' => $split1_lastMem,
        'unapproved_posts' => $split1_unapprovedposts,
        'id_topic' => $split1_ID_TOPIC,
    );
    $split2 = array(
        'num_replies' => $split2_replies,
        'id_first_msg' => $split2_first_msg,
        'id_last_msg' => $split2_last_msg,
        'id_member_started' => $split2_firstMem,
        'id_member_updated' => $split2_lastMem,
        'unapproved_posts' => $split2_unapprovedposts,
        'id_topic' => $split2_ID_TOPIC,
    );
    call_integration_hook('integrate_split_topic', array($split1, $split2, $new_subject, $id_board));

    // Return the ID of the newly created topic.
    return $split2_ID_TOPIC;
}

/**
 * merges two or more topics into one topic.
 * delegates to the other functions (based on the URL parameter sa).
 * loads the SplitTopics template.
 * requires the merge_any permission.
 * is accessed with ?action=mergetopics.
 */
function MergeTopics()
{
    // Load the template....
    loadTemplate('MoveTopic');

    $subActions = array(
        'done' => 'MergeDone',
        'execute' => 'MergeExecute',
        'index' => 'MergeIndex',
        'options' => 'MergeExecute',
    );

    // ?action=mergetopics;sa=LETSBREAKIT won't work, sorry.
    if (empty($_REQUEST['sa']) || !isset($subActions[$_REQUEST['sa']]))
        MergeIndex();

    else
        call_helper($subActions[$_REQUEST['sa']]);
}

/**
 * allows to pick a topic to merge the current topic with.
 * is accessed with ?action=mergetopics;sa=index
 * default sub action for ?action=mergetopics.
 * uses 'merge' sub template of the MoveTopic template.
 * allows to set a different target board.
 */
function MergeIndex()
{
    global $txt, $board, $context, $smcFunc, $sourcedir;
    global $scripturl, $modSettings;

    if (!isset($_GET['from']))
        fatal_lang_error('no_access', false);

    $_GET['from'] = (int) $_GET['from'];

    $_REQUEST['targetboard'] = isset($_REQUEST['targetboard']) ? (int) $_REQUEST['targetboard'] : $board;
    $context['target_board'] = $_REQUEST['targetboard'];

    // Prepare a handy query bit for approval...
    if ($modSettings['postmod_active'])
    {
        $can_approve_boards = boardsAllowedTo('approve_posts');
        $onlyApproved = $can_approve_boards !== array(0) && !in_array($_REQUEST['targetboard'], $can_approve_boards);
    }

    else
        $onlyApproved = false;

    // How many topics are on this board?  (used for paging.)
    $request = $smcFunc['db_query']('', '
        SELECT COUNT(*)
        FROM {db_prefix}topics AS t
        WHERE t.id_board = {int:id_board}' . ($onlyApproved ? '
            AND t.approved = {int:is_approved}' : ''),
        array(
            'id_board' => $_REQUEST['targetboard'],
            'is_approved' => 1,
        )
    );

    list ($topiccount) = $smcFunc['db_fetch_row']($request);
    $smcFunc['db_free_result']($request);

    // Make the page list.
    $context['page_index'] = constructPageIndex($scripturl . '?action=mergetopics;from=' . $_GET['from'] . ';targetboard=' . $_REQUEST['targetboard'] . ';board=' . $board . '.%1$d', $_REQUEST['start'], $topiccount, $modSettings['defaultMaxTopics'], true);

    // Get the topic's subject.
    $request = $smcFunc['db_query']('', '
        SELECT m.subject
        FROM {db_prefix}topics AS t
            INNER JOIN {db_prefix}messages AS m ON (m.id_msg = t.id_first_msg)
        WHERE t.id_topic = {int:id_topic}
            AND t.id_board = {int:current_board}' . ($onlyApproved ? '
            AND t.approved = {int:is_approved}' : '') . '
        LIMIT 1',
        array(
            'current_board' => $board,
            'id_topic' => $_GET['from'],
            'is_approved' => 1,
        )
    );

    if ($smcFunc['db_num_rows']($request) == 0)
        fatal_lang_error('no_board');

    list ($subject) = $smcFunc['db_fetch_row']($request);
    $smcFunc['db_free_result']($request);

    // Tell the template a few things..
    $context['origin_topic'] = $_GET['from'];
    $context['origin_subject'] = $subject;
    $context['origin_js_subject'] = addcslashes(addslashes($subject), '/');
    $context['page_title'] = $txt['merge'];

    // Check which boards you have merge permissions on.
    $merge_boards = boardsAllowedTo('merge_any');

    if (empty($merge_boards))
        fatal_lang_error('cannot_merge_any', 'user');

    // No sense in loading this if you can only merge on this board
    if (count($merge_boards) > 1 || in_array(0, $merge_boards))
    {
        require_once($sourcedir . '/Subs-MessageIndex.php');

        // Set up a couple of options for our board list
        $options = array(
            'not_redirection' => true,
            'selected_board' => $context['target_board'],
        );

        // Only include these boards in the list (0 means you're an admin')
        if (!in_array(0, $merge_boards))
            $options['included_boards'] = $merge_boards;

        $context['merge_categories'] = getBoardList($options);
    }

    // Get some topics to merge it with.
    $request = $smcFunc['db_query']('', '
        SELECT t.id_topic, m.subject, m.id_member, COALESCE(mem.real_name, m.poster_name) AS poster_name
        FROM {db_prefix}topics AS t
            INNER JOIN {db_prefix}messages AS m ON (m.id_msg = t.id_first_msg)
            LEFT JOIN {db_prefix}members AS mem ON (mem.id_member = m.id_member)
        WHERE t.id_board = {int:id_board}
            AND t.id_topic != {int:id_topic}
            AND t.id_redirect_topic = {int:not_redirect}' . ($onlyApproved ? '
            AND t.approved = {int:is_approved}' : '') . '
        ORDER BY {raw:sort}
        LIMIT {int:offset}, {int:limit}',
        array(
            'id_board' => $_REQUEST['targetboard'],
            'id_topic' => $_GET['from'],
            'sort' => 't.is_sticky DESC, t.id_last_msg DESC',
            'offset' => $_REQUEST['start'],
            'limit' => $modSettings['defaultMaxTopics'],
            'is_approved' => 1,
            'not_redirect' => 0,
        )
    );
    $context['topics'] = array();
    while ($row = $smcFunc['db_fetch_assoc']($request))
    {
        censorText($row['subject']);

        $context['topics'][] = array(
            'id' => $row['id_topic'],
            'poster' => array(
                'id' => $row['id_member'],
                'name' => $row['poster_name'],
                'href' => empty($row['id_member']) ? '' : $scripturl . '?action=profile;u=' . $row['id_member'],
                'link' => empty($row['id_member']) ? $row['poster_name'] : '<a href="' . $scripturl . '?action=profile;u=' . $row['id_member'] . '" target="_blank" rel="noopener">' . $row['poster_name'] . '</a>'
            ),
            'subject' => $row['subject'],
            'js_subject' => addcslashes(addslashes($row['subject']), '/')
        );
    }
    $smcFunc['db_free_result']($request);

    if (empty($context['topics']) && count($merge_boards) <= 1 && !in_array(0, $merge_boards))
        fatal_lang_error('merge_need_more_topics');

    $context['sub_template'] = 'merge';
}

/**
 * set merge options and do the actual merge of two or more topics.
 *
 * the merge options screen:
 * * shows topics to be merged and allows to set some merge options.
 * * is accessed by ?action=mergetopics;sa=options.and can also internally be called by QuickModeration() (Subs-Boards.php).
 * * uses 'merge_extra_options' sub template of the MoveTopic template.
 *
 * the actual merge:
 * * is accessed with ?action=mergetopics;sa=execute.
 * * updates the statistics to reflect the merge.
 * * logs the action in the moderation log.
 * * sends a notification is sent to all users monitoring this topic.
 * * redirects to ?action=mergetopics;sa=done.
 *
 * @param array $topics The IDs of the topics to merge
 */
function MergeExecute($topics = array())
{
    global $user_info, $txt, $context, $scripturl, $sourcedir;
    global $smcFunc, $language, $modSettings;

    // Check the session.
    checkSession('request');

    // Handle URLs from MergeIndex.
    if (!empty($_GET['from']) && !empty($_GET['to']))
        $topics = array((int) $_GET['from'], (int) $_GET['to']);

    // If we came from a form, the topic IDs came by post.
    if (!empty($_POST['topics']) && is_array($_POST['topics']))
        $topics = $_POST['topics'];

    // There's nothing to merge with just one topic...
    if (empty($topics) || !is_array($topics) || count($topics) == 1)
        fatal_lang_error('merge_need_more_topics');

    // Make sure every topic is numeric, or some nasty things could be done with the DB.
    foreach ($topics as $id => $topic)
        $topics[$id] = (int) $topic;

    // Joy of all joys, make sure they're not messing about with unapproved topics they can't see :P
    if ($modSettings['postmod_active'])
        $can_approve_boards = boardsAllowedTo('approve_posts');

    // Get info about the topics and polls that will be merged.
    $request = $smcFunc['db_query']('', '
        SELECT
            t.id_topic, t.id_board, t.id_poll, t.num_views, t.is_sticky, t.approved, t.num_replies, t.unapproved_posts, t.id_redirect_topic,
            m1.subject, m1.poster_time AS time_started, COALESCE(mem1.id_member, 0) AS id_member_started, COALESCE(mem1.real_name, m1.poster_name) AS name_started,
            m2.poster_time AS time_updated, COALESCE(mem2.id_member, 0) AS id_member_updated, COALESCE(mem2.real_name, m2.poster_name) AS name_updated
        FROM {db_prefix}topics AS t
            INNER JOIN {db_prefix}messages AS m1 ON (m1.id_msg = t.id_first_msg)
            INNER JOIN {db_prefix}messages AS m2 ON (m2.id_msg = t.id_last_msg)
            LEFT JOIN {db_prefix}members AS mem1 ON (mem1.id_member = m1.id_member)
            LEFT JOIN {db_prefix}members AS mem2 ON (mem2.id_member = m2.id_member)
        WHERE t.id_topic IN ({array_int:topic_list})
        ORDER BY t.id_first_msg
        LIMIT {int:limit}',
        array(
            'topic_list' => $topics,
            'limit' => count($topics),
        )
    );
    if ($smcFunc['db_num_rows']($request) < 2)
        fatal_lang_error('no_topic_id');

    $num_views = 0;
    $is_sticky = 0;
    $boardTotals = array();
    $boards = array();
    $polls = array();
    $firstTopic = 0;
    $context['is_approved'] = 1;
    $lowestTopicId = 0;
    $lowestTopicBoard = 0;

    while ($row = $smcFunc['db_fetch_assoc']($request))
    {
        // Sorry, redirection topics can't be merged
        if (!empty($row['id_redirect_topic']))
            fatal_lang_error('cannot_merge_redirect', false);

        // Make a note for the board counts...
        if (!isset($boardTotals[$row['id_board']]))
            $boardTotals[$row['id_board']] = array(
                'posts' => 0,
                'topics' => 0,
                'unapproved_posts' => 0,
                'unapproved_topics' => 0
            );

        // We can't see unapproved topics here?
        if ($modSettings['postmod_active'] && !$row['approved'] && $can_approve_boards != array(0) && in_array($row['id_board'], $can_approve_boards))
        {
            unset($topics[$row['id_topic']]); // If we can't see it, we should not merge it and not adjust counts! Instead skip it.
            continue;
        }
        elseif (!$row['approved'])
            $boardTotals[$row['id_board']]['unapproved_topics']++;
        else
            $boardTotals[$row['id_board']]['topics']++;

        $boardTotals[$row['id_board']]['unapproved_posts'] += $row['unapproved_posts'];
        $boardTotals[$row['id_board']]['posts'] += $row['num_replies'] + ($row['approved'] ? 1 : 0);

        // In the case of making a redirect, the topic count goes up by one due to the redirect topic.
        if (isset($_POST['postRedirect']))
            $boardTotals[$row['id_board']]['topics']--;

        $topic_data[$row['id_topic']] = array(
            'id' => $row['id_topic'],
            'board' => $row['id_board'],
            'poll' => $row['id_poll'],
            'num_views' => $row['num_views'],
            'subject' => $row['subject'],
            'started' => array(
                'time' => timeformat($row['time_started']),
                'timestamp' => forum_time(true, $row['time_started']),
                'href' => empty($row['id_member_started']) ? '' : $scripturl . '?action=profile;u=' . $row['id_member_started'],
                'link' => empty($row['id_member_started']) ? $row['name_started'] : '<a href="' . $scripturl . '?action=profile;u=' . $row['id_member_started'] . '">' . $row['name_started'] . '</a>'
            ),
            'updated' => array(
                'time' => timeformat($row['time_updated']),
                'timestamp' => forum_time(true, $row['time_updated']),
                'href' => empty($row['id_member_updated']) ? '' : $scripturl . '?action=profile;u=' . $row['id_member_updated'],
                'link' => empty($row['id_member_updated']) ? $row['name_updated'] : '<a href="' . $scripturl . '?action=profile;u=' . $row['id_member_updated'] . '">' . $row['name_updated'] . '</a>'
            ),
            'approved' => $row['approved']
        );
        $num_views += $row['num_views'];
        $boards[] = $row['id_board'];

        // If there's no poll, id_poll == 0...
        if ($row['id_poll'] > 0)
            $polls[] = $row['id_poll'];
        // Store the id_topic with the lowest id_first_msg.
        if (empty($firstTopic))
            $firstTopic = $row['id_topic'];

        // Lowest topic id gets selected as surviving topic id. We need to store this board so we can adjust the topic count (This one will not have a redirect topic)
        if ($row['id_topic'] < $lowestTopicId || empty($lowestTopicId))
        {
            $lowestTopicId = $row['id_topic'];
            $lowestTopicBoard = $row['id_board'];
        }

        $is_sticky = max($is_sticky, $row['is_sticky']);
    }
    $smcFunc['db_free_result']($request);

    // If we didn't get any topics then they've been messing with unapproved stuff.
    if (empty($topic_data))
        fatal_lang_error('no_topic_id');

    if (isset($_POST['postRedirect']) && !empty($lowestTopicBoard))
        $boardTotals[$lowestTopicBoard]['topics']++;

    // Will this be approved?
    $context['is_approved'] = $topic_data[$firstTopic]['approved'];

    $boards = array_values(array_unique($boards));

    // The parameters of MergeExecute were set, so this must've been an internal call.
    if (!empty($topics))
    {
        isAllowedTo('merge_any', $boards);
        loadTemplate('MoveTopic');
    }

    // Get the boards a user is allowed to merge in.
    $merge_boards = boardsAllowedTo('merge_any');
    if (empty($merge_boards))
        fatal_lang_error('cannot_merge_any', 'user');

    // Make sure they can see all boards....
    $request = $smcFunc['db_query']('', '
        SELECT b.id_board
        FROM {db_prefix}boards AS b
        WHERE b.id_board IN ({array_int:boards})
            AND {query_see_board}' . (!in_array(0, $merge_boards) ? '
            AND b.id_board IN ({array_int:merge_boards})' : '') . '
        LIMIT {int:limit}',
        array(
            'boards' => $boards,
            'merge_boards' => $merge_boards,
            'limit' => count($boards),
        )
    );
    // If the number of boards that's in the output isn't exactly the same as we've put in there, you're in trouble.
    if ($smcFunc['db_num_rows']($request) != count($boards))
        fatal_lang_error('no_board');
    $smcFunc['db_free_result']($request);

    if (empty($_REQUEST['sa']) || $_REQUEST['sa'] == 'options')
    {
        if (count($polls) > 1)
        {
            $request = $smcFunc['db_query']('', '
                SELECT t.id_topic, t.id_poll, m.subject, p.question
                FROM {db_prefix}polls AS p
                    INNER JOIN {db_prefix}topics AS t ON (t.id_poll = p.id_poll)
                    INNER JOIN {db_prefix}messages AS m ON (m.id_msg = t.id_first_msg)
                WHERE p.id_poll IN ({array_int:polls})
                LIMIT {int:limit}',
                array(
                    'polls' => $polls,
                    'limit' => count($polls),
                )
            );
            while ($row = $smcFunc['db_fetch_assoc']($request))
                $context['polls'][] = array(
                    'id' => $row['id_poll'],
                    'topic' => array(
                        'id' => $row['id_topic'],
                        'subject' => $row['subject']
                    ),
                    'question' => $row['question'],
                    'selected' => $row['id_topic'] == $firstTopic
                );
            $smcFunc['db_free_result']($request);
        }
        if (count($boards) > 1)
        {
            $request = $smcFunc['db_query']('', '
                SELECT id_board, name
                FROM {db_prefix}boards
                WHERE id_board IN ({array_int:boards})
                ORDER BY name
                LIMIT {int:limit}',
                array(
                    'boards' => $boards,
                    'limit' => count($boards),
                )
            );
            while ($row = $smcFunc['db_fetch_assoc']($request))
                $context['boards'][] = array(
                    'id' => $row['id_board'],
                    'name' => $row['name'],
                    'selected' => $row['id_board'] == $topic_data[$firstTopic]['board']
                );
            $smcFunc['db_free_result']($request);
        }

        $context['topics'] = $topic_data;
        foreach ($topic_data as $id => $topic)
            $context['topics'][$id]['selected'] = $topic['id'] == $firstTopic;

        $context['page_title'] = $txt['merge'];
        $context['sub_template'] = 'merge_extra_options';
        return;
    }

    // Determine target board.
    $target_board = count($boards) > 1 ? (int) $_REQUEST['board'] : $boards[0];
    if (!in_array($target_board, $boards))
        fatal_lang_error('no_board');

    // Determine which poll will survive and which polls won't.
    $target_poll = count($polls) > 1 ? (int) $_POST['poll'] : (count($polls) == 1 ? $polls[0] : 0);
    if ($target_poll > 0 && !in_array($target_poll, $polls))
        fatal_lang_error('no_access', false);
    $deleted_polls = empty($target_poll) ? $polls : array_diff($polls, array($target_poll));

    // Determine the subject of the newly merged topic - was a custom subject specified?
    if (empty($_POST['subject']) && isset($_POST['custom_subject']) && $_POST['custom_subject'] != '')
    {
        $target_subject = strtr($smcFunc['htmltrim']($smcFunc['htmlspecialchars']($_POST['custom_subject'])), array("\r" => '', "\n" => '', "\t" => ''));
        // Keep checking the length.
        if ($smcFunc['strlen']($target_subject) > 100)
            $target_subject = $smcFunc['substr']($target_subject, 0, 100);

        // Nothing left - odd but pick the first topics subject.
        if ($target_subject == '')
            $target_subject = $topic_data[$firstTopic]['subject'];
    }
    // A subject was selected from the list.
    elseif (!empty($topic_data[(int) $_POST['subject']]['subject']))
        $target_subject = $topic_data[(int) $_POST['subject']]['subject'];
    // Nothing worked? Just take the subject of the first message.
    else
        $target_subject = $topic_data[$firstTopic]['subject'];

    // Get the first and last message and the number of messages....
    $request = $smcFunc['db_query']('', '
        SELECT approved, MIN(id_msg) AS first_msg, MAX(id_msg) AS last_msg, COUNT(*) AS message_count
        FROM {db_prefix}messages
        WHERE id_topic IN ({array_int:topics})
        GROUP BY approved
        ORDER BY approved DESC',
        array(
            'topics' => $topics,
        )
    );
    $topic_approved = 1;
    $first_msg = 0;
    while ($row = $smcFunc['db_fetch_assoc']($request))
    {
        // If this is approved, or is fully unapproved.
        if ($row['approved'] || !empty($first_msg))
        {
            $first_msg = $row['first_msg'];
            $last_msg = $row['last_msg'];
            if ($row['approved'])
            {
                $num_replies = $row['message_count'] - 1;
                $num_unapproved = 0;
            }
            else
            {
                $topic_approved = 0;
                $num_replies = 0;
                $num_unapproved = $row['message_count'];
            }
        }
        else
        {
            // If this has a lower first_msg then the first post is not approved and hence the number of replies was wrong!
            if ($first_msg > $row['first_msg'])
            {
                $first_msg = $row['first_msg'];
                $num_replies++;
                $topic_approved = 0;
            }
            $num_unapproved = $row['message_count'];
        }
    }
    $smcFunc['db_free_result']($request);

    // Ensure we have a board stat for the target board.
    if (!isset($boardTotals[$target_board]))
    {
        $boardTotals[$target_board] = array(
            'posts' => 0,
            'topics' => 0,
            'unapproved_posts' => 0,
            'unapproved_topics' => 0
        );
    }

    // Fix the topic count stuff depending on what the new one counts as.
    $boardTotals[$target_board][(!$topic_approved) ? 'unapproved_topics' : 'topics']--;

    $boardTotals[$target_board]['unapproved_posts'] -= $num_unapproved;
    $boardTotals[$target_board]['posts'] -= $topic_approved ? $num_replies + 1 : $num_replies;

    // Get the member ID of the first and last message.
    $request = $smcFunc['db_query']('', '
        SELECT id_member
        FROM {db_prefix}messages
        WHERE id_msg IN ({int:first_msg}, {int:last_msg})
        ORDER BY id_msg
        LIMIT 2',
        array(
            'first_msg' => $first_msg,
            'last_msg' => $last_msg,
        )
    );
    list ($member_started) = $smcFunc['db_fetch_row']($request);
    list ($member_updated) = $smcFunc['db_fetch_row']($request);

    // First and last message are the same, so only row was returned.
    if ($member_updated === null)
        $member_updated = $member_started;

    $smcFunc['db_free_result']($request);

    // Obtain all the message ids we are going to affect.
    $affected_msgs = array();
    $request = $smcFunc['db_query']('', '
        SELECT id_msg
        FROM {db_prefix}messages
        WHERE id_topic IN ({array_int:topic_list})',
        array(
            'topic_list' => $topics,
        )
    );
    while ($row = $smcFunc['db_fetch_row']($request))
        $affected_msgs[] = $row[0];
    $smcFunc['db_free_result']($request);

    // Assign the first topic ID to be the merged topic.
    $id_topic = min($topics);

    $deleted_topics = array_diff($topics, array($id_topic));
    $updated_topics = array();

    // Create stub topics out of the remaining topics.
    // We don't want the search index data though (For non-redirect merges).
    if (!isset($_POST['postRedirect']))
    {
        $smcFunc['db_query']('', '
            DELETE FROM {db_prefix}log_search_subjects
            WHERE id_topic IN ({array_int:deleted_topics})',
            array(
                'deleted_topics' => $deleted_topics,
            )
        );
    }

    require_once($sourcedir . '/Subs-Post.php');
    $posterOptions = array(
        'id' => $user_info['id'],
        'update_post_count' => false,
    );

    // We only need to do this if we're posting redirection topics...
    if (isset($_POST['postRedirect']))
    {
        $_POST['reason'] = $smcFunc['htmlspecialchars']($_POST['reason'], ENT_QUOTES);
        preparsecode($_POST['reason']);

        // Add a URL onto the message.
        $reason = strtr($_POST['reason'], array(
            $txt['movetopic_auto_topic'] => '[iurl=' . $scripturl . '?topic=' . $id_topic . '.0]' . $target_subject . '[/iurl]'
        ));

        // Automatically remove this MERGED redirection topic in the future?
        $redirect_expires = !empty($_POST['redirect_expires']) ? ((int) ($_POST['redirect_expires'] * 60) + time()) : 0;

        // Redirect to the MERGED topic from topic list?
        $redirect_topic = isset($_POST['redirect_topic']) ? $id_topic : 0;

        foreach ($deleted_topics as $this_old_topic)
        {
            $redirect_subject = sprintf($txt['merged_subject'], $topic_data[$this_old_topic]['subject']);

            $msgOptions = array(
                'icon' => 'moved',
                'subject' => $redirect_subject,
                'body' => $reason,
                'approved' => 1,
            );
            $topicOptions = array(
                'id' => $this_old_topic,
                'is_approved' => true,
                'lock_mode' => 1,
                'board' => $topic_data[$this_old_topic]['board'],
                'mark_as_read' => true,
            );

            // So we have to make the post. We need to do *this* here so we don't foul up indexes later
            // and we have to fix them up later once everything else has happened.
            if (createPost($msgOptions, $topicOptions, $posterOptions))
            {
                $updated_topics[$this_old_topic] = $msgOptions['id'];
            }

            // Update subject search index
            updateStats('subject', $this_old_topic, $redirect_subject);
        }
    }

    // Grab the response prefix (like 'Re: ') in the default forum language.
    if (!isset($context['response_prefix']) && !($context['response_prefix'] = cache_get_data('response_prefix')))
    {
        if ($language === $user_info['language'])
            $context['response_prefix'] = $txt['response_prefix'];
        else
        {
            loadLanguage('index', $language, false);
            $context['response_prefix'] = $txt['response_prefix'];
            loadLanguage('index');
        }
        cache_put_data('response_prefix', $context['response_prefix'], 600);
    }

    // Change the topic IDs of all messages that will be merged.  Also adjust subjects if 'enforce subject' was checked.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}messages
        SET
            id_topic = {int:id_topic},
            id_board = {int:target_board}' . (empty($_POST['enforce_subject']) ? '' : ',
            subject = {string:subject}') . '
        WHERE id_topic IN ({array_int:topic_list})' . (!empty($updated_topics) ? '
            AND id_msg NOT IN ({array_int:merge_msg})' : ''),
        array(
            'topic_list' => $topics,
            'id_topic' => $id_topic,
            'merge_msg' => $updated_topics,
            'target_board' => $target_board,
            'subject' => $context['response_prefix'] . $target_subject,
        )
    );

    // Any reported posts should reflect the new board.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}log_reported
        SET
            id_topic = {int:id_topic},
            id_board = {int:target_board}
        WHERE id_topic IN ({array_int:topics_list})',
        array(
            'topics_list' => $topics,
            'id_topic' => $id_topic,
            'target_board' => $target_board,
        )
    );

    // Change the subject of the first message...
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}messages
        SET subject = {string:target_subject}
        WHERE id_msg = {int:first_msg}',
        array(
            'first_msg' => $first_msg,
            'target_subject' => $target_subject,
        )
    );

    // Adjust all calendar events to point to the new topic.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}calendar
        SET
            id_topic = {int:id_topic},
            id_board = {int:target_board}
        WHERE id_topic IN ({array_int:deleted_topics})',
        array(
            'deleted_topics' => $deleted_topics,
            'id_topic' => $id_topic,
            'target_board' => $target_board,
        )
    );

    // Merge log topic entries.
    // The unwatch setting comes from the oldest topic
    $request = $smcFunc['db_query']('', '
        SELECT id_member, MIN(id_msg) AS new_id_msg, unwatched
        FROM {db_prefix}log_topics
        WHERE id_topic IN ({array_int:topics})
        GROUP BY id_member, unwatched',
        array(
            'topics' => $topics,
        )
    );
    if ($smcFunc['db_num_rows']($request) > 0)
    {
        $replaceEntries = array();
        while ($row = $smcFunc['db_fetch_assoc']($request))
            $replaceEntries[] = array($row['id_member'], $id_topic, $row['new_id_msg'], $row['unwatched']);

        $smcFunc['db_insert']('replace',
            '{db_prefix}log_topics',
            array('id_member' => 'int', 'id_topic' => 'int', 'id_msg' => 'int', 'unwatched' => 'int'),
            $replaceEntries,
            array('id_member', 'id_topic')
        );
        unset($replaceEntries);

        // Get rid of the old log entries.
        $smcFunc['db_query']('', '
            DELETE FROM {db_prefix}log_topics
            WHERE id_topic IN ({array_int:deleted_topics})',
            array(
                'deleted_topics' => $deleted_topics,
            )
        );
    }
    $smcFunc['db_free_result']($request);

    // Merge topic notifications.
    $notifications = isset($_POST['notifications']) && is_array($_POST['notifications']) ? array_intersect($topics, $_POST['notifications']) : array();
    if (!empty($notifications))
    {
        $request = $smcFunc['db_query']('', '
            SELECT id_member, MAX(sent) AS sent
            FROM {db_prefix}log_notify
            WHERE id_topic IN ({array_int:topics_list})
            GROUP BY id_member',
            array(
                'topics_list' => $notifications,
            )
        );
        if ($smcFunc['db_num_rows']($request) > 0)
        {
            $replaceEntries = array();
            while ($row = $smcFunc['db_fetch_assoc']($request))
                $replaceEntries[] = array($row['id_member'], $id_topic, 0, $row['sent']);

            $smcFunc['db_insert']('replace',
                '{db_prefix}log_notify',
                array('id_member' => 'int', 'id_topic' => 'int', 'id_board' => 'int', 'sent' => 'int'),
                $replaceEntries,
                array('id_member', 'id_topic', 'id_board')
            );
            unset($replaceEntries);

            $smcFunc['db_query']('', '
                DELETE FROM {db_prefix}log_topics
                WHERE id_topic IN ({array_int:deleted_topics})',
                array(
                    'deleted_topics' => $deleted_topics,
                )
            );
        }
        $smcFunc['db_free_result']($request);
    }

    // Get rid of the redundant polls.
    if (!empty($deleted_polls))
    {
        $smcFunc['db_query']('', '
            DELETE FROM {db_prefix}polls
            WHERE id_poll IN ({array_int:deleted_polls})',
            array(
                'deleted_polls' => $deleted_polls,
            )
        );
        $smcFunc['db_query']('', '
            DELETE FROM {db_prefix}poll_choices
            WHERE id_poll IN ({array_int:deleted_polls})',
            array(
                'deleted_polls' => $deleted_polls,
            )
        );
        $smcFunc['db_query']('', '
            DELETE FROM {db_prefix}log_polls
            WHERE id_poll IN ({array_int:deleted_polls})',
            array(
                'deleted_polls' => $deleted_polls,
            )
        );
    }

    // Cycle through each board...
    foreach ($boardTotals as $id_board => $stats)
    {
        $smcFunc['db_query']('', '
            UPDATE {db_prefix}boards
            SET
                num_topics = CASE WHEN {int:topics} > num_topics THEN 0 ELSE num_topics - {int:topics} END,
                unapproved_topics = CASE WHEN {int:unapproved_topics} > unapproved_topics THEN 0 ELSE unapproved_topics - {int:unapproved_topics} END,
                num_posts = CASE WHEN {int:posts} > num_posts THEN 0 ELSE num_posts - {int:posts} END,
                unapproved_posts = CASE WHEN {int:unapproved_posts} > unapproved_posts THEN 0 ELSE unapproved_posts - {int:unapproved_posts} END
            WHERE id_board = {int:id_board}',
            array(
                'id_board' => $id_board,
                'topics' => $stats['topics'],
                'unapproved_topics' => $stats['unapproved_topics'],
                'posts' => $stats['posts'],
                'unapproved_posts' => $stats['unapproved_posts'],
            )
        );
    }

    // Determine the board the final topic resides in
    $request = $smcFunc['db_query']('', '
        SELECT id_board
        FROM {db_prefix}topics
        WHERE id_topic = {int:id_topic}
        LIMIT 1',
        array(
            'id_topic' => $id_topic,
        )
    );
    list($id_board) = $smcFunc['db_fetch_row']($request);
    $smcFunc['db_free_result']($request);

    // Again, only do this if we're redirecting - otherwise delete
    if (isset($_POST['postRedirect']))
    {
        // Having done all that, now make sure we fix the merge/redirect topics upp before we
        // leave here. Specifically: that there are no replies, no unapproved stuff, that the first
        // and last posts are the same and so on and so forth.
        foreach ($updated_topics as $old_topic => $id_msg)
        {
            $smcFunc['db_query']('', '
                UPDATE {db_prefix}topics
                SET id_first_msg = id_last_msg,
                    id_member_started = {int:current_user},
                    id_member_updated = {int:current_user},
                    id_poll = 0,
                    approved = 1,
                    num_replies = 0,
                    unapproved_posts = 0,
                    id_redirect_topic = {int:redirect_topic},
                    redirect_expires = {int:redirect_expires}
                WHERE id_topic = {int:old_topic}',
                array(
                    'current_user' => $user_info['id'],
                    'old_topic' => $old_topic,
                    'redirect_topic' => $redirect_topic,
                    'redirect_expires' => $redirect_expires
                )
            );
        }
    }

    // Ensure we don't accidentally delete the poll we want to keep...
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}topics
        SET id_poll = 0
        WHERE id_topic IN ({array_int:deleted_topics})',
        array(
            'deleted_topics' => $deleted_topics
        )
    );

    // Delete any remaining data regarding these topics, this is done before changing the properties of the merged topic (else we get duplicate keys)...
    if (!isset($_POST['postRedirect']))
    {
        // Remove any remaining info about these topics...
        include_once($sourcedir . '/RemoveTopic.php');
        // We do not need to remove the counts of the deleted topics, as we already removed these.
        removeTopics($deleted_topics, false, true, false);
    }

    // Asssign the properties of the newly merged topic.
    $smcFunc['db_query']('', '
        UPDATE {db_prefix}topics
        SET
            id_board = {int:id_board},
            id_member_started = {int:id_member_started},
            id_member_updated = {int:id_member_updated},
            id_first_msg = {int:id_first_msg},
            id_last_msg = {int:id_last_msg},
            id_poll = {int:id_poll},
            num_replies = {int:num_replies},
            unapproved_posts = {int:unapproved_posts},
            num_views = {int:num_views},
            is_sticky = {int:is_sticky},
            approved = {int:approved}
        WHERE id_topic = {int:id_topic}',
        array(
            'id_board' => $target_board,
            'is_sticky' => $is_sticky,
            'approved' => $topic_approved,
            'id_topic' => $id_topic,
            'id_member_started' => $member_started,
            'id_member_updated' => $member_updated,
            'id_first_msg' => $first_msg,
            'id_last_msg' => $last_msg,
            'id_poll' => $target_poll,
            'num_replies' => $num_replies,
            'unapproved_posts' => $num_unapproved,
            'num_views' => $num_views,
        )
    );

    // Update all the statistics.
    updateStats('topic');
    updateStats('subject', $id_topic, $target_subject);
    updateLastMessages($boards);

    logAction('merge', array('topic' => $id_topic, 'board' => $id_board));

    // Notify people that these topics have been merged?
    sendNotifications($id_topic, 'merge');

    // If there's a search index that needs updating, update it...
    require_once($sourcedir . '/Search.php');
    $searchAPI = findSearchAPI();
    if (is_callable(array($searchAPI, 'topicMerge')))
        $searchAPI->topicMerge($id_topic, $topics, $affected_msgs, empty($_POST['enforce_subject']) ? null : array($context['response_prefix'], $target_subject));

    // Merging is the sort of thing an external CMS might want to know about
    $merged_topic = array(
        'id_board' => $target_board,
        'is_sticky' => $is_sticky,
        'approved' => $topic_approved,
        'id_topic' => $id_topic,
        'id_member_started' => $member_started,
        'id_member_updated' => $member_updated,
        'id_first_msg' => $first_msg,
        'id_last_msg' => $last_msg,
        'id_poll' => $target_poll,
        'num_replies' => $num_replies,
        'unapproved_posts' => $num_unapproved,
        'num_views' => $num_views,
        'subject' => $target_subject,
    );
    call_integration_hook('integrate_merge_topic', array($merged_topic, $updated_topics, $deleted_topics, $deleted_polls));

    // Send them to the all done page.
    redirectexit('action=mergetopics;sa=done;to=' . $id_topic . ';targetboard=' . $target_board);
}

/**
 * Shows a 'merge completed' screen.
 * is accessed with ?action=mergetopics;sa=done.
 * uses 'merge_done' sub template of the SplitTopics template.
 */
function MergeDone()
{
    global $txt, $context;

    // Make sure the template knows everything...
    $context['target_board'] = (int) $_GET['targetboard'];
    $context['target_topic'] = (int) $_GET['to'];

    $context['page_title'] = $txt['merge'];
    $context['sub_template'] = 'merge_done';
}

?>