C:/xampp/htdocs/moodle/admin/tool/health/index.php

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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle 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 3 of the License, or
// (at your option) any later version.
//
// Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.

    ob_start(); //for whitespace test
    require('../../../config.php');
    $extraws = ob_get_clean();

    require_once($CFG->libdir.'/adminlib.php');

    admin_externalpage_setup('toolhealth');

    define('SEVERITY_NOTICE',      'notice');
    define('SEVERITY_ANNOYANCE',   'annoyance');
    define('SEVERITY_SIGNIFICANT', 'significant');
    define('SEVERITY_CRITICAL',    'critical');

    $solution = optional_param('solution', 0, PARAM_PLUGIN);

    require_login();
    require_capability('moodle/site:config', get_context_instance(CONTEXT_SYSTEM));

    $site = get_site();

    echo $OUTPUT->header();

    if(strpos($solution, 'problem_') === 0 && class_exists($solution)) {
        health_print_solution($solution);
    }
    else {
        health_find_problems();
    }


    echo $OUTPUT->footer();


function health_find_problems() {
    global $OUTPUT;

    echo $OUTPUT->heading(get_string('pluginname', 'tool_health'));

    $issues   = array(
        SEVERITY_CRITICAL    => array(),
        SEVERITY_SIGNIFICANT => array(),
        SEVERITY_ANNOYANCE   => array(),
        SEVERITY_NOTICE      => array(),
    );
    $problems = 0;

    for($i = 1; $i < 1000000; ++$i) {
        $classname = sprintf('problem_%06d', $i);
        if(!class_exists($classname)) {
            continue;
        }
        $problem = new $classname;

        if($problem->exists()) {
            $severity = $problem->severity();
            $issues[$severity][$classname] = array(
                'severity'    => $severity,
                'description' => $problem->description(),
                'title'       => $problem->title()
            );
            ++$problems;
        }
        unset($problem);
    }

    if($problems == 0) {
        echo '<div id="healthnoproblemsfound">';
        echo get_string('healthnoproblemsfound', 'tool_health');
        echo '</div>';
    }
    else {
        echo $OUTPUT->heading(get_string('healthproblemsdetected', 'tool_health'));
        $severities = array(SEVERITY_CRITICAL, SEVERITY_SIGNIFICANT, SEVERITY_ANNOYANCE, SEVERITY_NOTICE);
        foreach($severities as $severity) {
            if(!empty($issues[$severity])) {
                echo '<dl class="healthissues '.$severity.'">';
                foreach($issues[$severity] as $classname => $data) {
                    echo '<dt id="'.$classname.'">'.$data['title'].'</dt>';
                    echo '<dd>'.$data['description'];
                    echo '<form action="index.php#solution" method="get">';
                    echo '<input type="hidden" name="solution" value="'.$classname.'" /><input type="submit" value="'.get_string('viewsolution').'" />';
                    echo '</form></dd>';
                }
                echo '</dl>';
            }
        }
    }
}

function health_print_solution($classname) {
    global $OUTPUT;
    $problem = new $classname;
    $data = array(
        'title'       => $problem->title(),
        'severity'    => $problem->severity(),
        'description' => $problem->description(),
        'solution'    => $problem->solution()
    );

    echo $OUTPUT->heading(get_string('pluginname', 'tool_health'));
    echo $OUTPUT->heading(get_string('healthproblemsolution', 'tool_health'));
    echo '<dl class="healthissues '.$data['severity'].'">';
    echo '<dt>'.$data['title'].'</dt>';
    echo '<dd>'.$data['description'].'</dd>';
    echo '<dt id="solution" class="solution">'.get_string('healthsolution', 'tool_health').'</dt>';
    echo '<dd class="solution">'.$data['solution'].'</dd></dl>';
    echo '<form id="healthformreturn" action="index.php#'.$classname.'" method="get">';
    echo '<input type="submit" value="'.get_string('healthreturntomain', 'tool_health').'" />';
    echo '</form>';
}

class problem_base {
    function exists() {
        return false;
    }
    function title() {
        return '???';
    }
    function severity() {
        return SEVERITY_NOTICE;
    }
    function description() {
        return '';
    }
    function solution() {
        return '';
    }
}

class problem_000002 extends problem_base {
    function title() {
        return 'Extra characters at the end of config.php or other library function';
    }
    function exists() {
        global $extraws;

        if($extraws === '') {
            return false;
        }
        return true;
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        return 'Your Moodle configuration file config.php or another library file, contains some characters after the closing PHP tag (?>). This causes Moodle to exhibit several kinds of problems (such as broken downloaded files) and must be fixed.';
    }
    function solution() {
        global $CFG;
        return 'You need to edit <strong>'.$CFG->dirroot.'/config.php</strong> and remove all characters (including spaces and returns) after the ending ?> tag. These two characters should be the very last in that file. The extra trailing whitespace may be also present in other PHP files that are included from lib/setup.php.';
    }
}

class problem_000003 extends problem_base {
    function title() {
        return '$CFG->dataroot does not exist or does not have write permissions';
    }
    function exists() {
        global $CFG;
        if(!is_dir($CFG->dataroot) || !is_writable($CFG->dataroot)) {
            return true;
        }
        return false;
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        global $CFG;
        return 'Your <strong>config.php</strong> says that your "data root" directory is <strong>'.$CFG->dataroot.'</strong>. However, this directory either does not exist or cannot be written to by Moodle. This means that a variety of problems will be present, such as users not being able to log in and not being able to upload any files. It is imperative that you address this problem for Moodle to work correctly.';
    }
    function solution() {
        global $CFG;
        return 'First of all, make sure that the directory <strong>'.$CFG->dataroot.'</strong> exists. If the directory does exist, then you must make sure that Moodle is able to write to it. Contact your web server administrator and request that he gives write permissions for that directory to the user that the web server process is running as.';
    }
}

class problem_000004 extends problem_base {
    function title() {
        return 'cron.php is not set up to run automatically';
    }
    function exists() {
        global $DB;
        $lastcron = $DB->get_field_sql('SELECT max(lastcron) FROM {modules}');
        return (time() - $lastcron > 3600 * 24);
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        return 'The cron.php mainenance script has not been run in the past 24 hours. This probably means that your server is not configured to automatically run this script in regular time intervals. If this is the case, then Moodle will mostly work as it should but some operations (notably sending email to users) will not be carried out at all.';
    }
    function solution() {
        global $CFG;
        return 'For detailed instructions on how to enable cron, see <a href="'.$CFG->wwwroot.'/doc/?file=install.html#cron">this section</a> of the installation manual.';
    }
}

class problem_000005 extends problem_base {
    function title() {
        return 'PHP: session.auto_start is enabled';
    }
    function exists() {
        return ini_get_bool('session.auto_start');
    }
    function severity() {
        return SEVERITY_CRITICAL;
    }
    function description() {
        return 'Your PHP configuration includes an enabled setting, session.auto_start, that <strong>must be disabled</strong> in order for Moodle to work correctly. Notable symptoms arising from this misconfiguration include fatal errors and/or blank pages when trying to log in.';
    }
    function solution() {
        global $CFG;
        return '<p>There are two ways you can solve this problem:</p><ol><li>If you have access to your main <strong>php.ini</strong> file, then find the line that looks like this: <pre>session.auto_start = 1</pre> and change it to <pre>session.auto_start = 0</pre> and then restart your web server. Be warned that this, as any other PHP setting change, might affect other web applications running on the server.</li><li>Finally, you may be able to change this setting just for your site by creating or editing the file <strong>'.$CFG->dirroot.'/.htaccess</strong> to contain this line: <pre>php_value session.auto_start "0"</pre></li></ol>';
    }
}

class problem_000006 extends problem_base {
    function title() {
        return 'PHP: magic_quotes_runtime is enabled';
    }
    function exists() {
        return (ini_get_bool('magic_quotes_runtime'));
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        return 'Your PHP configuration includes an enabled setting, magic_quotes_runtime, that <strong>must be disabled</strong> in order for Moodle to work correctly. Notable symptoms arising from this misconfiguration include strange display errors whenever a text field that includes single or double quotes is processed.';
    }
    function solution() {
        global $CFG;
        return '<p>There are two ways you can solve this problem:</p><ol><li>If you have access to your main <strong>php.ini</strong> file, then find the line that looks like this: <pre>magic_quotes_runtime = On</pre> and change it to <pre>magic_quotes_runtime = Off</pre> and then restart your web server. Be warned that this, as any other PHP setting change, might affect other web applications running on the server.</li><li>Finally, you may be able to change this setting just for your site by creating or editing the file <strong>'.$CFG->dirroot.'/.htaccess</strong> to contain this line: <pre>php_value magic_quotes_runtime "Off"</pre></li></ol>';
    }
}

class problem_000007 extends problem_base {
    function title() {
        return 'PHP: file_uploads is disabled';
    }
    function exists() {
        return !ini_get_bool('file_uploads');
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        return 'Your PHP configuration includes a disabled setting, file_uploads, that <strong>must be enabled</strong> to let Moodle offer its full functionality. Until this setting is enabled, it will not be possible to upload any files into Moodle. This includes, for example, course content and user pictures.';
    }
    function solution() {
        global $CFG;
        return '<p>There are two ways you can solve this problem:</p><ol><li>If you have access to your main <strong>php.ini</strong> file, then find the line that looks like this: <pre>file_uploads = Off</pre> and change it to <pre>file_uploads = On</pre> and then restart your web server. Be warned that this, as any other PHP setting change, might affect other web applications running on the server.</li><li>Finally, you may be able to change this setting just for your site by creating or editing the file <strong>'.$CFG->dirroot.'/.htaccess</strong> to contain this line: <pre>php_value file_uploads "On"</pre></li></ol>';
    }
}

class problem_000008 extends problem_base {
    function title() {
        return 'PHP: memory_limit cannot be controlled by Moodle';
    }
    function exists() {
        global $CFG;

        $oldmemlimit = @ini_get('memory_limit');
        if (empty($oldmemlimit)) {
            // PHP not compiled with memory limits, this means that it's
            // probably limited to 8M or in case of Windows not at all.
            // We can ignore it for now - there is not much to test anyway
            // TODO: add manual test that fills memory??
            return false;
        }
        $oldmemlimit = get_real_size($oldmemlimit);
        //now lets change the memory limit to something higher
        $newmemlimit = ($oldmemlimit + 1024*1024*5);
        raise_memory_limit($newmemlimit);
        $testmemlimit = get_real_size(@ini_get('memory_limit'));
        //verify the change had any effect at all
        if ($oldmemlimit == $testmemlimit) {
            //memory limit can not be changed - is it big enough then?
            if ($oldmemlimit < get_real_size('128M')) {
                return true;
            } else {
                return false;
            }
        }
        reduce_memory_limit($oldmemlimit);
        return false;
    }
    function severity() {
        return SEVERITY_NOTICE;
    }
    function description() {
        return 'The settings for PHP on your server do not allow a script to request more memory during its execution. '.
               'This means that there is a hard limit of '.@ini_get('memory_limit').' for each script. '.
               'It is possible that certain operations within Moodle will require more than this amount in order '.
               'to complete successfully, especially if there are lots of data to be processed.';
    }
    function solution() {
        return 'It is recommended that you contact your web server administrator to address this issue.';
    }
}

class problem_000009 extends problem_base {
    function title() {
        return 'SQL: using account without password';
    }
    function exists() {
        global $CFG;
        return empty($CFG->dbpass);
    }
    function severity() {
        return SEVERITY_CRITICAL;
    }
    function description() {
        global $CFG;
        return 'The user account your are connecting to the database server with is set up without a password. This is a very big security risk and is only somewhat lessened if your database is configured to not accept connections from any hosts other than the server Moodle is running on. Unless you use a strong password to connect to the database, you risk unauthorized access to and manipulation of your data.'.($CFG->dbuser != 'root'?'':' <strong>This is especially alarming because such access to the database would be as the superuser (root)!</strong>');
    }
    function solution() {
        global $CFG;
        return 'You should change the password of the user <strong>'.$CFG->dbuser.'</strong> both in your database and in your Moodle <strong>config.php</strong> immediately!'.($CFG->dbuser != 'root'?'':' It would also be a good idea to change the user account from root to something else, because this would lessen the impact in the event that your database is compromised anyway.');
    }
}
/* // not implemented in 2.0 yet
class problem_000010 extends problem_base {
    function title() {
        return 'Uploaded files: slasharguments disabled or not working';
    }
    function exists() {
        if (!$this->is_enabled()) {
            return true;
        }
        if ($this->status() < 1) {
            return true;
        }
        return false;
    }
    function severity() {
        if ($this->is_enabled() and $this->status() == 0) {
            return SEVERITY_SIGNIFICANT;
        } else {
            return SEVERITY_ANNOYANCE;
        }
    }
    function description() {
        global $CFG;
        $desc = 'Slasharguments are needed for relative linking in uploaded resources:<ul>';
        if (!$this->is_enabled()) {
            $desc .= '<li>slasharguments are <strong>disabled</strong> in Moodle configuration</li>';
        } else {
            $desc .= '<li>slasharguments are enabled in Moodle configuration</li>';
        }
        if ($this->status() == -1) {
            $desc .= '<li>can not run automatic test, you can verify it <a href="'.$CFG->wwwroot.'/file.php/testslasharguments" target="_blank">here</a> manually</li>';
        } else if ($this->status() == 0) {
            $desc .= '<li>slashargument test <strong>failed</strong>, please check server configuration</li>';
        } else {
            $desc .= '<li>slashargument test passed</li>';
        }
        $desc .= '</ul>';
        return $desc;
    }
    function solution() {
        global $CFG;
        $enabled = $this->is_enabled();
        $status = $this->status();
        $solution = '';
        if ($enabled and ($status == 0)) {
            $solution .= 'Slasharguments are enabled, but the test failed. Please disable slasharguments in Moodle configuration or fix the server configuration.<hr />';
        } else if ((!$enabled) and ($status == 0)) {
            $solution .= 'Slasharguments are disabled and the test failed. You may try to fix the server configuration.<hr />';
        } else if ($enabled and ($status == -1)) {
            $solution .= 'Slasharguments are enabled, <a href="'.$CFG->wwwroot.'/file.php/testslasharguments">automatic testing</a> not possible.<hr />';
        } else if ((!$enabled) and ($status == -1)) {
            $solution .= 'Slasharguments are disabled, <a href="'.$CFG->wwwroot.'/file.php/testslasharguments">automatic testing</a> not possible.<hr />';
        } else if ((!$enabled) and ($status > 0)) {
            $solution .= 'Slasharguments are disabled though the iternal test is OK. You should enable slasharguments in Moodle configuration.';
        } else if ($enabled and ($status > 0)) {
            $solution .= 'Congratulations - everything seems OK now :-D';
        }
        if ($status < 1) {
            $solution .= '<p>IIS:<ul><li>try to add <code>cgi.fix_pathinfo=1</code> to php.ini</li><li>do NOT enable AllowPathInfoForScriptMappings !!!</li><li>slasharguments may not work when using ISAPI and PHP 4.3.10 and older</li></ul></p>';
            $solution .= '<p>Apache 1:<ul><li>try to add <code>cgi.fix_pathinfo=1</code> to php.ini</li></ul></p>';
            $solution .= '<p>Apache 2:<ul><li>you must add <code>AcceptPathInfo on</code> to php.ini or .htaccess</li><li>try to add <code>cgi.fix_pathinfo=1</code> to php.ini</li></ul></p>';
        }
        return $solution;
    }
    function is_enabled() {
        global $CFG;
        return !empty($CFG->slasharguments);
    }
    function status() {
        global $CFG;
        $handle = @fopen($CFG->wwwroot.'/file.php?file=/testslasharguments', "r");
        $contents = @trim(fread($handle, 10));
        @fclose($handle);
        if ($contents != 'test -1') {
            return -1;
        }
        $handle = @fopen($CFG->wwwroot.'/file.php/testslasharguments', "r");
        $contents = trim(@fread($handle, 10));
        @fclose($handle);
        switch ($contents) {
            case 'test 1': return 1;
            case 'test 2': return 2;
            default:  return 0;
        }
    }
}*/

class problem_000012 extends problem_base {
    function title() {
        return 'Random questions data consistency';
    }
    function exists() {
        global $DB;
        return $DB->record_exists_select('question', "qtype = 'random' AND parent <> id", array());
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        return '<p>For random questions, question.parent should equal question.id. ' .
        'There are some questions in your database for which this is not true. ' .
        'One way that this could have happened is for random questions restored from backup before ' .
        '<a href="http://tracker.moodle.org/browse/MDL-5482">MDL-5482</a> was fixed.</p>';
    }
    function solution() {
        global $CFG;
        return '<p>Upgrade to Moodle 1.9.1 or later, or manually execute the SQL</p>' .
        '<pre>UPDATE ' . $CFG->prefix . 'question SET parent = id WHERE qtype = \'random\' and parent &lt;> id;</pre>';
    }
}

class problem_000013 extends problem_base {
    function title() {
        return 'Multi-answer questions data consistency';
    }
    function exists() {
        global $DB;
        $positionexpr = $DB->sql_position($DB->sql_concat("','", "q.id", "','"),
                $DB->sql_concat("','", "qma.sequence", "','"));
        return $DB->record_exists_sql("
                SELECT * FROM {question} q
                    JOIN {question_multianswer} qma ON $positionexpr > 0
                WHERE qma.question <> q.parent") ||
            $DB->record_exists_sql("
                SELECT * FROM {question} q
                    JOIN {question} parent_q ON parent_q.id = q.parent
                WHERE q.category <> parent_q.category");
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        return '<p>For each sub-question whose id is listed in ' .
        'question_multianswer.sequence, its question.parent field should equal ' .
        'question_multianswer.question; and each sub-question should be in the same ' .
        'category as its parent. There are questions in your database for ' .
        'which this is not the case. One way that this could have happened is ' .
        'for multi-answer questions restored from backup before ' .
        '<a href="http://tracker.moodle.org/browse/MDL-14750">MDL-14750</a> was fixed.</p>';
    }
    function solution() {
        return '<p>Upgrade to Moodle 1.9.1 or later, or manually execute the ' .
        'code in question_multianswer_fix_subquestion_parents_and_categories in ' .
        '<a href="http://cvs.moodle.org/moodle/question/type/multianswer/db/upgrade.php?revision=1.1.10.2&amp;view=markup">/question/type/multianswer/db/upgrade.php' .
        'from the 1.9 stable branch</a>.</p>';
    }
}

class problem_000014 extends problem_base {
    function title() {
        return 'Only multianswer and random questions should be the parent of another question';
    }
    function exists() {
        global $DB;
        return $DB->record_exists_sql("
                SELECT * FROM {question} q
                    JOIN {question} parent_q ON parent_q.id = q.parent
                WHERE parent_q.qtype NOT IN ('random', 'multianswer')");
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        return '<p>You have questions that violate this in your databse. ' .
        'You will need to investigate to determine how this happened.</p>';
    }
    function solution() {
        return '<p>It is impossible to give a solution without knowing more about ' .
        ' how the problem was caused. You may be able to get help from the ' .
        '<a href="http://moodle.org/mod/forum/view.php?f=121">Quiz forum</a>.</p>';
    }
}

class problem_000015 extends problem_base {
    function title() {
        return 'Question categories should belong to a valid context';
    }
    function exists() {
        global $DB;
        return $DB->record_exists_sql("
            SELECT qc.*, (SELECT COUNT(1) FROM {question} q WHERE q.category = qc.id) AS numquestions
            FROM {question_categories} qc
                LEFT JOIN {context} con ON qc.contextid = con.id
            WHERE con.id IS NULL");
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        global $DB;
        $problemcategories = $DB->get_records_sql("
            SELECT qc.id, qc.name, qc.contextid, (SELECT COUNT(1) FROM {question} q WHERE q.category = qc.id) AS numquestions
            FROM {question_categories} qc
                LEFT JOIN {context} con ON qc.contextid = con.id
            WHERE con.id IS NULL
            ORDER BY numquestions DESC, qc.name");
        $table = '<table><thead><tr><th>Cat id</th><th>Category name</th>' .
        "<th>Context id</th><th>Num Questions</th></tr></thead><tbody>\n";
        foreach ($problemcategories as $cat) {
            $table .= "<tr><td>$cat->id</td><td>" . s($cat->name) . "</td><td>" .
            $cat->contextid ."</td><td>$cat->numquestions</td></tr>\n";
        }
        $table .= '</tbody></table>';
        return '<p>All question categories are linked to a context id, and, ' .
        'the context they are linked to must exist. The following categories ' .
        'belong to a non-existant category:</p>' . $table . '<p>Any of these ' .
        'categories that contain no questions can just be deleted form the database. ' .
        'Other categories will require more thought.</p>';
    }
    function solution() {
        global $CFG;
        return '<p>You can delete the empty categories by executing the following SQL:</p><pre>
DELETE FROM ' . $CFG->prefix . 'question_categories
WHERE
    NOT EXISTS (SELECT * FROM ' . $CFG->prefix . 'question q WHERE q.category = ' . $CFG->prefix . 'question_categories.id)
AND NOT EXISTS (SELECT * FROM ' . $CFG->prefix . 'context con WHERE contextid = con.id)
        </pre><p>Any remaining categories that contain questions will require more thought. ' .
        'People in the <a href="http://moodle.org/mod/forum/view.php?f=121">Quiz forum</a> may be able to help.</p>';
    }
}

class problem_000016 extends problem_base {
    function title() {
        return 'Question categories should belong to the same context as their parent';
    }
    function exists() {
        global $DB;
        return $DB->record_exists_sql("
            SELECT parent_qc.id AS parent, child_qc.id AS child, child_qc.contextid
            FROM {question_categories} child_qc
                JOIN {question_categories} parent_qc ON child_qc.parent = parent_qc.id
            WHERE child_qc.contextid <> parent_qc.contextid");
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        global $DB;
        $problemcategories = $DB->get_records_sql("
            SELECT
                parent_qc.id AS parentid, parent_qc.name AS parentname, parent_qc.contextid AS parentcon,
                child_qc.id AS childid, child_qc.name AS childname, child_qc.contextid AS childcon
            FROM {question_categories} child_qc
                JOIN {question_categories} parent_qc ON child_qc.parent = parent_qc.id
            WHERE child_qc.contextid <> parent_qc.contextid");
        $table = '<table><thead><tr><th colspan="3">Child category</th><th colspan="3">Parent category</th></tr><tr>' .
        '<th>Id</th><th>Name</th><th>Context id</th>' .
        '<th>Id</th><th>Name</th><th>Context id</th>' .
        "</tr></thead><tbody>\n";
        foreach ($problemcategories as $cat) {
            $table .= "<tr><td>$cat->childid</td><td>" . s($cat->childname) .
            "</td><td>$cat->childcon</td><td>$cat->parentid</td><td>" . s($cat->parentname) .
            "</td><td>$cat->parentcon</td></tr>\n";
        }
        $table .= '</tbody></table>';
        return '<p>When one question category is the parent of another, then they ' .
        'should both belong to the same context. This is not true for the following categories:</p>' .
        $table;
    }
    function solution() {
        return '<p>An automated solution is difficult. It depends whether the ' .
        'parent or child category is in the wrong pace.' .
        'People in the <a href="http://moodle.org/mod/forum/view.php?f=121">Quiz forum</a> may be able to help.</p>';
    }
}

class problem_000017 extends problem_base {
    function title() {
        return 'Question categories tree structure';
    }
    function find_problems() {
        global $DB;
        static $answer = null;

        if (is_null($answer)) {
            $categories = $DB->get_records('question_categories', array(), 'id');

            // Look for missing parents.
            $missingparent = array();
            foreach ($categories as $category) {
                if ($category->parent != 0 && !array_key_exists($category->parent, $categories)) {
                    $missingparent[$category->id] = $category;
                }
            }

            // Look for loops.
            $loops = array();
            while (!empty($categories)) {
                $current = array_pop($categories);
                $thisloop = array($current->id => $current);
                while (true) {
                    if (isset($thisloop[$current->parent])) {
                        // Loop detected
                        $loops[$current->id] = $thisloop;
                        break;
                    } else if (!isset($categories[$current->parent])) {
                        // Got to the top level, or a category we already know is OK.
                        break;
                    } else {
                        // Continue following the path.
                        $current = $categories[$current->parent];
                        $thisloop[$current->id] = $current;
                        unset($categories[$current->id]);
                    }
                }
            }

            $answer = array($missingparent, $loops);
        }

        return $answer;
    }
    function exists() {
        list($missingparent, $loops) = $this->find_problems();
        return !empty($missingparent) || !empty($loops);
    }
    function severity() {
        return SEVERITY_ANNOYANCE;
    }
    function description() {
        list($missingparent, $loops) = $this->find_problems();

        $description = '<p>The question categories should be arranged into tree ' .
                ' structures by the question_categories.parent field. Sometimes ' .
                ' this tree structure gets messed up.</p>';

        if (!empty($missingparent)) {
            $description .= '<p>The following categories are missing their parents:</p><ul>';
            foreach ($missingparent as $cat) {
                $description .= "<li>Category $cat->id: " . s($cat->name) . "</li>\n";
            }
            $description .= "</ul>\n";
        }

        if (!empty($loops)) {
            $description .= '<p>The following categories form a loop of parents:</p><ul>';
            foreach ($loops as $loop) {
                $description .= "<li><ul>\n";
                foreach ($loop as $cat) {
                    $description .= "<li>Category $cat->id: " . s($cat->name) . " has parent $cat->parent</li>\n";
                }
                $description .= "</ul></li>\n";
            }
            $description .= "</ul>\n";
        }

        return $description;
    }
    function solution() {
        global $CFG;
        list($missingparent, $loops) = $this->find_problems();

        $solution = '<p>Consider executing the following SQL queries. These fix ' .
                'the problem by moving some categories to the top level.</p>';

        if (!empty($missingparent)) {
            $solution .= "<pre>UPDATE " . $CFG->prefix . "question_categories\n" .
                    "        SET parent = 0\n" .
                    "        WHERE id IN (" . implode(',', array_keys($missingparent)) . ");</pre>\n";
        }

        if (!empty($loops)) {
            $solution .= "<pre>UPDATE " . $CFG->prefix . "question_categories\n" .
                    "        SET parent = 0\n" .
                    "        WHERE id IN (" . implode(',', array_keys($loops)) . ");</pre>\n";
        }

        return $solution;
    }
}

class problem_00000x extends problem_base {
    function title() {
        return '';
    }
    function exists() {
        return false;
    }
    function severity() {
        return SEVERITY_SIGNIFICANT;
    }
    function description() {
        return '';
    }
    function solution() {
        global $CFG;
        return '';
    }
}

/*

TODO:

    session.save_path -- it doesn't really matter because we are already IN a session, right?
    detect unsupported characters in $CFG->wwwroot - see bug Bug #6091 - relative vs absolute path during backup/restore process

*/