lib/datalib.php

   1 <?php
   2 // This file is part of Moodle - http://moodle.org/
   3 //
   4 // Moodle is free software: you can redistribute it and/or modify
   5 // it under the terms of the GNU General Public License as published by
   6 // the Free Software Foundation, either version 3 of the License, or
   7 // (at your option) any later version.
   8 //
   9 // Moodle is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13 //
  14 // You should have received a copy of the GNU General Public License
  15 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 /**
  18  * Library of functions for database manipulation.
  19  *
  20  * Other main libraries:
  21  * - weblib.php - functions that produce web output
  22  * - moodlelib.php - general-purpose Moodle functions
  23  *
  24  * @package    core
  25  * @copyright  1999 onwards Martin Dougiamas  {@link http://moodle.com}
  26  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  27  */
  28
  29 defined('MOODLE_INTERNAL') || die();
  30
  31 /**
  32  * The maximum courses in a category
  33  * MAX_COURSES_IN_CATEGORY * MAX_COURSE_CATEGORIES must not be more than max integer!
  34  */
  35 define('MAX_COURSES_IN_CATEGORY', 10000);
  36
  37 /**
  38   * The maximum number of course categories
  39   * MAX_COURSES_IN_CATEGORY * MAX_COURSE_CATEGORIES must not be more than max integer!
  40   */
  41 define('MAX_COURSE_CATEGORIES', 10000);
  42
  43 /**
  44  * Number of seconds to wait before updating lastaccess information in DB.
  45  *
  46  * We allow overwrites from config.php, useful to ensure coherence in performance
  47  * tests results.
  48  */
  49 if (!defined('LASTACCESS_UPDATE_SECS')) {
  50     define('LASTACCESS_UPDATE_SECS', 60);
  51 }
  52
  53 /**
  54  * Returns $user object of the main admin user
  55  *
  56  * @static stdClass $mainadmin
  57  * @return stdClass {@link $USER} record from DB, false if not found
  58  */
  59 function get_admin() {
  60     global $CFG, $DB;
  61
  62     static $mainadmin = null;
  63     static $prevadmins = null;
  64
  65     if (empty($CFG->siteadmins)) {
  66         // Should not happen on an ordinary site.
  67         // It does however happen during unit tests.
  68         return false;
  69     }
  70
  71     if (isset($mainadmin) and $prevadmins === $CFG->siteadmins) {
  72         return clone($mainadmin);
  73     }
  74
  75     $mainadmin = null;
  76
  77     foreach (explode(',', $CFG->siteadmins) as $id) {
  78         if ($user = $DB->get_record('user', array('id'=>$id, 'deleted'=>0))) {
  79             $mainadmin = $user;
  80             break;
  81         }
  82     }
  83
  84     if ($mainadmin) {
  85         $prevadmins = $CFG->siteadmins;
  86         return clone($mainadmin);
  87     } else {
  88         // this should not happen
  89         return false;
  90     }
  91 }
  92
  93 /**
  94  * Returns list of all admins, using 1 DB query
  95  *
  96  * @return array
  97  */
  98 function get_admins() {
  99     global $DB, $CFG;
 100
 101     if (empty($CFG->siteadmins)) {  // Should not happen on an ordinary site
 102         return array();
 103     }
 104
 105     $sql = "SELECT u.*
 106               FROM {user} u
 107              WHERE u.deleted = 0 AND u.id IN ($CFG->siteadmins)";
 108
 109     // We want the same order as in $CFG->siteadmins.
 110     $records = $DB->get_records_sql($sql);
 111     $admins = array();
 112     foreach (explode(',', $CFG->siteadmins) as $id) {
 113         $id = (int)$id;
 114         if (!isset($records[$id])) {
 115             // User does not exist, this should not happen.
 116             continue;
 117         }
 118         $admins[$records[$id]->id] = $records[$id];
 119     }
 120
 121     return $admins;
 122 }
 123
 124 /**
 125  * Search through course users
 126  *
 127  * If $coursid specifies the site course then this function searches
 128  * through all undeleted and confirmed users
 129  *
 130  * @global object
 131  * @uses SITEID
 132  * @uses SQL_PARAMS_NAMED
 133  * @uses CONTEXT_COURSE
 134  * @param int $courseid The course in question.
 135  * @param int $groupid The group in question.
 136  * @param string $searchtext The string to search for
 137  * @param string $sort A field to sort by
 138  * @param array $exceptions A list of IDs to ignore, eg 2,4,5,8,9,10
 139  * @return array
 140  */
 141 function search_users($courseid, $groupid, $searchtext, $sort='', array $exceptions=null) {
 142     global $DB;
 143
 144     $fullname  = $DB->sql_fullname('u.firstname', 'u.lastname');
 145
 146     if (!empty($exceptions)) {
 147         list($exceptions, $params) = $DB->get_in_or_equal($exceptions, SQL_PARAMS_NAMED, 'ex', false);
 148         $except = "AND u.id $exceptions";
 149     } else {
 150         $except = "";
 151         $params = array();
 152     }
 153
 154     if (!empty($sort)) {
 155         $order = "ORDER BY $sort";
 156     } else {
 157         $order = "";
 158     }
 159
 160     $select = "u.deleted = 0 AND u.confirmed = 1 AND (".$DB->sql_like($fullname, ':search1', false)." OR ".$DB->sql_like('u.email', ':search2', false).")";
 161     $params['search1'] = "%$searchtext%";
 162     $params['search2'] = "%$searchtext%";
 163
 164     if (!$courseid or $courseid == SITEID) {
 165         $sql = "SELECT u.id, u.firstname, u.lastname, u.email
 166                   FROM {user} u
 167                  WHERE $select
 168                        $except
 169                 $order";
 170         return $DB->get_records_sql($sql, $params);
 171
 172     } else {
 173         if ($groupid) {
 174             $sql = "SELECT u.id, u.firstname, u.lastname, u.email
 175                       FROM {user} u
 176                       JOIN {groups_members} gm ON gm.userid = u.id
 177                      WHERE $select AND gm.groupid = :groupid
 178                            $except
 179                      $order";
 180             $params['groupid'] = $groupid;
 181             return $DB->get_records_sql($sql, $params);
 182
 183         } else {
 184             $context = context_course::instance($courseid);
 185
 186             // We want to query both the current context and parent contexts.
 187             list($relatedctxsql, $relatedctxparams) = $DB->get_in_or_equal($context->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'relatedctx');
 188
 189             $sql = "SELECT u.id, u.firstname, u.lastname, u.email
 190                       FROM {user} u
 191                       JOIN {role_assignments} ra ON ra.userid = u.id
 192                      WHERE $select AND ra.contextid $relatedctxsql
 193                            $except
 194                     $order";
 195             $params = array_merge($params, $relatedctxparams);
 196             return $DB->get_records_sql($sql, $params);
 197         }
 198     }
 199 }
 200
 201 /**
 202  * Returns SQL used to search through user table to find users (in a query
 203  * which may also join and apply other conditions).
 204  *
 205  * You can combine this SQL with an existing query by adding 'AND $sql' to the
 206  * WHERE clause of your query (where $sql is the first element in the array
 207  * returned by this function), and merging in the $params array to the parameters
 208  * of your query (where $params is the second element). Your query should use
 209  * named parameters such as :param, rather than the question mark style.
 210  *
 211  * There are examples of basic usage in the unit test for this function.
 212  *
 213  * @param string $search the text to search for (empty string = find all)
 214  * @param string $u the table alias for the user table in the query being
 215  *     built. May be ''.
 216  * @param bool $searchanywhere If true (default), searches in the middle of
 217  *     names, otherwise only searches at start
 218  * @param array $extrafields Array of extra user fields to include in search
 219  * @param array $exclude Array of user ids to exclude (empty = don't exclude)
 220  * @param array $includeonly If specified, only returns users that have ids
 221  *     incldued in this array (empty = don't restrict)
 222  * @return array an array with two elements, a fragment of SQL to go in the
 223  *     where clause the query, and an associative array containing any required
 224  *     parameters (using named placeholders).
 225  */
 226 function users_search_sql($search, $u = 'u', $searchanywhere = true, array $extrafields = array(),
 227         array $exclude = null, array $includeonly = null) {
 228     global $DB, $CFG;
 229     $params = array();
 230     $tests = array();
 231
 232     if ($u) {
 233         $u .= '.';
 234     }
 235
 236     // If we have a $search string, put a field LIKE '$search%' condition on each field.
 237     if ($search) {
 238         $conditions = array(
 239             $DB->sql_fullname($u . 'firstname', $u . 'lastname'),
 240             $conditions[] = $u . 'lastname'
 241         );
 242         foreach ($extrafields as $field) {
 243             $conditions[] = $u . $field;
 244         }
 245         if ($searchanywhere) {
 246             $searchparam = '%' . $search . '%';
 247         } else {
 248             $searchparam = $search . '%';
 249         }
 250         $i = 0;
 251         foreach ($conditions as $key => $condition) {
 252             $conditions[$key] = $DB->sql_like($condition, ":con{$i}00", false, false);
 253             $params["con{$i}00"] = $searchparam;
 254             $i++;
 255         }
 256         $tests[] = '(' . implode(' OR ', $conditions) . ')';
 257     }
 258
 259     // Add some additional sensible conditions.
 260     $tests[] = $u . "id <> :guestid";
 261     $params['guestid'] = $CFG->siteguest;
 262     $tests[] = $u . 'deleted = 0';
 263     $tests[] = $u . 'confirmed = 1';
 264
 265     // If we are being asked to exclude any users, do that.
 266     if (!empty($exclude)) {
 267         list($usertest, $userparams) = $DB->get_in_or_equal($exclude, SQL_PARAMS_NAMED, 'ex', false);
 268         $tests[] = $u . 'id ' . $usertest;
 269         $params = array_merge($params, $userparams);
 270     }
 271
 272     // If we are validating a set list of userids, add an id IN (...) test.
 273     if (!empty($includeonly)) {
 274         list($usertest, $userparams) = $DB->get_in_or_equal($includeonly, SQL_PARAMS_NAMED, 'val');
 275         $tests[] = $u . 'id ' . $usertest;
 276         $params = array_merge($params, $userparams);
 277     }
 278
 279     // In case there are no tests, add one result (this makes it easier to combine
 280     // this with an existing query as you can always add AND $sql).
 281     if (empty($tests)) {
 282         $tests[] = '1 = 1';
 283     }
 284
 285     // Combing the conditions and return.
 286     return array(implode(' AND ', $tests), $params);
 287 }
 288
 289
 290 /**
 291  * This function generates the standard ORDER BY clause for use when generating
 292  * lists of users. If you don't have a reason to use a different order, then
 293  * you should use this method to generate the order when displaying lists of users.
 294  *
 295  * If the optional $search parameter is passed, then exact matches to the search
 296  * will be sorted first. For example, suppose you have two users 'Al Zebra' and
 297  * 'Alan Aardvark'. The default sort is Alan, then Al. If, however, you search for
 298  * 'Al', then Al will be listed first. (With two users, this is not a big deal,
 299  * but with thousands of users, it is essential.)
 300  *
 301  * The list of fields scanned for exact matches are:
 302  *  - firstname
 303  *  - lastname
 304  *  - $DB->sql_fullname
 305  *  - those returned by get_extra_user_fields
 306  *
 307  * If named parameters are used (which is the default, and highly recommended),
 308  * then the parameter names are like :usersortexactN, where N is an int.
 309  *
 310  * The simplest possible example use is:
 311  * list($sort, $params) = users_order_by_sql();
 312  * $sql = 'SELECT * FROM {users} ORDER BY ' . $sort;
 313  *
 314  * A more complex example, showing that this sort can be combined with other sorts:
 315  * list($sort, $sortparams) = users_order_by_sql('u');
 316  * $sql = "SELECT g.id AS groupid, gg.groupingid, u.id AS userid, u.firstname, u.lastname, u.idnumber, u.username
 317  *           FROM {groups} g
 318  *      LEFT JOIN {groupings_groups} gg ON g.id = gg.groupid
 319  *      LEFT JOIN {groups_members} gm ON g.id = gm.groupid
 320  *      LEFT JOIN {user} u ON gm.userid = u.id
 321  *          WHERE g.courseid = :courseid $groupwhere $groupingwhere
 322  *       ORDER BY g.name, $sort";
 323  * $params += $sortparams;
 324  *
 325  * An example showing the use of $search:
 326  * list($sort, $sortparams) = users_order_by_sql('u', $search, $this->get_context());
 327  * $order = ' ORDER BY ' . $sort;
 328  * $params += $sortparams;
 329  * $availableusers = $DB->get_records_sql($fields . $sql . $order, $params, $page*$perpage, $perpage);
 330  *
 331  * @param string $usertablealias (optional) any table prefix for the {users} table. E.g. 'u'.
 332  * @param string $search (optional) a current search string. If given,
 333  *      any exact matches to this string will be sorted first.
 334  * @param context $context the context we are in. Use by get_extra_user_fields.
 335  *      Defaults to $PAGE->context.
 336  * @return array with two elements:
 337  *      string SQL fragment to use in the ORDER BY clause. For example, "firstname, lastname".
 338  *      array of parameters used in the SQL fragment.
 339  */
 340 function users_order_by_sql($usertablealias = '', $search = null, context $context = null) {
 341     global $DB, $PAGE;
 342
 343     if ($usertablealias) {
 344         $tableprefix = $usertablealias . '.';
 345     } else {
 346         $tableprefix = '';
 347     }
 348
 349     $sort = "{$tableprefix}lastname, {$tableprefix}firstname, {$tableprefix}id";
 350     $params = array();
 351
 352     if (!$search) {
 353         return array($sort, $params);
 354     }
 355
 356     if (!$context) {
 357         $context = $PAGE->context;
 358     }
 359
 360     $exactconditions = array();
 361     $paramkey = 'usersortexact1';
 362
 363     $exactconditions[] = $DB->sql_fullname($tableprefix . 'firstname', $tableprefix  . 'lastname') .
 364             ' = :' . $paramkey;
 365     $params[$paramkey] = $search;
 366     $paramkey++;
 367
 368     $fieldstocheck = array_merge(array('firstname', 'lastname'), get_extra_user_fields($context));
 369     foreach ($fieldstocheck as $key => $field) {
 370         $exactconditions[] = 'LOWER(' . $tableprefix . $field . ') = LOWER(:' . $paramkey . ')';
 371         $params[$paramkey] = $search;
 372         $paramkey++;
 373     }
 374
 375     $sort = 'CASE WHEN ' . implode(' OR ', $exactconditions) .
 376             ' THEN 0 ELSE 1 END, ' . $sort;
 377
 378     return array($sort, $params);
 379 }
 380
 381 /**
 382  * Returns a subset of users
 383  *
 384  * @global object
 385  * @uses DEBUG_DEVELOPER
 386  * @uses SQL_PARAMS_NAMED
 387  * @param bool $get If false then only a count of the records is returned
 388  * @param string $search A simple string to search for
 389  * @param bool $confirmed A switch to allow/disallow unconfirmed users
 390  * @param array $exceptions A list of IDs to ignore, eg 2,4,5,8,9,10
 391  * @param string $sort A SQL snippet for the sorting criteria to use
 392  * @param string $firstinitial Users whose first name starts with $firstinitial
 393  * @param string $lastinitial Users whose last name starts with $lastinitial
 394  * @param string $page The page or records to return
 395  * @param string $recordsperpage The number of records to return per page
 396  * @param string $fields A comma separated list of fields to be returned from the chosen table.
 397  * @return array|int|bool  {@link $USER} records unless get is false in which case the integer count of the records found is returned.
 398  *                        False is returned if an error is encountered.
 399  */
 400 function get_users($get=true, $search='', $confirmed=false, array $exceptions=null, $sort='firstname ASC',
 401                    $firstinitial='', $lastinitial='', $page='', $recordsperpage='', $fields='*', $extraselect='', array $extraparams=null) {
 402     global $DB, $CFG;
 403
 404     if ($get && !$recordsperpage) {
 405         debugging('Call to get_users with $get = true no $recordsperpage limit. ' .
 406                 'On large installations, this will probably cause an out of memory error. ' .
 407                 'Please think again and change your code so that it does not try to ' .
 408                 'load so much data into memory.', DEBUG_DEVELOPER);
 409     }
 410
 411     $fullname  = $DB->sql_fullname();
 412
 413     $select = " id <> :guestid AND deleted = 0";
 414     $params = array('guestid'=>$CFG->siteguest);
 415
 416     if (!empty($search)){
 417         $search = trim($search);
 418         $select .= " AND (".$DB->sql_like($fullname, ':search1', false)." OR ".$DB->sql_like('email', ':search2', false)." OR username = :search3)";
 419         $params['search1'] = "%$search%";
 420         $params['search2'] = "%$search%";
 421         $params['search3'] = "$search";
 422     }
 423
 424     if ($confirmed) {
 425         $select .= " AND confirmed = 1";
 426     }
 427
 428     if ($exceptions) {
 429         list($exceptions, $eparams) = $DB->get_in_or_equal($exceptions, SQL_PARAMS_NAMED, 'ex', false);
 430         $params = $params + $eparams;
 431         $select .= " AND id $exceptions";
 432     }
 433
 434     if ($firstinitial) {
 435         $select .= " AND ".$DB->sql_like('firstname', ':fni', false, false);
 436         $params['fni'] = "$firstinitial%";
 437     }
 438     if ($lastinitial) {
 439         $select .= " AND ".$DB->sql_like('lastname', ':lni', false, false);
 440         $params['lni'] = "$lastinitial%";
 441     }
 442
 443     if ($extraselect) {
 444         $select .= " AND $extraselect";
 445         $params = $params + (array)$extraparams;
 446     }
 447
 448     if ($get) {
 449         return $DB->get_records_select('user', $select, $params, $sort, $fields, $page, $recordsperpage);
 450     } else {
 451         return $DB->count_records_select('user', $select, $params);
 452     }
 453 }
 454
 455
 456 /**
 457  * Return filtered (if provided) list of users in site, except guest and deleted users.
 458  *
 459  * @param string $sort An SQL field to sort by
 460  * @param string $dir The sort direction ASC|DESC
 461  * @param int $page The page or records to return
 462  * @param int $recordsperpage The number of records to return per page
 463  * @param string $search A simple string to search for
 464  * @param string $firstinitial Users whose first name starts with $firstinitial
 465  * @param string $lastinitial Users whose last name starts with $lastinitial
 466  * @param string $extraselect An additional SQL select statement to append to the query
 467  * @param array $extraparams Additional parameters to use for the above $extraselect
 468  * @param stdClass $extracontext If specified, will include user 'extra fields'
 469  *   as appropriate for current user and given context
 470  * @return array Array of {@link $USER} records
 471  */
 472 function get_users_listing($sort='lastaccess', $dir='ASC', $page=0, $recordsperpage=0,
 473                            $search='', $firstinitial='', $lastinitial='', $extraselect='',
 474                            array $extraparams=null, $extracontext = null) {
 475     global $DB, $CFG;
 476
 477     $fullname  = $DB->sql_fullname();
 478
 479     $select = "deleted <> 1 AND id <> :guestid";
 480     $params = array('guestid' => $CFG->siteguest);
 481
 482     if (!empty($search)) {
 483         $search = trim($search);
 484         $select .= " AND (". $DB->sql_like($fullname, ':search1', false, false).
 485                    " OR ". $DB->sql_like('email', ':search2', false, false).
 486                    " OR username = :search3)";
 487         $params['search1'] = "%$search%";
 488         $params['search2'] = "%$search%";
 489         $params['search3'] = "$search";
 490     }
 491
 492     if ($firstinitial) {
 493         $select .= " AND ". $DB->sql_like('firstname', ':fni', false, false);
 494         $params['fni'] = "$firstinitial%";
 495     }
 496     if ($lastinitial) {
 497         $select .= " AND ". $DB->sql_like('lastname', ':lni', false, false);
 498         $params['lni'] = "$lastinitial%";
 499     }
 500
 501     if ($extraselect) {
 502         $select .= " AND $extraselect";
 503         $params = $params + (array)$extraparams;
 504     }
 505
 506     if ($sort) {
 507         $sort = " ORDER BY $sort $dir";
 508     }
 509
 510     // If a context is specified, get extra user fields that the current user
 511     // is supposed to see.
 512     $extrafields = '';
 513     if ($extracontext) {
 514         $extrafields = get_extra_user_fields_sql($extracontext, '', '',
 515                 array('id', 'username', 'email', 'firstname', 'lastname', 'city', 'country',
 516                 'lastaccess', 'confirmed', 'mnethostid'));
 517     }
 518     $namefields = get_all_user_name_fields(true);
 519     $extrafields = "$extrafields, $namefields";
 520
 521     // warning: will return UNCONFIRMED USERS
 522     return $DB->get_records_sql("SELECT id, username, email, city, country, lastaccess, confirmed, mnethostid, suspended $extrafields
 523                                    FROM {user}
 524                                   WHERE $select
 525                                   $sort", $params, $page, $recordsperpage);
 526
 527 }
 528
 529
 530 /**
 531  * Full list of users that have confirmed their accounts.
 532  *
 533  * @global object
 534  * @return array of unconfirmed users
 535  */
 536 function get_users_confirmed() {
 537     global $DB, $CFG;
 538     return $DB->get_records_sql("SELECT *
 539                                    FROM {user}
 540                                   WHERE confirmed = 1 AND deleted = 0 AND id <> ?", array($CFG->siteguest));
 541 }
 542
 543
 544 /// OTHER SITE AND COURSE FUNCTIONS /////////////////////////////////////////////
 545
 546
 547 /**
 548  * Returns $course object of the top-level site.
 549  *
 550  * @return object A {@link $COURSE} object for the site, exception if not found
 551  */
 552 function get_site() {
 553     global $SITE, $DB;
 554
 555     if (!empty($SITE->id)) {   // We already have a global to use, so return that
 556         return $SITE;
 557     }
 558
 559     if ($course = $DB->get_record('course', array('category'=>0))) {
 560         return $course;
 561     } else {
 562         // course table exists, but the site is not there,
 563         // unfortunately there is no automatic way to recover
 564         throw new moodle_exception('nosite', 'error');
 565     }
 566 }
 567
 568 /**
 569  * Gets a course object from database. If the course id corresponds to an
 570  * already-loaded $COURSE or $SITE object, then the loaded object will be used,
 571  * saving a database query.
 572  *
 573  * If it reuses an existing object, by default the object will be cloned. This
 574  * means you can modify the object safely without affecting other code.
 575  *
 576  * @param int $courseid Course id
 577  * @param bool $clone If true (default), makes a clone of the record
 578  * @return stdClass A course object
 579  * @throws dml_exception If not found in database
 580  */
 581 function get_course($courseid, $clone = true) {
 582     global $DB, $COURSE, $SITE;
 583     if (!empty($COURSE->id) && $COURSE->id == $courseid) {
 584         return $clone ? clone($COURSE) : $COURSE;
 585     } else if (!empty($SITE->id) && $SITE->id == $courseid) {
 586         return $clone ? clone($SITE) : $SITE;
 587     } else {
 588         return $DB->get_record('course', array('id' => $courseid), '*', MUST_EXIST);
 589     }
 590 }
 591
 592 /**
 593  * Returns list of courses, for whole site, or category
 594  *
 595  * Returns list of courses, for whole site, or category
 596  * Important: Using c.* for fields is extremely expensive because
 597  *            we are using distinct. You almost _NEVER_ need all the fields
 598  *            in such a large SELECT
 599  *
 600  * @global object
 601  * @global object
 602  * @global object
 603  * @uses CONTEXT_COURSE
 604  * @param string|int $categoryid Either a category id or 'all' for everything
 605  * @param string $sort A field and direction to sort by
 606  * @param string $fields The additional fields to return
 607  * @return array Array of courses
 608  */
 609 function get_courses($categoryid="all", $sort="c.sortorder ASC", $fields="c.*") {
 610
 611     global $USER, $CFG, $DB;
 612
 613     $params = array();
 614
 615     if ($categoryid !== "all" && is_numeric($categoryid)) {
 616         $categoryselect = "WHERE c.category = :catid";
 617         $params['catid'] = $categoryid;
 618     } else {
 619         $categoryselect = "";
 620     }
 621
 622     if (empty($sort)) {
 623         $sortstatement = "";
 624     } else {
 625         $sortstatement = "ORDER BY $sort";
 626     }
 627
 628     $visiblecourses = array();
 629
 630     $ccselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
 631     $ccjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
 632     $params['contextlevel'] = CONTEXT_COURSE;
 633
 634     $sql = "SELECT $fields $ccselect
 635               FROM {course} c
 636            $ccjoin
 637               $categoryselect
 638               $sortstatement";
 639
 640     // pull out all course matching the cat
 641     if ($courses = $DB->get_records_sql($sql, $params)) {
 642
 643         // loop throught them
 644         foreach ($courses as $course) {
 645             context_helper::preload_from_record($course);
 646             if (isset($course->visible) && $course->visible <= 0) {
 647                 // for hidden courses, require visibility check
 648                 if (has_capability('moodle/course:viewhiddencourses', context_course::instance($course->id))) {
 649                     $visiblecourses [$course->id] = $course;
 650                 }
 651             } else {
 652                 $visiblecourses [$course->id] = $course;
 653             }
 654         }
 655     }
 656     return $visiblecourses;
 657 }
 658
 659
 660 /**
 661  * Returns list of courses, for whole site, or category
 662  *
 663  * Similar to get_courses, but allows paging
 664  * Important: Using c.* for fields is extremely expensive because
 665  *            we are using distinct. You almost _NEVER_ need all the fields
 666  *            in such a large SELECT
 667  *
 668  * @global object
 669  * @global object
 670  * @global object
 671  * @uses CONTEXT_COURSE
 672  * @param string|int $categoryid Either a category id or 'all' for everything
 673  * @param string $sort A field and direction to sort by
 674  * @param string $fields The additional fields to return
 675  * @param int $totalcount Reference for the number of courses
 676  * @param string $limitfrom The course to start from
 677  * @param string $limitnum The number of courses to limit to
 678  * @return array Array of courses
 679  */
 680 function get_courses_page($categoryid="all", $sort="c.sortorder ASC", $fields="c.*",
 681                           &$totalcount, $limitfrom="", $limitnum="") {
 682     global $USER, $CFG, $DB;
 683
 684     $params = array();
 685
 686     $categoryselect = "";
 687     if ($categoryid !== "all" && is_numeric($categoryid)) {
 688         $categoryselect = "WHERE c.category = :catid";
 689         $params['catid'] = $categoryid;
 690     } else {
 691         $categoryselect = "";
 692     }
 693
 694     $ccselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
 695     $ccjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
 696     $params['contextlevel'] = CONTEXT_COURSE;
 697
 698     $totalcount = 0;
 699     if (!$limitfrom) {
 700         $limitfrom = 0;
 701     }
 702     $visiblecourses = array();
 703
 704     $sql = "SELECT $fields $ccselect
 705               FROM {course} c
 706               $ccjoin
 707            $categoryselect
 708           ORDER BY $sort";
 709
 710     // pull out all course matching the cat
 711     $rs = $DB->get_recordset_sql($sql, $params);
 712     // iteration will have to be done inside loop to keep track of the limitfrom and limitnum
 713     foreach($rs as $course) {
 714         context_helper::preload_from_record($course);
 715         if ($course->visible <= 0) {
 716             // for hidden courses, require visibility check
 717             if (has_capability('moodle/course:viewhiddencourses', context_course::instance($course->id))) {
 718                 $totalcount++;
 719                 if ($totalcount > $limitfrom && (!$limitnum or count($visiblecourses) < $limitnum)) {
 720                     $visiblecourses [$course->id] = $course;
 721                 }
 722             }
 723         } else {
 724             $totalcount++;
 725             if ($totalcount > $limitfrom && (!$limitnum or count($visiblecourses) < $limitnum)) {
 726                 $visiblecourses [$course->id] = $course;
 727             }
 728         }
 729     }
 730     $rs->close();
 731     return $visiblecourses;
 732 }
 733
 734 /**
 735  * A list of courses that match a search
 736  *
 737  * @global object
 738  * @global object
 739  * @param array $searchterms An array of search criteria
 740  * @param string $sort A field and direction to sort by
 741  * @param int $page The page number to get
 742  * @param int $recordsperpage The number of records per page
 743  * @param int $totalcount Passed in by reference.
 744  * @param array $requiredcapabilities Extra list of capabilities used to filter courses
 745  * @return object {@link $COURSE} records
 746  */
 747 function get_courses_search($searchterms, $sort, $page, $recordsperpage, &$totalcount,
 748                             $requiredcapabilities = array()) {
 749     global $CFG, $DB;
 750
 751     if ($DB->sql_regex_supported()) {
 752         $REGEXP    = $DB->sql_regex(true);
 753         $NOTREGEXP = $DB->sql_regex(false);
 754     }
 755
 756     $searchcond = array();
 757     $params     = array();
 758     $i = 0;
 759
 760     // Thanks Oracle for your non-ansi concat and type limits in coalesce. MDL-29912
 761     if ($DB->get_dbfamily() == 'oracle') {
 762         $concat = "(c.summary|| ' ' || c.fullname || ' ' || c.idnumber || ' ' || c.shortname)";
 763     } else {
 764         $concat = $DB->sql_concat("COALESCE(c.summary, '')", "' '", 'c.fullname', "' '", 'c.idnumber', "' '", 'c.shortname');
 765     }
 766
 767     foreach ($searchterms as $searchterm) {
 768         $i++;
 769
 770         $NOT = false; /// Initially we aren't going to perform NOT LIKE searches, only MSSQL and Oracle
 771                    /// will use it to simulate the "-" operator with LIKE clause
 772
 773     /// Under Oracle and MSSQL, trim the + and - operators and perform
 774     /// simpler LIKE (or NOT LIKE) queries
 775         if (!$DB->sql_regex_supported()) {
 776             if (substr($searchterm, 0, 1) == '-') {
 777                 $NOT = true;
 778             }
 779             $searchterm = trim($searchterm, '+-');
 780         }
 781
 782         // TODO: +- may not work for non latin languages
 783
 784         if (substr($searchterm,0,1) == '+') {
 785             $searchterm = trim($searchterm, '+-');
 786             $searchterm = preg_quote($searchterm, '|');
 787             $searchcond[] = "$concat $REGEXP :ss$i";
 788             $params['ss'.$i] = "(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)";
 789
 790         } else if ((substr($searchterm,0,1) == "-") && (core_text::strlen($searchterm) > 1)) {
 791             $searchterm = trim($searchterm, '+-');
 792             $searchterm = preg_quote($searchterm, '|');
 793             $searchcond[] = "$concat $NOTREGEXP :ss$i";
 794             $params['ss'.$i] = "(^|[^a-zA-Z0-9])$searchterm([^a-zA-Z0-9]|$)";
 795
 796         } else {
 797             $searchcond[] = $DB->sql_like($concat,":ss$i", false, true, $NOT);
 798             $params['ss'.$i] = "%$searchterm%";
 799         }
 800     }
 801
 802     if (empty($searchcond)) {
 803         $searchcond = array('1 = 1');
 804     }
 805
 806     $searchcond = implode(" AND ", $searchcond);
 807
 808     $courses = array();
 809     $c = 0; // counts how many visible courses we've seen
 810
 811     // Tiki pagination
 812     $limitfrom = $page * $recordsperpage;
 813     $limitto   = $limitfrom + $recordsperpage;
 814
 815     $ccselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
 816     $ccjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
 817     $params['contextlevel'] = CONTEXT_COURSE;
 818
 819     $sql = "SELECT c.* $ccselect
 820               FROM {course} c
 821            $ccjoin
 822              WHERE $searchcond AND c.id <> ".SITEID."
 823           ORDER BY $sort";
 824
 825     $rs = $DB->get_recordset_sql($sql, $params);
 826     foreach($rs as $course) {
 827         // Preload contexts only for hidden courses or courses we need to return.
 828         context_helper::preload_from_record($course);
 829         $coursecontext = context_course::instance($course->id);
 830         if (!$course->visible && !has_capability('moodle/course:viewhiddencourses', $coursecontext)) {
 831             continue;
 832         }
 833         if (!empty($requiredcapabilities)) {
 834             if (!has_all_capabilities($requiredcapabilities, $coursecontext)) {
 835                 continue;
 836             }
 837         }
 838         // Don't exit this loop till the end
 839         // we need to count all the visible courses
 840         // to update $totalcount
 841         if ($c >= $limitfrom && $c < $limitto) {
 842             $courses[$course->id] = $course;
 843         }
 844         $c++;
 845     }
 846     $rs->close();
 847
 848     // our caller expects 2 bits of data - our return
 849     // array, and an updated $totalcount
 850     $totalcount = $c;
 851     return $courses;
 852 }
 853
 854 /**
 855  * Fixes course category and course sortorder, also verifies category and course parents and paths.
 856  * (circular references are not fixed)
 857  *
 858  * @global object
 859  * @global object
 860  * @uses MAX_COURSES_IN_CATEGORY
 861  * @uses MAX_COURSE_CATEGORIES
 862  * @uses SITEID
 863  * @uses CONTEXT_COURSE
 864  * @return void
 865  */
 866 function fix_course_sortorder() {
 867     global $DB, $SITE;
 868
 869     //WARNING: this is PHP5 only code!
 870
 871     // if there are any changes made to courses or categories we will trigger
 872     // the cache events to purge all cached courses/categories data
 873     $cacheevents = array();
 874
 875     if ($unsorted = $DB->get_records('course_categories', array('sortorder'=>0))) {
 876         //move all categories that are not sorted yet to the end
 877         $DB->set_field('course_categories', 'sortorder', MAX_COURSES_IN_CATEGORY*MAX_COURSE_CATEGORIES, array('sortorder'=>0));
 878         $cacheevents['changesincoursecat'] = true;
 879     }
 880
 881     $allcats = $DB->get_records('course_categories', null, 'sortorder, id', 'id, sortorder, parent, depth, path');
 882     $topcats    = array();
 883     $brokencats = array();
 884     foreach ($allcats as $cat) {
 885         $sortorder = (int)$cat->sortorder;
 886         if (!$cat->parent) {
 887             while(isset($topcats[$sortorder])) {
 888                 $sortorder++;
 889             }
 890             $topcats[$sortorder] = $cat;
 891             continue;
 892         }
 893         if (!isset($allcats[$cat->parent])) {
 894             $brokencats[] = $cat;
 895             continue;
 896         }
 897         if (!isset($allcats[$cat->parent]->children)) {
 898             $allcats[$cat->parent]->children = array();
 899         }
 900         while(isset($allcats[$cat->parent]->children[$sortorder])) {
 901             $sortorder++;
 902         }
 903         $allcats[$cat->parent]->children[$sortorder] = $cat;
 904     }
 905     unset($allcats);
 906
 907     // add broken cats to category tree
 908     if ($brokencats) {
 909         $defaultcat = reset($topcats);
 910         foreach ($brokencats as $cat) {
 911             $topcats[] = $cat;
 912         }
 913     }
 914
 915     // now walk recursively the tree and fix any problems found
 916     $sortorder = 0;
 917     $fixcontexts = array();
 918     if (_fix_course_cats($topcats, $sortorder, 0, 0, '', $fixcontexts)) {
 919         $cacheevents['changesincoursecat'] = true;
 920     }
 921
 922     // detect if there are "multiple" frontpage courses and fix them if needed
 923     $frontcourses = $DB->get_records('course', array('category'=>0), 'id');
 924     if (count($frontcourses) > 1) {
 925         if (isset($frontcourses[SITEID])) {
 926             $frontcourse = $frontcourses[SITEID];
 927             unset($frontcourses[SITEID]);
 928         } else {
 929             $frontcourse = array_shift($frontcourses);
 930         }
 931         $defaultcat = reset($topcats);
 932         foreach ($frontcourses as $course) {
 933             $DB->set_field('course', 'category', $defaultcat->id, array('id'=>$course->id));
 934             $context = context_course::instance($course->id);
 935             $fixcontexts[$context->id] = $context;
 936             $cacheevents['changesincourse'] = true;
 937         }
 938         unset($frontcourses);
 939     } else {
 940         $frontcourse = reset($frontcourses);
 941     }
 942
 943     // now fix the paths and depths in context table if needed
 944     if ($fixcontexts) {
 945         foreach ($fixcontexts as $fixcontext) {
 946             $fixcontext->reset_paths(false);
 947         }
 948         context_helper::build_all_paths(false);
 949         unset($fixcontexts);
 950         $cacheevents['changesincourse'] = true;
 951         $cacheevents['changesincoursecat'] = true;
 952     }
 953
 954     // release memory
 955     unset($topcats);
 956     unset($brokencats);
 957     unset($fixcontexts);
 958
 959     // fix frontpage course sortorder
 960     if ($frontcourse->sortorder != 1) {
 961         $DB->set_field('course', 'sortorder', 1, array('id'=>$frontcourse->id));
 962         $cacheevents['changesincourse'] = true;
 963     }
 964
 965     // now fix the course counts in category records if needed
 966     $sql = "SELECT cc.id, cc.coursecount, COUNT(c.id) AS newcount
 967               FROM {course_categories} cc
 968               LEFT JOIN {course} c ON c.category = cc.id
 969           GROUP BY cc.id, cc.coursecount
 970             HAVING cc.coursecount <> COUNT(c.id)";
 971
 972     if ($updatecounts = $DB->get_records_sql($sql)) {
 973         // categories with more courses than MAX_COURSES_IN_CATEGORY
 974         $categories = array();
 975         foreach ($updatecounts as $cat) {
 976             $cat->coursecount = $cat->newcount;
 977             if ($cat->coursecount >= MAX_COURSES_IN_CATEGORY) {
 978                 $categories[] = $cat->id;
 979             }
 980             unset($cat->newcount);
 981             $DB->update_record_raw('course_categories', $cat, true);
 982         }
 983         if (!empty($categories)) {
 984             $str = implode(', ', $categories);
 985             debugging("The number of courses (category id: $str) has reached MAX_COURSES_IN_CATEGORY (" . MAX_COURSES_IN_CATEGORY . "), it will cause a sorting performance issue, please increase the value of MAX_COURSES_IN_CATEGORY in lib/datalib.php file. See tracker issue: MDL-25669", DEBUG_DEVELOPER);
 986         }
 987         $cacheevents['changesincoursecat'] = true;
 988     }
 989
 990     // now make sure that sortorders in course table are withing the category sortorder ranges
 991     $sql = "SELECT DISTINCT cc.id, cc.sortorder
 992               FROM {course_categories} cc
 993               JOIN {course} c ON c.category = cc.id
 994              WHERE c.sortorder < cc.sortorder OR c.sortorder > cc.sortorder + ".MAX_COURSES_IN_CATEGORY;
 995
 996     if ($fixcategories = $DB->get_records_sql($sql)) {
 997         //fix the course sortorder ranges
 998         foreach ($fixcategories as $cat) {
 999             $sql = "UPDATE {course}
1000                        SET sortorder = ".$DB->sql_modulo('sortorder', MAX_COURSES_IN_CATEGORY)." + ?
1001                      WHERE category = ?";
1002             $DB->execute($sql, array($cat->sortorder, $cat->id));
1003         }
1004         $cacheevents['changesincoursecat'] = true;
1005     }
1006     unset($fixcategories);
1007
1008     // categories having courses with sortorder duplicates or having gaps in sortorder
1009     $sql = "SELECT DISTINCT c1.category AS id , cc.sortorder
1010               FROM {course} c1
1011               JOIN {course} c2 ON c1.sortorder = c2.sortorder
1012               JOIN {course_categories} cc ON (c1.category = cc.id)
1013              WHERE c1.id <> c2.id";
1014     $fixcategories = $DB->get_records_sql($sql);
1015
1016     $sql = "SELECT cc.id, cc.sortorder, cc.coursecount, MAX(c.sortorder) AS maxsort, MIN(c.sortorder) AS minsort
1017               FROM {course_categories} cc
1018               JOIN {course} c ON c.category = cc.id
1019           GROUP BY cc.id, cc.sortorder, cc.coursecount
1020             HAVING (MAX(c.sortorder) <>  cc.sortorder + cc.coursecount) OR (MIN(c.sortorder) <>  cc.sortorder + 1)";
1021     $gapcategories = $DB->get_records_sql($sql);
1022
1023     foreach ($gapcategories as $cat) {
1024         if (isset($fixcategories[$cat->id])) {
1025             // duplicates detected already
1026
1027         } else if ($cat->minsort == $cat->sortorder and $cat->maxsort == $cat->sortorder + $cat->coursecount - 1) {
1028             // easy - new course inserted with sortorder 0, the rest is ok
1029             $sql = "UPDATE {course}
1030                        SET sortorder = sortorder + 1
1031                      WHERE category = ?";
1032             $DB->execute($sql, array($cat->id));
1033
1034         } else {
1035             // it needs full resorting
1036             $fixcategories[$cat->id] = $cat;
1037         }
1038         $cacheevents['changesincourse'] = true;
1039     }
1040     unset($gapcategories);
1041
1042     // fix course sortorders in problematic categories only
1043     foreach ($fixcategories as $cat) {
1044         $i = 1;
1045         $courses = $DB->get_records('course', array('category'=>$cat->id), 'sortorder ASC, id DESC', 'id, sortorder');
1046         foreach ($courses as $course) {
1047             if ($course->sortorder != $cat->sortorder + $i) {
1048                 $course->sortorder = $cat->sortorder + $i;
1049                 $DB->update_record_raw('course', $course, true);
1050                 $cacheevents['changesincourse'] = true;
1051             }
1052             $i++;
1053         }
1054     }
1055
1056     // advise all caches that need to be rebuilt
1057     foreach (array_keys($cacheevents) as $event) {
1058         cache_helper::purge_by_event($event);
1059     }
1060 }
1061
1062 /**
1063  * Internal recursive category verification function, do not use directly!
1064  *
1065  * @todo Document the arguments of this function better
1066  *
1067  * @global object
1068  * @uses MAX_COURSES_IN_CATEGORY
1069  * @uses CONTEXT_COURSECAT
1070  * @param array $children
1071  * @param int $sortorder
1072  * @param string $parent
1073  * @param int $depth
1074  * @param string $path
1075  * @param array $fixcontexts
1076  * @return bool if changes were made
1077  */
1078 function _fix_course_cats($children, &$sortorder, $parent, $depth, $path, &$fixcontexts) {
1079     global $DB;
1080
1081     $depth++;
1082     $changesmade = false;
1083
1084     foreach ($children as $cat) {
1085         $sortorder = $sortorder + MAX_COURSES_IN_CATEGORY;
1086         $update = false;
1087         if ($parent != $cat->parent or $depth != $cat->depth or $path.'/'.$cat->id != $cat->path) {
1088             $cat->parent = $parent;
1089             $cat->depth  = $depth;
1090             $cat->path   = $path.'/'.$cat->id;
1091             $update = true;
1092
1093             // make sure context caches are rebuild and dirty contexts marked
1094             $context = context_coursecat::instance($cat->id);
1095             $fixcontexts[$context->id] = $context;
1096         }
1097         if ($cat->sortorder != $sortorder) {
1098             $cat->sortorder = $sortorder;
1099             $update = true;
1100         }
1101         if ($update) {
1102             $DB->update_record('course_categories', $cat, true);
1103             $changesmade = true;
1104         }
1105         if (isset($cat->children)) {
1106             if (_fix_course_cats($cat->children, $sortorder, $cat->id, $cat->depth, $cat->path, $fixcontexts)) {
1107                 $changesmade = true;
1108             }
1109         }
1110     }
1111     return $changesmade;
1112 }
1113
1114 /**
1115  * List of remote courses that a user has access to via MNET.
1116  * Works only on the IDP
1117  *
1118  * @global object
1119  * @global object
1120  * @param int @userid The user id to get remote courses for
1121  * @return array Array of {@link $COURSE} of course objects
1122  */
1123 function get_my_remotecourses($userid=0) {
1124     global $DB, $USER;
1125
1126     if (empty($userid)) {
1127         $userid = $USER->id;
1128     }
1129
1130     // we can not use SELECT DISTINCT + text field (summary) because of MS SQL and Oracle, subselect used therefore
1131     $sql = "SELECT c.id, c.remoteid, c.shortname, c.fullname,
1132                    c.hostid, c.summary, c.summaryformat, c.categoryname AS cat_name,
1133                    h.name AS hostname
1134               FROM {mnetservice_enrol_courses} c
1135               JOIN (SELECT DISTINCT hostid, remotecourseid
1136                       FROM {mnetservice_enrol_enrolments}
1137                      WHERE userid = ?
1138                    ) e ON (e.hostid = c.hostid AND e.remotecourseid = c.remoteid)
1139               JOIN {mnet_host} h ON h.id = c.hostid";
1140
1141     return $DB->get_records_sql($sql, array($userid));
1142 }
1143
1144 /**
1145  * List of remote hosts that a user has access to via MNET.
1146  * Works on the SP
1147  *
1148  * @global object
1149  * @global object
1150  * @return array|bool Array of host objects or false
1151  */
1152 function get_my_remotehosts() {
1153     global $CFG, $USER;
1154
1155     if ($USER->mnethostid == $CFG->mnet_localhost_id) {
1156         return false; // Return nothing on the IDP
1157     }
1158     if (!empty($USER->mnet_foreign_host_array) && is_array($USER->mnet_foreign_host_array)) {
1159         return $USER->mnet_foreign_host_array;
1160     }
1161     return false;
1162 }
1163
1164
1165 /**
1166  * Returns a menu of all available scales from the site as well as the given course
1167  *
1168  * @global object
1169  * @param int $courseid The id of the course as found in the 'course' table.
1170  * @return array
1171  */
1172 function get_scales_menu($courseid=0) {
1173     global $DB;
1174
1175     $sql = "SELECT id, name
1176               FROM {scale}
1177              WHERE courseid = 0 or courseid = ?
1178           ORDER BY courseid ASC, name ASC";
1179     $params = array($courseid);
1180
1181     return $scales = $DB->get_records_sql_menu($sql, $params);
1182 }
1183
1184 /**
1185  * Increment standard revision field.
1186  *
1187  * The revision are based on current time and are incrementing.
1188  * There is a protection for runaway revisions, it may not go further than
1189  * one hour into future.
1190  *
1191  * The field has to be XMLDB_TYPE_INTEGER with size 10.
1192  *
1193  * @param string $table
1194  * @param string $field name of the field containing revision
1195  * @param string $select use empty string when updating all records
1196  * @param array $params optional select parameters
1197  */
1198 function increment_revision_number($table, $field, $select, array $params = null) {
1199     global $DB;
1200
1201     $now = time();
1202     $sql = "UPDATE {{$table}}
1203                    SET $field = (CASE
1204                        WHEN $field IS NULL THEN $now
1205                        WHEN $field < $now THEN $now
1206                        WHEN $field > $now + 3600 THEN $now
1207                        ELSE $field + 1 END)";
1208     if ($select) {
1209         $sql = $sql . " WHERE $select";
1210     }
1211     $DB->execute($sql, $params);
1212 }
1213
1214
1215 /// MODULE FUNCTIONS /////////////////////////////////////////////////
1216
1217 /**
1218  * Just gets a raw list of all modules in a course
1219  *
1220  * @global object
1221  * @param int $courseid The id of the course as found in the 'course' table.
1222  * @return array
1223  */
1224 function get_course_mods($courseid) {
1225     global $DB;
1226
1227     if (empty($courseid)) {
1228         return false; // avoid warnings
1229     }
1230
1231     return $DB->get_records_sql("SELECT cm.*, m.name as modname
1232                                    FROM {modules} m, {course_modules} cm
1233                                   WHERE cm.course = ? AND cm.module = m.id AND m.visible = 1",
1234                                 array($courseid)); // no disabled mods
1235 }
1236
1237
1238 /**
1239  * Given an id of a course module, finds the coursemodule description
1240  *
1241  * Please note that this function performs 1-2 DB queries. When possible use cached
1242  * course modinfo. For example get_fast_modinfo($courseorid)->get_cm($cmid)
1243  * See also {@link cm_info::get_course_module_record()}
1244  *
1245  * @global object
1246  * @param string $modulename name of module type, eg. resource, assignment,... (optional, slower and less safe if not specified)
1247  * @param int $cmid course module id (id in course_modules table)
1248  * @param int $courseid optional course id for extra validation
1249  * @param bool $sectionnum include relative section number (0,1,2 ...)
1250  * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1251  *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1252  *                        MUST_EXIST means throw exception if no record or multiple records found
1253  * @return stdClass
1254  */
1255 function get_coursemodule_from_id($modulename, $cmid, $courseid=0, $sectionnum=false, $strictness=IGNORE_MISSING) {
1256     global $DB;
1257
1258     $params = array('cmid'=>$cmid);
1259
1260     if (!$modulename) {
1261         if (!$modulename = $DB->get_field_sql("SELECT md.name
1262                                                  FROM {modules} md
1263                                                  JOIN {course_modules} cm ON cm.module = md.id
1264                                                 WHERE cm.id = :cmid", $params, $strictness)) {
1265             return false;
1266         }
1267     } else {
1268         if (!core_component::is_valid_plugin_name('mod', $modulename)) {
1269             throw new coding_exception('Invalid modulename parameter');
1270         }
1271     }
1272
1273     $params['modulename'] = $modulename;
1274
1275     $courseselect = "";
1276     $sectionfield = "";
1277     $sectionjoin  = "";
1278
1279     if ($courseid) {
1280         $courseselect = "AND cm.course = :courseid";
1281         $params['courseid'] = $courseid;
1282     }
1283
1284     if ($sectionnum) {
1285         $sectionfield = ", cw.section AS sectionnum";
1286         $sectionjoin  = "LEFT JOIN {course_sections} cw ON cw.id = cm.section";
1287     }
1288
1289     $sql = "SELECT cm.*, m.name, md.name AS modname $sectionfield
1290               FROM {course_modules} cm
1291                    JOIN {modules} md ON md.id = cm.module
1292                    JOIN {".$modulename."} m ON m.id = cm.instance
1293                    $sectionjoin
1294              WHERE cm.id = :cmid AND md.name = :modulename
1295                    $courseselect";
1296
1297     return $DB->get_record_sql($sql, $params, $strictness);
1298 }
1299
1300 /**
1301  * Given an instance number of a module, finds the coursemodule description
1302  *
1303  * Please note that this function performs DB query. When possible use cached course
1304  * modinfo. For example get_fast_modinfo($courseorid)->instances[$modulename][$instance]
1305  * See also {@link cm_info::get_course_module_record()}
1306  *
1307  * @global object
1308  * @param string $modulename name of module type, eg. resource, assignment,...
1309  * @param int $instance module instance number (id in resource, assignment etc. table)
1310  * @param int $courseid optional course id for extra validation
1311  * @param bool $sectionnum include relative section number (0,1,2 ...)
1312  * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
1313  *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
1314  *                        MUST_EXIST means throw exception if no record or multiple records found
1315  * @return stdClass
1316  */
1317 function get_coursemodule_from_instance($modulename, $instance, $courseid=0, $sectionnum=false, $strictness=IGNORE_MISSING) {
1318     global $DB;
1319
1320     if (!core_component::is_valid_plugin_name('mod', $modulename)) {
1321         throw new coding_exception('Invalid modulename parameter');
1322     }
1323
1324     $params = array('instance'=>$instance, 'modulename'=>$modulename);
1325
1326     $courseselect = "";
1327     $sectionfield = "";
1328     $sectionjoin  = "";
1329
1330     if ($courseid) {
1331         $courseselect = "AND cm.course = :courseid";
1332         $params['courseid'] = $courseid;
1333     }
1334
1335     if ($sectionnum) {
1336         $sectionfield = ", cw.section AS sectionnum";
1337         $sectionjoin  = "LEFT JOIN {course_sections} cw ON cw.id = cm.section";
1338     }
1339
1340     $sql = "SELECT cm.*, m.name, md.name AS modname $sectionfield
1341               FROM {course_modules} cm
1342                    JOIN {modules} md ON md.id = cm.module
1343                    JOIN {".$modulename."} m ON m.id = cm.instance
1344                    $sectionjoin
1345              WHERE m.id = :instance AND md.name = :modulename
1346                    $courseselect";
1347
1348     return $DB->get_record_sql($sql, $params, $strictness);
1349 }
1350
1351 /**
1352  * Returns all course modules of given activity in course
1353  *
1354  * @param string $modulename The module name (forum, quiz, etc.)
1355  * @param int $courseid The course id to get modules for
1356  * @param string $extrafields extra fields starting with m.
1357  * @return array Array of results
1358  */
1359 function get_coursemodules_in_course($modulename, $courseid, $extrafields='') {
1360     global $DB;
1361
1362     if (!core_component::is_valid_plugin_name('mod', $modulename)) {
1363         throw new coding_exception('Invalid modulename parameter');
1364     }
1365
1366     if (!empty($extrafields)) {
1367         $extrafields = ", $extrafields";
1368     }
1369     $params = array();
1370     $params['courseid'] = $courseid;
1371     $params['modulename'] = $modulename;
1372
1373
1374     return $DB->get_records_sql("SELECT cm.*, m.name, md.name as modname $extrafields
1375                                    FROM {course_modules} cm, {modules} md, {".$modulename."} m
1376                                   WHERE cm.course = :courseid AND
1377                                         cm.instance = m.id AND
1378                                         md.name = :modulename AND
1379                                         md.id = cm.module", $params);
1380 }
1381
1382 /**
1383  * Returns an array of all the active instances of a particular module in given courses, sorted in the order they are defined
1384  *
1385  * Returns an array of all the active instances of a particular
1386  * module in given courses, sorted in the order they are defined
1387  * in the course. Returns an empty array on any errors.
1388  *
1389  * The returned objects includle the columns cw.section, cm.visible,
1390  * cm.groupmode, and cm.groupingid, and are indexed by cm.id.
1391  *
1392  * @global object
1393  * @global object
1394  * @param string $modulename The name of the module to get instances for
1395  * @param array $courses an array of course objects.
1396  * @param int $userid
1397  * @param int $includeinvisible
1398  * @return array of module instance objects, including some extra fields from the course_modules
1399  *          and course_sections tables, or an empty array if an error occurred.
1400  */
1401 function get_all_instances_in_courses($modulename, $courses, $userid=NULL, $includeinvisible=false) {
1402     global $CFG, $DB;
1403
1404     if (!core_component::is_valid_plugin_name('mod', $modulename)) {
1405         throw new coding_exception('Invalid modulename parameter');
1406     }
1407
1408     $outputarray = array();
1409
1410     if (empty($courses) || !is_array($courses) || count($courses) == 0) {
1411         return $outputarray;
1412     }
1413
1414     list($coursessql, $params) = $DB->get_in_or_equal(array_keys($courses), SQL_PARAMS_NAMED, 'c0');
1415     $params['modulename'] = $modulename;
1416
1417     if (!$rawmods = $DB->get_records_sql("SELECT cm.id AS coursemodule, m.*, cw.section, cm.visible AS visible,
1418                                                  cm.groupmode, cm.groupingid
1419                                             FROM {course_modules} cm, {course_sections} cw, {modules} md,
1420                                                  {".$modulename."} m
1421                                            WHERE cm.course $coursessql AND
1422                                                  cm.instance = m.id AND
1423                                                  cm.section = cw.id AND
1424                                                  md.name = :modulename AND
1425                                                  md.id = cm.module", $params)) {
1426         return $outputarray;
1427     }
1428
1429     foreach ($courses as $course) {
1430         $modinfo = get_fast_modinfo($course, $userid);
1431
1432         if (empty($modinfo->instances[$modulename])) {
1433             continue;
1434         }
1435
1436         foreach ($modinfo->instances[$modulename] as $cm) {
1437             if (!$includeinvisible and !$cm->uservisible) {
1438                 continue;
1439             }
1440             if (!isset($rawmods[$cm->id])) {
1441                 continue;
1442             }
1443             $instance = $rawmods[$cm->id];
1444             if (!empty($cm->extra)) {
1445                 $instance->extra = $cm->extra;
1446             }
1447             $outputarray[] = $instance;
1448         }
1449     }
1450
1451     return $outputarray;
1452 }
1453
1454 /**
1455  * Returns an array of all the active instances of a particular module in a given course,
1456  * sorted in the order they are defined.
1457  *
1458  * Returns an array of all the active instances of a particular
1459  * module in a given course, sorted in the order they are defined
1460  * in the course. Returns an empty array on any errors.
1461  *
1462  * The returned objects includle the columns cw.section, cm.visible,
1463  * cm.groupmode, and cm.groupingid, and are indexed by cm.id.
1464  *
1465  * Simply calls {@link all_instances_in_courses()} with a single provided course
1466  *
1467  * @param string $modulename The name of the module to get instances for
1468  * @param object $course The course obect.
1469  * @return array of module instance objects, including some extra fields from the course_modules
1470  *          and course_sections tables, or an empty array if an error occurred.
1471  * @param int $userid
1472  * @param int $includeinvisible
1473  */
1474 function get_all_instances_in_course($modulename, $course, $userid=NULL, $includeinvisible=false) {
1475     return get_all_instances_in_courses($modulename, array($course->id => $course), $userid, $includeinvisible);
1476 }
1477
1478
1479 /**
1480  * Determine whether a module instance is visible within a course
1481  *
1482  * Given a valid module object with info about the id and course,
1483  * and the module's type (eg "forum") returns whether the object
1484  * is visible or not according to the 'eye' icon only.
1485  *
1486  * NOTE: This does NOT take into account visibility to a particular user.
1487  * To get visibility access for a specific user, use get_fast_modinfo, get a
1488  * cm_info object from this, and check the ->uservisible property; or use
1489  * the \core_availability\info_module::is_user_visible() static function.
1490  *
1491  * @global object
1492
1493  * @param $moduletype Name of the module eg 'forum'
1494  * @param $module Object which is the instance of the module
1495  * @return bool Success
1496  */
1497 function instance_is_visible($moduletype, $module) {
1498     global $DB;
1499
1500     if (!empty($module->id)) {
1501         $params = array('courseid'=>$module->course, 'moduletype'=>$moduletype, 'moduleid'=>$module->id);
1502         if ($records = $DB->get_records_sql("SELECT cm.instance, cm.visible, cm.groupingid, cm.id, cm.course
1503                                                FROM {course_modules} cm, {modules} m
1504                                               WHERE cm.course = :courseid AND
1505                                                     cm.module = m.id AND
1506                                                     m.name = :moduletype AND
1507                                                     cm.instance = :moduleid", $params)) {
1508
1509             foreach ($records as $record) { // there should only be one - use the first one
1510                 return $record->visible;
1511             }
1512         }
1513     }
1514     return true;  // visible by default!
1515 }
1516
1517
1518 /// LOG FUNCTIONS /////////////////////////////////////////////////////
1519
1520 /**
1521  * Get instance of log manager.
1522  *
1523  * @param bool $forcereload
1524  * @return \core\log\manager
1525  */
1526 function get_log_manager($forcereload = false) {
1527     /** @var \core\log\manager $singleton */
1528     static $singleton = null;
1529
1530     if ($forcereload and isset($singleton)) {
1531         $singleton->dispose();
1532         $singleton = null;
1533     }
1534
1535     if (isset($singleton)) {
1536         return $singleton;
1537     }
1538
1539     $classname = '\tool_log\log\manager';
1540     if (defined('LOG_MANAGER_CLASS')) {
1541         $classname = LOG_MANAGER_CLASS;
1542     }
1543
1544     if (!class_exists($classname)) {
1545         if (!empty($classname)) {
1546             debugging("Cannot find log manager class '$classname'.", DEBUG_DEVELOPER);
1547         }
1548         $classname = '\core\log\dummy_manager';
1549     }
1550
1551     $singleton = new $classname();
1552     return $singleton;
1553 }
1554
1555 /**
1556  * Add an entry to the config log table.
1557  *
1558  * These are "action" focussed rather than web server hits,
1559  * and provide a way to easily reconstruct changes to Moodle configuration.
1560  *
1561  * @package core
1562  * @category log
1563  * @global moodle_database $DB
1564  * @global stdClass $USER
1565  * @param    string  $name     The name of the configuration change action
1566                                For example 'filter_active' when activating or deactivating a filter
1567  * @param    string  $oldvalue The config setting's previous value
1568  * @param    string  $value    The config setting's new value
1569  * @param    string  $plugin   Plugin name, for example a filter name when changing filter configuration
1570  * @return void
1571  */
1572 function add_to_config_log($name, $oldvalue, $value, $plugin) {
1573     global $USER, $DB;
1574
1575     $log = new stdClass();
1576     $log->userid       = during_initial_install() ? 0 :$USER->id; // 0 as user id during install
1577     $log->timemodified = time();
1578     $log->name         = $name;
1579     $log->oldvalue  = $oldvalue;
1580     $log->value     = $value;
1581     $log->plugin    = $plugin;
1582     $DB->insert_record('config_log', $log);
1583 }
1584
1585 /**
1586  * Store user last access times - called when use enters a course or site
1587  *
1588  * @package core
1589  * @category log
1590  * @global stdClass $USER
1591  * @global stdClass $CFG
1592  * @global moodle_database $DB
1593  * @uses LASTACCESS_UPDATE_SECS
1594  * @uses SITEID
1595  * @param int $courseid  empty courseid means site
1596  * @return void
1597  */
1598 function user_accesstime_log($courseid=0) {
1599     global $USER, $CFG, $DB;
1600
1601     if (!isloggedin() or \core\session\manager::is_loggedinas()) {
1602         // no access tracking
1603         return;
1604     }
1605
1606     if (isguestuser()) {
1607         // Do not update guest access times/ips for performance.
1608         return;
1609     }
1610
1611     if (empty($courseid)) {
1612         $courseid = SITEID;
1613     }
1614
1615     $timenow = time();
1616
1617 /// Store site lastaccess time for the current user
1618     if ($timenow - $USER->lastaccess > LASTACCESS_UPDATE_SECS) {
1619     /// Update $USER->lastaccess for next checks
1620         $USER->lastaccess = $timenow;
1621
1622         $last = new stdClass();
1623         $last->id         = $USER->id;
1624         $last->lastip     = getremoteaddr();
1625         $last->lastaccess = $timenow;
1626
1627         $DB->update_record_raw('user', $last);
1628     }
1629
1630     if ($courseid == SITEID) {
1631     ///  no user_lastaccess for frontpage
1632         return;
1633     }
1634
1635 /// Store course lastaccess times for the current user
1636     if (empty($USER->currentcourseaccess[$courseid]) or ($timenow - $USER->currentcourseaccess[$courseid] > LASTACCESS_UPDATE_SECS)) {
1637
1638         $lastaccess = $DB->get_field('user_lastaccess', 'timeaccess', array('userid'=>$USER->id, 'courseid'=>$courseid));
1639
1640         if ($lastaccess === false) {
1641             // Update course lastaccess for next checks
1642             $USER->currentcourseaccess[$courseid] = $timenow;
1643
1644             $last = new stdClass();
1645             $last->userid     = $USER->id;
1646             $last->courseid   = $courseid;
1647             $last->timeaccess = $timenow;
1648             try {
1649                 $DB->insert_record_raw('user_lastaccess', $last, false);
1650             } catch (dml_write_exception $e) {
1651                 // During a race condition we can fail to find the data, then it appears.
1652                 // If we still can't find it, rethrow the exception.
1653                 $lastaccess = $DB->get_field('user_lastaccess', 'timeaccess', array('userid' => $USER->id,
1654                                                                                     'courseid' => $courseid));
1655                 if ($lastaccess === false) {
1656                     throw $e;
1657                 }
1658                 // If we did find it, the race condition was true and another thread has inserted the time for us.
1659                 // We can just continue without having to do anything.
1660             }
1661
1662         } else if ($timenow - $lastaccess <  LASTACCESS_UPDATE_SECS) {
1663             // no need to update now, it was updated recently in concurrent login ;-)
1664
1665         } else {
1666             // Update course lastaccess for next checks
1667             $USER->currentcourseaccess[$courseid] = $timenow;
1668
1669             $DB->set_field('user_lastaccess', 'timeaccess', $timenow, array('userid'=>$USER->id, 'courseid'=>$courseid));
1670         }
1671     }
1672 }
1673
1674 /**
1675  * Select all log records based on SQL criteria
1676  *
1677  * @package core
1678  * @category log
1679  * @global moodle_database $DB
1680  * @param string $select SQL select criteria
1681  * @param array $params named sql type params
1682  * @param string $order SQL order by clause to sort the records returned
1683  * @param string $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set)
1684  * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set)
1685  * @param int $totalcount Passed in by reference.
1686  * @return array
1687  */
1688 function get_logs($select, array $params=null, $order='l.time DESC', $limitfrom='', $limitnum='', &$totalcount) {
1689     global $DB;
1690
1691     if ($order) {
1692         $order = "ORDER BY $order";
1693     }
1694
1695     $selectsql = "";
1696     $countsql  = "";
1697
1698     if ($select) {
1699         $select = "WHERE $select";
1700     }
1701
1702     $sql = "SELECT COUNT(*)
1703               FROM {log} l
1704            $select";
1705
1706     $totalcount = $DB->count_records_sql($sql, $params);
1707     $allnames = get_all_user_name_fields(true, 'u');
1708     $sql = "SELECT l.*, $allnames, u.picture
1709               FROM {log} l
1710               LEFT JOIN {user} u ON l.userid = u.id
1711            $select
1712             $order";
1713
1714     return $DB->get_records_sql($sql, $params, $limitfrom, $limitnum) ;
1715 }
1716
1717
1718 /**
1719  * Select all log records for a given course and user
1720  *
1721  * @package core
1722  * @category log
1723  * @global moodle_database $DB
1724  * @uses DAYSECS
1725  * @param int $userid The id of the user as found in the 'user' table.
1726  * @param int $courseid The id of the course as found in the 'course' table.
1727  * @param string $coursestart unix timestamp representing course start date and time.
1728  * @return array
1729  */
1730 function get_logs_usercourse($userid, $courseid, $coursestart) {
1731     global $DB;
1732
1733     $params = array();
1734
1735     $courseselect = '';
1736     if ($courseid) {
1737         $courseselect = "AND course = :courseid";
1738         $params['courseid'] = $courseid;
1739     }
1740     $params['userid'] = $userid;
1741     // We have to sanitize this param ourselves here instead of relying on DB.
1742     // Postgres complains if you use name parameter or column alias in GROUP BY.
1743     // See MDL-27696 and 51c3e85 for details.
1744     $coursestart = (int)$coursestart;
1745
1746     return $DB->get_records_sql("SELECT FLOOR((time - $coursestart)/". DAYSECS .") AS day, COUNT(*) AS num
1747                                    FROM {log}
1748                                   WHERE userid = :userid
1749                                         AND time > $coursestart $courseselect
1750                                GROUP BY FLOOR((time - $coursestart)/". DAYSECS .")", $params);
1751 }
1752
1753 /**
1754  * Select all log records for a given course, user, and day
1755  *
1756  * @package core
1757  * @category log
1758  * @global moodle_database $DB
1759  * @uses HOURSECS
1760  * @param int $userid The id of the user as found in the 'user' table.
1761  * @param int $courseid The id of the course as found in the 'course' table.
1762  * @param string $daystart unix timestamp of the start of the day for which the logs needs to be retrived
1763  * @return array
1764  */
1765 function get_logs_userday($userid, $courseid, $daystart) {
1766     global $DB;
1767
1768     $params = array('userid'=>$userid);
1769
1770     $courseselect = '';
1771     if ($courseid) {
1772         $courseselect = "AND course = :courseid";
1773         $params['courseid'] = $courseid;
1774     }
1775     $daystart = (int)$daystart; // note: unfortunately pg complains if you use name parameter or column alias in GROUP BY
1776
1777     return $DB->get_records_sql("SELECT FLOOR((time - $daystart)/". HOURSECS .") AS hour, COUNT(*) AS num
1778                                    FROM {log}
1779                                   WHERE userid = :userid
1780                                         AND time > $daystart $courseselect
1781                                GROUP BY FLOOR((time - $daystart)/". HOURSECS .") ", $params);
1782 }
1783
1784 /// GENERAL HELPFUL THINGS  ///////////////////////////////////
1785
1786 /**
1787  * Dumps a given object's information for debugging purposes
1788  *
1789  * When used in a CLI script, the object's information is written to the standard
1790  * error output stream. When used in a web script, the object is dumped to a
1791  * pre-formatted block with the "notifytiny" CSS class.
1792  *
1793  * @param mixed $object The data to be printed
1794  * @return void output is echo'd
1795  */
1796 function print_object($object) {
1797
1798     // we may need a lot of memory here
1799     raise_memory_limit(MEMORY_EXTRA);
1800
1801     if (CLI_SCRIPT) {
1802         fwrite(STDERR, print_r($object, true));
1803         fwrite(STDERR, PHP_EOL);
1804     } else {
1805         echo html_writer::tag('pre', s(print_r($object, true)), array('class' => 'notifytiny'));
1806     }
1807 }
1808
1809 /**
1810  * This function is the official hook inside XMLDB stuff to delegate its debug to one
1811  * external function.
1812  *
1813  * Any script can avoid calls to this function by defining XMLDB_SKIP_DEBUG_HOOK before
1814  * using XMLDB classes. Obviously, also, if this function doesn't exist, it isn't invoked ;-)
1815  *
1816  * @uses DEBUG_DEVELOPER
1817  * @param string $message string contains the error message
1818  * @param object $object object XMLDB object that fired the debug
1819  */
1820 function xmldb_debug($message, $object) {
1821
1822     debugging($message, DEBUG_DEVELOPER);
1823 }
1824
1825 /**
1826  * @global object
1827  * @uses CONTEXT_COURSECAT
1828  * @return boolean Whether the user can create courses in any category in the system.
1829  */
1830 function user_can_create_courses() {
1831     global $DB;
1832     $catsrs = $DB->get_recordset('course_categories');
1833     foreach ($catsrs as $cat) {
1834         if (has_capability('moodle/course:create', context_coursecat::instance($cat->id))) {
1835             $catsrs->close();
1836             return true;
1837         }
1838     }
1839     $catsrs->close();
1840     return false;
1841 }
1842
1843 /**
1844  * This method can update the values in mulitple database rows for a colum with
1845  * a unique index, without violating that constraint.
1846  *
1847  * Suppose we have a table with a unique index on (otherid, sortorder), and
1848  * for a particular value of otherid, we want to change all the sort orders.
1849  * You have to do this carefully or you will violate the unique index at some time.
1850  * This method takes care of the details for you.
1851  *
1852  * Note that, it is the responsibility of the caller to make sure that the
1853  * requested rename is legal. For example, if you ask for [1 => 2, 2 => 2]
1854  * then you will get a unique key violation error from the database.
1855  *
1856  * @param string $table The database table to modify.
1857  * @param string $field the field that contains the values we are going to change.
1858  * @param array $newvalues oldvalue => newvalue how to change the values.
1859  *      E.g. [1 => 4, 2 => 1, 3 => 3, 4 => 2].
1860  * @param array $otherconditions array fieldname => requestedvalue extra WHERE clause
1861  *      conditions to restrict which rows are affected. E.g. array('otherid' => 123).
1862  * @param int $unusedvalue (defaults to -1) a value that is never used in $ordercol.
1863  */
1864 function update_field_with_unique_index($table, $field, array $newvalues,
1865         array $otherconditions, $unusedvalue = -1) {
1866     global $DB;
1867     $safechanges = decompose_update_into_safe_changes($newvalues, $unusedvalue);
1868
1869     $transaction = $DB->start_delegated_transaction();
1870     foreach ($safechanges as $change) {
1871         list($from, $to) = $change;
1872         $otherconditions[$field] = $from;
1873         $DB->set_field($table, $field, $to, $otherconditions);
1874     }
1875     $transaction->allow_commit();
1876 }
1877
1878 /**
1879  * Helper used by {@link update_field_with_unique_index()}. Given a desired
1880  * set of changes, break them down into single udpates that can be done one at
1881  * a time without breaking any unique index constraints.
1882  *
1883  * Suppose the input is array(1 => 2, 2 => 1) and -1. Then the output will be
1884  * array (array(1, -1), array(2, 1), array(-1, 2)). This function solves this
1885  * problem in the general case, not just for simple swaps. The unit tests give
1886  * more examples.
1887  *
1888  * Note that, it is the responsibility of the caller to make sure that the
1889  * requested rename is legal. For example, if you ask for something impossible
1890  * like array(1 => 2, 2 => 2) then the results are undefined. (You will probably
1891  * get a unique key violation error from the database later.)
1892  *
1893  * @param array $newvalues The desired re-ordering.
1894  *      E.g. array(1 => 4, 2 => 1, 3 => 3, 4 => 2).
1895  * @param int $unusedvalue A value that is not currently used.
1896  * @return array A safe way to perform the re-order. An array of two-element
1897  *      arrays array($from, $to).
1898  *      E.g. array(array(1, -1), array(2, 1), array(4, 2), array(-1, 4)).
1899  */
1900 function decompose_update_into_safe_changes(array $newvalues, $unusedvalue) {
1901     $nontrivialmap = array();
1902     foreach ($newvalues as $from => $to) {
1903         if ($from == $unusedvalue || $to == $unusedvalue) {
1904             throw new \coding_exception('Supposedly unused value ' . $unusedvalue . ' is actually used!');
1905         }
1906         if ($from != $to) {
1907             $nontrivialmap[$from] = $to;
1908         }
1909     }
1910
1911     if (empty($nontrivialmap)) {
1912         return array();
1913     }
1914
1915     // First we deal with all renames that are not part of cycles.
1916     // This bit is O(n^2) and it ought to be possible to do better,
1917     // but it does not seem worth the effort.
1918     $safechanges = array();
1919     $nontrivialmapchanged = true;
1920     while ($nontrivialmapchanged) {
1921         $nontrivialmapchanged = false;
1922
1923         foreach ($nontrivialmap as $from => $to) {
1924             if (array_key_exists($to, $nontrivialmap)) {
1925                 continue; // Cannot currenly do this rename.
1926             }
1927             // Is safe to do this rename now.
1928             $safechanges[] = array($from, $to);
1929             unset($nontrivialmap[$from]);
1930             $nontrivialmapchanged = true;
1931         }
1932     }
1933
1934     // Are we done?
1935     if (empty($nontrivialmap)) {
1936         return $safechanges;
1937     }
1938
1939     // Now what is left in $nontrivialmap must be a permutation,
1940     // which must be a combination of disjoint cycles. We need to break them.
1941     while (!empty($nontrivialmap)) {
1942         // Extract the first cycle.
1943         reset($nontrivialmap);
1944         $current = $cyclestart = key($nontrivialmap);
1945         $cycle = array();
1946         do {
1947             $cycle[] = $current;
1948             $next = $nontrivialmap[$current];
1949             unset($nontrivialmap[$current]);
1950             $current = $next;
1951         } while ($current != $cyclestart);
1952
1953         // Now convert it to a sequence of safe renames by using a temp.
1954         $safechanges[] = array($cyclestart, $unusedvalue);
1955         $cycle[0] = $unusedvalue;
1956         $to = $cyclestart;
1957         while ($from = array_pop($cycle)) {
1958             $safechanges[] = array($from, $to);
1959             $to = $from;
1960         }
1961     }
1962
1963     return $safechanges;
1964 }