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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/>.
/**
* A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
*
* @package core_question
* @copyright 2015 The Open University
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
namespace core_question\engine\variants;
defined('MOODLE_INTERNAL') || die();
/**
* A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
*
* If all variants have been used at least once in the set of usages under
* consideration, then then it picks one of the least often used.
*
* Within one particular use of this class, each seed will always select the
* same variant. This is so that shared datasets work in calculated questions,
* and similar features in question types like varnumeric and STACK.
*
* @copyright 2015 The Open University
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
class least_used_strategy implements \question_variant_selection_strategy {
/** @var array seed => variant number => number of uses. */
protected $variantsusecounts = array();
/** @var array seed => variant number. */
protected $selectedvariant = array();
/**
* Constructor.
* @param question_usage_by_activity $quba the question usage we will be picking variants for.
* @param qubaid_condition $qubaids ids of the usages to consider when counting previous uses of each variant.
*/
public function __construct(\question_usage_by_activity $quba, \qubaid_condition $qubaids) {
$questionidtoseed = array();
foreach ($quba->get_attempt_iterator() as $qa) {
$question = $qa->get_question();
if ($question->get_num_variants() > 1) {
$questionidtoseed[$question->id] = $question->get_variants_selection_seed();
}
}
if (empty($questionidtoseed)) {
return;
}
$this->variantsusecounts = array_fill_keys($questionidtoseed, array());
$variantsused = \question_engine::load_used_variants(array_keys($questionidtoseed), $qubaids);
foreach ($variantsused as $questionid => $usagecounts) {
$seed = $questionidtoseed[$questionid];
foreach ($usagecounts as $variant => $count) {
if (isset($this->variantsusecounts[$seed][$variant])) {
$this->variantsusecounts[$seed][$variant] += $count;
} else {
$this->variantsusecounts[$seed][$variant] = $count;
}
}
}
}
public function choose_variant($maxvariants, $seed) {
if ($maxvariants == 1) {
return 1;
}
if (isset($this->selectedvariant[$seed])) {
return $this->selectedvariant[$seed];
}
// Catch a possible programming error, and make the problem clear.
if (!isset($this->variantsusecounts[$seed])) {
debugging('Variant requested for unknown seed ' . $seed . '. ' .
'You must add all questions to the usage before creating the least_used_strategy. ' .
'Continuing, but the variant choses may not actually be least used.',
DEBUG_DEVELOPER);
$this->variantsusecounts[$seed] = array();
}
if ($maxvariants > 2 * count($this->variantsusecounts[$seed])) {
// Many many more variants exist than have been used so far.
// It will be quicker to just pick until we miss a collision.
do {
$variant = rand(1, $maxvariants);
} while (isset($this->variantsusecounts[$seed][$variant]));
} else {
// We need to work harder to find a least-used one.
$leastusedvariants = array();
for ($variant = 1; $variant <= $maxvariants; ++$variant) {
if (!isset($this->variantsusecounts[$seed][$variant])) {
$leastusedvariants[$variant] = 1;
}
}
if (empty($leastusedvariants)) {
// All variants used at least once, try again.
$leastuses = min($this->variantsusecounts[$seed]);
foreach ($this->variantsusecounts[$seed] as $variant => $uses) {
if ($uses == $leastuses) {
$leastusedvariants[$variant] = 1;
}
}
}
$variant = array_rand($leastusedvariants);
}
$this->selectedvariant[$seed] = $variant;
if (isset($variantsusecounts[$seed][$variant])) {
$variantsusecounts[$seed][$variant] += 1;
} else {
$variantsusecounts[$seed][$variant] = 1;
}
return $variant;
}
}