Proyectos de Subversion Moodle

<?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;

    }

}