<?php

/**
 * Periodic table question generator.
 *
 * Changes from the original:
 *  - element index could reach 118 at 300+ answers (the table has indexes
 *    0-117); now capped at the table size
 *  - difficulty() always returns ['percent' => .., 'count' => ..] (it returned
 *    int 1 for new users and the code then indexed it like an array)
 *  - the question type is chosen without float arguments to rand()
 *  - the stored `question` is now a readable string ("element 12, missing
 *    symbol") instead of a nested array, which the checker imploded into
 *    "Array" in its messages; the element data the form needs is stored
 *    separately (server-side, via TkAnswerStore)
 *  - periodicTable.json and the template are loaded by absolute path
 *  - user escaped in SQL; `e107.` database name replaced by MPREFIX
 *  - previous tkLastQuestion row removed before inserting the new one
 */
class elements2 {

    private $user;

    /** Human wording for each element property, used in the checker's messages. */
    private $labels = [
        'symbol' => 'symbol',
        'phase' => 'phase',
        'name' => 'name',
        'number' => 'atomic number',
        'atomic_mass' => 'atomic mass',
    ];

    /**
     * @param string $user User to supply the question for.
     */
    public function __construct($user) {
        $this->user = $user;
    }

    public function getElements() {
        $difficulty = $this->difficulty();

        // 0..4, widening as accuracy improves (one more type per 20%).
        $maxType = min(4, (int) floor($difficulty['percent'] / 20));
        $question = $this->elementSwitch(mt_rand(0, $maxType), $difficulty);

        if ($question === null) {
            e107::getRender()->tablerender('Elements', 'The periodic table data could not be loaded.');
            return;
        }

        $questionHtml = $this->htmlify($question);

        $db = e107::getDb();
        $db->delete('tkLastQuestion', "user = '" . $db->escape($this->user) . "'");
        $db->insert('tkLastQuestion', ['user' => $this->user, 'LastQuestionHtml' => base64_encode($questionHtml)]);

        e107::getRender()->tablerender('Elements', $questionHtml);
    }

    private function elementSwitch($switchValue, $difficulty) {
        switch ($switchValue) {
            case 0:
                return $this->elementValues('symbol', $difficulty);
            case 1:
                return $this->elementValues('phase', $difficulty);
            case 2:
                return $this->elementValues('name', $difficulty);
            case 3:
                return $this->elementValues('number', $difficulty);
            default:
                return $this->elementValues('atomic_mass', $difficulty);
        }
    }

    /**
     * Difficulty based on the last month of answers.
     *
     * @return array ['percent' => float 0-100, 'count' => int]
     */
    private function difficulty() {
        $db = e107::getDb();
        $stats = $db->retrieve(
                "SELECT (SUM(correct)/COUNT(correct)*100) AS percent, COUNT(correct) AS count
             FROM `" . MPREFIX . "tkReport`
             WHERE answereddatestamp >= UNIX_TIMESTAMP(NOW() - INTERVAL 1 MONTH)
             AND username = '" . $db->escape($this->user) . "' AND subject = 'elements'"
        );

        if (!is_array($stats) || (int) $stats['count'] === 0) {
            return ['percent' => 0, 'count' => 0];
        }

        return ['percent' => (float) $stats['percent'], 'count' => (int) $stats['count']];
    }

    private function loadElements() {
        $path = dirname(__DIR__, 2) . '/resources/periodicTable.json';
        $json = is_file($path) ? json_decode(file_get_contents($path), true) : null;

        return (is_array($json) && !empty($json['elements'])) ? $json['elements'] : null;
    }

    private function elementValues($sign, $difficulty) {
        $count = (int) $difficulty['count'];

        if ($count >= 300) {
            $incrementalNumber = mt_rand(1, 100);
        } elseif ($count >= 200) {
            $incrementalNumber = mt_rand(1, 50);
        } elseif ($count >= 100) {
            $incrementalNumber = mt_rand(1, 20);
        } else {
            $incrementalNumber = mt_rand(1, 10);
        }

        $elements = $this->loadElements();
        if ($elements === null) {
            return null;
        }

        $selectedElement = mt_rand(0, min((int) ($incrementalNumber * 1.18), count($elements) - 1));
        $element = $elements[$selectedElement];

        return [
            'answer1' => $element[$sign],
            'question' => 'element ' . $element['number'] . ', missing ' . $this->labels[$sign],
            'type' => 'elements',
            'element' => $element,
            'sign' => $sign,
        ];
    }

    private function htmlify($question) {
        // Expected answer stays on the server; the form only carries a token.
        $token = TkAnswerStore::issue($this->user, $question);

        $frm = e107::getForm();
        $tp = e107::getParser();
        $sc = e107::getScBatch('timekeeper', TRUE);

        $fString = $frm->open('questionForm', 'post', '', ['autocomplete' => 'off', 'class' => 'formclass']);
        $fString .= $frm->label('<h4>Elements</h4>') . "</br>\n";
        $fString .= $frm->label('Periodic Table of Elements. Fill in the missing information.') . "\n";
        $fString .= '</br>';

        $elementData = $question['element'];
        $elementData[$question['sign']] = '???';
        $sc->setVars($elementData);
        $fString .= $tp->parseTemplate(file_get_contents(dirname(__DIR__, 2) . '/templates/elementTable.html'), true, $sc);

        $fString .= '</br></br>';
        $fString .= $frm->text('a1', '', 80, ['placeholder' => 'Write answer here!', 'autocomplete' => "off", 'spellcheck' => "false"]) . "\n";
        $fString .= $frm->hidden('checkerData', $token, ['id' => 'checkerData']);
        $fString .= $frm->hidden('subject', 'elements', ['id' => 'subject']);
        $fString .= '</br>' . "\n";
        $fString .= $frm->button('Answer', 'Check answer') . "\n";
        $fString .= $frm->close();
        $fString .= '</br></br>';

        return $fString;
    }
}