<?php

/**
 * General knowledge ("generalKnowledge"): a multiple choice question from the
 * tkGeneralKnowledge table.
 *
 * Replaces the placeholder, which was a copy of the "find the missing number"
 * generator under another class name: it never read tkGeneralKnowledge and
 * still used the old client-side checkerData, so every answer would have
 * been refused.
 *
 *  - Works on the table as imported from general_knowledge_10000_mcq.csv, and
 *    on the cleaned table (general_knowledge/tkGeneralKnowledge.sql). That file
 *    holds 1,018 questions, each copied about ten times with
 *    "(Choose the correct answer.)" added to the question (and the question
 *    mark dropped). So the question text is cleaned when it is read, and rows
 *    with the same cleaned question count as one.
 *  - The columns are found by name, ignoring case, spaces and underscores:
 *    Question, Option A..D (option_a, optionA ...), Correct Answer
 *    (correct_answer ...), Correct Option, Category. The correct answer is
 *    taken from the answer text, or the letter, or both (a row where they
 *    disagree is never asked).
 *  - The options are shuffled for each question.
 *  - A question isn't repeated within the student's last 200 answers.
 *  - A category is picked first, with big categories counted for less than
 *    their size (square root), so Geography (three quarters of the file) is
 *    not nearly everything.
 *  - The Difficulty column is not used: in the file it just repeats Easy,
 *    Medium, Hard by row.
 *
 * The right answer and the options as shown are stored server-side
 * (TkAnswerStore). The student ticks a letter; the checker
 * (answerChecker2::checkGeneralKnowledge) turns it back into the option text.
 */
class generalKnowledge {

    const SUBJECT = 'generalKnowledge';
    const TABLE = 'tkGeneralKnowledge';
    const RECENT = 200; // questions not repeated within this many of a student's answers
    const SAMPLE = 40;  // random rows looked at to find a question

    private $user;

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

    /**
     * Make a question, show it, and remember it as the student's open question.
     */
    public function getGeneralKnowledge() {
        $problem = $this->getProblem();

        if ($problem === null) {
            e107::getRender()->tablerender('General knowledge', 'There are no general knowledge questions available yet. Please refresh the page.');
            return;
        }

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

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

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

    /**
     * Choose a question without showing it.
     *
     * @return array|null ['answer1' => correct option text, 'question' => string, 'type' => 'generalKnowledge',
     *                     'options' => the four options in the order shown, 'category' => string],
     *                     or null when no question can be asked.
     */
    public function getProblem() {
        $columns = $this->columns();
        if ($columns === null) {
            return null;
        }

        $recent = $this->recentQuestions();
        $category = $this->pickCategory($columns);

        $problem = $this->pickQuestion($columns, $category, $recent);
        if ($problem === null && $category !== null) {
            $problem = $this->pickQuestion($columns, null, $recent);   // that category had nothing new
        }
        if ($problem === null) {
            $problem = $this->pickQuestion($columns, null, []);        // everything was asked recently: repeat
        }

        return $problem;
    }

    /**
     * The real column names, found by name: ['question', 'a', 'b', 'c', 'd', and 'answer' and/or 'letter',
     * optionally 'category'], or null when the table isn't usable.
     */
    private function columns() {
        $db = e107::getDb();
        $db->gen("SHOW COLUMNS FROM `" . MPREFIX . self::TABLE . "`");

        $found = [];
        while ($row = $db->fetch()) {
            $found[strtolower(preg_replace('/[^a-z0-9]/i', '', $row['Field']))] = $row['Field'];
        }

        $aliases = [
            'question' => ['question', 'questiontext'],
            'a' => ['optiona', 'choicea', 'answera', 'a'],
            'b' => ['optionb', 'choiceb', 'answerb', 'b'],
            'c' => ['optionc', 'choicec', 'answerc', 'c'],
            'd' => ['optiond', 'choiced', 'answerd', 'd'],
            'answer' => ['correctanswer', 'answertext', 'rightanswer'],
            'letter' => ['correctoption', 'correctletter', 'correctchoice'],
            'category' => ['category', 'topic', 'subject'],
        ];

        $map = [];
        foreach ($aliases as $name => $names) {
            foreach ($names as $alias) {
                if (isset($found[$alias])) {
                    $map[$name] = $found[$alias];
                    break;
                }
            }
        }

        foreach (['question', 'a', 'b', 'c', 'd'] as $required) {
            if (!isset($map[$required])) {
                return null;
            }
        }
        if (!isset($map['answer']) && !isset($map['letter'])) {
            return null;
        }

        return $map;
    }

    /**
     * Keys of the questions in the student's last answers (cleaned text, lower case).
     * The report stores the question as "General knowledge: <question>".
     */
    private function recentQuestions() {
        $db = e107::getDb();
        $recent = [];
        $db->gen("SELECT `question` FROM `" . MPREFIX . "tkReport`
            WHERE `username` = '" . $db->escape($this->user) . "' AND `subject` = '" . self::SUBJECT . "'
            ORDER BY `id` DESC LIMIT " . (int) self::RECENT);
        while ($row = $db->fetch()) {
            $recent[$this->key(preg_replace('/^General knowledge:\s*/', '', (string) $row['question']))] = true;
        }
        return $recent;
    }

    /**
     * A category chosen at random, each weighted by the square root of how many
     * rows it has. Null when there is no category column.
     */
    private function pickCategory(array $columns) {
        if (!isset($columns['category'])) {
            return null;
        }

        $db = e107::getDb();
        $field = '`' . $columns['category'] . '`';
        $db->gen("SELECT " . $field . " AS category, COUNT(*) AS n FROM `" . MPREFIX . self::TABLE . "` GROUP BY " . $field);

        $weights = [];
        $total = 0.0;
        while ($row = $db->fetch()) {
            $weight = sqrt((int) $row['n']);
            if ($weight > 0) {
                $weights[$row['category']] = $weight;
                $total += $weight;
            }
        }
        if ($total <= 0) {
            return null;
        }

        $point = (mt_rand() / mt_getrandmax()) * $total;
        foreach ($weights as $category => $weight) {
            $point -= $weight;
            if ($point <= 0) {
                return (string) $category;
            }
        }
        return (string) key($weights);
    }

    /**
     * The first usable question, not asked recently, among SAMPLE random rows.
     */
    private function pickQuestion(array $columns, $category, array $recent) {
        $db = e107::getDb();

        $where = '';
        if ($category !== null && isset($columns['category'])) {
            $where = " WHERE `" . $columns['category'] . "` = '" . $db->escape($category) . "'";
        }

        $db->gen("SELECT * FROM `" . MPREFIX . self::TABLE . "`" . $where . " ORDER BY RAND() LIMIT " . (int) self::SAMPLE);
        $rows = [];
        while ($row = $db->fetch()) {
            $rows[] = $row;
        }

        foreach ($rows as $row) {
            $problem = $this->buildProblem($columns, $row);
            if ($problem !== null && !isset($recent[$this->key($problem['question'])])) {
                return $problem;
            }
        }
        return null;
    }

    /**
     * One table row as a question, or null when the row can't be used (missing
     * text, repeated options, no single correct option, or the answer text and
     * the letter disagree).
     */
    private function buildProblem(array $columns, array $row) {
        $question = $this->cleanQuestion($row[$columns['question']]);
        $options = [
            $this->decode($row[$columns['a']]),
            $this->decode($row[$columns['b']]),
            $this->decode($row[$columns['c']]),
            $this->decode($row[$columns['d']]),
        ];

        if ($question === '' || in_array('', $options, true) || count(array_unique($options)) < 4) {
            return null;
        }

        $correct = null;
        if (isset($columns['answer'])) {
            $text = $this->decode($row[$columns['answer']]);
            if (count(array_keys($options, $text, true)) === 1) {
                $correct = $text;
            }
        }
        if (isset($columns['letter'])) {
            $letter = strtoupper(trim((string) $row[$columns['letter']]));
            $byLetter = (strlen($letter) === 1 && $letter >= 'A' && $letter <= 'D') ? $options[ord($letter) - 65] : null;
            if ($correct === null) {
                $correct = $byLetter;
            } elseif ($byLetter !== null && $byLetter !== $correct) {
                return null;
            }
        }
        if ($correct === null) {
            return null;
        }

        shuffle($options);

        return [
            'answer1' => $correct,
            'question' => $question,
            'type' => self::SUBJECT,
            'options' => $options,
            'category' => isset($columns['category']) ? $this->decode($row[$columns['category']]) : '',
        ];
    }

    /**
     * e107 may have stored apostrophes as &#039;: show and compare the real text.
     */
    private function decode($value) {
        return trim(html_entity_decode((string) $value, ENT_QUOTES | ENT_HTML5, 'UTF-8'));
    }

    /**
     * The question as it should be shown: decoded, without the
     * "(Choose the correct answer.)" padding of the imported file (which also
     * dropped the question mark: it is put back).
     */
    private function cleanQuestion($text) {
        $text = $this->decode($text);
        $stripped = preg_replace('/(?:\s*\(Choose the correct answer\.\))+\s*$/u', '', $text, -1, $count);
        if ($stripped === null) {
            return $text;
        }
        if ($count > 0) {
            $stripped = rtrim(trim($stripped), '?') . '?';
        }
        return trim($stripped);
    }

    /**
     * What makes two questions "the same": the cleaned text, lower case, no final punctuation.
     */
    private function key($question) {
        return mb_strtolower(rtrim(trim((string) $question), "?. \t"), 'UTF-8');
    }

    private function htmlify($problem) {
        // The right answer and the order of the options stay on the server; the form only carries a token.
        $token = TkAnswerStore::issue($this->user, $problem);

        $frm = e107::getForm();

        $fString = $frm->open('questionForm', 'post', '', ['autocomplete' => 'off', 'class' => 'formclass']);
        $fString .= $frm->label('<h4>General knowledge</h4>') . "</br>\n";
        if ($problem['category'] !== '') {
            $fString .= '<p class="smalltext">Category: ' . htmlspecialchars($problem['category']) . '</p>';
        }
        $fString .= '<p style="font-size:140%;font-weight:bold;">' . htmlspecialchars($problem['question']) . '</p>';

        foreach ($problem['options'] as $i => $option) {
            $letter = chr(65 + $i);
            $fString .= '<div style="margin:8px 0;"><label style="font-size:120%;cursor:pointer;">'
                    . '<input type="radio" name="a1" value="' . $letter . '" required> '
                    . '<b>' . $letter . '.</b> ' . htmlspecialchars($option)
                    . '</label></div>';
        }

        $fString .= $frm->hidden('checkerData', $token, ['id' => 'checkerData']);
        $fString .= $frm->hidden('subject', self::SUBJECT, ['id' => 'subject']);
        $fString .= '</br>' . "\n";
        $fString .= $frm->button('Answer', 'Check answer') . "\n";
        $fString .= $frm->close();
        $fString .= '</br></br>';

        return $fString;
    }
}