<?php

/**
 * Numeracy question generator (addition, subtraction, multiplication,
 * division, rounding).
 *
 * Changes from the original:
 *  - the expected answer is stored server-side (TkAnswerStore) and the form
 *    carries only an opaque token in `checkerData`
 *  - difficulty() always returns ['percent' => .., 'count' => ..]
 *  - Division() used $numbers[1]/$numbers[2] (index 2 doesn't exist, so the
 *    divisor was null -> division by zero); now uses [0]/[1] and never divides
 *    by zero
 *  - Rounding() always produced 1.00 (int cast of an array); now scales with
 *    the user's accuracy and works in whole cents
 *  - subtraction can no longer go negative (numbers are always ordered)
 *  - mt_rand() always receives integers (float args are deprecated in 8.1+)
 *  - user/subject are escaped in SQL, and the hard-coded `e107.` database
 *    name is replaced by MPREFIX
 *  - the previous tkLastQuestion row is removed before inserting the new one
 */
class numeracy2 {

    private $user;
    private $subSubject;

    /**
     * @param string $user User to supply the question for.
     * @param string $sub  Sub-subject: addition|subtraction|multiplication|division|rounding
     */
    public function __construct($user, $sub) {
        $this->user = $user;
        $this->subSubject = $sub;
    }

    public function getNumeracy() {
        $difficulty = $this->difficulty();
        $question = $this->numeracySwitch($difficulty);

        if ($question === null) {
            e107::getRender()->tablerender('Numeracy', 'Unknown numeracy subject.');
            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('Numeracy', $questionHtml);
    }

    private function numeracySwitch($difficulty) {
        switch ($this->subSubject) {
            case 'addition':
                return $this->basic('+', $difficulty);
            case 'subtraction':
                return $this->basic('-', $difficulty);
            case 'multiplication':
                return $this->basic('x', $difficulty);
            case 'rounding':
                return $this->Rounding($difficulty);
            case 'division':
                return $this->Division($difficulty);
        }
        return null;
    }

    /**
     * Difficulty based on the last month of answers for this sub-subject.
     *
     * @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 = '" . $db->escape($this->subSubject) . "'"
        );

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

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

    /**
     * Two random whole numbers, larger first.
     */
    private function getNumbers($difficulty, $sign) {
        //TODO add finer grain control for multiplication here
        $count = (float) $difficulty['count'];
        $percent = (float) $difficulty['percent'];

        if ($sign == 'x' || $sign == '/') {
            $count = floor($count / 4);
            $percent = $percent / 6;
        }

        if ($count >= 300) {
            $max = (int) pow($count, ($percent / 100) * 2);
        } elseif ($count >= 200) {
            $max = (int) ($count + ($percent / 100) * 2);
        } elseif ($count >= 100) {
            $max = (int) ($percent * 2);
        } else {
            $max = (int) $count + 1;
        }

        return $this->flipNumbers(mt_rand(0, $max), mt_rand(0, $max));
    }

    private function flipNumbers($startingNumber, $endingNumber) {
        if ($startingNumber > $endingNumber) {
            return [$startingNumber, $endingNumber];
        }
        return [$endingNumber, $startingNumber];
    }

    private function basic($sign, $difficulty) {
        $numbers = $this->getNumbers($difficulty, $sign);
        $firstNumber = $numbers[0];
        $secondNumber = $numbers[1];

        $solution = [
            '+' => $firstNumber + $secondNumber,
            '-' => $firstNumber - $secondNumber,
            'x' => $firstNumber * $secondNumber,
        ];

        return ['answer1' => $solution[$sign], 'question' => [$firstNumber, $sign, $secondNumber], 'type' => $this->subSubject];
    }

    private function Division($difficulty) {
        $numbers = $this->getNumbers($difficulty, '/');
        $quotient = max(1, $numbers[0]);
        $divisor = max(1, $numbers[1]);
        $dividend = $quotient * $divisor;

        return ['answer1' => $quotient, 'question' => [$dividend, '/', $divisor], 'type' => $this->subSubject];
    }

    /**
     * Round an amount of money to the nearest 5 cents. The amount grows with
     * the user's accuracy: up to $5.00 at 0%, up to $25.00 at 100%.
     */
    private function Rounding($difficulty) {
        $maxCents = (5 + (int) floor($difficulty['percent'] / 10) * 2) * 100;
        $cents = mt_rand(100, $maxCents);
        $roundedCents = (int) (round($cents / 5) * 5);

        return [
            'answer1' => sprintf('%01.2f', $roundedCents / 100),
            'question' => [sprintf('%01.2f', $cents / 100), 'r'],
            'type' => $this->subSubject,
        ];
    }

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

        $instruction = ($this->subSubject === 'rounding')
            ? 'Round to the nearest 5 cents.'
            : 'Solve the following equation.';

        $frm = e107::getForm();

        $fString = $frm->open('questionForm', 'post', '', ['autocomplete' => 'off', 'class' => 'formclass']);
        $fString .= $frm->label('<h4>' . htmlspecialchars(ucfirst($this->subSubject)) . '</h4>') . "</br>\n";
        $fString .= $frm->label($instruction) . "\n";
        $fString .= '</br>';

        foreach ($question['question'] as $seq) {
            $fString .= $frm->label($seq . " &nbsp; ") . "\n";
        }

        $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', $this->subSubject, ['id' => 'subject']);
        $fString .= '</br>' . "\n";
        $fString .= $frm->button('Answer', 'Check answer') . "\n";
        $fString .= $frm->close();
        $fString .= '</br></br>';

        return $fString;
    }
}