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Filename : FunctionExtension.php
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<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\CssSelector\XPath\Extension;

use Symfony\Component\CssSelector\Exception\ExpressionErrorException;
use Symfony\Component\CssSelector\Exception\SyntaxErrorException;
use Symfony\Component\CssSelector\Node\FunctionNode;
use Symfony\Component\CssSelector\Parser\Parser;
use Symfony\Component\CssSelector\XPath\Translator;
use Symfony\Component\CssSelector\XPath\XPathExpr;

/**
 * XPath expression translator function extension.
 *
 * This component is a port of the Python cssselect library,
 * which is copyright Ian Bicking, @see https://github.com/SimonSapin/cssselect.
 *
 * @author Jean-François Simon <jeanfrancois.simon@sensiolabs.com>
 *
 * @internal
 */
class FunctionExtension extends AbstractExtension
{
    public function getFunctionTranslators(): array
    {
        return [
            'nth-child' => $this->translateNthChild(...),
            'nth-last-child' => $this->translateNthLastChild(...),
            'nth-of-type' => $this->translateNthOfType(...),
            'nth-last-of-type' => $this->translateNthLastOfType(...),
            'contains' => $this->translateContains(...),
            'lang' => $this->translateLang(...),
        ];
    }

    /**
     * @throws ExpressionErrorException
     */
    public function translateNthChild(XPathExpr $xpath, FunctionNode $function, bool $last = false, bool $addNameTest = true): XPathExpr
    {
        try {
            [$a, $b] = Parser::parseSeries($function->getArguments());
        } catch (SyntaxErrorException $e) {
            throw new ExpressionErrorException(sprintf('Invalid series: "%s".', implode('", "', $function->getArguments())), 0, $e);
        }

        $xpath->addStarPrefix();
        if ($addNameTest) {
            $xpath->addNameTest();
        }

        if (0 === $a) {
            return $xpath->addCondition('position() = '.($last ? 'last() - '.($b - 1) : $b));
        }

        if ($a < 0) {
            if ($b < 1) {
                return $xpath->addCondition('false()');
            }

            $sign = '<=';
        } else {
            $sign = '>=';
        }

        $expr = 'position()';

        if ($last) {
            $expr = 'last() - '.$expr;
            --$b;
        }

        if (0 !== $b) {
            $expr .= ' - '.$b;
        }

        $conditions = [sprintf('%s %s 0', $expr, $sign)];

        if (1 !== $a && -1 !== $a) {
            $conditions[] = sprintf('(%s) mod %d = 0', $expr, $a);
        }

        return $xpath->addCondition(implode(' and ', $conditions));

        // todo: handle an+b, odd, even
        // an+b means every-a, plus b, e.g., 2n+1 means odd
        // 0n+b means b
        // n+0 means a=1, i.e., all elements
        // an means every a elements, i.e., 2n means even
        // -n means -1n
        // -1n+6 means elements 6 and previous
    }

    public function translateNthLastChild(XPathExpr $xpath, FunctionNode $function): XPathExpr
    {
        return $this->translateNthChild($xpath, $function, true);
    }

    public function translateNthOfType(XPathExpr $xpath, FunctionNode $function): XPathExpr
    {
        return $this->translateNthChild($xpath, $function, false, false);
    }

    /**
     * @throws ExpressionErrorException
     */
    public function translateNthLastOfType(XPathExpr $xpath, FunctionNode $function): XPathExpr
    {
        if ('*' === $xpath->getElement()) {
            throw new ExpressionErrorException('"*:nth-of-type()" is not implemented.');
        }

        return $this->translateNthChild($xpath, $function, true, false);
    }

    /**
     * @throws ExpressionErrorException
     */
    public function translateContains(XPathExpr $xpath, FunctionNode $function): XPathExpr
    {
        $arguments = $function->getArguments();
        foreach ($arguments as $token) {
            if (!($token->isString() || $token->isIdentifier())) {
                throw new ExpressionErrorException('Expected a single string or identifier for :contains(), got '.implode(', ', $arguments));
            }
        }

        return $xpath->addCondition(sprintf(
            'contains(string(.), %s)',
            Translator::getXpathLiteral($arguments[0]->getValue())
        ));
    }

    /**
     * @throws ExpressionErrorException
     */
    public function translateLang(XPathExpr $xpath, FunctionNode $function): XPathExpr
    {
        $arguments = $function->getArguments();
        foreach ($arguments as $token) {
            if (!($token->isString() || $token->isIdentifier())) {
                throw new ExpressionErrorException('Expected a single string or identifier for :lang(), got '.implode(', ', $arguments));
            }
        }

        return $xpath->addCondition(sprintf(
            'lang(%s)',
            Translator::getXpathLiteral($arguments[0]->getValue())
        ));
    }

    public function getName(): string
    {
        return 'function';
    }
}