class PseudoClassExtension

class PseudoClassExtension extends AbstractExtension {
    public function getPseudoClassTranslators() : array {
        return [
            'root' => $this->translateRoot(...),
            'scope' => $this->translateScopePseudo(...),
            'first-child' => $this->translateFirstChild(...),
            'last-child' => $this->translateLastChild(...),
            'first-of-type' => $this->translateFirstOfType(...),
            'last-of-type' => $this->translateLastOfType(...),
            'only-child' => $this->translateOnlyChild(...),
            'only-of-type' => $this->translateOnlyOfType(...),
            'empty' => $this->translateEmpty(...),
        ];
    }
    public function translateRoot(XPathExpr $xpath) : XPathExpr {
        return $xpath->addCondition('not(parent::*)');
    }
    public function translateScopePseudo(XPathExpr $xpath) : XPathExpr {
        return $xpath->addCondition('1');
    }
    public function translateFirstChild(XPathExpr $xpath) : XPathExpr {
        return $xpath->addStarPrefix()
            ->addNameTest()
            ->addCondition('position() = 1');
    }
    public function translateLastChild(XPathExpr $xpath) : XPathExpr {
        return $xpath->addStarPrefix()
            ->addNameTest()
            ->addCondition('position() = last()');
    }
    
    /**
     * @throws ExpressionErrorException
     */
    public function translateFirstOfType(XPathExpr $xpath) : XPathExpr {
        if ('*' === $xpath->getElement()) {
            throw new ExpressionErrorException('"*:first-of-type" is not implemented.');
        }
        return $xpath->addStarPrefix()
            ->addCondition('position() = 1');
    }
    
    /**
     * @throws ExpressionErrorException
     */
    public function translateLastOfType(XPathExpr $xpath) : XPathExpr {
        if ('*' === $xpath->getElement()) {
            throw new ExpressionErrorException('"*:last-of-type" is not implemented.');
        }
        return $xpath->addStarPrefix()
            ->addCondition('position() = last()');
    }
    public function translateOnlyChild(XPathExpr $xpath) : XPathExpr {
        return $xpath->addStarPrefix()
            ->addNameTest()
            ->addCondition('last() = 1');
    }
    public function translateOnlyOfType(XPathExpr $xpath) : XPathExpr {
        $element = $xpath->getElement();
        return $xpath->addCondition(\sprintf('count(preceding-sibling::%s)=0 and count(following-sibling::%s)=0', $element, $element));
    }
    public function translateEmpty(XPathExpr $xpath) : XPathExpr {
        return $xpath->addCondition('not(*) and not(string-length())');
    }
    public function getName() : string {
        return 'pseudo-class';
    }

}