class FunctionExtension

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';
    }

}