<?php

declare(strict_types=1);

namespace SpomkyLabs\Pki\X501\DN;

use SpomkyLabs\Pki\ASN1\Element;
use SpomkyLabs\Pki\ASN1\Exception\DecodeException;
use SpomkyLabs\Pki\ASN1\Feature\ElementBase;
use UnexpectedValueException;
use function mb_strlen;
use function sprintf;

/**
 * Distinguished Name parsing conforming to RFC 2253 and RFC 1779.
 *
 * @see https://tools.ietf.org/html/rfc1779
 * @see https://tools.ietf.org/html/rfc2253
 */
final class DNParser
{
    /**
     * RFC 2253 special characters.
     *
     * @var string
     */
    final public const SPECIAL_CHARS = ',=+<>#;';

    /**
     * DN string length.
     */
    private readonly int $_len;

    /**
     * @param string $_dn Distinguised name
     */
    private function __construct(
        private readonly string $_dn
    ) {
        $this->_len = mb_strlen($_dn, '8bit');
    }

    /**
     * Parse distinguished name string to name-components.
     *
     * @return array<array<string>>
     */
    public static function parseString(string $dn): array
    {
        $parser = new self($dn);
        return $parser->parse();
    }

    /**
     * Escape a AttributeValue string conforming to RFC 2253.
     *
     * @see https://tools.ietf.org/html/rfc2253#section-2.4
     */
    public static function escapeString(string $str): string
    {
        // one of the characters ",", "+", """, "\", "<", ">" or ";"
        $str = preg_replace('/([,\+"\\\<\>;])/u', '\\\\$1', $str);
        // a space character occurring at the end of the string
        $str = preg_replace('/( )$/u', '\\\\$1', (string) $str);
        // a space or "#" character occurring at the beginning of the string
        $str = preg_replace('/^([ #])/u', '\\\\$1', (string) $str);
        // implementation specific special characters
        $str = preg_replace_callback(
            '/([\pC])/u',
            function ($m) {
                $octets = mb_str_split(bin2hex($m[1]), 2, '8bit');
                return implode('', array_map(static fn ($octet) => '\\' . mb_strtoupper($octet, '8bit'), $octets));
            },
            (string) $str
        );
        return $str;
    }

    /**
     * Parse DN to name-components.
     *
     * @return array<array<string>>
     */
    private function parse(): array
    {
        $offset = 0;
        $name = $this->_parseName($offset);
        if ($offset < $this->_len) {
            $remains = mb_substr($this->_dn, $offset, null, '8bit');
            throw new UnexpectedValueException(sprintf(
                'Parser finished before the end of string, remaining: %s',
                $remains
            ));
        }
        return $name;
    }

    /**
     * Parse 'name'.
     *
     * name-component *("," name-component)
     *
     * @return array<array<string>> Array of name-components
     */
    private function _parseName(int &$offset): array
    {
        $idx = $offset;
        $names = [];
        while ($idx < $this->_len) {
            $names[] = $this->_parseNameComponent($idx);
            if ($idx >= $this->_len) {
                break;
            }
            $this->_skipWs($idx);
            if ($this->_dn[$idx] !== ',' && $this->_dn[$idx] !== ';') {
                break;
            }
            ++$idx;
            $this->_skipWs($idx);
        }
        $offset = $idx;
        return array_reverse($names);
    }

    /**
     * Parse 'name-component'.
     *
     * attributeTypeAndValue *("+" attributeTypeAndValue)
     *
     * @return array<array<string, string|ElementBase>> Array of [type, value] tuples
     */
    private function _parseNameComponent(int &$offset): array
    {
        $idx = $offset;
        $tvpairs = [];
        while ($idx < $this->_len) {
            $tvpairs[] = $this->_parseAttrTypeAndValue($idx);
            $this->_skipWs($idx);
            if ($idx >= $this->_len || $this->_dn[$idx] !== '+') {
                break;
            }
            ++$idx;
            $this->_skipWs($idx);
        }
        $offset = $idx;
        return $tvpairs;
    }

    /**
     * Parse 'attributeTypeAndValue'.
     *
     * attributeType "=" attributeValue
     *
     * @return array<string, string|ElementBase> A tuple of [type, value]. Value may be either a string or
     * an Element, if it's encoded as hexstring.
     */
    private function _parseAttrTypeAndValue(int &$offset): array
    {
        $idx = $offset;
        $type = $this->_parseAttrType($idx);
        $this->_skipWs($idx);
        if ($idx >= $this->_len || $this->_dn[$idx++] !== '=') {
            throw new UnexpectedValueException('Invalid type and value pair.');
        }
        $this->_skipWs($idx);
        // hexstring
        if ($idx < $this->_len && $this->_dn[$idx] === '#') {
            ++$idx;
            $data = $this->_parseAttrHexValue($idx);
            try {
                $value = Element::fromDER($data);
            } catch (DecodeException $e) {
                throw new UnexpectedValueException('Invalid DER encoding from hexstring.', 0, $e);
            }
        } else {
            $value = $this->_parseAttrStringValue($idx);
        }
        $offset = $idx;
        return [$type, $value];
    }

    /**
     * Parse 'attributeType'.
     *
     * (ALPHA 1*keychar) / oid
     */
    private function _parseAttrType(int &$offset): string
    {
        $idx = $offset;
        // dotted OID
        $type = $this->_regexMatch('/^(?:oid\.)?([0-9]+(?:\.[0-9]+)*)/i', $idx);
        if ($type === null) {
            // name
            $type = $this->_regexMatch('/^[a-z][a-z0-9\-]*/i', $idx);
            if ($type === null) {
                throw new UnexpectedValueException('Invalid attribute type.');
            }
        }
        $offset = $idx;
        return $type;
    }

    /**
     * Parse 'attributeValue' of string type.
     */
    private function _parseAttrStringValue(int &$offset): string
    {
        $idx = $offset;
        if ($idx >= $this->_len) {
            return '';
        }
        if ($this->_dn[$idx] === '"') { // quoted string
            $val = $this->_parseQuotedAttrString($idx);
        } else { // string
            $val = $this->_parseAttrString($idx);
        }
        $offset = $idx;
        return $val;
    }

    /**
     * Parse plain 'attributeValue' string.
     */
    private function _parseAttrString(int &$offset): string
    {
        $idx = $offset;
        $val = '';
        $wsidx = null;
        while ($idx < $this->_len) {
            $c = $this->_dn[$idx];
            // pair (escape sequence)
            if ($c === '\\') {
                ++$idx;
                $val .= $this->_parsePairAfterSlash($idx);
                $wsidx = null;
                continue;
            }
            if ($c === '"') {
                throw new UnexpectedValueException('Unexpected quotation.');
            }
            if (mb_strpos(self::SPECIAL_CHARS, $c, 0, '8bit') !== false) {
                break;
            }
            // keep track of the first consecutive whitespace
            if ($c === ' ') {
                if ($wsidx === null) {
                    $wsidx = $idx;
                }
            } else {
                $wsidx = null;
            }
            // stringchar
            $val .= $c;
            ++$idx;
        }
        // if there was non-escaped whitespace in the end of the value
        if ($wsidx !== null) {
            $val = mb_substr($val, 0, -($idx - $wsidx), '8bit');
        }
        $offset = $idx;
        return $val;
    }

    /**
     * Parse quoted 'attributeValue' string.
     *
     * @param int $offset Offset to starting quote
     */
    private function _parseQuotedAttrString(int &$offset): string
    {
        $idx = $offset + 1;
        $val = '';
        while ($idx < $this->_len) {
            $c = $this->_dn[$idx];
            if ($c === '\\') { // pair
                ++$idx;
                $val .= $this->_parsePairAfterSlash($idx);
                continue;
            }
            if ($c === '"') {
                ++$idx;
                break;
            }
            $val .= $c;
            ++$idx;
        }
        $offset = $idx;
        return $val;
    }

    /**
     * Parse 'attributeValue' of binary type.
     */
    private function _parseAttrHexValue(int &$offset): string
    {
        $idx = $offset;
        $hexstr = $this->_regexMatch('/^(?:[0-9a-f]{2})+/i', $idx);
        if ($hexstr === null) {
            throw new UnexpectedValueException('Invalid hexstring.');
        }
        $data = hex2bin($hexstr);
        $offset = $idx;
        return $data;
    }

    /**
     * Parse 'pair' after leading slash.
     */
    private function _parsePairAfterSlash(int &$offset): string
    {
        $idx = $offset;
        if ($idx >= $this->_len) {
            throw new UnexpectedValueException('Unexpected end of escape sequence.');
        }
        $c = $this->_dn[$idx++];
        // special | \ | " | SPACE
        if (mb_strpos(self::SPECIAL_CHARS . '\\" ', $c, 0, '8bit') !== false) {
            $val = $c;
        } else { // hexpair
            if ($idx >= $this->_len) {
                throw new UnexpectedValueException('Unexpected end of hexpair.');
            }
            $val = @hex2bin($c . $this->_dn[$idx++]);
            if ($val === false) {
                throw new UnexpectedValueException('Invalid hexpair.');
            }
        }
        $offset = $idx;
        return $val;
    }

    /**
     * Match DN to pattern and extract the last capture group.
     *
     * Updates offset to fully matched pattern.
     *
     * @return null|string Null if pattern doesn't match
     */
    private function _regexMatch(string $pattern, int &$offset): ?string
    {
        $idx = $offset;
        if (preg_match($pattern, mb_substr($this->_dn, $idx, null, '8bit'), $match) !== 1) {
            return null;
        }
        $idx += mb_strlen($match[0], '8bit');
        $offset = $idx;
        return end($match);
    }

    /**
     * Skip consecutive spaces.
     */
    private function _skipWs(int &$offset): void
    {
        $idx = $offset;
        while ($idx < $this->_len) {
            if ($this->_dn[$idx] !== ' ') {
                break;
            }
            ++$idx;
        }
        $offset = $idx;
    }
}