<?php

/**
 * HTML API: WP_HTML_Decoder class
 *
 * Decodes spans of raw text found inside HTML content.
 *
 * @package WordPress
 * @subpackage HTML-API
 * @since 6.6.0
 */
class WP_HTML_Decoder {
    /**
     * Indicates if an attribute value starts with a given raw string value.
     *
     * Use this method to determine if an attribute value starts with a given string, regardless
     * of how it might be encoded in HTML. For instance, `http:` could be represented as `http:`
     * or as `http&colon;` or as `&#x68;ttp:` or as `h&#116;tp&colon;`, or in many other ways.
     *
     * Example:
     *
     *     $value = 'http&colon;//wordpress.org/';
     *     true   === WP_HTML_Decoder::attribute_starts_with( $value, 'http:', 'ascii-case-insensitive' );
     *     false  === WP_HTML_Decoder::attribute_starts_with( $value, 'https:', 'ascii-case-insensitive' );
     *
     * @since 6.6.0
     *
     * @param string $haystack         String containing the raw non-decoded attribute value.
     * @param string $search_text      Does the attribute value start with this plain string.
     * @param string $case_sensitivity Optional. Pass 'ascii-case-insensitive' to ignore ASCII case when matching.
     *                                 Default 'case-sensitive'.
     * @return bool Whether the attribute value starts with the given string.
     */
    public static function attribute_starts_with( $haystack, $search_text, $case_sensitivity = 'case-sensitive' ): bool {
        $search_length = strlen( $search_text );
        $loose_case    = 'ascii-case-insensitive' === $case_sensitivity;
        $haystack_end  = strlen( $haystack );
        $search_at     = 0;
        $haystack_at   = 0;

        while ( $search_at < $search_length && $haystack_at < $haystack_end ) {
            $chars_match = $loose_case
                ? strtolower( $haystack[ $haystack_at ] ) === strtolower( $search_text[ $search_at ] )
                : $haystack[ $haystack_at ] === $search_text[ $search_at ];

            $is_introducer = '&' === $haystack[ $haystack_at ];
            $next_chunk    = $is_introducer
                ? self::read_character_reference( 'attribute', $haystack, $haystack_at, $token_length )
                : null;

            // If there's no character reference and the characters don't match, the match fails.
            if ( null === $next_chunk && ! $chars_match ) {
                return false;
            }

            // If there's no character reference but the character do match, then it could still match.
            if ( null === $next_chunk && $chars_match ) {
                ++$haystack_at;
                ++$search_at;
                continue;
            }

            // If there is a character reference, then the decoded value must exactly match what follows in the search string.
            if ( 0 !== substr_compare( $search_text, $next_chunk, $search_at, strlen( $next_chunk ), $loose_case ) ) {
                return false;
            }

            // The character reference matched, so continue checking.
            $haystack_at += $token_length;
            $search_at   += strlen( $next_chunk );
        }

        return true;
    }

    /**
     * Returns a string containing the decoded value of a given HTML text node.
     *
     * Text nodes appear in HTML DATA sections, which are the text segments inside
     * and around tags, excepting SCRIPT and STYLE elements (and some others),
     * whose inner text is not decoded. Use this function to read the decoded
     * value of such a text span in an HTML document.
     *
     * Example:
     *
     *     '“😄”' === WP_HTML_Decode::decode_text_node( '&#x93;&#x1f604;&#x94' );
     *
     * @since 6.6.0
     *
     * @param string $text Text containing raw and non-decoded text node to decode.
     * @return string Decoded UTF-8 value of given text node.
     */
    public static function decode_text_node( $text ): string {
        return static::decode( 'data', $text );
    }

    /**
     * Returns a string containing the decoded value of a given HTML attribute.
     *
     * Text found inside an HTML attribute has different parsing rules than for
     * text found inside other markup, or DATA segments. Use this function to
     * read the decoded value of an HTML string inside a quoted attribute.
     *
     * Example:
     *
     *     '“😄”' === WP_HTML_Decode::decode_attribute( '&#x93;&#x1f604;&#x94' );
     *
     * @since 6.6.0
     *
     * @param string $text Text containing raw and non-decoded attribute value to decode.
     * @return string Decoded UTF-8 value of given attribute value.
     */
    public static function decode_attribute( $text ): string {
        return static::decode( 'attribute', $text );
    }

    /**
     * Decodes a span of HTML text, depending on the context in which it's found.
     *
     * This is a low-level method; prefer calling WP_HTML_Decoder::decode_attribute() or
     * WP_HTML_Decoder::decode_text_node() instead. It's provided for cases where this
     * may be difficult to do from calling code.
     *
     * Example:
     *
     *     '©' = WP_HTML_Decoder::decode( 'data', '&copy;' );
     *
     * @since 6.6.0
     *
     * @access private
     *
     * @param string $context `attribute` for decoding attribute values, `data` otherwise.
     * @param string $text    Text document containing span of text to decode.
     * @return string Decoded UTF-8 string.
     */
    public static function decode( $context, $text ): string {
        $decoded = '';
        $end     = strlen( $text );
        $at      = 0;
        $was_at  = 0;

        while ( $at < $end ) {
            $next_character_reference_at = strpos( $text, '&', $at );
            if ( false === $next_character_reference_at ) {
                break;
            }

            $character_reference = self::read_character_reference( $context, $text, $next_character_reference_at, $token_length );
            if ( isset( $character_reference ) ) {
                $at       = $next_character_reference_at;
                $decoded .= substr( $text, $was_at, $at - $was_at );
                $decoded .= $character_reference;
                $at      += $token_length;
                $was_at   = $at;
                continue;
            }

            ++$at;
        }

        if ( 0 === $was_at ) {
            return $text;
        }

        if ( $was_at < $end ) {
            $decoded .= substr( $text, $was_at, $end - $was_at );
        }

        return $decoded;
    }

    /**
     * Attempt to read a character reference at the given location in a given string,
     * depending on the context in which it's found.
     *
     * If a character reference is found, this function will return the translated value
     * that the reference maps to. It will then set `$match_byte_length` the
     * number of bytes of input it read while consuming the character reference. This
     * gives calling code the opportunity to advance its cursor when traversing a string
     * and decoding.
     *
     * Example:
     *
     *     null === WP_HTML_Decoder::read_character_reference( 'attribute', 'Ships&hellip;', 0 );
     *     '…'  === WP_HTML_Decoder::read_character_reference( 'attribute', 'Ships&hellip;', 5, $token_length );
     *     8    === $token_length; // `&hellip;`
     *
     *     null === WP_HTML_Decoder::read_character_reference( 'attribute', '&notin', 0 );
     *     '∉'  === WP_HTML_Decoder::read_character_reference( 'attribute', '&notin;', 0, $token_length );
     *     7    === $token_length; // `&notin;`
     *
     *     '¬'  === WP_HTML_Decoder::read_character_reference( 'data', '&notin', 0, $token_length );
     *     4    === $token_length; // `&not`
     *     '∉'  === WP_HTML_Decoder::read_character_reference( 'data', '&notin;', 0, $token_length );
     *     7    === $token_length; // `&notin;`
     *
     * @since 6.6.0
     *
     * @global WP_Token_Map $html5_named_character_references Mappings for HTML5 named character references.
     *
     * @param string $context            `attribute` for decoding attribute values, `data` otherwise.
     * @param string $text               Text document containing span of text to decode.
     * @param int    $at                 Optional. Byte offset into text where span begins, defaults to the beginning (0).
     * @param int    &$match_byte_length Optional. Set to byte-length of character reference if provided and if a match
     *                                   is found, otherwise not set. Default null.
     * @return ?string Decoded character reference in UTF-8 if found, otherwise null.
     */
    public static function read_character_reference( $context, $text, $at = 0, &$match_byte_length = null ) {
        /**
         * Mappings for HTML5 named character references.
         *
         * @var WP_Token_Map $html5_named_character_references
         */
        global $html5_named_character_references;

        $length = strlen( $text );
        if ( $at + 1 >= $length ) {
            return null;
        }

        if ( '&' !== $text[ $at ] ) {
            return null;
        }

        /*
         * Numeric character references.
         *
         * When truncated, these will encode the code point found by parsing the
         * digits that are available. For example, when `&#x1f170;` is truncated
         * to `&#x1f1` it will encode `DZ`. It does not:
         *  - know how to parse the original `🅰`.
         *  - fail to parse and return plaintext `&#x1f1`.
         *  - fail to parse and return the replacement character `�`
         */
        if ( '#' === $text[ $at + 1 ] ) {
            if ( $at + 2 >= $length ) {
                return null;
            }

            /** Tracks inner parsing within the numeric character reference. */
            $digits_at = $at + 2;

            if ( 'x' === $text[ $digits_at ] || 'X' === $text[ $digits_at ] ) {
                $numeric_base   = 16;
                $numeric_digits = '0123456789abcdefABCDEF';
                $max_digits     = 6; // &#x10FFFF;
                ++$digits_at;
            } else {
                $numeric_base   = 10;
                $numeric_digits = '0123456789';
                $max_digits     = 7; // &#1114111;
            }

            // Cannot encode invalid Unicode code points. Max is to U+10FFFF.
            $zero_count    = strspn( $text, '0', $digits_at );
            $digit_count   = strspn( $text, $numeric_digits, $digits_at + $zero_count );
            $after_digits  = $digits_at + $zero_count + $digit_count;
            $has_semicolon = $after_digits < $length && ';' === $text[ $after_digits ];
            $end_of_span   = $has_semicolon ? $after_digits + 1 : $after_digits;

            // `&#` or `&#x` without digits returns into plaintext.
            if ( 0 === $digit_count && 0 === $zero_count ) {
                return null;
            }

            // Whereas `&#` and only zeros is invalid.
            if ( 0 === $digit_count ) {
                $match_byte_length = $end_of_span - $at;
                return '�';
            }

            // If there are too many digits then it's not worth parsing. It's invalid.
            if ( $digit_count > $max_digits ) {
                $match_byte_length = $end_of_span - $at;
                return '�';
            }

            $digits     = substr( $text, $digits_at + $zero_count, $digit_count );
            $code_point = intval( $digits, $numeric_base );

            /*
             * Noncharacters, 0x0D, and non-ASCII-whitespace control characters.
             *
             * > A noncharacter is a code point that is in the range U+FDD0 to U+FDEF,
             * > inclusive, or U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, U+2FFFE, U+2FFFF,
             * > U+3FFFE, U+3FFFF, U+4FFFE, U+4FFFF, U+5FFFE, U+5FFFF, U+6FFFE,
             * > U+6FFFF, U+7FFFE, U+7FFFF, U+8FFFE, U+8FFFF, U+9FFFE, U+9FFFF,
             * > U+AFFFE, U+AFFFF, U+BFFFE, U+BFFFF, U+CFFFE, U+CFFFF, U+DFFFE,
             * > U+DFFFF, U+EFFFE, U+EFFFF, U+FFFFE, U+FFFFF, U+10FFFE, or U+10FFFF.
             *
             * A C0 control is a code point that is in the range of U+00 to U+1F,
             * but ASCII whitespace includes U+09, U+0A, U+0C, and U+0D.
             *
             * These characters are invalid but still decode as any valid character.
             * This comment is here to note and explain why there's no check to
             * remove these characters or replace them.
             *
             * @see https://infra.spec.whatwg.org/#noncharacter
             */

            /*
             * Code points in the C1 controls area need to be remapped as if they
             * were stored in Windows-1252. Note! This transformation only happens
             * for numeric character references. The raw code points in the byte
             * stream are not translated.
             *
             * > If the number is one of the numbers in the first column of
             * > the following table, then find the row with that number in
             * > the first column, and set the character reference code to
             * > the number in the second column of that row.
             */
            if ( $code_point >= 0x80 && $code_point <= 0x9F ) {
                $windows_1252_mapping = array(
                    0x20AC, // 0x80 -> EURO SIGN (€).
                    0x81,   // 0x81 -> (no change).
                    0x201A, // 0x82 -> SINGLE LOW-9 QUOTATION MARK (‚).
                    0x0192, // 0x83 -> LATIN SMALL LETTER F WITH HOOK (ƒ).
                    0x201E, // 0x84 -> DOUBLE LOW-9 QUOTATION MARK („).
                    0x2026, // 0x85 -> HORIZONTAL ELLIPSIS (…).
                    0x2020, // 0x86 -> DAGGER (†).
                    0x2021, // 0x87 -> DOUBLE DAGGER (‡).
                    0x02C6, // 0x88 -> MODIFIER LETTER CIRCUMFLEX ACCENT (ˆ).
                    0x2030, // 0x89 -> PER MILLE SIGN (‰).
                    0x0160, // 0x8A -> LATIN CAPITAL LETTER S WITH CARON (Š).
                    0x2039, // 0x8B -> SINGLE LEFT-POINTING ANGLE QUOTATION MARK (‹).
                    0x0152, // 0x8C -> LATIN CAPITAL LIGATURE OE (Œ).
                    0x8D,   // 0x8D -> (no change).
                    0x017D, // 0x8E -> LATIN CAPITAL LETTER Z WITH CARON (Ž).
                    0x8F,   // 0x8F -> (no change).
                    0x90,   // 0x90 -> (no change).
                    0x2018, // 0x91 -> LEFT SINGLE QUOTATION MARK (‘).
                    0x2019, // 0x92 -> RIGHT SINGLE QUOTATION MARK (’).
                    0x201C, // 0x93 -> LEFT DOUBLE QUOTATION MARK (“).
                    0x201D, // 0x94 -> RIGHT DOUBLE QUOTATION MARK (”).
                    0x2022, // 0x95 -> BULLET (•).
                    0x2013, // 0x96 -> EN DASH (–).
                    0x2014, // 0x97 -> EM DASH (—).
                    0x02DC, // 0x98 -> SMALL TILDE (˜).
                    0x2122, // 0x99 -> TRADE MARK SIGN (™).
                    0x0161, // 0x9A -> LATIN SMALL LETTER S WITH CARON (š).
                    0x203A, // 0x9B -> SINGLE RIGHT-POINTING ANGLE QUOTATION MARK (›).
                    0x0153, // 0x9C -> LATIN SMALL LIGATURE OE (œ).
                    0x9D,   // 0x9D -> (no change).
                    0x017E, // 0x9E -> LATIN SMALL LETTER Z WITH CARON (ž).
                    0x0178, // 0x9F -> LATIN CAPITAL LETTER Y WITH DIAERESIS (Ÿ).
                );

                $code_point = $windows_1252_mapping[ $code_point - 0x80 ];
            }

            $match_byte_length = $end_of_span - $at;
            return self::code_point_to_utf8_bytes( $code_point );
        }

        /** Tracks inner parsing within the named character reference. */
        $name_at = $at + 1;
        // Minimum named character reference is two characters. E.g. `GT`.
        if ( $name_at + 2 > $length ) {
            return null;
        }

        $name_length = 0;
        $replacement = $html5_named_character_references->read_token( $text, $name_at, $name_length );
        if ( false === $replacement ) {
            return null;
        }

        $after_name = $name_at + $name_length;

        // If the match ended with a semicolon then it should always be decoded.
        if ( ';' === $text[ $name_at + $name_length - 1 ] ) {
            $match_byte_length = $after_name - $at;
            return $replacement;
        }

        /*
         * At this point though there's a match for an entry in the named
         * character reference table but the match doesn't end in `;`.
         * It may be allowed if it's followed by something unambiguous.
         */
        $ambiguous_follower = (
            $after_name < $length &&
            $name_at < $length &&
            (
                ctype_alnum( $text[ $after_name ] ) ||
                '=' === $text[ $after_name ]
            )
        );

        // It's non-ambiguous, safe to leave it in.
        if ( ! $ambiguous_follower ) {
            $match_byte_length = $after_name - $at;
            return $replacement;
        }

        // It's ambiguous, which isn't allowed inside attributes.
        if ( 'attribute' === $context ) {
            return null;
        }

        $match_byte_length = $after_name - $at;
        return $replacement;
    }

    /**
     * Encode a code point number into the UTF-8 encoding.
     *
     * This encoder implements the UTF-8 encoding algorithm for converting
     * a code point into a byte sequence. If it receives an invalid code
     * point it will return the Unicode Replacement Character U+FFFD `�`.
     *
     * Example:
     *
     *     '🅰' === WP_HTML_Decoder::code_point_to_utf8_bytes( 0x1f170 );
     *
     *     // Half of a surrogate pair is an invalid code point.
     *     '�' === WP_HTML_Decoder::code_point_to_utf8_bytes( 0xd83c );
     *
     * @since 6.6.0
     *
     * @see https://www.rfc-editor.org/rfc/rfc3629 For the UTF-8 standard.
     *
     * @param int $code_point Which code point to convert.
     * @return string Converted code point, or `�` if invalid.
     */
    public static function code_point_to_utf8_bytes( $code_point ): string {
        // Pre-check to ensure a valid code point.
        if (
            $code_point <= 0 ||
            ( $code_point >= 0xD800 && $code_point <= 0xDFFF ) ||
            $code_point > 0x10FFFF
        ) {
            return '�';
        }

        if ( $code_point <= 0x7F ) {
            return chr( $code_point );
        }

        if ( $code_point <= 0x7FF ) {
            $byte1 = chr( ( $code_point >> 6 ) | 0xC0 );
            $byte2 = chr( $code_point & 0x3F | 0x80 );

            return "{$byte1}{$byte2}";
        }

        if ( $code_point <= 0xFFFF ) {
            $byte1 = chr( ( $code_point >> 12 ) | 0xE0 );
            $byte2 = chr( ( $code_point >> 6 ) & 0x3F | 0x80 );
            $byte3 = chr( $code_point & 0x3F | 0x80 );

            return "{$byte1}{$byte2}{$byte3}";
        }

        // Any values above U+10FFFF are eliminated above in the pre-check.
        $byte1 = chr( ( $code_point >> 18 ) | 0xF0 );
        $byte2 = chr( ( $code_point >> 12 ) & 0x3F | 0x80 );
        $byte3 = chr( ( $code_point >> 6 ) & 0x3F | 0x80 );
        $byte4 = chr( $code_point & 0x3F | 0x80 );

        return "{$byte1}{$byte2}{$byte3}{$byte4}";
    }
}