<?php

namespace ActivityPub\Utils;

/**
 * HTTP header utility functions.
 *
 * @author Christian Schmidt <github@chsc.dk>
 */
class HeaderUtils
{
    const DISPOSITION_ATTACHMENT = 'attachment';
    const DISPOSITION_INLINE = 'inline';

    /**
     * This class should not be instantiated.
     */
    private function __construct()
    {
    }

    /**
     * Splits an HTTP header by one or more separators.
     *
     * Example:
     *
     *     HeaderUtils::split("da, en-gb;q=0.8", ",;")
     *     // => ['da'], ['en-gb', 'q=0.8']]
     *
     * @param string $header HTTP header value
     * @param string $separators List of characters to split on, ordered by
     *                           precedence, e.g. ",", ";=", or ",;="
     *
     * @return array Nested array with as many levels as there are characters in
     *               $separators
     */
    public static function split($header, $separators)
    {
        $quotedSeparators = preg_quote( $separators, '/' );
        preg_match_all( "\n            /\n                (?!\s)\n                    (?:\n                        # quoted-string\n                        \"(?:[^\"\\]|\\.)*(?:\"|\\|$)\n                    |\n                        # token\n                        [^\"" . $quotedSeparators . "]+\n                    )+\n                (?<!\s)\n            |\n                # separator\n                \s*\n                (?<separator>[" . $quotedSeparators . "])\n                \s*\n            /x", trim( $header ), $matches, PREG_SET_ORDER );
        return self::groupParts( $matches, $separators );
    }

    private static function groupParts(array $matches, $separators)
    {
        $separator = $separators[0];
        $partSeparators = substr( $separators, 1 );
        $i = 0;
        $partMatches = [];
        foreach ( $matches as $match ) {
            if ( isset( $match['separator'] ) && $match['separator'] === $separator ) {
                ++$i;
            } else {
                $partMatches[$i][] = $match;
            }
        }
        $parts = [];
        if ( $partSeparators ) {
            foreach ( $partMatches as $matches ) {
                $parts[] = self::groupParts( $matches, $partSeparators );
            }
        } else {
            foreach ( $partMatches as $matches ) {
                $parts[] = self::unquote( $matches[0][0] );
            }
        }
        return $parts;
    }

    /**
     * Decodes a quoted string.
     *
     * If passed an unquoted string that matches the "token" construct (as
     * defined in the HTTP specification), it is passed through verbatimly.
     * @param $s
     * @return string|string[]|null
     */
    public static function unquote($s)
    {
        return preg_replace( '/\\\\(.)|"/', '$1', $s );
    }

    /**
     * Combines an array of arrays into one associative array.
     *
     * Each of the nested arrays should have one or two elements. The first
     * value will be used as the keys in the associative array, and the second
     * will be used as the values, or true if the nested array only contains one
     * element. Array keys are lowercased.
     *
     * Example:
     *
     *     HeaderUtils::combine([["foo", "abc"], ["bar"]])
     *     // => ["foo" => "abc", "bar" => true]
     * @param array $parts
     * @return array
     */
    public static function combine(array $parts)
    {
        $assoc = [];
        foreach ( $parts as $part ) {
            $name = strtolower( $part[0] );
            if ( isset( $part[1] ) ) {
                $value = $part[1];
            } else {
                $value = true;
            }
            $assoc[$name] = $value;
        }
        return $assoc;
    }

    /**
     * Generates a HTTP Content-Disposition field-value.
     *
     * @param string $disposition One of "inline" or "attachment"
     * @param string $filename A unicode string
     * @param string $filenameFallback A string containing only ASCII characters that
     *                                 is semantically equivalent to $filename. If the filename is already ASCII,
     *                                 it can be omitted, or just copied from $filename
     *
     * @return string A string suitable for use as a Content-Disposition field-value
     *
     * @throws \InvalidArgumentException
     *
     * @see RFC 6266
     */
    public static function makeDisposition($disposition, $filename, $filenameFallback = '')
    {
        if ( !\in_array( $disposition, [ self::DISPOSITION_ATTACHMENT, self::DISPOSITION_INLINE ] ) ) {
            throw new \InvalidArgumentException( sprintf( 'The disposition must be either "%s" or "%s".', self::DISPOSITION_ATTACHMENT, self::DISPOSITION_INLINE ) );
        }
        if ( '' === $filenameFallback ) {
            $filenameFallback = $filename;
        }
        // filenameFallback is not ASCII.
        if ( !preg_match( '/^[\x20-\x7e]*$/', $filenameFallback ) ) {
            throw new \InvalidArgumentException( 'The filename fallback must only contain ASCII characters.' );
        }
        // percent characters aren't safe in fallback.
        if ( false !== strpos( $filenameFallback, '%' ) ) {
            throw new \InvalidArgumentException( 'The filename fallback cannot contain the "%" character.' );
        }
        // path separators aren't allowed in either.
        if ( false !== strpos( $filename, '/' ) || false !== strpos( $filename, '\\' ) || false !== strpos( $filenameFallback, '/' ) || false !== strpos( $filenameFallback, '\\' ) ) {
            throw new \InvalidArgumentException( 'The filename and the fallback cannot contain the "/" and "\\" characters.' );
        }
        $params = [ 'filename' => $filenameFallback ];
        if ( $filename !== $filenameFallback ) {
            $params['filename*'] = "utf-8''" . rawurlencode( $filename );
        }
        return $disposition . '; ' . self::toString( $params, ';' );
    }

    /**
     * Joins an associative array into a string for use in an HTTP header.
     *
     * The key and value of each entry are joined with "=", and all entries
     * are joined with the specified separator and an additional space (for
     * readability). Values are quoted if necessary.
     *
     * Example:
     *
     *     HeaderUtils::toString(["foo" => "abc", "bar" => true, "baz" => "a b c"], ",")
     *     // => 'foo=abc, bar, baz="a b c"'
     * @param array $assoc
     * @param $separator
     * @return string
     */
    public static function toString(array $assoc, $separator)
    {
        $parts = [];
        foreach ( $assoc as $name => $value ) {
            if ( true === $value ) {
                $parts[] = $name;
            } else {
                $parts[] = $name . '=' . self::quote( $value );
            }
        }
        return implode( $separator . ' ', $parts );
    }

    /**
     * Encodes a string as a quoted string, if necessary.
     *
     * If a string contains characters not allowed by the "token" construct in
     * the HTTP specification, it is backslash-escaped and enclosed in quotes
     * to match the "quoted-string" construct.
     * @param $s
     * @return string
     */
    public static function quote($s)
    {
        if ( preg_match( '/^[a-z0-9!#$%&\'*.^_`|~-]+$/i', $s ) ) {
            return $s;
        }
        return '"' . addcslashes( $s, '"\\"' ) . '"';
    }
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