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<?php

/**
 * IDNA URL encoder
 *
 * Note: Not fully compliant, as nameprep does nothing yet.
 *
 * @package Requests
 * @subpackage Utilities
 * @see https://tools.ietf.org/html/rfc3490 IDNA specification
 * @see https://tools.ietf.org/html/rfc3492 Punycode/Bootstrap specification
 */
class Requests_IDNAEncoder {
    /**
     * ACE prefix used for IDNA
     *
     * @see https://tools.ietf.org/html/rfc3490#section-5
     * @var string
     */
    const ACE_PREFIX = 'xn--';

    /**#@+
     * Bootstrap constant for Punycode
     *
     * @see https://tools.ietf.org/html/rfc3492#section-5
     * @var int
     */
    const BOOTSTRAP_BASE         = 36;
    const BOOTSTRAP_TMIN         = 1;
    const BOOTSTRAP_TMAX         = 26;
    const BOOTSTRAP_SKEW         = 38;
    const BOOTSTRAP_DAMP         = 700;
    const BOOTSTRAP_INITIAL_BIAS = 72;
    const BOOTSTRAP_INITIAL_N    = 128;
    /**#@-*/

    /**
     * Encode a hostname using Punycode
     *
     * @param string $string Hostname
     * @return string Punycode-encoded hostname
     */
    public static function encode($string) {
        $parts = explode('.', $string);
        foreach ($parts as &$part) {
            $part = self::to_ascii($part);
        }
        return implode('.', $parts);
    }

    /**
     * Convert a UTF-8 string to an ASCII string using Punycode
     *
     * @throws Requests_Exception Provided string longer than 64 ASCII characters (`idna.provided_too_long`)
     * @throws Requests_Exception Prepared string longer than 64 ASCII characters (`idna.prepared_too_long`)
     * @throws Requests_Exception Provided string already begins with xn-- (`idna.provided_is_prefixed`)
     * @throws Requests_Exception Encoded string longer than 64 ASCII characters (`idna.encoded_too_long`)
     *
     * @param string $string ASCII or UTF-8 string (max length 64 characters)
     * @return string ASCII string
     */
    public static function to_ascii($string) {
        // Step 1: Check if the string is already ASCII
        if (self::is_ascii($string)) {
            // Skip to step 7
            if (strlen($string) < 64) {
                return $string;
            }

            throw new Requests_Exception('Provided string is too long', 'idna.provided_too_long', $string);
        }

        // Step 2: nameprep
        $string = self::nameprep($string);

        // Step 3: UseSTD3ASCIIRules is false, continue
        // Step 4: Check if it's ASCII now
        if (self::is_ascii($string)) {
            // Skip to step 7
            if (strlen($string) < 64) {
                return $string;
            }

            throw new Requests_Exception('Prepared string is too long', 'idna.prepared_too_long', $string);
        }

        // Step 5: Check ACE prefix
        if (strpos($string, self::ACE_PREFIX) === 0) {
            throw new Requests_Exception('Provided string begins with ACE prefix', 'idna.provided_is_prefixed', $string);
        }

        // Step 6: Encode with Punycode
        $string = self::punycode_encode($string);

        // Step 7: Prepend ACE prefix
        $string = self::ACE_PREFIX . $string;

        // Step 8: Check size
        if (strlen($string) < 64) {
            return $string;
        }

        throw new Requests_Exception('Encoded string is too long', 'idna.encoded_too_long', $string);
    }

    /**
     * Check whether a given string contains only ASCII characters
     *
     * @internal (Testing found regex was the fastest implementation)
     *
     * @param string $string
     * @return bool Is the string ASCII-only?
     */
    protected static function is_ascii($string) {
        return (preg_match('/(?:[^\x00-\x7F])/', $string) !== 1);
    }

    /**
     * Prepare a string for use as an IDNA name
     *
     * @todo Implement this based on RFC 3491 and the newer 5891
     * @param string $string
     * @return string Prepared string
     */
    protected static function nameprep($string) {
        return $string;
    }

    /**
     * Convert a UTF-8 string to a UCS-4 codepoint array
     *
     * Based on Requests_IRI::replace_invalid_with_pct_encoding()
     *
     * @throws Requests_Exception Invalid UTF-8 codepoint (`idna.invalidcodepoint`)
     * @param string $input
     * @return array Unicode code points
     */
    protected static function utf8_to_codepoints($input) {
        $codepoints = array();

        // Get number of bytes
        $strlen = strlen($input);

        // phpcs:ignore Generic.CodeAnalysis.JumbledIncrementer -- This is a deliberate choice.
        for ($position = 0; $position < $strlen; $position++) {
            $value = ord($input[$position]);

            // One byte sequence:
            if ((~$value & 0x80) === 0x80) {
                $character = $value;
                $length    = 1;
                $remaining = 0;
            }
            // Two byte sequence:
            elseif (($value & 0xE0) === 0xC0) {
                $character = ($value & 0x1F) << 6;
                $length    = 2;
                $remaining = 1;
            }
            // Three byte sequence:
            elseif (($value & 0xF0) === 0xE0) {
                $character = ($value & 0x0F) << 12;
                $length    = 3;
                $remaining = 2;
            }
            // Four byte sequence:
            elseif (($value & 0xF8) === 0xF0) {
                $character = ($value & 0x07) << 18;
                $length    = 4;
                $remaining = 3;
            }
            // Invalid byte:
            else {
                throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $value);
            }

            if ($remaining > 0) {
                if ($position + $length > $strlen) {
                    throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
                }
                for ($position++; $remaining > 0; $position++) {
                    $value = ord($input[$position]);

                    // If it is invalid, count the sequence as invalid and reprocess the current byte:
                    if (($value & 0xC0) !== 0x80) {
                        throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
                    }

                    --$remaining;
                    $character |= ($value & 0x3F) << ($remaining * 6);
                }
                $position--;
            }

            if (// Non-shortest form sequences are invalid
                $length > 1 && $character <= 0x7F
                || $length > 2 && $character <= 0x7FF
                || $length > 3 && $character <= 0xFFFF
                // Outside of range of ucschar codepoints
                // Noncharacters
                || ($character & 0xFFFE) === 0xFFFE
                || $character >= 0xFDD0 && $character <= 0xFDEF
                || (
                    // Everything else not in ucschar
                    $character > 0xD7FF && $character < 0xF900
                    || $character < 0x20
                    || $character > 0x7E && $character < 0xA0
                    || $character > 0xEFFFD
                )
            ) {
                throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
            }

            $codepoints[] = $character;
        }

        return $codepoints;
    }

    /**
     * RFC3492-compliant encoder
     *
     * @internal Pseudo-code from Section 6.3 is commented with "#" next to relevant code
     * @throws Requests_Exception On character outside of the domain (never happens with Punycode) (`idna.character_outside_domain`)
     *
     * @param string $input UTF-8 encoded string to encode
     * @return string Punycode-encoded string
     */
    public static function punycode_encode($input) {
        $output = '';
        // let n = initial_n
        $n = self::BOOTSTRAP_INITIAL_N;
        // let delta = 0
        $delta = 0;
        // let bias = initial_bias
        $bias = self::BOOTSTRAP_INITIAL_BIAS;
        // let h = b = the number of basic code points in the input
        $h = 0;
        $b = 0; // see loop
        // copy them to the output in order
        $codepoints = self::utf8_to_codepoints($input);
        $extended   = array();

        foreach ($codepoints as $char) {
            if ($char < 128) {
                // Character is valid ASCII
                // TODO: this should also check if it's valid for a URL
                $output .= chr($char);
                $h++;
            }
            // Check if the character is non-ASCII, but below initial n
            // This never occurs for Punycode, so ignore in coverage
            // @codeCoverageIgnoreStart
            elseif ($char < $n) {
                throw new Requests_Exception('Invalid character', 'idna.character_outside_domain', $char);
            }
            // @codeCoverageIgnoreEnd
            else {
                $extended[$char] = true;
            }
        }
        $extended = array_keys($extended);
        sort($extended);
        $b = $h;
        // [copy them] followed by a delimiter if b > 0
        if (strlen($output) > 0) {
            $output .= '-';
        }
        // {if the input contains a non-basic code point < n then fail}
        // while h < length(input) do begin
        $codepointcount = count($codepoints);
        while ($h < $codepointcount) {
            // let m = the minimum code point >= n in the input
            $m = array_shift($extended);
            //printf('next code point to insert is %s' . PHP_EOL, dechex($m));
            // let delta = delta + (m - n) * (h + 1), fail on overflow
            $delta += ($m - $n) * ($h + 1);
            // let n = m
            $n = $m;
            // for each code point c in the input (in order) do begin
            for ($num = 0; $num < $codepointcount; $num++) {
                $c = $codepoints[$num];
                // if c < n then increment delta, fail on overflow
                if ($c < $n) {
                    $delta++;
                }
                // if c == n then begin
                elseif ($c === $n) {
                    // let q = delta
                    $q = $delta;
                    // for k = base to infinity in steps of base do begin
                    for ($k = self::BOOTSTRAP_BASE; ; $k += self::BOOTSTRAP_BASE) {
                        // let t = tmin if k <= bias {+ tmin}, or
                        //     tmax if k >= bias + tmax, or k - bias otherwise
                        if ($k <= ($bias + self::BOOTSTRAP_TMIN)) {
                            $t = self::BOOTSTRAP_TMIN;
                        }
                        elseif ($k >= ($bias + self::BOOTSTRAP_TMAX)) {
                            $t = self::BOOTSTRAP_TMAX;
                        }
                        else {
                            $t = $k - $bias;
                        }
                        // if q < t then break
                        if ($q < $t) {
                            break;
                        }
                        // output the code point for digit t + ((q - t) mod (base - t))
                        $digit   = $t + (($q - $t) % (self::BOOTSTRAP_BASE - $t));
                        $output .= self::digit_to_char($digit);
                        // let q = (q - t) div (base - t)
                        $q = floor(($q - $t) / (self::BOOTSTRAP_BASE - $t));
                    } // end
                    // output the code point for digit q
                    $output .= self::digit_to_char($q);
                    // let bias = adapt(delta, h + 1, test h equals b?)
                    $bias = self::adapt($delta, $h + 1, $h === $b);
                    // let delta = 0
                    $delta = 0;
                    // increment h
                    $h++;
                } // end
            } // end
            // increment delta and n
            $delta++;
            $n++;
        } // end

        return $output;
    }

    /**
     * Convert a digit to its respective character
     *
     * @see https://tools.ietf.org/html/rfc3492#section-5
     * @throws Requests_Exception On invalid digit (`idna.invalid_digit`)
     *
     * @param int $digit Digit in the range 0-35
     * @return string Single character corresponding to digit
     */
    protected static function digit_to_char($digit) {
        // @codeCoverageIgnoreStart
        // As far as I know, this never happens, but still good to be sure.
        if ($digit < 0 || $digit > 35) {
            throw new Requests_Exception(sprintf('Invalid digit %d', $digit), 'idna.invalid_digit', $digit);
        }
        // @codeCoverageIgnoreEnd
        $digits = 'abcdefghijklmnopqrstuvwxyz0123456789';
        return substr($digits, $digit, 1);
    }

    /**
     * Adapt the bias
     *
     * @see https://tools.ietf.org/html/rfc3492#section-6.1
     * @param int $delta
     * @param int $numpoints
     * @param bool $firsttime
     * @return int New bias
     *
     * function adapt(delta,numpoints,firsttime):
     */
    protected static function adapt($delta, $numpoints, $firsttime) {
        // if firsttime then let delta = delta div damp
        if ($firsttime) {
            $delta = floor($delta / self::BOOTSTRAP_DAMP);
        }
        // else let delta = delta div 2
        else {
            $delta = floor($delta / 2);
        }
        // let delta = delta + (delta div numpoints)
        $delta += floor($delta / $numpoints);
        // let k = 0
        $k = 0;
        // while delta > ((base - tmin) * tmax) div 2 do begin
        $max = floor(((self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN) * self::BOOTSTRAP_TMAX) / 2);
        while ($delta > $max) {
            // let delta = delta div (base - tmin)
            $delta = floor($delta / (self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN));
            // let k = k + base
            $k += self::BOOTSTRAP_BASE;
        } // end
        // return k + (((base - tmin + 1) * delta) div (delta + skew))
        return $k + floor(((self::BOOTSTRAP_BASE - self::BOOTSTRAP_TMIN + 1) * $delta) / ($delta + self::BOOTSTRAP_SKEW));
    }
}