<?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));

	}

}