/Jyxo/Mail/Encoding.php

<?php declare(strict_types = 1);

/**
 * Jyxo PHP Library
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file license.txt.
 * It is also available through the world-wide-web at this URL:
 * https://github.com/jyxo/php/blob/master/license.txt
 */

namespace Jyxo\Mail;

use InvalidArgumentException;
use Jyxo\StringUtil;
use LogicException;
use function base64_encode;
use function chunk_split;
use function explode;
use function ord;
use function preg_replace_callback;
use function sprintf;
use function strlen;
use function strrpos;
use function substr;
use function trim;

/**
 * List of possible content encodings.
 *
 * @copyright Copyright (c) 2005-2011 Jyxo, s.r.o.
 * @license https://github.com/jyxo/php/blob/master/license.txt
 * @author Jaroslav Hanslík
 */
class Encoding
{

	/**
	 * 8-bit encoding.
	 */
	public const BIT8 = '8bit';

	/**
	 * 7-bit encoding.
	 */
	public const BIT7 = '7bit';

	/**
	 * Binary encoding.
	 */
	public const BINARY = 'binary';

	/**
	 * Base64 encoding.
	 */
	public const BASE64 = 'base64';

	/**
	 * Quoted printable encoding.
	 */
	public const QUOTED_PRINTABLE = 'quoted-printable';

	/**
	 * Constructor preventing from creating instances.
	 *
	 * @throws LogicException When trying to create an instance
	 */
	final public function __construct()
	{
		throw new LogicException(sprintf('Cannot create an instance of a static class %s.', static::class));
	}

	/**
	 * Checks if the given encoding is compatible.
	 *
	 * @param string $encoding Encoding name
	 * @return bool
	 */
	public static function isCompatible(string $encoding): bool
	{
		static $encodings = [
			self::BIT7 => true,
			self::BIT8 => true,
			self::BINARY => true,
			self::BASE64 => true,
			self::QUOTED_PRINTABLE => true,
		];

		return isset($encodings[$encoding]);
	}

	/**
	 * Encodes a string using the given encoding.
	 *
	 * @param string $string Input string
	 * @param string $encoding Encoding name
	 * @param int $lineLength Line length
	 * @param string $lineEnd Line ending
	 * @return string
	 * @throws InvalidArgumentException If an incompatible encoding was provided
	 */
	public static function encode(string $string, string $encoding, int $lineLength, string $lineEnd): string
	{
		switch ($encoding) {
			case self::BASE64:
				return self::encodeBase64($string, $lineLength, $lineEnd);
			case self::BIT7:
				// Break missing intentionally
			case self::BIT8:
				return StringUtil::fixLineEnding(trim($string), $lineEnd) . $lineEnd;
			case self::QUOTED_PRINTABLE:
				return self::encodeQuotedPrintable($string, $lineLength, $lineEnd);
			case self::BINARY:
				return $string;
			default:
				throw new InvalidArgumentException(sprintf('Incompatible encoding %s.', $encoding));
		}
	}

	/**
	 * Encodes a string using the quoted-printable encoding.
	 *
	 * @param string $string Input string
	 * @param int $lineLength Line length
	 * @param string $lineEnd Line ending
	 * @return string
	 */
	private static function encodeQuotedPrintable(string $string, int $lineLength, string $lineEnd): string
	{
		$encoded = StringUtil::fixLineEnding(trim($string), $lineEnd);

		// Replaces all high ASCII characters, control codes and '='
		$encoded = preg_replace_callback('~([\000-\010\013\014\016-\037\075\177-\377])~', static function ($matches) {
			return '=' . sprintf('%02X', ord($matches[1]));
		}, $encoded);

		// Replaces tabs and spaces if on line ends
		$encoded = preg_replace_callback('~([\011\040])' . $lineEnd . '~', static function ($matches) use ($lineEnd) {
			return '=' . sprintf('%02X', ord($matches[1])) . $lineEnd;
		}, $encoded);

		$output = '';
		$lines = explode($lineEnd, $encoded);
		// Release from memory
		unset($encoded);
		foreach ($lines as $line) {
			// Line length is less than maximum
			if (strlen($line) <= $lineLength) {
				$output .= $line . $lineEnd;

				continue;
			}

			do {
				$partLength = strlen($line);
				if ($partLength > $lineLength) {
					$partLength = $lineLength;
				}

				// Cannot break a line in the middle of a character
				$pos = strrpos(substr($line, 0, $partLength), '=');
				if (($pos !== false) && ($pos >= $partLength - 2)) {
					$partLength = $pos;
				}

				// If the last char is a break, move one character backwards
				if (($partLength > 0) && ($line[$partLength - 1] === ' ')) {
					$partLength--;
				}

				// Saves string parts, trims the string and continues
				$output .= substr($line, 0, $partLength);
				$line = substr($line, $partLength);

				// We are in the middle of a line
				if (!empty($line)) {
					$output .= '=';
				}
				$output .= $lineEnd;
			} while (!empty($line));
		}

		return $output;
	}

	/**
	 * Encodes a string using the base64 encoding.
	 *
	 * @param string $string Input string
	 * @param int $lineLength Line length
	 * @param string $lineEnd Line ending
	 * @return string
	 */
	private static function encodeBase64(string $string, int $lineLength, string $lineEnd): string
	{
		return trim(chunk_split(base64_encode($string), $lineLength, $lineEnd));
	}

}