<?php

namespace WordfenceLS\Crypto;
/**
 * Binary-to-text PHP Utilities
 *
 * @package     binary-to-text-php
 * @link        https://github.com/ademarre/binary-to-text-php
 * @author      Andre DeMarre
 * @copyright   2009-2013 Andre DeMarre
 * @license     https://opensource.org/licenses/MIT  MIT
 */

/**
 * Class for binary-to-text encoding with a base of 2^n
 *
 * The Base2n class is for binary-to-text conversion. It employs a
 * generalization of the algorithms used by many encoding schemes that
 * use a fixed number of bits to encode each character. In other words,
 * the base is a power of 2.
 *
 * Earlier versions of this class were named
 * FixedBitNotation and FixedBitEncoding.
 *
 * @package binary-to-text-php
 */
class Model_Base2n
{
	protected $_chars;
	protected $_bitsPerCharacter;
	protected $_radix;
	protected $_rightPadFinalBits;
	protected $_padFinalGroup;
	protected $_padCharacter;
	protected $_caseSensitive;
	protected $_charmap;
	
	/**
	 * Constructor
	 *
	 * @param   integer $bitsPerCharacter   Bits to use for each encoded character
	 * @param   string  $chars              Base character alphabet
	 * @param   boolean $caseSensitive      To decode in a case-sensitive manner
	 * @param   boolean $rightPadFinalBits  How to encode last character
	 * @param   boolean $padFinalGroup      Add padding to end of encoded output
	 * @param   string  $padCharacter       Character to use for padding
	 *
	 * @throws  InvalidArgumentException    for incompatible parameters
	 */
	public function __construct(
		$bitsPerCharacter,
		$chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_',
		$caseSensitive = TRUE, $rightPadFinalBits = FALSE,
		$padFinalGroup = FALSE, $padCharacter = '=')
	{
		// Ensure validity of $chars
		if (!is_string($chars) || ($charLength = strlen($chars)) < 2) {
			throw new \InvalidArgumentException('$chars must be a string of at least two characters');
		}
		
		// Ensure validity of $padCharacter
		if ($padFinalGroup) {
			if (!is_string($padCharacter) || !isset($padCharacter[0])) {
				throw new \InvalidArgumentException('$padCharacter must be a string of one character');
			}
			
			if ($caseSensitive) {
				$padCharFound = strpos($chars, $padCharacter[0]);
			} else {
				$padCharFound = stripos($chars, $padCharacter[0]);
			}
			
			if ($padCharFound !== FALSE) {
				throw new \InvalidArgumentException('$padCharacter can not be a member of $chars');
			}
		}
		
		// Ensure validity of $bitsPerCharacter
		if (!is_int($bitsPerCharacter)) {
			throw new \InvalidArgumentException('$bitsPerCharacter must be an integer');
		}
		
		if ($bitsPerCharacter < 1) {
			// $bitsPerCharacter must be at least 1
			throw new \InvalidArgumentException('$bitsPerCharacter can not be less than 1');
			
		} elseif ($charLength < 1 << $bitsPerCharacter) {
			// Character length of $chars is too small for $bitsPerCharacter
			// Find greatest acceptable value of $bitsPerCharacter
			$bitsPerCharacter = 1;
			$radix = 2;
			
			while ($charLength >= ($radix <<= 1) && $bitsPerCharacter < 8) {
				$bitsPerCharacter++;
			}
			
			$radix >>= 1;
			throw new \InvalidArgumentException(
				'$bitsPerCharacter can not be more than ' . $bitsPerCharacter
				. ' given $chars length of ' . $charLength
				. ' (max radix ' . $radix . ')');
			
		} elseif ($bitsPerCharacter > 8) {
			// $bitsPerCharacter must not be greater than 8
			throw new \InvalidArgumentException('$bitsPerCharacter can not be greater than 8');
			
		} else {
			$radix = 1 << $bitsPerCharacter;
		}
		
		$this->_chars             = $chars;
		$this->_bitsPerCharacter  = $bitsPerCharacter;
		$this->_radix             = $radix;
		$this->_rightPadFinalBits = $rightPadFinalBits;
		$this->_padFinalGroup     = $padFinalGroup;
		$this->_padCharacter      = $padCharacter[0];
		$this->_caseSensitive     = $caseSensitive;
	}
	
	/**
	 * Encode a string
	 *
	 * @param   string  $rawString  Binary data to encode
	 * @return  string
	 */
	public function encode($rawString)
	{
		// Unpack string into an array of bytes
		$bytes = unpack('C*', $rawString);
		$byteCount = count($bytes);
		
		$encodedString = '';
		$byte = array_shift($bytes);
		$bitsRead = 0;
		$oldBits = 0;
		
		$chars             = $this->_chars;
		$bitsPerCharacter  = $this->_bitsPerCharacter;
		$rightPadFinalBits = $this->_rightPadFinalBits;
		$padFinalGroup     = $this->_padFinalGroup;
		$padCharacter      = $this->_padCharacter;
		
		$charsPerByte = 8 / $bitsPerCharacter;
		$encodedLength = $byteCount * $charsPerByte;
		
		// Generate encoded output; each loop produces one encoded character
		for ($c = 0; $c < $encodedLength; $c++) {
			
			// Get the bits needed for this encoded character
			if ($bitsRead + $bitsPerCharacter > 8) {
				// Not enough bits remain in this byte for the current character
				// Save the remaining bits before getting the next byte
				$oldBitCount = 8 - $bitsRead;
				$oldBits = $byte ^ ($byte >> $oldBitCount << $oldBitCount);
				$newBitCount = $bitsPerCharacter - $oldBitCount;
				
				if (!$bytes) {
					// Last bits; match final character and exit loop
					if ($rightPadFinalBits) $oldBits <<= $newBitCount;
					$encodedString .= $chars[$oldBits];
					
					if ($padFinalGroup) {
						// Array of the lowest common multiples of $bitsPerCharacter and 8, divided by 8
						$lcmMap = array(1 => 1, 2 => 1, 3 => 3, 4 => 1, 5 => 5, 6 => 3, 7 => 7, 8 => 1);
						$bytesPerGroup = $lcmMap[$bitsPerCharacter];
						$pads = $bytesPerGroup * $charsPerByte - ceil((strlen($rawString) % $bytesPerGroup) * $charsPerByte);
						$encodedString .= str_repeat($padCharacter, $pads);
					}
					
					break;
				}
				
				// Get next byte
				$byte = array_shift($bytes);
				$bitsRead = 0;
				
			} else {
				$oldBitCount = 0;
				$newBitCount = $bitsPerCharacter;
			}
			
			// Read only the needed bits from this byte
			$bits = $byte >> 8 - ($bitsRead + ($newBitCount));
			$bits ^= $bits >> $newBitCount << $newBitCount;
			$bitsRead += $newBitCount;
			
			if ($oldBitCount) {
				// Bits come from seperate bytes, add $oldBits to $bits
				$bits = ($oldBits << $newBitCount) | $bits;
			}
			
			$encodedString .= $chars[$bits];
		}
		
		return $encodedString;
	}
	
	/**
	 * Decode a string
	 *
	 * @param   string  $encodedString  Data to decode
	 * @param   boolean $strict         Returns NULL if $encodedString contains an undecodable character
	 * @return  string
	 */
	public function decode($encodedString, $strict = FALSE)
	{
		if (!$encodedString || !is_string($encodedString)) {
			// Empty string, nothing to decode
			return '';
		}
		
		$chars             = $this->_chars;
		$bitsPerCharacter  = $this->_bitsPerCharacter;
		$radix             = $this->_radix;
		$rightPadFinalBits = $this->_rightPadFinalBits;
		$padFinalGroup     = $this->_padFinalGroup;
		$padCharacter      = $this->_padCharacter;
		$caseSensitive     = $this->_caseSensitive;
		
		// Get index of encoded characters
		if ($this->_charmap) {
			$charmap = $this->_charmap;
			
		} else {
			$charmap = array();
			
			for ($i = 0; $i < $radix; $i++) {
				$charmap[$chars[$i]] = $i;
			}
			
			$this->_charmap = $charmap;
		}
		
		// The last encoded character is $encodedString[$lastNotatedIndex]
		$lastNotatedIndex = strlen($encodedString) - 1;
		
		// Remove trailing padding characters
		if ($padFinalGroup) {
			while ($encodedString[$lastNotatedIndex] === $padCharacter) {
				$encodedString = substr($encodedString, 0, $lastNotatedIndex);
				$lastNotatedIndex--;
			}
		}
		
		$rawString = '';
		$byte = 0;
		$bitsWritten = 0;
		
		// Convert each encoded character to a series of unencoded bits
		for ($c = 0; $c <= $lastNotatedIndex; $c++) {
			
			if (!$caseSensitive && !isset($charmap[$encodedString[$c]])) {
				// Encoded character was not found; try other case
				if (isset($charmap[$cUpper = strtoupper($encodedString[$c])])) {
					$charmap[$encodedString[$c]] = $charmap[$cUpper];
					
				} elseif (isset($charmap[$cLower = strtolower($encodedString[$c])])) {
					$charmap[$encodedString[$c]] = $charmap[$cLower];
				}
			}
			
			if (isset($charmap[$encodedString[$c]])) {
				$bitsNeeded = 8 - $bitsWritten;
				$unusedBitCount = $bitsPerCharacter - $bitsNeeded;
				
				// Get the new bits ready
				if ($bitsNeeded > $bitsPerCharacter) {
					// New bits aren't enough to complete a byte; shift them left into position
					$newBits = $charmap[$encodedString[$c]] << $bitsNeeded - $bitsPerCharacter;
					$bitsWritten += $bitsPerCharacter;
					
				} elseif ($c !== $lastNotatedIndex || $rightPadFinalBits) {
					// Zero or more too many bits to complete a byte; shift right
					$newBits = $charmap[$encodedString[$c]] >> $unusedBitCount;
					$bitsWritten = 8; //$bitsWritten += $bitsNeeded;
					
				} else {
					// Final bits don't need to be shifted
					$newBits = $charmap[$encodedString[$c]];
					$bitsWritten = 8;
				}
				
				$byte |= $newBits;
				
				if ($bitsWritten === 8 || $c === $lastNotatedIndex) {
					// Byte is ready to be written
					$rawString .= pack('C', $byte);
					
					if ($c !== $lastNotatedIndex) {
						// Start the next byte
						$bitsWritten = $unusedBitCount;
						$byte = ($charmap[$encodedString[$c]] ^ ($newBits << $unusedBitCount)) << 8 - $bitsWritten;
					}
				}
				
			} elseif ($strict) {
				// Unable to decode character; abort
				return NULL;
			}
		}
		
		return $rawString;
	}
}