<?php

$strings = array('This is an example of encoding strings', 'wrox.com', 'really basic encoding');

foreach($strings as $string)
{
	echo 'String: ' . $string . '<br />';
	echo 'Encoded: ' . do_encode($string) . '<br /><br />';
}

$string = do_encode($strings[0]);
echo '<br /><br />';
echo 'String: ' . $strings[0] . '<br />';
echo 'Encoded: ' . $string . '<br />';
echo 'Decoded: ' . do_encode($string, true) . '<br />';


/*
* Encode the passed string
* passing 'true' as the second parameter will decode and encoded string
*/
function do_encode($string, $decode = false)
{
	$code = array();
	
	if( !sizeof($code) )
	{
		$a = range('a', 'z');
		$b = range('b', 'z');
		$b[] = 'a';

		if( !$decode )
		{
			$code = array_combine($a, $b);
		}
		else
		{
			$code = array_combine($b, $a);
		}
		unset($a, $b);
	}

	$return = '';
	for($i = 0, $i_end = strlen($string); $i < $i_end; $i++)
	{
		if( array_key_exists(substr($string, $i, 1), $code) )
		{
			$return .= $code[substr($string, $i, 1)];
		}
		else
		{
			$return .= substr($string, $i, 1);
		}
	}
	
	return $return;
}

?>