HTML Minification

minify.php

<?php

define('SAFE', 1);
define('EXTREME', 2);
define('EXTREME_SAVE_COMMENTS', 4);
define('EXTREME_SAVE_PRE', 3);

function minify($html, $level=2)
{
	switch((int)$level)
	{
		case 0:
			//Don't minify
		break;
		
		case 1: //Safe Minify
		
			// Replace all whitespace characters between tags with a single space
			$html = preg_replace("`>\s+<`", "> <", $html);
		break;
		
		case 2: //Extreme Minify
			
			// Placeholder to save conditional comment hack, <pre> and <code> tags
			$place_holders = array(
				'<!-->' => '_!--_',
			);
			
			//Set placeholders
			$html = strtr($html, $place_holders);
			
			// Remove all normal comments - save conditionals
			$html = preg_replace('/<!--[^(\[|(<!))](.*)-->/Uis', '', $html);
			
			// Replace all whitespace characters with a single space
			$html = preg_replace("`\s+`", " ", $html);
			
			// Remove the spaces between adjacent html tags
			$html = preg_replace("`> <`", "><", $html);
			
			// Replace space between adjacent a tags for readability
			$html = str_replace("</a><a", "</a> <a", $html);
			
			// Restore placeholders
			$html = strtr($html, array_flip($place_holders));
		break;
		
		case 3: //Extreme, save pre and code tags
			// Placeholder to save conditional comment hack, <pre> and <code> tags
			$place_holders = array(
				'<!-->' => '_!--_',
				'<pre>' => '_pre_',
				'</pre>' => '_/pre_',
				'<code>' => '_code_',
				'</code>' => '_/code_'
			);
			
			//Set placeholders
			$html = strtr($html, $place_holders);
			
			// Remove all normal comments - save conditionals
			$html = preg_replace('/<!--[^(\[|(<!))](.*)-->/Uis', '', $html);
			
			// Replace all whitespace characters with a single space
			$html = preg_replace(">`\s+`<", "> <", $html);
			
			// Remove the spaces between adjacent html tags
			$html = preg_replace("`> <`", "><", $html);
			
			// Replace space between adjacent a tags for readability
			$html = str_replace("</a><a", "</a> <a", $html);
			
			// Restore placeholders
			$html = strtr($html, array_flip($place_holders));
		
		break;
		
		case 4: //Extreme minify, save comments
			
			// Replace all whitespace characters with a single space
			$html = preg_replace("`\s+`", " ", $html);
			
			// Remove spaces between adjacent html tags
			$html = preg_replace("`> <`", "><", $html);
			
			// Restore space between ajacent a tags
			$html = str_replace("</a><a", "</a> <a", $html);
		break;
	}

	//Normalize ampersands
	$html = str_replace("&amp;", "&", $html);
	$html = str_replace("&", "&amp;", $html);
	
	//Replace common entities with more compatible versions
	$replace = array(
		'&nbsp;' => '&#160;',
		'&copy;' => '&#169;',
		'&acirc;' => '&#226;',
		'&cent;' => '&#162;',
		'&raquo;' => '&#187;',
		'&laquo;' => '&#171;'
	);
	
	$html = strtr($html, $replace);
	
	//Return minified html
	return $html;
}