WordpressMinifyHTML

class WP_HTML_Compression
{
    // Settings
    protected $compress_css = true;
    protected $compress_js = true;
    protected $info_comment = true;
    protected $remove_comments = true;
    
    // Variables
    protected $html;
    public function __construct($html)
    {
        if (!empty($html)) {
            $this->parseHTML($html);
        }
    }
    public function __toString()
    {
        return $this->html;
    }
    protected function bottomComment($raw, $compressed)
    {
        $raw        = strlen($raw);
        $compressed = strlen($compressed);
        
        $savings = ($raw - $compressed) / $raw * 100;
        
        $savings = round($savings, 2);
        
        return '<!--HTML compressed, size saved ' . $savings . '%. From ' . $raw . ' bytes, now ' . $compressed . ' bytes-->';
    }
    protected function minifyHTML($html)
    {
        $pattern = '/<(?<script>script).*?<\/script\s*>|<(?<style>style).*?<\/style\s*>|<!(?<comment>--).*?-->|<(?<tag>[\/\w.:-]*)(?:".*?"|\'.*?\'|[^\'">]+)*>|(?<text>((<[^!\/\w.:-])?[^<]*)+)|/si';
        preg_match_all($pattern, $html, $matches, PREG_SET_ORDER);
        $overriding = false;
        $raw_tag    = false;
        // Variable reused for output
        $html       = '';
        foreach ($matches as $token) {
            $tag = (isset($token['tag'])) ? strtolower($token['tag']) : null;
            
            $content = $token[0];
            
            if (is_null($tag)) {
                if (!empty($token['script'])) {
                    $strip = $this->compress_js;
                } else if (!empty($token['style'])) {
                    $strip = $this->compress_css;
                } else if ($content == '<!--wp-html-compression no compression-->') {
                    $overriding = !$overriding;
                    
                    // Don't print the comment
                    continue;
                } else if ($this->remove_comments) {
                    if (!$overriding && $raw_tag != 'textarea') {
                        // Remove any HTML comments, except MSIE conditional comments
                        $content = preg_replace('/<!--(?!\s*(?:\[if [^\]]+]|<!|>))(?:(?!-->).)*-->/s', '', $content);
                    }
                }
            } else {
                if ($tag == 'pre' || $tag == 'textarea') {
                    $raw_tag = $tag;
                } else if ($tag == '/pre' || $tag == '/textarea') {
                    $raw_tag = false;
                } else {
                    if ($raw_tag || $overriding) {
                        $strip = false;
                    } else {
                        $strip = true;
                        
                        // Remove any empty attributes, except:
                        // action, alt, content, src
                        $content = preg_replace('/(\s+)(\w++(?<!\baction|\balt|\bcontent|\bsrc)="")/', '$1', $content);
                        
                        // Remove any space before the end of self-closing XHTML tags
                        // JavaScript excluded
                        $content = str_replace(' />', '/>', $content);
                    }
                }
            }
            
            if ($strip) {
                $content = $this->removeWhiteSpace($content);
            }
            
            $html .= $content;
        }
        
        return $html;
    }
    
    public function parseHTML($html)
    {
        $this->html = $this->minifyHTML($html);
        
        if ($this->info_comment) {
            $this->html .= "\n" . $this->bottomComment($html, $this->html);
        }
    }
    
    protected function removeWhiteSpace($str)
    {
        $str = str_replace("\t", ' ', $str);
        $str = str_replace("\n", '', $str);
        $str = str_replace("\r", '', $str);
        
        while (stristr($str, '  ')) {
            $str = str_replace('  ', ' ', $str);
        }
        
        return $str;
    }
}

function wp_html_compression_finish($html)
{
    return new WP_HTML_Compression($html);
}

function wp_html_compression_start()
{
    ob_start('wp_html_compression_finish');
}
add_action('get_header', 'wp_html_compression_start');