Code is need some optimisations, but I needed to do it fast
Well ok, instruction:
1. Download minify from http://code.google.com/p/minify/
2. Unpack Compressor.php from /min/lib/Minify/CSS/ to sapphire/thirdparty/minify
3. Open sapphire/core/Requirements.php
4. Find and replace foreach on 1000th line with that =))

foreach(array_diff($fileList, $this->blocked) as $file) {
				$fileContent = file_get_contents($base . $file);
				// if we have a javascript file and jsmin is enabled, minify the content
				$isJS = stripos($file, '.js');
				if($isJS && $this->combine_js_with_jsmin) {
					require_once('thirdparty/jsmin/jsmin.php');
					
					increase_time_limit_to();
					$fileContent = JSMin::minify($fileContent);
				} else {
					$isCSS = stripos($file, '.css');
					if($isCSS) {
						require_once('thirdparty/minify/Compressor.php');
						increase_time_limit_to();
						$fileContent = Minify_CSS_Compressor::process($fileContent);
					}					
				}
				
				// write a header comment for each file for easier identification and debugging
				// also the semicolon between each file is required for jQuery to be combinable properly
				$combinedData .= "/****** FILE: $file *****/\n" . $fileContent . "\n".($isJS ? ';' : '')."\n";
			}

To-do:

1. replace $isCSS && $isJS with one property
2. add $this->combine_css_with_minify property
3. add minify option for all required css's (not only combined)
4. like 3rd, but for JS and JSmin

Note that 2.4 is using compressed javascript files for combined files.

You can do the same for CSS without touching core files.

See this method in Page::init();

http://www.sspaste.com/paste/show/4c2d0737ae58e

You have to set the site in live mode to use combined files.....

jsmin doesn't minify css and google minify deletes all comments, spaces, new lines and etc in css files

See this part:

if(file_exists(Director::baseFolder() . '/' .$combinepath.'/combined.css')){
				$bf = file_get_contents(Director::baseFolder() . '/' .$combinepath.'/combined.css');
				$bf = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $bf);
				$bf = str_replace(array("\r\n", "\r", "\n", "\t", '  ', '    ', '    '), '', $bf);
				$fh = fopen(Director::baseFolder() . '/' .$combinepath.'/combined.css', 'w');
				fwrite($fh, $bf);
				fclose($fh);
			}

Great stuff.

I was looking for a way of doing just this and came across minify.

Think I'll use a combination of both ideas, create a class based on minify and call it using Martijn's method. That way I get the best of both worlds; an external library to do the work and no need to edit core files.

Cheers,

Rich

Tonyair I think this would be good to have in core. I think it might have an older version which needs upgrading anyway and being able to combine CSS as well as JS by default would be good.

If you can get the contents of this thread together and submit a patch it would be good to include. See http://doc.silverstripe.org/contributing#submitting_patches for submission guidelines.

Of note;

There's a nice project in PHP Minify that handles CSS & JS minification & combining, and support some "advanced" features like skipping files w/ a .min.(css|js) extension (already minified files) while processing as well as security & group definitions.

Project URL is: http://code.google.com/p/minify/

It would be great to see SS combine_files on par w/ this project, or perhaps to utilize it instead.

Willr, i will be glad, but I made too many changes so I can update my version only manually.
For example i changed structure of SS I believe that in public_html should be placed only public files like css, images, javascript, swf, assets and index.php all other files should be placed in the upper directory