Symphony RDF content negotiation (hacky as crap)

extension.driver.php

<?php
	require_once(CORE . '/class.frontend.php');
	
	Class extension_seme4_semantics extends Extension {
		
		public function about()	{
			return array('name' => 'Seme4 Semantics',
						 'version' => '1.1',
						 'release-date' => '2010-03-01',
						 'author' => array('name' => 'Nick Dunn',
											 'website' => 'http://nick-dunn.co.uk/',
											 'email' => 'nick@nick-dunn.co.uk'),
 						 'description' => 'Allows content negotiation for URIs and serving of HTML and RDF versions.'
				 		);
		}
		
		public function getSubscribedDelegates() {
			return array(
				array(
					'page'		=> '/frontend/',
					'delegate'	=> 'FrontendInitialised',
					'callback'	=> 'frontendInitialised'
				)
			);
		}

		/*-------------------------------------------------------------------------
			Caching
		-------------------------------------------------------------------------*/
		
	public function frontendInitialised(&$context) {			

		$uri = getCurrentPage();
		$uri = trim($uri, '/');
	
		// is the request for a specific render resource (HTML or RDF)
		if (preg_match('/(rdf|html)$/', $uri)) {
			$extension = end(explode('.', $uri));
		}
	
		// translate URL into a possible RDF file name
		$rdf_file = preg_replace('/\//', '-', $uri);
		// remove file extension from end of URI
		if ($extension) $rdf_file = preg_replace('/.' . $extension . '$/', '', $rdf_file);
		$rdf_file = trim($rdf_file, '-');
		$rdf_file .= '.rdf';
	
		$rdf_file_path = WORKSPACE . '/rdf/' . $rdf_file;
	
		// does the client accept application/rdf+xml?
		$accepts_rdf = preg_match('/application\/rdf\+xml/', $_SERVER['HTTP_ACCEPT']);
	
		// if the RDF file exists, this URI has been semanticised...		
		if (file_exists($rdf_file_path)) {
		
			// no extension (this is the resource identifier URI), so perform content negotiation
			if (!$extension) {
				$resource_type = 'html';
				if ($accepts_rdf) $resource_type = 'rdf';
				header('Location: ' . URL . '/' . $uri . '.' . $resource_type, true, 303);
			}
			// this is not a resource identifier URI, but a rendering, so serve correct content
			else {
				switch ($extension) {
					// read RDF file
					case 'rdf':
						$rdf_data = fopen($rdf_file_path, 'r');
						header('Content-Type: application/rdf+xml');							
						echo fread($rdf_data, filesize($rdf_file_path));
						fclose($rdf_data);				
						exit();
					break;
					// manipulate URL and allow Symphony to serve
					case 'html':
						$context['page'] = preg_replace('/.' . $extension . '$/', '', $uri);
					break;
				}
			}
		
		}
		// no RDF exists
		else {
			// but client is expecting RDF
			if ($accepts_rdf) header("HTTP/1.1 406 Not acceptable");
		}
	}

	}