<?php

	/* Version: 1.3 - now with more cache */
	
	define('DEBUG',              false);    // Write debugging information to a log file
	define('SEND_ETAG',          true);     // You will want to disable this if you load balance multiple servers 
	define('SEND_EXPIRES',       true);     // 
	define('SEND_CACHE_CONTROL', true);     // 
	define('CACHE_TIME',         24*60*60); // default: 1 day

	$document_root  = $_SERVER['DOCUMENT_ROOT'];
	$requested_uri  = parse_url(urldecode($_SERVER['REQUEST_URI']), PHP_URL_PATH);
	$requested_file = basename($requested_uri);
	$source_file    = $document_root.$requested_uri;
	$source_ext     = strtolower(pathinfo($source_file, PATHINFO_EXTENSION));

	if (DEBUG) {
		$_debug_fh = fopen('retinaimages.log', 'a');
		fwrite($_debug_fh, "* * * * * * * * * * * * * * * * * * * * * * * * * * * *\n\n");
		fwrite($_debug_fh, print_r($_COOKIE, true)."\n\n");
		fwrite($_debug_fh, "document_root:     {$document_root}\n");
		fwrite($_debug_fh, "requested_uri:     {$requested_uri}\n");
		fwrite($_debug_fh, "requested_file:    {$requested_file}\n");
		fwrite($_debug_fh, "source_file:       {$source_file}\n");
		fwrite($_debug_fh, "source_ext:        {$source_ext}\n");
	}

	// Image was requested
	if (in_array($source_ext, array('png', 'gif', 'jpg', 'jpeg', 'bmp'))) {

		// Check if DPR is high enough to warrant retina image
		if (DEBUG) { fwrite($_debug_fh, "devicePixelRatio:  {$_COOKIE['devicePixelRatio']}\n"); }
		if (isset($_COOKIE['devicePixelRatio']) && intval($_COOKIE['devicePixelRatio']) > 1) {
			// Check if retina image exists
			$retina_file = pathinfo($source_file, PATHINFO_DIRNAME).'/'.pathinfo($source_file, PATHINFO_FILENAME).'@2x.'.pathinfo($source_file, PATHINFO_EXTENSION);
			if (DEBUG) { fwrite($_debug_fh, "retina_file:       {$retina_file}\n"); }
			if (file_exists($retina_file)) {
				$source_file = $retina_file;
			}
		}


		// Send cache headers
		if (SEND_CACHE_CONTROL) {
			header('Cache-Control: private, max-age='.CACHE_TIME, true);  
		}
		if (SEND_EXPIRES) {
			date_default_timezone_set('GMT');
			header('Expires: '.gmdate('D, d M Y H:i:s', time()+CACHE_TIME).' GMT', true);
		}
		if (SEND_ETAG) {
			$etag = '"'.fileinode($source_file).'"';
			header("ETag: $etag", true);

			if (DEBUG) {
				fwrite($_debug_fh, "generated etag:    {$etag}\n");
				if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
					fwrite($_debug_fh, "received etag:     {$_SERVER['HTTP_IF_NONE_MATCH']}\n\n");
				}
			}

			if (isset($_SERVER['HTTP_IF_NONE_MATCH']) && ($_SERVER['HTTP_IF_NONE_MATCH']) === $etag) {
				// File in cache hasn't change
				header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($source_file)).' GMT', true, 304);
				exit();
			}
		}
		if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && (strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) === filemtime($source_file))) {
			// File in cache hasn't change
			header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($source_file)).' GMT', true, 304);
			exit();
		}

		// Send image headers
		if (in_array($source_ext, array('png', 'gif', 'jpeg', 'bmp'))) {
			header("Content-Type: image/".$source_ext, true);
		}
		else {
			header("Content-Type: image/jpeg", true);
		}
		header('Content-Length: '.filesize($source_file), true);

		// Close debug session if open
		if (DEBUG) {
			fwrite($_debug_fh, "sending file:      {$source_file}\n\n");
			fclose($_debug_fh);
		}

		// Send file
		readfile($source_file);
		exit();
	}

	// DPR value was sent
	elseif(isset($_GET['devicePixelRatio'])) {
		$dpr = $_GET['devicePixelRatio'];

		// Validate value before setting cookie
		if (''.intval($dpr) !== $dpr) {
			$dpr = '1';
		}

		setcookie('devicePixelRatio', $dpr);
		exit();
	}

	// Respond with an empty content
	header('HTTP/1.1 204 No Content', true);