<?php
	/* Version: 1.0 */

	$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));

	// 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 (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 (file_exists($retina_file)) {
				$source_file = $retina_file;
			}
		}

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

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

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

		// Tell the browser we are sending an image
		header("Content-Type: image/jpeg");

		// 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');