Media.php

<?php
/**
 * Lithium: the most rad php framework
 *
 * @copyright     Copyright 2010, Union of RAD (http://union-of-rad.org)
 * @license       http://opensource.org/licenses/bsd-license.php The BSD License
 */

namespace lithium\net\http;

use lithium\util\String;
use lithium\core\Libraries;
use lithium\net\http\MediaException;

/**
 * The `Media` class facilitates content-type mapping (mapping between content-types and file
 * extensions), handling static assets and globally configuring how the framework handles output in
 * different formats.
 *
 * Using the `Media` class, you can globally configure input and output of different types of
 * content, i.e.:
 * {{{ embed:lithium\tests\cases\net\http\MediaTest::testCustomEncodeHandler(4-12) }}}
 *
 * You may then render CSV content from anywhere in your application. For example, in a controller
 * you may do the following:
 *
 * {{{
 * 	$this->render(array('csv' => Post::find('all')));
 * }}}
 */
class Media extends \lithium\core\StaticObject {

	/**
	 * Maps file extensions to content-types.  Used to set response types and determine request
	 * types. Can be modified with `Media::type()`.
	 *
	 * @var array
	 * @see lithium\net\http\Media::type()
	 */
	protected static $_types = array();

	/**
	 * A map of media handler objects or callbacks, mapped to media types.
	 *
	 * @var array
	 */
	protected static $_handlers = array();

	/**
	 * Contains default path settings for various asset types.
	 *
	 * For each type, the corresponding array key maps to the general type name, i.e. `'js'` or
	 * `'image'`. Each type contains a set of keys which define their locations and default
	 * behavior. For more information how each key works, see `Media::assets()`.
	 *
	 * @var array
	 * @see lithium\net\http\Media::assets()
	 */
	protected static $_assets = array();

	/**
	 * Returns the list of registered media types.  New types can be set with the `type()` method.
	 *
	 * @return array Returns an array of media type extensions or short-names, which comprise the
	 *         list of types handled.
	 */
	public static function types() {
		return array_keys(static::_types());
	}

	/**
	 * Alias for `types()`; included for interface compatibility with
	 * `lithium\util\Collection::to()`, which allows a collection object to be exported to any
	 * format supported by a `Media` handler. See the documentation for `Collection::to()` for more
	 * information.
	 *
	 * @see lithium\net\http\Media
	 * @return array Returns the value of `Media::types()`.
	 */
	public static function formats() {
		return static::types();
	}

	/**
	 * Alias for `encode()`; included for interface compatibility with
	 * `lithium\util\Collection::to()`, which allows a collection object to be exported to any
	 * format supported by a `Media` handler. See the documentation for `Collection::to()` for more
	 * information.
	 *
	 * @param mixed $format Format into which data will be converted, i.e. `'json'`.
	 * @param mixed $data Either an array or object (usually an instance of `Collection`) which will
	 *              be converted into the specified format.
	 * @param array $options Additional handler-specific options to pass to the content handler.
	 * @return mixed
	 */
	public static function to($format, $data, array $options = array()) {
		return static::encode($format, $data, $options);
	}

	/**
	 * Maps a type name to a particular content-type (or multiple types) with a set of options, or
	 * retrieves information about a type that has been defined.
	 *
	 * Examples:
	 * {{{ embed:lithium\tests\cases\net\http\MediaTest::testMediaTypes(1-2) }}}
	 *
	 * {{{ embed:lithium\tests\cases\net\http\MediaTest::testMediaTypes(19-20) }}}
	 *
	 * {{{ embed:lithium\tests\cases\net\http\MediaTest::testMediaTypes(35-36) }}}
	 *
	 * Alternatively, can be used to detect the type name of a registered content type:
	 * {{{
	 * Media::type('application/json'); // returns 'json'
	 * Media::type('application/javascript'); // returns 'javascript'
	 * Media::type('text/javascript'); // also returns 'javascript'
	 *
	 * Media::type('text/html'); // returns 'html'
	 * Media::type('application/xhtml+xml'); // also returns 'html'
	 * }}}
	 *
	 * #### Content negotiation
	 *
	 * When creating custom media types, specifying which content-type(s) to match isn't always
	 * enough. For example, if you wish to serve a different set of templates to mobile web
	 * browsers, you'd still want those templates served as HTML. You might add something like this:
	 *
	 * {{{
	 * Media::type('mobile', array('application/xhtml+xml', 'text/html'));
	 * }}}
	 *
	 * However, this would cause _all_ requests for HTML content to be interpreted as
	 * `'mobile'`-type requests. Instead, we can use _content negotiation_ to granularly specify how
	 * to match a particular type. Content negotiation is the process of examining the HTTP headers
	 * provided in the request (including the content-types listed in the `Accept` header, and
	 * optionally other things as well, like the `Accept-Language` or `User-Agent` headers), in
	 * order to produce the best representation of the requested resource for the client; in other
	 * words, the resource that most closely matches what the client is asking for.
	 *
	 * Content negotiation with media types is made possible through the `'conditions'` key of the
	 * `$options` parameter, which contains an array of assertions made against the `Request`
	 * object. Each assertion (array key) can be one of three different things:
	 *
	 * - `'type'` _boolean_: In the default routing, some routes have `{:type}` keys, which are
	 *   designed to match file extensions in URLs. These values act as overrides for the HTTP
	 *   `Accept` header, allowing different formats to be served with the same content type. For
	 *    example, if you're serving [ JSONP](http://en.wikipedia.org/wiki/JSON#JSONP), you'll want
	 *    to serve it with the same content-type as JavaScript (since it is JavaScript), but you
	 *    probably won't want to use the same template(s) or other settings. Therefore, when serving
	 *    JSONP content, you can specify that the extension defined in the type must be present in
	 *    the URL:
	 *  {{{
	 *  Media::type('jsonp', array('text/html'), array(
	 *  	// template settings...
	 *  	'conditions' => array('type' => true)
	 *  ));
	 *  }}}
	 *  Then, JSONP content will only ever be served when the request URL ends in `.jsonp`.
	 *
	 * - `'<prefix>:<key>'` _string_: This type of assertion can be used to match against arbitrary
	 *   information in the request, including headers (i.e. `'http:user_agent'`), environment
	 *   varialbes (i.e. `'env:home'`), GET and POST data (i.e. `'query:foo'` or `'data:foo'`,
	 *   respectively), and the HTTP method (`'http:method'`) of the request. For more information
	 *   on possible keys, see `lithium\action\Request::get()`.
	 *
	 * - `'<detector>'` _boolean_: Uses detector checks added to the `Request` object to make
	 *   boolean assertions against the request. For example, if a detector called `'iPhone'` is
	 *   attached, you can add `'iPhone' => true` to the `'conditions'` array in order to filter for
	 *   iPhone requests only. See `lithium\action\Request::detect()` for more information on adding
	 *   detectors.
	 *
	 * @see lithium\net\http\Media::$_types
	 * @see lithium\net\http\Media::$_handlers
	 * @see lithium\net\http\Media::negotiate()
	 * @see lithium\action\Request::get()
	 * @see lithium\action\Request::is()
	 * @see lithium\action\Request::detect()
	 * @see lithium\util\String::insert()
	 * @param string $type A file-extension-style type name, i.e. `'txt'`, `'js'`, or `'atom'`.
	 *               Alternatively, a mapped content type, i.e. `'text/html'`,
	 *               `'application/atom+xml'`, etc.; in which case, the matching type name (i.e.
	 *               '`html'` or `'atom'`) will be returned.
	 * @param mixed $content Optional. A string or array containing the content-type(s) that
	 *        `$type` should map to.  If `$type` is an array of content-types, the first one listed
	 *        should be the "primary" type, and will be used as the `Content-type` header of any
	 *        `Response` objects served through this type.
	 * @param array $options Optional.  The handling options for this media type. Possible keys are:
	 *        - `'decode'` _mixed_: A (string) function name or (object) closure that handles
	 *          decoding or unserializing content from this format.
	 *        - `'encode'` _mixed_: A (string) function name or (object) closure that handles
	 *          encoding or serializing content into this format.
	 *        - `'cast'` _boolean_: Used with `'encode'`. If `true`, all data passed into the
	 *          specified encode function is first cast to array structures.
	 *        - `'layout'` _mixed_: Specifies one or more `String::insert()`-style paths to use when
	 *          searching for layout files (either a string or array of strings).
	 *        - `'template'` _mixed_: Specifies one or more `String::insert()`-style paths to use
	 *          when searching for template files (either a string or array of strings).
	 *        - `'view'` _string_: Specifies the view class to use when rendering this content.
	 *        - `'conditions'` _array_: Optional key/value pairs used as assertions in content
	 *          negotiation. See the above section on **Content Negotiation**.
	 * @return mixed If `$content` and `$options` are empty, returns an array with `'content'` and
	 *         `'options'` keys, where `'content'` is the content-type(s) that correspond to
	 *         `$type` (can be a string or array, if multiple content-types are available), and
	 *         `'options'` is the array of options which define how this content-type should be
	 *         handled.  If `$content` or `$options` are non-empty, returns `null`.
	 */
	public static function type($type, $content = null, array $options = array()) {
		$defaults = array(
			'view' => false,
			'template' => false,
			'layout' => false,
			'encode' => false,
			'decode' => false,
			'cast'   => true,
			'conditions' => array(),
		);

		if ($content === false) {
			unset(static::$_types[$type], static::$_handlers[$type]);
		}
		if (!$content && !$options) {
			if (!$content = static::_types($type)) {
				return;
			}
			if (strpos($type, '/')) {
				return $content;
			}
			if (is_array($content) && isset($content['alias'])) {
				return static::type($content['alias']);
			}
			return compact('content') + array('options' => static::_handlers($type));
		}
		if ($content) {
			static::$_types[$type] = $content;
		}
		static::$_handlers[$type] = $options ? ($options + $defaults) : array();
	}

	/**
	 * Performs content-type negotiation on a `Request` object, by iterating over the accepted
	 * types in sequence, from most preferred to least, and attempting to match each one against a
	 * content type defined by `Media::type()`, until a match is found. If more than one defined
	 * type matches for a given content type, they will be checked in the order they were added
	 * (usually, this corresponds to the order they were defined in the application bootstrapping
	 * process).
	 *
	 * @see lithium\net\http\Media::type()
	 * @see lithium\net\http\Media::match()
	 * @see lithium\action\Request
	 * @param object $request The instance of `lithium\action\Request` which contains the details of
	 *               the request to be content-negotiated.
	 * @return string Returns the first matching type name, i.e. `'html'` or `'json'`.
	 */
	public static function negotiate($request) {
		$self = get_called_class();

		$match = function($name) use ($self, $request) {
			if (($cfg = $self::type($name)) && $self::match($request, compact('name') + $cfg)) {
				return true;
			}
			return false;
		};

		if (($type = $request->type) && $match($type)) {
			return $type;
		}

		foreach ($request->accepts(true) as $type) {
			if (!$types = (array) static::_types($type)) {
				continue;
			}
			foreach ($types as $name) {
				if (!$match($name)) {
					continue;
				}
				return $name;
			}
		}
	}

	/**
	 * Assists `Media::negotiate()` in processing the negotiation conditions of a content type, by
	 * iterating through the conditions and checking each one against the `Request` object.
	 *
	 * @see lithium\net\http\Media::negotiate()
	 * @see lithium\net\http\Media::type()
	 * @see lithium\action\Request
	 * @param object $request The instance of `lithium\action\Request` to be checked against a
	 *               set of conditions (if applicable).
	 * @param array $config Represents a content type configuration, which is an array containing 3
	 *              keys:
	 *              - `'name'` _string_: The type name, i.e. `'html'` or `'json'`.
	 *              - `'content'` _mixed_: One or more content types that the configuration
	 *                represents, i.e. `'text/html'`, `'application/xhtml+xml'` or
	 *                `'application/json'`, or an array containing multiple content types.
	 *              - `'options'` _array_: An array containing rendering information, and an
	 *                optional `'conditions'` key, which contains an array of matching parameters.
	 *                For more details on these matching parameters, see `Media::type()`.
	 * @return boolean Returns `true` if the information in `$request` matches the type
	 *         configuration in `$config`, otherwise false.
	 */
	public static function match($request, array $config) {
		if (!isset($config['options']['conditions'])) {
			return true;
		}
		$conditions = $config['options']['conditions'];

		foreach ($conditions as $key => $value) {
			switch (true) {
				case $key == 'type':
					if ($value !== ($request->type === $config['name'])) {
						return false;
					}
				break;
				case strpos($key, ':'):
					if ($request->get($key) !== $value) {
						return false;
					}
				break;
				case ($request->is($key) !== $value):
					return false;
				break;
			}
		}
		return true;
	}

	/**
	 * Gets or sets options for various asset types.
	 *
	 * @see lithium\util\String::insert()
	 * @param string $type The name of the asset type, i.e. `'js'` or `'css'`.
	 * @param array $options If registering a new asset type or modifying an existing asset type,
	 *        contains settings for the asset type, where the available keys are as follows:
	 *        - `'suffix'`: The standard suffix for this content type, with leading dot ('.') if
	 *          applicable.
	 *        - `'filter'`: An array of key/value pairs representing simple string replacements to
	 *          be done on a path once it is generated.
	 *        - `'path'`: An array of key/value pairs where the keys are `String::insert()`
	 *          compatible paths, and the values are array lists of keys to be inserted into the
	 *          path string.
	 * @return array If `$type` is empty, an associative array of all registered types and all
	 *         associated options is returned. If `$type` is a string and `$options` is empty,
	 *         returns an associative array with the options for `$type`. If `$type` and `$options`
	 *         are both non-empty, returns `null`.
	 */
	public static function assets($type = null, $options = array()) {
		$defaults = array('suffix' => null, 'filter' => null, 'path' => array());

		if (!$type) {
			return static::_assets();
		}
		if ($options === false) {
			unset(static::$_assets[$type]);
		}
		if (!$options) {
			return static::_assets($type);
		}
		$options = (array) $options + $defaults;

		if ($base = static::_assets($type)) {
			$options = array_merge($base, array_filter($options));
		}
		static::$_assets[$type] = $options;
	}

	/**
	 * Calculates the web-accessible path to a static asset, usually a JavaScript, CSS or image
	 * file.
	 *
	 * @see lithium\net\http\Media::$_assets
	 * @see lithium\action\Request::env()
	 * @param string $path The path to the asset, relative to the given `$type`s path and without a
	 *        suffix. If the path contains a URI Scheme (eg. `http://`), no path munging will occur.
	 * @param string $type The asset type. See `Media::$_assets` or `Media::assets()`.
	 * @param array $options Contains setting for finding and handling the path, where the keys are
	 *        the following:
	 *        - `'base'`: The base URL of your application. Defaults to `null` for no base path.
	 *          This is usually set with the return value of a call to `env('base')` on an instance
	 *          of `lithium\action\Request`.
	 *        - `'check'`: Check for the existence of the file before returning. Defaults to
	 *          `false`.
	 *        - `'filter'`: An array of key/value pairs representing simple string replacements to
	 *          be done on a path once it is generated.
	 *        - `'path'`: An array of paths to search for the asset in. The paths should use
	 *          `String::insert()` formatting. See `Media::$_assets` for more.
	 *        - `suffix`: The suffix to attach to the path, generally a file extension.
	 *        - `'timestamp'`: Appends the last modified time of the file to the path if `true`.
	 *          Defaults to `false`.
	 *        - `'library'`: The name of the library from which to load the asset. Defaults to
	 *           `true`, for the default library.
	 * @return string Returns the publicly-accessible absolute path to the static asset. If checking
	 *         for the asset's existence (`$options['check']`), returns `false` if it does not exist
	 *         in your `/webroot` directory, or the `/webroot` directories of one of your included
	 *         plugins.
	 * @filter
	 */
	public static function asset($path, $type, array $options = array()) {
		$defaults = array(
			'base' => null,
			'timestamp' => false,
			'filter' => null,
			'path' => array(),
			'suffix' => null,
			'check' => false,
			'library' => true,
		);
		if (!$base = static::_assets($type)) {
			$type = 'generic';
			$base = static::_assets('generic');
		}
		$options += ($base + $defaults);
		$params = compact('path', 'type', 'options');

		return static::_filter(__FUNCTION__, $params, function($self, $params) {
			$path = $params['path'];
			$type = $params['type'];
			$options = $params['options'];
			$library = $options['library'];

			if (preg_match('/^[a-z0-9-]+:\/\//i', $path)) {
				return $path;
			}
			$config = Libraries::get($library);
			$paths = $options['path'];

			$config['default'] ? end($paths) : reset($paths);
			$options['library'] = basename($config['path']);

			if ($options['suffix'] && strpos($path, $options['suffix']) === false) {
				$path .= $options['suffix'];
			}

			if ($options['check'] || $options['timestamp']) {
				$file = $self::path($path, $type, $options);
			}

			if ($path[0] === '/') {
				if ($options['base'] && strpos($path, $options['base']) !== 0) {
					$path = "{$options['base']}{$path}";
				}
			} else {
				$path = String::insert(key($paths), compact('path') + $options);
			}

			if ($options['check'] && !is_file($file)) {
				return false;
			}

			if (is_array($options['filter']) && !empty($options['filter'])) {
				$keys = array_keys($options['filter']);
				$values = array_values($options['filter']);
				$path = str_replace($keys, $values, $path);
			}

			if ($options['timestamp'] && is_file($file)) {
				$separator = (strpos($path, '?') !== false) ? '&' : '?';
				$path .= $separator . filemtime($file);
			}
			return $path;
		});
	}

	/**
	 * Gets the physical path to the web assets (i.e. `/webroot`) directory of a library.
	 *
	 * @param string|boolean $library The name of the library for which to find the path, or `true`
	 *        for the default library.
	 * @return string Returns the physical path to the web assets directory for a library. For
	 *         example, the `/webroot` directory of the default library would be
	 *         `LITHIUM_APP_PATH . '/webroot'`.
	 */
	public static function webroot($library = true) {
		if (!$config = Libraries::get($library)) {
			return null;
		}
		if (isset($config['webroot'])) {
			return $config['webroot'];
		}
		if (isset($config['path'])) {
			return $config['path'] . '/webroot';
		}
	}

	/**
	 * Returns the physical path to an asset in the `/webroot` directory of an application or
	 * plugin.
	 *
	 * @param string $path The path to a web asset, relative to the root path for its type. For
	 *               example, for a JavaScript file in `/webroot/js/subpath/file.js`, the correct
	 *               value for `$path` would be `'subpath/file.js'`.
	 * @param string $type A valid asset type, i.e. `'js'`, `'cs'`, `'image'`, or another type
	 *               registered with `Media::assets()`, or `'generic'`.
	 * @param array $options The options used to calculate the path to the file.
	 * @return string Returns the physical filesystem path to an asset in the `/webroot` directory.
	 */
	public static function path($path, $type, array $options = array()) {
		$defaults = array(
			'base' => null,
			'path' => array(),
			'suffix' => null,
			'library' => true,
		);
		if (!$base = static::_assets($type)) {
			$type = 'generic';
			$base = static::_assets('generic');
		}
		$options += ($base + $defaults);
		$config = Libraries::get($options['library']);
		$root = static::webroot($options['library']);
		$paths = $options['path'];

		$config['default'] ? end($paths) : reset($paths);
		$options['library'] = basename($config['path']);

		if ($qOffset = strpos($path, '?')) {
			$path = substr($path, 0, $qOffset);
		}

		if ($path[0] === '/') {
			$file = $root . $path;
		} else {
			$template = str_replace('{:library}/', '', key($paths));
			$insert = array('base' => $root) + compact('path');
			$file = String::insert($template, $insert);
		}
		return realpath($file);
	}

	/**
	 * Renders data (usually the result of a controller action) and generates a string
	 * representation of it, based on the type of expected output.
	 *
	 * @param object $response A reference to a Response object into which the operation will be
	 *        rendered. The content of the render operation will be assigned to the `$body`
	 *        property of the object, and the `'Content-type'` header will be set accordingly.
	 * @param mixed $data
	 * @param array $options
	 * @return void
	 * @filter
	 */
	public static function render(&$response, $data = null, array $options = array()) {
		$params = array('response' => &$response) + compact('data', 'options');
		$types = static::_types();
		$handlers = static::_handlers();

		static::_filter(__FUNCTION__, $params, function($self, $params) use ($types, $handlers) {
			$defaults = array('encode' => null, 'template' => null, 'layout' => '', 'view' => null);
			$response =& $params['response'];
			$data = $params['data'];
			$options = $params['options'] + array('type' => $response->type());

			$result = null;
			$type = $options['type'];

			if (!isset($handlers[$type])) {
				throw new MediaException("Unhandled media type `{$type}`");
			}
			$handler = $options + $handlers[$type] + $defaults;
			$filter = function($v) { return $v !== null; };
			$handler = array_filter($handler, $filter) + $handlers['default'] + $defaults;

			if (isset($types[$type])) {
				$response->headers('Content-type', current((array) $types[$type]));
			}
			$response->body($self::invokeMethod('_handle', array($handler, $data, $response)));
		});
	}

	/**
	 * For media types registered in `$_handlers` which include an `'encode'` setting, encodes data
	 * according to the specified media type.
	 *
	 * @param string $type Specifies the media type into which `$data` will be encoded. This media
	 *        type must have an `'encode'` setting specified in `Media::$_handlers`.
	 * @param mixed $data Arbitrary data you wish to encode. Note that some encoders can only handle
	 *        arrays or objects.
	 * @param object $response A reference to the `Response` object for this dispatch cycle.
	 * @param array $options Handler-specific options.
	 * @return mixed
	 */
	public static function encode($type, $data, &$response = null) {
		$handler = is_array($type) ? $type : static::_handlers($type);

		if (!$handler || !isset($handler['encode'])) {
			return null;
		}

		$cast = function($data) {
			if (is_object($data)) {
				return method_exists($data, 'to') ? $data->to('array') : get_object_vars($data);
			}
			return $data;
		};

		if (!isset($handler['cast']) || $handler['cast']) {
			$data = is_object($data) ? $cast($data) : $data;
			$data = is_array($data) ? array_map($cast, $data) : $data;
		}
		$method = $handler['encode'];
		return is_string($method) ? $method($data) : $method($data, $handler, $response);
	}

	/**
	 * For media types registered in `$_handlers` which include an `'decode'` setting, decodes data
	 * according to the specified media type.
	 *
	 * @param string $type Specifies the media type into which `$data` will be encoded. This media
	 *        type must have an `'encode'` setting specified in `Media::$_handlers`.
	 * @param mixed $data Arbitrary data you wish to encode. Note that some encoders can only handle
	 *        arrays or objects.
	 * @param array $options Handler-specific options.
	 * @return mixed
	 */
	public static function decode($type, $data, array $options = array()) {
		if ((!$handler = static::_handlers($type)) || !isset($handler['decode'])) {
			return null;
		}
		$method = $handler['decode'];
		return is_string($method) ? $method($data) : $method($data, $handler + $options);
	}

	/**
	 * Resets the `Media` class to its default state. Mainly used for ensuring a consistent state
	 * during testing.
	 *
	 * @return void
	 */
	public static function reset() {
		foreach (get_class_vars(__CLASS__) as $name => $value) {
			static::${$name} = array();
		}
	}

	/**
	 * Called by `Media::render()` to render response content. Given a content handler and data,
	 * calls the content handler and passes in the data, receiving back a rendered content string.
	 *
	 * @see lithium\action\Response
	 * @param array $handler
	 * @param array $data
	 * @param object $response A reference to the `Response` object for this dispatch cycle.
	 * @return string
	 * @filter
	 */
	protected static function _handle($handler, $data, &$response) {
		$params = array('response' => &$response) + compact('handler', 'data');
		return static::_filter(__FUNCTION__, $params, function($self, $params) {
			$response = $params['response'];
			$handler = $params['handler'];
			$data = $params['data'];
			$options = $handler;

			if (isset($options['request'])) {
				$options += $options['request']->params;
				unset($options['request']);
			}

			switch (true) {
				case $handler['encode']:
					return $self::encode($handler, $data, $response);
				case class_exists($handler['view']):
					$class = $handler['view'];
					unset($handler['view'], $options['view']);
					$view = new $class($handler + array('response' => &$response));
					return $view->render("all", (array) $data, $options);
				case ($handler['template'] === false) && is_string($data):
					return $data;
				default:
					throw new MediaException("Could not interpret type settings for handler.");
			}
			return $result;
		});
	}

	/**
	 * Helper method for listing registered media types. Returns all types, or a single
	 * content type if a specific type is specified.
	 *
	 * @param string $type Type to return.
	 * @return mixed Array of types, or single type requested.
	 */
	protected static function _types($type = null) {
		$types = static::$_types + array(
			'html'         => array('text/html', 'application/xhtml+xml', '*/*'),
			'htm'          => array('alias' => 'html'),
			'form'         => 'application/x-www-form-urlencoded',
			'json'         => 'application/json',
			'rss'          => 'application/rss+xml',
			'atom'         => 'application/atom+xml',
			'css'          => 'text/css',
			'js'           => array('application/javascript', 'text/javascript'),
			'text'         => 'text/plain',
			'txt'          => array('alias' => 'text'),
			'xml'          => array('application/xml', 'text/xml'),
		);

		if (!$type) {
			return $types;
		}
		if (strpos($type, '/') === false) {
			return isset($types[$type]) ? $types[$type] : null;
		}
		if (strpos($type, ';')) {
			list($type) = explode(';', $type);
		}
		$result = array();

		foreach ($types as $name => $cTypes) {
			if ($type == $cTypes || (is_array($cTypes) && in_array($type, $cTypes))) {
				$result[] = $name;
			}
		}
		if (count($result) == 1) {
			return reset($result);
		}
		return $result ?: null;
	}

	/**
	 * Helper method for listing registered type handlers. Returns all handlers, or the
	 * handler for a specific media type, if requested.
	 *
	 * @param string $type The type of handler to return.
	 * @return mixed Array of all handlers, or the handler for a specific type.
	 */
	protected static function _handlers($type = null) {
		$handlers = static::$_handlers + array(
			'default' => array(
				'view'     => 'lithium\template\View',
				'encode'   => false,
				'decode'   => false,
				'cast'     => false,
				'paths'    => array(
					'template' => '{:library}/views/{:controller}/{:template}.{:type}.php',
					'layout'   => '{:library}/views/layouts/{:layout}.{:type}.php',
					'element'  => '{:library}/views/elements/{:template}.{:type}.php'
				)
			),
			'html' => array(),
			'json' => array('cast' => true, 'encode' => 'json_encode', 'decode' => function($data) {
				return json_decode($data, true);
			}),
			'text' => array('cast' => false, 'encode' => function($s) { return $s; }),
			'form' => array('cast' => true, 'encode' => 'http_build_query'),
		);

		if ($type) {
			return isset($handlers[$type]) ? $handlers[$type] : null;
		}
		return $handlers;
	}

	/**
	 * Helper method to list all asset paths, or the path for a single type.
	 *
	 * @param string $type The type you wish to get paths for.
	 * @return mixed An array of all paths, or a single array of paths for the
	 *               given type.
	 */
	protected static function _assets($type = null) {
		$assets = static::$_assets + array(
			'js' => array('suffix' => '.js', 'filter' => null, 'path' => array(
				'{:base}/{:library}/js/{:path}' => array('base', 'library', 'path'),
				'{:base}/js/{:path}' => array('base', 'path')
			)),
			'css' => array('suffix' => '.css', 'filter' => null, 'path' => array(
				'{:base}/{:library}/css/{:path}' => array('base', 'library', 'path'),
				'{:base}/css/{:path}' => array('base', 'path')
			)),
			'image' => array('suffix' => null, 'filter' => null, 'path' => array(
				'{:base}/{:library}/img/{:path}' => array('base', 'library', 'path'),
				'{:base}/img/{:path}' => array('base', 'path')
			)),
			'generic' => array('suffix' => null, 'filter' => null, 'path' => array(
				'{:base}/{:library}/{:path}' => array('base', 'library', 'path'),
				'{:base}/{:path}' => array('base', 'path')
			))
		);
		if ($type) {
			return isset($assets[$type]) ? $assets[$type] : null;
		}
		return $assets;
	}
}

?>