wp_mime_type_icon( string|int $mime )

function wp_mime_type_icon( $mime = 0 ) {
	if ( !is_numeric($mime) )
		$icon = wp_cache_get("mime_type_icon_$mime");

	$post_id = 0;
	if ( empty($icon) ) {
		$post_mimes = array();
		if ( is_numeric($mime) ) {
			$mime = (int) $mime;
			if ( $post = get_post( $mime ) ) {
				$post_id = (int) $post->ID;
				$file = get_attached_file( $post_id );
				$ext = preg_replace('/^.+?\.([^.]+)$/', '$1', $file);
				if ( !empty($ext) ) {
					$post_mimes[] = $ext;
					if ( $ext_type = wp_ext2type( $ext ) )
						$post_mimes[] = $ext_type;
				}
				$mime = $post->post_mime_type;
			} else {
				$mime = 0;
			}
		} else {
			$post_mimes[] = $mime;
		}

		$icon_files = wp_cache_get('icon_files');

		if ( !is_array($icon_files) ) {
			/**
			 * Filters the icon directory path.
			 *
			 * @since WP-2.0.0
			 *
			 * @param string $path Icon directory absolute path.
			 */
			$icon_dir = apply_filters( 'icon_dir', ABSPATH . WPINC . '/images/media' );

			/**
			 * Filters the icon directory URI.
			 *
			 * @since WP-2.0.0
			 *
			 * @param string $uri Icon directory URI.
			 */
			$icon_dir_uri = apply_filters( 'icon_dir_uri', includes_url( 'images/media' ) );

			/**
			 * Filters the list of icon directory URIs.
			 *
			 * @since WP-2.5.0
			 *
			 * @param array $uris List of icon directory URIs.
			 */
			$dirs = apply_filters( 'icon_dirs', array( $icon_dir => $icon_dir_uri ) );
			$icon_files = array();
			while ( $dirs ) {
				$keys = array_keys( $dirs );
				$dir = array_shift( $keys );
				$uri = array_shift($dirs);
				if ( $dh = opendir($dir) ) {
					while ( false !== $file = readdir($dh) ) {
						$file = basename($file);
						if ( substr($file, 0, 1) == '.' )
							continue;
						if ( !in_array(strtolower(substr($file, -4)), array('.png', '.gif', '.jpg') ) ) {
							if ( is_dir("$dir/$file") )
								$dirs["$dir/$file"] = "$uri/$file";
							continue;
						}
						$icon_files["$dir/$file"] = "$uri/$file";
					}
					closedir($dh);
				}
			}
			wp_cache_add( 'icon_files', $icon_files, 'default', 600 );
		}

		$types = array();
		// Icon basename - extension = MIME wildcard.
		foreach ( $icon_files as $file => $uri )
			$types[ preg_replace('/^([^.]*).*$/', '$1', basename($file)) ] =& $icon_files[$file];

		if ( ! empty($mime) ) {
			$post_mimes[] = substr($mime, 0, strpos($mime, '/'));
			$post_mimes[] = substr($mime, strpos($mime, '/') + 1);
			$post_mimes[] = str_replace('/', '_', $mime);
		}

		$matches = wp_match_mime_types(array_keys($types), $post_mimes);
		$matches['default'] = array('default');

		foreach ( $matches as $match => $wilds ) {
			foreach ( $wilds as $wild ) {
				if ( ! isset( $types[ $wild ] ) ) {
					continue;
				}

				$icon = $types[ $wild ];
				if ( ! is_numeric( $mime ) ) {
					wp_cache_add( "mime_type_icon_$mime", $icon );
				}
				break 2;
			}
		}
	}

	/**
	 * Filters the mime type icon.
	 *
	 * @since WP-2.1.0
	 *
	 * @param string $icon    Path to the mime type icon.
	 * @param string $mime    Mime type.
	 * @param int    $post_id Attachment ID. Will equal 0 if the function passed
	 *                        the mime type.
	 */
	return apply_filters( 'wp_mime_type_icon', $icon, $mime, $post_id );
}