Custom_Background::handle_upload

	public function handle_upload() {
		if ( empty( $_FILES ) ) {
			return;
		}

		check_admin_referer( 'custom-background-upload', '_wpnonce-custom-background-upload' );
		$overrides = array( 'test_form' => false );

		$uploaded_file = $_FILES['import'];
		$wp_filetype   = wp_check_filetype_and_ext( $uploaded_file['tmp_name'], $uploaded_file['name'] );
		if ( ! wp_match_mime_types( 'image', $wp_filetype['type'] ) ) {
			wp_die( __( 'The uploaded file is not a valid image. Please try again.' ) );
		}

		$file = wp_handle_upload( $uploaded_file, $overrides );

		if ( isset( $file['error'] ) ) {
			wp_die( $file['error'] );
		}

		$url      = $file['url'];
		$type     = $file['type'];
		$file     = $file['file'];
		$filename = wp_basename( $file );

		// Construct the object array.
		$object = array(
			'post_title'     => $filename,
			'post_content'   => $url,
			'post_mime_type' => $type,
			'guid'           => $url,
			'context'        => 'custom-background',
		);

		// Save the data.
		$id = wp_insert_attachment( $object, $file );

		// Add the metadata.
		wp_update_attachment_metadata( $id, wp_generate_attachment_metadata( $id, $file ) );
		update_post_meta( $id, '_wp_attachment_is_custom_background', get_option( 'stylesheet' ) );

		set_theme_mod( 'background_image', esc_url_raw( $url ) );

		$thumbnail = wp_get_attachment_image_src( $id, 'thumbnail' );
		set_theme_mod( 'background_image_thumb', esc_url_raw( $thumbnail[0] ) );

		/** This action is documented in wp-admin/includes/class-custom-image-header.php */
		do_action( 'wp_create_file_in_uploads', $file, $id ); // For replication.
		$this->updated = true;
	}