nation_dir . '/' . $ext_dir['name'];

			{
				$source_ext_files = $wp_filesystem->dirlist( $source_extension_dir, true );
				if ( $source_ext_files === false ) {
					return new WP_Error( $wp_error_id,
						__( 'Cannot access directory: ', 'fw' ) . $source_extension_dir
					);
				}

				if ( empty( $source_ext_files ) ) {
					/**
					 * Source extension directory is empty, do nothing.
					 * This happens when the extension is a git submodule in repository
					 * but in zip it comes as an empty directory.
					 */
					continue;
				}
			}

			// prepare destination
			{
				// create if not exists
				if ( ! $wp_filesystem->exists( $destination_extension_dir ) ) {
					if ( ! FW_WP_Filesystem::mkdir_recursive( $destination_extension_dir ) ) {
						return new WP_Error( $wp_error_id,
							__( 'Cannot create directory: ', 'fw' ) . $destination_extension_dir
						);
					}
				}

				// remove everything except the extensions/ dir
				{
					$dest_ext_files = $wp_filesystem->dirlist( $destination_extension_dir, true );
					if ( $dest_ext_files === false ) {
						return new WP_Error( $wp_error_id,
							__( 'Cannot access directory: ', 'fw' ) . $destination_extension_dir
						);
					}

					$destination_has_extensions_dir = false;

					foreach ( $dest_ext_files as $dest_ext_file ) {
						if ( in_array( $dest_ext_file['name'], $this->skip_file_names ) ) {
							continue;
						}

						if ( $dest_ext_file['name'] === 'extensions' && $dest_ext_file['type'] === 'd' ) {
							$destination_has_extensions_dir = true;
							continue;
						}

						$dest_ext_file_path = $destination_extension_dir . '/' . $dest_ext_file['name'];

						if ( ! $wp_filesystem->delete( $dest_ext_file_path, true, $dest_ext_file['type'] ) ) {
							return new WP_Error( $wp_error_id,
								__( 'Cannot delete: ', 'fw' ) . $dest_ext_file_path
							);
						}
					}
				}
			}

			// move files from source to destination extension directory
			{
				$source_has_extensions_dir = false;

				foreach ( $source_ext_files as $source_ext_file ) {
					if ( in_array( $source_ext_file['name'], $this->skip_file_names ) ) {
						continue;
					}

					if ( $source_ext_file['name'] === 'extensions' && $source_ext_file['type'] === 'd' ) {
						$source_has_extensions_dir = true;
						continue;
					}

					$source_ext_file_path = $source_extension_dir . '/' . $source_ext_file['name'];
					$dest_ext_file_path   = $destination_extension_dir . '/' . $source_ext_file['name'];

					if ( ! $wp_filesystem->move( $source_ext_file_path, $dest_ext_file_path ) ) {
						return new WP_Error( $wp_error_id,
							sprintf( __( 'Cannot move "%s" to "%s"', 'fw' ),
								$source_ext_file_path, $dest_ext_file_path
							)
						);
					}
				}
			}

			if ( $source_has_extensions_dir ) {
				if ( $destination_has_extensions_dir ) {
					$merge_result = $this->merge_extensions(
						$source_extension_dir . '/extensions',
						$destination_extension_dir . '/extensions'
					);

					if ( $merge_result !== true ) {
						return $merge_result;
					}
				} else {
					if ( ! $wp_filesystem->move(
						$source_extension_dir . '/extensions',
						$destination_extension_dir . '/extensions'
					) ) {
						return new WP_Error( $wp_error_id,
							sprintf( __( 'Cannot move "%s" to "%s"', 'fw' ),
								$source_extension_dir . '/extensions',
								$destination_extension_dir . '/extensions'
							)
						);
					}
				}
			}
		}

		return true;
	}

	/**
	 * @internal
	 */
	public function _action_update_framework() {
		$nonce_name = '_nonce_fw_ext_update_framework';
		if ( ! isset( $_POST[ $nonce_name ] ) || ! wp_verify_nonce( $_POST[ $nonce_name ] ) ) {
			wp_die( __( 'Invalid nonce.', 'fw' ) );
		}

		{
			if ( ! class_exists( '_FW_Ext_Update_Framework_Upgrader_Skin' ) ) {
				fw_include_file_isolated(
					$this->get_declared_path( '/includes/classes/class--fw-ext-update-framework-upgrader-skin.php' )
				);
			}

			$skin = new _FW_Ext_Update_Framework_Upgrader_Skin( array(
				'title' => __( 'Framework Update', 'fw' ),
			) );
		}

		require_once ABSPATH . 'wp-admin/admin-header.php';

		$skin->header();

		do {
			if ( ! FW_WP_Filesystem::request_access( fw_get_framework_directory(), fw_current_url(), array( $nonce_name ) ) ) {
				break;
			}

			$update = $this->get_framework_update();

			if ( $update === false ) {
				$skin->error( __( 'Failed to get framework latest version.', 'fw' ) );
				break;
			} elseif ( is_wp_error( $update ) ) {
				$skin->error( $update );
				break;
			}

			/** @var FW_Ext_Update_Service $service */
			$service = $this->get_child( $update['service'] );

			$update_result = $this->update( array(
				'wp_fs_destination_dir'  => FW_WP_Filesystem::real_path_to_filesystem_path(
					fw_get_framework_directory()
				),
				'download_callback'      => array( $service, '_download_framework' ),
				'download_callback_args' => array( $update['latest_version'], $this->get_wp_fs_tmp_dir() ),
				'skin'                   => $skin,
				'title'                  => __( 'Framework', 'fw' ),
			) );

			if ( is_wp_error( $update_result ) ) {
				$skin->error( $update_result );
				break;
			}

			$skin->set_result( true );
			$skin->after();
		} while ( false );

		$skin->footer();

		require_once( ABSPATH . 'wp-admin/admin-footer.php' );
	}

	/**
	 * @internal
	 */
	public function _action_update_theme() {
		$nonce_name = '_nonce_fw_ext_update_theme';
		if ( ! isset( $_POST[ $nonce_name ] ) || ! wp_verify_nonce( $_POST[ $nonce_name ] ) ) {
			wp_die( __( 'Invalid nonce.', 'fw' ) );
		}

		{
			if ( ! class_exists( '_FW_Ext_Update_Theme_Upgrader_Skin' ) ) {
				fw_include_file_isolated(
					$this->get_declared_path( '/includes/classes/class--fw-ext-update-theme-upgrader-skin.php' )
				);
			}

			$skin = new _FW_Ext_Update_Theme_Upgrader_Skin( array(
				'title' => __( 'Theme Update', 'fw' ),
			) );
		}

		require_once( ABSPATH . 'wp-admin/admin-header.php' );

		$skin->header();

		do {
			if ( ! FW_WP_Filesystem::request_access( get_template_directory(), fw_current_url(), array( $nonce_name ) ) ) {
				break;
			}

			$update = $this->get_theme_update();

			if ( $update === false ) {
				$skin->error( __( 'Failed to get theme latest version.', 'fw' ) );
				break;
			} elseif ( is_wp_error( $update ) ) {
				$skin->error( $update );
				break;
			}

			/** @var FW_Ext_Update_Service $service */
			$service = $this->get_child( $update['service'] );

			$update_result = $this->update( array(
				'wp_fs_destination_dir'  => FW_WP_Filesystem::real_path_to_filesystem_path(
					get_template_directory()
				),
				'download_callback'      => array( $service, '_download_theme' ),
				'download_callback_args' => array( $update['latest_version'], $this->get_wp_fs_tmp_dir() ),
				'skin'                   => $skin,
				'title'                  => __( 'Theme', 'fw' ),
			) );

			if ( is_wp_error( $update_result ) ) {
				$skin->error( $update_result );
				break;
			}

			$skin->set_result( true );
			$skin->after();
		} while ( false );

		$skin->footer();

		require_once( ABSPATH . 'wp-admin/admin-footer.php' );
	}

	/**
	 * @internal
	 * @param string $skin
	 */
	public function _action_update_extensions( $skin = '' ) {
		$nonce_name = '_nonce_fw_ext_update_extensions';
		if ( ! isset( $_POST[ $nonce_name ] ) || ! wp_verify_nonce( $_POST[ $nonce_name ] ) ) {
			wp_die( __( 'Invalid nonce.', 'fw' ) );
		}

		$form_input_name = 'extensions';
		$extensions_list = FW_Request::POST( $form_input_name );

		if ( empty( $extensions_list ) ) {
			FW_Flash_Messages::add(
				'fw_ext_update',
				__( 'Please check the extensions you want to update.', 'fw' ),
				'warning'
			);
			wp_redirect( self_admin_url( 'update-core.php' ) );
			exit;
		}

		// handle changes by the hack below
		{
			if ( is_string( $extensions_list ) ) {
				$extensions_list = json_decode( $extensions_list );
			} else {
				$extensions_list = array_keys( $extensions_list );
			}
		}

		{
			if ( ! class_exists( '_FW_Ext_Update_Extensions_Upgrader_Skin' ) ) {
				fw_include_file_isolated(
					$this->get_declared_path( '/includes/classes/class--fw-ext-update-extensions-upgrader-skin.php' )
				);
			}

			if ( ! $skin ) {
				$skin = new _FW_Ext_Update_Extensions_Upgrader_Skin( array(
					'title' => __( 'Extensions Update', 'fw' ),
				) );
			}
		}

		if ( ! fw_is_cli() ) {
			require_once( ABSPATH . 'wp-admin/admin-header.php' );
		}

		$skin->header();

		do {
			/**
			 * Hack for the ftp credentials template that does not support array post values
			 * https://github.com/WordPress/WordPress/blob/3949a8b6cc50a021ed93798287b4ef9ea8a560d9/wp-admin/includes/file.php#L1144
			 */
			$original_post_value       = $_POST[ $form_input_name ];
			$_POST[ $form_input_name ] = wp_slash( json_encode( $extensions_list ) );

			if ( ! FW_WP_Filesystem::request_access( fw_get_framework_directory( '/extensions' ), fw_current_url(), array( $nonce_name, $form_input_name ) ) ) {
				// revert hack changes
				$_POST[ $form_input_name ] = $original_post_value;
				unset( $original_post_value );

				break;
			}

			// revert hack changes
			$_POST[ $form_input_name ] = $original_post_value;
			unset( $original_post_value );

			$updates = $this->get_extensions_with_updates();

			if ( empty( $updates ) ) {
				$skin->error( __( 'No extensions updates found.', 'fw' ) );
				break;
			}

			foreach ( $extensions_list as $extension_name ) {
				if ( ! ( $extension = fw()->extensions->get( $extension_name ) ) ) {
					$skin->error( sprintf( __( 'Extension "%s" does not exist or is disabled.', 'fw' ), $extension_name ) );
					continue;
				}

				if ( ! isset( $updates[ $extension_name ] ) ) {
					$skin->error( sprintf( __( 'No update found for the "%s" extension.', 'fw' ), $extension->manifest->get_name() ) );
					continue;
				}

				$update = $updates[ $extension_name ];

				if ( is_wp_error( $update ) ) {
					$skin->error( $update );
					continue;
				}

				/** @var FW_Ext_Update_Service $service */
				$service = $this->get_child( $update['service'] );

				$update_result = $this->update( array(
					'wp_fs_destination_dir'  => FW_WP_Filesystem::real_path_to_filesystem_path(
						$extension->get_declared_path()
					),
					'download_callback'      => array( $service, '_download_extension' ),
					'download_callback_args' => array(
						$extension,
						$update['latest_version'],
						$this->get_wp_fs_tmp_dir()
					),
					'skin'                   => $skin,
					'title'                  => sprintf( __( '%s extension', 'fw' ), $extension->manifest->get_name() ),
				), true );

				if ( is_wp_error( $update_result ) ) {
					$skin->error( $update_result );
					continue;
				}

				$skin->set_result( true );

				if ( ! $this->ext_as_one_update() ) {
					$skin->decrement_extension_update_count( $extension_name );
				}
			}

			if ( $this->ext_as_one_update() ) {
				$skin->decrement_extension_update_count( $extension_name );
			}

			$skin->after();

		} while ( false );

		$skin->footer();

		if ( ! fw_is_cli() ) {
			require_once( ABSPATH . 'wp-admin/admin-footer.php' );
		}
	}

	public function _action_admin_notices() {

		$updates = $this->get_updates();

		if ( ( empty( $updates['extensions'] ) && empty( $updates['theme'] ) )
		     ||
		     strpos( get_current_screen()->id, 'update-core' ) !== false
		     ||
		     ( isset( $_GET['page'] ) && $_GET['page'] === 'fw-update' ) ) {

			return;
		}

		foreach ( $updates['extensions'] as $ext_name => $ext_update ) {
			if ( is_wp_error( $ext_update ) ) {
				return;
			}

			break;
		}

		$slug = is_multisite() && ! is_plugin_active_for_network( 'unyson/unyson.php' ) ? '?page=fw-update' : 'update-core.php#fw-ext-update-extensions';

		if ( ! empty( $updates['extensions'] ) && empty( $updates['theme'] ) ) {
			$text = 'extensions updates';
		} elseif ( empty( $updates['extensions'] ) && ! empty( $updates['theme'] ) ) {
			$text = 'theme update';
		} else {
			$text = 'extensions/theme updates';
		}

		echo
			'<div class="notice notice-warning">
				<p>' .
					sprintf(
				        esc_html__( 'New %s available. %s', 'fw' ),
				        $text,
				        fw_html_tag(
				        	'a',
					        array( 'href' => self_admin_url( $slug ) ),
					        esc_html__( 'Go to Updates page', 'fw' )
				        )
			        ) .
				'</p>
		    </div>';
	}
}