blockly/core/keyboard_nav/flyout_navigation_policy.ts

/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import type {IFlyout} from '../interfaces/i_flyout.js';
import type {IFocusableNode} from '../interfaces/i_focusable_node.js';
import type {INavigationPolicy} from '../interfaces/i_navigation_policy.js';

/**
 * Generic navigation policy that navigates between items in the flyout.
 */
export class FlyoutNavigationPolicy<T> implements INavigationPolicy<T> {
  /**
   * Creates a new FlyoutNavigationPolicy instance.
   *
   * @param policy The policy to defer to for parents/children.
   * @param flyout The flyout this policy will control navigation in.
   */
  constructor(
    private policy: INavigationPolicy<T>,
    private flyout: IFlyout,
  ) {}

  /**
   * Returns null to prevent navigating into flyout items.
   *
   * @param _current The flyout item to navigate from.
   * @returns Null to prevent navigating into flyout items.
   */
  getFirstChild(_current: T): IFocusableNode | null {
    return null;
  }

  /**
   * Returns the parent of the given flyout item.
   *
   * @param current The flyout item to navigate from.
   * @returns The parent of the given flyout item.
   */
  getParent(current: T): IFocusableNode | null {
    return this.policy.getParent(current);
  }

  /**
   * Returns the next item in the flyout relative to the given item.
   *
   * @param current The flyout item to navigate from.
   * @returns The flyout item following the given one.
   */
  getNextSibling(current: T): IFocusableNode | null {
    const flyoutContents = this.flyout.getContents();
    if (!flyoutContents) return null;

    let index = flyoutContents.findIndex(
      (flyoutItem) => flyoutItem.getElement() === current,
    );

    if (index === -1) return null;
    index++;
    if (index >= flyoutContents.length) {
      index = 0;
    }

    return flyoutContents[index].getElement();
  }

  /**
   * Returns the previous item in the flyout relative to the given item.
   *
   * @param current The flyout item to navigate from.
   * @returns The flyout item preceding the given one.
   */
  getPreviousSibling(current: T): IFocusableNode | null {
    const flyoutContents = this.flyout.getContents();
    if (!flyoutContents) return null;

    let index = flyoutContents.findIndex(
      (flyoutItem) => flyoutItem.getElement() === current,
    );

    if (index === -1) return null;
    index--;
    if (index < 0) {
      index = flyoutContents.length - 1;
    }

    return flyoutContents[index].getElement();
  }

  /**
   * Returns whether or not the given flyout item can be navigated to.
   *
   * @param current The instance to check for navigability.
   * @returns True if the given flyout item can be focused.
   */
  isNavigable(current: T): boolean {
    return this.policy.isNavigable(current);
  }

  /**
   * Returns whether the given object can be navigated from by this policy.
   *
   * @param current The object to check if this policy applies to.
   * @returns True if the object is a BlockSvg.
   */
  isApplicable(current: any): current is T {
    return this.policy.isApplicable(current);
  }
}