blockly/core/flyout_base.ts

/**
 * @license
 * Copyright 2011 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * Flyout tray containing blocks which may be created.
 *
 * @class
 */
// Former goog.module ID: Blockly.Flyout

import {BlockSvg} from './block_svg.js';
import * as browserEvents from './browser_events.js';
import {ComponentManager} from './component_manager.js';
import {DeleteArea} from './delete_area.js';
import type {Abstract as AbstractEvent} from './events/events_abstract.js';
import {EventType} from './events/type.js';
import * as eventUtils from './events/utils.js';
import {FlyoutItem} from './flyout_item.js';
import {FlyoutMetricsManager} from './flyout_metrics_manager.js';
import {FlyoutSeparator, SeparatorAxis} from './flyout_separator.js';
import {getFocusManager} from './focus_manager.js';
import {IAutoHideable} from './interfaces/i_autohideable.js';
import type {IFlyout} from './interfaces/i_flyout.js';
import type {IFlyoutInflater} from './interfaces/i_flyout_inflater.js';
import {IFocusableNode} from './interfaces/i_focusable_node.js';
import {IFocusableTree} from './interfaces/i_focusable_tree.js';
import type {Options} from './options.js';
import * as registry from './registry.js';
import * as renderManagement from './render_management.js';
import {ScrollbarPair} from './scrollbar_pair.js';
import {SEPARATOR_TYPE} from './separator_flyout_inflater.js';
import * as blocks from './serialization/blocks.js';
import {Coordinate} from './utils/coordinate.js';
import * as dom from './utils/dom.js';
import * as idGenerator from './utils/idgenerator.js';
import {Svg} from './utils/svg.js';
import * as toolbox from './utils/toolbox.js';
import * as Variables from './variables.js';
import {WorkspaceSvg} from './workspace_svg.js';

/**
 * Class for a flyout.
 */
export abstract class Flyout
  extends DeleteArea
  implements IAutoHideable, IFlyout, IFocusableNode
{
  /**
   * Position the flyout.
   */
  abstract position(): void;

  /**
   * Determine if a drag delta is toward the workspace, based on the position
   * and orientation of the flyout. This is used in determineDragIntention_ to
   * determine if a new block should be created or if the flyout should scroll.
   *
   * @param currentDragDeltaXY How far the pointer has
   *     moved from the position at mouse down, in pixel units.
   * @returns True if the drag is toward the workspace.
   */
  abstract isDragTowardWorkspace(currentDragDeltaXY: Coordinate): boolean;

  /**
   * Sets the translation of the flyout to match the scrollbars.
   *
   * @param xyRatio Contains a y property which is a float
   *     between 0 and 1 specifying the degree of scrolling and a
   *     similar x property.
   */
  protected abstract setMetrics_(xyRatio: {x?: number; y?: number}): void;

  /**
   * Lay out the elements in the flyout.
   *
   * @param contents The flyout elements to lay out.
   */
  protected abstract layout_(contents: FlyoutItem[]): void;

  /**
   * Scroll the flyout.
   *
   * @param e Mouse wheel scroll event.
   */
  protected abstract wheel_(e: WheelEvent): void;

  /**
   * Compute bounds of flyout.
   * For RTL: Lay out the elements right-aligned.
   */
  protected abstract reflowInternal_(): void;

  /**
   * Calculates the x coordinate for the flyout position.
   *
   * @returns X coordinate.
   */
  abstract getX(): number;

  /**
   * Calculates the y coordinate for the flyout position.
   *
   * @returns Y coordinate.
   */
  abstract getY(): number;

  /**
   * Scroll the flyout to the beginning of its contents.
   */
  abstract scrollToStart(): void;

  protected workspace_: WorkspaceSvg;
  RTL: boolean;
  /**
   * Whether the flyout should be laid out horizontally or not.
   *
   * @internal
   */
  horizontalLayout = false;
  protected toolboxPosition_: number;

  /**
   * Array holding info needed to unbind events.
   * Used for disposing.
   * Ex: [[node, name, func], [node, name, func]].
   */
  private boundEvents: browserEvents.Data[] = [];

  /**
   * Function that will be registered as a change listener on the workspace
   * to reflow when elements in the flyout workspace change.
   */
  private reflowWrapper: ((e: AbstractEvent) => void) | null = null;

  /**
   * List of flyout elements.
   */
  protected contents: FlyoutItem[] = [];

  protected readonly tabWidth_: number;

  /**
   * The target workspace.
   *
   * @internal
   */
  targetWorkspace!: WorkspaceSvg;

  /**
   * Does the flyout automatically close when a block is created?
   */
  autoClose = true;

  /**
   * Whether the flyout is visible.
   */
  private visible = false;

  /**
   * Whether the workspace containing this flyout is visible.
   */
  private containerVisible = true;

  /**
   * Corner radius of the flyout background.
   */
  readonly CORNER_RADIUS: number = 8;
  readonly MARGIN: number;
  readonly GAP_X: number;
  readonly GAP_Y: number;

  /**
   * Top/bottom padding between scrollbar and edge of flyout background.
   */
  readonly SCROLLBAR_MARGIN: number = 2.5;

  /**
   * Width of flyout.
   */
  protected width_ = 0;

  /**
   * Height of flyout.
   */
  protected height_ = 0;
  // clang-format off
  /**
   * Range of a drag angle from a flyout considered "dragging toward
   * workspace". Drags that are within the bounds of this many degrees from
   * the orthogonal line to the flyout edge are considered to be "drags toward
   * the workspace".
   *
   * @example
   *
   * ```
   * Flyout                                                 Edge   Workspace
   * [block] /  <-within this angle, drags "toward workspace" |
   * [block] ---- orthogonal to flyout boundary ----          |
   * [block] \                                                |
   * ```
   *
   * The angle is given in degrees from the orthogonal.
   *
   * This is used to know when to create a new block and when to scroll the
   * flyout. Setting it to 360 means that all drags create a new block.
   */
  // clang-format on
  protected dragAngleRange_ = 70;

  /**
   * The path around the background of the flyout, which will be filled with a
   * background colour.
   */
  protected svgBackground_: SVGPathElement | null = null;

  /**
   * The root SVG group for the button or label.
   */
  protected svgGroup_: SVGGElement | null = null;

  /**
   * Map from flyout content type to the corresponding inflater class
   * responsible for creating concrete instances of the content type.
   */
  protected inflaters = new Map<string, IFlyoutInflater>();

  /**
   * @param workspaceOptions Dictionary of options for the
   *     workspace.
   */
  constructor(workspaceOptions: Options) {
    super();
    workspaceOptions.setMetrics = this.setMetrics_.bind(this);

    this.workspace_ = new WorkspaceSvg(workspaceOptions);
    this.workspace_.setMetricsManager(
      new FlyoutMetricsManager(this.workspace_, this),
    );

    this.workspace_.internalIsFlyout = true;
    // Keep the workspace visibility consistent with the flyout's visibility.
    this.workspace_.setVisible(this.visible);

    /**
     * The unique id for this component that is used to register with the
     * ComponentManager.
     */
    this.id = idGenerator.genUid();

    /**
     * Is RTL vs LTR.
     */
    this.RTL = !!workspaceOptions.RTL;

    /**
     * Position of the toolbox and flyout relative to the workspace.
     */
    this.toolboxPosition_ = workspaceOptions.toolboxPosition;

    /**
     * Width of output tab.
     */
    this.tabWidth_ = this.workspace_.getRenderer().getConstants().TAB_WIDTH;

    /**
     * Margin around the edges of the elements in the flyout.
     */
    this.MARGIN = this.CORNER_RADIUS;

    // TODO: Move GAP_X and GAP_Y to their appropriate files.
    /**
     * Gap between items in horizontal flyouts. Can be overridden with the "sep"
     * element.
     */
    this.GAP_X = this.MARGIN * 3;

    /**
     * Gap between items in vertical flyouts. Can be overridden with the "sep"
     * element.
     */
    this.GAP_Y = this.MARGIN * 3;
  }

  /**
   * Creates the flyout's DOM.  Only needs to be called once.  The flyout can
   * either exist as its own SVG element or be a g element nested inside a
   * separate SVG element.
   *
   * @param tagName The type of tag to
   *     put the flyout in. This should be <svg> or <g>.
   * @returns The flyout's SVG group.
   */
  createDom(
    tagName: string | Svg<SVGSVGElement> | Svg<SVGGElement>,
  ): SVGElement {
    /*
        <svg | g>
          <path class="blocklyFlyoutBackground"/>
          <g class="blocklyFlyout"></g>
        </ svg | g>
        */
    // Setting style to display:none to start. The toolbox and flyout
    // hide/show code will set up proper visibility and size later.
    this.svgGroup_ = dom.createSvgElement(tagName, {
      'class': 'blocklyFlyout',
      'tabindex': '0',
    });
    this.svgGroup_.style.display = 'none';
    this.svgBackground_ = dom.createSvgElement(
      Svg.PATH,
      {'class': 'blocklyFlyoutBackground'},
      this.svgGroup_,
    );
    this.svgGroup_.appendChild(this.workspace_.createDom());
    this.workspace_
      .getThemeManager()
      .subscribe(this.svgBackground_, 'flyoutBackgroundColour', 'fill');
    this.workspace_
      .getThemeManager()
      .subscribe(this.svgBackground_, 'flyoutOpacity', 'fill-opacity');

    getFocusManager().registerTree(this);

    return this.svgGroup_;
  }

  /**
   * Initializes the flyout.
   *
   * @param targetWorkspace The workspace in which to
   *     create new blocks.
   */
  init(targetWorkspace: WorkspaceSvg) {
    this.targetWorkspace = targetWorkspace;
    this.workspace_.targetWorkspace = targetWorkspace;

    this.workspace_.scrollbar = new ScrollbarPair(
      this.workspace_,
      this.horizontalLayout,
      !this.horizontalLayout,
      'blocklyFlyoutScrollbar',
      this.SCROLLBAR_MARGIN,
    );

    this.hide();

    this.boundEvents.push(
      browserEvents.conditionalBind(
        this.svgGroup_ as SVGGElement,
        'wheel',
        this,
        this.wheel_,
      ),
    );

    // Dragging the flyout up and down.
    this.boundEvents.push(
      browserEvents.conditionalBind(
        this.svgBackground_ as SVGPathElement,
        'pointerdown',
        this,
        this.onMouseDown,
      ),
    );

    // A flyout connected to a workspace doesn't have its own current gesture.
    this.workspace_.getGesture = this.targetWorkspace.getGesture.bind(
      this.targetWorkspace,
    );

    // Get variables from the main workspace rather than the target workspace.
    this.workspace_.setVariableMap(this.targetWorkspace.getVariableMap());

    this.workspace_.createPotentialVariableMap();

    targetWorkspace.getComponentManager().addComponent({
      component: this,
      weight: ComponentManager.ComponentWeight.FLYOUT_WEIGHT,
      capabilities: [
        ComponentManager.Capability.AUTOHIDEABLE,
        ComponentManager.Capability.DELETE_AREA,
        ComponentManager.Capability.DRAG_TARGET,
      ],
    });
  }

  /**
   * Dispose of this flyout.
   * Unlink from all DOM elements to prevent memory leaks.
   */
  dispose() {
    this.hide();
    this.targetWorkspace.getComponentManager().removeComponent(this.id);
    for (const event of this.boundEvents) {
      browserEvents.unbind(event);
    }
    this.boundEvents.length = 0;
    if (this.workspace_) {
      this.workspace_.getThemeManager().unsubscribe(this.svgBackground_!);
      this.workspace_.dispose();
    }
    if (this.svgGroup_) {
      dom.removeNode(this.svgGroup_);
    }
    getFocusManager().unregisterTree(this);
  }

  /**
   * Get the width of the flyout.
   *
   * @returns The width of the flyout.
   */
  getWidth(): number {
    return this.width_;
  }

  /**
   * Get the height of the flyout.
   *
   * @returns The width of the flyout.
   */
  getHeight(): number {
    return this.height_;
  }

  /**
   * Get the scale (zoom level) of the flyout. By default,
   * this matches the target workspace scale, but this can be overridden.
   *
   * @returns Flyout workspace scale.
   */
  getFlyoutScale(): number {
    return this.targetWorkspace.scale;
  }

  /**
   * Get the workspace inside the flyout.
   *
   * @returns The workspace inside the flyout.
   */
  getWorkspace(): WorkspaceSvg {
    return this.workspace_;
  }

  /**
   * Sets whether this flyout automatically closes when blocks are dragged out,
   * the workspace is clicked, etc, or not.
   */
  setAutoClose(autoClose: boolean) {
    this.autoClose = autoClose;
    this.targetWorkspace.recordDragTargets();
    this.targetWorkspace.resizeContents();
  }

  /** Automatically hides the flyout if it is an autoclosing flyout. */
  autoHide(onlyClosePopups: boolean): void {
    if (
      !onlyClosePopups &&
      this.targetWorkspace.getFlyout(true) === this &&
      this.autoClose
    )
      this.hide();
  }

  /**
   * Get the target workspace inside the flyout.
   *
   * @returns The target workspace inside the flyout.
   */
  getTargetWorkspace(): WorkspaceSvg {
    return this.targetWorkspace;
  }

  /**
   * Is the flyout visible?
   *
   * @returns True if visible.
   */
  isVisible(): boolean {
    return this.visible;
  }

  /**
   * Set whether the flyout is visible. A value of true does not necessarily
   * mean that the flyout is shown. It could be hidden because its container is
   * hidden.
   *
   * @param visible True if visible.
   */
  setVisible(visible: boolean) {
    const visibilityChanged = visible !== this.isVisible();

    this.visible = visible;
    if (visibilityChanged) {
      if (!this.autoClose) {
        // Auto-close flyouts are ignored as drag targets, so only non
        // auto-close flyouts need to have their drag target updated.
        this.targetWorkspace.recordDragTargets();
      }
      this.updateDisplay();
    }
  }

  /**
   * Set whether this flyout's container is visible.
   *
   * @param visible Whether the container is visible.
   */
  setContainerVisible(visible: boolean) {
    const visibilityChanged = visible !== this.containerVisible;
    this.containerVisible = visible;
    if (visibilityChanged) {
      this.updateDisplay();
    }
  }

  /**
   * Get the list of elements of the current flyout.
   *
   * @returns The array of flyout elements.
   */
  getContents(): FlyoutItem[] {
    return this.contents;
  }

  /**
   * Store the list of elements on the flyout.
   *
   * @param contents - The array of items for the flyout.
   */
  setContents(contents: FlyoutItem[]): void {
    this.contents = contents;
  }
  /**
   * Update the display property of the flyout based whether it thinks it should
   * be visible and whether its containing workspace is visible.
   */
  private updateDisplay() {
    let show = true;
    if (!this.containerVisible) {
      show = false;
    } else {
      show = this.isVisible();
    }
    if (this.svgGroup_) {
      this.svgGroup_.style.display = show ? 'block' : 'none';
    }
    // Update the scrollbar's visibility too since it should mimic the
    // flyout's visibility.
    this.workspace_.scrollbar?.setContainerVisible(show);
  }

  /**
   * Update the view based on coordinates calculated in position().
   *
   * @param width The computed width of the flyout's SVG group
   * @param height The computed height of the flyout's SVG group.
   * @param x The computed x origin of the flyout's SVG group.
   * @param y The computed y origin of the flyout's SVG group.
   */
  protected positionAt_(width: number, height: number, x: number, y: number) {
    this.svgGroup_?.setAttribute('width', `${width}`);
    this.svgGroup_?.setAttribute('height', `${height}`);
    this.workspace_.setCachedParentSvgSize(width, height);

    if (this.svgGroup_) {
      const transform = 'translate(' + x + 'px,' + y + 'px)';
      dom.setCssTransform(this.svgGroup_, transform);
    }

    // Update the scrollbar (if one exists).
    const scrollbar = this.workspace_.scrollbar;
    if (scrollbar) {
      // Set the scrollbars origin to be the top left of the flyout.
      scrollbar.setOrigin(x, y);
      scrollbar.resize();
      // If origin changed and metrics haven't changed enough to trigger
      // reposition in resize, we need to call setPosition. See issue #4692.
      if (scrollbar.hScroll) {
        scrollbar.hScroll.setPosition(
          scrollbar.hScroll.position.x,
          scrollbar.hScroll.position.y,
        );
      }
      if (scrollbar.vScroll) {
        scrollbar.vScroll.setPosition(
          scrollbar.vScroll.position.x,
          scrollbar.vScroll.position.y,
        );
      }
    }
  }

  /**
   * Hide and empty the flyout.
   */
  hide() {
    if (!this.isVisible()) {
      return;
    }
    this.setVisible(false);
    if (this.reflowWrapper) {
      this.workspace_.removeChangeListener(this.reflowWrapper);
      this.reflowWrapper = null;
    }
    // Do NOT delete the flyout contents here.  Wait until Flyout.show.
    // https://neil.fraser.name/news/2014/08/09/
  }

  /**
   * Show and populate the flyout.
   *
   * @param flyoutDef Contents to display
   *     in the flyout. This is either an array of Nodes, a NodeList, a
   *     toolbox definition, or a string with the name of the dynamic category.
   */
  show(flyoutDef: toolbox.FlyoutDefinition | string) {
    this.workspace_.setResizesEnabled(false);
    this.hide();
    this.clearOldBlocks();

    // Handle dynamic categories, represented by a name instead of a list.
    if (typeof flyoutDef === 'string') {
      flyoutDef = this.getDynamicCategoryContents(flyoutDef);
    }
    this.setVisible(true);

    // Parse the Array, Node or NodeList into a a list of flyout items.
    const parsedContent = toolbox.convertFlyoutDefToJsonArray(flyoutDef);
    const flyoutInfo = this.createFlyoutInfo(parsedContent);

    renderManagement.triggerQueuedRenders(this.workspace_);

    this.setContents(flyoutInfo);

    this.layout_(flyoutInfo);

    if (this.horizontalLayout) {
      this.height_ = 0;
    } else {
      this.width_ = 0;
    }
    this.reflow();
    this.workspace_.setResizesEnabled(true);

    // Listen for block change events, and reflow the flyout in response. This
    // accommodates e.g. resizing a non-autoclosing flyout in response to the
    // user typing long strings into fields on the blocks in the flyout.
    this.reflowWrapper = (event) => {
      if (
        event.type === EventType.BLOCK_CHANGE ||
        event.type === EventType.BLOCK_FIELD_INTERMEDIATE_CHANGE
      ) {
        this.reflow();
      }
    };
    this.workspace_.addChangeListener(this.reflowWrapper);
  }

  /**
   * Create the contents array and gaps array necessary to create the layout for
   * the flyout.
   *
   * @param parsedContent The array
   *     of objects to show in the flyout.
   * @returns The list of contents needed to lay out the flyout.
   */
  private createFlyoutInfo(
    parsedContent: toolbox.FlyoutItemInfoArray,
  ): FlyoutItem[] {
    const contents: FlyoutItem[] = [];
    const defaultGap = this.horizontalLayout ? this.GAP_X : this.GAP_Y;
    for (const info of parsedContent) {
      if ('custom' in info) {
        const customInfo = info as toolbox.DynamicCategoryInfo;
        const categoryName = customInfo['custom'];
        const flyoutDef = this.getDynamicCategoryContents(categoryName);
        const parsedDynamicContent =
          toolbox.convertFlyoutDefToJsonArray(flyoutDef);
        contents.push(...this.createFlyoutInfo(parsedDynamicContent));
      }

      const type = info['kind'].toLowerCase();
      const inflater = this.getInflaterForType(type);
      if (inflater) {
        contents.push(inflater.load(info, this));
        const gap = inflater.gapForItem(info, defaultGap);
        if (gap) {
          contents.push(
            new FlyoutItem(
              new FlyoutSeparator(
                gap,
                this.horizontalLayout ? SeparatorAxis.X : SeparatorAxis.Y,
              ),
              SEPARATOR_TYPE,
              false,
            ),
          );
        }
      }
    }

    return this.normalizeSeparators(contents);
  }

  /**
   * Updates and returns the provided list of flyout contents to flatten
   * separators as needed.
   *
   * When multiple separators occur one after another, the value of the last one
   * takes precedence and the earlier separators in the group are removed.
   *
   * @param contents The list of flyout contents to flatten separators in.
   * @returns An updated list of flyout contents with only one separator between
   *     each non-separator item.
   */
  protected normalizeSeparators(contents: FlyoutItem[]): FlyoutItem[] {
    for (let i = contents.length - 1; i > 0; i--) {
      const elementType = contents[i].getType().toLowerCase();
      const previousElementType = contents[i - 1].getType().toLowerCase();
      if (
        elementType === SEPARATOR_TYPE &&
        previousElementType === SEPARATOR_TYPE
      ) {
        // Remove previousElement from the array, shifting the current element
        // forward as a result. This preserves the behavior where explicit
        // separator elements override the value of prior implicit (or explicit)
        // separator elements.
        contents.splice(i - 1, 1);
      }
    }

    return contents;
  }

  /**
   * Gets the flyout definition for the dynamic category.
   *
   * @param categoryName The name of the dynamic category.
   * @returns The definition of the
   *     flyout in one of its many forms.
   */
  private getDynamicCategoryContents(
    categoryName: string,
  ): toolbox.FlyoutDefinition {
    // Look up the correct category generation function and call that to get a
    // valid XML list.
    const fnToApply =
      this.workspace_.targetWorkspace!.getToolboxCategoryCallback(categoryName);
    if (typeof fnToApply !== 'function') {
      throw TypeError(
        "Couldn't find a callback function when opening" +
          ' a toolbox category.',
      );
    }
    return fnToApply(this.workspace_.targetWorkspace!);
  }

  /**
   * Delete elements from a previous showing of the flyout.
   */
  private clearOldBlocks() {
    this.getContents().forEach((item) => {
      const inflater = this.getInflaterForType(item.getType());
      inflater?.disposeItem(item);
    });

    // Clear potential variables from the previous showing.
    this.workspace_.getPotentialVariableMap()?.clear();
  }

  /**
   * Pointer down on the flyout background.  Start a vertical scroll drag.
   *
   * @param e Pointer down event.
   */
  private onMouseDown(e: PointerEvent) {
    const gesture = this.targetWorkspace.getGesture(e);
    if (gesture) {
      gesture.handleFlyoutStart(e, this);
    }
  }

  /**
   * Does this flyout allow you to create a new instance of the given block?
   * Used for deciding if a block can be "dragged out of" the flyout.
   *
   * @param block The block to copy from the flyout.
   * @returns True if you can create a new instance of the block, false
   *    otherwise.
   * @internal
   */
  isBlockCreatable(block: BlockSvg): boolean {
    return block.isEnabled() && !this.getTargetWorkspace().isReadOnly();
  }

  /**
   * Create a copy of this block on the workspace.
   *
   * @param originalBlock The block to copy from the flyout.
   * @returns The newly created block.
   * @throws {Error} if something went wrong with deserialization.
   * @internal
   */
  createBlock(originalBlock: BlockSvg): BlockSvg {
    let newBlock = null;
    eventUtils.disable();
    const variablesBeforeCreation = this.targetWorkspace.getAllVariables();
    this.targetWorkspace.setResizesEnabled(false);
    try {
      newBlock = this.placeNewBlock(originalBlock);
    } finally {
      eventUtils.enable();
    }

    // Close the flyout.
    this.targetWorkspace.hideChaff();

    const newVariables = Variables.getAddedVariables(
      this.targetWorkspace,
      variablesBeforeCreation,
    );

    if (eventUtils.isEnabled()) {
      eventUtils.setGroup(true);
      // Fire a VarCreate event for each (if any) new variable created.
      for (let i = 0; i < newVariables.length; i++) {
        const thisVariable = newVariables[i];
        eventUtils.fire(
          new (eventUtils.get(EventType.VAR_CREATE))(thisVariable),
        );
      }

      // Block events come after var events, in case they refer to newly created
      // variables.
      eventUtils.fire(new (eventUtils.get(EventType.BLOCK_CREATE))(newBlock));
    }
    if (this.autoClose) {
      this.hide();
    }
    return newBlock;
  }

  /**
   * Reflow flyout contents.
   */
  reflow() {
    if (this.reflowWrapper) {
      this.workspace_.removeChangeListener(this.reflowWrapper);
    }
    this.reflowInternal_();
    if (this.reflowWrapper) {
      this.workspace_.addChangeListener(this.reflowWrapper);
    }
  }

  /**
   * @returns True if this flyout may be scrolled with a scrollbar or
   *     by dragging.
   * @internal
   */
  isScrollable(): boolean {
    return this.workspace_.scrollbar
      ? this.workspace_.scrollbar.isVisible()
      : false;
  }

  /**
   * Copy a block from the flyout to the workspace and position it correctly.
   *
   * @param oldBlock The flyout block to copy.
   * @returns The new block in the main workspace.
   */
  private placeNewBlock(oldBlock: BlockSvg): BlockSvg {
    const targetWorkspace = this.targetWorkspace;
    const svgRootOld = oldBlock.getSvgRoot();
    if (!svgRootOld) {
      throw Error('oldBlock is not rendered');
    }

    // Clone the block.
    const json = this.serializeBlock(oldBlock);
    // Normally this resizes leading to weird jumps. Save it for terminateDrag.
    targetWorkspace.setResizesEnabled(false);
    const block = blocks.append(json, targetWorkspace) as BlockSvg;

    this.positionNewBlock(oldBlock, block);

    return block;
  }

  /**
   * Serialize a block to JSON.
   *
   * @param block The block to serialize.
   * @returns A serialized representation of the block.
   */
  protected serializeBlock(block: BlockSvg): blocks.State {
    return blocks.save(block) as blocks.State;
  }

  /**
   * Positions a block on the target workspace.
   *
   * @param oldBlock The flyout block being copied.
   * @param block The block to posiiton.
   */
  private positionNewBlock(oldBlock: BlockSvg, block: BlockSvg) {
    const targetWorkspace = this.targetWorkspace;

    // The offset in pixels between the main workspace's origin and the upper
    // left corner of the injection div.
    const mainOffsetPixels = targetWorkspace.getOriginOffsetInPixels();

    // The offset in pixels between the flyout workspace's origin and the upper
    // left corner of the injection div.
    const flyoutOffsetPixels = this.workspace_.getOriginOffsetInPixels();

    // The position of the old block in flyout workspace coordinates.
    const oldBlockPos = oldBlock.getRelativeToSurfaceXY();
    // The position of the old block in pixels relative to the flyout
    // workspace's origin.
    oldBlockPos.scale(this.workspace_.scale);

    // The position of the old block in pixels relative to the upper left corner
    // of the injection div.
    const oldBlockOffsetPixels = Coordinate.sum(
      flyoutOffsetPixels,
      oldBlockPos,
    );

    // The position of the old block in pixels relative to the origin of the
    // main workspace.
    const finalOffset = Coordinate.difference(
      oldBlockOffsetPixels,
      mainOffsetPixels,
    );
    // The position of the old block in main workspace coordinates.
    finalOffset.scale(1 / targetWorkspace.scale);

    // No 'reason' provided since events are disabled.
    block.moveTo(new Coordinate(finalOffset.x, finalOffset.y));
  }

  /**
   * Returns the inflater responsible for constructing items of the given type.
   *
   * @param type The type of flyout content item to provide an inflater for.
   * @returns An inflater object for the given type, or null if no inflater
   *     is registered for that type.
   */
  protected getInflaterForType(type: string): IFlyoutInflater | null {
    if (this.inflaters.has(type)) {
      return this.inflaters.get(type) ?? null;
    }

    const InflaterClass = registry.getClass(
      registry.Type.FLYOUT_INFLATER,
      type,
    );
    if (InflaterClass) {
      const inflater = new InflaterClass();
      this.inflaters.set(type, inflater);
      return inflater;
    }

    return null;
  }

  /** See IFocusableNode.getFocusableElement. */
  getFocusableElement(): HTMLElement | SVGElement {
    if (!this.svgGroup_) throw new Error('Flyout DOM is not yet created.');
    return this.svgGroup_;
  }

  /** See IFocusableNode.getFocusableTree. */
  getFocusableTree(): IFocusableTree {
    return this;
  }

  /** See IFocusableNode.onNodeFocus. */
  onNodeFocus(): void {}

  /** See IFocusableNode.onNodeBlur. */
  onNodeBlur(): void {}

  /** See IFocusableTree.getRootFocusableNode. */
  getRootFocusableNode(): IFocusableNode {
    return this;
  }

  /** See IFocusableTree.getRestoredFocusableNode. */
  getRestoredFocusableNode(
    _previousNode: IFocusableNode | null,
  ): IFocusableNode | null {
    return null;
  }

  /** See IFocusableTree.getNestedTrees. */
  getNestedTrees(): Array<IFocusableTree> {
    return [this.workspace_];
  }

  /** See IFocusableTree.lookUpFocusableNode. */
  lookUpFocusableNode(_id: string): IFocusableNode | null {
    // No focusable node needs to be returned since the flyout's subtree is a
    // workspace that will manage its own focusable state.
    return null;
  }

  /** See IFocusableTree.onTreeFocus. */
  onTreeFocus(
    _node: IFocusableNode,
    _previousTree: IFocusableTree | null,
  ): void {}

  /** See IFocusableTree.onTreeBlur. */
  onTreeBlur(nextTree: IFocusableTree | null): void {
    const toolbox = this.targetWorkspace.getToolbox();
    // If focus is moving to either the toolbox or the flyout's workspace, do
    // not close the flyout. For anything else, do close it since the flyout is
    // no longer focused.
    if (toolbox && nextTree === toolbox) return;
    if (nextTree == this.workspace_) return;
    if (toolbox) toolbox.clearSelection();
    this.autoHide(false);
  }
}