/**
 * @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 type {Abstract as AbstractEvent} from './events/events_abstract.js';
import type {Block} from './block.js';
import type {BlockSvg} from './block_svg.js';
import * as browserEvents from './browser_events.js';
import * as common from './common.js';
import {ComponentManager} from './component_manager.js';
import {DeleteArea} from './delete_area.js';
import * as eventUtils from './events/utils.js';
import {FlyoutButton} from './flyout_button.js';
import {FlyoutMetricsManager} from './flyout_metrics_manager.js';
import type {IFlyout} from './interfaces/i_flyout.js';
import type {Options} from './options.js';
import {ScrollbarPair} from './scrollbar_pair.js';
import * as blocks from './serialization/blocks.js';
import * as Tooltip from './tooltip.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';
import * as utilsXml from './utils/xml.js';
import * as Xml from './xml.js';
import * as renderManagement from './render_management.js';

enum FlyoutItemType {
  BLOCK = 'block',
  BUTTON = 'button',
}

/**
 * Class for a flyout.
 */
export abstract class Flyout extends DeleteArea implements IFlyout {
  /**
   * 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 blocks in the flyout.
   *
   * @param contents The blocks and buttons to lay out.
   * @param gaps The visible gaps between blocks.
   */
  protected abstract layout_(contents: FlyoutItem[], gaps: number[]): void;

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

  /**
   * Compute height of flyout.  Position mat under each block.
   * For RTL: Lay out the blocks 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;

  /**
   * The type of a flyout content item.
   */
  static FlyoutItemType = FlyoutItemType;

  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 blocks in the flyout workspace change.
   */
  private reflowWrapper: ((e: AbstractEvent) => void) | null = null;

  /**
   * Function that disables blocks in the flyout based on max block counts
   * allowed in the target workspace. Registered as a change listener on the
   * target workspace.
   */
  private filterWrapper: ((e: AbstractEvent) => void) | null = null;

  /**
   * List of background mats that lurk behind each block to catch clicks
   * landing in the blocks' lakes and bays.
   */
  private mats: SVGElement[] = [];

  /**
   * List of visible buttons.
   */
  protected buttons_: FlyoutButton[] = [];

  /**
   * List of event listeners.
   */
  private listeners: browserEvents.Data[] = [];

  /**
   * List of blocks that should always be disabled.
   */
  private permanentlyDisabled: Block[] = [];

  protected readonly tabWidth_: number;

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

  /**
   * A list of blocks that can be reused.
   */
  private recycledBlocks: BlockSvg[] = [];

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

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

  /**
   * Whether the workspace containing this flyout is visible.
   */
  private containerVisible = true;
  protected rectMap_: WeakMap<BlockSvg, SVGElement>;

  /**
   * 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;
  /**
   * @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.isVisible_);

    /**
     * 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;

    /**
     * A map from blocks to the rects which are beneath them to act as input
     * targets.
     *
     * @internal
     */
    this.rectMap_ = new WeakMap();

    /**
     * Margin around the edges of the blocks 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',
    });
    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');
    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_,
      ),
    );
    if (!this.autoClose) {
      this.filterWrapper = this.filterForCapacity.bind(this);
      this.targetWorkspace.addChangeListener(this.filterWrapper);
    }

    // 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: 1,
      capabilities: [
        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.workspace_.getComponentManager().removeComponent(this.id);
    for (const event of this.boundEvents) {
      browserEvents.unbind(event);
    }
    this.boundEvents.length = 0;
    if (this.filterWrapper) {
      this.targetWorkspace.removeChangeListener(this.filterWrapper);
    }
    if (this.workspace_) {
      this.workspace_.getThemeManager().unsubscribe(this.svgBackground_!);
      this.workspace_.dispose();
    }
    if (this.svgGroup_) {
      dom.removeNode(this.svgGroup_);
    }
  }

  /**
   * 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_;
  }

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

  /**
   * 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.isVisible_ = 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.workspace_.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();
    }
  }

  /**
   * 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);
    // Delete all the event listeners.
    for (const listen of this.listeners) {
      browserEvents.unbind(listen);
    }
    this.listeners.length = 0;
    if (this.reflowWrapper) {
      this.workspace_.removeChangeListener(this.reflowWrapper);
      this.reflowWrapper = null;
    }
    // Do NOT delete the blocks 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.layout_(flyoutInfo.contents, flyoutInfo.gaps);

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

    this.filterForCapacity();

    // Correctly position the flyout's scrollbar when it opens.
    this.position();

    this.reflowWrapper = this.reflow.bind(this);
    this.workspace_.addChangeListener(this.reflowWrapper);
    this.emptyRecycledBlocks();
  }

  /**
   * 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 and gaps needed to lay out the flyout.
   */
  private createFlyoutInfo(parsedContent: toolbox.FlyoutItemInfoArray): {
    contents: FlyoutItem[];
    gaps: number[];
  } {
    const contents: FlyoutItem[] = [];
    const gaps: number[] = [];
    this.permanentlyDisabled.length = 0;
    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);
        const {contents: dynamicContents, gaps: dynamicGaps} =
          this.createFlyoutInfo(parsedDynamicContent);
        contents.push(...dynamicContents);
        gaps.push(...dynamicGaps);
      }

      switch (info['kind'].toUpperCase()) {
        case 'BLOCK': {
          const blockInfo = info as toolbox.BlockInfo;
          const block = this.createFlyoutBlock(blockInfo);
          contents.push({type: FlyoutItemType.BLOCK, block: block});
          this.addBlockGap(blockInfo, gaps, defaultGap);
          break;
        }
        case 'SEP': {
          const sepInfo = info as toolbox.SeparatorInfo;
          this.addSeparatorGap(sepInfo, gaps, defaultGap);
          break;
        }
        case 'LABEL': {
          const labelInfo = info as toolbox.LabelInfo;
          // A label is a button with different styling.
          const label = this.createButton(labelInfo, /** isLabel */ true);
          contents.push({type: FlyoutItemType.BUTTON, button: label});
          gaps.push(defaultGap);
          break;
        }
        case 'BUTTON': {
          const buttonInfo = info as toolbox.ButtonInfo;
          const button = this.createButton(buttonInfo, /** isLabel */ false);
          contents.push({type: FlyoutItemType.BUTTON, button: button});
          gaps.push(defaultGap);
          break;
        }
      }
    }

    return {contents: contents, gaps: gaps};
  }

  /**
   * 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!);
  }

  /**
   * Creates a flyout button or a flyout label.
   *
   * @param btnInfo The object holding information about a button or a label.
   * @param isLabel True if the button is a label, false otherwise.
   * @returns The object used to display the button in the
   *    flyout.
   */
  private createButton(
    btnInfo: toolbox.ButtonOrLabelInfo,
    isLabel: boolean,
  ): FlyoutButton {
    const curButton = new FlyoutButton(
      this.workspace_,
      this.targetWorkspace as WorkspaceSvg,
      btnInfo,
      isLabel,
    );
    return curButton;
  }

  /**
   * Create a block from the xml and permanently disable any blocks that were
   * defined as disabled.
   *
   * @param blockInfo The info of the block.
   * @returns The block created from the blockInfo.
   */
  private createFlyoutBlock(blockInfo: toolbox.BlockInfo): BlockSvg {
    let block;
    if (blockInfo['blockxml']) {
      const xml = (
        typeof blockInfo['blockxml'] === 'string'
          ? utilsXml.textToDom(blockInfo['blockxml'])
          : blockInfo['blockxml']
      ) as Element;
      block = this.getRecycledBlock(xml.getAttribute('type')!);
      if (!block) {
        block = Xml.domToBlockInternal(xml, this.workspace_);
      }
    } else {
      block = this.getRecycledBlock(blockInfo['type']!);
      if (!block) {
        if (blockInfo['enabled'] === undefined) {
          blockInfo['enabled'] =
            blockInfo['disabled'] !== 'true' && blockInfo['disabled'] !== true;
        }
        block = blocks.appendInternal(
          blockInfo as blocks.State,
          this.workspace_,
        );
      }
    }

    if (!block.isEnabled()) {
      // Record blocks that were initially disabled.
      // Do not enable these blocks as a result of capacity filtering.
      this.permanentlyDisabled.push(block);
    }
    return block as BlockSvg;
  }

  /**
   * Returns a block from the array of recycled blocks with the given type, or
   * undefined if one cannot be found.
   *
   * @param blockType The type of the block to try to recycle.
   * @returns The recycled block, or undefined if
   *     one could not be recycled.
   */
  private getRecycledBlock(blockType: string): BlockSvg | undefined {
    let index = -1;
    for (let i = 0; i < this.recycledBlocks.length; i++) {
      if (this.recycledBlocks[i].type === blockType) {
        index = i;
        break;
      }
    }
    return index === -1 ? undefined : this.recycledBlocks.splice(index, 1)[0];
  }

  /**
   * Adds a gap in the flyout based on block info.
   *
   * @param blockInfo Information about a block.
   * @param gaps The list of gaps between items in the flyout.
   * @param defaultGap The default gap between one element and the
   *     next.
   */
  private addBlockGap(
    blockInfo: toolbox.BlockInfo,
    gaps: number[],
    defaultGap: number,
  ) {
    let gap;
    if (blockInfo['gap']) {
      gap = parseInt(String(blockInfo['gap']));
    } else if (blockInfo['blockxml']) {
      const xml = (
        typeof blockInfo['blockxml'] === 'string'
          ? utilsXml.textToDom(blockInfo['blockxml'])
          : blockInfo['blockxml']
      ) as Element;
      gap = parseInt(xml.getAttribute('gap')!);
    }
    gaps.push(!gap || isNaN(gap) ? defaultGap : gap);
  }

  /**
   * Add the necessary gap in the flyout for a separator.
   *
   * @param sepInfo The object holding
   *    information about a separator.
   * @param gaps The list gaps between items in the flyout.
   * @param defaultGap The default gap between the button and next
   *     element.
   */
  private addSeparatorGap(
    sepInfo: toolbox.SeparatorInfo,
    gaps: number[],
    defaultGap: number,
  ) {
    // Change the gap between two toolbox elements.
    // <sep gap="36"></sep>
    // The default gap is 24, can be set larger or smaller.
    // This overwrites the gap attribute on the previous element.
    const newGap = parseInt(String(sepInfo['gap']));
    // Ignore gaps before the first block.
    if (!isNaN(newGap) && gaps.length > 0) {
      gaps[gaps.length - 1] = newGap;
    } else {
      gaps.push(defaultGap);
    }
  }

  /**
   * Delete blocks, mats and buttons from a previous showing of the flyout.
   */
  private clearOldBlocks() {
    // Delete any blocks from a previous showing.
    const oldBlocks = this.workspace_.getTopBlocks(false);
    for (let i = 0, block; (block = oldBlocks[i]); i++) {
      if (this.blockIsRecyclable_(block)) {
        this.recycleBlock(block);
      } else {
        block.dispose(false, false);
      }
    }
    // Delete any mats from a previous showing.
    for (let j = 0; j < this.mats.length; j++) {
      const rect = this.mats[j];
      if (rect) {
        Tooltip.unbindMouseEvents(rect);
        dom.removeNode(rect);
      }
    }
    this.mats.length = 0;
    // Delete any buttons from a previous showing.
    for (let i = 0, button; (button = this.buttons_[i]); i++) {
      button.dispose();
    }
    this.buttons_.length = 0;

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

  /**
   * Empties all of the recycled blocks, properly disposing of them.
   */
  private emptyRecycledBlocks() {
    for (let i = 0; i < this.recycledBlocks.length; i++) {
      this.recycledBlocks[i].dispose();
    }
    this.recycledBlocks = [];
  }

  /**
   * Returns whether the given block can be recycled or not.
   *
   * @param _block The block to check for recyclability.
   * @returns True if the block can be recycled. False otherwise.
   */
  protected blockIsRecyclable_(_block: BlockSvg): boolean {
    // By default, recycling is disabled.
    return false;
  }

  /**
   * Puts a previously created block into the recycle bin and moves it to the
   * top of the workspace. Used during large workspace swaps to limit the number
   * of new DOM elements we need to create.
   *
   * @param block The block to recycle.
   */
  private recycleBlock(block: BlockSvg) {
    const xy = block.getRelativeToSurfaceXY();
    block.moveBy(-xy.x, -xy.y);
    this.recycledBlocks.push(block);
  }

  /**
   * Add listeners to a block that has been added to the flyout.
   *
   * @param root The root node of the SVG group the block is in.
   * @param block The block to add listeners for.
   * @param rect The invisible rectangle under the block that acts
   *     as a mat for that block.
   */
  protected addBlockListeners_(
    root: SVGElement,
    block: BlockSvg,
    rect: SVGElement,
  ) {
    this.listeners.push(
      browserEvents.conditionalBind(
        root,
        'pointerdown',
        null,
        this.blockMouseDown(block),
      ),
    );
    this.listeners.push(
      browserEvents.conditionalBind(
        rect,
        'pointerdown',
        null,
        this.blockMouseDown(block),
      ),
    );
    this.listeners.push(
      browserEvents.bind(root, 'pointerenter', block, block.addSelect),
    );
    this.listeners.push(
      browserEvents.bind(root, 'pointerleave', block, block.removeSelect),
    );
    this.listeners.push(
      browserEvents.bind(rect, 'pointerenter', block, block.addSelect),
    );
    this.listeners.push(
      browserEvents.bind(rect, 'pointerleave', block, block.removeSelect),
    );
  }

  /**
   * Handle a pointerdown on an SVG block in a non-closing flyout.
   *
   * @param block The flyout block to copy.
   * @returns Function to call when block is clicked.
   */
  private blockMouseDown(block: BlockSvg): Function {
    return (e: PointerEvent) => {
      const gesture = this.targetWorkspace.getGesture(e);
      if (gesture) {
        gesture.setStartBlock(block);
        gesture.handleFlyoutStart(e, this);
      }
    };
  }

  /**
   * 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();
  }

  /**
   * 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(eventUtils.VAR_CREATE))(thisVariable),
        );
      }

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

  /**
   * Initialize the given button: move it to the correct location,
   * add listeners, etc.
   *
   * @param button The button to initialize and place.
   * @param x The x position of the cursor during this layout pass.
   * @param y The y position of the cursor during this layout pass.
   */
  protected initFlyoutButton_(button: FlyoutButton, x: number, y: number) {
    const buttonSvg = button.createDom();
    button.moveTo(x, y);
    button.show();
    // Clicking on a flyout button or label is a lot like clicking on the
    // flyout background.
    this.listeners.push(
      browserEvents.conditionalBind(
        buttonSvg,
        'pointerdown',
        this,
        this.onMouseDown,
      ),
    );

    this.buttons_.push(button);
  }

  /**
   * Create and place a rectangle corresponding to the given block.
   *
   * @param block The block to associate the rect to.
   * @param x The x position of the cursor during this layout pass.
   * @param y The y position of the cursor during this layout pass.
   * @param blockHW The height and width of
   *     the block.
   * @param index The index into the mats list where this rect should
   *     be placed.
   * @returns Newly created SVG element for the rectangle behind
   *     the block.
   */
  protected createRect_(
    block: BlockSvg,
    x: number,
    y: number,
    blockHW: {height: number; width: number},
    index: number,
  ): SVGElement {
    // Create an invisible rectangle under the block to act as a button.  Just
    // using the block as a button is poor, since blocks have holes in them.
    const rect = dom.createSvgElement(Svg.RECT, {
      'fill-opacity': 0,
      'x': x,
      'y': y,
      'height': blockHW.height,
      'width': blockHW.width,
    });
    (rect as AnyDuringMigration).tooltip = block;
    Tooltip.bindMouseEvents(rect);
    // Add the rectangles under the blocks, so that the blocks' tooltips work.
    this.workspace_.getCanvas().insertBefore(rect, block.getSvgRoot());

    this.rectMap_.set(block, rect);
    this.mats[index] = rect;
    return rect;
  }

  /**
   * Move a rectangle to sit exactly behind a block, taking into account tabs,
   * hats, and any other protrusions we invent.
   *
   * @param rect The rectangle to move directly behind the block.
   * @param block The block the rectangle should be behind.
   */
  protected moveRectToBlock_(rect: SVGElement, block: BlockSvg) {
    const blockHW = block.getHeightWidth();
    rect.setAttribute('width', String(blockHW.width));
    rect.setAttribute('height', String(blockHW.height));

    const blockXY = block.getRelativeToSurfaceXY();
    rect.setAttribute('y', String(blockXY.y));
    rect.setAttribute(
      'x',
      String(this.RTL ? blockXY.x - blockHW.width : blockXY.x),
    );
  }

  /**
   * Filter the blocks on the flyout to disable the ones that are above the
   * capacity limit.  For instance, if the user may only place two more blocks
   * on the workspace, an "a + b" block that has two shadow blocks would be
   * disabled.
   */
  private filterForCapacity() {
    const blocks = this.workspace_.getTopBlocks(false);
    for (let i = 0, block; (block = blocks[i]); i++) {
      if (this.permanentlyDisabled.indexOf(block) === -1) {
        const enable = this.targetWorkspace.isCapacityAvailable(
          common.getBlockTypeCounts(block),
        );
        while (block) {
          block.setEnabled(enable);
          block = block.getNextBlock();
        }
      }
    }
  }

  /**
   * Reflow blocks and their mats.
   */
  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.
    // TODO(#7432): Add a saveIds parameter to `save`.
    const json = blocks.save(oldBlock) as blocks.State;
    // Normallly 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;
  }

  /**
   * 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));
  }
}

/**
 * A flyout content item.
 */
export interface FlyoutItem {
  type: FlyoutItemType;
  button?: FlyoutButton | undefined;
  block?: BlockSvg | undefined;
}