front_end/ui/legacy/SplitWidget.ts

/*
 * Copyright (C) 2012 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import * as Common from '../../core/common/common.js';
import * as Platform from '../../core/platform/platform.js';
import * as VisualLogging from '../visual_logging/visual_logging.js';

import * as ARIAUtils from './ARIAUtils.js';
import {Constraints} from './Geometry.js';
import {Events as ResizerWidgetEvents, type ResizeUpdatePositionEvent, SimpleResizerWidget} from './ResizerWidget.js';
import splitWidgetStyles from './splitWidget.css.legacy.js';
import {ToolbarButton} from './Toolbar.js';
import {Widget} from './Widget.js';
import {Events as ZoomManagerEvents, ZoomManager} from './ZoomManager.js';

export class SplitWidget extends Common.ObjectWrapper.eventMixin<EventTypes, typeof Widget>(Widget) {
  private sidebarElementInternal: HTMLElement;
  private mainElement: HTMLElement;
  private resizerElementInternal: HTMLElement;
  private resizerElementSize: number|null;
  private readonly resizerWidget: SimpleResizerWidget;
  private defaultSidebarWidth: number;
  private defaultSidebarHeight: number;
  private readonly constraintsInDip: boolean;
  private resizeStartSizeDIP: number;
  // TODO(crbug.com/1172300) Ignored during the jsdoc to ts migration
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  private setting: Common.Settings.Setting<any>|null;
  private totalSizeCSS: number;
  private totalSizeOtherDimensionCSS: number;
  private mainWidgetInternal: Widget|null;
  private sidebarWidgetInternal: Widget|null;
  private animationFrameHandle: number;
  private animationCallback: (() => void)|null;
  private showSidebarButtonTitle: Common.UIString.LocalizedString;
  private hideSidebarButtonTitle: Common.UIString.LocalizedString;
  private shownSidebarString: Common.UIString.LocalizedString;
  private hiddenSidebarString: Common.UIString.LocalizedString;
  private showHideSidebarButton: ToolbarButton|null;
  private isVerticalInternal: boolean;
  private sidebarMinimized: boolean;
  private detaching: boolean;
  private sidebarSizeDIP: number;
  private savedSidebarSizeDIP: number;
  private secondIsSidebar: boolean;
  private shouldSaveShowMode: boolean;
  private savedVerticalMainSize: number|null;
  private savedHorizontalMainSize: number|null;
  private showModeInternal: string;
  private savedShowMode: string;

  constructor(
      isVertical: boolean, secondIsSidebar: boolean, settingName?: string, defaultSidebarWidth?: number,
      defaultSidebarHeight?: number, constraintsInDip?: boolean) {
    super(true);
    this.element.classList.add('split-widget');
    this.registerRequiredCSS(splitWidgetStyles);

    this.contentElement.classList.add('shadow-split-widget');
    this.sidebarElementInternal =
        this.contentElement.createChild('div', 'shadow-split-widget-contents shadow-split-widget-sidebar vbox');
    this.mainElement =
        this.contentElement.createChild('div', 'shadow-split-widget-contents shadow-split-widget-main vbox');
    (this.mainElement.createChild('slot') as HTMLSlotElement).name = 'insertion-point-main';
    (this.sidebarElementInternal.createChild('slot') as HTMLSlotElement).name = 'insertion-point-sidebar';
    this.resizerElementInternal = this.contentElement.createChild('div', 'shadow-split-widget-resizer');
    this.resizerElementSize = null;

    this.resizerWidget = new SimpleResizerWidget();
    this.resizerWidget.setEnabled(true);
    this.resizerWidget.addEventListener(ResizerWidgetEvents.ResizeStart, this.onResizeStart, this);
    this.resizerWidget.addEventListener(ResizerWidgetEvents.ResizeUpdatePosition, this.onResizeUpdate, this);
    this.resizerWidget.addEventListener(ResizerWidgetEvents.ResizeEnd, this.onResizeEnd, this);

    this.defaultSidebarWidth = defaultSidebarWidth || 200;
    this.defaultSidebarHeight = defaultSidebarHeight || this.defaultSidebarWidth;
    this.constraintsInDip = Boolean(constraintsInDip);
    this.resizeStartSizeDIP = 0;
    this.setting = settingName ? Common.Settings.Settings.instance().createSetting(settingName, {}) : null;

    this.totalSizeCSS = 0;
    this.totalSizeOtherDimensionCSS = 0;
    this.mainWidgetInternal = null;
    this.sidebarWidgetInternal = null;
    this.animationFrameHandle = 0;
    this.animationCallback = null;
    this.showSidebarButtonTitle = Common.UIString.LocalizedEmptyString;
    this.hideSidebarButtonTitle = Common.UIString.LocalizedEmptyString;
    this.shownSidebarString = Common.UIString.LocalizedEmptyString;
    this.hiddenSidebarString = Common.UIString.LocalizedEmptyString;
    this.showHideSidebarButton = null;
    this.isVerticalInternal = false;
    this.sidebarMinimized = false;
    this.detaching = false;
    this.sidebarSizeDIP = -1;
    this.savedSidebarSizeDIP = this.sidebarSizeDIP;
    this.secondIsSidebar = false;
    this.shouldSaveShowMode = false;
    this.savedVerticalMainSize = null;
    this.savedHorizontalMainSize = null;

    this.setSecondIsSidebar(secondIsSidebar);

    this.innerSetVertical(isVertical);
    this.showModeInternal = ShowMode.Both;
    this.savedShowMode = this.showModeInternal;

    // Should be called after isVertical has the right value.
    this.installResizer(this.resizerElementInternal);
  }

  isVertical(): boolean {
    return this.isVerticalInternal;
  }

  setVertical(isVertical: boolean): void {
    if (this.isVerticalInternal === isVertical) {
      return;
    }

    this.innerSetVertical(isVertical);

    if (this.isShowing()) {
      this.updateLayout();
    }
  }

  private innerSetVertical(isVertical: boolean): void {
    this.contentElement.classList.toggle('vbox', !isVertical);
    this.contentElement.classList.toggle('hbox', isVertical);
    this.isVerticalInternal = isVertical;

    this.resizerElementSize = null;
    this.sidebarSizeDIP = -1;
    this.restoreSidebarSizeFromSettings();
    if (this.shouldSaveShowMode) {
      this.restoreAndApplyShowModeFromSettings();
    }
    this.updateShowHideSidebarButton();
    // FIXME: reverse SplitWidget.isVertical meaning.
    this.resizerWidget.setVertical(!isVertical);
    this.invalidateConstraints();
  }

  private updateLayout(animate?: boolean): void {
    this.totalSizeCSS = 0;  // Lazy update.
    this.totalSizeOtherDimensionCSS = 0;

    // Remove properties that might affect total size calculation.
    this.mainElement.style.removeProperty('width');
    this.mainElement.style.removeProperty('height');
    this.sidebarElementInternal.style.removeProperty('width');
    this.sidebarElementInternal.style.removeProperty('height');

    this.innerSetSidebarSizeDIP(this.preferredSidebarSizeDIP(), Boolean(animate));
  }

  setMainWidget(widget: Widget): void {
    if (this.mainWidgetInternal === widget) {
      return;
    }
    this.suspendInvalidations();
    if (this.mainWidgetInternal) {
      this.mainWidgetInternal.detach();
    }
    this.mainWidgetInternal = widget;
    if (widget) {
      widget.element.slot = 'insertion-point-main';
      if (this.showModeInternal === ShowMode.OnlyMain || this.showModeInternal === ShowMode.Both) {
        widget.show(this.element);
      }
    }
    this.resumeInvalidations();
  }

  setSidebarWidget(widget: Widget): void {
    if (this.sidebarWidgetInternal === widget) {
      return;
    }
    this.suspendInvalidations();
    if (this.sidebarWidgetInternal) {
      this.sidebarWidgetInternal.detach();
    }
    this.sidebarWidgetInternal = widget;
    if (widget) {
      widget.element.slot = 'insertion-point-sidebar';
      if (this.showModeInternal === ShowMode.OnlySidebar || this.showModeInternal === ShowMode.Both) {
        widget.show(this.element);
      }
    }
    this.resumeInvalidations();
  }

  mainWidget(): Widget|null {
    return this.mainWidgetInternal;
  }

  sidebarWidget(): Widget|null {
    return this.sidebarWidgetInternal;
  }

  sidebarElement(): HTMLElement {
    return this.sidebarElementInternal;
  }

  override childWasDetached(widget: Widget): void {
    if (this.detaching) {
      return;
    }
    if (this.mainWidgetInternal === widget) {
      this.mainWidgetInternal = null;
    }
    if (this.sidebarWidgetInternal === widget) {
      this.sidebarWidgetInternal = null;
    }
    this.invalidateConstraints();
  }

  isSidebarSecond(): boolean {
    return this.secondIsSidebar;
  }

  enableShowModeSaving(): void {
    this.shouldSaveShowMode = true;
    this.restoreAndApplyShowModeFromSettings();
  }

  showMode(): string {
    return this.showModeInternal;
  }

  setSecondIsSidebar(secondIsSidebar: boolean): void {
    if (secondIsSidebar === this.secondIsSidebar) {
      return;
    }
    this.secondIsSidebar = secondIsSidebar;
    if (!this.mainWidgetInternal || !this.mainWidgetInternal.shouldHideOnDetach()) {
      if (secondIsSidebar) {
        this.contentElement.insertBefore(this.mainElement, this.sidebarElementInternal);
      } else {
        this.contentElement.insertBefore(this.mainElement, this.resizerElementInternal);
      }
    } else if (!this.sidebarWidgetInternal || !this.sidebarWidgetInternal.shouldHideOnDetach()) {
      if (secondIsSidebar) {
        this.contentElement.insertBefore(this.sidebarElementInternal, this.resizerElementInternal);
      } else {
        this.contentElement.insertBefore(this.sidebarElementInternal, this.mainElement);
      }
    } else {
      console.error('Could not swap split widget side. Both children widgets contain iframes.');
      this.secondIsSidebar = !secondIsSidebar;
    }
  }

  sidebarSide(): string|null {
    if (this.showModeInternal !== ShowMode.Both) {
      return null;
    }
    return this.isVerticalInternal ? (this.secondIsSidebar ? 'right' : 'left') :
                                     (this.secondIsSidebar ? 'bottom' : 'top');
  }

  resizerElement(): Element {
    return this.resizerElementInternal;
  }

  hideMain(animate?: boolean): void {
    this.showOnly(
        this.sidebarWidgetInternal, this.mainWidgetInternal, this.sidebarElementInternal, this.mainElement, animate);
    this.updateShowMode(ShowMode.OnlySidebar);
  }

  hideSidebar(animate?: boolean): void {
    this.showOnly(
        this.mainWidgetInternal, this.sidebarWidgetInternal, this.mainElement, this.sidebarElementInternal, animate);
    this.updateShowMode(ShowMode.OnlyMain);
  }

  setSidebarMinimized(minimized: boolean): void {
    this.sidebarMinimized = minimized;
    this.invalidateConstraints();
  }

  isSidebarMinimized(): boolean {
    return this.sidebarMinimized;
  }

  private showOnly(
      sideToShow: Widget|null, sideToHide: Widget|null, shadowToShow: Element, shadowToHide: Element,
      animate?: boolean): void {
    this.cancelAnimation();

    function callback(this: SplitWidget): void {
      if (sideToShow) {
        // Make sure main is first in the children list.
        if (sideToShow === this.mainWidgetInternal) {
          this.mainWidgetInternal.show(
              this.element, this.sidebarWidgetInternal ? this.sidebarWidgetInternal.element : null);
        } else if (this.sidebarWidgetInternal) {
          this.sidebarWidgetInternal.show(this.element);
        }
      }
      if (sideToHide) {
        this.detaching = true;
        sideToHide.detach();
        this.detaching = false;
      }

      this.resizerElementInternal.classList.add('hidden');
      shadowToShow.classList.remove('hidden');
      shadowToShow.classList.add('maximized');
      shadowToHide.classList.add('hidden');
      shadowToHide.classList.remove('maximized');
      this.removeAllLayoutProperties();
      this.doResize();
      this.showFinishedForTest();
    }

    if (animate) {
      this.animate(true, callback.bind(this));
    } else {
      callback.call(this);
    }

    this.sidebarSizeDIP = -1;
    this.setResizable(false);
  }

  private showFinishedForTest(): void {
    // This method is sniffed in tests.
  }

  private removeAllLayoutProperties(): void {
    this.sidebarElementInternal.style.removeProperty('flexBasis');

    this.mainElement.style.removeProperty('width');
    this.mainElement.style.removeProperty('height');
    this.sidebarElementInternal.style.removeProperty('width');
    this.sidebarElementInternal.style.removeProperty('height');

    this.resizerElementInternal.style.removeProperty('left');
    this.resizerElementInternal.style.removeProperty('right');
    this.resizerElementInternal.style.removeProperty('top');
    this.resizerElementInternal.style.removeProperty('bottom');

    this.resizerElementInternal.style.removeProperty('margin-left');
    this.resizerElementInternal.style.removeProperty('margin-right');
    this.resizerElementInternal.style.removeProperty('margin-top');
    this.resizerElementInternal.style.removeProperty('margin-bottom');
  }

  showBoth(animate?: boolean): void {
    if (this.showModeInternal === ShowMode.Both) {
      animate = false;
    }

    this.cancelAnimation();
    this.mainElement.classList.remove('maximized', 'hidden');
    this.sidebarElementInternal.classList.remove('maximized', 'hidden');
    this.resizerElementInternal.classList.remove('hidden');
    this.setResizable(true);

    // Make sure main is the first in the children list.
    this.suspendInvalidations();
    if (this.sidebarWidgetInternal) {
      this.sidebarWidgetInternal.show(this.element);
    }
    if (this.mainWidgetInternal) {
      this.mainWidgetInternal.show(
          this.element, this.sidebarWidgetInternal ? this.sidebarWidgetInternal.element : null);
    }
    this.resumeInvalidations();
    // Order widgets in DOM properly.
    this.setSecondIsSidebar(this.secondIsSidebar);

    this.sidebarSizeDIP = -1;
    this.updateShowMode(ShowMode.Both);
    this.updateLayout(animate);
  }

  setResizable(resizable: boolean): void {
    this.resizerWidget.setEnabled(resizable);
  }

  forceSetSidebarWidth(width: number): void {
    this.defaultSidebarWidth = width;
    this.savedSidebarSizeDIP = width;
    this.updateLayout();
  }

  isResizable(): boolean {
    return this.resizerWidget.isEnabled();
  }

  setSidebarSize(size: number): void {
    const sizeDIP = ZoomManager.instance().cssToDIP(size);
    this.savedSidebarSizeDIP = sizeDIP;
    this.saveSetting();
    this.innerSetSidebarSizeDIP(sizeDIP, false, true);
  }

  sidebarSize(): number {
    const sizeDIP = Math.max(0, this.sidebarSizeDIP);
    return ZoomManager.instance().dipToCSS(sizeDIP);
  }

  /**
   * Returns total size in DIP.
   */
  private totalSizeDIP(): number {
    if (!this.totalSizeCSS) {
      this.totalSizeCSS = this.isVerticalInternal ? this.contentElement.offsetWidth : this.contentElement.offsetHeight;
      this.totalSizeOtherDimensionCSS =
          this.isVerticalInternal ? this.contentElement.offsetHeight : this.contentElement.offsetWidth;
    }
    return ZoomManager.instance().cssToDIP(this.totalSizeCSS);
  }

  private updateShowMode(showMode: string): void {
    this.showModeInternal = showMode;
    this.saveShowModeToSettings();
    this.updateShowHideSidebarButton();
    this.dispatchEventToListeners(Events.ShowModeChanged, showMode);
    this.invalidateConstraints();
  }

  private innerSetSidebarSizeDIP(sizeDIP: number, animate: boolean, userAction?: boolean): void {
    if (this.showModeInternal !== ShowMode.Both || !this.isShowing()) {
      return;
    }

    sizeDIP = this.applyConstraints(sizeDIP, userAction);
    if (this.sidebarSizeDIP === sizeDIP) {
      return;
    }

    if (!this.resizerElementSize) {
      this.resizerElementSize =
          this.isVerticalInternal ? this.resizerElementInternal.offsetWidth : this.resizerElementInternal.offsetHeight;
    }

    // Invalidate layout below.

    this.removeAllLayoutProperties();

    // this.totalSizeDIP is available below since we successfully applied constraints.
    const roundSizeCSS = Math.round(ZoomManager.instance().dipToCSS(sizeDIP));
    const sidebarSizeValue = roundSizeCSS + 'px';
    const mainSizeValue = (this.totalSizeCSS - roundSizeCSS) + 'px';
    this.sidebarElementInternal.style.flexBasis = sidebarSizeValue;

    // Make both sides relayout boundaries.
    if (this.isVerticalInternal) {
      this.sidebarElementInternal.style.width = sidebarSizeValue;
      this.mainElement.style.width = mainSizeValue;
      this.sidebarElementInternal.style.height = this.totalSizeOtherDimensionCSS + 'px';
      this.mainElement.style.height = this.totalSizeOtherDimensionCSS + 'px';
    } else {
      this.sidebarElementInternal.style.height = sidebarSizeValue;
      this.mainElement.style.height = mainSizeValue;
      this.sidebarElementInternal.style.width = this.totalSizeOtherDimensionCSS + 'px';
      this.mainElement.style.width = this.totalSizeOtherDimensionCSS + 'px';
    }

    // Position resizer.
    if (this.isVerticalInternal) {
      if (this.secondIsSidebar) {
        this.resizerElementInternal.style.right = sidebarSizeValue;
        this.resizerElementInternal.style.marginRight = -this.resizerElementSize / 2 + 'px';
      } else {
        this.resizerElementInternal.style.left = sidebarSizeValue;
        this.resizerElementInternal.style.marginLeft = -this.resizerElementSize / 2 + 'px';
      }
    } else {
      if (this.secondIsSidebar) {
        this.resizerElementInternal.style.bottom = sidebarSizeValue;
        this.resizerElementInternal.style.marginBottom = -this.resizerElementSize / 2 + 'px';
      } else {
        this.resizerElementInternal.style.top = sidebarSizeValue;
        this.resizerElementInternal.style.marginTop = -this.resizerElementSize / 2 + 'px';
      }
    }

    this.sidebarSizeDIP = sizeDIP;

    // Force layout.

    if (animate) {
      this.animate(false);
    } else {
      // No need to recalculate this.sidebarSizeDIP and this.totalSizeDIP again.
      this.doResize();
      this.dispatchEventToListeners(Events.SidebarSizeChanged, this.sidebarSize());
    }
  }

  private animate(reverse: boolean, callback?: (() => void)): void {
    const animationTime = 50;
    this.animationCallback = callback || null;

    let animatedMarginPropertyName: string;
    if (this.isVerticalInternal) {
      animatedMarginPropertyName = this.secondIsSidebar ? 'margin-right' : 'margin-left';
    } else {
      animatedMarginPropertyName = this.secondIsSidebar ? 'margin-bottom' : 'margin-top';
    }

    const marginFrom = reverse ? '0' : '-' + ZoomManager.instance().dipToCSS(this.sidebarSizeDIP) + 'px';
    const marginTo = reverse ? '-' + ZoomManager.instance().dipToCSS(this.sidebarSizeDIP) + 'px' : '0';

    // This order of things is important.
    // 1. Resize main element early and force layout.
    this.contentElement.style.setProperty(animatedMarginPropertyName, marginFrom);
    this.contentElement.style.setProperty('overflow', 'hidden');
    if (!reverse) {
      suppressUnused(this.mainElement.offsetWidth);
      suppressUnused(this.sidebarElementInternal.offsetWidth);
    }

    // 2. Issue onresize to the sidebar element, its size won't change.
    if (!reverse && this.sidebarWidgetInternal) {
      this.sidebarWidgetInternal.doResize();
    }

    // 3. Configure and run animation
    this.contentElement.style.setProperty('transition', animatedMarginPropertyName + ' ' + animationTime + 'ms linear');

    const boundAnimationFrame = animationFrame.bind(this);
    let startTime: number|null = null;
    function animationFrame(this: SplitWidget): void {
      this.animationFrameHandle = 0;

      if (!startTime) {
        // Kick animation on first frame.
        this.contentElement.style.setProperty(animatedMarginPropertyName, marginTo);
        startTime = window.performance.now();
      } else if (window.performance.now() < startTime + animationTime) {
        // Process regular animation frame.
        if (this.mainWidgetInternal) {
          this.mainWidgetInternal.doResize();
        }
      } else {
        // Complete animation.
        this.cancelAnimation();
        if (this.mainWidgetInternal) {
          this.mainWidgetInternal.doResize();
        }
        this.dispatchEventToListeners(Events.SidebarSizeChanged, this.sidebarSize());
        return;
      }
      this.animationFrameHandle = this.contentElement.window().requestAnimationFrame(boundAnimationFrame);
    }
    this.animationFrameHandle = this.contentElement.window().requestAnimationFrame(boundAnimationFrame);
  }

  private cancelAnimation(): void {
    this.contentElement.style.removeProperty('margin-top');
    this.contentElement.style.removeProperty('margin-right');
    this.contentElement.style.removeProperty('margin-bottom');
    this.contentElement.style.removeProperty('margin-left');
    this.contentElement.style.removeProperty('transition');
    this.contentElement.style.removeProperty('overflow');

    if (this.animationFrameHandle) {
      this.contentElement.window().cancelAnimationFrame(this.animationFrameHandle);
      this.animationFrameHandle = 0;
    }
    if (this.animationCallback) {
      this.animationCallback();
      this.animationCallback = null;
    }
  }

  private applyConstraints(sidebarSize: number, userAction?: boolean): number {
    const totalSize = this.totalSizeDIP();
    const zoomFactor = this.constraintsInDip ? 1 : ZoomManager.instance().zoomFactor();

    let constraints: Constraints =
        this.sidebarWidgetInternal ? this.sidebarWidgetInternal.constraints() : new Constraints();
    let minSidebarSize: 20|number = this.isVertical() ? constraints.minimum.width : constraints.minimum.height;
    if (!minSidebarSize) {
      minSidebarSize = MinPadding;
    }
    minSidebarSize *= zoomFactor;
    if (this.sidebarMinimized) {
      sidebarSize = minSidebarSize;
    }

    let preferredSidebarSize: 20|number =
        this.isVertical() ? constraints.preferred.width : constraints.preferred.height;
    if (!preferredSidebarSize) {
      preferredSidebarSize = MinPadding;
    }
    preferredSidebarSize *= zoomFactor;
    // Allow sidebar to be less than preferred by explicit user action.
    if (sidebarSize < preferredSidebarSize) {
      preferredSidebarSize = Math.max(sidebarSize, minSidebarSize);
    }
    preferredSidebarSize += zoomFactor;  // 1 css pixel for splitter border.

    constraints = this.mainWidgetInternal ? this.mainWidgetInternal.constraints() : new Constraints();
    let minMainSize: 20|number = this.isVertical() ? constraints.minimum.width : constraints.minimum.height;
    if (!minMainSize) {
      minMainSize = MinPadding;
    }
    minMainSize *= zoomFactor;

    let preferredMainSize: 20|number = this.isVertical() ? constraints.preferred.width : constraints.preferred.height;
    if (!preferredMainSize) {
      preferredMainSize = MinPadding;
    }
    preferredMainSize *= zoomFactor;
    const savedMainSize = this.isVertical() ? this.savedVerticalMainSize : this.savedHorizontalMainSize;
    if (savedMainSize !== null) {
      preferredMainSize = Math.min(preferredMainSize, savedMainSize * zoomFactor);
    }
    if (userAction) {
      preferredMainSize = minMainSize;
    }

    // Enough space for preferred.
    const totalPreferred = preferredMainSize + preferredSidebarSize;
    if (totalPreferred <= totalSize) {
      return Platform.NumberUtilities.clamp(sidebarSize, preferredSidebarSize, totalSize - preferredMainSize);
    }

    // Enough space for minimum.
    if (minMainSize + minSidebarSize <= totalSize) {
      const delta = totalPreferred - totalSize;
      const sidebarDelta = delta * preferredSidebarSize / totalPreferred;
      sidebarSize = preferredSidebarSize - sidebarDelta;
      return Platform.NumberUtilities.clamp(sidebarSize, minSidebarSize, totalSize - minMainSize);
    }

    // Not enough space even for minimum sizes.
    return Math.max(0, totalSize - minMainSize);
  }

  override wasShown(): void {
    this.forceUpdateLayout();
    ZoomManager.instance().addEventListener(ZoomManagerEvents.ZoomChanged, this.onZoomChanged, this);
  }

  override willHide(): void {
    ZoomManager.instance().removeEventListener(ZoomManagerEvents.ZoomChanged, this.onZoomChanged, this);
  }

  override onResize(): void {
    this.updateLayout();
  }

  override onLayout(): void {
    this.updateLayout();
  }

  override calculateConstraints(): Constraints {
    if (this.showModeInternal === ShowMode.OnlyMain) {
      return this.mainWidgetInternal ? this.mainWidgetInternal.constraints() : new Constraints();
    }
    if (this.showModeInternal === ShowMode.OnlySidebar) {
      return this.sidebarWidgetInternal ? this.sidebarWidgetInternal.constraints() : new Constraints();
    }

    let mainConstraints: Constraints =
        this.mainWidgetInternal ? this.mainWidgetInternal.constraints() : new Constraints();
    let sidebarConstraints: Constraints =
        this.sidebarWidgetInternal ? this.sidebarWidgetInternal.constraints() : new Constraints();
    const min = MinPadding;
    if (this.isVerticalInternal) {
      mainConstraints = mainConstraints.widthToMax(min).addWidth(1);  // 1 for splitter
      sidebarConstraints = sidebarConstraints.widthToMax(min);
      return mainConstraints.addWidth(sidebarConstraints).heightToMax(sidebarConstraints);
    }
    mainConstraints = mainConstraints.heightToMax(min).addHeight(1);  // 1 for splitter
    sidebarConstraints = sidebarConstraints.heightToMax(min);
    return mainConstraints.widthToMax(sidebarConstraints).addHeight(sidebarConstraints);
  }

  private onResizeStart(): void {
    this.resizeStartSizeDIP = this.sidebarSizeDIP;
  }

  private onResizeUpdate(event: Common.EventTarget.EventTargetEvent<ResizeUpdatePositionEvent>): void {
    const offset = event.data.currentPosition - event.data.startPosition;
    const offsetDIP = ZoomManager.instance().cssToDIP(offset);
    const newSizeDIP = this.secondIsSidebar ? this.resizeStartSizeDIP - offsetDIP : this.resizeStartSizeDIP + offsetDIP;
    const constrainedSizeDIP = this.applyConstraints(newSizeDIP, true);
    this.savedSidebarSizeDIP = constrainedSizeDIP;
    this.saveSetting();
    this.innerSetSidebarSizeDIP(constrainedSizeDIP, false, true);
    if (this.isVertical()) {
      this.savedVerticalMainSize = this.totalSizeDIP() - this.sidebarSizeDIP;
    } else {
      this.savedHorizontalMainSize = this.totalSizeDIP() - this.sidebarSizeDIP;
    }
  }

  private onResizeEnd(): void {
    this.resizeStartSizeDIP = 0;
  }

  hideDefaultResizer(noSplitter?: boolean): void {
    this.resizerElementInternal.classList.toggle('hidden', Boolean(noSplitter));
    this.uninstallResizer(this.resizerElementInternal);
    this.sidebarElementInternal.classList.toggle('no-default-splitter', Boolean(noSplitter));
  }

  installResizer(resizerElement: Element): void {
    this.resizerWidget.addElement((resizerElement as HTMLElement));
  }

  uninstallResizer(resizerElement: Element): void {
    this.resizerWidget.removeElement((resizerElement as HTMLElement));
  }

  hasCustomResizer(): boolean {
    const elements = this.resizerWidget.elements();
    return elements.length > 1 || (elements.length === 1 && elements[0] !== this.resizerElementInternal);
  }

  toggleResizer(resizer: Element, on: boolean): void {
    if (on) {
      this.installResizer(resizer);
    } else {
      this.uninstallResizer(resizer);
    }
  }

  private settingForOrientation(): SettingForOrientation|null {
    const state = this.setting ? this.setting.get() : {};
    return this.isVerticalInternal ? state.vertical : state.horizontal;
  }

  private preferredSidebarSizeDIP(): number {
    let size: number = this.savedSidebarSizeDIP;
    if (!size) {
      size = this.isVerticalInternal ? this.defaultSidebarWidth : this.defaultSidebarHeight;
      // If we have default value in percents, calculate it on first use.
      if (0 < size && size < 1) {
        size *= this.totalSizeDIP();
      }
    }
    return size;
  }

  private restoreSidebarSizeFromSettings(): void {
    const settingForOrientation = this.settingForOrientation();
    this.savedSidebarSizeDIP = settingForOrientation ? settingForOrientation.size : 0;
  }

  private restoreAndApplyShowModeFromSettings(): void {
    const orientationState = this.settingForOrientation();
    this.savedShowMode =
        orientationState && orientationState.showMode ? orientationState.showMode : this.showModeInternal;
    this.showModeInternal = this.savedShowMode;

    switch (this.savedShowMode) {
      case ShowMode.Both:
        this.showBoth();
        break;
      case ShowMode.OnlyMain:
        this.hideSidebar();
        break;
      case ShowMode.OnlySidebar:
        this.hideMain();
        break;
    }
  }

  private saveShowModeToSettings(): void {
    this.savedShowMode = this.showModeInternal;
    this.saveSetting();
  }

  private saveSetting(): void {
    if (!this.setting) {
      return;
    }
    const state = this.setting.get();
    const orientationState = (this.isVerticalInternal ? state.vertical : state.horizontal) || {};

    orientationState.size = this.savedSidebarSizeDIP;
    if (this.shouldSaveShowMode) {
      orientationState.showMode = this.savedShowMode;
    }

    if (this.isVerticalInternal) {
      state.vertical = orientationState;
    } else {
      state.horizontal = orientationState;
    }
    this.setting.set(state);
  }

  private forceUpdateLayout(): void {
    // Force layout even if sidebar size does not change.
    this.sidebarSizeDIP = -1;
    this.updateLayout();
  }

  private onZoomChanged(): void {
    this.forceUpdateLayout();
  }

  createShowHideSidebarButton(
      showTitle: Common.UIString.LocalizedString, hideTitle: Common.UIString.LocalizedString,
      shownString: Common.UIString.LocalizedString, hiddenString: Common.UIString.LocalizedString,
      jslogContext?: string): ToolbarButton {
    this.showSidebarButtonTitle = showTitle;
    this.hideSidebarButtonTitle = hideTitle;
    this.shownSidebarString = shownString;
    this.hiddenSidebarString = hiddenString;
    this.showHideSidebarButton = new ToolbarButton('', '');
    this.showHideSidebarButton.addEventListener(ToolbarButton.Events.Click, buttonClicked, this);
    if (jslogContext) {
      this.showHideSidebarButton.element.setAttribute(
          'jslog', `${VisualLogging.toggleSubpane().track({click: true}).context(jslogContext)}`);
    }
    this.updateShowHideSidebarButton();

    function buttonClicked(this: SplitWidget): void {
      this.toggleSidebar();
    }

    return this.showHideSidebarButton;
  }

  /**
   * @returns true if this call makes the sidebar visible, and false otherwise.
   */
  toggleSidebar(): boolean {
    if (this.showModeInternal !== ShowMode.Both) {
      this.showBoth(true);
      ARIAUtils.alert(this.shownSidebarString);
      return true;
    }
    this.hideSidebar(true);
    ARIAUtils.alert(this.hiddenSidebarString);
    return false;
  }

  private updateShowHideSidebarButton(): void {
    if (!this.showHideSidebarButton) {
      return;
    }
    const sidebarHidden = this.showModeInternal === ShowMode.OnlyMain;
    let glyph = '';
    if (sidebarHidden) {
      glyph = this.isVertical() ? (this.isSidebarSecond() ? 'right-panel-open' : 'left-panel-open') :
                                  (this.isSidebarSecond() ? 'bottom-panel-open' : 'top-panel-open');
    } else {
      glyph = this.isVertical() ? (this.isSidebarSecond() ? 'right-panel-close' : 'left-panel-close') :
                                  (this.isSidebarSecond() ? 'bottom-panel-close' : 'top-panel-close');
    }
    this.showHideSidebarButton.setGlyph(glyph);
    this.showHideSidebarButton.setTitle(sidebarHidden ? this.showSidebarButtonTitle : this.hideSidebarButtonTitle);
  }
}

export const enum ShowMode {
  Both = 'Both',
  OnlyMain = 'OnlyMain',
  OnlySidebar = 'OnlySidebar',
}

export const enum Events {
  SidebarSizeChanged = 'SidebarSizeChanged',
  ShowModeChanged = 'ShowModeChanged',
}

export type EventTypes = {
  [Events.SidebarSizeChanged]: number,
  [Events.ShowModeChanged]: string,
};

const MinPadding = 20;
export interface SettingForOrientation {
  showMode: string;
  size: number;
}

const suppressUnused = function(_value: unknown): void {};