Generic hover service support

packages/core/src/browser/frontend-application-module.ts

@@ -135,6 +135,7 @@ import { bindStatusBar } from './status-bar';
 import { MarkdownRenderer, MarkdownRendererFactory, MarkdownRendererImpl } from './markdown-rendering/markdown-renderer';
 import { StylingParticipant, StylingService } from './styling-service';
 import { bindCommonStylingParticipants } from './common-styling-participants';
+import { HoverService } from './hover-service';
 
 export { bindResourceProvider, bindMessageService, bindPreferenceService };
 
@@ -186,7 +187,8 @@ export const frontendApplicationModule = new ContainerModule((bind, _unbind, _is
         const selectionService = container.get(SelectionService);
         const commandService = container.get<CommandService>(CommandService);
         const corePreferences = container.get<CorePreferences>(CorePreferences);
-        return new TabBarRenderer(contextMenuRenderer, tabBarDecoratorService, iconThemeService, selectionService, commandService, corePreferences);
+        const hoverService = container.get(HoverService);
+        return new TabBarRenderer(contextMenuRenderer, tabBarDecoratorService, iconThemeService, selectionService, commandService, corePreferences, hoverService);
     });
     bind(TheiaDockPanel.Factory).toFactory(({ container }) => options => {
         const corePreferences = container.get<CorePreferences>(CorePreferences);
@@ -433,6 +435,8 @@ export const frontendApplicationModule = new ContainerModule((bind, _unbind, _is
     bind(SaveResourceService).toSelf().inSingletonScope();
     bind(UserWorkingDirectoryProvider).toSelf().inSingletonScope();
 
+    bind(HoverService).toSelf().inSingletonScope();
+
     bind(StylingService).toSelf().inSingletonScope();
     bindContributionProvider(bind, StylingParticipant);
     bind(FrontendApplicationContribution).toService(StylingService);

packages/core/src/browser/hover-service.ts

@@ -0,0 +1,189 @@
+// *****************************************************************************
+// Copyright (C) 2022 Ericsson and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// http://www.eclipse.org/legal/epl-2.0.
+//
+// This Source Code may also be made available under the following Secondary
+// Licenses when the conditions for such availability set forth in the Eclipse
+// Public License v. 2.0 are satisfied: GNU General Public License, version 2
+// with the GNU Classpath Exception which is available at
+// https://www.gnu.org/software/classpath/license.html.
+//
+// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+// *****************************************************************************
+
+import { inject, injectable } from 'inversify';
+import { Disposable, DisposableCollection, disposableTimeout, isOSX } from '../common';
+import { MarkdownString } from '../common/markdown-rendering/markdown-string';
+import { animationFrame } from './browser';
+import { MarkdownRenderer, MarkdownRendererFactory } from './markdown-rendering/markdown-renderer';
+import { PreferenceService } from './preferences';
+
+import '../../src/browser/style/hover-service.css';
+
+export type HoverPosition = 'left' | 'right' | 'top' | 'bottom';
+
+export namespace HoverPosition {
+    export function invertIfNecessary(position: HoverPosition, target: DOMRect, host: DOMRect, totalWidth: number, totalHeight: number): HoverPosition {
+        if (position === 'left') {
+            if (target.left - host.width - 5 < 0) {
+                return 'right';
+            }
+        } else if (position === 'right') {
+            if (target.right + host.width + 5 > totalWidth) {
+                return 'left';
+            }
+        } else if (position === 'top') {
+            if (target.top - host.height - 5 < 0) {
+                return 'bottom';
+            }
+        } else if (position === 'bottom') {
+            if (target.bottom + host.height + 5 > totalHeight) {
+                return 'top';
+            }
+        }
+        return position;
+    }
+}
+
+export interface HoverRequest {
+    content: string | MarkdownString | HTMLElement
+    target: HTMLElement
+    /**
+     * The position where the hover should appear.
+     * Note that the hover service will try to invert the position (i.e. right -> left)
+     * if the specified content does not fit in the window next to the target element
+     */
+    position: HoverPosition
+}
+
+@injectable()
+export class HoverService {
+    protected static hostClassName = 'theia-hover';
+    protected static styleSheetId = 'theia-hover-style';
+    @inject(PreferenceService) protected readonly preferences: PreferenceService;
+    @inject(MarkdownRendererFactory) protected readonly markdownRendererFactory: MarkdownRendererFactory;
+
+    protected _markdownRenderer: MarkdownRenderer | undefined;
+    protected get markdownRenderer(): MarkdownRenderer {
+        this._markdownRenderer ||= this.markdownRendererFactory();
+        return this._markdownRenderer;
+    }
+
+    protected _hoverHost: HTMLElement | undefined;
+    protected get hoverHost(): HTMLElement {
+        if (!this._hoverHost) {
+            this._hoverHost = document.createElement('div');
+            this._hoverHost.classList.add(HoverService.hostClassName);
+            this._hoverHost.style.position = 'absolute';
+        }
+        return this._hoverHost;
+    }
+    protected pendingTimeout: Disposable | undefined;
+    protected hoverTarget: HTMLElement | undefined;
+    protected lastHidHover = Date.now();
+    protected readonly disposeOnHide = new DisposableCollection();
+
+    requestHover(request: HoverRequest): void {
+        if (request.target !== this.hoverTarget) {
+            this.cancelHover();
+            this.pendingTimeout = disposableTimeout(() => this.renderHover(request), this.getHoverDelay());
+        }
+    }
+
+    protected getHoverDelay(): number {
+        return Date.now() - this.lastHidHover < 200
+            ? 0
+            : this.preferences.get('workbench.hover.delay', isOSX ? 1500 : 500);
+    }
+
+    protected async renderHover(request: HoverRequest): Promise<void> {
+        const host = this.hoverHost;
+        const { target, content, position } = request;
+        this.hoverTarget = target;
+        if (content instanceof HTMLElement) {
+            host.appendChild(content);
+        } else if (typeof content === 'string') {
+            host.textContent = content;
+        } else {
+            const renderedContent = this.markdownRenderer.render(content);
+            this.disposeOnHide.push(renderedContent);
+            host.appendChild(renderedContent.element);
+        }
+        // browsers might insert linebreaks when the hover appears at the edge of the window
+        // resetting the position prevents that
+        host.style.left = '0px';
+        host.style.top = '0px';
+        document.body.append(host);
+        await animationFrame(); // Allow the browser to size the host
+        const updatedPosition = this.setHostPosition(target, host, position);
+
+        this.disposeOnHide.push({
+            dispose: () => {
+                this.lastHidHover = Date.now();
+                host.classList.remove(updatedPosition);
+            }
+        });
+
+        this.listenForMouseOut();
+    }
+
+    protected setHostPosition(target: HTMLElement, host: HTMLElement, position: HoverPosition): HoverPosition {
+        const targetDimensions = target.getBoundingClientRect();
+        const hostDimensions = host.getBoundingClientRect();
+        const documentWidth = document.body.getBoundingClientRect().width;
+        // document.body.getBoundingClientRect().height doesn't work as expected
+        // scrollHeight will always be accurate here: https://stackoverflow.com/a/44077777
+        const documentHeight = document.documentElement.scrollHeight;
+        position = HoverPosition.invertIfNecessary(position, targetDimensions, hostDimensions, documentWidth, documentHeight);
+        if (position === 'top' || position === 'bottom') {
+            const targetMiddleWidth = targetDimensions.left + (targetDimensions.width / 2);
+            const middleAlignment = targetMiddleWidth - (hostDimensions.width / 2);
+            const furthestRight = Math.min(documentWidth - hostDimensions.width, middleAlignment);
+            const left = Math.max(0, furthestRight);
+            const top = position === 'top'
+                ? targetDimensions.top - hostDimensions.height - 5
+                : targetDimensions.bottom + 5;
+            host.style.setProperty('--theia-hover-before-position', `${targetMiddleWidth - left - 5}px`);
+            host.style.top = `${top}px`;
+            host.style.left = `${left}px`;
+        } else {
+            const targetMiddleHeight = targetDimensions.top + (targetDimensions.height / 2);
+            const middleAlignment = targetMiddleHeight - (hostDimensions.height / 2);
+            const furthestTop = Math.min(documentHeight - hostDimensions.height, middleAlignment);
+            const top = Math.max(0, furthestTop);
+            const left = position === 'left'
+                ? targetDimensions.left - hostDimensions.width - 5
+                : targetDimensions.right + 5;
+            host.style.setProperty('--theia-hover-before-position', `${targetMiddleHeight - top - 5}px`);
+            host.style.left = `${left}px`;
+            host.style.top = `${top}px`;
+        }
+        host.classList.add(position);
+        return position;
+    }
+
+    protected listenForMouseOut(): void {
+        const handleMouseMove = (e: MouseEvent) => {
+            if (e.target instanceof Node && !this.hoverHost.contains(e.target) && !this.hoverTarget?.contains(e.target)) {
+                this.cancelHover();
+            }
+        };
+        document.addEventListener('mousemove', handleMouseMove);
+        this.disposeOnHide.push({ dispose: () => document.removeEventListener('mousemove', handleMouseMove) });
+    }
+
+    cancelHover(): void {
+        this.pendingTimeout?.dispose();
+        this.unRenderHover();
+        this.disposeOnHide.dispose();
+        this.hoverTarget = undefined;
+    }
+
+    protected unRenderHover(): void {
+        this.hoverHost.remove();
+        this.hoverHost.replaceChildren();
+    }
+}

packages/core/src/browser/index.ts

@@ -43,3 +43,4 @@ export * from './breadcrumbs';
 export * from './tooltip-service';
 export * from './decoration-style';
 export * from './styling-service';
+export * from './hover-service';