Display suggestions popover when at-mentioning

src/sidebar/components/Annotation/AnnotationEditor.tsx

@@ -179,6 +179,7 @@ function AnnotationEditor({
         label={isReplyAnno ? 'Enter reply' : 'Enter comment'}
         text={text}
         onEditText={onEditText}
+        atMentionsEnabled={store.isFeatureEnabled('at_mentions')}
       />
       <TagEditor
         onAddTag={onAddTag}

src/sidebar/components/Annotation/test/AnnotationEditor-test.js

@@ -61,6 +61,7 @@ describe('AnnotationEditor', () => {
       setDefault: sinon.stub(),
       removeDraft: sinon.stub(),
       removeAnnotations: sinon.stub(),
+      isFeatureEnabled: sinon.stub().returns(false),
     };
 
     $imports.$mock(mockImportedComponents());

src/sidebar/components/MarkdownEditor.tsx

@@ -1,4 +1,10 @@
-import { Button, IconButton, Link } from '@hypothesis/frontend-shared';
+import {
+  Button,
+  IconButton,
+  Link,
+  Popover,
+  useSyncedRef,
+} from '@hypothesis/frontend-shared';
 import {
   EditorLatexIcon,
   EditorQuoteIcon,
@@ -16,6 +22,7 @@ import classnames from 'classnames';
 import type { Ref, JSX } from 'preact';
 import { useEffect, useMemo, useRef, useState } from 'preact/hooks';
 
+import { ListenerCollection } from '../../shared/listener-collection';
 import { isMacOS } from '../../shared/user-agent';
 import {
   LinkType,
@@ -24,6 +31,7 @@ import {
   toggleSpanStyle,
 } from '../markdown-commands';
 import type { EditorState } from '../markdown-commands';
+import { termBeforePosition } from '../util/term-before-position';
 import MarkdownView from './MarkdownView';
 
 /**
@@ -176,24 +184,69 @@ function ToolbarButton({
 type TextAreaProps = {
   classes?: string;
   containerRef?: Ref<HTMLTextAreaElement>;
+  atMentionsEnabled: boolean;
 };
 
 function TextArea({
   classes,
   containerRef,
+  atMentionsEnabled,
   ...restProps
 }: TextAreaProps & JSX.TextareaHTMLAttributes<HTMLTextAreaElement>) {
+  const [popoverOpen, setPopoverOpen] = useState(false);
+  const textareaRef = useSyncedRef(containerRef);
+
+  useEffect(() => {
+    if (!atMentionsEnabled) {
+      return () => {};
+    }
+
+    const textarea = textareaRef.current!;
+    const listenerCollection = new ListenerCollection();
+
+    // We listen for `keyup` to make sure the text in the textarea reflects the
+    // just-pressed key when we evaluate it
+    listenerCollection.add(textarea, 'keyup', e => {
+      // `Esc` key is used to close the popover. Do nothing and let users close
+      // it that way, even if the caret is in a mention
+      if (e.key === 'Escape') {
+        return;
+      }
+      setPopoverOpen(
+        termBeforePosition(textarea.value, textarea.selectionStart).startsWith(
+          '@',
+        ),
+      );
+    });
+
+    return () => {
+      listenerCollection.removeAll();
+    };
+  }, [atMentionsEnabled, popoverOpen, textareaRef]);
+
   return (
-    <textarea
-      className={classnames(
-        'border rounded p-2',
-        'text-color-text-light bg-grey-0',
-        'focus:bg-white focus:outline-none focus:shadow-focus-inner',
-        classes,
+    <div className="relative">
+      <textarea
+        className={classnames(
+          'border rounded p-2',
+          'text-color-text-light bg-grey-0',
+          'focus:bg-white focus:outline-none focus:shadow-focus-inner',
+          classes,
+        )}
+        {...restProps}
+        ref={textareaRef}
+      />
+      {atMentionsEnabled && (
+        <Popover
+          open={popoverOpen}
+          onClose={() => setPopoverOpen(false)}
+          anchorElementRef={textareaRef}
+          classes="p-2"
+        >
+          Suggestions
+        </Popover>
       )}
-      {...restProps}
-      ref={containerRef}
-    />
+    </div>
   );
 }
 
@@ -322,6 +375,12 @@ function Toolbar({ isPreviewing, onCommand, onTogglePreview }: ToolbarProps) {
 }
 
 export type MarkdownEditorProps = {
+  /**
+   * Whether the at-mentions feature ir enabled or not.
+   * Defaults to false.
+   */
+  atMentionsEnabled?: boolean;
+
   /** An accessible label for the input field */
   label: string;
 
@@ -338,6 +397,7 @@ export type MarkdownEditorProps = {
  * Viewer/editor for the body of an annotation in markdown format.
  */
 export default function MarkdownEditor({
+  atMentionsEnabled = false,
   label,
   onEditText = () => {},
   text,
@@ -411,6 +471,7 @@ export default function MarkdownEditor({
           }
           value={text}
           style={textStyle}
+          atMentionsEnabled={atMentionsEnabled}
         />
       )}
     </div>

src/sidebar/components/test/MarkdownEditor-test.js

@@ -50,11 +50,20 @@ describe('MarkdownEditor', () => {
 
   function createComponent(props = {}, mountProps = {}) {
     return mount(
-      <MarkdownEditor label="Test editor" text="test" {...props} />,
+      <MarkdownEditor
+        label="Test editor"
+        text="test"
+        atMentionsEnabled={false}
+        {...props}
+      />,
       mountProps,
     );
   }
 
+  function createConnectedComponent(props = {}) {
+    return createComponent(props, { connected: true });
+  }
+
   const commands = [
     {
       command: 'Bold',
@@ -373,6 +382,98 @@ describe('MarkdownEditor', () => {
     assert.deepEqual(wrapper.find('MarkdownView').prop('style'), textStyle);
   });
 
+  context('when @mentions are enabled', () => {
+    function typeInTextarea(wrapper, text, key = undefined) {
+      const textarea = wrapper.find('textarea');
+      const textareaDOMNode = textarea.getDOMNode();
+
+      textareaDOMNode.value = text;
+      act(() =>
+        textareaDOMNode.dispatchEvent(new KeyboardEvent('keyup', { key })),
+      );
+      wrapper.update();
+    }
+
+    [true, false].forEach(atMentionsEnabled => {
+      it('renders Popover if @mentions are enabled', () => {
+        const wrapper = createComponent({ atMentionsEnabled });
+        assert.equal(wrapper.exists('Popover'), atMentionsEnabled);
+      });
+    });
+
+    it('opens Popover when an @mention is typed in textarea', () => {
+      const wrapper = createConnectedComponent({ atMentionsEnabled: true });
+      typeInTextarea(wrapper, '@johndoe');
+
+      assert.isTrue(wrapper.find('Popover').prop('open'));
+    });
+
+    it('closes Popover when cursor moves away from @mention', () => {
+      const wrapper = createConnectedComponent({ atMentionsEnabled: true });
+
+      // Popover is open after typing the at-mention
+      typeInTextarea(wrapper, '@johndoe');
+      assert.isTrue(wrapper.find('Popover').prop('open'));
+
+      // Once a space is typed after the at-mention, the popover is closed
+      typeInTextarea(wrapper, '@johndoe ');
+      assert.isFalse(wrapper.find('Popover').prop('open'));
+    });
+
+    it('closes Popover when @mention is removed', () => {
+      const wrapper = createConnectedComponent({ atMentionsEnabled: true });
+
+      // Popover is open after typing the at-mention
+      typeInTextarea(wrapper, '@johndoe');
+      assert.isTrue(wrapper.find('Popover').prop('open'));
+
+      // Once the at-mention is removed, the popover is closed
+      typeInTextarea(wrapper, '');
+      assert.isFalse(wrapper.find('Popover').prop('open'));
+    });
+
+    it('opens Popover when cursor moves into an @mention', () => {
+      const text = '@johndoe ';
+      const wrapper = createConnectedComponent({
+        text,
+        atMentionsEnabled: true,
+      });
+
+      const textarea = wrapper.find('textarea');
+      const textareaDOMNode = textarea.getDOMNode();
+
+      // Popover is initially closed
+      assert.isFalse(wrapper.find('Popover').prop('open'));
+
+      // Move cursor to the left
+      textareaDOMNode.selectionStart = text.length - 1;
+      act(() => textareaDOMNode.dispatchEvent(new KeyboardEvent('keyup')));
+      wrapper.update();
+
+      assert.isTrue(wrapper.find('Popover').prop('open'));
+    });
+
+    it('closes Popover when onClose is called', () => {
+      const wrapper = createConnectedComponent({ atMentionsEnabled: true });
+
+      // Popover is initially open
+      typeInTextarea(wrapper, '@johndoe');
+      assert.isTrue(wrapper.find('Popover').prop('open'));
+
+      wrapper.find('Popover').props().onClose();
+      wrapper.update();
+      assert.isFalse(wrapper.find('Popover').prop('open'));
+    });
+
+    it('ignores `Escape` key press in textarea', () => {
+      const wrapper = createConnectedComponent({ atMentionsEnabled: true });
+
+      // Popover is still closed if the key is `Escape`
+      typeInTextarea(wrapper, '@johndoe', 'Escape');
+      assert.isFalse(wrapper.find('Popover').prop('open'));
+    });
+  });
+
   it(
     'should pass a11y checks',
     checkAccessibility([

src/sidebar/util/term-before-position.ts

@@ -0,0 +1,9 @@
+/**
+ * Returns the "word" right before a specific position in an input string.
+ *
+ * In this context, a word is anything between a space or newline, and provided
+ * position.
+ */
+export function termBeforePosition(text: string, position: number): string {
+  return text.slice(0, position).match(/\S+$/)?.[0] ?? '';
+}

src/sidebar/util/test/term-before-position-test.js

@@ -0,0 +1,72 @@
+import { termBeforePosition } from '../term-before-position';
+
+describe('term-before-position', () => {
+  // To make these tests more predictable, we place the `$` sign in the position
+  // to be checked. That way it's easier to see what is the "word" preceding it.
+  // The test will then get the `$` sign index and remove it from the text
+  // before passing it to `termBeforePosition`.
+  [
+    // First and last positions
+    {
+      text: '$Hello world',
+      expectedTerm: '',
+    },
+    {
+      text: 'Hello world$',
+      expectedTerm: 'world',
+    },
+
+    // Position in the middle of words
+    {
+      text: 'Hell$o world',
+      expectedTerm: 'Hell',
+    },
+    {
+      text: 'Hello wor$ld',
+      expectedTerm: 'wor',
+    },
+
+    // Position preceded by "empty space"
+    {
+      text: 'Hello $world',
+      expectedTerm: '',
+    },
+    {
+      text: `Text with
+      multiple
+      $
+      lines
+      `,
+      expectedTerm: '',
+    },
+
+    // Position preceded by/in the middle of a word for multi-line text
+    {
+      text: `Text with$
+      multiple
+      
+      lines
+      `,
+      expectedTerm: 'with',
+    },
+    {
+      text: `Text with
+      multiple
+      
+      li$nes
+      `,
+      expectedTerm: 'li',
+    },
+  ].forEach(({ text, expectedTerm }) => {
+    it('returns the term right before provided position', () => {
+      // Get the position of the `$` sign in the text, then remove it
+      const position = text.indexOf('$');
+      const textWithoutDollarSign = text.replace('$', '');
+
+      assert.equal(
+        termBeforePosition(textWithoutDollarSign, position),
+        expectedTerm,
+      );
+    });
+  });
+});