Add Export tab to `ShareAnnotationsPanel` when export feature flag on

Add basic Export tab with placeholder UI, if `export_annotations`
feature flag is enabled. For other users, share panel looks the same as
before.

src/sidebar/components/ShareAnnotationsPanel.tsx

 import {
+  Button,
+  Card,
+  CardActions,
+  CardTitle,
+  CloseButton,
   CopyIcon,
   IconButton,
   Input,
   InputGroup,
   LockIcon,
   Spinner,
+  TabList,
+  Tab,
 } from '@hypothesis/frontend-shared';
-import { useCallback } from 'preact/hooks';
+import classnames from 'classnames';
+import type { ComponentChildren, JSX } from 'preact';
+import { useCallback, useState } from 'preact/hooks';
 
 import { pageSharingLink } from '../helpers/annotation-sharing';
 import { withServices } from '../service-context';
@@ -16,10 +25,73 @@ import { copyText } from '../util/copy-to-clipboard';
 import ShareLinks from './ShareLinks';
 import SidebarPanel from './SidebarPanel';
 
-export type ShareAnnotationPanelProps = {
-  // injected
-  toastMessenger: ToastMessengerService;
-};
+function LoadingSpinner() {
+  return (
+    <div
+      className="flex flex-row items-center justify-center"
+      data-testid="loading-spinner"
+    >
+      <Spinner size="md" />
+    </div>
+  );
+}
+
+/**
+ * Render a header to go above a Card, with contents in a TabList
+ */
+function TabHeader({ children }: { children: ComponentChildren }) {
+  return (
+    <div data-testid="tab-header" className="flex items-center">
+      <CloseButton
+        classes={classnames(
+          // This element comes first in source order before tabs, but is
+          // positioned last. This puts this button earlier in the tab
+          // sequence than the tabs, allowing tabs to be immediately adjacent
+          // to their controlled tab panels/tab content in the tab sequence.
+          'order-last',
+          // Always render this button at 16px square regardless of parent
+          // font size
+          'text-[16px]',
+          'text-grey-6 hover:text-grey-7 hover:bg-grey-3/50'
+        )}
+        title="Close"
+        variant="custom"
+        size="sm"
+      />
+      <TabList classes="grow gap-x-1 -mb-[1px] z-2">{children}</TabList>
+    </div>
+  );
+}
+
+type TabPanelProps = {
+  active?: boolean;
+  title?: ComponentChildren;
+} & JSX.HTMLAttributes<HTMLDivElement>;
+
+/**
+ * Render a `role="tabpanel"` element within a Card layout. It will be
+ * visually hidden unless `active`.
+ */
+function TabPanel({
+  children,
+  active,
+  title,
+  ...htmlAttributes
+}: TabPanelProps) {
+  return (
+    <div
+      role="tabpanel"
+      {...htmlAttributes}
+      className={classnames('p-3 focus-visible-ring ring-inset', {
+        hidden: !active,
+      })}
+      hidden={!active}
+    >
+      {title && <CardTitle>{title}</CardTitle>}
+      <div className="space-y-3 pt-2">{children}</div>
+    </div>
+  );
+}
 
 type SharePanelContentProps = {
   loading: boolean;
@@ -31,7 +103,7 @@ type SharePanelContentProps = {
 };
 
 /**
- * Render content for "share" panel or tab
+ * Render content for "share" panel or tab.
  */
 function SharePanelContent({
   groupName,
@@ -41,11 +113,7 @@ function SharePanelContent({
   shareURI,
 }: SharePanelContentProps) {
   if (loading) {
-    return (
-      <div className="flex flex-row items-center justify-center">
-        <Spinner size="md" />
-      </div>
-    );
+    return <LoadingSpinner />;
   }
 
   return (
@@ -113,6 +181,43 @@ function SharePanelContent({
   );
 }
 
+type ExportPanelContentProps = {
+  loading: boolean;
+  annotationCount: number;
+};
+
+/**
+ * Render content for "export" tab panel
+ */
+function ExportPanelContent({
+  loading,
+  annotationCount,
+}: ExportPanelContentProps) {
+  if (loading) {
+    return <LoadingSpinner />;
+  }
+
+  // TODO: Handle 0 annotations
+  return (
+    <>
+      <p>
+        Export <strong>{annotationCount} annotations</strong> in a file named:
+      </p>
+      <Input id="export-filename" value="filename-tbd-export.json" />
+      <CardActions>
+        <Button variant="primary" disabled>
+          Export
+        </Button>
+      </CardActions>
+    </>
+  );
+}
+
+export type ShareAnnotationPanelProps = {
+  // injected
+  toastMessenger: ToastMessengerService;
+};
+
 /**
  * A panel for sharing the current group's annotations on the current document.
  *
@@ -126,14 +231,21 @@ function ShareAnnotationsPanel({ toastMessenger }: ShareAnnotationPanelProps) {
   const focusedGroup = store.focusedGroup();
   const groupName = (focusedGroup && focusedGroup.name) || '...';
   const panelTitle = `Share Annotations in ${groupName}`;
+  const allAnnotations = store.allAnnotations();
+
+  const tabbedDialog = store.isFeatureEnabled('export_annotations');
+  const [selectedTab, setSelectedTab] = useState<'share' | 'export'>('share');
 
   // To be able to concoct a sharing link, a focused group and frame need to
   // be available
   const sharingReady = focusedGroup && mainFrame;
+  // Show a loading spinner in the export tab if annotations are loading
+  const exportReady = focusedGroup && !store.isLoading();
 
   const shareURI =
     sharingReady && pageSharingLink(mainFrame.uri, focusedGroup.id);
 
+  // TODO: Move into Share-panel-content component once extracted
   const copyShareLink = useCallback(() => {
     try {
       if (shareURI) {
@@ -146,7 +258,65 @@ function ShareAnnotationsPanel({ toastMessenger }: ShareAnnotationPanelProps) {
   }, [shareURI, toastMessenger]);
 
   return (
-    <SidebarPanel title={panelTitle} panelName="shareGroupAnnotations">
+    <SidebarPanel
+      title={panelTitle}
+      panelName="shareGroupAnnotations"
+      variant={tabbedDialog ? 'custom' : 'panel'}
+    >
+      {tabbedDialog && (
+        <>
+          <TabHeader>
+            <Tab
+              id="share-panel-tab"
+              aria-controls="share-panel"
+              variant="tab"
+              selected={selectedTab === 'share'}
+              onClick={() => setSelectedTab('share')}
+              textContent={'Share'}
+            >
+              Share
+            </Tab>
+            <Tab
+              id="export-panel-tab"
+              aria-controls="export-panel"
+              variant="tab"
+              selected={selectedTab === 'export'}
+              onClick={() => setSelectedTab('export')}
+              textContent="Export"
+            >
+              Export
+            </Tab>
+          </TabHeader>
+          <Card>
+            <TabPanel
+              id="share-panel"
+              active={selectedTab === 'share'}
+              aria-labelledby="share-panel-tab"
+              title={panelTitle}
+            >
+              <SharePanelContent
+                groupName={focusedGroup?.name}
+                groupType={focusedGroup?.type}
+                loading={!sharingReady}
+                onCopyShareLink={copyShareLink}
+                shareURI={shareURI}
+              />
+            </TabPanel>
+            <TabPanel
+              id="export-panel"
+              active={selectedTab === 'export'}
+              aria-labelledby="export-panel-tab"
+              title={`Export from ${focusedGroup?.name ?? '...'}`}
+            >
+              <ExportPanelContent
+                annotationCount={allAnnotations.length}
+                loading={!exportReady}
+              />
+            </TabPanel>
+          </Card>
+        </>
+      )}
+      {!tabbedDialog && (
         <SharePanelContent
           groupName={focusedGroup?.name}
           groupType={focusedGroup?.type}
@@ -154,6 +324,7 @@ function ShareAnnotationsPanel({ toastMessenger }: ShareAnnotationPanelProps) {
           onCopyShareLink={copyShareLink}
           shareURI={shareURI}
         />
+      )}
     </SidebarPanel>
   );
 }

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

 import { mount } from 'enzyme';
+import { act } from 'preact/test-utils';
 
 import { checkAccessibility } from '../../../test-util/accessibility';
 import { mockImportedComponents } from '../../../test-util/mock-imported-components';
@@ -36,7 +37,10 @@ describe('ShareAnnotationsPanel', () => {
     };
 
     fakeStore = {
+      allAnnotations: sinon.stub().returns(0),
       focusedGroup: sinon.stub().returns(fakePrivateGroup),
+      isLoading: sinon.stub().returns(false),
+      isFeatureEnabled: sinon.stub().returns(false),
       mainFrame: () => ({
         uri: 'https://www.example.com',
       }),
@@ -56,8 +60,8 @@ describe('ShareAnnotationsPanel', () => {
     $imports.$restore();
   });
 
-  describe('panel title', () => {
-    it("sets sidebar panel title to include group's name", () => {
+  describe('panel dialog title', () => {
+    it("sets sidebar panel dialog title to include group's name", () => {
       const wrapper = createShareAnnotationsPanel();
 
       assert.equal(
@@ -77,8 +81,8 @@ describe('ShareAnnotationsPanel', () => {
     });
   });
 
-  describe('panel content', () => {
-    it('does not render panel content if needed info not available', () => {
+  describe('share panel content', () => {
+    it('does not render share panel content if needed info not available', () => {
       fakeStore.focusedGroup.returns(undefined);
 
       const wrapper = createShareAnnotationsPanel();
@@ -200,6 +204,92 @@ describe('ShareAnnotationsPanel', () => {
     });
   });
 
+  describe('tabbed dialog panel', () => {
+    it('does not render a tabbed dialog if export feature flag is not enabled', () => {
+      const wrapper = createShareAnnotationsPanel();
+
+      assert.isFalse(wrapper.find('TabHeader').exists());
+    });
+
+    context('export feature enabled', () => {
+      beforeEach(() => {
+        fakeStore.isFeatureEnabled.withArgs('export_annotations').returns(true);
+      });
+
+      it('renders a tabbed dialog with share panel active', () => {
+        const wrapper = createShareAnnotationsPanel();
+
+        assert.isTrue(wrapper.find('TabHeader').exists());
+        assert.isTrue(
+          wrapper.find('Tab[aria-controls="share-panel"]').props().selected
+        );
+        assert.isTrue(
+          wrapper.find('TabPanel[id="share-panel"]').props().active
+        );
+      });
+
+      it('shows the export tab panel when export tab clicked', () => {
+        const wrapper = createShareAnnotationsPanel();
+        const shareTabSelector = 'Tab[aria-controls="share-panel"]';
+        const exportTabSelector = 'Tab[aria-controls="export-panel"]';
+
+        act(() => {
+          wrapper
+            .find(exportTabSelector)
+            .getDOMNode()
+            .dispatchEvent(new Event('click'));
+        });
+        wrapper.update();
+
+        const selectedTab = wrapper.find('Tab').filter({ selected: true });
+        assert.equal(selectedTab.text(), 'Export');
+        assert.equal(selectedTab.props()['aria-controls'], 'export-panel');
+
+        const activeTabPanel = wrapper
+          .find('TabPanel')
+          .filter({ active: true });
+        assert.equal(activeTabPanel.props().id, 'export-panel');
+        assert.isTrue(activeTabPanel.find('Input').exists());
+
+        // Now, reselect share tab
+        act(() => {
+          wrapper
+            .find(shareTabSelector)
+            .getDOMNode()
+            .dispatchEvent(new Event('click'));
+        });
+        wrapper.update();
+
+        const shareTabPanel = wrapper.find('TabPanel').filter({ active: true });
+        assert.equal(shareTabPanel.props().id, 'share-panel');
+      });
+
+      it('shows a loading indicator on the export tab if not ready', () => {
+        const wrapper = createShareAnnotationsPanel();
+        const exportTabSelector = 'Tab[aria-controls="export-panel"]';
+        fakeStore.isLoading.returns(true);
+
+        act(() => {
+          wrapper
+            .find(exportTabSelector)
+            .getDOMNode()
+            .dispatchEvent(new Event('click'));
+        });
+        wrapper.update();
+
+        const activeTabPanel = wrapper
+          .find('TabPanel')
+          .filter({ active: true });
+        assert.equal(activeTabPanel.props().id, 'export-panel');
+        assert.isFalse(activeTabPanel.find('Input').exists());
+        assert.isTrue(
+          activeTabPanel.find('[data-testid="loading-spinner"]').exists()
+        );
+      });
+    });
+  });
+
+  // TODO: Add a11y test for tabbed interface
   it(
     'should pass a11y checks',
     checkAccessibility({