(core) Direct users to last visited site when possible

Summary:
When clicking the logo in the top-left corner, or finishing a tutorial, we
now direct users to the site they last visited, if possible. If unknown, a
new redirect endpoint, /welcome/home, is used instead, which directs users
to a sensible location based on the number of sites they have.

Test Plan: Browser tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3878

app/client/ui/AppHeader.ts

@@ -1,4 +1,4 @@
-import {urlState} from 'app/client/models/gristUrlState';
+import {getWelcomeHomeUrl, urlState} from 'app/client/models/gristUrlState';
 import {buildAppMenuBillingItem} from 'app/client/ui/BillingButtons';
 import {getTheme} from 'app/client/ui/CustomThemes';
 import {cssLeftPane} from 'app/client/ui/PagePanels';
@@ -48,7 +48,7 @@ export class AppHeader extends Disposable {
       cssAppLogo(
         {title: `Version ${version.version}` +
           ((version.gitcommit as string) !== 'unknown' ? ` (${version.gitcommit})` : '')},
-        urlState().setLinkUrl({}),
+        this._setHomePageUrl(),
         testId('dm-logo')
       ),
       cssOrg(
@@ -79,6 +79,15 @@ export class AppHeader extends Disposable {
       ),
     );
   }
+
+  private _setHomePageUrl() {
+    const lastVisitedOrg = this._appModel.lastVisitedOrgDomain.get();
+    if (lastVisitedOrg) {
+      return urlState().setLinkUrl({org: lastVisitedOrg});
+    } else {
+      return {href: getWelcomeHomeUrl()};
+    }
+  }
 }
 
 export function productPill(org: Organization|null, options: {large?: boolean} = {}): DomContents {

app/client/ui/DocTutorial.ts

@@ -1,5 +1,5 @@
 import {GristDoc} from 'app/client/components/GristDoc';
-import {urlState} from 'app/client/models/gristUrlState';
+import {getWelcomeHomeUrl, urlState} from 'app/client/models/gristUrlState';
 import {renderer} from 'app/client/ui/DocTutorialRenderer';
 import {cssPopupBody, FloatingPopup} from 'app/client/ui/FloatingPopup';
 import {sanitizeHTML} from 'app/client/ui/sanitizeHTML';
@@ -242,7 +242,12 @@ export class DocTutorial extends FloatingPopup {
   private async _finishTutorial() {
     this._saveCurrentSlidePositionDebounced.cancel();
     await this._saveCurrentSlidePosition();
-    await urlState().pushUrl({});
+    const lastVisitedOrg = this._appModel.lastVisitedOrgDomain.get();
+    if (lastVisitedOrg) {
+      await urlState().pushUrl({org: lastVisitedOrg});
+    } else {
+      window.location.assign(getWelcomeHomeUrl());
+    }
   }
 
   private async _restartTutorial() {