feat: multiple playground choices (#5207)

* poc of using netlify functions for playground redirections

* push

* cleanup

* restore files

* fix netlify functions?

* fix netlify functions?

* implement serverless functions for playgrounds with persistent cookie

* move new.docusaurus.io to monorepo packages

* move new.docusaurus.io to monorepo packages

* lockfile

* push

* catch-all redirect

* Translate/Interpolate: add better error message if not used correctly

* Add /docs/playground page

* Add some additional doc

admin/new.docusaurus.io/functionUtils/playgroundUtils.ts

@@ -0,0 +1,77 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {HandlerEvent, HandlerResponse} from '@netlify/functions';
+
+const CookieName = 'DocusaurusPlaygroundName';
+
+const PlaygroundConfigs = {
+  codesandbox: 'https://codesandbox.io/s/docusaurus',
+  stackblitz: 'https://stackblitz.com/fork/docusaurus',
+};
+
+const PlaygroundDocumentationUrl = 'https://docusaurus.io/docs/playground';
+
+export type PlaygroundName = keyof typeof PlaygroundConfigs;
+
+function isValidPlaygroundName(
+  playgroundName: string,
+): playgroundName is PlaygroundName {
+  return Object.keys(PlaygroundConfigs).includes(playgroundName);
+}
+
+export function createPlaygroundDocumentationResponse(): HandlerResponse {
+  return {
+    statusCode: 302,
+    headers: {
+      Location: PlaygroundDocumentationUrl,
+    },
+  };
+}
+
+export function createPlaygroundResponse(
+  playgroundName: PlaygroundName,
+): HandlerResponse {
+  const playgroundUrl = PlaygroundConfigs[playgroundName];
+  return {
+    statusCode: 302,
+    headers: {
+      Location: playgroundUrl,
+      'Set-Cookie': `${CookieName}=${playgroundName}`,
+    },
+  };
+}
+
+// Inspired by https://stackoverflow.com/a/3409200/82609
+function parseCookieString(cookieString: string): Record<string, string> {
+  const result: Record<string, string> = {};
+  cookieString.split(';').forEach(function (cookie) {
+    const [name, value] = cookie.split('=');
+    result[name.trim()] = decodeURI(value);
+  });
+  return result;
+}
+
+export function readPlaygroundName(
+  event: HandlerEvent,
+): PlaygroundName | undefined {
+  const parsedCookie: Record<string, string> = event.headers.cookie
+    ? parseCookieString(event.headers.cookie)
+    : {};
+  const playgroundName: string | undefined = parsedCookie[CookieName];
+
+  if (playgroundName) {
+    if (isValidPlaygroundName(playgroundName)) {
+      return playgroundName;
+    } else {
+      console.error(
+        `playgroundName found in cookie was invalid: ${playgroundName}`,
+      );
+    }
+  }
+  return undefined;
+}