Don't allow AB test to reset once it's set (#3945)

Author: CompuIves

packages/homepage/src/pages/index.js

@@ -1,5 +1,4 @@
 import React from 'react';
-import { identify } from '@codesandbox/common/lib/utils/analytics';
 
 import TitleAndMetaTags from '../components/TitleAndMetaTags';
 import Layout, { WRAPPER_STYLING } from '../components/layout';
@@ -14,6 +13,8 @@ import Share from '../screens/home/share';
 import Join from '../screens/home/join';
 import Explore from '../screens/home/explore';
 
+import { identifyFromCookie } from '../utils/identifyFromCookie';
+
 // eslint-disable-next-line
 console.log(
   'Hi, We love curious people that dive in to see how things are working! We are always looking for talented, hard working people. Drop us a line and show us your work. We are hiring: https://codesandbox.io/jobs'
@@ -59,6 +60,6 @@ const Homepage = () => (
   </Layout>
 );
 
-identify('hero0420', 'A');
+identifyFromCookie('heroAB', 'hero0420');
 
 export default Homepage;

packages/homepage/src/pages/index2.js

@@ -1,5 +1,4 @@
 import React from 'react';
-import { identify } from '@codesandbox/common/lib/utils/analytics';
 
 import TitleAndMetaTags from '../components/TitleAndMetaTags';
 import Layout, { WRAPPER_STYLING } from '../components/layout';
@@ -13,6 +12,8 @@ import Share from '../screens/home/share';
 import Join from '../screens/home/join';
 import Explore from '../screens/home/explore';
 
+import { identifyFromCookie } from '../utils/identifyFromCookie';
+
 // eslint-disable-next-line
 console.log(
   'Hi, We love curious people that dive in to see how things are working! We are always looking for talented, hard working people. Drop us a line and show us your work. We are hiring: https://codesandbox.io/jobs'
@@ -57,6 +58,6 @@ const Homepage = () => (
   </Layout>
 );
 
-identify('hero0420', 'B');
+identifyFromCookie('heroAB', 'hero0420');
 
 export default Homepage;

packages/homepage/src/utils/identifyFromCookie.js

@@ -0,0 +1,23 @@
+import { identify } from '@codesandbox/common/lib/utils/analytics';
+
+function getCookie(name) {
+  const pattern = RegExp(name + '=.[^;]*');
+  const matched = document.cookie.match(pattern);
+  if (matched) {
+    const cookie = matched[0].split('=');
+    return cookie[1];
+  }
+  return false;
+}
+
+export function identifyFromCookie(cookie, identifyKey) {
+  if (typeof document === 'undefined') {
+    return;
+  }
+
+  const cookieValue = getCookie(cookie);
+
+  if (cookieValue) {
+    identify(identifyKey, cookieValue);
+  }
+}