From 87b3654bff30bedf4eff75843ea3266be98e00fd Mon Sep 17 00:00:00 2001
From: Alexandre Bourdin <abourdin@users.noreply.github.com>
Date: Thu, 6 May 2021 16:07:54 +0200
Subject: [PATCH] Merge pull request #4001 from overleaf/ab-hash-split-test

Add hashing to compute the user's percentile in a split test

GitOrigin-RevId: 94302cd1c0ab9e9075a506096b4f36ba50b9b7fa
---
 .../src/Features/Project/ProjectCreationHandler.js  |  5 +++--
 .../app/src/Features/SplitTests/SplitTestHandler.js | 13 +++++++++++--
 services/web/config/settings.defaults.coffee        |  2 +-
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/services/web/app/src/Features/Project/ProjectCreationHandler.js b/services/web/app/src/Features/Project/ProjectCreationHandler.js
index ed303f84cb..70bfcc1fb9 100644
--- a/services/web/app/src/Features/Project/ProjectCreationHandler.js
+++ b/services/web/app/src/Features/Project/ProjectCreationHandler.js
@@ -30,6 +30,7 @@ const MONTH_NAMES = [
   'November',
   'December',
 ]
+const EXAMPLE_PROJECT_SPLITTEST_ID = 'example-project-v2'
 
 async function createBlankProject(ownerId, projectName, attributes = {}) {
   const isImport = attributes && attributes.overleaf
@@ -72,7 +73,7 @@ async function createExampleProject(ownerId, projectName) {
 
   const testSegmentation = SplitTestHandler.getTestSegmentation(
     ownerId,
-    'example-project'
+    EXAMPLE_PROJECT_SPLITTEST_ID
   )
 
   if (testSegmentation.variant === 'example-frog') {
@@ -84,7 +85,7 @@ async function createExampleProject(ownerId, projectName) {
   if (testSegmentation.enabled) {
     AnalyticsManager.recordEvent(ownerId, 'project-created', {
       projectId: project._id,
-      splitTestId: 'example-project',
+      splitTestId: EXAMPLE_PROJECT_SPLITTEST_ID,
       splitTestVariantId: testSegmentation.variant,
     })
   } else {
diff --git a/services/web/app/src/Features/SplitTests/SplitTestHandler.js b/services/web/app/src/Features/SplitTests/SplitTestHandler.js
index b5ce435373..54b4cd8921 100644
--- a/services/web/app/src/Features/SplitTests/SplitTestHandler.js
+++ b/services/web/app/src/Features/SplitTests/SplitTestHandler.js
@@ -1,6 +1,6 @@
 const Settings = require('settings-sharelatex')
 const _ = require('lodash')
-const { ObjectId } = require('mongodb')
+const crypto = require('crypto')
 const OError = require('@overleaf/o-error')
 
 const ACTIVE_SPLIT_TESTS = []
@@ -34,7 +34,7 @@ for (const splitTest of Settings.splitTests) {
 function getTestSegmentation(userId, splitTestId) {
   const splitTest = _.find(ACTIVE_SPLIT_TESTS, ['id', splitTestId])
   if (splitTest) {
-    let userIdAsPercentile = (ObjectId(userId).getTimestamp() / 1000) % 100
+    let userIdAsPercentile = _getPercentile(userId, splitTestId)
     for (const variant of splitTest.variants) {
       if (userIdAsPercentile < variant.rolloutPercent) {
         return {
@@ -55,6 +55,15 @@ function getTestSegmentation(userId, splitTestId) {
   }
 }
 
+function _getPercentile(userId, splitTestId) {
+  const hash = crypto
+    .createHash('md5')
+    .update(userId + splitTestId)
+    .digest('hex')
+  const hashPrefix = hash.substr(0, 8)
+  return Math.floor((parseInt(hashPrefix, 16) / 0xffffffff) * 100)
+}
+
 module.exports = {
   getTestSegmentation,
 }
diff --git a/services/web/config/settings.defaults.coffee b/services/web/config/settings.defaults.coffee
index 82ab2a2932..ae84ea8c14 100644
--- a/services/web/config/settings.defaults.coffee
+++ b/services/web/config/settings.defaults.coffee
@@ -238,7 +238,7 @@ module.exports = settings =
 
 	splitTests: [
 		{
-			id: 'example-project'
+			id: 'example-project-v2'
 			active:  process.env['SPLITTEST_EXAMPLE_PROJECT_ACTIVE'] == 'true'
 			variants: [
 				{