From b183ac3bf3693ec769cee074227bca0a73a7c6dd Mon Sep 17 00:00:00 2001
From: jdlrobson <jdlrobson@gmail.com>
Date: Wed, 17 Mar 2021 16:04:42 -0700
Subject: [PATCH] Inform anonymous A/B test by tracking time from
 navigationStart

This will inform us on the approach taken in
I315ea30b88e43f3df29b0a0b37907272ec77d0a7

Additional change:
Flesh out TypeScript with eventLogging interface

Bug:  T275807
Change-Id: I9789cd1dfab5181fa093bce46c5c9b0d338339f5
---
 resources/mediawiki.d.ts          | 12 ++++++++++++
 resources/skins.vector.js/skin.js | 21 +++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/resources/mediawiki.d.ts b/resources/mediawiki.d.ts
index b0ffcb1..ec22494 100644
--- a/resources/mediawiki.d.ts
+++ b/resources/mediawiki.d.ts
@@ -9,9 +9,16 @@ interface MwUri {
 	toString(): string;
 }
 
+interface MwEventLog {
+	eventInSample( population: Object ): () => boolean;
+	inSample( num: Number ): () => boolean;
+	logEvent( schema: string, data: Object ): () => void;
+}
+
 type UriConstructor = new( uri: string ) => MwUri;
 
 interface MediaWiki {
+	eventLog?: MwEventLog,
 	util: {
 		/**
 		 * @param {string} id of portlet
@@ -80,6 +87,11 @@ interface MediaWiki {
 	 */
 	msg( messageName: string|null ): string;
 
+	/**
+	 * Get current timestamp
+	 */
+	now(): number,
+
 	/**
 	 * Track an analytic event.
 	 *
diff --git a/resources/skins.vector.js/skin.js b/resources/skins.vector.js/skin.js
index 7763f30..bf133d1 100644
--- a/resources/skins.vector.js/skin.js
+++ b/resources/skins.vector.js/skin.js
@@ -42,6 +42,27 @@ function enableCssAnimations( document ) {
  * @return {void}
  */
 function main( window ) {
+	var now = mw.now();
+	// This is the earliest time we can run JS for users (and bucket anonymous
+	// users for A/B tests).
+	// Where the browser supports it, for a 10% sample of users
+	// we record a value to give us a sense of the expected delay in running A/B tests or
+	// disabling JS features. This will inform us on various things including what to expect
+	// with regards to delay while running A/B tests to anonymous users.
+	// When EventLogging is not available this will reject.
+	// This code can be removed by the end of the Desktop improvements project.
+	// https://www.mediawiki.org/wiki/Desktop_improvements
+	mw.loader.using( 'ext.eventLogging' ).then( function () {
+		if (
+			mw.eventLog &&
+			mw.eventLog.eventInSample( 100 /* 1 in 100 */ ) &&
+			window.performance &&
+			window.performance.timing &&
+			window.performance.timing.navigationStart
+		) {
+			mw.track( 'timing.Vector.ready', now - window.performance.timing.navigationStart ); // milliseconds
+		}
+	} );
 	enableCssAnimations( window.document );
 	collapsibleTabs.init();
 	sidebar.init( window );