From 365d3902c9c9a80d4020190cb0ebc0adf34dbc28 Mon Sep 17 00:00:00 2001
From: Jon Robson <jdlrobson@gmail.com>
Date: Thu, 1 Sep 2022 14:22:31 -0700
Subject: [PATCH] Sidebar: Collapses at lower resolutions

On resize, or when booted in a small window the sidebar will collapse
and remain collapsed for subsequent page views

Bug: T316191
Change-Id: Ib4961975630871d6630cd747a78cc2ec4f1cdeeb
---
 .../skins.vector.js/sidebarPersistence.js     | 59 ++++++++++++++++++-
 1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/resources/skins.vector.js/sidebarPersistence.js b/resources/skins.vector.js/sidebarPersistence.js
index 8014d017..d0291310 100644
--- a/resources/skins.vector.js/sidebarPersistence.js
+++ b/resources/skins.vector.js/sidebarPersistence.js
@@ -11,6 +11,18 @@ var /** @type {MwApi} */api,
 	SIDEBAR_CHECKBOX_ID = 'mw-sidebar-checkbox',
 	SIDEBAR_PREFERENCE_NAME = 'VectorSidebarVisible';
 
+/**
+ * Checks if persistent is enabled at current time.
+ * When a user is using a browser with a screen resolution of < 1000 it is assumed
+ * that it is preferred that the sidebar remains closed across page views, as otherwise
+ * it gets in the way of reading. More context at T316191.
+ *
+ * @return {boolean}
+ */
+function isPersistentEnabled() {
+	return window.innerWidth >= 1000;
+}
+
 /**
  * Execute a debounced API request to save the sidebar user preference.
  * The request is meant to fire 1000 milliseconds after the last click on
@@ -46,17 +58,60 @@ function saveSidebarState( checkbox ) {
  */
 function bindSidebarClickEvent( checkbox, button ) {
 	if ( checkbox instanceof HTMLInputElement && button ) {
-		checkbox.addEventListener( 'input', saveSidebarState( checkbox ) );
+		var handler = saveSidebarState( checkbox );
+		checkbox.addEventListener( 'input', function () {
+			if ( isPersistentEnabled() ) {
+				handler();
+			}
+		} );
+	}
+}
+
+/**
+ * Collapses the sidebar if screen resolution too small.
+ *
+ * @param {HTMLInputElement} checkbox
+ */
+function collapseSidebar( checkbox ) {
+	if ( checkbox.checked ) {
+		checkbox.checked = false;
+		saveSidebarState( checkbox )();
 	}
 }
 
 function init() {
-	var checkbox = window.document.getElementById( SIDEBAR_CHECKBOX_ID ),
+	var checkbox = /** @type {HTMLInputElement|null} */ (
+			window.document.getElementById( SIDEBAR_CHECKBOX_ID )
+		),
 		button = window.document.getElementById( SIDEBAR_BUTTON_ID );
 
 	if ( mw.config.get( 'wgUserName' ) && !mw.config.get( 'wgVectorDisableSidebarPersistence' ) ) {
 		bindSidebarClickEvent( checkbox, button );
 	}
+
+	// If the user has resized their window, an open sidebar will be taking up lots of space
+	// so we should disable it.
+	// When this happens the user must expand it again manually, to avoid conflicts with multiple
+	// open windows (for example when an editor is viewing 2 articles side by side).
+	if ( checkbox ) {
+		var mediaQuery = window.matchMedia( '(max-width: 1000px)' );
+		var onMediaQueryChange = function ( /** @type {MediaQueryListEvent} */ event ) {
+			if ( event.matches ) {
+				// @ts-ignore we checked it already.
+				collapseSidebar( checkbox );
+			}
+		};
+		if ( mediaQuery.matches ) {
+			collapseSidebar( checkbox );
+		}
+		if ( mediaQuery.addEventListener ) {
+			mediaQuery.addEventListener( 'change', onMediaQueryChange );
+		} else {
+			//  Before Safari 14, MediaQueryList is based on EventTarget,
+			// so you must use addListener() and removeListener() to observe media query lists.
+			mediaQuery.addListener( onMediaQueryChange );
+		}
+	}
 }
 
 module.exports = {