From c36f3b7878d94723c9c2d5576a724acc36aef3dc Mon Sep 17 00:00:00 2001
From: George Cushen <gcushen@users.noreply.github.com>
Date: Wed, 10 Feb 2021 08:25:28 +0000
Subject: [PATCH] feat: auto scroll active book menu and ToC links into view

Also, fix ScrollSpy highlighting previous ToC link for some Book anchors.

Close #1964
---
 wowchemy/assets/js/wowchemy-utils.js | 30 +++++++++++++++++++++-
 wowchemy/assets/js/wowchemy.js       | 38 +++++++++++++++++++++++-----
 2 files changed, 60 insertions(+), 8 deletions(-)

diff --git a/wowchemy/assets/js/wowchemy-utils.js b/wowchemy/assets/js/wowchemy-utils.js
index c38d9f9d..ad28d727 100644
--- a/wowchemy/assets/js/wowchemy-utils.js
+++ b/wowchemy/assets/js/wowchemy-utils.js
@@ -23,4 +23,32 @@ function fixMermaid() {
   }
 }
 
-export {fixMermaid};
+/**
+ * @param {Element} parent
+ * @param {Element} child
+ */
+function scrollParentToChild(parent, child) {
+  // Where is the parent on the page?
+  const parentRect = parent.getBoundingClientRect();
+
+  // What can the client see?
+  const parentViewableArea = {
+    height: parent.clientHeight,
+    width: parent.clientWidth,
+  };
+
+  // Where is the child?
+  const childRect = child.getBoundingClientRect();
+
+  // Is the child in view?
+  const isChildInView =
+    childRect.top >= parentRect.top && childRect.bottom <= parentRect.top + parentViewableArea.height;
+
+  // If the child isn't in view, attempt to scroll the parent to it.
+  if (!isChildInView) {
+    // Scroll by offset relative to parent.
+    parent.scrollTop = childRect.top + parent.scrollTop - parentRect.top;
+  }
+}
+
+export {fixMermaid, scrollParentToChild};
diff --git a/wowchemy/assets/js/wowchemy.js b/wowchemy/assets/js/wowchemy.js
index c7621325..68c12eea 100644
--- a/wowchemy/assets/js/wowchemy.js
+++ b/wowchemy/assets/js/wowchemy.js
@@ -7,7 +7,7 @@
 
 import {hugoEnvironment, codeHighlighting, searchEnabled} from '@params';
 
-import {fixMermaid} from './wowchemy-utils';
+import {fixMermaid, scrollParentToChild} from './wowchemy-utils';
 
 import {
   changeThemeModeClick,
@@ -33,10 +33,11 @@ function getNavBarHeight() {
 /**
  * Responsive hash scrolling.
  * Check for a URL hash as an anchor.
- * If it exists on current page, scroll to it responsively.
+ * If page anchor matches hash, scroll to it responsively considering dynamic height elements.
  * If `target` argument omitted (e.g. after event), assume it's the window's hash.
+ * Default to 0ms animation duration as don't want animation for fixing scrollspy Book page ToC highlighting.
  */
-function scrollToAnchor(target, duration = 600) {
+function scrollToAnchor(target, duration = 0) {
   // If `target` is undefined or HashChangeEvent object, set it to window's hash.
   // Decode the hash as browsers can encode non-ASCII characters (e.g. Chinese symbols).
   target =
@@ -434,6 +435,13 @@ $(document).ready(function () {
   // Render theme variation, including any HLJS and Mermaid themes.
   let {isDarkTheme, themeMode} = initThemeVariation();
   renderThemeVariation(isDarkTheme, themeMode, true);
+
+  // Scroll Book page's active menu sidebar link into view.
+  let child = document.querySelector('.docs-links .active');
+  let parent = document.querySelector('.docs-links');
+  if (child && parent) {
+    scrollParentToChild(parent, child);
+  }
 });
 
 /* ---------------------------------------------------------------------------
@@ -441,9 +449,28 @@ $(document).ready(function () {
  * --------------------------------------------------------------------------- */
 
 $(window).on('load', function () {
-  // Init Isotope Layout Engine for instances of the Portfolio widget.
+  // Re-initialize Scrollspy with dynamic navbar height offset.
+  fixScrollspy();
+
+  // Detect instances of the Portfolio widget.
   let isotopeInstances = document.querySelectorAll('.projects-container');
   let isotopeInstancesCount = isotopeInstances.length;
+
+  // Fix ScrollSpy highlighting previous Book page ToC link for some anchors.
+  // Check if isotopeInstancesCount>0 as that case performs its own scrollToAnchor.
+  if (window.location.hash && isotopeInstancesCount === 0) {
+    scrollToAnchor(decodeURIComponent(window.location.hash), 0);
+  }
+
+  // Scroll Book page's active ToC sidebar link into view.
+  // Action after calling scrollToAnchor to fix Scrollspy highlighting otherwise wrong link may have active class.
+  let child = document.querySelector('.docs-toc .nav-link.active');
+  let parent = document.querySelector('.docs-toc');
+  if (child && parent) {
+    scrollParentToChild(parent, child);
+  }
+
+  // Init Isotope Layout Engine for instances of the Portfolio widget.
   let isotopeCounter = 0;
   isotopeInstances.forEach(function (isotopeInstance, index) {
     console.debug(`Loading Isotope instance ${index}`);
@@ -610,9 +637,6 @@ $(window).on('load', function () {
 
   // Init. author notes (tooltips).
   $('[data-toggle="tooltip"]').tooltip();
-
-  // Re-initialize Scrollspy with dynamic navbar height offset.
-  fixScrollspy();
 });
 
 // Theme chooser events.