From 084bcbe6bfbdae6b3e4135bb00a49f45d9ebc68a Mon Sep 17 00:00:00 2001
From: fargelus <ddraudred@gmail.com>
Date: Tue, 1 Feb 2022 10:12:51 +0300
Subject: [PATCH 1/3] Highlighting sidebar links

---
 js/book.js | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/js/book.js b/js/book.js
index e9fd6a9..f12fb22 100644
--- a/js/book.js
+++ b/js/book.js
@@ -268,3 +268,49 @@ window.onunload = function () { };
         previousScrollTop = document.scrollingElement.scrollTop;
     }, { passive: true });
 })();
+
+(function highlightSideBarLink() {
+    var anchorsToLink = {};
+    var $sidebarLinks = $('#sidebar .chapter a');
+    $sidebarLinks.each(function(_, link) {
+        var match = link.href.match(/#(.+)$/);
+        if (match) {
+            anchorsToLink[ match[1] ] = link;
+        }
+    });
+
+    function getActiveHeaderId() {
+        var sectionHeaders = $(':header').filter(function(_, el) {
+            return anchorsToLink[ el.id ];
+        });
+
+        var visibleHeaders = getHeadersInViewport(sectionHeaders);
+        if (visibleHeaders.length == 0) return null;
+
+        var activeHeader = visibleHeaders.sort(function(header) {
+            return header.getBoundingClientRect().y;
+        })[0];
+
+        return activeHeader.id;
+    }
+
+    function getHeadersInViewport(headers) {
+        return headers.filter(function(_, header) {
+            var headerRect = header.getBoundingClientRect();
+            var headerTop = headerRect.top;
+            var headerBottom = headerRect.bottom;
+
+            return headerTop >= 0 && headerBottom <= window.innerHeight;
+        });
+    }
+
+    var activeLinkClass = 'active';
+    $('#content').on('scroll', function() {
+        var activeHeaderId = getActiveHeaderId();
+        if (!activeHeaderId) return;
+
+        $sidebarLinks.removeClass(activeLinkClass);
+        var activeLink = anchorsToLink[activeHeaderId];
+        $(activeLink).addClass(activeLinkClass);
+    });
+})();

From 08f4dbcb5862b458efa72da1fa378862b402f6fb Mon Sep 17 00:00:00 2001
From: fargelus <ddraudred@gmail.com>
Date: Tue, 1 Feb 2022 10:21:57 +0300
Subject: [PATCH 2/3] Some review fixes

---
 js/book.js | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/js/book.js b/js/book.js
index f12fb22..63a142f 100644
--- a/js/book.js
+++ b/js/book.js
@@ -279,12 +279,12 @@ window.onunload = function () { };
         }
     });
 
-    function getActiveHeaderId() {
-        var sectionHeaders = $(':header').filter(function(_, el) {
-            return anchorsToLink[ el.id ];
-        });
+    var sectionHeaders = $(':header').filter(function(_, el) {
+        return anchorsToLink[ el.id ];
+    });
 
-        var visibleHeaders = getHeadersInViewport(sectionHeaders);
+    function getActiveHeaderId() {
+        var visibleHeaders = getHeadersInViewport();
         if (visibleHeaders.length == 0) return null;
 
         var activeHeader = visibleHeaders.sort(function(header) {
@@ -294,8 +294,8 @@ window.onunload = function () { };
         return activeHeader.id;
     }
 
-    function getHeadersInViewport(headers) {
-        return headers.filter(function(_, header) {
+    function getHeadersInViewport() {
+        return sectionHeaders.filter(function(_, header) {
             var headerRect = header.getBoundingClientRect();
             var headerTop = headerRect.top;
             var headerBottom = headerRect.bottom;

From ee3c9537b484e9add74636dd5382dfd7904be201 Mon Sep 17 00:00:00 2001
From: fargelus <ddraudred@gmail.com>
Date: Tue, 1 Feb 2022 10:29:01 +0300
Subject: [PATCH 3/3] Variable renaming

---
 js/book.js | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/js/book.js b/js/book.js
index 63a142f..b07376f 100644
--- a/js/book.js
+++ b/js/book.js
@@ -279,21 +279,21 @@ window.onunload = function () { };
         }
     });
 
-    var sectionHeaders = $(':header').filter(function(_, el) {
-        return anchorsToLink[ el.id ];
-    });
-
-    function getActiveHeaderId() {
+    function getViewableHeaderId() {
         var visibleHeaders = getHeadersInViewport();
         if (visibleHeaders.length == 0) return null;
 
-        var activeHeader = visibleHeaders.sort(function(header) {
+        var viewableHeader = visibleHeaders.sort(function(header) {
             return header.getBoundingClientRect().y;
         })[0];
 
-        return activeHeader.id;
+        return viewableHeader.id;
     }
 
+    var sectionHeaders = $(':header').filter(function(_, el) {
+        return anchorsToLink[ el.id ];
+    });
+
     function getHeadersInViewport() {
         return sectionHeaders.filter(function(_, header) {
             var headerRect = header.getBoundingClientRect();
@@ -306,11 +306,11 @@ window.onunload = function () { };
 
     var activeLinkClass = 'active';
     $('#content').on('scroll', function() {
-        var activeHeaderId = getActiveHeaderId();
-        if (!activeHeaderId) return;
+        var viewableHeaderId = getViewableHeaderId();
+        if (!viewableHeaderId) return;
 
         $sidebarLinks.removeClass(activeLinkClass);
-        var activeLink = anchorsToLink[activeHeaderId];
+        var activeLink = anchorsToLink[viewableHeaderId];
         $(activeLink).addClass(activeLinkClass);
     });
 })();