From bdb772755f1a7eb5fc48076e355bbb0101cb7701 Mon Sep 17 00:00:00 2001
From: Andrew Scholer <ascholer@chemeketa.edu>
Date: Sat, 20 Apr 2024 20:23:56 -0700
Subject: [PATCH] Javascript: improve scrolling ToC to active entry (PR #2158)

---
 js/pretext.js | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/js/pretext.js b/js/pretext.js
index ba586834b..6750932f7 100644
--- a/js/pretext.js
+++ b/js/pretext.js
@@ -12,20 +12,31 @@
  */
 
 function scrollTocToActive() {
-    pagefilename  = window.location.href;
-    pagefilename  = pagefilename.match(/[^\/]*$/)[0];
-    possibletocentries = document.querySelectorAll('#ptx-toc a[href="' + pagefilename + '"]');
-    if (possibletocentries.length == 0) {
-        console.log("linked below a subsection");
-        pagefilename  = pagefilename.match(/^[^\#]*/)[0];
-        possibletocentries = document.querySelectorAll('#ptx-toc a[href="' + pagefilename + '"]');
+    //Try to figure out current TocItem from URL
+    let fileNameWHash = window.location.href.split("/").pop();
+    let fileName = fileNameWHash.split("#")[0];
+
+    //Find just the filename in ToC
+    let tocEntry = document.querySelector('#ptx-toc a[href="' + fileName + '"]');
+    if (!tocEntry) {
+        return; //complete failure, get out
     }
-    if (possibletocentries.length == 0) {
-        console.log("error, cannot find", pagefilename, "in TOC");
-        return
+
+    //See if we can also match fileName#hash
+    let tocEntryWHash = document.querySelector(
+        '#ptx-toc a[href="' + fileNameWHash + '"]'
+    );
+    if (tocEntryWHash) {
+        //Matched something below a subsection - activate the list item that contains it
+        tocEntryWHash.closest("li").classList.add("active");
     }
-    possibletocentries[0].scrollIntoView({block: "center"});
-    possibletocentries[0].classList.add("active");}
+
+    //Now activate ToC item for fileName and scroll to it
+    //  Don't use scrollIntoView because it changes users tab position in Chrome
+    //  and messes up keyboard navigation
+    tocEntry.closest("li").classList.add("active");
+    document.querySelector("#ptx-toc").scrollTop = tocEntry.offsetTop;
+}
 
 function toggletoc() {
    thesidebar = document.getElementById("ptx-sidebar");