From f6235a1845313b79cb31cefcc5d54a7145e86be3 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 22 Feb 2021 09:53:46 +0530
Subject: [PATCH] E-book viewer: Have the Table of Contents view automatically
 scroll to keep the chapter being read currently visible. Fixes #1916411
 [Enhancement Request: ToC Behavior - Default to Current
 Chapter](https://bugs.launchpad.net/calibre/+bug/1916411)

---
 src/calibre/gui2/viewer/toc.py | 24 ++++++++++++++++++++----
 src/calibre/gui2/viewer/ui.py  |  5 ++++-
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/calibre/gui2/viewer/toc.py b/src/calibre/gui2/viewer/toc.py
index 9289d6362b..ad6f26755e 100644
--- a/src/calibre/gui2/viewer/toc.py
+++ b/src/calibre/gui2/viewer/toc.py
@@ -52,7 +52,13 @@ class TOCView(QTreeView):
 
     def setModel(self, model):
         QTreeView.setModel(self, model)
-        model.auto_expand_nodes.connect(self.auto_expand_indices, type=Qt.ConnectionType.QueuedConnection)
+        model.current_toc_nodes_changed.connect(self.current_toc_nodes_changed, type=Qt.ConnectionType.QueuedConnection)
+
+    def current_toc_nodes_changed(self, ancestors, nodes):
+        if ancestors:
+            self.auto_expand_indices(ancestors)
+        if nodes:
+            self.scrollTo(nodes[-1].index())
 
     def auto_expand_indices(self, indices):
         for idx in indices:
@@ -116,6 +122,11 @@ class TOCView(QTreeView):
     def update_current_toc_nodes(self, families):
         self.model().update_current_toc_nodes(families)
 
+    def scroll_to_current_toc_node(self):
+        nodes = self.model().viewed_nodes()
+        if nodes:
+            self.scrollTo(nodes[-1].index())
+
 
 class TOCSearch(QWidget):
 
@@ -202,7 +213,7 @@ class TOCItem(QStandardItem):
 
 class TOC(QStandardItemModel):
 
-    auto_expand_nodes = pyqtSignal(object)
+    current_toc_nodes_changed = pyqtSignal(object, object)
 
     def __init__(self, toc=None):
         QStandardItemModel.__init__(self)
@@ -259,12 +270,17 @@ class TOC(QStandardItemModel):
                 viewed_nodes |= {x.node_id for x in ansc}
                 for x in ansc:
                     ancestors[x.node_id] = x.index()
-        if ancestors:
-            self.auto_expand_nodes.emit(tuple(ancestors.values()))
+        nodes = []
         for node in self.all_items:
             is_being_viewed = node.node_id in viewed_nodes
+            if is_being_viewed:
+                nodes.append(node)
             if is_being_viewed != node.is_being_viewed:
                 node.set_being_viewed(is_being_viewed)
+        self.current_toc_nodes_changed.emit(tuple(ancestors.values()), nodes)
+
+    def viewed_nodes(self):
+        return tuple(node for node in self.all_items if node.is_being_viewed)
 
     @property
     def as_plain_text(self):
diff --git a/src/calibre/gui2/viewer/ui.py b/src/calibre/gui2/viewer/ui.py
index af302b7719..d09974a49d 100644
--- a/src/calibre/gui2/viewer/ui.py
+++ b/src/calibre/gui2/viewer/ui.py
@@ -297,7 +297,10 @@ class EbookViewer(MainWindow):
         self.inspector_dock.setVisible(not visible)
 
     def toggle_toc(self):
-        self.toc_dock.setVisible(not self.toc_dock.isVisible())
+        is_visible = self.toc_dock.isVisible()
+        self.toc_dock.setVisible(not is_visible)
+        if not is_visible:
+            self.toc.scroll_to_current_toc_node()
 
     def show_search(self, text, trigger=False):
         self.search_dock.setVisible(True)