From 195ff72d4473bf6998309a335b5872951ea7006b Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 7 Jul 2020 21:49:44 +0530
Subject: [PATCH] Edit book: Fix initial sync of preview panel to cursor
 position sometimes not working when a new HTML file is opened for editing

---
 src/calibre/gui2/tweak_book/boss.py             |  8 ++++++--
 .../gui2/tweak_book/editor/syntax/base.py       |  4 ++++
 src/calibre/gui2/tweak_book/editor/widget.py    |  4 ++++
 src/calibre/gui2/tweak_book/preview.py          | 17 +++++++++++------
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index 2041684bf1..b933e6542c 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -12,7 +12,7 @@ from functools import partial, wraps
 
 from PyQt5.Qt import (
     QApplication, QCheckBox, QDialog, QDialogButtonBox, QGridLayout, QIcon,
-    QInputDialog, QLabel, QMimeData, QObject, QSize, Qt, QUrl, QVBoxLayout,
+    QInputDialog, QLabel, QMimeData, QObject, QSize, Qt, QTimer, QUrl, QVBoxLayout,
     pyqtSignal
 )
 
@@ -1497,7 +1497,11 @@ class Boss(QObject):
         if ed is not None:
             name = editor_name(ed)
             if name is not None and getattr(ed, 'syntax', None) == 'html':
-                self.gui.preview.sync_to_editor(name, ed.current_tag())
+                ct = ed.current_tag()
+                self.gui.preview.sync_to_editor(name, ct)
+                hl = getattr(ed, 'highlighter', None)
+                if hl is not None and hl.is_working:
+                    QTimer.singleShot(75, self.sync_preview_to_editor)
 
     def show_partial_cfi_in_editor(self, name, cfi):
         editor = self.edit_file(name, 'html')
diff --git a/src/calibre/gui2/tweak_book/editor/syntax/base.py b/src/calibre/gui2/tweak_book/editor/syntax/base.py
index 538bd4d726..12d7a8d291 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/base.py
+++ b/src/calibre/gui2/tweak_book/editor/syntax/base.py
@@ -201,6 +201,10 @@ class SyntaxHighlighter(object):
         finally:
             self.ignore_requests = False
 
+    @property
+    def is_working(self):
+        return bool(self.requests)
+
     def parse_single_block(self, block):
         ud, is_new_ud = self.get_user_data(block)
         orig_state = ud.state
diff --git a/src/calibre/gui2/tweak_book/editor/widget.py b/src/calibre/gui2/tweak_book/editor/widget.py
index 11509790c5..1b5999c03a 100644
--- a/src/calibre/gui2/tweak_book/editor/widget.py
+++ b/src/calibre/gui2/tweak_book/editor/widget.py
@@ -182,6 +182,10 @@ class Editor(QMainWindow):
     def current_tag(self, for_position_sync=True):
         return self.editor.current_tag(for_position_sync=for_position_sync)
 
+    @property
+    def highlighter(self):
+        return self.editor.highlighter
+
     @property
     def number_of_lines(self):
         return self.editor.blockCount()
diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index 0ecb330d03..e6804113ef 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -438,6 +438,7 @@ class Preview(QWidget):
         self.l = l = QVBoxLayout()
         self.setLayout(l)
         l.setContentsMargins(0, 0, 0, 0)
+        self.current_sync_retry_count = 0
         self.view = WebView(self)
         self.view._page.bridge.request_sync.connect(self.request_sync)
         self.view._page.bridge.request_split.connect(self.request_split)
@@ -533,20 +534,24 @@ class Preview(QWidget):
         if self.current_name:
             self.split_requested.emit(self.current_name, loc, totals)
 
+    @property
+    def bridge_ready(self):
+        return self.view._page.bridge.ready
+
     def sync_to_editor(self, name, sourceline_address):
         self.current_sync_request = (name, sourceline_address)
+        self.current_sync_retry_count = 0
         QTimer.singleShot(100, self._sync_to_editor)
 
     def _sync_to_editor(self):
-        if not actions['sync-preview-to-editor'].isChecked():
+        if not actions['sync-preview-to-editor'].isChecked() or self.current_sync_retry_count >= 3000 or self.current_sync_request is None:
             return
-        try:
-            if self.refresh_timer.isActive() or self.current_sync_request[0] != self.current_name:
-                return QTimer.singleShot(100, self._sync_to_editor)
-        except TypeError:
-            return  # Happens if current_sync_request is None
+        if self.refresh_timer.isActive() or not self.bridge_ready or self.current_sync_request[0] != self.current_name:
+            self.current_sync_retry_count += 1
+            return QTimer.singleShot(100, self._sync_to_editor)
         sourceline_address = self.current_sync_request[1]
         self.current_sync_request = None
+        self.current_sync_retry_count = 0
         self.view._page.go_to_sourceline_address(sourceline_address)
 
     def report_worker_launch_error(self):