From c3f536017aff2453df35aea1657ea4043d9a76f4 Mon Sep 17 00:00:00 2001
From: Tobias Manske <tobias.manske@mailbox.org>
Date: Fri, 24 Mar 2023 21:48:44 +0100
Subject: [PATCH] WIP: Keep scroll position steady

---
 src/__init__.py | 40 +++++++++++++++++++++++++++++++++++-----
 src/config.json |  3 ++-
 src/config.md   |  3 +++
 3 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/src/__init__.py b/src/__init__.py
index 3e7fd9e..ae4889f 100644
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -19,6 +19,7 @@ class EditorPreview(object):
     def __init__(self):
         gui_hooks.editor_did_init.append(self.editor_init_hook)
         gui_hooks.editor_did_init_buttons.append(self.editor_init_button_hook)
+        self.scrollLock = config["enableScrollLockByDefault"]
         if int(buildinfo.version.split(".")[2]) < 45:  # < 2.1.45
             self.js = [
                 "js/vendor/jquery.min.js",
@@ -86,20 +87,38 @@ class EditorPreview(object):
         split = self._get_splitter(editor)
         layout.insertWidget(web_index, split)
 
+    def isScrollLocked(self):
+        return self.scrollLock
+
+    def toggleScrollLock(self):
+        self.scrollLock = not self.scrollLock
+
     def editor_note_hook(self, editor):
-        self.onedit_hook(editor, editor.note)
+        # Dont lock the editor in place when loading a new note
+        # i.e. when using the cards browser
+        self.onedit_hook(editor, editor.note, keep_scrollbar_value=False)
 
     def editor_init_button_hook(self, buttons, editor):
         addon_path = os.path.dirname(__file__)
         icons_dir = os.path.join(addon_path, "icons")
-        b = editor.addButton(
+        previewButton = editor.addButton(
             icon=os.path.join(icons_dir, "file.svg"),
             cmd="_editor_toggle_preview",
             tip="Toggle Live Preview",
             func=lambda o=editor: self.onEditorPreviewButton(o),
             disables=False,
         )
-        buttons.append(b)
+        scrollLockButton = editor.addButton(
+            # icon=os.path.join(icons_dir, "file.svg"),
+            icon=None,
+            label="🔒",
+            cmd="_editor_toggle_scroll_lock",
+            tip="Toggle Scroll Locking",
+            func=lambda o=editor: self.onEditorScrollLockButton(o),
+            disables=True,
+        )
+        buttons.append(previewButton)
+        buttons.append(scrollLockButton)
 
     def onEditorPreviewButton(self, origin: editor.Editor):
         if origin.editor_preview.isHidden():
@@ -107,18 +126,29 @@ class EditorPreview(object):
         else:
             origin.editor_preview.hide()
 
+    def onEditorScrollLockButton(self, origin: editor.Editor):
+        self.toggleScrollLock()
+
     def _obtainCardText(self, note):
         c = note.ephemeral_card()
         a = mw.prepare_card_text_for_display(c.answer())
         a = gui_hooks.card_will_show(a, c, "clayoutAnswer")
-        bodyclass = theme_manager.body_classes_for_card_ord(c.ord, theme_manager.night_mode)
+        bodyclass = theme_manager.body_classes_for_card_ord(
+            c.ord, theme_manager.night_mode
+        )
         bodyclass += " editor-preview"
 
         return f"_showAnswer({json.dumps(a)},'{bodyclass}');"
 
-    def onedit_hook(self, editor, origin):
+    def onedit_hook(self, editor, origin, keep_scrollbar_value=True):
         if editor.note == origin:
+            page: QWebEnginePage = editor.editor_preview.page()
+            scrollbar_value = page.scrollPosition()
             editor.editor_preview.eval(self._obtainCardText(editor.note))
+            if keep_scrollbar_value and self.isScrollLocked():
+                page.runJavaScript(
+                    f"window.scrollTo({scrollbar_value.x()}, {scrollbar_value.y()});"
+                )
 
 
 eprev = EditorPreview()
diff --git a/src/config.json b/src/config.json
index 8ab917f..4612117 100644
--- a/src/config.json
+++ b/src/config.json
@@ -1,5 +1,6 @@
 {
   "showPreviewAutomatically": true,
   "splitRatio": "1:1",
-  "location": "below"
+  "location": "below",
+  "enableScrollLockByDefault": true
 }
diff --git a/src/config.md b/src/config.md
index 2acf2c8..e9ad26e 100644
--- a/src/config.md
+++ b/src/config.md
@@ -7,3 +7,6 @@
 \- `location` [string (above | below | left | right)]:<br/>
 &nbsp;&nbsp;&nbsp;Defines where to render the preview (default: below)
 <br/>
+\- `showPreviewAutomatically` [boolean (true | false)]:<br/>
+&nbsp;&nbsp;&nbsp;Whether to keep the scrollbar at the same location when text changed or not (default: true)<br/>
+<br/>