Profiles basically work in standalone viewer

src/calibre/gui2/viewer/web_view.py

@@ -695,6 +695,8 @@ class WebView(RestartingWebEngineView):
             self.standalone_misc_settings_changed.emit()
         elif key != '*':
             sd = vprefs['session_data']
+            changed = sd.get(key) == val
+            if changed:
                 sd[key] = val
                 vprefs['session_data'] = sd
                 if key in ('standalone_font_settings', 'base_font_size'):

src/pyj/read_book/overlay.pyj

@@ -540,10 +540,13 @@ class PrefsOverlay: # {{{
     def on_container_click(self, evt):
         pass  # Dont allow panel to be closed by a click
 
+    def create_panel_impl(self, container):
+        return create_prefs_panel(container, self.overlay.hide_current_panel, self.on_change)
+
     def show(self, container):
         self.changes_occurred = False
         container.style.backgroundColor = get_color('window-background')
-        self.prefs = create_prefs_panel(container, self.overlay.hide_current_panel, self.on_change)
+        self.prefs = self.create_panel_impl(container)
 
     def on_change(self):
         self.changes_occurred = True
@@ -556,6 +559,11 @@ class PrefsOverlay: # {{{
             self.changes_occurred = False
             self.overlay.view.preferences_changed()
 
+
+class ProfilesOverlay(PrefsOverlay):
+    def create_panel_impl(self, container):
+        return create_profiles_panel(container, self.overlay.hide_current_panel, self.on_change)
+
 # }}}
 
 class FontSizeOverlay:  # {{{
@@ -749,7 +757,7 @@ class Overlay:
 
     def show_profiles(self):
         self.hide_current_panel()
-        self.panels.push(TOCOverlay(self, create_profiles_panel.bind(None, self.hide_current_panel), _('Profiles')))
+        self.panels.push(ProfilesOverlay(self))
         self.show_current_panel()
 
     def show_goto(self):

src/pyj/read_book/profiles.pyj

@@ -10,7 +10,7 @@ from dom import clear, unique_id
 from gettext import gettext as _
 from modals import question_dialog
 from read_book.globals import ui_operations
-from session import settings_for_reader_profile
+from session import apply_reader_profile, settings_for_reader_profile
 from widgets import create_button
 
 
@@ -36,9 +36,12 @@ def use_profile(container_id, profile_name, profile_data):
     container = document.getElementById(container_id)
     if not container:
         return
+    apply_reader_profile(get_session_data(), profile_data)
+    container.dispatchEvent(new Event('settings_changed'))
     container.dispatchEvent(new Event('close_panel'))
 
 
+
 def delete_profile(container_id, profile_name):
     question_dialog(_('Are you sure?'), _('Are you sure you want to delete the saved profile named: {}?').format(profile_name),
         def (ok):
@@ -84,9 +87,10 @@ def load_profiles(container_id):
     ui_operations.get_all_profiles(got_all_profiles.bind(None, container_id))
 
 
-def create_profiles_panel(hide_panel, book, container, onclick):
+def create_profiles_panel(container, hide_panel, on_change):
     c = E.div(style='margin: 1rem', id=unique_id('placeholder-prefs'))
     c.addEventListener('close_panel', def(): hide_panel();, False)
+    c.addEventListener('settings_changed', def(): on_change();, False)
     container_id = c.id
     a = E.div(
         style='display:flex',

src/pyj/session.pyj

@@ -234,6 +234,21 @@ def get_subset_of_settings(sd, filter_func):
             ans[setting_name] = window.structuredClone(curval if is_set else metadata.default)
     return ans
 
+def apply_profile(sd, profile, filter_func):
+    sentinel = {}
+    for setting_name in Object.keys(all_settings):
+        metadata = all_settings[setting_name]
+        curval = sd.get(setting_name, sentinel)
+        is_set = curval is not sentinel
+        if filter_func(setting_name, metadata, is_set, curval):
+            newval = None
+            if Object.prototype.hasOwnProperty.call(profile, setting_name):
+                newval = profile[setting_name]
+                if deep_eq(newval, metadata.default):
+                    newval = None
+            sd.set(setting_name, window.structuredClone(newval))
+
+
 standalone_reader_defaults = {
     'remember_window_geometry': False,
     'remember_last_read': True,
@@ -270,6 +285,12 @@ def settings_for_reader_profile(sd):
     return get_subset_of_settings(sd, filter_func)
 
 
+def apply_reader_profile(sd, profile):
+    def filter_func(setting_name, metadata, is_set, curval):
+        return metadata.category is 'read_book'
+    apply_profile(sd, profile, filter_func)
+
+
 default_interface_data = {
     'username': None,
     'output_format': 'EPUB',

src/pyj/viewer-main.pyj

@@ -161,7 +161,7 @@ class SessionData:
 
     def set(self, key, val):
         if val is None:
-            self.data[key] = session_defaults()[key]
+            self.data[key] = val = session_defaults()[key]
         else:
             self.data[key] = val
         to_python.set_session_data(key, val)