E-book viewer: When displaying estimated time to completion for reading a book, remember the reading rate the next time the book is opened so that the period spent calculating the time remaining is reduced. Fixes #1852929 [Time to read book is not saved](https://bugs.launchpad.net/calibre/+bug/1852929)

src/calibre/gui2/viewer/config.py

@@ -1,9 +1,13 @@
 #!/usr/bin/env python
 # License: GPL v3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
 
+import json
 import os
-from calibre.constants import config_dir
+import tempfile
+
+from calibre.constants import cache_dir, config_dir
 from calibre.utils.config import JSONConfig
+from calibre.utils.filenames import atomic_rename
 
 vprefs = JSONConfig('viewer-webengine')
 viewer_config_dir = os.path.join(config_dir, 'viewer')
@@ -26,3 +30,43 @@ def get_session_pref(name, default=None, group='standalone_misc_settings'):
 def get_pref_group(name):
     sd = vprefs['session_data']
     return sd.get(name) or {}
+
+
+def reading_rates_path():
+    return os.path.join(cache_dir(), 'viewer-reading-rates.json')
+
+
+def save_reading_rates(key, rates):
+    path = reading_rates_path()
+    try:
+        with open(path, 'rb') as f:
+            raw = f.read()
+    except OSError:
+        existing = {}
+    else:
+        existing = json.loads(raw)
+    existing.pop(key, None)
+    existing[key] = rates
+    while len(existing) > 50:
+        expired = next(iter(existing))
+        del existing[expired]
+    ddata = json.dumps(existing, indent=2).encode('utf-8')
+    try:
+        with tempfile.NamedTemporaryFile(dir=os.path.dirname(path), delete=False) as f:
+            f.write(ddata)
+        atomic_rename(f.name, path)
+    except Exception:
+        import traceback
+        traceback.print_exc()
+
+
+def load_reading_rates(key):
+    path = reading_rates_path()
+    try:
+        with open(path, 'rb') as f:
+            raw = f.read()
+    except OSError:
+        existing = {}
+    else:
+        existing = json.loads(raw)
+    return existing.get(key)

src/calibre/gui2/viewer/ui.py

@@ -30,7 +30,9 @@ from calibre.gui2.viewer.annotations import (
     AnnotationsSaveWorker, annotations_dir, parse_annotations
 )
 from calibre.gui2.viewer.bookmarks import BookmarkManager
-from calibre.gui2.viewer.config import get_session_pref, vprefs
+from calibre.gui2.viewer.config import (
+    get_session_pref, load_reading_rates, save_reading_rates, vprefs
+)
 from calibre.gui2.viewer.convert_book import clean_running_workers, prepare_book
 from calibre.gui2.viewer.highlights import HighlightsPanel
 from calibre.gui2.viewer.integration import (
@@ -191,6 +193,7 @@ class EbookViewer(MainWindow):
         self.web_view.scrollbar_context_menu.connect(self.scrollbar_context_menu)
         self.web_view.close_prep_finished.connect(self.close_prep_finished)
         self.web_view.highlights_changed.connect(self.highlights_changed)
+        self.web_view.update_reading_rates.connect(self.update_reading_rates)
         self.web_view.edit_book.connect(self.edit_book)
         self.actions_toolbar.initialize(self.web_view, self.search_dock.toggleViewAction())
         at.update_action_state(False)
@@ -487,6 +490,7 @@ class EbookViewer(MainWindow):
         self.setWindowTitle(_('Loading book') + f'… — {self.base_window_title}')
         self.loading_overlay(_('Loading book, please wait'))
         self.save_annotations()
+        self.save_reading_rates()
         self.current_book_data = {}
         get_current_book_data(self.current_book_data)
         self.search_widget.clear_searches()
@@ -577,7 +581,8 @@ class EbookViewer(MainWindow):
                 initial_position = {'type': 'bookpos', 'data': float(open_at)}
         highlights = self.current_book_data['annotations_map']['highlight']
         self.highlights_widget.load(highlights)
-        self.web_view.start_book_load(initial_position=initial_position, highlights=highlights, current_book_data=self.current_book_data)
+        rates = load_reading_rates(self.current_book_data['annotations_path_key'])
+        self.web_view.start_book_load(initial_position=initial_position, highlights=highlights, current_book_data=self.current_book_data, reading_rates=rates)
         performance_monitor('webview loading requested')
 
     def load_book_data(self, calibre_book_data=None):
@@ -666,6 +671,20 @@ class EbookViewer(MainWindow):
             get_session_pref('sync_annots_user', default='')
         )
 
+    def update_reading_rates(self, rates):
+        if not self.current_book_data:
+            return
+        self.current_book_data['reading_rates'] = rates
+        self.save_reading_rates()
+
+    def save_reading_rates(self):
+        if not self.current_book_data:
+            return
+        key = self.current_book_data.get('annotations_path_key')
+        rates = self.current_book_data.get('reading_rates')
+        if key and rates:
+            save_reading_rates(key, rates)
+
     def highlights_changed(self, highlights):
         if not self.current_book_data:
             return
@@ -763,6 +782,7 @@ class EbookViewer(MainWindow):
         try:
             self.save_state()
             self.save_annotations()
+            self.save_reading_rates()
             if self.annotations_saver is not None:
                 self.annotations_saver.shutdown()
                 self.annotations_saver = None

src/calibre/gui2/viewer/web_view.py

@@ -274,6 +274,7 @@ class ViewerBridge(Bridge):
     edit_book = from_js(object, object, object)
     show_book_folder = from_js()
     show_help = from_js(object)
+    update_reading_rates = from_js(object)
 
     create_view = to_js()
     start_book_load = to_js()
@@ -472,6 +473,7 @@ class WebView(RestartingWebEngineView):
     scrollbar_context_menu = pyqtSignal(object, object, object)
     close_prep_finished = pyqtSignal(object)
     highlights_changed = pyqtSignal(object)
+    update_reading_rates = pyqtSignal(object)
     edit_book = pyqtSignal(object, object, object)
     shortcuts_changed = pyqtSignal(object)
     paged_mode_changed = pyqtSignal()
@@ -534,6 +536,7 @@ class WebView(RestartingWebEngineView):
         self.bridge.scrollbar_context_menu.connect(self.scrollbar_context_menu)
         self.bridge.close_prep_finished.connect(self.close_prep_finished)
         self.bridge.highlights_changed.connect(self.highlights_changed)
+        self.bridge.update_reading_rates.connect(self.update_reading_rates)
         self.bridge.edit_book.connect(self.edit_book)
         self.bridge.show_book_folder.connect(self.show_book_folder)
         self.bridge.show_help.connect(self.show_help)
@@ -638,10 +641,10 @@ class WebView(RestartingWebEngineView):
     def on_content_file_changed(self, data):
         self.current_content_file = data
 
-    def start_book_load(self, initial_position=None, highlights=None, current_book_data=None):
+    def start_book_load(self, initial_position=None, highlights=None, current_book_data=None, reading_rates=None):
         key = (set_book_path.path,)
         book_url = link_prefix_for_location_links(add_open_at=False)
-        self.execute_when_ready('start_book_load', key, initial_position, set_book_path.pathtoebook, highlights or [], book_url)
+        self.execute_when_ready('start_book_load', key, initial_position, set_book_path.pathtoebook, highlights or [], book_url, reading_rates)
 
     def execute_when_ready(self, action, *args):
         if self.bridge.ready:

src/pyj/read_book/timers.pyj

@@ -2,6 +2,8 @@
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 from __python__ import bound_methods, hash_literals
 
+from read_book.globals import ui_operations
+
 THRESHOLD = 5
 FILTER_THRESHOLD = 25
 MAX_SAMPLES = 256
@@ -16,6 +18,8 @@ class Timers:
     def start_book(self, book):
         self.reset_read_timer()
         self.rates = v'[]'
+        if book.saved_reading_rates?.rates:
+            self.rates = book.saved_reading_rates.rates.slice(0)
 
     def reset_read_timer(self):
         self.last_scroll_at = None
@@ -54,6 +58,8 @@ class Timers:
             self.rates.shift()
         self.rates.push(rate)
         self.calculate()
+        if ui_operations.update_reading_rates:
+            ui_operations.update_reading_rates({'rates': self.rates.slice(0)})
 
     def time_for(self, length):
         if length >= 0 and self.rates.length >= THRESHOLD and self.average > 0:

src/pyj/viewer-main.pyj

@@ -95,7 +95,7 @@ def show_error(title, msg, details):
     to_python.show_error(title, msg, details)
 
 
-def manifest_received(key, initial_position, pathtoebook, highlights, book_url, end_type, xhr, ev):
+def manifest_received(key, initial_position, pathtoebook, highlights, book_url, reading_rates, end_type, xhr, ev):
     nonlocal book
     end_type = workaround_qt_bug(xhr, end_type)
     if end_type is 'load':
@@ -107,6 +107,7 @@ def manifest_received(key, initial_position, pathtoebook, highlights, book_url,
         book.highlights = highlights
         book.stored_files = {}
         book.calibre_book_url = book_url
+        book.saved_reading_rates = reading_rates
         book.is_complete = True
         v'delete book.manifest["metadata"]'
         v'delete book.manifest["last_read_positions"]'
@@ -228,8 +229,8 @@ def show_home_page():
 
 
 @from_python
-def start_book_load(key, initial_position, pathtoebook, highlights, book_url):
-    xhr = ajax('manifest', manifest_received.bind(None, key, initial_position, pathtoebook, highlights, book_url), ok_code=0)
+def start_book_load(key, initial_position, pathtoebook, highlights, book_url, reading_rates):
+    xhr = ajax('manifest', manifest_received.bind(None, key, initial_position, pathtoebook, highlights, book_url, reading_rates), ok_code=0)
     xhr.responseType = 'json'
     xhr.send()
 
@@ -439,6 +440,8 @@ if window is window.top:
         to_python.show_help(which)
     ui_operations.on_iframe_ready = def():
         to_python.on_iframe_ready()
+    ui_operations.update_reading_rates = def(rates):
+        to_python.update_reading_rates(rates)
 
     document.body.appendChild(E.div(id='view'))
     window.onerror = onerror