[books] Allow timezone changes when importing from KOReader

Turns out you need a city-based timezone for DST stuff to work properly.
The US/Eastern timezone doesn't mess with DST because it can be so wonky
in different regions. So while we fix timezone defaulting to a
DST-friendly timezone too.

vrobbler/apps/profiles/models.py

@@ -1,4 +1,8 @@
-import pytz
+from zoneinfo import ZoneInfo
+import pendulum
+from datetime import datetime
+from django.utils import timezone
+import logging
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.db import models
@@ -10,6 +14,7 @@ from profiles.constants import PRETTY_TIMEZONE_CHOICES
 User = get_user_model()
 BNULL = {"blank": True, "null": True}
 
+logger = logging.getLogger(__name__)
 
 class UserProfile(TimeStampedModel):
     user = models.OneToOneField(
@@ -18,6 +23,7 @@ class UserProfile(TimeStampedModel):
     timezone = models.CharField(
         max_length=255, choices=PRETTY_TIMEZONE_CHOICES, default="UTC"
     )
+    timezone_change_log = models.TextField(**BNULL)
     lastfm_username = models.CharField(max_length=255, **BNULL)
     lastfm_password = EncryptedField(**BNULL)
     lastfm_auto_import = models.BooleanField(default=False)
@@ -59,7 +65,51 @@ class UserProfile(TimeStampedModel):
 
     @property
     def tzinfo(self):
-        return pytz.timezone(self.timezone)
+        return ZoneInfo(self.timezone)
+
+    def save(self, *args, **kwargs):
+        if not self._state.adding:
+            old_instance = UserProfile.objects.get(pk=self.pk)
+            is_timezone_change = self.timezone != old_instance.timezone
+            if is_timezone_change:
+                logger.info("Updating timezone changelog for user", extra={"profile_id": self.id})
+                previous_changes = old_instance.timezone_change_log
+                now = timezone.now().replace(microsecond=0)
+                new_log = f"{self.timezone} - {now}"
+                if previous_changes:
+                    new_log = previous_changes + f"\n{new_log}"
+                self.timezone_change_log = new_log
+        super(UserProfile, self).save(*args, **kwargs)
+
+    @property
+    def historic_timezone_changes(self) -> list:
+        """Return a list of datetimes with timezones for the specific changed time"""
+        history = [pendulum.datetime(1900, 1, 1, 0, 0, 0, tz=self.tzinfo.key)]
+        if self.timezone_change_log:
+            for change in self.timezone_change_log.split("\n"):
+                if " - " in change:
+                    tz, date = change.split(" - ")
+                    history.append(pendulum.parse(date).in_timezone(tz))
+        return history
+
+    def get_timestamp_with_tz(self, timestamp):
+        timezone = self.tzinfo
+        if self.timezone_change_log:
+            change_list = self.historic_timezone_changes
+            for idx, start in enumerate(change_list):
+                try:
+                    end = change_list[idx+1]
+                except IndexError:
+                    end = None
+
+                if end:
+                    if start <= timestamp.replace(tzinfo=end.timezone) <= end:
+                        timezone = start.timezone
+                else:
+                    if start <= timestamp.replace(tzinfo=start.timezone):
+                        timezone = start.timezone
+
+        return timestamp.replace(tzinfo=timezone)
 
     @cached_property
     def task_context_tags(self) -> list[str]: