Add proper time zone support

Until now event timestamps were saved in the server’s time zone.  Now they are saved in UTC,
considering the time zone set by the creator of the event.

calsocial/forms.py

@@ -1,6 +1,7 @@
 from flask_babelex import lazy_gettext as _
 from flask_wtf import FlaskForm
-from wtforms import PasswordField, StringField, BooleanField
+import pytz
+from wtforms import BooleanField, PasswordField, SelectField, StringField
 from wtforms.ext.dateutil.fields import DateTimeField
 from wtforms.validators import DataRequired, Email, ValidationError
 from wtforms.widgets import TextArea
@@ -17,14 +18,72 @@ class RegistrationForm(FlaskForm):
             raise ValidationError(_('The two passwords must match!'))
 
 
+class TimezoneField(SelectField):
+    def __init__(self, *args, **kwargs):
+        kwargs.update({
+            'choices': [
+                (pytz.timezone(tz), tz.replace('_', ' '))
+                for tz in pytz.common_timezones
+            ],
+        })
+
+        SelectField.__init__(self, *args, **kwargs)
+
+    def process_formdata(self, valuelist):
+        if not valuelist:
+            self.data = None
+
+            return
+
+        try:
+            self.data = pytz.timezone(valuelist[0])
+        except pytz.exceptions.UnknownTimeZoneError:
+            self.data = None
+
+            raise ValueError('Unknown time zone')
+
+    @staticmethod
+    def is_pytz_instance(value):
+        return value is pytz.UTC or isinstance(value, pytz.tzinfo.BaseTzInfo)
+
+    def process_data(self, value):
+        if value is None:
+            self.data = None
+
+            return
+
+        if is_pytz_instance(value):
+            self.data = value
+
+            return
+
+        try:
+            self.data = pytz.timezone(value)
+        except Exception as exc:
+            raise ValueError(f'Unknown time zone {value}')
+
+    def iter_choices(self):
+        for value, label in self.choices:
+            yield (value, label, value == self.data)
+
+
 class EventForm(FlaskForm):
     title = StringField(_('Title'), validators=[DataRequired()])
-    time_zone = StringField(_('Time zone'), validators=[DataRequired()])
+    time_zone = TimezoneField(_('Time zone'), validators=[DataRequired()])
     start_time = DateTimeField(_('Start time'), validators=[DataRequired()])
     end_time = DateTimeField(_('End time'), validators=[DataRequired()])
     all_day = BooleanField(_('All day'))
     description = StringField(_('Description'), widget=TextArea())
 
+    def populate_obj(self, obj):
+        FlaskForm.populate_obj(self, obj)
+
+        tz = self.time_zone.data
+
+        obj.time_zone = str(tz)
+        obj.start_time = tz.localize(self.start_time.data).astimezone(pytz.utc)
+        obj.end_time = tz.localize(self.end_time.data).astimezone(pytz.utc)
+
     def validate_end_time(self, field):
         if field.data < self.start_time.data:
             raise ValidationError(_('End time must be later than start time!'))

calsocial/models.py

@@ -83,5 +83,18 @@ class Event(db.Model):
     #: The description of the event
     description = db.Column(db.UnicodeText())
 
+    def __as_tz(self, timestamp):
+        from pytz import timezone, utc
+
+        return utc.localize(timestamp).astimezone(timezone(self.time_zone))
+
+    @property
+    def start_time_tz(self):
+        return self.__as_tz(self.start_time)
+
+    @property
+    def end_time_tz(self):
+        return self.__as_tz(self.end_time)
+
     def __repr__(self):
         return f'<Event {self.id} ({self.title}) of {self.user}>'

calsocial/templates/month-view.html

@@ -6,6 +6,7 @@
  table.calendar {
      width: 100%;
      border-collapse: collapse;
+     table-layout: fixed;
  }
 
  tr.month > td {
@@ -46,14 +47,31 @@
      background-color: #d8d8d8;
  }
 
- td > div.event {
+ tr.week > td > div.event {
      border: 1px solid green;
      background-color: white;
      border-radius: 2px;
+     text-overflow: ellipsis;
+     white-space: nowrap;
+     overflow: hidden;
+ }
+
+ tr.sizer > td {
+     width: 14.2857%;
+     height: 0;
  }
 </style>
 <table class="calendar">
     <thead>
+        <tr class="sizer">
+            <td></td>
+            <td></td>
+            <td></td>
+            <td></td>
+            <td></td>
+            <td></td>
+            <td></td>
+        </tr>
         <tr class="month">
             <td>
                 <a href="{{ url_for('hello', date=calendar.prev_year) }}">« {{ calendar.prev_year_year }}</a>
@@ -101,6 +119,8 @@
                 <span class="day-num">{{ day.day }}</span>
     {% for event in calendar.day_events(day, user=current_user) %}
                 <div class="event">
+                    {{ event.start_time_tz.strftime('%H:%M') }}–{{ event.end_time_tz.strftime('%H:%M') }}
+                    ({{ event.time_zone }})
                     {{ event.title }}
                 </div>
     {% endfor %}