Adding activities in retrospect is very hard

NEWS.md

@@ -1,3 +1,7 @@
+## Changes in 3.0.3 (unreleased)
+
+* Fixed Adding activities in retrospect is very hard (issue 627)
+
 ## Changes in 3.0.2
 
 * Switch from deprecated xml2po to itstool for translating help files

src/hamster/edit_activity.py

@@ -135,15 +135,8 @@ def date(self):
 
     @date.setter
     def date(self, value):
-        delta = value - self._date if self._date else None
         self._date = value
         self.cmdline.default_day = value
-        if self.fact and delta:
-            if self.fact.start_time:
-                self.fact.start_time += delta
-            if self.fact.end_time:
-                self.fact.end_time += delta
-            # self.update_fields() here would enter an infinite loop
 
     def on_prev_day_clicked(self, button):
         self.increment_date(-1)
@@ -161,7 +154,7 @@ def get_widget(self, name):
 
     def increment_date(self, days):
         delta = dt.timedelta(days=days)
-        self.date += delta
+        self.change_start_date(self.date + delta)
         self.update_fields()
 
     def show(self):
@@ -240,18 +233,21 @@ def on_end_time_changed(self, widget):
 
     def on_start_date_changed(self, widget):
         if not self.master_is_cmdline:
-            if self.fact.start_time:
-                previous_date = self.fact.start_time.date()
-                new_date = self.start_date.date
-                delta = new_date - previous_date
-                self.fact.start_time += delta
-                if self.fact.end_time:
-                    # preserve fact duration
-                    self.fact.end_time += delta
-                    self.end_date.date = self.fact.end_time
-            self.date = self.fact.date or dt.hday.today()
-            self.validate_fields()
-            self.update_cmdline()
+            new_date = self.start_date.date
+            self.change_start_date(new_date)
+
+    def change_start_date(self, new_date):
+        if self.fact.start_time:
+            previous_date = self.fact.start_time.date()
+            delta = new_date - previous_date
+            self.fact.start_time += delta
+            if self.fact.end_time:
+                # preserve fact duration
+                self.fact.end_time += delta
+                self.end_date.date = self.fact.end_time
+        self.date = self.fact.date or dt.hday.today()
+        self.validate_fields()
+        self.update_cmdline()
 
     def on_start_date_expander_activated(self, widget):
         # state has not changed yet, toggle also end_date calendar visibility
@@ -302,8 +298,8 @@ def update_fields(self):
         self.start_time.time = self.fact.start_time
         self.end_time.time = self.fact.end_time
         self.end_time.set_start_time(self.fact.start_time)
-        self.start_date.date = self.fact.start_time
-        self.end_date.date = self.fact.end_time
+        self.start_date.date = self.fact.date or self.date
+        self.end_date.date = self.fact.date or self.date
         self.activity_entry.set_text(self.fact.activity)
         self.category_entry.set_text(self.fact.category)
         self.description_buffer.set_text(self.fact.description)