GWR ticket date mail shows weekends

GWR advance ticket change email now shows Saturdays and Sundays in
addition to Weekdays.

Switched from ISO dates to human readable dates.

Closes: #177

update.py

@@ -54,26 +54,49 @@ def update_gwr_advance_ticket_date(config: flask.config.Config) -> None:
     """Update GWR advance ticket date cache."""
     filename = os.path.join(config["DATA_DIR"], "advance-tickets.html")
     existing_html = open(filename).read()
-    existing_date = agenda.gwr.extract_weekday_date(existing_html)
+
+    existing_dates = agenda.gwr.extract_dates(existing_html)
+    assert existing_dates
+    assert list(existing_dates.keys()) == ["Weekdays", "Saturdays", "Sundays"]
 
     new_html = requests.get(agenda.gwr.url).text
-    open(filename, "w").write(new_html)
 
-    new_date = agenda.gwr.extract_weekday_date(new_html)
+    new_dates = agenda.gwr.extract_dates(new_html)
+    assert new_dates
+    assert list(new_dates.keys()) == ["Weekdays", "Saturdays", "Sundays"]
 
-    if existing_date == new_date:
+    if existing_dates == new_dates:
         if sys.stdin.isatty():
-            print("date has't changed:", existing_date)
+            print(filename)
+            print(agenda.gwr.url)
+            print("dates haven't changed:", existing_dates)
         return
 
-    subject = f"New GWR advance ticket booking date: {new_date}"
-    body = f"""Old date: {existing_date}
-New date: {new_date}
+    open(filename, "w").write(new_html)
+
+    subject = (
+        "New GWR advance ticket booking date: "
+        + f'{new_dates["Weekdays"].strftime("%d %b %Y")} (Weekdays)'
+    )
+    body = f"""
+{"\n".join(f'{key}: {when.strftime("%d %b %Y")}' for key, when in new_dates.items())}
 
 {agenda.gwr.url}
 
 Agenda: https://edwardbetts.com/agenda/
 """
+
+    if sys.stdin.isatty():
+        print(filename)
+        print(agenda.gwr.url)
+        print()
+        print("dates have changed")
+        print("old:", existing_dates)
+        print("new:", new_dates)
+        print()
+        print(subject)
+        print(body)
+
     agenda.mail.send_mail(config, subject, body)