Add Windmill Hill Market dates

Closes: #36

agenda/__init__.py

@@ -5,7 +5,7 @@ import os
 import re
 import typing
 import warnings
-from datetime import date, datetime, timedelta, timezone
+from datetime import date, datetime, time, timedelta, timezone
 from decimal import Decimal
 from time import time as unixtime
 from typing import List
@@ -21,7 +21,7 @@ import pytz
 import requests
 import yaml
 from dateutil.easter import easter
-from dateutil.relativedelta import FR, relativedelta
+from dateutil.relativedelta import FR, SA, relativedelta
 
 from agenda import thespacedevs
 
@@ -327,6 +327,50 @@ def critical_mass(start_date: date, limit: int = 12) -> list[Event]:
     return events
 
 
+def windmill_hill_market_days(start_date: date) -> list[Event]:
+    """Windmill Hill Market days for the next 12 months from a given date."""
+    events: list[Event] = []
+    current_date = start_date
+
+    # To keep count of how many market days have been calculated
+    count = 0
+
+    tz = pytz.timezone("Europe/London")
+
+    while count < 12:
+        # Skip months outside of April to December
+        if current_date.month < 4 or current_date.month > 12:
+            current_date += relativedelta(months=1)
+            current_date = date(current_date.year, current_date.month, 1)
+            continue
+
+        # Calculate the first Saturday of the current month
+        first_saturday = current_date + relativedelta(day=1, weekday=SA(+1))
+
+        # Include it in the list only if it's on or after the start_date
+        if first_saturday >= start_date:
+            events.append(
+                Event(
+                    name="market",
+                    title="Windmill Hill Market",
+                    date=tz.localize(datetime.combine(first_saturday, time(10, 0))),
+                )
+            )
+            count += 1
+
+        # Move to the next month
+        current_date += relativedelta(months=1)
+        current_date = date(current_date.year, current_date.month, 1)
+
+    return events
+
+
+# Test the function
+if __name__ == "__main__":
+    start_date = date(2023, 10, 29)
+    print(windmill_hill_market_days(start_date))
+
+
 def as_date(d: date | datetime) -> date:
     """Return date for given date or datetime."""
     return d.date() if isinstance(d, datetime) else d
@@ -500,6 +544,7 @@ def get_data(now: datetime) -> typing.Mapping[str, str | object]:
         "xmas_last_posting_dates": xmas_last_posting_dates,
         "gwr_advance_tickets": find_gwr_advance_ticket_date(),
         "critical_mass": critical_mass(today),
+        "market": windmill_hill_market_days(today),
         "rockets": thespacedevs.get_launches(rocket_dir, limit=40),
     }