Add upcoming birthdays

Closes: #1

agenda/__init__.py

@@ -265,6 +265,37 @@ def get_us_holiday(input_date: date) -> dict[str, date | str]:
     return {"date": next_hol[0], "title": next_hol[1]}
 
 
+def next_birthday(from_date: date, birth_date: date) -> dict[str, int | date]:
+    """Calculate the date of the next birthday based on a given birth date."""
+    next_birthday_date = birth_date.replace(year=from_date.year)
+
+    if from_date > next_birthday_date:
+        next_birthday_date = birth_date.replace(year=from_date.year + 1)
+
+    age_at_next_birthday = next_birthday_date.year - birth_date.year
+
+    return {"next_birthday": next_birthday_date, "age": age_at_next_birthday}
+
+
+def get_birthdays(
+    from_date: date, config: configparser.ConfigParser
+) -> list[dict[str, date | str]]:
+    if "birthdays" not in config:
+        return []
+    events = []
+    for name, date_str in config["birthdays"].items():
+        bday = next_birthday(from_date, datetime.strptime(date_str, "%Y-%m-%d").date())
+        events.append(
+            {
+                "date": bday["next_birthday"],
+                "name": "birthday",
+                "title": f"{name} (aged {bday['age']})",
+            }
+        )
+
+    return events
+
+
 def get_data(now: datetime) -> dict[str, str | object]:
     """Get data to display on agenda dashboard."""
     rocket_dir = os.path.join(data_dir, "thespacedevs")
@@ -305,6 +336,8 @@ def get_data(now: datetime) -> dict[str, str | object]:
     for key, value in xmas_last_posting_dates.items():
         events.append({"name": f"xmas_last_{key}", "date": value})
 
+    events += get_birthdays(today, config)
+
     next_up_series = {
         "date": date(2026, 6, 1),
         "title": "70 Up",