Maintenance window now scheduled weekly on Tuesdays (#20089)

#19031 
- Maintenance window now scheduled weekly on Tuesdays
# Checklist for submitter

If some of the following don't apply, delete the relevant line.

<!-- Note that API documentation changes are now addressed by the
product design team. -->

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Added/updated tests
- [x] Manual QA for all new/changed functionality

changes/19031-maintenance-windows-every-week

@@ -0,0 +1 @@
+- Maintenance window now scheduled weekly on Tuesdays (previously monthly on the third Tuesday of the month)

server/cron/calendar_cron.go

@@ -475,27 +475,14 @@ func attemptCreatingEventOnUserCalendar(
 
 func getPreferredCalendarEventDate(year int, month time.Month, today int) time.Time {
 	const (
-		// 3rd Tuesday of Month
+		// Any Tuesday of Month
 		preferredWeekDay = time.Tuesday
-		preferredOrdinal = 3
 	)
-
-	firstDayOfMonth := time.Date(year, month, 1, 0, 0, 0, 0, time.UTC)
-	offset := int(preferredWeekDay - firstDayOfMonth.Weekday())
-	if offset < 0 {
-		offset += 7
+	currentDate := time.Date(year, month, today, 0, 0, 0, 0, time.UTC)
+	for currentDate.Weekday() != preferredWeekDay {
+		currentDate = currentDate.AddDate(0, 0, 1)
 	}
-	preferredDate := firstDayOfMonth.AddDate(0, 0, offset+(7*(preferredOrdinal-1)))
-	if today > preferredDate.Day() {
-		// We are past the preferred date, so we move to next month and calculate again.
-		month := month + 1
-		if month == 13 {
-			month = 1
-			year += 1
-		}
-		return getPreferredCalendarEventDate(year, month, 1)
-	}
-	return preferredDate
+	return currentDate
 }
 
 func addBusinessDay(date time.Time) time.Time {

server/cron/calendar_cron_test.go

@@ -39,28 +39,28 @@ func TestGetPreferredCalendarEventDate(t *testing.T) {
 		expected time.Time
 	}{
 		{
-			name:      "March 2024 (before 3rd Tuesday)",
+			name:      "March 2024 (before 1st Tuesday)",
 			year:      2024,
 			month:     3,
 			daysStart: 1,
-			daysEnd:   19,
+			daysEnd:   5,
 
-			expected: date(2024, 3, 19),
+			expected: date(2024, 3, 5),
 		},
 		{
-			name:      "March 2024 (past 3rd Tuesday)",
+			name:      "March 2024 (past 1st Tuesday)",
 			year:      2024,
 			month:     3,
-			daysStart: 20,
-			daysEnd:   31,
+			daysStart: 6,
+			daysEnd:   12,
 
-			expected: date(2024, 4, 16),
+			expected: date(2024, 3, 12),
 		},
 		{
 			name:      "April 2024 (before 3rd Tuesday)",
 			year:      2024,
 			month:     4,
-			daysStart: 1,
+			daysStart: 10,
 			daysEnd:   16,
 
 			expected: date(2024, 4, 16),
@@ -70,45 +70,45 @@ func TestGetPreferredCalendarEventDate(t *testing.T) {
 			year:      2024,
 			month:     4,
 			daysStart: 17,
-			daysEnd:   30,
+			daysEnd:   23,
 
-			expected: date(2024, 5, 21),
+			expected: date(2024, 4, 23),
 		},
 		{
-			name:      "May 2024 (before 3rd Tuesday)",
-			year:      2024,
-			month:     5,
-			daysStart: 1,
-			daysEnd:   21,
-
-			expected: date(2024, 5, 21),
-		},
-		{
-			name:      "May 2024 (after 3rd Tuesday)",
+			name:      "May 2024 (before last Tuesday)",
 			year:      2024,
 			month:     5,
 			daysStart: 22,
-			daysEnd:   31,
+			daysEnd:   28,
 
-			expected: date(2024, 6, 18),
+			expected: date(2024, 5, 28),
 		},
 		{
-			name:      "Dec 2024 (before 3rd Tuesday)",
+			name:      "May 2024 (after last Tuesday)",
 			year:      2024,
-			month:     12,
-			daysStart: 1,
-			daysEnd:   17,
-
-			expected: date(2024, 12, 17),
-		},
-		{
-			name:      "Dec 2024 (after 3rd Tuesday)",
-			year:      2024,
-			month:     12,
-			daysStart: 18,
+			month:     5,
+			daysStart: 29,
 			daysEnd:   31,
 
-			expected: date(2025, 1, 21),
+			expected: date(2024, 6, 4),
+		},
+		{
+			name:      "Dec 2025 (before last Tuesday)",
+			year:      2025,
+			month:     12,
+			daysStart: 24,
+			daysEnd:   30,
+
+			expected: date(2025, 12, 30),
+		},
+		{
+			name:      "Dec 2025 (after last Tuesday)",
+			year:      2025,
+			month:     12,
+			daysStart: 31,
+			daysEnd:   31,
+
+			expected: date(2026, 1, 6),
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {