should be it

external/duckdb/extension/icu/include/tz_calendar.hpp

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//                         DuckDB
+//
+// tz_calendar.hpp
+//
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include "unicode/calendar.h"
+#include "duckdb/common/string_util.hpp"
+
+namespace duckdb {
+
+using CalendarPtr = duckdb::unique_ptr<icu::Calendar>;
+
+struct TZCalendar {
+	TZCalendar(icu::Calendar &calendar_p, const string &cal_setting)
+	    : calendar(CalendarPtr(calendar_p.clone())),
+	      is_gregorian(cal_setting.empty() || StringUtil::CIEquals(cal_setting, "gregorian")),
+	      supports_intervals(calendar->getMaximum(UCAL_MONTH) < 12) { // 0-based
+	}
+
+	icu::Calendar *GetICUCalendar() {
+		return calendar.get();
+	}
+	bool IsGregorian() const {
+		return is_gregorian;
+	}
+	bool SupportsIntervals() const {
+		return supports_intervals;
+	}
+
+	CalendarPtr calendar;
+	const bool is_gregorian;
+	const bool supports_intervals;
+};
+
+} // namespace duckdb