day which is xth [weekDay] from yth [week] of zth [month] of a [year]

lib/src/time/util.dart

@@ -54,3 +54,51 @@ int clampDayOfMonth({
   required int day,
 }) =>
     day.clamp(1, daysInMonth(year, month));
+
+///return the day which is xth [weekDay] from yth [week] of zth [month] of a [year]
+///eg. DateTime.Friday from 2nd week of DateTime.july of a 2022 year.
+/// [weekDay] ranges from 1 to 7. 1 = monday and 7 = sunday.
+/// [week] ranges from 1 to 4 or 5 month depending upon the month.
+/// [month] ranges from 1 to 12. 1 is january and 12 is december.
+/// [year] the year in which you are calculating
+/// if the number of week is more than the weeks in specific month day will be from another month
+DateTime nthDayOnNthWeekOfAMonth(
+  int weekDay,
+  int week,
+  int month,
+  int year,
+) {
+  final firstDateOfMonth = DateTime(year, month, 1);
+  return firstDateOfMonth.add(
+    Duration(
+      days: 7 * (week - 1) +
+          ((firstDateOfMonth.weekday > weekDay ? 7 : 0) +
+              weekDay -
+              firstDateOfMonth.weekday),
+    ),
+  );
+}
+
+///return the day which is xth last [weekDay] from yth [week] of zth [month] of a [year]
+///eg. DateTime.Friday from 2nd last week of DateTime.july of a 2022 year.
+/// [weekDay] ranges from 1 to 7. 1 = monday and 7 = sunday.
+/// [week] ranges from 1 to 4 or 5 month depending upon the month.
+/// [month] ranges from 1 to 12. 1 is january and 12 is december.
+/// [year] the year in which you are calculating
+/// if the number of week is more than the weeks in specific month day will be from another month
+DateTime lastNthDayOnNthWeekOfAMonth(
+  int weekDay,
+  int week,
+  int month,
+  int year,
+) {
+  final lastDateOfMonth = DateTime(year, month, daysInMonth(year, month));
+
+  return lastDateOfMonth.subtract(
+    Duration(
+      days: (7 - weekDay) +
+          7 * (week - 1) -
+          (lastDateOfMonth.weekday < weekDay ? 7 : 0),
+    ),
+  );
+}

test/time/all_tests.dart

@@ -15,7 +15,9 @@
 library quiver.time.all_tests;
 
 import 'clock_test.dart' as clock;
+import 'util_test.dart' as util;
 
 void main() {
   clock.main();
+  util.main();
 }

test/time/util_test.dart

@@ -0,0 +1,39 @@
+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the 'License');
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an 'AS IS' BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+library quiver.time.util_test;
+
+import 'package:quiver/src/time/util.dart';
+import 'package:test/test.dart';
+
+void expectDate(DateTime date, int y, [int m = 1, int d = 1]) {
+  expect(date, DateTime(y, m, d));
+}
+
+void main() {
+  group('util', () {
+    test('should return the date of friday from 2nd week of july of 2022', () {
+      final calculatedDate =
+          nthDayOnNthWeekOfAMonth(DateTime.friday, 2, DateTime.july, 2022);
+      expectDate(calculatedDate, 2022, 7, 8);
+    });
+
+    test('should return the date of friday from 2nd last week of feb of 2022',
+        () {
+      final calculatedDate = lastNthDayOnNthWeekOfAMonth(
+          DateTime.friday, 2, DateTime.february, 2022);
+      expectDate(calculatedDate, 2022, 2, 26);
+    });
+  });
+}