First and Last days extensions added

lib/src/extensions.dart

@@ -204,6 +204,26 @@ extension DateTimeTimeExtension on DateTime {
             microsecond ?? this.microsecond,
           );
   }
+
+  /// Returns the Monday of this week
+  DateTime get firstDayOfWeek =>
+      isUtc ? DateTime.utc(year, month, day + 1 - weekday) : DateTime(year, month, day + 1 - weekday);
+
+  /// Returns the Sunday of this week
+  DateTime get lastDayOfWeek =>
+      isUtc ? DateTime.utc(year, month, day + 7 - weekday) : DateTime(year, month, day + 7 - weekday);
+
+  /// Returns the first day of this month
+  DateTime get firstDayOfMonth => isUtc ? DateTime.utc(year, month, 1) : DateTime(year, month, 1);
+
+  /// Returns the last day of this month (considers leap years)
+  DateTime get lastDayOfMonth => isUtc ? DateTime.utc(year, month + 1, 0) : DateTime(year, month + 1, 0);
+
+  /// Returns the first day of this year
+  DateTime get firstDayOfYear => isUtc ? DateTime.utc(year, 1, 1) : DateTime(year, 1, 1);
+
+  /// Returns the last day of this year
+  DateTime get lastDayOfYear => isUtc ? DateTime.utc(year, 12, 31) : DateTime(year, 12, 31);
 }
 
 extension DurationTimeExtension on Duration {

test/time_test.dart

@@ -527,6 +527,58 @@ void main() {
           expect(later.isUtc, isTrue);
         });
       });
+
+      group('can get first/last days', () {
+        test('first day of week', () {
+          final initial = DateTime(2022, 5, 20);
+          final expected = DateTime(2022, 5, 16);
+          expect(initial.firstDayOfWeek, expected);
+        });
+
+        test('last day of week', () {
+          final initial = DateTime(2022, 5, 20);
+          final expected = DateTime(2022, 5, 22);
+          expect(initial.lastDayOfWeek, expected);
+        });
+
+        test('first day of month', () {
+          final initial = DateTime(2022, 5, 20);
+          final expected = DateTime(2022, 5, 1);
+          expect(initial.firstDayOfMonth, expected);
+        });
+
+        group('last day of month', (){
+          test('last day of month', () {
+            final initial = DateTime(2022, 5, 20);
+            final expected = DateTime(2022, 5, 31);
+            expect(initial.lastDayOfMonth, expected);
+          });
+          test('february not leap year', () {
+            final initial = DateTime(2022, 2, 20);
+            final expected = DateTime(2022, 2, 28);
+            expect(initial.lastDayOfMonth, expected);
+          });
+
+          test('february leap year', () {
+            final initial = DateTime(2020, 2, 20);
+            final expected = DateTime(2020, 2, 29);
+            expect(initial.lastDayOfMonth, expected);
+          });
+
+        });
+
+        test('first day of year', () {
+          final initial = DateTime(2022, 5, 20);
+          final expected = DateTime(2022, 1, 1);
+          expect(initial.firstDayOfYear, expected);
+        });
+
+        test('last day of year', () {
+          final initial = DateTime(2022, 5, 20);
+          final expected = DateTime(2022, 12, 31);
+          expect(initial.lastDayOfYear, expected);
+        });
+      });
     });
   });
 
@@ -564,4 +616,4 @@ void main() {
       expect(extraTime >= 0, true);
     });
   });
-}
+}