Fix hotel cost calculation and refactor Specification implementation

solutions/java/src/hotelmanagementsystem/HotelManagerFacade.java

@@ -15,6 +15,7 @@
 import hotelmanagementsystem.specification.Specification;
 
 import java.time.LocalDate;
+import java.time.temporal.ChronoUnit;
 import java.util.List;
 import java.util.Optional;
 
@@ -44,7 +45,7 @@ public Booking bookRoom(Guest guest, RoomType type, RoomStyle style, LocalDate s
             Booking booking = bookingService.createBooking(guest, room, start, end);
 
             // 3. Use Decorator pattern to calculate total cost with amenities
-            Bookable bookable = new RoomBooking(room);
+            Bookable bookable = new RoomBooking(room, (int) ChronoUnit.DAYS.between(start, end));
             for (String amenity : amenities) {
                 if ("breakfast".equalsIgnoreCase(amenity)) {
                     bookable = new BreakfastDecorator(bookable);

solutions/java/src/hotelmanagementsystem/decorator/RoomBooking.java

@@ -4,14 +4,16 @@
 
 public class RoomBooking implements Bookable {
     private final Room room;
+    private final int numberOfNights;
 
-    public RoomBooking(Room room) {
+    public RoomBooking(Room room, int numberOfNights) {
         this.room = room;
+        this.numberOfNights = numberOfNights;
     }
 
     @Override
     public double getCost() {
-        return room.getPrice();
+        return room.getPrice() * numberOfNights;
     }
 
     @Override

solutions/java/src/hotelmanagementsystem/specification/RoomAvailableSpecification.java

@@ -3,7 +3,7 @@
 import hotelmanagementsystem.model.Room;
 import hotelmanagementsystem.state.AvailableState;
 
-public class RoomAvailableSpecification extends AbstractSpecification<Room> {
+public class RoomAvailableSpecification implements Specification<Room> {
     @Override
     public boolean isSatisfiedBy(Room item) {
         return item.getState() instanceof AvailableState;

solutions/java/src/hotelmanagementsystem/specification/RoomStyleSpecification.java

@@ -3,7 +3,7 @@
 import hotelmanagementsystem.enums.RoomStyle;
 import hotelmanagementsystem.model.Room;
 
-public class RoomStyleSpecification extends AbstractSpecification<Room> {
+public class RoomStyleSpecification implements Specification<Room> {
     private final RoomStyle style;
 
     public RoomStyleSpecification(RoomStyle style) {

solutions/java/src/hotelmanagementsystem/specification/RoomTypeSpecification.java

@@ -3,7 +3,7 @@
 import hotelmanagementsystem.enums.RoomType;
 import hotelmanagementsystem.model.Room;
 
-public class RoomTypeSpecification extends AbstractSpecification<Room> {
+public class RoomTypeSpecification implements Specification<Room> {
     private final RoomType type;
 
     public RoomTypeSpecification(RoomType type) {

solutions/java/src/hotelmanagementsystem/specification/Specification.java

@@ -2,5 +2,15 @@
 
 public interface Specification<T> {
     boolean isSatisfiedBy(T item);
-    Specification<T> and(Specification<T> other);
+    default Specification<T> and(Specification<T> other) {
+        return item -> this.isSatisfiedBy(item) && other.isSatisfiedBy(item);
+    }
+
+    default Specification<T> or(Specification<T> other) {
+        return item -> this.isSatisfiedBy(item) || other.isSatisfiedBy(item);
+    }
+
+    default Specification<T> not() {
+        return item -> !this.isSatisfiedBy(item);
+    }
 }