Feat: Implemented a pub/sub design

src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/event/EventData.java

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+package edu.ntnu.idi.idatt2003.g40.mappe.service.event;
+
+/**
+ * Data object sent through the event system by the {@link EventManager}.
+ *
+ * @param <T>       the type of data this object represents.
+ * @param eventType the event type this object represents.
+ * @param data      the data this object contains.
+ *
+ */
+public record EventData<T>(EventType eventType, T data) {
+
+}

src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/event/EventManager.java

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+package edu.ntnu.idi.idatt2003.g40.mappe.service.event;
+
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Event broker in the pub/sub model.
+ *
+ * <p>Read more about pub/sub
+ * <a href = "https://www.geeksforgeeks.org/system-design/what-is-pub-sub/">
+ * Here
+ * </a>
+ * </p>
+ *
+ * @see EventSubscriber
+ * @see EventPublisher
+ *
+ */
+public final class EventManager {
+
+  /**
+   * Map where key is {@link EventType} and value is list of {@link EventSubscriber} objects.
+   *
+   * <p>Used to identify which subscribers to fire the event towards.</p>
+   *
+   */
+  private final Map<EventType, List<EventSubscriber>> subscriberMap =
+      new EnumMap<>(EventType.class);
+
+  /**
+   * Method for adding a subscriber to the subscriber map given an event type.
+   *
+   * @param subscriber the {@link EventSubscriber} object to add.
+   * @param eventType  the {@link EventType} this subscriber should subscribe to.
+   *
+   *
+   */
+  public void addSubscriber(final EventSubscriber subscriber, final EventType eventType) {
+    subscriberMap.computeIfAbsent(eventType, k -> new ArrayList<>()).add(subscriber);
+  }
+
+  /**
+   * Method for invoking event to all subscriber of that type.
+   *
+   * @param <T>  the type of event data to send.
+   * @param data the data to send.
+   *
+   *
+   */
+  public <T> void invokeEvent(final EventData<T> data) {
+    for (EventSubscriber e : subscriberMap.get(data.eventType())) {
+      e.handleEvent(data);
+    }
+  }
+}

src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/event/EventPublisher.java

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+package edu.ntnu.idi.idatt2003.g40.mappe.service.event;
+
+/**
+ * Interface representing a publisher in the pub/sub model (observer pattern).
+ *
+ * @see EventManager
+ * @see EventSubscriber
+ */
+public interface EventPublisher {
+
+  /**
+   * Method for triggering (invoking) the event.
+   *
+   * @param <T>          the type of event data to invoke.
+   * @param data         the data to invoke.
+   * @param eventManager the {@link EventManager} object to use as broker when invoking event.
+   */
+  <T> void invoke(EventData<T> data, EventManager eventManager);
+}
+

src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/event/EventSubscriber.java

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+package edu.ntnu.idi.idatt2003.g40.mappe.service.event;
+
+/**
+ * Interface representing a subscriber in a pub/sub model.
+ *
+ * @see EventManager
+ * @see EventSubscriber
+ */
+public interface EventSubscriber {
+
+  /**
+   * Method for handling the event subscribed to.
+   *
+   * @param <T>  the type of event data to handle.
+   * @param data the actual data to handle.
+   */
+  <T> void handleEvent(EventData<T> data);
+}

src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/service/event/EventType.java

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+package edu.ntnu.idi.idatt2003.g40.mappe.service.event;
+
+/**
+ * Enum representing different event types.
+ *
+ * <p>Examples:</p>
+ * <ul>
+ *   <li>Scene changes</li>
+ *   <li>Database operations</li>
+ *   <li>Other</li>
+ * </ul>
+ *
+ *
+ */
+public enum EventType {
+
+  /**
+   * Event type representing events that causes the current scene to change.
+   *
+   * <p>Primarily handled by the active
+   * {@link edu.ntnu.idi.idatt2003.g40.mappe.view.ViewManager} object.</p>
+   *
+   * @see edu.ntnu.idi.idatt2003.g40.mappe.view.ViewManager
+   *
+   */
+  SCENE_CHANGE,
+
+  /**
+   * Event type representing events that causes the scene to change to the previous one.
+   *
+   * <p>Primarily handled by the active
+   * {@link edu.ntnu.idi.idatt2003.g40.mappe.view.ViewManager} object.</p>
+   *
+   * @see edu.ntnu.idi.idatt2003.g40.mappe.view.ViewManager
+   *
+   */
+  SCENE_BACK,
+}