OccupancySensor support

src/main/java/com/beowulfe/hap/accessories/OccupancySensor.java

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+package com.beowulfe.hap.accessories;
+
+import com.beowulfe.hap.HomekitAccessory;
+import com.beowulfe.hap.HomekitCharacteristicChangeCallback;
+import com.beowulfe.hap.Service;
+import com.beowulfe.hap.impl.services.OccupancySensorService;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * An occupancy sensor that reports whether occupancy has been detected.
+ *
+ * <p>Occupancy sensors that run on batteries will need to implement this interface and also
+ * implement {@link BatteryStatusAccessory}.
+ *
+ * @author Tim Harper
+ */
+public interface OccupancySensor extends HomekitAccessory {
+  /**
+   * Retrieves the state of the occupancy sensor. If true then occupancy has been detected.
+   *
+   * @return a future that will contain the occupancy sensor's state
+   */
+  CompletableFuture<Boolean> getOccupancyDetected();
+
+  @Override
+  default Collection<Service> getServices() {
+    return Collections.singleton(new OccupancySensorService(this));
+  }
+
+  /**
+   * Subscribes to changes in the occupancy sensor.
+   *
+   * @param callback the function to call when the state changes.
+   */
+  void subscribeOccupancyDetected(HomekitCharacteristicChangeCallback callback);
+
+  /** Unsubscribes from changes in the occupancy sensor. */
+  void unsubscribeOccupancyDetected();
+}

src/main/java/com/beowulfe/hap/impl/characteristics/occupancysensor/OccupancyDetectedStateCharacteristic.java

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+package com.beowulfe.hap.impl.characteristics.occupancysensor;
+
+import com.beowulfe.hap.HomekitCharacteristicChangeCallback;
+import com.beowulfe.hap.accessories.OccupancySensor;
+import com.beowulfe.hap.characteristics.BooleanCharacteristic;
+import com.beowulfe.hap.characteristics.EventableCharacteristic;
+import java.util.concurrent.CompletableFuture;
+
+public class OccupancyDetectedStateCharacteristic extends BooleanCharacteristic
+    implements EventableCharacteristic {
+
+  private final OccupancySensor occupancySensor;
+
+  public OccupancyDetectedStateCharacteristic(OccupancySensor occupancySensor) {
+    super("00000071-0000-1000-8000-0026BB765291", false, true, "Occupancy Detected");
+    this.occupancySensor = occupancySensor;
+  }
+
+  @Override
+  protected CompletableFuture<Boolean> getValue() {
+    return occupancySensor.getOccupancyDetected();
+  }
+
+  @Override
+  protected void setValue(Boolean value) throws Exception {
+    // Read Only
+  }
+
+  @Override
+  public void subscribe(HomekitCharacteristicChangeCallback callback) {
+    occupancySensor.subscribeOccupancyDetected(callback);
+  }
+
+  @Override
+  public void unsubscribe() {
+    occupancySensor.unsubscribeOccupancyDetected();
+  }
+}

src/main/java/com/beowulfe/hap/impl/services/OccupancySensorService.java

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+package com.beowulfe.hap.impl.services;
+
+import com.beowulfe.hap.accessories.OccupancySensor;
+import com.beowulfe.hap.impl.characteristics.occupancysensor.OccupancyDetectedStateCharacteristic;
+
+public class OccupancySensorService extends AbstractServiceImpl {
+
+  public OccupancySensorService(OccupancySensor occupancySensor) {
+    this(occupancySensor, occupancySensor.getLabel());
+  }
+
+  public OccupancySensorService(OccupancySensor occupancySensor, String serviceName) {
+    super("00000086-0000-1000-8000-0026BB765291", occupancySensor, serviceName);
+    addCharacteristic(new OccupancyDetectedStateCharacteristic(occupancySensor));
+  }
+}