fix thermostat for io13. make temprature unit changeable

Author: Eugen Freiter

src/main/java/io/github/hapjava/accessories/TemperatureSensor.java

@@ -60,4 +60,14 @@ default Collection<Service> getServices() {
   default TemperatureUnit getTemperatureUnit() {
     return TemperatureUnit.CELSIUS;
   }
+
+  /**
+   * set default temperature unit of the thermostat. this is the unit thermostat use to display
+   * temprature. the homekit interface uses celsius.
+   *
+   * @param unit the temperature unit of the thermostat.
+   */
+  default void setTemperatureUnit(TemperatureUnit unit) {
+    // override depending on the thermostat if required.
+  }
 }

src/main/java/io/github/hapjava/impl/characteristics/thermostat/TemperatureUnitsCharacteristic.java

@@ -1,25 +1,36 @@
 package io.github.hapjava.impl.characteristics.thermostat;
 
+import io.github.hapjava.HomekitCharacteristicChangeCallback;
+import io.github.hapjava.accessories.properties.TemperatureUnit;
 import io.github.hapjava.accessories.thermostat.BasicThermostat;
 import io.github.hapjava.characteristics.EnumCharacteristic;
+import io.github.hapjava.characteristics.EventableCharacteristic;
 import java.util.concurrent.CompletableFuture;
 
-public class TemperatureUnitsCharacteristic extends EnumCharacteristic {
+public class TemperatureUnitsCharacteristic extends EnumCharacteristic
+    implements EventableCharacteristic {
 
   private final BasicThermostat thermostat;
 
   public TemperatureUnitsCharacteristic(BasicThermostat thermostat) {
-    super("00000036-0000-1000-8000-0026BB765291", false, true, "The temperature unit", 1);
+    super("00000036-0000-1000-8000-0026BB765291", true, true, "The temperature unit", 1);
     this.thermostat = thermostat;
   }
 
   @Override
   protected void setValue(Integer value) throws Exception {
-    // Not writable
+    thermostat.setTemperatureUnit(
+        value == 1 ? TemperatureUnit.FAHRENHEIT : TemperatureUnit.CELSIUS);
   }
 
   @Override
   protected CompletableFuture<Integer> getValue() {
     return CompletableFuture.completedFuture(thermostat.getTemperatureUnit().getCode());
   }
+
+  @Override
+  public void subscribe(final HomekitCharacteristicChangeCallback callback) {}
+
+  @Override
+  public void unsubscribe() {}
 }