[#124](#124

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

@@ -0,0 +1,42 @@
+package io.github.hapjava.accessories;
+
+import io.github.hapjava.characteristics.HomekitCharacteristicChangeCallback;
+import io.github.hapjava.characteristics.impl.filtermaintenance.FilterChangeIndicationEnum;
+import io.github.hapjava.services.Service;
+import io.github.hapjava.services.impl.FilterMaintenanceService;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * A Filter maintenance with mandatory characteristics.
+ *
+ * <p>The HomeKit app doesn't support a seperate FilterMaintenance, but as a linked service to
+ * AirPurifier.
+ *
+ * @see AirPurifierAccessory#getFilterMaintenanceAccessory()
+ */
+public interface FilterMaintenanceAccessory extends HomekitAccessory {
+
+  /**
+   * The filter change indictaion. It's either yes or no.
+   *
+   * @return FilterChangeIndicationEnum
+   */
+  CompletableFuture<FilterChangeIndicationEnum> getFilterChangeIndication();
+
+  /**
+   * Subscribes to changes in the filter change indication.
+   *
+   * @param callback the function to call when the state changes.
+   */
+  void subscribeFilterChangeIndication(HomekitCharacteristicChangeCallback callback);
+
+  /** Unsubscribes from changes in the filter change indication. */
+  void unsubscribeFilterChangeIndication();
+
+  @Override
+  default Collection<Service> getServices() {
+    return Collections.singleton(new FilterMaintenanceService(this));
+  }
+}

src/main/java/io/github/hapjava/accessories/optionalcharacteristic/AccessoryWithFilterLifeLevel.java

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+package io.github.hapjava.accessories.optionalcharacteristic;
+
+import io.github.hapjava.characteristics.HomekitCharacteristicChangeCallback;
+import java.util.concurrent.CompletableFuture;
+
+/** Accessory with filter level characteristics */
+public interface AccessoryWithFilterLifeLevel {
+
+  /**
+   * what's the filter life level, percentage wise
+   *
+   * @return filter life level
+   */
+  CompletableFuture<Double> getFilterLifeLevel();
+
+  /**
+   * Subscribes to changes in the filter life level.
+   *
+   * @param callback the function to call when the level changes.
+   */
+  void subscribeFilterLifeLevel(HomekitCharacteristicChangeCallback callback);
+
+  /** Unsubscribes from changes in the current filter life level. */
+  void unsubscribeFilterLifeLevel();
+}

src/main/java/io/github/hapjava/accessories/optionalcharacteristic/AccessoryWithResetFilterIndication.java

@@ -0,0 +1,14 @@
+package io.github.hapjava.accessories.optionalcharacteristic;
+
+import java.util.concurrent.CompletableFuture;
+
+/** Accessory with filter reset characteristics */
+public interface AccessoryWithResetFilterIndication {
+
+  /**
+   * Request to reset the filter level
+   *
+   * @param indication always 1, by HomeKit protocol. (to be ignored)
+   */
+  CompletableFuture<Void> resetFilterIndication(Integer indication) throws Exception;
+}

src/main/java/io/github/hapjava/characteristics/impl/filtermaintenance/FilterChangeIndicationCharacteristic.java

@@ -0,0 +1,27 @@
+package io.github.hapjava.characteristics.impl.filtermaintenance;
+
+import io.github.hapjava.characteristics.EventableCharacteristic;
+import io.github.hapjava.characteristics.HomekitCharacteristicChangeCallback;
+import io.github.hapjava.characteristics.impl.base.EnumCharacteristic;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+public class FilterChangeIndicationCharacteristic
+    extends EnumCharacteristic<FilterChangeIndicationEnum> implements EventableCharacteristic {
+
+  public FilterChangeIndicationCharacteristic(
+      Supplier<CompletableFuture<FilterChangeIndicationEnum>> getter,
+      Consumer<HomekitCharacteristicChangeCallback> subscriber,
+      Runnable unsubscriber) {
+    super(
+        "000000AC-0000-1000-8000-0026BB765291",
+        "filter change indication",
+        FilterChangeIndicationEnum.values(),
+        Optional.of(getter),
+        Optional.empty(),
+        Optional.of(subscriber),
+        Optional.of(unsubscriber));
+  }
+}

src/main/java/io/github/hapjava/characteristics/impl/filtermaintenance/FilterChangeIndicationEnum.java

@@ -0,0 +1,34 @@
+package io.github.hapjava.characteristics.impl.filtermaintenance;
+
+import io.github.hapjava.characteristics.CharacteristicEnum;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public enum FilterChangeIndicationEnum implements CharacteristicEnum {
+  NO_CHANGE_NEEDED(0),
+  CHANGE_NEEDED(1);
+
+  private static final Map<Integer, FilterChangeIndicationEnum> reverse;
+
+  static {
+    reverse =
+        Arrays.stream(FilterChangeIndicationEnum.values())
+            .collect(Collectors.toMap(FilterChangeIndicationEnum::getCode, t -> t));
+  }
+
+  public static FilterChangeIndicationEnum fromCode(Integer code) {
+    return reverse.get(code);
+  }
+
+  private final int code;
+
+  FilterChangeIndicationEnum(int code) {
+    this.code = code;
+  }
+
+  @Override
+  public int getCode() {
+    return code;
+  }
+}

src/main/java/io/github/hapjava/characteristics/impl/filtermaintenance/FilterLifeLevelCharacteristic.java

@@ -0,0 +1,30 @@
+package io.github.hapjava.characteristics.impl.filtermaintenance;
+
+import io.github.hapjava.characteristics.EventableCharacteristic;
+import io.github.hapjava.characteristics.HomekitCharacteristicChangeCallback;
+import io.github.hapjava.characteristics.impl.base.FloatCharacteristic;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+public class FilterLifeLevelCharacteristic extends FloatCharacteristic
+    implements EventableCharacteristic {
+
+  public FilterLifeLevelCharacteristic(
+      Supplier<CompletableFuture<Double>> getter,
+      Consumer<HomekitCharacteristicChangeCallback> subscriber,
+      Runnable unsubscriber) {
+    super(
+        "000000AB-0000-1000-8000-0026BB765291",
+        "Filter Life Level",
+        0,
+        100,
+        1,
+        "%",
+        Optional.of(getter),
+        Optional.empty(),
+        Optional.of(subscriber),
+        Optional.of(unsubscriber));
+  }
+}

src/main/java/io/github/hapjava/characteristics/impl/filtermaintenance/ResetFilterIndicationCharacteristic.java

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+package io.github.hapjava.characteristics.impl.filtermaintenance;
+
+import io.github.hapjava.characteristics.ExceptionalConsumer;
+import io.github.hapjava.characteristics.impl.base.IntegerCharacteristic;
+import java.util.Optional;
+
+public class ResetFilterIndicationCharacteristic extends IntegerCharacteristic {
+
+  public ResetFilterIndicationCharacteristic(ExceptionalConsumer<Integer> setter) {
+    super(
+        "000000AD-0000-1000-8000-0026BB765291",
+        "Reset Filter Indication",
+        1,
+        1,
+        null,
+        Optional.empty(),
+        Optional.of(setter),
+        Optional.empty(),
+        Optional.empty());
+  }
+}

src/main/java/io/github/hapjava/services/impl/FilterMaintenanceService.java

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+package io.github.hapjava.services.impl;
+
+import io.github.hapjava.accessories.FilterMaintenanceAccessory;
+import io.github.hapjava.accessories.optionalcharacteristic.AccessoryWithFilterLifeLevel;
+import io.github.hapjava.accessories.optionalcharacteristic.AccessoryWithName;
+import io.github.hapjava.accessories.optionalcharacteristic.AccessoryWithResetFilterIndication;
+import io.github.hapjava.characteristics.impl.common.NameCharacteristic;
+import io.github.hapjava.characteristics.impl.filtermaintenance.FilterChangeIndicationCharacteristic;
+import io.github.hapjava.characteristics.impl.filtermaintenance.FilterLifeLevelCharacteristic;
+import io.github.hapjava.characteristics.impl.filtermaintenance.ResetFilterIndicationCharacteristic;
+
+/** This service describes a filter maintenance. */
+public class FilterMaintenanceService extends AbstractServiceImpl {
+
+  public FilterMaintenanceService(FilterChangeIndicationCharacteristic filerChange) {
+    super("000000BA-0000-1000-8000-0026BB765291");
+    addCharacteristic(filerChange);
+  }
+
+  public FilterMaintenanceService(FilterMaintenanceAccessory accessory) {
+    this(
+        new FilterChangeIndicationCharacteristic(
+            accessory::getFilterChangeIndication,
+            accessory::subscribeFilterChangeIndication,
+            accessory::unsubscribeFilterChangeIndication));
+
+    if (accessory instanceof AccessoryWithName) {
+      addOptionalCharacteristic(new NameCharacteristic(((AccessoryWithName) accessory)::getName));
+    }
+
+    if (accessory instanceof AccessoryWithFilterLifeLevel) {
+      addOptionalCharacteristic(
+          new FilterLifeLevelCharacteristic(
+              ((AccessoryWithFilterLifeLevel) accessory)::getFilterLifeLevel,
+              ((AccessoryWithFilterLifeLevel) accessory)::subscribeFilterLifeLevel,
+              ((AccessoryWithFilterLifeLevel) accessory)::unsubscribeFilterLifeLevel));
+    }
+
+    if (accessory instanceof AccessoryWithResetFilterIndication) {
+      addOptionalCharacteristic(
+          new ResetFilterIndicationCharacteristic(
+              ((AccessoryWithResetFilterIndication) accessory)::resetFilterIndication));
+    }
+  }
+
+  public void addOptionalCharacteristic(NameCharacteristic name) {
+    addCharacteristic(name);
+  }
+
+  public void addOptionalCharacteristic(FilterLifeLevelCharacteristic filterLifeLevel) {
+    addCharacteristic(filterLifeLevel);
+  }
+
+  public void addOptionalCharacteristic(ResetFilterIndicationCharacteristic resetFilterIndication) {
+    addCharacteristic(resetFilterIndication);
+  }
+}