content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package androidx.test.internal.platform;
  
  import android.os.StrictMode;
  import androidx.annotation.RestrictTo;
  import java.util.ArrayList;
  import java.util.HashSet;
  import java.util.List;
  import java.util.ServiceLoader;
  import java.util.Set;
  
  /**
   * Wrapper class for {@link ServiceLoader} that disables StrictMode.
   *
   * <p>Loading a service via ServiceLoader can result in disk I/O. Disk I/O on Android can be
   * restricted via StrictMode. This class disables disk access checking and then reenables StrictMode
   * when loading a service.
   *
   * @hide
   */
  @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP) // used by core, espresso, rule
  public final class ServiceLoaderWrapper {
  
    private ServiceLoaderWrapper() {}
  
    /**
     * Loads the implementing classes for given service.
     *
     * @return List of implementing classes. Returns an empty list if no implementing classes were
     *     defined.
     */
    public static <T> List<T> loadService(Class<T> serviceClass) {
      StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();
  
      // load using ServiceLoader
      List<T> services = new ArrayList<>();
      for (T element : ServiceLoader.load(serviceClass)) {
        services.add(element);
      }
      StrictMode.setThreadPolicy(oldPolicy);
      return services;
    }
  
    /** A factory for creating default implementations of service classes. */
    public interface Factory<T> {
      T create();
    }
  
    /**
     * A wrapper method around {@link #loadService(Class)} that strictly enforces there is only one
     * implementation of the service.
     *
     * @param serviceClass the service type class to load implementation for
     * @param defaultImplFactory the factory implementation for creating instances
     * @return the implementing service, or a new instance via defaultImplFactory.create() if no
     *     implementations are defined.
     * @throws IllegalStateException if more than one service implementations are found
     */
    public static <T> T loadSingleService(Class<T> serviceClass, Factory<T> defaultImplFactory) {
      T impl = loadSingleServiceOrNull(serviceClass);
      if (impl == null) {
        return defaultImplFactory.create();
      } else {
        return impl;
      }
    }
  
    /**
     * A wrapper method around {@link #loadService(Class)} that returns one implementation of the
     * service or {@code null} if no implementation is found. If an implementation is marked with
     * {@link Supersedes}, the implementation in Supersedes will be filtered out.
     *
     * @param serviceClass the service type class to load implementation for
     * @return the implementing service or null if none is found. If an implementation is marked with
     *     {@link Supersedes}, the implementation in Supersedes will be filtered out.
     * @throws IllegalStateException if more than one service implementations are found
     */
    public static <T> T loadSingleServiceOrNull(Class<T> serviceClass) {
      List<T> impls = filter(ServiceLoaderWrapper.loadService(serviceClass));
      if (impls.isEmpty()) {
        return null;
      } else if (impls.size() == 1) {
        return impls.get(0);
      } else {
        String combinedImpls = null;
        for (T impl : impls) {
          combinedImpls = (combinedImpls != null) ? combinedImpls + ", " : ": ";
          combinedImpls += impl.getClass().getName();
        }
  
        throw new IllegalStateException(
            "Found more than one implementation for " + serviceClass.getName() + combinedImpls);
      }
    }
  
    @SuppressWarnings("unchecked")
    private static <T> List<T> filter(List<T> services) {
      Set<Class<?>> superseded = new HashSet<>();
      for (T service : services) {
        Class<? extends T> clazz = (Class<? extends T>) service.getClass();
        Supersedes supersedes = clazz.getAnnotation(Supersedes.class);
        if (supersedes != null) {
          superseded.add(supersedes.value());
        }
      }
      if (superseded.isEmpty()) {
        return services;
      } else {
        List<T> filtered = new ArrayList<>();
        for (T service : services) {
          if (!superseded.contains(service.getClass())) {
            filtered.add(service);
          }
        }
        return filtered;
      }
    }
  }
  