/*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty5.util;
  
  import io.netty5.util.internal.ObjectUtil;
  import io.netty5.util.internal.PlatformDependent;
  import io.netty5.util.internal.SystemPropertyUtil;
  import io.netty5.util.internal.logging.InternalLogger;
  import io.netty5.util.internal.logging.InternalLoggerFactory;
  
  import java.lang.reflect.Constructor;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * This static factory should be used to load {@link ResourceLeakDetector}s as needed
   */
  public abstract class ResourceLeakDetectorFactory {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(ResourceLeakDetectorFactory.class);
  
      private static volatile ResourceLeakDetectorFactory factoryInstance = new DefaultResourceLeakDetectorFactory();
  
      /**
       * Get the singleton instance of this factory class.
       *
       * @return the current {@link ResourceLeakDetectorFactory}
       */
      public static ResourceLeakDetectorFactory instance() {
          return factoryInstance;
      }
  
      /**
       * Set the factory's singleton instance. This has to be called before the static initializer of the
       * {@link ResourceLeakDetector} is called by all the callers of this factory. That is, before initializing a
       * Netty Bootstrap.
       *
       * @param factory the instance that will become the current {@link ResourceLeakDetectorFactory}'s singleton
       */
      public static void setResourceLeakDetectorFactory(ResourceLeakDetectorFactory factory) {
          factoryInstance = requireNonNull(factory, "factory");
      }
  
      /**
       * Returns a new instance of a {@link ResourceLeakDetector} with the given resource class.
       *
       * @param resource the resource class used to initialize the {@link ResourceLeakDetector}
       * @param <T> the type of the resource class
       * @return a new instance of {@link ResourceLeakDetector}
       */
      public final <T> ResourceLeakDetector<T> newResourceLeakDetector(Class<T> resource) {
          return newResourceLeakDetector(resource, ResourceLeakDetector.SAMPLING_INTERVAL);
      }
  
      /**
       * Returns a new instance of a {@link ResourceLeakDetector} with the given resource class.
       *
       * @param resource the resource class used to initialize the {@link ResourceLeakDetector}
       * @param samplingInterval the interval on which sampling takes place
       * @param <T> the type of the resource class
       * @return a new instance of {@link ResourceLeakDetector}
       */
      public abstract <T> ResourceLeakDetector<T> newResourceLeakDetector(
              Class<T> resource, int samplingInterval);
  
      /**
       * Default implementation that loads custom leak detector via system property
       */
      private static final class DefaultResourceLeakDetectorFactory extends ResourceLeakDetectorFactory {
          private final Constructor<?> customClassConstructor;
  
          DefaultResourceLeakDetectorFactory() {
              String customLeakDetector;
              try {
                  customLeakDetector = SystemPropertyUtil.get("io.netty5.customResourceLeakDetector");
              } catch (Throwable cause) {
                  logger.error("Could not access System property: io.netty5.customResourceLeakDetector", cause);
                  customLeakDetector = null;
              }
              if (customLeakDetector == null) {
                  customClassConstructor = null;
              } else {
                  customClassConstructor = customClassConstructor(customLeakDetector);
              }
          }
  
         private static Constructor<?> customClassConstructor(String customLeakDetector) {
             try {
                 final Class<?> detectorClass = Class.forName(customLeakDetector, true,
                         PlatformDependent.getSystemClassLoader());
 
                 if (ResourceLeakDetector.class.isAssignableFrom(detectorClass)) {
                     return detectorClass.getConstructor(Class.class, int.class);
                 } else {
                     logger.error("Class {} does not inherit from ResourceLeakDetector.", customLeakDetector);
                 }
             } catch (Throwable t) {
                 logger.error("Could not load custom resource leak detector class provided: {}",
                         customLeakDetector, t);
             }
             return null;
         }
 
         @Override
         public <T> ResourceLeakDetector<T> newResourceLeakDetector(Class<T> resource, int samplingInterval) {
             ObjectUtil.checkPositive(samplingInterval, "samplingInterval");
             if (customClassConstructor != null) {
                 try {
                     @SuppressWarnings("unchecked")
                     ResourceLeakDetector<T> leakDetector =
                             (ResourceLeakDetector<T>) customClassConstructor.newInstance(resource, samplingInterval);
                     logger.debug("Loaded custom ResourceLeakDetector: {}",
                             customClassConstructor.getDeclaringClass().getName());
                     return leakDetector;
                 } catch (Throwable t) {
                     logger.error(
                             "Could not load custom resource leak detector provided: {} with the given resource: {}",
                             customClassConstructor.getDeclaringClass().getName(), resource, t);
                 }
             }
 
             ResourceLeakDetector<T> resourceLeakDetector = new ResourceLeakDetector<>(resource, samplingInterval);
             logger.debug("Loaded default ResourceLeakDetector: {}", resourceLeakDetector);
             return resourceLeakDetector;
         }
     }
 }