/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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
    *
   *   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 org.eclipse.aether.util.concurrency;
  
  import java.util.concurrent.Callable;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Future;
  import java.util.concurrent.Semaphore;
  
  /**
   * Utilities for executors and sizing them.
   * <em>Big fat note:</em> Do not use this class outside of resolver. This and related classes are not meant as "drop
   * in replacement" for Jave Executors, is used in very controlled fashion only.
   *
   * @since 2.0.11
   */
  public interface SmartExecutor extends AutoCloseable {
      /**
       * Submits a {@link Runnable} to execution.
       */
      void submit(Runnable runnable);
  
      /**
       * Submits a {@link Callable} to execution, returns a {@link CompletableFuture}.
       */
      <T> Future<T> submit(Callable<T> callable);
  
      /**
       * Shut down this instance (ideally used in try-with-resource construct).
       */
      void close();
  
      /**
       * Direct executor (caller executes).
       */
      class Direct implements SmartExecutor {
          @Override
          public void submit(Runnable runnable) {
              runnable.run();
          }
  
          @Override
          public <T> CompletableFuture<T> submit(Callable<T> callable) {
              CompletableFuture<T> future = new CompletableFuture<>();
              try {
                  future.complete(callable.call());
              } catch (Exception e) {
                  future.completeExceptionally(e);
              }
              return future;
          }
  
          @Override
          public void close() {}
      }
  
      /**
       * Pooled executor backed by {@link ExecutorService}.
       */
      class Pooled implements SmartExecutor {
          private final ExecutorService executor;
  
          Pooled(ExecutorService executor) {
              this.executor = executor;
          }
  
          @Override
          public void submit(Runnable runnable) {
              ClassLoader tccl = Thread.currentThread().getContextClassLoader();
              executor.submit(() -> {
                  ClassLoader old = Thread.currentThread().getContextClassLoader();
                  Thread.currentThread().setContextClassLoader(tccl);
                  try {
                      runnable.run();
                  } finally {
                      Thread.currentThread().setContextClassLoader(old);
                  }
              });
          }
  
          @Override
          public <T> Future<T> submit(Callable<T> callable) {
             ClassLoader tccl = Thread.currentThread().getContextClassLoader();
             CompletableFuture<T> future = new CompletableFuture<>();
             executor.submit(() -> {
                 ClassLoader old = Thread.currentThread().getContextClassLoader();
                 Thread.currentThread().setContextClassLoader(tccl);
                 try {
                     future.complete(callable.call());
                 } catch (Exception e) {
                     future.completeExceptionally(e);
                 } finally {
                     Thread.currentThread().setContextClassLoader(old);
                 }
             });
             return future;
         }
 
         @Override
         public void close() {
             executor.shutdown();
         }
     }
 
     /**
      * Limited executor, where the actual goal is to protect accessed resource, like when virtual threads
      * are being used, so the "pool" itself does not provide any kind of back-pressure.
      */
     class Limited implements SmartExecutor {
         private final SmartExecutor executor;
         private final Semaphore semaphore;
 
         Limited(SmartExecutor executor, int limit) {
             this.executor = executor;
             this.semaphore = new Semaphore(limit);
         }
 
         @Override
         public void submit(Runnable runnable) {
             try {
                 semaphore.acquire();
                 executor.submit(() -> {
                     try {
                         runnable.run();
                     } finally {
                         semaphore.release();
                     }
                 });
             } catch (InterruptedException e) {
                 Thread.currentThread().interrupt();
             }
         }
 
         @Override
         public <T> Future<T> submit(Callable<T> callable) {
             try {
                 semaphore.acquire();
                 CompletableFuture<T> future = new CompletableFuture<>();
                 executor.submit(() -> {
                     try {
                         future.complete(callable.call());
                     } catch (Exception e) {
                         future.completeExceptionally(e);
                     } finally {
                         semaphore.release();
                     }
                 });
                 return future;
             } catch (InterruptedException e) {
                 Thread.currentThread().interrupt();
                 CompletableFuture<T> failed = new CompletableFuture<>();
                 failed.completeExceptionally(e);
                 return failed;
             }
         }
 
         @Override
         public void close() {
             executor.close();
         }
     }
 
     /**
      * Wrapper to prevent closing.
      */
     class NonClosing implements SmartExecutor {
         private final SmartExecutor smartExecutor;
 
         NonClosing(SmartExecutor smartExecutor) {
             this.smartExecutor = smartExecutor;
         }
 
         @Override
         public void submit(Runnable runnable) {
             smartExecutor.submit(runnable);
         }
 
         @Override
         public <T> Future<T> submit(Callable<T> callable) {
             return smartExecutor.submit(callable);
         }
 
         @Override
         public void close() {
             // nope; delegate is managed
         }
     }
 }