/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.hc.core5.reactor;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.nio.channels.ClosedSelectorException;
  import java.nio.channels.SelectionKey;
  import java.nio.channels.Selector;
  import java.util.Set;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.apache.hc.core5.function.Callback;
  import org.apache.hc.core5.io.CloseMode;
  import org.apache.hc.core5.io.Closer;
  import org.apache.hc.core5.util.Args;
  import org.apache.hc.core5.util.TimeValue;
  import org.apache.hc.core5.util.Timeout;
  
  abstract class AbstractSingleCoreIOReactor implements IOReactor {
  
      private final Callback<Exception> exceptionCallback;
      private final AtomicReference<IOReactorStatus> status;
      private final AtomicBoolean terminated;
      private final Object shutdownMutex;
  
      final Selector selector;
  
      AbstractSingleCoreIOReactor(final Callback<Exception> exceptionCallback) {
          super();
          this.exceptionCallback = exceptionCallback;
          this.shutdownMutex = new Object();
          this.status = new AtomicReference<>(IOReactorStatus.INACTIVE);
          this.terminated = new AtomicBoolean();
          try {
              this.selector = Selector.open();
          } catch (final IOException ex) {
              throw new IllegalStateException("Unexpected failure opening I/O selector", ex);
          }
      }
  
      @Override
      public final IOReactorStatus getStatus() {
          return this.status.get();
      }
  
      void logException(final Exception ex) {
          if (exceptionCallback != null) {
              exceptionCallback.execute(ex);
          }
      }
  
      abstract void doExecute() throws IOException;
  
      abstract void doTerminate() throws IOException;
  
      public void execute() {
          if (this.status.compareAndSet(IOReactorStatus.INACTIVE, IOReactorStatus.ACTIVE)) {
              try {
                  doExecute();
              } catch (final ClosedSelectorException ignore) {
                  // ignore
              } catch (final Exception ex) {
                  logException(ex);
              } finally {
                  try {
                      doTerminate();
                  } catch (final Exception ex) {
                      logException(ex);
                  } finally {
                      close(CloseMode.IMMEDIATE);
                  }
              }
         }
     }
 
     @Override
     public final void awaitShutdown(final TimeValue waitTime) throws InterruptedException {
         Args.notNull(waitTime, "Wait time");
         final long deadline = System.currentTimeMillis() + waitTime.toMilliseconds();
         long remaining = waitTime.toMilliseconds();
         synchronized (this.shutdownMutex) {
             while (this.status.get().compareTo(IOReactorStatus.SHUT_DOWN) < 0) {
                 this.shutdownMutex.wait(remaining);
                 remaining = deadline - System.currentTimeMillis();
                 if (remaining <= 0) {
                     return;
                 }
             }
         }
     }
 
     @Override
     public final void initiateShutdown() {
         if (this.status.compareAndSet(IOReactorStatus.INACTIVE, IOReactorStatus.SHUT_DOWN)) {
             synchronized (this.shutdownMutex) {
                 this.shutdownMutex.notifyAll();
             }
         } else if (this.status.compareAndSet(IOReactorStatus.ACTIVE, IOReactorStatus.SHUTTING_DOWN)) {
             this.selector.wakeup();
         }
     }
 
     @Override
     public final void close(final CloseMode closeMode) {
         close(closeMode, Timeout.ofSeconds(5));
     }
 
     /**
      * Shuts down the I/O reactor either gracefully or immediately.
      * During graceful shutdown individual I/O sessions should be
      * informed about imminent termination and be given a grace period
      * to complete the ongoing I/O sessions. During immediate shutdown
      * all ongoing I/O sessions get aborted immediately.
      *
      * @param closeMode How to close the IO reactor.
      * @param timeout  How long to wait for the IO reactor to close gracefully.
      * @since 5.2
      */
     public void close(final CloseMode closeMode, final Timeout timeout) {
         if (closeMode == CloseMode.GRACEFUL) {
             initiateShutdown();
             try {
                 awaitShutdown(timeout);
             } catch (final InterruptedException e) {
                 Thread.currentThread().interrupt();
             }
         }
         this.status.set(IOReactorStatus.SHUT_DOWN);
         if (terminated.compareAndSet(false, true)) {
             try {
                 final Set<SelectionKey> keys = this.selector.keys();
                 for (final SelectionKey key : keys) {
                     try {
                         Closer.close((Closeable) key.attachment());
                     } catch (final IOException ex) {
                         logException(ex);
                     }
                     key.channel().close();
                 }
                 selector.close();
             } catch (final Exception ex) {
                 logException(ex);
             }
         }
         synchronized (this.shutdownMutex) {
             this.shutdownMutex.notifyAll();
         }
     }
 
     @Override
     public final void close() {
         close(CloseMode.GRACEFUL);
     }
 
     @Override
     public String toString() {
         return super.toString() + " [status=" + status + "]";
     }
 
 }