/*
    * ====================================================================
    * 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.util.concurrent.atomic.AtomicInteger;
  
  final class IOWorkers {
  
      interface Selector {
  
          SingleCoreIOReactor next();
  
      }
  
      static Selector newSelector(final SingleCoreIOReactor[] dispatchers) {
          return isPowerOfTwo(dispatchers.length)
                          ? new PowerOfTwoSelector(dispatchers)
                          : new GenericSelector(dispatchers);
      }
  
      private static boolean isPowerOfTwo(final int val) {
          return (val & -val) == val;
      }
  
      private static void validate(final SingleCoreIOReactor dispatcher) {
          if (dispatcher.getStatus() == IOReactorStatus.SHUT_DOWN) {
              throw new IOReactorShutdownException("I/O reactor has been shut down");
          }
      }
  
      private static final class PowerOfTwoSelector implements Selector {
  
          private final AtomicInteger idx = new AtomicInteger(0);
          private final SingleCoreIOReactor[] dispatchers;
  
          PowerOfTwoSelector(final SingleCoreIOReactor[] dispatchers) {
              this.dispatchers = dispatchers;
          }
  
          @Override
          public SingleCoreIOReactor next() {
              final SingleCoreIOReactor dispatcher = dispatchers[idx.getAndIncrement() & (dispatchers.length - 1)];
              validate(dispatcher);
              return dispatcher;
          }
      }
  
      private static final class GenericSelector implements Selector {
  
          private final AtomicInteger idx = new AtomicInteger(0);
          private final SingleCoreIOReactor[] dispatchers;
  
          GenericSelector(final SingleCoreIOReactor[] dispatchers) {
              this.dispatchers = dispatchers;
          }
  
          @Override
          public SingleCoreIOReactor next() {
              final SingleCoreIOReactor dispatcher = dispatchers[(idx.getAndIncrement() & Integer.MAX_VALUE) % dispatchers.length];
              validate(dispatcher);
              return dispatcher;
          }
      }
  
  }