/*
    * 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.apache.maven.surefire.booter;
  
  import java.util.Collections;
  import java.util.Iterator;
  
  import org.apache.maven.surefire.api.booter.MasterProcessChannelEncoder;
  import org.apache.maven.surefire.api.provider.SurefireProvider;
  import org.apache.maven.surefire.api.util.CloseableIterator;
  import org.apache.maven.surefire.api.util.TestsToRun;
  
  import static org.apache.maven.surefire.api.util.ReflectionUtils.loadClass;
  
  /**
   * A variant of TestsToRun that is provided with test class names
   * from an {@code System.in}.
   * The method {@link #iterator()} returns an Iterator that blocks on calls to
   * {@link Iterator#hasNext()} or {@link Iterator#next()} until new classes are available, or no more
   * classes will be available or the internal stream is closed.
   * The iterator can be used only in one Thread and it is the thread which executes
   * {@link SurefireProvider provider implementation}.
   *
   * @author Andreas Gudian
   * @author Tibor Digana
   */
  final class LazyTestsToRun extends TestsToRun {
      private final MasterProcessChannelEncoder eventChannel;
      private final CommandReader commandReader;
  
      /**
       * C'tor.
       *
       * @param eventChannel the output stream to use when requesting new new tests
       */
      LazyTestsToRun(MasterProcessChannelEncoder eventChannel, CommandReader commandReader) {
          super(Collections.<Class<?>>emptySet());
          this.eventChannel = eventChannel;
          this.commandReader = commandReader;
      }
  
      private final class BlockingIterator implements Iterator<Class<?>> {
          private final Iterator<String> it =
                  commandReader.getIterableClasses(eventChannel).iterator();
  
          @Override
          public boolean hasNext() {
              return it.hasNext();
          }
  
          @Override
          public Class<?> next() {
              return findClass(it.next());
          }
  
          @Override
          public void remove() {
              throw new UnsupportedOperationException();
          }
      }
  
      /**
       * @return test classes which have been retrieved by {@link LazyTestsToRun#iterator()}
       */
      @Override
      public Iterator<Class<?>> iterated() {
          return newWeakIterator();
      }
  
      /**
       * The iterator can be used only in one Thread.
       * {@inheritDoc}
       *
       * @see TestsToRun#iterator()
       */
      @Override
      public Iterator<Class<?>> iterator() {
          return new BlockingIterator();
      }
  
      /* (non-Javadoc)
       * {@inheritDoc}
       * @see org.apache.maven.surefire.util.TestsToRun#toString()
      */
     @Override
     public String toString() {
         return "LazyTestsToRun";
     }
 
     /* (non-Javadoc)
      * {@inheritDoc}
      * @see org.apache.maven.surefire.util.TestsToRun#allowEagerReading()
      */
     @Override
     public boolean allowEagerReading() {
         return false;
     }
 
     private static Class<?> findClass(String clazz) {
         return loadClass(Thread.currentThread().getContextClassLoader(), clazz);
     }
 
     /**
      * @return snapshot of tests upon constructs of {@link CommandReader#iterated() iterator}.
      * Therefore weakly consistent while {@link LazyTestsToRun#iterator()} is being iterated.
      */
     private Iterator<Class<?>> newWeakIterator() {
         final Iterator<String> it = commandReader.iterated();
         return new CloseableIterator<Class<?>>() {
             @Override
             protected boolean isClosed() {
                 return LazyTestsToRun.this.isFinished();
             }
 
             @Override
             protected boolean doHasNext() {
                 return it.hasNext();
             }
 
             @Override
             protected Class<?> doNext() {
                 return findClass(it.next());
             }
 
             @Override
             protected void doRemove() {}
 
             @Override
             public void remove() {
                 throw new UnsupportedOperationException("unsupported remove");
             }
         };
     }
 }