package cz.cuni.amis.utils.flag;
   
   import java.util.ArrayList;
   import java.util.Collection;
   import java.util.List;
   import java.util.concurrent.CountDownLatch;
   import java.util.concurrent.TimeUnit;
   
   import cz.cuni.amis.utils.collections.MyCollections;
  import cz.cuni.amis.utils.exception.PogamutInterruptedException;
  
  /**
   * This class is implementing the waiting on some flag value.
   * <BR><BR>
   * Note that you may call only one AWAIT() at time.
   * <BR><BR>
   * Typical usage:
   * <BR>
   * boolean flagValue = new WaitForFlagChange&lt;Boolean&gt;(booleanFlag, Boolean.TRUE).await();
   * <BR>
   * int flagValue = new WaitForFlagChange&lt;Integer&gt;(integerFlag, new Integer[]{1,3}).await();
   * 
   * @author Jimmy
   *
   * @param <TYPE>
   */
  public class WaitForFlagChange<TYPE> {
  	
  	public static interface IAccept<TYPE> {
  		
  		public boolean accept(TYPE flagValue);
  		
  	}
  	
  	private class ListAccept implements IAccept<TYPE> {
  		
  		private List<TYPE> waitingFor;
  		
  		public ListAccept(Collection<TYPE> list) {
  			waitingFor = new ArrayList<TYPE>(list.size());
  			waitingFor.addAll(list);
  		}
  		
  		/**
  		 * Accepts all.
  		 */
  		public ListAccept() {
  			this.waitingFor = null;
  		}
  		
  		public ListAccept(TYPE... accept) {
  			waitingFor = new ArrayList(accept.length);
  			waitingFor.addAll(MyCollections.asList(accept));
  		}
  
  		@Override
  		public boolean accept(TYPE flagValue) {
  			if (waitingFor == null) return true;
  			return waitingFor.contains(flagValue);
  		}
  		
  	}
  	
  	private IAccept<TYPE> accept;
  	private IFlag<TYPE> flag;
  	
  	private Object latchAccessMutex = new Object();
  	private Object mutex = new Object();
  	
  	private CountDownLatch latch = null;
  	
  	private boolean isResult = false;
  	private TYPE result = null;
  	
  	private class Listener implements FlagListener<TYPE> {
  		
  		public Listener(IFlag<TYPE> flag) {
  			WaitForFlagChange.this.result = flag.getFlag();			
  			if (!(isResult = isDesiredValue(WaitForFlagChange.this.result))) {
  				flag.addListener(this);
  			}
  			// must do second check because of the flag that has been just attached
  			if (!isResult) {
  				TYPE result = flag.getFlag();
  				if (isDesiredValue(result)) { 
  					isResult = true;
  					WaitForFlagChange.this.result = result;
  					flag.removeListener(this);
  					synchronized(latchAccessMutex) {
  						if (latch != null) {
  							latch.countDown();
  						}
  					}	
  				}
  			}
  		}
  
  		@Override
  		public void flagChanged(TYPE changedValue) {
 			if (!isResult && isDesiredValue(changedValue)) {
 				flag.removeListener(this);
 				synchronized(latchAccessMutex) {
 					isResult = true;
 					result = changedValue;
 					if (latch != null) {
 						latch.countDown();
 					}
 				}				
 			}
 		}
 		
 	}
 	
 	/**
 	 * Wait for the next flag change.
 	 * @param flag
 	 */
 	public WaitForFlagChange(IFlag<TYPE> flag) {
 		this.flag = flag;
 		this.accept = new ListAccept();
 	}
 	
 	public WaitForFlagChange(IFlag<TYPE> flag, IAccept<TYPE> waitingFor) {
 		this.flag = flag;
 		this.accept = waitingFor;
 	}
 	
 	public WaitForFlagChange(IFlag<TYPE> flag, TYPE waitingFor) {
 		this.flag = flag;
 		this.accept = new ListAccept(waitingFor);
 	}
 	
 	public WaitForFlagChange(IFlag<TYPE> flag, TYPE[] waitingFor) {
 		this.flag = flag;
 		this.accept = new ListAccept(waitingFor);		
 	}
 	
 	public WaitForFlagChange(IFlag<TYPE> flag, Collection<TYPE> waitingFor) {
 		this.flag = flag;
 		this.accept = new ListAccept(waitingFor);		
 	}
 		
 	private boolean isDesiredValue(TYPE value) {
 		return accept.accept(value);
 	}
 	
 	/**
 	 * Note that you may call only await() from one thread! If the instance is already in used
 	 * it may produce unwanted behavior (e.g. dead-lock).
 	 * 
 	 * @return value from the flag that raised the latch
 	 * @throws InterruptedException
 	 */
 	public TYPE await() throws PogamutInterruptedException {
 		synchronized(mutex) {
 			synchronized(latchAccessMutex) {
 				latch = new CountDownLatch(1);
 			}
 			// instantiation checks whether we doesn't have desired result already, 
 			// if not adds itself as a listener to a flag
 			Listener listener = new Listener(flag); 
 			if (isResult) return result;			
 			try {
 				latch.await(); // the latch is raised whenever a listener receive a correct result
 			} catch (InterruptedException e) {
 				throw new PogamutInterruptedException(e, this);
 			}
 			synchronized(latchAccessMutex) {
 				flag.removeListener(listener);
 				latch = null;
 			}
 			return result;
 		}
 	}
 	
 	/**
 	 * Note that you may call only await() from one thread! If the instance is already in used
 	 * it may produce unwanted behavior.
 	 * <p><p>
 	 * Returns null if desired value hasn't been set at the flag before timeout.
 	 * 
 	 * @param timeout
 	 * @param timeUnit
 	 * @return value of the flag
 	 * @throws PogamutInterruptedException
 	 */
 	public TYPE await(long timeout, TimeUnit timeUnit) throws PogamutInterruptedException {
 		synchronized(mutex) {
 			synchronized(latchAccessMutex) {
 				latch = new CountDownLatch(1);
 			}
 			// instantiation checks whether we doesn't have desired result already, 
 			// if not adds itself as a listener to a flag
 			Listener listener = new Listener(flag); 
 			if (isResult) return result;			
 			try {
 				latch.await(timeout, timeUnit); // the latch is raised whenever a listener receive a correct result
 			} catch (InterruptedException e) {
 				throw new PogamutInterruptedException(e, this);
 			}
 			synchronized(latchAccessMutex) {
 				flag.removeListener(listener);
 				latch = null;
 			}
 			return result;
 		}
 	}
 
 }