package cz.cuni.amis.pogamut.base.utils.guice;
   
   import java.util.HashMap;
   import java.util.Map;
   
   import com.google.inject.Key;
   import com.google.inject.Provider;
   
   /**
   * Scope used during the construction of the agent - treating all new instances (of classes annotated with {@link AgentScoped})
   * as singletons.
   * <p><p>
   * After instantiation of the agent, Pogamut calls clearScope() to release all
   * references to instantiated objects that allows to reuse the injector again
   * to get another instance of the agent.
   * <p><p>
   * We need this, because we're usually have one connection object that must be injected
   * into two different classes thus must be treated "as a singleton for one instantiation
   * of the agent". (This is not the only example...)
   * <p><p>
   * Every pogamut.base class is {@link AgentScoped}.
   * 
   * @author Jimmy
   *
   */
  public class AgentScope implements IAgentScope {
  	
  	public static class SingletonProvider<T> implements Provider<T> {
  		
  		private Provider<T> creator;
  		
  		private T singleton = null;
  		
  		public SingletonProvider(Provider<T> creator) {
  			this.creator = creator;
  		}
  
  		@Override
  		public T get() {
  			if (singleton != null) {
  				return singleton;
  			}
  			singleton = creator.get();
  			return singleton;
  		}
  		
  		public void clear() {
  			singleton = null;
  		}
  		
  	}
  	
  	@SuppressWarnings("unchecked")
  	private Map<Key, Provider> providers = new HashMap<Key, Provider>(); 
  
  	@SuppressWarnings("unchecked")
  	@Override
  	public <T> Provider scope(Key<T> key, Provider<T> creator) {
  		synchronized(providers) {
  			Provider p = providers.get(key);
  			if (p != null) { 
  				return p;
  			}
  			SingletonProvider<T> provider = new SingletonProvider<T>(creator);
  			providers.put(key, provider);
  			return provider;
  		}
  	}
  	
  	@SuppressWarnings("unchecked")
  	public void clearScope() {
  		synchronized(providers) {
  			for (Provider provider : providers.values()) {
  				((SingletonProvider)provider).clear();
  			}
  		}
  	}
  
  }