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//$Id: Interceptor.java 7883 2005-08-12 20:03:07Z oneovthafew $
package org.hibernate;

import java.io.Serializable;
import java.util.Iterator;

import org.hibernate.type.Type;

/**
 * Allows user code to inspect and/or change property values.
 * 


 * Inspection occurs before property values are written and after they are read
 * from the database.

 * 

 * There might be a single instance of Interceptor for a SessionFactory, or a new instance
 * might be specified for each Session. Whichever approach is used, the interceptor must be
 * serializable if the Session is to be serializable. This means that SessionFactory-scoped
 * interceptors should implement readResolve().

 * 

 * The Session may not be invoked from a callback (nor may a callback cause a collection or proxy to
 * be lazily initialized).

 * 

 * Instead of implementing this interface directly, it is usually better to extend EmptyInterceptor
 * and override only the callback methods of interest.
 *
 * @see SessionFactory#openSession(Interceptor)
 * @see org.hibernate.cfg.Configuration#setInterceptor(Interceptor)
 * @see EmptyInterceptor
 * @author Gavin King
 */
public interface Interceptor {
	/**
	 * Called just before an object is initialized. The interceptor may change the state, which will
	 * be propagated to the persistent object. Note that when this method is called, entity will be
	 * an empty uninitialized instance of the class.
	 *
	 * @return true if the user modified the state in any way.
	 */
	public boolean onLoad(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) throws CallbackException;
	/**
	 * Called when an object is detected to be dirty, during a flush. The interceptor may modify the detected
	 * currentState, which will be propagated to both the database and the persistent object.
	 * Note that not all flushes end in actual synchronization with the database, in which case the
	 * new currentState will be propagated to the object, but not necessarily (immediately) to
	 * the database. It is strongly recommended that the interceptor not modify the previousState.
	 *
	 * @return true if the user modified the currentState in any way.
	 */
	public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) throws CallbackException;
	/**
	 * Called before an object is saved. The interceptor may modify the state, which will be used for
	 * the SQL INSERT and propagated to the persistent object.
	 *
	 * @return true if the user modified the state in any way.
	 */
	public boolean onSave(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) throws CallbackException;
	/**
	 *  Called before an object is deleted. It is not recommended that the interceptor modify the state.
	 */
	public void onDelete(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) throws CallbackException;
	/**
	 * Called before a collection is (re)created.
	 */
	public void onCollectionRecreate(Object collection, Serializable key) throws CallbackException;
	/**
	 * Called before a collection is deleted.
	 */
	public void onCollectionRemove(Object collection, Serializable key) throws CallbackException;
	/**
	 * Called before a collection is updated.
	 */
	public void onCollectionUpdate(Object collection, Serializable key) throws CallbackException;
	/**
	 * Called before a flush
	 */
	public void preFlush(Iterator entities) throws CallbackException;
	/**
	 * Called after a flush that actually ends in execution of the SQL statements required to synchronize
	 * in-memory state with the database.
	 */
	public void postFlush(Iterator entities) throws CallbackException;
	/**
	 * Called to distinguish between transient and detached entities. The return value determines the
	 * state of the entity with respect to the current session.
	 * 
	 * Boolean.TRUE - the entity is transient
	 * 
Boolean.FALSE - the entity is detached
	 * 
null - Hibernate uses the unsaved-value mapping and other heuristics to 
	 * determine if the object is unsaved
	 * 
	 * @param entity a transient or detached entity
	 * @return Boolean or null to choose default behaviour
	 */
	public Boolean isTransient(Object entity);
	/**
	 * Called from flush(). The return value determines whether the entity is updated
	 * 
	 * an array of property indices - the entity is dirty
	 * 
an empty array - the entity is not dirty
	 * 
null - use Hibernate's default dirty-checking algorithm
	 * 
	 * @param entity a persistent entity
	 * @return array of dirty property indices or null to choose default behaviour
	 */
	public int[] findDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types);
	/**
	 * Instantiate the entity class. Return null to indicate that Hibernate should use
	 * the default constructor of the class. The identifier property of the returned instance
	 * should be initialized with the given identifier.
	 *
	 * @param entityName the name of the entity
	 * @param entityMode The type of entity instance to be returned.
	 * @param id the identifier of the new instance
	 * @return an instance of the class, or null to choose default behaviour
	 */
	public Object instantiate(String entityName, EntityMode entityMode, Serializable id) throws CallbackException;

	/**
	 * Get the entity name for a persistent or transient instance
	 * @param object an entity instance
	 * @return the name of the entity
	 */
	public String getEntityName(Object object) throws CallbackException;

	/**
	 * Get a fully loaded entity instance that is cached externally
	 * @param entityName the name of the entity
	 * @param id the instance identifier
	 * @return a fully initialized entity
	 * @throws CallbackException
	 */
	public Object getEntity(String entityName, Serializable id) throws CallbackException;
	
	/**
	 * Called when a Hibernate transaction is begun via the Hibernate Transaction 
	 * API. Will not be called if transactions are being controlled via some other 
	 * mechanism (CMT, for example).
	 */
	public void afterTransactionBegin(Transaction tx);
	/**
	 * Called before a transaction is committed (but not before rollback).
	 */
	public void beforeTransactionCompletion(Transaction tx);
	/**
	 * Called after a transaction is committed or rolled back.
	 */
	public void afterTransactionCompletion(Transaction tx);

	/**
	 * Called when sql string is being prepared. 
	 * @param sql sql to be prepared
	 * @return original or modified sql
	 */
	public String onPrepareStatement(String sql);
}