//$Id: Interceptor.java,v 1.8 2005/08/12 20:03:07 oneovthafew Exp $
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.
 * <br><br>
 * Inspection occurs before property values are written and after they are read
 * from the database.<br>
 * <br>
 * There might be a single instance of <tt>Interceptor</tt> for a <tt>SessionFactory</tt>, or a new instance
 * might be specified for each <tt>Session</tt>. Whichever approach is used, the interceptor must be
 * serializable if the <tt>Session</tt> is to be serializable. This means that <tt>SessionFactory</tt>-scoped
 * interceptors should implement <tt>readResolve()</tt>.<br>
 * <br>
 * The <tt>Session</tt> may not be invoked from a callback (nor may a callback cause a collection or proxy to
 * be lazily initialized).<br>
 * <br>
 * Instead of implementing this interface directly, it is usually better to extend <tt>EmptyInterceptor</tt>
 * 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 <tt>state</tt>, which will
	 * be propagated to the persistent object. Note that when this method is called, <tt>entity</tt> will be
	 * an empty uninitialized instance of the class.
	 *
	 * @return <tt>true</tt> if the user modified the <tt>state</tt> 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
	 * <tt>currentState</tt>, 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 <tt>currentState</tt> will be propagated to the object, but not necessarily (immediately) to
	 * the database. It is strongly recommended that the interceptor <b>not</b> modify the <tt>previousState</tt>.
	 *
	 * @return <tt>true</tt> if the user modified the <tt>currentState</tt> 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 <tt>state</tt>, which will be used for
	 * the SQL <tt>INSERT</tt> and propagated to the persistent object.
	 *
	 * @return <tt>true</tt> if the user modified the <tt>state</tt> 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 <tt>state</tt>.
	 */
	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.
	 * <ul>
	 * <li><tt>Boolean.TRUE</tt> - the entity is transient
	 * <li><tt>Boolean.FALSE</tt> - the entity is detached
	 * <li><tt>null</tt> - Hibernate uses the <tt>unsaved-value</tt> mapping and other heuristics to 
	 * determine if the object is unsaved
	 * </ul>
	 * @param entity a transient or detached entity
	 * @return Boolean or <tt>null</tt> to choose default behaviour
	 */
	public Boolean isTransient(Object entity);
	/**
	 * Called from <tt>flush()</tt>. The return value determines whether the entity is updated
	 * <ul>
	 * <li>an array of property indices - the entity is dirty
	 * <li>an empty array - the entity is not dirty
	 * <li><tt>null</tt> - use Hibernate's default dirty-checking algorithm
	 * </ul>
	 * @param entity a persistent entity
	 * @return array of dirty property indices or <tt>null</tt> to choose default behaviour
	 */
	public int[] findDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types);
	/**
	 * Instantiate the entity class. Return <tt>null</tt> 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 <tt>null</tt> 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 <tt>Transaction</tt> 
	 * 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);
}
