package org.hibernate.engine.loading;

import java.sql.ResultSet;
import java.io.Serializable;
import java.util.List;
import java.util.Iterator;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.Set;
import java.util.HashSet;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.hibernate.collection.PersistentCollection;
import org.hibernate.persister.collection.CollectionPersister;
import org.hibernate.EntityMode;
import org.hibernate.CacheMode;
import org.hibernate.cache.entry.CollectionCacheEntry;
import org.hibernate.cache.CacheKey;
import org.hibernate.pretty.MessageHelper;
import org.hibernate.engine.CollectionKey;
import org.hibernate.engine.Status;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.engine.CollectionEntry;
import org.hibernate.engine.SessionFactoryImplementor;

/**
 * Represents state associated with the processing of a given {@link ResultSet}
 * in regards to loading collections.
 * <p/>
 * Another implementation option to consider is to not expose {@link ResultSet}s
 * directly (in the JDBC redesign) but to always "wrap" them and apply a
 * [series of] context[s] to that wrapper.
 *
 * @author Steve Ebersole
 */
public class CollectionLoadContext {
	private static final Log log = LogFactory.getLog( CollectionLoadContext.class );

	private final LoadContexts loadContexts;
	private final ResultSet resultSet;
	private Set localLoadingCollectionKeys = new HashSet();

	/**
	 * Creates a collection load context for the given result set.
	 *
	 * @param loadContexts Callback to other collection load contexts.
	 * @param resultSet The result set this is "wrapping".
	 */
	public CollectionLoadContext(LoadContexts loadContexts, ResultSet resultSet) {
		this.loadContexts = loadContexts;
		this.resultSet = resultSet;
	}

	public ResultSet getResultSet() {
		return resultSet;
	}

	public LoadContexts getLoadContext() {
		return loadContexts;
	}

	/**
	 * Retrieve the collection that is being loaded as part of processing this
	 * result set.
	 * <p/>
	 * Basically, there are two valid return values from this method:<ul>
	 * <li>an instance of {@link PersistentCollection} which indicates to
	 * continue loading the result set row data into that returned collection
	 * instance; this may be either an instance already associated and in the
	 * midst of being loaded, or a newly instantiated instance as a matching
	 * associated collection was not found.</li>
	 * <li><i>null</i> indicates to ignore the corresponding result set row
	 * data relating to the requested collection; this indicates that either
	 * the collection was found to already be associated with the persistence
	 * context in a fully loaded state, or it was found in a loading state
	 * associated with another result set processing context.</li>
	 * </ul>
	 *
	 * @param persister The persister for the collection being requested.
	 * @param key The key of the collection being requested.
	 *
	 * @return The loading collection (see discussion above).
	 */
	public PersistentCollection getLoadingCollection(final CollectionPersister persister, final Serializable key) {
		final EntityMode em = loadContexts.getPersistenceContext().getSession().getEntityMode();
		final CollectionKey collectionKey = new CollectionKey( persister, key, em );
		if ( log.isTraceEnabled() ) {
			log.trace( "starting attempt to find loading collection [" + MessageHelper.collectionInfoString( persister.getRole(), key ) + "]" );
		}
		final LoadingCollectionEntry loadingCollectionEntry = loadContexts.locateLoadingCollectionEntry( collectionKey );
		if ( loadingCollectionEntry == null ) {
			// look for existing collection as part of the persistence context
			PersistentCollection collection = loadContexts.getPersistenceContext().getCollection( collectionKey );
			if ( collection != null ) {
				if ( collection.wasInitialized() ) {
					log.trace( "collection already initialized; ignoring" );
					return null; // ignore this row of results! Note the early exit
				}
				else {
					// initialize this collection
					log.trace( "collection not yet initialized; initializing" );
				}
			}
			else {
				Object owner = loadContexts.getPersistenceContext().getCollectionOwner( key, persister );
				final boolean newlySavedEntity = owner != null
						&& loadContexts.getPersistenceContext().getEntry( owner ).getStatus() != Status.LOADING
						&& em != EntityMode.DOM4J;
				if ( newlySavedEntity ) {
					// important, to account for newly saved entities in query
					// todo : some kind of check for new status...
					log.trace( "owning entity already loaded; ignoring" );
					return null;
				}
				else {
					// create one
					if ( log.isTraceEnabled() ) {
						log.trace( "instantiating new collection [key=" + key + ", rs=" + resultSet + "]" );
					}
					collection = persister.getCollectionType()
							.instantiate( loadContexts.getPersistenceContext().getSession(), persister, key );
				}
			}
			collection.beforeInitialize( persister, -1 );
			collection.beginRead();
			localLoadingCollectionKeys.add( collectionKey );
			loadContexts.registerLoadingCollectionXRef( collectionKey, new LoadingCollectionEntry( resultSet, persister, key, collection ) );
			return collection;
		}
		else {
			if ( loadingCollectionEntry.getResultSet() == resultSet ) {
				log.trace( "found loading collection bound to current result set processing; reading row" );
				return loadingCollectionEntry.getCollection();
			}
			else {
				// ignore this row, the collection is in process of
				// being loaded somewhere further "up" the stack
				log.trace( "collection is already being initialized; ignoring row" );
				return null;
			}
		}
	}

	/**
	 * Finish the process of collection-loading for this bound result set.  Mainly this
	 * involves cleaning up resources and notifying the collections that loading is
	 * complete.
	 *
	 * @param persister The persister for which to complete loading.
	 */
	public void endLoadingCollections(CollectionPersister persister) {
		SessionImplementor session = getLoadContext().getPersistenceContext().getSession();
		if ( !loadContexts.hasLoadingCollectionEntries()
				|| localLoadingCollectionKeys.isEmpty() ) {
			return;
		}

		// in an effort to avoid concurrent-modification-exceptions (from
		// potential recursive calls back through here as a result of the
		// eventual call to PersistentCollection#endRead), we scan the
		// internal loadingCollections map for matches and store those matches
		// in a temp collection.  the temp collection is then used to "drive"
		// the #endRead processing.
		List matches = null;
		Iterator iter = localLoadingCollectionKeys.iterator();
		while ( iter.hasNext() ) {
			final CollectionKey collectionKey = (CollectionKey) iter.next();
			final LoadingCollectionEntry lce = loadContexts.locateLoadingCollectionEntry( collectionKey );
			if ( lce == null) {
				log.warn( "In CollectionLoadContext#endLoadingCollections, localLoadingCollectionKeys contained [" + collectionKey + "], but no LoadingCollectionEntry was found in loadContexts" );
			}
			else if ( lce.getResultSet() == resultSet && lce.getPersister() == persister ) {
				if ( matches == null ) {
					matches = new ArrayList();
				}
				matches.add( lce );
				if ( lce.getCollection().getOwner() == null ) {
					session.getPersistenceContext().addUnownedCollection(
							new CollectionKey( persister, lce.getKey(), session.getEntityMode() ),
							lce.getCollection()
					);
				}
				if ( log.isTraceEnabled() ) {
					log.trace( "removing collection load entry [" + lce + "]" );
				}

				// todo : i'd much rather have this done from #endLoadingCollection(CollectionPersister,LoadingCollectionEntry)...
				loadContexts.unregisterLoadingCollectionXRef( collectionKey );
				iter.remove();
			}
		}

		endLoadingCollections( persister, matches );
		if ( localLoadingCollectionKeys.isEmpty() ) {
			// todo : hack!!!
			// NOTE : here we cleanup the load context when we have no more local
			// LCE entries.  This "works" for the time being because really
			// only the collection load contexts are implemented.  Long term,
			// this cleanup should become part of the "close result set"
			// processing from the (sandbox/jdbc) jdbc-container code.
			loadContexts.cleanup( resultSet );
		}
	}

	private void endLoadingCollections(CollectionPersister persister, List matchedCollectionEntries) {
		if ( matchedCollectionEntries == null ) {
			if ( log.isDebugEnabled() ) {
				log.debug( "no collections were found in result set for role: " + persister.getRole() );
			}
			return;
		}

		final int count = matchedCollectionEntries.size();
		if ( log.isDebugEnabled() ) {
			log.debug( count + " collections were found in result set for role: " + persister.getRole() );
		}

		for ( int i = 0; i < count; i++ ) {
			LoadingCollectionEntry lce = ( LoadingCollectionEntry ) matchedCollectionEntries.get( i );
			endLoadingCollection( lce, persister );
		}

		if ( log.isDebugEnabled() ) {
			log.debug( count + " collections initialized for role: " + persister.getRole() );
		}
	}

	private void endLoadingCollection(LoadingCollectionEntry lce, CollectionPersister persister) {
		if ( log.isTraceEnabled() ) {
			log.debug( "ending loading collection [" + lce + "]" );
		}
		final SessionImplementor session = getLoadContext().getPersistenceContext().getSession();
		final EntityMode em = session.getEntityMode();

		boolean hasNoQueuedAdds = lce.getCollection().endRead(); // warning: can cause a recursive calls! (proxy initialization)

		if ( persister.getCollectionType().hasHolder( em ) ) {
			getLoadContext().getPersistenceContext().addCollectionHolder( lce.getCollection() );
		}

		CollectionEntry ce = getLoadContext().getPersistenceContext().getCollectionEntry( lce.getCollection() );
		if ( ce == null ) {
			ce = getLoadContext().getPersistenceContext().addInitializedCollection( persister, lce.getCollection(), lce.getKey() );
		}
		else {
			ce.postInitialize( lce.getCollection() );
		}

		boolean addToCache = hasNoQueuedAdds && // there were no queued additions
				persister.hasCache() &&             // and the role has a cache
				session.getCacheMode().isPutEnabled() &&
				!ce.isDoremove();                   // and this is not a forced initialization during flush
		if ( addToCache ) {
			addCollectionToCache( lce, persister );
		}

		if ( log.isDebugEnabled() ) {
			log.debug( "collection fully initialized: " + MessageHelper.collectionInfoString(persister, lce.getKey(), session.getFactory() ) );
		}

		if ( session.getFactory().getStatistics().isStatisticsEnabled() ) {
			session.getFactory().getStatisticsImplementor().loadCollection( persister.getRole() );
		}
	}

	/**
	 * Add the collection to the second-level cache
	 *
	 * @param lce The entry representing the collection to add
	 * @param persister The persister
	 */
	private void addCollectionToCache(LoadingCollectionEntry lce, CollectionPersister persister) {
		final SessionImplementor session = getLoadContext().getPersistenceContext().getSession();
		final SessionFactoryImplementor factory = session.getFactory();

		if ( log.isDebugEnabled() ) {
			log.debug( "Caching collection: " + MessageHelper.collectionInfoString( persister, lce.getKey(), factory ) );
		}

		if ( !session.getEnabledFilters().isEmpty() && persister.isAffectedByEnabledFilters( session ) ) {
			// some filters affecting the collection are enabled on the session, so do not do the put into the cache.
			log.debug( "Refusing to add to cache due to enabled filters" );
			// todo : add the notion of enabled filters to the CacheKey to differentiate filtered collections from non-filtered;
			//      but CacheKey is currently used for both collections and entities; would ideally need to define two seperate ones;
			//      currently this works in conjuction with the check on
			//      DefaultInitializeCollectionEventHandler.initializeCollectionFromCache() (which makes sure to not read from
			//      cache with enabled filters).
			return; // EARLY EXIT!!!!!
		}

		final Comparator versionComparator;
		final Object version;
		if ( persister.isVersioned() ) {
			versionComparator = persister.getOwnerEntityPersister().getVersionType().getComparator();
			final Object collectionOwner = getLoadContext().getPersistenceContext().getCollectionOwner( lce.getKey(), persister );
			version = getLoadContext().getPersistenceContext().getEntry( collectionOwner ).getVersion();
		}
		else {
			version = null;
			versionComparator = null;
		}

		CollectionCacheEntry entry = new CollectionCacheEntry( lce.getCollection(), persister );
		CacheKey cacheKey = new CacheKey(
				lce.getKey(),
				persister.getKeyType(),
				persister.getRole(),
				session.getEntityMode(),
				session.getFactory()
		);
		boolean put = persister.getCache().put(
				cacheKey,
				persister.getCacheEntryStructure().structure(entry),
				session.getTimestamp(),
				version,
				versionComparator,
				factory.getSettings().isMinimalPutsEnabled() && session.getCacheMode()!= CacheMode.REFRESH
		);

		if ( put && factory.getStatistics().isStatisticsEnabled() ) {
			factory.getStatisticsImplementor().secondLevelCachePut( persister.getCache().getRegionName() );
		}
	}

	void cleanup() {
		if ( !localLoadingCollectionKeys.isEmpty() ) {
			log.warn( "On CollectionLoadContext#cleanup, localLoadingCollectionKeys contained [" + localLoadingCollectionKeys.size() + "] entries" );
		}
		loadContexts.cleanupCollectionXRefs( localLoadingCollectionKeys );
		localLoadingCollectionKeys.clear();
	}


	public String toString() {
		return super.toString() + "<rs=" + resultSet + ">";
	}
}