// This Source Code is in the Public Domain per: http://litesoft.org/License.txt
package org.litesoft.orsup.nonpublic;

import java.util.*;

import org.litesoft.orsup.base.*;

public abstract class AbstractPOQueryIterator<T extends PersistentObject> extends POQueryIterator<T>
{
    protected final MetaDataForPOinternalExtension mMetaDataForPO;
    protected final Finder mFinder;
    private final POInstanceQueryFilter mPOInstanceQueryFilter;
    private T mPreFetchedPO = null;
    private boolean mPOsourcePrepared = false;

    protected AbstractPOQueryIterator( MetaDataForPOinternalExtension pMetaDataForPO, Finder pFinder, POInstanceQueryFilter pPOInstanceQueryFilter )
    {
        mMetaDataForPO = pMetaDataForPO;
        mFinder = pFinder;
        mPOInstanceQueryFilter = (pPOInstanceQueryFilter != null) ? //
                                 pPOInstanceQueryFilter : //
                                 POInstanceQueryFilter.ALL_ACCEPTABLE;
    }

    @Override
    public void releaseResources()
    {
        mPreFetchedPO = null;
        releasePOsource();
        super.releaseResources();
    }

    @Override
    public final boolean hasNext()
    {
        return (mPreFetchedPO != null);
    }

    @Override
    public final T next()
    {
        if ( !hasNext() )
        {
            throw new NoSuchElementException();
        }
        try
        {
            T rv = mPreFetchedPO;
            preFetchPO();
            return rv;
        }
        catch ( RuntimeException e )
        {
            releaseResources();
            throw e;
        }
    }

    protected final void preFetchPO()
    {
        mPreFetchedPO = getNextPO();
    }

    private T getNextPO()
    {
        if ( !mPOsourcePrepared )
        {
            mPOsourcePrepared = true;
            preparePOsource();
        }
        for ( T zPO; null != (zPO = LLfetchPO()); )
        {
            if ( mPOInstanceQueryFilter.isPO_Acceptable( zPO ) )
            {
                return zPO;
            }
            POQueryFilter.LOGGER.trace.log( getMD(), " PO '", zPO, "' filtered out by ", mPOInstanceQueryFilter.getClass() );
        }
        releasePOsource();
        return null;
    }

    protected void preparePOsource()
    {
    }

    abstract protected T LLfetchPO();

    protected void releasePOsource()
    {
    }

    protected String getMD()
    {
        return (mMetaDataForPO != null) ? mMetaDataForPO.getPOregistrationName() : null;
    }
}