package net.sf.logdistiller;

/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.text.ParseException;
import java.util.*;

/**
 * Combines logevents fetched from multiple factories. The resulting factory chooses the next logevent according to the
 * order provided.
 */
public class FactoryMultiplexer
    extends LogEvent.Factory
{
    private final Comparator<LogEvent> logeventComparator;

    private final List<Entry> factories = new ArrayList<Entry>();

    private boolean initialized = false;

    private Comparator<Entry> entryComparator;

    public FactoryMultiplexer( LogType.Description description )
    {
        this( description, null );
    }

    public FactoryMultiplexer( LogType.Description description, Comparator<LogEvent> logeventComparator )
    {
        super( description, "multiplexer" );
        this.logeventComparator = logeventComparator;
    }

    public void addFactory( LogEvent.Factory factory )
    {
        if ( initialized )
        {
            throw new IllegalStateException( "cannot add a new LogEvent.Factory after reading first event" );
        }
        if ( description != factory.getDescription() )
        {
            throw new IllegalArgumentException( "cannot add a new LogEvent.Factory with different description" );
        }
        factories.add( new Entry( factory ) );
    }

    protected LogEvent readNextEvent()
        throws IOException, ParseException
    {
        if ( !initialized )
        {
            init();
        }
        if ( factories.size() <= 0 )
        {
            return null;
        }
        Entry entry = factories.get( 0 );
        LogEvent nextEvent = entry.getEvent();
        if ( entry.nextEvent() == null )
        {
            factories.remove( 0 );
        }
        else
        {
            sort();
        }
        return nextEvent;
    }

    /**
     * Initialize the multiplexer: fetch first event in each factory, remove empty factories, init entry comparator and
     * sort the factories.
     *
     * @throws IOException
     * @throws ParseException
     */
    private void init()
        throws IOException, ParseException
    {
        initialized = true;
        LogEvent oneEvent = null;
        // fetch the first LogEvent
        List<Entry> emptyFactories = new ArrayList<Entry>();
        for ( Entry entry : factories )
        {
            LogEvent event = entry.nextEvent();
            if ( event == null )
            {
                emptyFactories.add( entry );
            }
            else
            {
                oneEvent = event;
            }
        }
        // remove empty factories
        factories.removeAll( emptyFactories );
        if ( factories.size() >= 0 )
        {
            // init entry comparator
            if ( logeventComparator != null )
            {
                entryComparator = new EntrySpecificComparator( logeventComparator );
            }
            else if ( oneEvent instanceof Comparable<?> )
            {
                entryComparator = new EntryNaturalComparator();
            }
            // sort the factories
            sort();
        }
    }

    /**
     * Sort the factories, if necessary (a logevent comparator has been provided, or logevent implements Comparable).
     */
    private void sort()
    {
        if ( entryComparator != null )
        {
            Collections.sort( factories, entryComparator );
        }
    }

    private static class Entry
    {
        protected LogEvent nextEvent;

        private final LogEvent.Factory factory;

        public Entry( LogEvent.Factory factory )
        {
            this.factory = factory;
        }

        public LogEvent getEvent()
        {
            return nextEvent;
        }

        public LogEvent nextEvent()
            throws IOException, ParseException
        {
            nextEvent = factory.nextEvent();
            return nextEvent;
        }
    }

    /**
     * Comparator for entries with logevents that implement Comparable.
     */
    private static class EntryNaturalComparator
        implements Comparator<Entry>
    {
        public int compare( Entry entry1, Entry entry2 )
        {
            return ( (Comparable) entry1.getEvent() ).compareTo( entry2.getEvent() );
        }
    }

    /**
     * Comparator for entries when a specific logevent Comparator is provided.
     */
    private static class EntrySpecificComparator
        implements Comparator<Entry>
    {
        private final Comparator<LogEvent> eventComparator;

        public EntrySpecificComparator( Comparator<LogEvent> eventComparator )
        {
            this.eventComparator = eventComparator;
        }

        public int compare( Entry entry1, Entry entry2 )
        {
            return eventComparator.compare( entry1.getEvent(), entry2.getEvent() );
        }
    }
}