/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

package org.apache.jena.tdb.base.recordbuffer;

import static org.apache.jena.atlas.lib.Alg.decodeIndex ;

import java.util.Iterator;
import java.util.NoSuchElementException;

import org.apache.jena.atlas.lib.Closeable ;
import org.apache.jena.tdb.base.StorageException ;
import org.apache.jena.tdb.base.block.BlockException ;
import org.apache.jena.tdb.base.record.Record ;

final public
class RecordRangeIterator implements Iterator<Record>, Closeable
{
    /** Iterate over a range of fromRec (inclusive) to toRec (exclusive) */
    public static Iterator<Record> iterator(int pageId, Record fromRec, Record toRec, RecordBufferPageMgr pageMgr)
    {
        if ( ! pageMgr.valid(pageId) ) {
            String msg = "RecordRangeIterator.iterator -- No such block (pageId="+pageId+", fromRec="+fromRec+", toRec="+toRec+ ")" ;
            System.err.println(msg) ;
            System.exit(0) ;
            throw new BlockException(msg) ;
        }
        return new RecordRangeIterator(pageId, fromRec, toRec, pageMgr) ;
    }
    
    private RecordBufferPage currentPage ;      // Set null when finished.
    private int currentIdx ;
    private Record slot = null ;
    
    private final RecordBufferPageMgr pageMgr ;
    private final Record maxRec ;
    private final Record minRec ;
    
    private long countRecords = 0 ;
    private long countBlocks = 0 ;

    private RecordRangeIterator(int id, Record fromRec, Record toRec, RecordBufferPageMgr pageMgr)
    {
        currentIdx = 0 ;
        this.pageMgr = pageMgr;
        this.minRec = fromRec ;
        this.maxRec = toRec ;
        
        if ( toRec != null && fromRec != null && Record.keyLE(toRec, fromRec) )
        {
            currentPage = null ;
            return ;
        }

        pageMgr.getBlockMgr().beginIterator(this) ;
        currentPage = pageMgr.getReadIterator(id) ;
        if ( currentPage.getCount() == 0 )
        {
            // Empty page.
            close() ;
            return ;
        }
            
        if ( fromRec != null )
        {
            currentIdx = currentPage.getRecordBuffer().find(fromRec) ;
            if ( currentIdx < 0 )
                currentIdx = decodeIndex(currentIdx) ;
        }
    }

    @Override
    public boolean hasNext()
    {
        if ( slot != null )
            return true ;
        if ( currentPage == null )
            return false ;
        // Set slot.
        while ( currentIdx >= currentPage.getCount() )
        {
            // Move to next.
            int link = currentPage.getLink() ;
            if ( link < 0 )
            {
                close() ;
                return false ;
            }
            
            if ( currentPage != null )
                pageMgr.release(currentPage) ;
            
            RecordBufferPage nextPage = pageMgr.getReadIterator(link) ;
            // Check currentPage -> nextPage is strictly increasing keys. 
            Record r1 = currentPage.getRecordBuffer().getHigh() ;
            Record r2 = nextPage.getRecordBuffer().getLow() ;
            if ( Record.keyGE(r1, r2) )
                throw new StorageException("RecordRangeIterator: records not strictly increasing: "+r1+" // "+r2) ;
            currentPage = nextPage ;
            countBlocks++ ;
            currentIdx = 0 ;
        }
            
        slot = currentPage.getRecordBuffer().get(currentIdx) ;
        currentIdx++ ;
        if ( maxRec != null && Record.keyGE(slot, maxRec) )
        {
            close() ;
            return false ;
        }
        
        if ( slot == null )
        {
            close() ;
            return false ;
        }
        countRecords++ ;
        return true ;
    }

    @Override
    public void close()
    {
        if (currentPage != null )
            pageMgr.release(currentPage) ;
        currentPage = null ;
        currentIdx = -99 ;
        slot = null ;
        pageMgr.getBlockMgr().endIterator(this) ;
    }

    @Override
    public Record next()
    {
        if ( ! hasNext() )
            throw new NoSuchElementException() ;
        
        Record x = slot ;
        slot = null ;
        return x ;
    }

    @Override
    public void remove()
    { throw new UnsupportedOperationException("remove") ; }

    final public long getCountRecords()     { return countRecords ; }

    final public long getCountBlocks()      { return countBlocks ; }
}