/*
 * 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
 *
 *   https://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.
 *
 *   SPDX-License-Identifier: Apache-2.0
 */

package org.apache.jena.sparql.engine.iterator;

import java.util.ArrayList ;
import java.util.Iterator ;
import java.util.List ;
import java.util.NoSuchElementException ;

import org.apache.jena.atlas.io.IndentedWriter ;
import org.apache.jena.atlas.lib.Lib ;
import org.apache.jena.sparql.engine.ExecutionContext ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.serializer.SerializationContext ;

/**
 * A query iterator that joins two or more iterators into a single iterator.
 */

public class QueryIterConcat extends QueryIter {
    boolean initialized = false;
    List<QueryIterator> iteratorList = new ArrayList<>();
    Iterator<QueryIterator> iterator;
    QueryIterator currentQIter = null;

    Binding binding;
    boolean doneFirst = false;

    public QueryIterConcat(ExecutionContext context) {
        super(context);
    }

    private void init() {
        if ( !initialized ) {
            currentQIter = null;
            if ( iterator == null )
                iterator = iteratorList.listIterator();
            if ( iterator.hasNext() )
                currentQIter = iterator.next();
            initialized = true;
        }
    }

    public void add(QueryIterator qIter) {
        if ( qIter != null )
            iteratorList.add(qIter);
    }

    @Override
    protected boolean hasNextBinding() {
        if ( isFinished() )
            return false;

        init();
        if ( currentQIter == null )
            return false;

        while (!currentQIter.hasNext()) {
            // End sub iterator
            // currentQIter.close() ;
            currentQIter = null;
            if ( iterator.hasNext() )
                currentQIter = iterator.next();
            if ( currentQIter == null ) {
                // No more.
                // close() ;
                return false;
            }
        }

        return true;
    }

    @Override
    protected Binding moveToNextBinding() {
        if ( !hasNextBinding() )
            throw new NoSuchElementException(Lib.className(this));
        if ( currentQIter == null )
            throw new NoSuchElementException(Lib.className(this));

        Binding binding = currentQIter.nextBinding();
        return binding;
    }

    @Override
    protected void closeIterator() {
        for ( QueryIterator qIter : iteratorList ) {
            performClose(qIter);
        }
    }

    @Override
    protected void requestCancel() {
        for ( QueryIterator qIter : iteratorList ) {
            performRequestCancel(qIter);
        }
    }

    @Override
    public void output(IndentedWriter out, SerializationContext sCxt) {
        out.println(Lib.className(this));
        out.incIndent();
        for ( QueryIterator qIter : iteratorList ) {
            qIter.output(out, sCxt);
        }
        out.decIndent();
        out.ensureStartOfLine();
    }
}
