/*
 * 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.phoenix.iterate;

import java.sql.SQLException;
import java.util.List;
import org.apache.phoenix.compile.ExplainPlanAttributes.ExplainPlanAttributesBuilder;
import org.apache.phoenix.schema.tuple.ResultTuple;
import org.apache.phoenix.schema.tuple.Tuple;

abstract public class LookAheadResultIterator implements PeekingResultIterator {
  public static PeekingResultIterator wrap(final ResultIterator iterator) {
    if (iterator instanceof PeekingResultIterator) {
      return (PeekingResultIterator) iterator;
    }

    return new LookAheadResultIterator() {

      @Override
      public void explain(List<String> planSteps) {
        iterator.explain(planSteps);
      }

      @Override
      public void explain(List<String> planSteps,
        ExplainPlanAttributesBuilder explainPlanAttributesBuilder) {
        iterator.explain(planSteps, explainPlanAttributesBuilder);
      }

      @Override
      public void close() throws SQLException {
        iterator.close();
      }

      @Override
      protected Tuple advance() throws SQLException {
        return iterator.next();
      }
    };
  }

  private final static Tuple UNINITIALIZED = ResultTuple.EMPTY_TUPLE;
  private Tuple next = UNINITIALIZED;

  abstract protected Tuple advance() throws SQLException;

  private void init() throws SQLException {
    if (next == UNINITIALIZED) {
      next = advance();
    }
  }

  @Override
  public Tuple next() throws SQLException {
    init();
    Tuple next = this.next;
    this.next = advance();
    return next;
  }

  @Override
  public Tuple peek() throws SQLException {
    init();
    return next;
  }
}
