/**
 * 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.tajo.engine.planner.physical;

import com.google.common.collect.Lists;
import org.apache.tajo.catalog.proto.CatalogProtos;
import org.apache.tajo.catalog.statistics.TableStats;
import org.apache.tajo.engine.planner.PlannerUtil;
import org.apache.tajo.engine.planner.logical.ScanNode;
import org.apache.tajo.storage.AbstractStorageManager;
import org.apache.tajo.storage.Tuple;
import org.apache.tajo.worker.TaskAttemptContext;

import java.io.IOException;
import java.util.Iterator;
import java.util.List;


/**
 * A Scanner that reads multiple partitions
 */
public class PartitionMergeScanExec extends PhysicalExec {
  private final ScanNode plan;
  private SeqScanExec currentScanner = null;

  private CatalogProtos.FragmentProto [] fragments;

  private List<SeqScanExec> scanners = Lists.newArrayList();
  private Iterator<SeqScanExec> iterator;

  private AbstractStorageManager sm;

  private float progress;
  protected TableStats inputStats;

  public PartitionMergeScanExec(TaskAttemptContext context, AbstractStorageManager sm,
                                ScanNode plan, CatalogProtos.FragmentProto[] fragments) throws IOException {
    super(context, plan.getInSchema(), plan.getOutSchema());

    this.plan = plan;
    this.fragments = fragments;
    this.sm = sm;

    inputStats = new TableStats();
  }

  public void init() throws IOException {
    for (CatalogProtos.FragmentProto fragment : fragments) {
      scanners.add(new SeqScanExec(context, sm, (ScanNode) PlannerUtil.clone(null, plan),
          new CatalogProtos.FragmentProto[] {fragment}));
    }
    progress = 0.0f;
    rescan();
  }

  @Override
  public Tuple next() throws IOException {
    Tuple tuple;
    while (currentScanner != null) {
      tuple = currentScanner.next();

      if (tuple != null) {
        return tuple;
      }

      if (iterator.hasNext()) {
        if (currentScanner != null) {
          currentScanner.close();
        }
        currentScanner = iterator.next();
        currentScanner.init();
      } else {
        break;
      }
    }
    return null;
  }

  @Override
  public void rescan() throws IOException {
    if (scanners.size() > 0) {
      iterator = scanners.iterator();
      currentScanner = iterator.next();
      currentScanner.init();
    }
  }

  @Override
  public void close() throws IOException {
    for (SeqScanExec scanner : scanners) {
      scanner.close();
      TableStats scannerTableStsts = scanner.getInputStats();
      if (scannerTableStsts != null) {
        inputStats.merge(scannerTableStsts);
      }
    }
    iterator = null;
    progress = 1.0f;
  }

  public String getTableName() {
    return plan.getTableName();
  }

  @Override
  public float getProgress() {
    if (iterator != null) {
      float progressSum = 0.0f;
      for (SeqScanExec scanner : scanners) {
        progressSum += scanner.getProgress();
      }
      if (progressSum > 0) {
        // get a average progress - divide progress summary by the number of scanners
        return progressSum / (float)(scanners.size());
      } else {
        return 0.0f;
      }
    } else {
      return progress;
    }
  }

  @Override
  public TableStats getInputStats() {
    return inputStats;
  }
}