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/**
 * 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.hadoop.hive.common;

import java.util.Arrays;

/**
 * An implmentation of {@link org.apache.hadoop.hive.common.ValidTxnList} for use by readers.
 * This class will view a transaction as valid only if it is committed.  Both open and aborted
 * transactions will be seen as invalid.
 */
public class ValidReadTxnList implements ValidTxnList {

  protected long[] exceptions;
  protected long highWatermark;

  public ValidReadTxnList() {
    this(new long[0], Long.MAX_VALUE);
  }

  public ValidReadTxnList(long[] exceptions, long highWatermark) {
    if (exceptions.length == 0) {
      this.exceptions = exceptions;
    } else {
      this.exceptions = exceptions.clone();
      Arrays.sort(this.exceptions);
    }
    this.highWatermark = highWatermark;
  }

  public ValidReadTxnList(String value) {
    readFromString(value);
  }

  @Override
  public boolean isTxnValid(long txnid) {
    if (highWatermark < txnid) {
      return false;
    }
    return Arrays.binarySearch(exceptions, txnid) < 0;
  }

  @Override
  public RangeResponse isTxnRangeValid(long minTxnId, long maxTxnId) {
    // check the easy cases first
    if (highWatermark < minTxnId) {
      return RangeResponse.NONE;
    } else if (exceptions.length > 0 && exceptions[0] > maxTxnId) {
      return RangeResponse.ALL;
    }

    // since the exceptions and the range in question overlap, count the
    // exceptions in the range
    long count = Math.max(0, maxTxnId - highWatermark);
    for(long txn: exceptions) {
      if (minTxnId <= txn && txn <= maxTxnId) {
        count += 1;
      }
    }

    if (count == 0) {
      return RangeResponse.ALL;
    } else if (count == (maxTxnId - minTxnId + 1)) {
      return RangeResponse.NONE;
    } else {
      return RangeResponse.SOME;
    }
  }

  @Override
  public String toString() {
    return writeToString();
  }

  @Override
  public String writeToString() {
    StringBuilder buf = new StringBuilder();
    buf.append(highWatermark);
    if (exceptions.length == 0) {
      buf.append(':');
    } else {
      for(long except: exceptions) {
        buf.append(':');
        buf.append(except);
      }
    }
    return buf.toString();
  }

  @Override
  public void readFromString(String src) {
    if (src == null) {
      highWatermark = Long.MAX_VALUE;
      exceptions = new long[0];
    } else {
      String[] values = src.split(":");
      highWatermark = Long.parseLong(values[0]);
      exceptions = new long[values.length - 1];
      for(int i = 1; i < values.length; ++i) {
        exceptions[i-1] = Long.parseLong(values[i]);
      }
    }
  }

  @Override
  public long getHighWatermark() {
    return highWatermark;
  }

  @Override
  public long[] getInvalidTransactions() {
    return exceptions;
  }
}