/*
    * 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.commons.statistics.descriptive;
  
  import java.math.BigInteger;
  
  /**
   * Returns the maximum of the available values. Uses {@link Math#max(long, long) Math.max} as an
   * underlying function to compute the {@code maximum}.
   *
   * <ul>
   *   <li>The result is {@link Long#MIN_VALUE} if no values are added.
   * </ul>
   *
   * <p>This class is designed to work with (though does not require)
   * {@linkplain java.util.stream streams}.
   *
   * <p><strong>This implementation is not thread safe.</strong>
   * If multiple threads access an instance of this class concurrently,
   * and at least one of the threads invokes the {@link java.util.function.LongConsumer#accept(long) accept} or
   * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
   *
   * <p>However, it is safe to use {@link java.util.function.LongConsumer#accept(long) accept}
   * and {@link StatisticAccumulator#combine(StatisticResult) combine}
   * as {@code accumulator} and {@code combiner} functions of
   * {@link java.util.stream.Collector Collector} on a parallel stream,
   * because the parallel implementation of {@link java.util.stream.Stream#collect Stream.collect()}
   * provides the necessary partitioning, isolation, and merging of results for
   * safe and efficient parallel execution.
   *
   * @since 1.1
   * @see Math#max(long, long)
   */
  public final class LongMax implements LongStatistic, StatisticAccumulator<LongMax> {
  
      /** Current maximum. */
      private long maximum = Long.MIN_VALUE;
  
      /**
       * Create an instance.
       */
      private LongMax() {
          // No-op
      }
  
      /**
       * Creates an instance.
       *
       * <p>The initial result is {@link Long#MIN_VALUE}.
       *
       * @return {@code LongMax} instance.
       */
      public static LongMax create() {
          return new LongMax();
      }
  
      /**
       * Returns an instance populated using the input {@code values}.
       *
       * <p>When the input is an empty array, the result is
       * {@link Long#MIN_VALUE}.
       *
       * @param values Values.
       * @return {@code LongMax} instance.
       */
      public static LongMax of(long... values) {
          return Statistics.add(new LongMax(), values);
      }
  
      /**
       * Returns an instance populated using the specified range of {@code values}.
       *
       * <p>When the range is empty, the result is
       * {@link Long#MIN_VALUE}.
       *
       * @param values Values.
       * @param from Inclusive start of the range.
       * @param to Exclusive end of the range.
       * @return {@code LongMax} instance.
       * @throws IndexOutOfBoundsException if the sub-range is out of bounds
       * @since 1.2
       */
      public static LongMax ofRange(long[] values, int from, int to) {
          Statistics.checkFromToIndex(from, to, values.length);
          return createFromRange(values, from, to);
     }
 
     /**
      * Create an instance using the specified range of {@code values}.
      *
      * <p>Warning: No range checks are performed.
      *
      * @param values Values.
      * @param from Inclusive start of the range.
      * @param to Exclusive end of the range.
      * @return {@code LongMax} instance.
      */
     static LongMax createFromRange(long[] values, int from, int to) {
         return Statistics.add(new LongMax(), values, from, to);
     }
 
     /**
      * Updates the state of the statistic to reflect the addition of {@code value}.
      *
      * @param value Value.
      */
     @Override
     public void accept(long value) {
         maximum = Math.max(maximum, value);
     }
 
     /**
      * Gets the maximum of all input values.
      *
      * <p>When no values have been added, the result is
      * {@link Long#MIN_VALUE}.
      *
      * @return maximum of all values.
      */
     @Override
     public long getAsLong() {
         return maximum;
     }
 
     /**
      * Gets the maximum of all input values.
      *
      * <p>This method will throw an {@link ArithmeticException} if the {@code long}
      * maximum overflows an {@code int}; or no values have been added.
      *
      * @return maximum of all values.
      * @see Math#toIntExact(long)
      */
     @Override
     public int getAsInt() {
         return Math.toIntExact(maximum);
     }
 
     @Override
     public double getAsDouble() {
         return maximum;
     }
 
     @Override
     public BigInteger getAsBigInteger() {
         return BigInteger.valueOf(maximum);
     }
 
     @Override
     public LongMax combine(LongMax other) {
         accept(other.getAsLong());
         return this;
     }
 }