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Core functionality for the RSocket library
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/*
 * Copyright 2014-2019 Real Logic Ltd.
 *
 * Licensed 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 io.rsocket.internal;

import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.ToIntFunction;

/** Utility functions for collection objects. */
public class CollectionUtil {
  /**
   * A getOrDefault that doesn't create garbage if its suppler is non-capturing.
   *
   * @param map to perform the lookup on.
   * @param key on which the lookup is done.
   * @param supplier of the default value if one is not found.
   * @param  type of the key
   * @param  type of the value
   * @return the value if found or a new default which as been added to the map.
   */
  public static  V getOrDefault(
      final Map map, final K key, final Function supplier) {
    V value = map.get(key);
    if (value == null) {
      value = supplier.apply(key);
      map.put(key, value);
    }

    return value;
  }

  /**
   * Garbage free sum function.
   *
   * Note: the list must implement {@link java.util.RandomAccess} to be efficient.
   *
   * @param values the list of input values
   * @param function function that map each value to an int
   * @param  the value to add up
   * @return the sum of all the int values returned for each member of the list.
   */
  public static  int sum(final List values, final ToIntFunction function) {
    int total = 0;

    final int size = values.size();
    for (int i = 0; i < size; i++) {
      final V value = values.get(i);
      total += function.applyAsInt(value);
    }

    return total;
  }

  /**
   * Validate that a load factor is in the range of 0.1 to 0.9.
   *
   * 
Load factors in the range 0.5 - 0.7 are recommended for open-addressing with linear probing.
   *
   * @param loadFactor to be validated.
   */
  public static void validateLoadFactor(final float loadFactor) {
    if (loadFactor < 0.1f || loadFactor > 0.9f) {
      throw new IllegalArgumentException(
          "load factor must be in the range of 0.1 to 0.9: " + loadFactor);
    }
  }

  /**
   * Validate that a number is a power of two.
   *
   * @param value to be validated.
   */
  public static void validatePositivePowerOfTwo(final int value) {
    if (value > 0 && 1 == (value & (value - 1))) {
      throw new IllegalStateException("value must be a positive power of two");
    }
  }

  /**
   * Remove element from a list if it matches a predicate.
   *
   * Note: the list must implement {@link java.util.RandomAccess} to be efficient.
   *
   * @param values to be iterated over.
   * @param predicate to test the value against
   * @param  type of the value.
   * @return the number of items remove.
   */
  public static  int removeIf(final List values, final Predicate predicate) {
    int size = values.size();
    int total = 0;

    for (int i = 0; i < size; ) {
      final T value = values.get(i);
      if (predicate.test(value)) {
        values.remove(i);
        total++;
        size--;
      } else {
        i++;
      }
    }

    return total;
  }
}