/*
 * Copyright (C) 2011 The Guava Authors
 *
 * 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 com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.LongBinaryOperator;
import java.util.function.LongUnaryOperator;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;

A map containing long values that can be atomically updated. While writes to a traditional Map rely on put(K, V), the typical mechanism for writing to this map is addAndGet(K, long), which adds a long to the value currently associated with K. If a key has not yet been associated with a value, its implicit value is zero. 
Most methods in this class treat absent values and zero values identically, as individually documented. Exceptions to this are containsKey, size, isEmpty, AtomicLongMap<K>.asMap, and toString. 
Instances of this class may be used by multiple threads concurrently. All operations are
atomic unless otherwise noted.
Note: If your values are always positive and less than 2^31, you may wish to use a Multiset such as ConcurrentHashMultiset instead. 
Warning: Unlike Multiset, entries whose values are zero are not automatically removed from the map. Instead they must be removed manually with removeAllZeros. 
Author:
Charles Fry
Since:
11.0/**
 * A map containing {@code long} values that can be atomically updated. While writes to a
 * traditional {@code Map} rely on {@code put(K, V)}, the typical mechanism for writing to this map
 * is {@code addAndGet(K, long)}, which adds a {@code long} to the value currently associated with
 * {@code K}. If a key has not yet been associated with a value, its implicit value is zero.
 *
 * <p>Most methods in this class treat absent values and zero values identically, as individually
 * documented. Exceptions to this are {@link #containsKey}, {@link #size}, {@link #isEmpty}, {@link
 * #asMap}, and {@link #toString}.
 *
 * <p>Instances of this class may be used by multiple threads concurrently. All operations are
 * atomic unless otherwise noted.
 *
 * <p><b>Note:</b> If your values are always positive and less than 2^31, you may wish to use a
 * {@link com.google.common.collect.Multiset} such as {@link
 * com.google.common.collect.ConcurrentHashMultiset} instead.
 *
 * <p><b>Warning:</b> Unlike {@code Multiset}, entries whose values are zero are not automatically
 * removed from the map. Instead they must be removed manually with {@link #removeAllZeros}.
 *
 * @author Charles Fry
 * @since 11.0
 */
@GwtCompatible
public final class AtomicLongMap<K> implements Serializable {
  private final ConcurrentHashMap<K, Long> map;

  private AtomicLongMap(ConcurrentHashMap<K, Long> map) {
    this.map = checkNotNull(map);
  }

  
Creates an AtomicLongMap. /** Creates an {@code AtomicLongMap}. */
  public static <K> AtomicLongMap<K> create() {
    return new AtomicLongMap<K>(new ConcurrentHashMap<>());
  }

  
Creates an AtomicLongMap with the same mappings as the specified Map. /** Creates an {@code AtomicLongMap} with the same mappings as the specified {@code Map}. */
  public static <K> AtomicLongMap<K> create(Map<? extends K, ? extends Long> m) {
    AtomicLongMap<K> result = create();
    result.putAll(m);
    return result;
  }

  
Returns the value associated with key, or zero if there is no value associated with key. /**
   * Returns the value associated with {@code key}, or zero if there is no value associated with
   * {@code key}.
   */
  public long get(K key) {
    return map.getOrDefault(key, 0L);
  }

  
Increments by one the value currently associated with key, and returns the new value. /**
   * Increments by one the value currently associated with {@code key}, and returns the new value.
   */
  @CanIgnoreReturnValue
  public long incrementAndGet(K key) {
    return addAndGet(key, 1);
  }

  
Decrements by one the value currently associated with key, and returns the new value. /**
   * Decrements by one the value currently associated with {@code key}, and returns the new value.
   */
  @CanIgnoreReturnValue
  public long decrementAndGet(K key) {
    return addAndGet(key, -1);
  }

  
Adds delta to the value currently associated with key, and returns the new value. /**
   * Adds {@code delta} to the value currently associated with {@code key}, and returns the new
   * value.
   */
  @CanIgnoreReturnValue
  public long addAndGet(K key, long delta) {
    return accumulateAndGet(key, delta, Long::sum);
  }

  
Increments by one the value currently associated with key, and returns the old value. /**
   * Increments by one the value currently associated with {@code key}, and returns the old value.
   */
  @CanIgnoreReturnValue
  public long getAndIncrement(K key) {
    return getAndAdd(key, 1);
  }

  
Decrements by one the value currently associated with key, and returns the old value. /**
   * Decrements by one the value currently associated with {@code key}, and returns the old value.
   */
  @CanIgnoreReturnValue
  public long getAndDecrement(K key) {
    return getAndAdd(key, -1);
  }

  
Adds delta to the value currently associated with key, and returns the old value. /**
   * Adds {@code delta} to the value currently associated with {@code key}, and returns the old
   * value.
   */
  @CanIgnoreReturnValue
  public long getAndAdd(K key, long delta) {
    return getAndAccumulate(key, delta, Long::sum);
  }

  
Updates the value currently associated with key with the specified function, and returns the new value. If there is not currently a value associated with key, the function is applied to 0L. 
Since:
21.0/**
   * Updates the value currently associated with {@code key} with the specified function, and
   * returns the new value. If there is not currently a value associated with {@code key}, the
   * function is applied to {@code 0L}.
   *
   * @since 21.0
   */
  @CanIgnoreReturnValue
  public long updateAndGet(K key, LongUnaryOperator updaterFunction) {
    checkNotNull(updaterFunction);
    return map.compute(
        key, (k, value) -> updaterFunction.applyAsLong((value == null) ? 0L : value.longValue()));
  }

  
Updates the value currently associated with key with the specified function, and returns the old value. If there is not currently a value associated with key, the function is applied to 0L. 
Since:
21.0/**
   * Updates the value currently associated with {@code key} with the specified function, and
   * returns the old value. If there is not currently a value associated with {@code key}, the
   * function is applied to {@code 0L}.
   *
   * @since 21.0
   */
  @CanIgnoreReturnValue
  public long getAndUpdate(K key, LongUnaryOperator updaterFunction) {
    checkNotNull(updaterFunction);
    AtomicLong holder = new AtomicLong();
    map.compute(
        key,
        (k, value) -> {
          long oldValue = (value == null) ? 0L : value.longValue();
          holder.set(oldValue);
          return updaterFunction.applyAsLong(oldValue);
        });
    return holder.get();
  }

  
Updates the value currently associated with key by combining it with x via the specified accumulator function, returning the new value. The previous value associated with key (or zero, if there is none) is passed as the first argument to 
accumulatorFunction, and x is passed as the second argument. 
Since:
21.0/**
   * Updates the value currently associated with {@code key} by combining it with {@code x} via the
   * specified accumulator function, returning the new value. The previous value associated with
   * {@code key} (or zero, if there is none) is passed as the first argument to {@code
   * accumulatorFunction}, and {@code x} is passed as the second argument.
   *
   * @since 21.0
   */
  @CanIgnoreReturnValue
  public long accumulateAndGet(K key, long x, LongBinaryOperator accumulatorFunction) {
    checkNotNull(accumulatorFunction);
    return updateAndGet(key, oldValue -> accumulatorFunction.applyAsLong(oldValue, x));
  }

  
Updates the value currently associated with key by combining it with x via the specified accumulator function, returning the old value. The previous value associated with key (or zero, if there is none) is passed as the first argument to 
accumulatorFunction, and x is passed as the second argument. 
Since:
21.0/**
   * Updates the value currently associated with {@code key} by combining it with {@code x} via the
   * specified accumulator function, returning the old value. The previous value associated with
   * {@code key} (or zero, if there is none) is passed as the first argument to {@code
   * accumulatorFunction}, and {@code x} is passed as the second argument.
   *
   * @since 21.0
   */
  @CanIgnoreReturnValue
  public long getAndAccumulate(K key, long x, LongBinaryOperator accumulatorFunction) {
    checkNotNull(accumulatorFunction);
    return getAndUpdate(key, oldValue -> accumulatorFunction.applyAsLong(oldValue, x));
  }

  
Associates newValue with key in this map, and returns the value previously associated with key, or zero if there was no such value. /**
   * Associates {@code newValue} with {@code key} in this map, and returns the value previously
   * associated with {@code key}, or zero if there was no such value.
   */
  @CanIgnoreReturnValue
  public long put(K key, long newValue) {
    return getAndUpdate(key, x -> newValue);
  }

  
Copies all of the mappings from the specified map to this map. The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress. /**
   * Copies all of the mappings from the specified map to this map. The effect of this call is
   * equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
   * {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
   * if the specified map is modified while the operation is in progress.
   */
  public void putAll(Map<? extends K, ? extends Long> m) {
    m.forEach(this::put);
  }

  
Removes and returns the value associated with key. If key is not in the map, this method has no effect and returns zero. /**
   * Removes and returns the value associated with {@code key}. If {@code key} is not in the map,
   * this method has no effect and returns zero.
   */
  @CanIgnoreReturnValue
  public long remove(K key) {
    Long result = map.remove(key);
    return (result == null) ? 0L : result.longValue();
  }

  
If (key, value) is currently in the map, this method removes it and returns true; otherwise, this method returns false. /**
   * If {@code (key, value)} is currently in the map, this method removes it and returns true;
   * otherwise, this method returns false.
   */
  boolean remove(K key, long value) {
    return map.remove(key, value);
  }

  
Atomically remove key from the map iff its associated value is 0. 
Since:
20.0/**
   * Atomically remove {@code key} from the map iff its associated value is 0.
   *
   * @since 20.0
   */
  @Beta
  @CanIgnoreReturnValue
  public boolean removeIfZero(K key) {
    return remove(key, 0);
  }

  
Removes all mappings from this map whose values are zero.
This method is not atomic: the map may be visible in intermediate states, where some of the
zero values have been removed and others have not.
/**
   * Removes all mappings from this map whose values are zero.
   *
   * <p>This method is not atomic: the map may be visible in intermediate states, where some of the
   * zero values have been removed and others have not.
   */
  public void removeAllZeros() {
    map.values().removeIf(x -> x == 0);
  }

  
Returns the sum of all values in this map.
This method is not atomic: the sum may or may not include other concurrent operations.
/**
   * Returns the sum of all values in this map.
   *
   * <p>This method is not atomic: the sum may or may not include other concurrent operations.
   */
  public long sum() {
    return map.values().stream().mapToLong(Long::longValue).sum();
  }

  private transient @MonotonicNonNull Map<K, Long> asMap;

  
Returns a live, read-only view of the map backing this AtomicLongMap. /** Returns a live, read-only view of the map backing this {@code AtomicLongMap}. */
  public Map<K, Long> asMap() {
    Map<K, Long> result = asMap;
    return (result == null) ? asMap = createAsMap() : result;
  }

  private Map<K, Long> createAsMap() {
    return Collections.unmodifiableMap(map);
  }

  
Returns true if this map contains a mapping for the specified key. /** Returns true if this map contains a mapping for the specified key. */
  public boolean containsKey(Object key) {
    return map.containsKey(key);
  }

  
Returns the number of key-value mappings in this map. If the map contains more than 
Integer.MAX_VALUE elements, returns Integer.MAX_VALUE. /**
   * Returns the number of key-value mappings in this map. If the map contains more than {@code
   * Integer.MAX_VALUE} elements, returns {@code Integer.MAX_VALUE}.
   */
  public int size() {
    return map.size();
  }

  
Returns true if this map contains no key-value mappings. /** Returns {@code true} if this map contains no key-value mappings. */
  public boolean isEmpty() {
    return map.isEmpty();
  }

  
Removes all of the mappings from this map. The map will be empty after this call returns.
This method is not atomic: the map may not be empty after returning if there were concurrent
writes.
/**
   * Removes all of the mappings from this map. The map will be empty after this call returns.
   *
   * <p>This method is not atomic: the map may not be empty after returning if there were concurrent
   * writes.
   */
  public void clear() {
    map.clear();
  }

  @Override
  public String toString() {
    return map.toString();
  }

  
If key is not already associated with a value or if key is associated with zero, associate it with newValue. Returns the previous value associated with 
key, or zero if there was no mapping for key. /**
   * If {@code key} is not already associated with a value or if {@code key} is associated with
   * zero, associate it with {@code newValue}. Returns the previous value associated with {@code
   * key}, or zero if there was no mapping for {@code key}.
   */
  long putIfAbsent(K key, long newValue) {
    AtomicBoolean noValue = new AtomicBoolean(false);
    Long result =
        map.compute(
            key,
            (k, oldValue) -> {
              if (oldValue == null || oldValue == 0) {
                noValue.set(true);
                return newValue;
              } else {
                return oldValue;
              }
            });
    return noValue.get() ? 0L : result.longValue();
  }

  
If (key, expectedOldValue) is currently in the map, this method replaces 
expectedOldValue with newValue and returns true; otherwise, this method returns false. 
If expectedOldValue is zero, this method will succeed if (key, zero) is currently in the map, or if key is not in the map at all. /**
   * If {@code (key, expectedOldValue)} is currently in the map, this method replaces {@code
   * expectedOldValue} with {@code newValue} and returns true; otherwise, this method returns false.
   *
   * <p>If {@code expectedOldValue} is zero, this method will succeed if {@code (key, zero)} is
   * currently in the map, or if {@code key} is not in the map at all.
   */
  boolean replace(K key, long expectedOldValue, long newValue) {
    if (expectedOldValue == 0L) {
      return putIfAbsent(key, newValue) == 0L;
    } else {
      return map.replace(key, expectedOldValue, newValue);
    }
  }
}