// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
package com.amazonaws.services.dynamodbv2.datamodeling.internal;

import com.amazonaws.annotation.ThreadSafe;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;

/**
 * A bounded cache that has a LRU eviction policy when the cache is full.
 *
 * @param <T> value type
 */
@ThreadSafe
public final class LRUCache<T> {
  /** Used for the internal cache. */
  private final Map<String, T> map;

  /** Maximum size of the cache. */
  private final int maxSize;

  /** @param maxSize the maximum number of entries of the cache */
  public LRUCache(final int maxSize) {
    if (maxSize < 1) {
      throw new IllegalArgumentException("maxSize " + maxSize + " must be at least 1");
    }
    this.maxSize = maxSize;
    map = Collections.synchronizedMap(new LRUHashMap<>(maxSize));
  }

  /** Adds an entry to the cache, evicting the earliest entry if necessary. */
  public T add(final String key, final T value) {
    return map.put(key, value);
  }

  /** Returns the value of the given key; or null of no such entry exists. */
  public T get(final String key) {
    return map.get(key);
  }

  /** Returns the current size of the cache. */
  public int size() {
    return map.size();
  }

  /** Returns the maximum size of the cache. */
  public int getMaxSize() {
    return maxSize;
  }

  public void clear() {
    map.clear();
  }

  public T remove(String key) {
    return map.remove(key);
  }

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

  @SuppressWarnings("serial")
  private static class LRUHashMap<T> extends LinkedHashMap<String, T> {
    private final int maxSize;

    private LRUHashMap(final int maxSize) {
      super(10, 0.75F, true);
      this.maxSize = maxSize;
    }

    @Override
    protected boolean removeEldestEntry(final Entry<String, T> eldest) {
      return size() > maxSize;
    }
  }
}