/*
 * 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.amoro.flink.util;

import org.apache.flink.annotation.Internal;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.function.Function;

/**
 * Provides a thread local cache with a maximum cache size per thread.
 *
 * <p>Note: Values must not be null.
 *
 * <p>Copied from flink-1.18
 */
@Internal
public abstract class ThreadLocalCache<K, V> {

  private static final int DEFAULT_CACHE_SIZE = 64;

  private final ThreadLocal<BoundedMap<K, V>> cache = new ThreadLocal<>();
  private final int maxSizePerThread;

  protected ThreadLocalCache() {
    this(DEFAULT_CACHE_SIZE);
  }

  protected ThreadLocalCache(int maxSizePerThread) {
    this.maxSizePerThread = maxSizePerThread;
  }

  public V get(K key) {
    BoundedMap<K, V> map = cache.get();
    if (map == null) {
      map = new BoundedMap<>(maxSizePerThread);
      cache.set(map);
    }
    V value = map.get(key);
    if (value == null) {
      value = getNewInstance(key);
      map.put(key, value);
    }
    return value;
  }

  public abstract V getNewInstance(K key);

  private static class BoundedMap<K, V> extends LinkedHashMap<K, V> {

    private static final long serialVersionUID = -211630219014422361L;

    private final int maxSize;

    private BoundedMap(int maxSize) {
      this.maxSize = maxSize;
    }

    @Override
    protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
      return this.size() > maxSize;
    }
  }

  public static <K, V> ThreadLocalCache<K, V> of(Function<K, V> creator) {
    return new ThreadLocalCache<K, V>() {
      @Override
      public V getNewInstance(K key) {
        return creator.apply(key);
      }
    };
  }
}
