/*
    * 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.giraph.object;
  
  import org.apache.giraph.function.Consumer;
  import org.apache.giraph.function.primitive.Int2ObjFunction;
  import org.apache.giraph.types.ops.PrimitiveIdTypeOps;
  import org.apache.giraph.types.ops.collections.Basic2ObjectMap;
  import org.apache.giraph.types.ops.collections.BasicSet;
  
  import com.google.common.base.Preconditions;
  
  import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  
  /**
   * Holds reusable objects of multiple sizes.
   * Example usecase, is when we need a hashmap - that we will insert and iterate
   * on, both clear() and iterate method depend on size. And if we want to reuse
   * objects, we want to have multiple objects of different sizes, that we will
   * reuse.
   *
   * Instead of creating object for each distinct size, it creates objects with
   * first larger power of 2.
   *
   * @param <T> Type of reusable object
   */
  public class MultiSizedReusable<T> implements Int2ObjFunction<T> {
    private final Int2ObjFunction<T> createSized;
    private final Consumer<T> init;
    @SuppressWarnings("unchecked")
    @SuppressFBWarnings("SE_TRANSIENT_FIELD_NOT_RESTORED")
    private final transient T[] holder = (T[]) new Object[Integer.SIZE];
  
    // No-arg constructor Kryo can call to initialize holder
    MultiSizedReusable() {
      this(null, null);
    }
  
    public MultiSizedReusable(Int2ObjFunction<T> createSized, Consumer<T> init) {
      this.createSized = createSized;
      this.init = init;
    }
  
    @Override
    public T apply(int size) {
      Preconditions.checkArgument(size >= 0);
      int shiftBits = (Integer.SIZE -
          Integer.numberOfLeadingZeros(Math.max(0, size - 1))) / 2;
      T result = holder[shiftBits];
      if (result == null) {
        if (shiftBits >= 15) {
          result = createSized.apply(Integer.MAX_VALUE);
        } else {
          result = createSized.apply(1 << (shiftBits * 2 + 1));
        }
        holder[shiftBits] = result;
      }
      if (init != null) {
        init.apply(result);
      }
      return result;
    }
  
    public static <I> MultiSizedReusable<BasicSet<I>> createForBasicSet(
        final PrimitiveIdTypeOps<I> idTypeOps) {
      return new MultiSizedReusable<>(
          new Int2ObjFunction<BasicSet<I>>() {
            @Override
            public BasicSet<I> apply(int value) {
              return idTypeOps.createOpenHashSet(value);
            }
          },
          new Consumer<BasicSet<I>>() {
            @Override
            public void apply(BasicSet<I> t) {
              t.clear();
            }
          });
    }
  
    public static <K, V>
    MultiSizedReusable<Basic2ObjectMap<K, V>> createForBasic2ObjectMap(
        final PrimitiveIdTypeOps<K> idTypeOps) {
      return new MultiSizedReusable<>(
         new Int2ObjFunction<Basic2ObjectMap<K, V>>() {
           @Override
           public Basic2ObjectMap<K, V> apply(int value) {
             return idTypeOps.create2ObjectOpenHashMap(value, null);
           }
         },
         new Consumer<Basic2ObjectMap<K, V>>() {
           @Override
           public void apply(Basic2ObjectMap<K, V> t) {
             t.clear();
           }
         });
   }
 }