content: /*
   * Copyright (C) 2015 AChep@xda <artemchep@gmail.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version 2
   * of the License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   * MA  02110-1301, USA.
   */
  package com.achep.base.utils;
  
  import androidx.annotation.NonNull;
  import androidx.annotation.Nullable;
  
  import java.lang.ref.Reference;
  import java.util.ArrayList;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * Created by Artem Chepurnoy on 02.03.2015.
   */
  public abstract class RefCacheBase<T> {
  
      @NonNull
      private final Map<CharSequence, Reference<T>> mCache = new ConcurrentHashMap<>();
  
      public final void put(@NonNull CharSequence key, @NonNull T object) {
          synchronized (this) {
              mCache.put(key, onCreateReference(object));
          }
      }
  
      @Nullable
      public final T remove(@NonNull CharSequence key) {
          synchronized (this) {
              Reference<T> ref = mCache.remove(key);
              if (ref == null) {
                  cleanDeadEntries();
                  return null;
              }
              return ref.get();
          }
      }
  
      @Nullable
      public final T get(@NonNull CharSequence key) {
          synchronized (this) {
              Reference<T> ref = mCache.get(key);
              if (ref == null) {
                  cleanDeadEntries();
                  return null;
              }
              return ref.get();
          }
      }
  
      private void cleanDeadEntries() {
          ArrayList<CharSequence> deaths = null;
  
          // Find empty links
          for (Map.Entry<CharSequence, Reference<T>> entry : mCache.entrySet()) {
              if (entry.getValue().get() == null) {
                  if (deaths == null) {
                      deaths = new ArrayList<>();
                  }
                  deaths.add(entry.getKey());
              }
          }
  
          // Clean-up
          if (deaths != null) {
              for (CharSequence key : deaths) {
                  mCache.remove(key);
              }
          }
      }
  
      /**
       * Removes all elements from this cache, leaving it empty.
       */
      public void clear() {
          synchronized (this) {
              mCache.clear();
          }
      }
  
      @NonNull
      protected abstract Reference<T> onCreateReference(@NonNull T object);
  
  }
  