package com.atlassian.cache.memory;
   
   import java.util.SortedMap;
   
   import com.atlassian.cache.CacheStatisticsKey;
   import com.atlassian.util.concurrent.Supplier;
   
   import com.google.common.cache.Cache;
   import com.google.common.cache.LoadingCache;
  import com.google.common.collect.ImmutableSortedMap;
  
  import static com.atlassian.cache.CacheStatisticsKey.EVICTION_COUNT;
  import static com.atlassian.cache.CacheStatisticsKey.HIT_COUNT;
  import static com.atlassian.cache.CacheStatisticsKey.MISS_COUNT;
  import static com.atlassian.cache.CacheStatisticsKey.SIZE;
  import static com.atlassian.cache.CacheStatisticsKey.TOTAL_MISS_TIME;
  
  /**
   * @since v2.4.0
   */
  public class DelegatingCacheStatistics
  {
      public static SortedMap<CacheStatisticsKey,Supplier<Long>> toStatistics(Cache<?, ?> internalCache)
      {
          ImmutableSortedMap.Builder<CacheStatisticsKey, Supplier<Long>> map = ImmutableSortedMap.<CacheStatisticsKey, Supplier<Long>>orderedBy(CacheStatisticsKey.SORT_BY_LABEL)
                  .put(SIZE, memoize(internalCache.size()))
                  .put(HIT_COUNT, memoize(internalCache.stats().hitCount()))
                  .put(MISS_COUNT, memoize(internalCache.stats().missCount()))
                  .put(EVICTION_COUNT, memoize(internalCache.stats().evictionCount()));
  
          // don't bother reporting this statistic as "zero" for caches that
          // can't even calculate it. Only LoadingCaches calculate it.
          if (internalCache instanceof LoadingCache)
          {
              map.put(TOTAL_MISS_TIME, memoize(internalCache.stats().totalLoadTime()));
          }
  
          return map.build();
      }
  
      private static <V> Supplier<V> memoize(final V value)
      {
          return new ImmediateSupplier<V>(value);
      }
  
      static class ImmediateSupplier<V> implements Supplier<V>
      {
          private final V value;
  
          ImmediateSupplier(final V value)
          {
              this.value = value;
          }
  
          @Override
          public V get()
          {
              return value;
          }
  
          @Override
          public String toString()
          {
              return "ImmediateSupplier[" + value + ']';
          }
      }
  }