package com.atlassian.vcache.internal.core;
   
   import com.atlassian.vcache.internal.RequestContext;
   
   import javax.annotation.Nullable;
   import java.util.Map;
   import java.util.Optional;
   import java.util.concurrent.ConcurrentHashMap;
   import java.util.function.Supplier;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * An implementation of the {@link RequestContext}.
   *
   * @since 1.0
   */
  public class DefaultRequestContext implements RequestContext {
      @Nullable
      private String partitionId;
      private final Supplier<String> partitionIdSupplier;
      private final Map<Object, Object> map = new ConcurrentHashMap<>();
  
      public DefaultRequestContext(Supplier<String> partitionIdSupplier) {
          this.partitionIdSupplier = requireNonNull(partitionIdSupplier);
      }
  
      @Override
      public String partitionIdentifier() {
          // It doesn't matter if multiple threads get the value from the supplier, it should be a relatively cheap call
          // and it should always return the same value.
          if (partitionId == null) {
              partitionId = partitionIdSupplier.get();
          }
          return partitionId;
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public <T> T computeIfAbsent(Object key, Supplier<T> supplier) {
          return (T) map.computeIfAbsent(requireNonNull(key), o -> requireNonNull(supplier.get()));
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public <T> Optional<T> get(Object key) {
          return Optional.ofNullable((T) map.get(key));
      }
  }