package org.opentrafficsim.core.gtu;
   
   import java.util.Arrays;
   import java.util.LinkedHashMap;
   import java.util.List;
   import java.util.Map;
   import java.util.Set;
   import java.util.function.Supplier;
   
  import org.djutils.exceptions.Throw;
  
  /**
   * Utility class to cache data based on a variable (between cache instances) number of keys of any type. This replaces nested
   * {@code Map}s.
   * <p>
   * Copyright (c) 2013-2019 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="http://opentrafficsim.org/node/13">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision$, $LastChangedDate$, by $Author$, initial version 20 apr. 2018 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   * @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
   * @param <T> value type
   */
  public class NestedCache<T>
  {
  
      /** Key types. */
      private final Class<?>[] types;
  
      /** Map with cache. */
      private final Map<Object, Object> map = new LinkedHashMap<>();
  
      /**
       * Constructor.
       * @param types Class&lt;?&gt;...; types
       */
      public NestedCache(final Class<?>... types)
      {
          this.types = types;
      }
  
      /**
       * Returns a value.
       * @param supplier Supplier&lt;T&gt;; supplier of {@code T} for if it wasn't cached yet
       * @param keys Object...; list of key objects
       * @return T; value
       */
      public T getValue(final Supplier<T> supplier, final Object... keys)
      {
          return getValue(supplier, Arrays.asList(keys));
      }
  
      /**
       * Returns a value. This uses a {@code List} rather than an array to allow flexible inner workings.
       * @param supplier Supplier&lt;T&gt;; supplier of {@code T} for if it wasn't cached yet
       * @param keys List&lt;Object&gt;; list of key objects
       * @return T; value
       */
      @SuppressWarnings("unchecked")
      private T getValue(final Supplier<T> supplier, final List<Object> keys)
      {
          Throw.when(keys.size() != this.types.length, IllegalArgumentException.class, "Incorrect number of keys.");
          Throw.when(keys.get(0) != null && !this.types[0].isAssignableFrom(keys.get(0).getClass()),
                  IllegalArgumentException.class, "Key %s is not of %s.", keys.get(0), this.types[0]);
          Object sub = this.map.get(keys.get(0));
          if (this.types.length == 1)
          {
              if (sub == null)
              {
                  sub = supplier.get();
                  this.map.put(keys.get(0), sub);
              }
              return (T) sub;
          }
          if (sub == null)
          {
              // create sub-NestedCache with 1 less key
              Class<Object>[] subTypes = new Class[this.types.length - 1];
              System.arraycopy(this.types, 1, subTypes, 0, this.types.length - 1);
              sub = new NestedCache<T>(subTypes);
              this.map.put(keys.get(0), sub);
          }
          // return from sub-NestedCache with 1 less key
          return ((NestedCache<T>) sub).getValue(supplier, keys.subList(1, keys.size()));
      }
  
      /**
       * Return set of key objects on this level.
       * @return Set; set of key objects on this level
       */
      public Set<Object> getKeys()
      {
          return this.map.keySet();
      }
  
      /**
       * Return branch for key.
       * @param key Object; key
      * @return NestedCache; branch for key
      * @throws IllegalStateException if this is not a branch level
      */
     @SuppressWarnings("unchecked")
     public NestedCache<T> getChild(final Object key) throws IllegalStateException
     {
         Throw.when(this.types.length < 2, IllegalStateException.class, "Children can only be obtained on branch levels.");
         return (NestedCache<T>) this.map.get(key);
     }
 
     /**
      * Return value for key.
      * @param key Object; key
      * @return T; value for key
      * @throws IllegalStateException if this is not a leaf level
      */
     @SuppressWarnings("unchecked")
     public T getValue(final Object key) throws IllegalStateException
     {
         Throw.when(this.types.length != 1, IllegalStateException.class, "Values can only be obtained on leaf levels.");
         return (T) this.map.get(key);
     }
 
     /** {@inheritDoc} */
     @Override
     public String toString()
     {
         return "NestedCache [types=" + Arrays.toString(this.types) + ", map=" + this.map + "]";
     }
 
 }