package org.djutils.reflection;
   
   import java.io.Serializable;
   import java.lang.reflect.Array;
   import java.util.LinkedHashMap;
   import java.util.Map;
   
   import org.djutils.primitives.Primitive;
   
  /**
   * A field descriptor represents the type of a class, instance, or local variable. It is a series of characters generated by the
   * grammar described at <a href = "https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html"> The Java Virtual Machine
   * class File Format </a>.
   * <p>
   * Copyright (c) 2002-2022 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
   * for project information <a href="https://djutils.org" target="_blank"> https://djutils.org</a>. The DJUTILS project is
   * distributed under a three-clause BSD-style license, which can be found at
   * <a href="https://djutils.org/docs/license.html" target="_blank"> https://djutils.org/docs/license.html</a>.
   * </p>
   * @author Peter Jacobs, Niels Lang, Alexander Verbraeck
   */
  public class FieldSignature implements Serializable
  {
      /** The default serial version UID for serializable classes. */
      private static final long serialVersionUID = 20191230L;
  
      /** the CAHCHe. */
      private static final Map<String, Class<?>> CACHE = new LinkedHashMap<String, Class<?>>();
  
      /** the value of the field descriptor. */
      private String value;
  
      /**
       * constructs a new FieldSignature.
       * @param value String; the value of the descriptor
       */
      public FieldSignature(final String value)
      {
          this.value = value;
      }
  
      /**
       * constructs a new FieldSignature.
       * @param clazz Class&lt;?&gt;; The class
       */
      public FieldSignature(final Class<?> clazz)
      {
          this(FieldSignature.toDescriptor(clazz));
      }
  
      /**
       * @return Returns the value of the field descriptor
       */
      public String getStringValue()
      {
          return this.value;
      }
  
      /**
       * @return Returns the value of the field descriptor
       * @throws ClassNotFoundException if the class cannot be found.
       */
      public Class<?> getClassValue() throws ClassNotFoundException
      {
          return FieldSignature.toClass(this.value);
      }
  
      /** {@inheritDoc} */
      @Override
      public String toString()
      {
          return this.value;
      }
  
      /**
       * converts an array of fields to its descriptor.
       * @param classes Class&lt;?&gt;[]; the classes to represent
       * @return String the descriptor String
       */
      public static final String toDescriptor(final Class<?>[] classes)
      {
          StringBuilder result = new StringBuilder();
          for (int i = 0; i < classes.length; i++)
          {
              result.append(FieldSignature.toDescriptor(classes[i]));
          }
          return result.toString();
      }
  
      /**
       * converts a field to its descriptor.
       * @param clazz Class&lt;?&gt;; the clazz to represent
       * @return String the descriptor String
       */
      public static final String toDescriptor(final Class<?> clazz)
      {
          if (clazz.getName().startsWith("["))
          {
              return clazz.getName().replace('.', '/');
         }
         if (clazz.isPrimitive())
         {
             if (clazz.equals(int.class))
             {
                 return "I";
             }
             if (clazz.equals(double.class))
             {
                 return "D";
             }
             if (clazz.equals(boolean.class))
             {
                 return "Z";
             }
             if (clazz.equals(char.class))
             {
                 return "C";
             }
             if (clazz.equals(byte.class))
             {
                 return "B";
             }
             if (clazz.equals(float.class))
             {
                 return "F";
             }
             if (clazz.equals(long.class))
             {
                 return "J";
             }
             if (clazz.equals(short.class))
             {
                 return "S";
             }
             return "V";
         }
         return "L" + clazz.getName().replace('.', '/') + ";";
     }
 
     /**
      * converts a fieldDescriptor to its class representation.
      * @param descriptor String; the descriptor
      * @return Class the class
      * @throws ClassNotFoundException on failure
      */
     public static final Class<?> toClass(final String descriptor) throws ClassNotFoundException
     {
         if (FieldSignature.CACHE.containsKey(descriptor))
         {
             return FieldSignature.CACHE.get(descriptor);
         }
         String className = descriptor;
         Class<?> result = null;
         int array = 0;
         while (className.charAt(array) == '[')
         {
             array++;
         }
         className = className.substring(array);
         if (className.startsWith("L"))
         {
             className = className.replaceAll("/", ".");
             className = className.substring(1, className.length() - 1);
             try
             {
                 result = Class.forName(className);
             }
             catch (Exception exception)
             {
                 result = Class.forName(className, true, Thread.currentThread().getContextClassLoader());
             }
         }
         else
         {
             result = Primitive.forName(className);
         }
         if (result == null && !descriptor.startsWith("["))
         {
             // For some reason not all classes start with L and end with ;
             return FieldSignature.toClass("L" + descriptor + ";");
         }
         if (array == 0)
         {
             FieldSignature.CACHE.put(descriptor, result);
             return result;
         }
         try
         {
             int[] dimensions = new int[array];
             result = Array.newInstance(result, dimensions).getClass();
         }
         catch (Exception exception)
         {
             throw new ClassNotFoundException(result + " class not found");
         }
         FieldSignature.CACHE.put(descriptor, result);
         return result;
     }
 }