/*
    * Copyright 2009 Ange Optimization ApS
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package eu.simuline.octave.type.cast;
  
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Map;
  
  import java.util.ServiceLoader;
  
  import eu.simuline.octave.exception.OctaveClassCastException;
  import eu.simuline.octave.exception.OctaveCastServiceException;
  import eu.simuline.octave.type.OctaveObject;
  
  /**
   * Helper class for the auto cast functionality. 
   * Currently, only a single caster is implemented: 
   * {@link DoubleToComplexCaster} but this can be dynamically extended. 
   */
  public final class Cast {
  
      private static final int PRIME = 31;
   
      /**
       * Maps a class pair to an according caster. 
       */
      private static Map<ClassPair<?, ?>, Caster<?, ?>> casterMap;
  
      private Cast() {
          throw new UnsupportedOperationException("Do not instantiate");
      }
  
      @SuppressWarnings("unchecked")
      private static synchronized void initIfNecessary() {
          if (casterMap == null) {
              casterMap = new HashMap<ClassPair<?, ?>, Caster<?, ?>>();
              @SuppressWarnings("rawtypes")
              final Iterator<Caster> sp = 
                 ServiceLoader.load(Caster.class).iterator();
  	    while (sp.hasNext()) {
                  register(sp.next());
              }
          }
      }
  
      private static <F, T> void register(final Caster<F, T> caster) {
          final ClassPair<F, T> cp = new ClassPair<F, T>(caster.from(),
  						       caster.to());
  	Caster<?, ?> overwritten = casterMap.put(cp, caster);
          if (overwritten != null) {
              throw new OctaveCastServiceException("casterMap.containsKey(cp)");
          }
      }
  
      /**
       * Cast and transform the object. 
       * 
       * @param <F>
       *    the class type of the object <code>from</code> to be cast.
       * @param <T>
       *    the target class <code>toClass</code> as a type variable.
       * @param toClass
       *    the class <code>from</code>
       * @param from
       *    the object to be cast or <code>null</code>.
       * @return
       *    The object of type <code>toClass</code> which is by casting <code>from</code>
       *    or <code>null</code> for <code>from == null</code>.
       */
      public static <F extends OctaveObject, 
  		   T extends OctaveObject> T cast(final Class<T> toClass, 
  						  final F from) {
          if (from == null) {
              return null;
          }
          if (toClass.isInstance(from)) {
              return toClass.cast(from);
          }
          final ClassPair<F, T> cp = new ClassPair<F, T>(unsafeGetClass(from),
  						       toClass);
          final Caster<F, T> caster = casterMapGet(cp);
          if (caster == null) {
              throw new OctaveClassCastException(null, from, toClass);
          }
          return caster.cast(from);
      }
 
     @SuppressWarnings("unchecked")
     private static <F> Class<F> unsafeGetClass(final F from) {
         return (Class<F>) from.getClass();
     }
 
     @SuppressWarnings("unchecked")
     private static <F extends OctaveObject, 
 		    T extends OctaveObject> 
     Caster<F, T> casterMapGet(final ClassPair<F, T> cp) {
         initIfNecessary();
         if (!casterMap.containsKey(cp)) {
             return null;
         }
         final Caster<F, T> caster = (Caster<F, T>) casterMap.get(cp);
         if (!caster.from().equals(cp.from)) {
             throw new OctaveCastServiceException
 		("!caster.from().equals(cp.from)");
         }
         if (!caster.to().equals(cp.to)) {
             throw new OctaveCastServiceException("!caster.to().equals(cp.to)");
         }
         return caster;
     }
 
     /**
      * Represents a pair of classes, 
      * essentially a cast from one to the other class. 
      *
      * @param <F> from class 
      * @param <T> to   class 
      */
     private static class ClassPair<F, T> {
         ClassPair(final Class<F> from, final Class<T> to) {
             this.from = from;
             this.to = to;
         }
 
         private final Class<F> from;
 
         private final Class<T> to;
 
         @Override
         public int hashCode() {
             int result = 1;
             result = PRIME * result + ((from == null) ? 0 : from.hashCode());
             result = PRIME * result + ((to   == null) ? 0 :   to.hashCode());
             return result;
         }
 
 	@Override
 	public boolean equals(final Object obj) {
             if (this == obj) {
                 return true;
             }
             if (obj == null) {
                 return false;
             }
             if (getClass() != obj.getClass()) {
                 return false;
             }
             final ClassPair<?, ?> other = (ClassPair<?, ?>) obj;
             if (from == null) {
                 if (other.from != null) {
                     return false;
                 }
             } else if (!from.equals(other.from)) {
                 return false;
             }
             if (to == null) {
                 if (other.to != null) {
                     return false;
                 }
             } else if (!to.equals(other.to)) {
                 return false;
             }
             return true;
         }
     }
 
 }