/*
    *  Copyright 2011 Chris Pheby
    *
    *  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 org.jadira.bindings.core.general.marshaller;
  
  import java.lang.invoke.MethodHandle;
  import java.lang.invoke.MethodHandles;
  import java.lang.reflect.Method;
  import java.lang.reflect.Modifier;
  
  import org.jadira.bindings.core.api.BindingException;
  import org.jadira.bindings.core.api.ToMarshaller;
  
  /**
   * Base class providing capability to perform marshalling of source object type
   * to target. This class uses reflection.
   * <p>
   * The marshal method must either
   * </p>
   * <p>
   * a) be instance scoped and defined as part of class S. It must accept no
   * parameters and return a type of T. For example:
   * </p>
   * <p>
   * {@code public String marshal()}
   * </p>
   * <p>
   * b) be statically scoped. It must accept a single parameter of type S and
   * return a type of T. For example:
   * </p>
   * <p>
   * {@code public static String marshal(BoundType param)}
   * </p>
   * @param <S> Source type for the conversion
   * @param <T> Source type
   */
  public class MethodToMarshaller<S, T> implements ToMarshaller<S, T> {
  
  	private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
  	
      private final Class<S> boundClass;
  
      private final Class<T> targetClass;
      
      private final MethodHandle marshalHandle;
  
      /**
       * Create a new instance
       * @param boundClass Bound class
       * @param targetClass Destination class
       * @param marshal Marshal instance method on the target class
       */
      public MethodToMarshaller(Class<S> boundClass, Class<T> targetClass, Method marshal) {
          
          if (marshal.getParameterTypes().length == 0 && Modifier.isStatic(marshal.getModifiers())) {
              throw new IllegalStateException("marshal method must either be instance scope or define a single parameter");
          } else if (marshal.getParameterTypes().length == 1 && (!Modifier.isStatic(marshal.getModifiers()))) {
              throw new IllegalStateException("marshal method must either be instance scope or define a single parameter");
          } else if (marshal.getParameterTypes().length >= 2) {
              throw new IllegalStateException("marshal method must either be instance scope or define a single parameter");
          }
          
          if (!targetClass.isAssignableFrom(marshal.getReturnType())) {
              throw new IllegalStateException("marshal method must return an instance of target class");
          }
          if (!marshal.getDeclaringClass().isAssignableFrom(boundClass) && !Modifier.isStatic(marshal.getModifiers())) {
              throw new IllegalStateException("marshal method must be defined as part of " + boundClass.getSimpleName());
          }
  
          this.boundClass = boundClass;
          this.targetClass = targetClass;
  
          try {
  			this.marshalHandle = LOOKUP.unreflect(marshal);
  		} catch (IllegalAccessException e) {
  			throw new IllegalStateException("Method is not accessible" + marshal);
  		}
  
      }
  
  	/**
  	 * {@inheritDoc}
  	 */
  	/* @Override */
      public T marshal(S object) {
  
          try {
         	final T result = (T) marshalHandle.invoke(object);
             return result;
         } catch (Throwable ex) {
         	if (ex.getCause() instanceof RuntimeException) {
                 throw (RuntimeException) ex.getCause();
             }
             throw new BindingException(ex.getMessage(), ex.getCause());
         }
     }
    
 	/**
 	 * {@inheritDoc}
 	 */
 	/* @Override */
     public Class<S> getBoundClass() {
         return boundClass;
     }
     
 	/**
 	 * {@inheritDoc}
 	 */
 	/* @Override */
 	public Class<T> getTargetClass() {
 		return targetClass;
 	}
 }