/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.juneau;

import static org.apache.juneau.commons.reflect.ReflectionUtils.*;
import static org.apache.juneau.commons.utils.ThrowableUtils.*;
import static org.apache.juneau.commons.utils.Utils.*;

import java.lang.reflect.*;
import java.util.*;

import org.apache.juneau.json.*;

/**
 * Provides an {@link InvocationHandler} for creating dynamic proxy instances of bean interfaces.
 *
 * <p>
 * This class enables the creation of bean instances from interfaces without requiring concrete implementations.
 * When the {@code useInterfaceProxies} setting is enabled in {@link BeanContext}, this handler is used to create
 * proxy instances that implement bean interfaces.
 *
 * <p>
 * The handler stores bean property values in an internal map and intercepts method calls to:
 * <ul>
 *    <li><b>Getter methods</b> - Returns values from the internal property map</li>
 *    <li><b>Setter methods</b> - Stores values in the internal property map</li>
 *    <li><b>{@code equals(Object)}</b> - Compares property maps, with special handling for other proxy instances</li>
 *    <li><b>{@code hashCode()}</b> - Returns hash code based on the property map</li>
 *    <li><b>{@code toString()}</b> - Serializes the property map to JSON</li>
 * </ul>
 *
 * <p>
 * When comparing two proxy instances using {@code equals()}, if both are created with {@code BeanProxyInvocationHandler},
 * the comparison is optimized by directly comparing their internal property maps rather than converting to {@link BeanMap}.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bjava'>
 *    <jc>// Define an interface</jc>
 *    <jk>public interface</jk> Person {
 *       <jk>String</jk> <jsm>getName</jsm>();
 *       <jk>void</jk> <jsm>setName</jsm>(<jk>String</jk> name);
 *       <jk>int</jk> <jsm>getAge</jsm>();
 *       <jk>void</jk> <jsm>setAge</jsm>(<jk>int</jk> age);
 *    }
 *
 *    <jc>// Create a proxy instance</jc>
 *    <jk>var</jk> bc = <jsm>BeanContext</jsm>.<jsm>create</jsm>().<jsm>useInterfaceProxies</jsm>().<jsm>build</jsm>();
 *    <jk>var</jk> person = bc.<jsm>getClassMeta</jsm>(Person.<jk>class</jk>).<jsm>newInstance</jsm>();
 *
 *    <jc>// Use it like a regular bean</jc>
 *    person.<jsm>setName</jsm>(<js>"John"</js>);
 *    person.<jsm>setAge</jsm>(25);
 *    <jk>var</jk> name = person.<jsm>getName</jsm>(); <jc>// Returns "John"</jc>
 * </p>
 *
 * @param <T> The interface class type
 * @see BeanContext#isUseInterfaceProxies()
 * @see BeanMeta#getBeanProxyInvocationHandler()
 * @see Proxy#newProxyInstance(ClassLoader, Class[], InvocationHandler)
 */
public class BeanProxyInvocationHandler<T> implements InvocationHandler {

   private final BeanMeta<T> meta;                 // The BeanMeta for this instance
   private Map<String,Object> beanProps;     // The map of property names to bean property values.

   /**
    * Constructor.
    *
    * @param meta The bean metadata for the interface. Must not be <jk>null</jk>.
    */
   public BeanProxyInvocationHandler(BeanMeta<T> meta) {
      this.meta = meta;
      this.beanProps = new HashMap<>();
   }

   /**
    * Handles method invocations on the proxy instance.
    *
    * <p>
    * This method intercepts all method calls on the proxy and routes them appropriately:
    * <ul>
    *    <li>If the method is {@code equals(Object)}, compares property maps</li>
    *    <li>If the method is {@code hashCode()}, returns the hash code of the property map</li>
    *    <li>If the method is {@code toString()}, serializes the property map to JSON</li>
    *    <li>If the method is a getter (identified via {@link BeanMeta#getGetterProps()}), returns the property value</li>
    *    <li>If the method is a setter (identified via {@link BeanMeta#getSetterProps()}), stores the property value</li>
    *    <li>Otherwise, throws {@link UnsupportedOperationException}</li>
    * </ul>
    *
    * <p>
    * The {@code equals()} method has special optimization: when comparing two proxy instances created with this handler,
    * it directly compares their internal property maps using {@link Proxy#getInvocationHandler(Object)} to access the
    * other instance's handler.
    *
    * @param proxy The proxy instance on which the method was invoked
    * @param method The method that was invoked
    * @param args The arguments passed to the method, or <jk>null</jk> if no arguments
    * @return The return value of the method invocation
    * @throws UnsupportedOperationException If the method is not a supported bean method (getter, setter, equals, hashCode, or toString)
    */
   @Override /* Overridden from InvocationHandler */
   public Object invoke(Object proxy, Method method, Object[] args) {
      var mi = info(method);
      if (mi.hasName("equals") && mi.hasParameterTypes(Object.class)) {
         var arg = args[0];
         if (arg == null)
            return false;
         if (proxy == arg)
            return true;
         if (eq(proxy.getClass(), arg.getClass())) {
            var ih = Proxy.getInvocationHandler(arg);
            if (ih instanceof BeanProxyInvocationHandler ih2) {
               return beanProps.equals(ih2.beanProps);
            }
         }
         return eq(beanProps, meta.getBeanContext().toBeanMap(arg));
      }

      if (mi.hasName("hashCode") && mi.getParameterCount() == 0)
         return Integer.valueOf(this.beanProps.hashCode());

      if (mi.hasName("toString") && mi.getParameterCount() == 0)
         return Json5Serializer.DEFAULT.toString(this.beanProps);

      var prop = meta.getGetterProps().get(method);
      if (nn(prop))
         return beanProps.get(prop);

      prop = meta.getSetterProps().get(method);
      if (nn(prop)) {
         beanProps.put(prop, args[0]);
         return null;
      }

      throw unsupportedOp("Unsupported bean method.  method=''{0}''", method);
   }
}