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Object mapper for the CQL Java Driver.

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/*
 * Copyright DataStax, Inc.
 *
 * 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 com.datastax.driver.mapping;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

class AccessorInvocationHandler implements InvocationHandler {

  private static final Object[] NO_ARGS = new Object[0];

  private static final Method TO_STRING;
  private static final Method EQUALS;
  private static final Method HASH_CODE;

  static {
    try {
      TO_STRING = Object.class.getMethod("toString");
      EQUALS = Object.class.getMethod("equals", Object.class);
      HASH_CODE = Object.class.getMethod("hashCode");
    } catch (NoSuchMethodException e) {
      throw new AssertionError(e); // Can't happen
    }
  }

  private final AccessorMapper mapper;

  private final Map methodMap = new HashMap();

  AccessorInvocationHandler(AccessorMapper mapper) {
    this.mapper = mapper;

    for (MethodMapper method : mapper.methods) methodMap.put(method.method, method);
  }

  @Override
  public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
    if (m.equals(TO_STRING))
      return mapper.daoClass.getSimpleName()
          + " implementation generated by the Cassandra driver mapper";

    // It's unlikely that equals and hashCode will be used on accessor implementations, but better
    // safe than sorry.
    // Identity equality is enough, given that the mapper always returns the same instance for a
    // given accessor.
    if (m.equals(EQUALS)) return proxy == args[0];

    if (m.equals(HASH_CODE)) return System.identityHashCode(proxy);

    MethodMapper method = methodMap.get(m);
    if (method == null) throw new UnsupportedOperationException();
    return method.invoke(args == null ? NO_ARGS : args);
  }
}