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/*
Copyright 2012 Twitter, 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.twitter.chill

import scala.util.control.Exception.allCatch
import scala.collection.mutable.{ Map => MMap }
import _root_.java.lang.reflect.Field

/**
 * Uses facts about how scala compiles object singletons to Java + reflection
 */

class ObjectSerializer[T] extends KSerializer[T] {
  val cachedObj = MMap[Class[_], Option[T]]()

  // Does nothing
  override def write(kser: Kryo, out: Output, obj: T) {}

  protected def createSingleton(cls: Class[_]): Option[T] = {
    moduleField(cls).map { _.get(null).asInstanceOf[T] }
  }

  protected def cachedRead(cls: Class[_]): Option[T] = {
    cachedObj.synchronized { cachedObj.getOrElseUpdate(cls, createSingleton(cls)) }
  }

  override def read(kser: Kryo, in: Input, cls: Class[T]): T = cachedRead(cls).get

  def accepts(cls: Class[_]): Boolean = cachedRead(cls).isDefined

  protected def moduleField(klass: Class[_]): Option[Field] =
    Some(klass)
      .filter { _.getName.last == '$' }
      .flatMap { k => allCatch.opt(k.getDeclaredField("MODULE$")) }
}