package scala
package reflect
package runtime

import scala.collection.mutable.WeakHashMap
import java.lang.ref.WeakReference

/** A cache that maintains a bijection between Java reflection type `J`
 *  and Scala reflection type `S`.
 *
 *  The cache is two-way weak (i.e. is powered by weak references),
 *  so that neither Java artifacts prevent Scala artifacts from being garbage collected,
 *  nor the other way around.
 */
private[runtime] class TwoWayCache[J, S] {

  private val toScalaMap = new WeakHashMap[J, WeakReference[S]]
  private val toJavaMap = new WeakHashMap[S, WeakReference[J]]

  def enter(j: J, s: S) = synchronized {
    // debugInfo("cached: "+j+"/"+s)
    toScalaMap(j) = new WeakReference(s)
    toJavaMap(s) = new WeakReference(j)
  }

  private object SomeRef {
    def unapply[T](optRef: Option[WeakReference[T]]): Option[T] =
      if (optRef.nonEmpty) {
        val result = optRef.get.get
        if (result != null) Some(result) else None
      } else None
  }

  def toScala(key: J)(body: => S): S = synchronized {
    toScalaMap get key match {
      case SomeRef(v) =>
        v
      case _ =>
        val result = body
        enter(key, result)
        result
    }
  }

  def toJava(key: S)(body: => J): J = synchronized {
    toJavaMap get key match {
      case SomeRef(v) =>
        v
      case _ =>
        val result = body
        enter(result, key)
        result
    }
  }
}
