/*
 * Copyright 2022 Google 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
 *
 *     https://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 javaemul.lang

import javaemul.internal.InternalPreconditions.Companion.checkState

class CauseHolder() {
  // Holds the cause (a Throwable or null), or this, if no cause was set
  private var thisOrCause: Any? = this

  var cause: Throwable?
    get() = if (hasCause()) thisOrCause as Throwable? else null
    set(value: Throwable?) {
      checkState(!hasCause(), "Can't overwrite cause")
      thisOrCause = value
    }

  private fun hasCause(): Boolean = thisOrCause !== this
}
