/*
 * 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.daffodil.util

import scala.collection.mutable

abstract class TransitiveClosure[T] {

  protected def func(sc: T): Seq[T]

  // LinkedHashSet so we get deterministic behavior.
  private val processed = new mutable.LinkedHashSet[T]
  private val items = new mutable.Queue[T]

  def apply(start: Seq[T]): mutable.LinkedHashSet[T] = {
    start.foreach{ items.enqueue(_) }
    tclose()
  }

  /**
   * Breadth first traversal.
   */
  private def tclose() = {
    while(!items.isEmpty) {
      val hd = items.dequeue
      if (!processed.contains(hd)) {
        processed += hd
        val newOnes = func(hd).filterNot(processed.contains(_)).distinct
        newOnes.foreach {
          items.enqueue(_)
        }
      }
    }
    processed
  }
}
