/*
 * Copyright 2013-present Facebook, 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.facebook.buck.graph;

/**
 * Minimal interface needed by {@link AbstractBottomUpTraversal} to traverse a graph.
 */
public interface TraversableGraph<T> {

  /** @return {@link Iterable} that the caller is not allowed to mutate. */
  public Iterable<T> getNodesWithNoIncomingEdges();

  /** @return {@link Iterable} that the caller is not allowed to mutate. */
  public Iterable<T> getNodesWithNoOutgoingEdges();

  /** @return {@link Iterable} that the caller is not allowed to mutate. */
  public Iterable<T> getIncomingNodesFor(T sink);

  /** @return {@link Iterable} that the caller is not allowed to mutate. */
  public Iterable<T> getOutgoingNodesFor(T source);
}