/*
    * Copyright (C) 2019, Google LLC. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  package org.eclipse.jgit.internal.revwalk;
  
  import java.io.IOException;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Optional;
  import java.util.stream.Stream;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.revwalk.ReachabilityChecker;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevSort;
  import org.eclipse.jgit.revwalk.RevWalk;
  
  /**
   * Checks the reachability walking the graph from the starters towards the
   * target.
   */
  public class PedestrianReachabilityChecker implements ReachabilityChecker {
  
  	private final boolean topoSort;
  
  	private final RevWalk walk;
  
  	/**
  	 * New instance of the reachability checker using a existing walk.
  	 *
  	 * @param topoSort
  	 *            walk commits in topological order
  	 * @param walk
  	 *            RevWalk instance to reuse. Caller retains ownership.
  	 */
  	public PedestrianReachabilityChecker(boolean topoSort,
  			RevWalk walk) {
  		this.topoSort = topoSort;
  		this.walk = walk;
  	}
  
  	@Override
  	public Optional<RevCommit> areAllReachable(Collection<RevCommit> targets,
  			Stream<RevCommit> starters)
  					throws MissingObjectException, IncorrectObjectTypeException,
  					IOException {
  		walk.reset();
  		if (topoSort) {
  			walk.sort(RevSort.TOPO);
  		}
  
  		for (RevCommit target: targets) {
  			walk.markStart(target);
  		}
  
  		Iterator<RevCommit> iterator = starters.iterator();
  		while (iterator.hasNext()) {
  			walk.markUninteresting(iterator.next());
  		}
  
  		return Optional.ofNullable(walk.next());
  	}
  }