DfsUtil.java

/*
 * Copyright 2000-2014 JetBrains s.r.o.
 *
 * 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.intellij.vcs.log.graph.utils;

import com.intellij.openapi.util.Pair;
import com.intellij.util.containers.IntStack;
import com.intellij.util.containers.Stack;
import com.intellij.vcs.log.graph.api.LiteLinearGraph;
import com.intellij.vcs.log.graph.utils.impl.BitSetFlags;
import org.jetbrains.annotations.NotNull;

public class DfsUtil {
  public interface NextNode {
    int NODE_NOT_FOUND = -1;
    int EXIT = -10;

    int fun(int currentNode);
  }

  public interface NodeVisitor {
    void enterNode(int node);

    void exitNode(int node);
  }

  /*
   * Depth-first walk for a graph. For each node, walks both into upward and downward siblings.
   * Tries to preserve direction of travel: when a node is entered from up-sibling, goes to the down-siblings first.
   * Then goes to the other up-siblings.
   * And when a node is entered from down-sibling, goes to the up-siblings first.
   * Then goes to the other down-siblings.
   * When a node is entered the first time, enterNode is called.
   * When a node is passes in the same direction, exitNode is called.
   * Nothing is called when a all the siblings of the node are visited.
   */
  public static void walk(@NotNull LiteLinearGraph graph, int start, @NotNull NodeVisitor visitor) {
    BitSetFlags visited = new BitSetFlags(graph.nodesCount(), false);
    BitSetFlags visitedInSameDirection = new BitSetFlags(graph.nodesCount(), false);

    Stack<Pair<Integer, Boolean>> stack = new Stack<>();
    stack.push(new Pair<>(start, true)); // commit + direction of travel

    outer:
    while (!stack.empty()) {
      int currentNode = stack.peek().first;
      boolean down = stack.peek().second;
      if (!visited.get(currentNode)) {
        visited.set(currentNode, true);
        visitor.enterNode(currentNode);
      }

      for (int nextNode : graph.getNodes(currentNode, down ? LiteLinearGraph.NodeFilter.DOWN : LiteLinearGraph.NodeFilter.UP)) {
        if (!visited.get(nextNode)) {
          stack.push(new Pair<>(nextNode, down));
          continue outer;
        }
      }

      if (!visitedInSameDirection.get(currentNode)) {
        visitedInSameDirection.set(currentNode, true);
        visitor.exitNode(currentNode);
      }

      for (int nextNode : graph.getNodes(currentNode, down ? LiteLinearGraph.NodeFilter.UP : LiteLinearGraph.NodeFilter.DOWN)) {
        if (!visited.get(nextNode)) {
          stack.push(new Pair<>(nextNode, !down));
          continue outer;
        }
      }

      stack.pop();
    }
  }

  public static void walk(int startRowIndex, @NotNull NextNode nextNodeFun) {
    IntStack stack = new IntStack();
    stack.push(startRowIndex);

    while (!stack.empty()) {
      int nextNode = nextNodeFun.fun(stack.peek());
      if (nextNode == NextNode.EXIT) return;
      if (nextNode != NextNode.NODE_NOT_FOUND) {
        stack.push(nextNode);
      }
      else {
        stack.pop();
      }
    }
    stack.clear();
  }
}