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/*
* Copyright 2008 The Closure Compiler Authors.
*
* 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.google.javascript.jscomp;
import com.google.common.base.Predicate;
import com.google.javascript.jscomp.graph.Annotation;
import com.google.javascript.jscomp.graph.DiGraph;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphEdge;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphNode;
/**
* See constructor, {@link #CheckPathsBetweenNodes(DiGraph,
* DiGraphNode, DiGraphNode, Predicate, Predicate)}, for a
* description of this algorithm.
*
* @param The node type.
* @param The edge type.
*/
public final class CheckPathsBetweenNodes {
private final Predicate nodePredicate;
private final Predicate> edgePredicate;
private final boolean inclusive;
// This algorithm works in two stages. First, the depth-first search (DFS)
// tree is calculated with A as the root. During when constructing the DFS
// tree, back edges are recorded. A back edge is a non-tree edge (X -> Y)
// where X is an descendant of Y in the DFS tree. The second step does a
// recursive traversal of the graph. Back edges are ignored during the
// recursive traversal, thus no cycles are encountered. Any recursive branch
// that encounters B without yet satisfying the predicate represents a path
// from the entry node to the exit without any nodes that satisfy the
// predicate.
//
// The implementation of discoverBackEdges follows the DFS-Visit algorithm in
// "Introduction to Algorithms" by Cormen, Leiseron, Rivest, and Stein, 2nd
// ed., on page 541. The calculation of back edges is described on page 546.
// A non-tree edge in the DFS that connects a node to one of its ancestors.
private static final Annotation BACK_EDGE = new Annotation() {};
private static final Annotation VISITED_EDGE = new Annotation() {};
// Not yet visited.
private static final Annotation WHITE = null;
// Being visited.
private static final Annotation GRAY = new Annotation() {};
// Finished visiting.
private static final Annotation BLACK = new Annotation() {};
private final DiGraph graph;
private final DiGraphNode start;
private final DiGraphNode end;
/**
* Given a graph G with nodes A and B, this algorithm determines if all paths
* from A to B contain at least one node satisfying a given predicate.
*
* Note that nodePredicate is not necessarily called for all nodes in G nor is
* edgePredicate called for all edges in G.
*
* @param graph Graph G to analyze.
* @param a The node A.
* @param b The node B.
* @param nodePredicate Predicate which at least one node on each path from an
* A node to B (inclusive) must match.
* @param edgePredicate Edges to consider as part of the graph. Edges in
* graph that don't match edgePredicate will be ignored.
* @param inclusive Includes node A and B in the test for the node predicate.
*/
CheckPathsBetweenNodes(DiGraph graph, DiGraphNode a,
DiGraphNode b, Predicate nodePredicate,
Predicate> edgePredicate, boolean inclusive) {
this.graph = graph;
this.start = a;
this.end = b;
this.nodePredicate = nodePredicate;
this.edgePredicate = edgePredicate;
this.inclusive = inclusive;
}
/**
* Inclusive check.
*/
public CheckPathsBetweenNodes(DiGraph graph, DiGraphNode a,
DiGraphNode b, Predicate nodePredicate,
Predicate> edgePredicate) {
this(graph, a, b, nodePredicate, edgePredicate, true);
}
/**
* @return true iff all paths contain at least one node that satisfy the
* predicate
*/
public boolean allPathsSatisfyPredicate() {
setUp();
boolean result = checkAllPathsWithoutBackEdges(start, end);
tearDown();
return result;
}
/**
* @return true iff some paths contain at least one node that satisfy the
* predicate
*/
public boolean somePathsSatisfyPredicate() {
setUp();
boolean result = checkSomePathsWithoutBackEdges(start, end);
tearDown();
return result;
}
private void setUp() {
graph.pushNodeAnnotations();
graph.pushEdgeAnnotations();
discoverBackEdges(this.start);
}
private void tearDown() {
graph.popNodeAnnotations();
graph.popEdgeAnnotations();
}
private void discoverBackEdges(DiGraphNode u) {
u.setAnnotation(GRAY);
for (DiGraphEdge e : u.getOutEdges()) {
if (ignoreEdge(e)) {
continue;
}
DiGraphNode v = e.getDestination();
if (v.getAnnotation() == WHITE) {
discoverBackEdges(v);
} else if (v.getAnnotation() == GRAY) {
e.setAnnotation(BACK_EDGE);
}
}
u.setAnnotation(BLACK);
}
private boolean ignoreEdge(DiGraphEdge e) {
return !edgePredicate.apply(e);
}
/**
* Verify that all non-looping paths from {@code a} to {@code b} pass
* through at least one node where {@code nodePredicate} is true.
*/
private boolean checkAllPathsWithoutBackEdges(DiGraphNode a,
DiGraphNode b) {
if (nodePredicate.apply(a.getValue()) &&
(inclusive || (a != start && a != end))) {
return true;
}
if (a == b) {
return false;
}
for (DiGraphEdge e : a.getOutEdges()) {
// Once we visited that edge once, we no longer need to
// re-visit it again.
if (e.getAnnotation() == VISITED_EDGE) {
continue;
}
e.setAnnotation(VISITED_EDGE);
if (ignoreEdge(e)) {
continue;
}
if (e.getAnnotation() == BACK_EDGE) {
continue;
}
DiGraphNode next = e.getDestination();
if (!checkAllPathsWithoutBackEdges(next, b)) {
return false;
}
}
return true;
}
/**
* Verify that some non-looping paths from {@code a} to {@code b} pass
* through at least one node where {@code nodePredicate} is true.
*/
private boolean checkSomePathsWithoutBackEdges(DiGraphNode a,
DiGraphNode b) {
if (nodePredicate.apply(a.getValue()) &&
(inclusive || (a != start && a != end))) {
return true;
}
if (a == b) {
return false;
}
for (DiGraphEdge e : a.getOutEdges()) {
// Once we visited that edge once, we no longer need to
// re-visit it again.
if (e.getAnnotation() == VISITED_EDGE) {
continue;
}
e.setAnnotation(VISITED_EDGE);
if (ignoreEdge(e)) {
continue;
}
if (e.getAnnotation() == BACK_EDGE) {
continue;
}
DiGraphNode next = e.getDestination();
if (checkSomePathsWithoutBackEdges(next, b)) {
return true;
}
}
return false;
}
}
