feat: add blocked() to NBA path finder. add documentation of feature

README.md

@@ -187,6 +187,47 @@ let pathFinder = aStar(graph, {
 });
 ```
 
+## blocked paths
+
+In scenarios where a path might be temporarily blocked between two nodes a `blocked()` function
+may be supplied to resolve blocked routes during path finding.
+
+For example, train routes with service disruptions could be modelled as follows:
+
+``` js
+let createGraph = require('ngraph.graph');
+let graph = createGraph();
+
+// Our graph has cities:
+graph.addNode('NYC');
+graph.addNode('Philadelphia');
+graph.addNode('Baltimore');
+graph.addNode('Pittsburgh');
+graph.addNode('Washington');
+
+// and railroads:
+graph.addLink('NYC', 'Philadelphia', { disruption: false });
+graph.addLink('Philadelphia', 'Baltimore', { disruption: true });
+graph.addLink('Philadelphia', 'Pittsburgh', { disruption: false });
+graph.addLink('Pittsburgh', 'Washington', { disruption: false });
+graph.addLink('Baltimore', 'Washington', { disruption: false });
+```
+
+While the Philadelphia to Baltimore route is facing a service disruption, the alternative 
+route to Washington is via Pittsburgh. The following is an example `blocked()` function implementation
+that may be supplied to yield this result:
+
+``` js
+let path = require('ngraph.path');
+
+let pathFinder = path.aStar(graph, {
+  blocked(fromNode, toNode, link) {
+    return link.data.disruption;
+  },
+});
+let result = pathFinder.find('NYC', 'Washington');
+```
+
 ## available finders
 
 The library implements a few A* based path finders:

a-star/a-greedy-star.js

@@ -27,6 +27,9 @@ module.exports.l1 = heuristics.l1;
  * @param {ngraph.graph} graph instance. See https://github.com/anvaka/ngraph.graph
  * 
  * @param {Object} options that configures search
+ * @param {Function(a, b, link)} options.blocked - a function that returns `true` if the link between 
+ * nodes `a` and `b` are blocked paths. This function is useful for temporarily blocking routes 
+ * while allowing the graph to be reused without rebuilding.
  * @param {Function(a, b)} options.heuristic - a function that returns estimated distance between
  * nodes `a` and `b`.  Defaults function returns 0, which makes this search equivalent to Dijkstra search.
  * @param {Function(a, b)} options.distance - a function that returns actual distance between two

a-star/a-star.js

@@ -23,6 +23,9 @@ module.exports.l1 = heuristics.l1;
  * 
  * @param {ngraph.graph} graph instance. See https://github.com/anvaka/ngraph.graph
  * @param {Object} options that configures search
+ * @param {Function(a, b, link)} options.blocked - a function that returns `true` if the link between 
+ * nodes `a` and `b` are blocked paths. This function is useful for temporarily blocking routes 
+ * while allowing the graph to be reused without rebuilding.
  * @param {Function(a, b)} options.heuristic - a function that returns estimated distance between
  * nodes `a` and `b`. This function should never overestimate actual distance between two
  * nodes (otherwise the found path will not be the shortest). Defaults function returns 0,

a-star/nba/index.js

@@ -22,6 +22,9 @@ module.exports.l1 = heuristics.l1;
  * 
  * @param {ngraph.graph} graph instance. See https://github.com/anvaka/ngraph.graph
  * @param {Object} options that configures search
+ * @param {Function(a, b, link)} options.blocked - a function that returns `true` if the link between 
+ * nodes `a` and `b` are blocked paths. This function is useful for temporarily blocking routes 
+ * while allowing the graph to be reused without rebuilding.
  * @param {Function(a, b)} options.heuristic - a function that returns estimated distance between
  * nodes `a` and `b`. This function should never overestimate actual distance between two
  * nodes (otherwise the found path will not be the shortest). Defaults function returns 0,
@@ -37,6 +40,9 @@ function nba(graph, options) {
   var oriented = options.oriented;
   var quitFast = options.quitFast;
 
+  var blocked = options.blocked;
+  if (!blocked) blocked = defaultSettings.blocked;
+
   var heuristic = options.heuristic;
   if (!heuristic) heuristic = defaultSettings.heuristic;
 
@@ -178,6 +184,8 @@ function nba(graph, options) {
 
       if (otherSearchState.closed) return;
 
+      if (blocked(cameFrom.node, otherNode, link)) return;
+
       var tentativeDistance = cameFrom.g1 + distance(cameFrom.node, otherNode, link);
 
       if (tentativeDistance < otherSearchState.g1) {
@@ -206,6 +214,8 @@ function nba(graph, options) {
 
       if (otherSearchState.closed) return;
 
+      if (blocked(cameFrom.node, otherNode, link)) return;
+
       var tentativeDistance = cameFrom.g2 + distance(cameFrom.node, otherNode, link);
 
       if (tentativeDistance < otherSearchState.g2) {

test/nba.js

@@ -24,6 +24,29 @@ test('it can find path', t => {
   t.end();
 });
 
+test('it can find path with blocked links', t => {
+  let graph = createGraph();
+
+  graph.addLink('a', 'b', {blocked: true});
+  graph.addLink('a', 'c', {blocked: false});
+  graph.addLink('c', 'd', {blocked: false});
+  graph.addLink('b', 'd', {blocked: false});
+
+
+  var pathFinder = nba(graph, {
+    blocked(a, b, link) {
+      return link.data.blocked;
+    }
+  });
+  let path = pathFinder.find('a', 'd');
+
+  t.equal(path[0].id, 'd', 'd is here');
+  t.equal(path[1].id, 'c', 'c is here');
+  t.equal(path[2].id, 'a', 'a is here');
+  t.end();
+});
+
+
 test('it can find directed path', t => {
   let graph = createGraph();