Move Graph::isSymmetric() helper to new Algorithm\Symmetric

CHANGELOG.md

@@ -11,6 +11,7 @@ you spot any mistakes.
 * BC break: Move `Graph::getDegree()`, `Graph::getDegreeMin()`, `Graph::getDegreeMax()`, `Graph::isRegular()` and `Graph::isBalanced()` to new `Algorithm\Degree` (#29)
 * BC break: Move `Graph::getBalance()` and `Graph::isBalancedFlow()` to new `Algorithm\Balance` (#30)
 * BC break: Move `Set::isDirected()` to new `Algorithm\Directed` (#34)
+* BC break: Move `Graph::isSymmetric()` to new `Algorithm\Symmetric` (#41)
 * BC break: Remove unneeded algorithm alias definitions to reduce complexity, improve testability and avoid tight coupling (#31)
   * `Graph::isConnected()` (=> `Algorithm\ConnectedComponents::isSingle()`)
   * `Graph::hasEulerianCycle()` (=> `Algorithm\Eulerian::hasCycle()`)

lib/Fhaculty/Graph/Algorithm/Symmetric.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Fhaculty\Graph\Algorithm;
+
+use Fhaculty\Graph\Edge\Directed as EdgeDirected;
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Vertex;
+
+/**
+ * Basic algorithms for working with symmetric digraphs
+ * 
+ * A directed graph is called symmetric if, for every arc that belongs to it,
+ * the corresponding reversed arc (antiparallel directed edge) also belongs to it.
+ * 
+ * @link http://en.wikipedia.org/wiki/Directed_graph#Classes_of_digraphs
+ */
+class Symmetric extends Base
+{
+    /**
+     * Graph to operate on
+     * 
+     * @var Graph
+     */
+    private $graph;
+
+    /**
+     * instantiate symmetric algorithm
+     * 
+     * @param Graph $graph Graph
+     */
+    public function __construct(Graph $graph)
+    {
+        $this->graph = $graph;
+    }
+
+    /**
+     * checks whether this graph is symmetric (for every edge a->b there's also an edge b->a)
+     *
+     * @return boolean
+     * @uses Graph::getEdges()
+     * @uses EdgeDirected::getVertexStart()
+     * @uses EdgeDirected::getVertedEnd()
+     * @uses Vertex::hasEdgeTo()
+     */
+    public function isSymmetric()
+    {
+        // check all edges
+        foreach ($this->graph->getEdges() as $edge) {
+            // only check directed edges (undirected ones are symmetric by definition)
+            if ($edge instanceof EdgeDirected) {
+                // check if end also has an edge to start
+                if (!$edge->getVertexEnd()->hasEdgeTo($edge->getVertexStart())) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+}

lib/Fhaculty/Graph/Graph.php

@@ -328,30 +328,6 @@ public function isTrivial()
         return (!$this->edges && count($this->vertices) === 1);
     }
 
-    /**
-     * checks whether this graph is symmetric (for every edge a->b there's also an edge b->a)
-     *
-     * @return boolean
-     * @uses EdgeDirected::getVertexStart()
-     * @uses EdgeDirected::getVertedEnd()
-     * @uses Vertex::hasEdgeTo()
-     */
-    public function isSymmetric()
-    {
-        // check all edges
-        foreach ($this->edges as $edge) {
-            // only check directed edges (undirected ones are symmetric by definition)
-            if ($edge instanceof EdgeDirected) {
-                // check if end also has an edge to start
-                if (!$edge->getVertexEnd()->hasEdgeTo($edge->getVertexStart())) {
-                    return false;
-                }
-            }
-        }
-
-        return true;
-    }
-
     /**
      * checks whether this graph has any parallel edges (aka multigraph)
      *

tests/Fhaculty/Graph/Algorithm/SymmetricTest.php

@@ -0,0 +1,61 @@
+<?php
+
+use Fhaculty\Graph\Algorithm\Symmetric as AlgorithmSymmetric;
+use Fhaculty\Graph\Graph;
+
+class SymmetricTest extends TestCase
+{
+    public function testGraphEmpty()
+    {
+        $graph = new Graph();
+
+        $alg = new AlgorithmSymmetric($graph);
+
+        $this->assertTrue($alg->isSymmetric());
+    }
+
+    public function testGraphIsolated()
+    {
+        $graph = new Graph();
+        $graph->createVertex(1);
+        $graph->createVertex(2);
+
+        $alg = new AlgorithmSymmetric($graph);
+
+        $this->assertTrue($alg->isSymmetric());
+    }
+
+    public function testGraphSingleArcIsNotSymmetricr()
+    {
+        // 1 -> 2
+        $graph = new Graph();
+        $graph->createVertex(1)->createEdgeTo($graph->createVertex(2));
+
+        $alg = new AlgorithmSymmetric($graph);
+
+        $this->assertFalse($alg->isSymmetric());
+    }
+
+    public function testGraphAntiparallelIsSymmetricr()
+    {
+        // 1 -> 2 -> 1
+        $graph = new Graph();
+        $graph->createVertex(1)->createEdgeTo($graph->createVertex(2));
+        $graph->getVertex(2)->createEdgeTo($graph->getVertex(1));
+
+        $alg = new AlgorithmSymmetric($graph);
+
+        $this->assertTrue($alg->isSymmetric());
+    }
+
+    public function testGraphSingleUndirectedIsSymmetricr()
+    {
+        // 1 -- 2
+        $graph = new Graph();
+        $graph->createVertex(1)->createEdge($graph->createVertex(2));
+
+        $alg = new AlgorithmSymmetric($graph);
+
+        $this->assertTrue($alg->isSymmetric());
+    }
+}