Skeleton for TrivialGraphFormat (TGF) exporter

Author: clue

src/TrivialGraphFormat.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace Fhaculty\Graph\Exporter;
+
+use Fhaculty\Graph\Edge\Directed;
+use Fhaculty\Graph\Edge\Base as Edge;
+use Fhaculty\Graph\Vertex;
+use Fhaculty\Graph\Graph;
+
+/**
+ *
+ * @author clue
+ * @link http://en.wikipedia.org/wiki/Trivial_Graph_Format
+ */
+class TrivialGraphFormat implements ExporterInterface
+{
+    const EOL = PHP_EOL;
+
+    public function getOutput(Graph $graph)
+    {
+        $output = '';
+
+        // build an array to map vertex IDs (which may contain complex strings) to temporary numeric IDs for output
+        $tid = 1;
+        $tids = array();
+
+        foreach ($graph->getVertices() as $vid => $vertex) {
+            $output .= $tid . ' ' . $this->getVertexLabel($vertex) . self::EOL;
+            $tids[$vid] = $tid++;
+        }
+
+        // end of vertex list, start of edge list
+        $output .= '#' . self::EOL;
+
+        foreach ($graph->getEdges() as $edge) {
+            $ids = $edge->getVerticesId();
+            $a = $tids[$ids[0]];
+            $b = $tids[$ids[1]];
+
+            $label = $this->getEdgeLabel($edge);
+            if ($label !== '') {
+                $label = ' ' . $label;
+            }
+
+            $output .= $a . ' ' . $b . $label . self::EOL;
+
+            // this is not a directed edge => also add back-edge with same label
+            if (!($edge instanceof Directed)) {
+                $output .= $b . ' ' . $a . $label . self::EOL;
+            }
+        }
+        return $output;
+    }
+
+    protected function getVertexLabel(Vertex $vertex)
+    {
+        // TODO: dump additional vertex attributes, such as group, balance, etc.
+        return $vertex->getId();
+    }
+
+    protected function getEdgeLabel(Edge $edge)
+    {
+        // TODO: dump additional edge attributes, such as flow, capacity, weight, etc.
+        return '';
+    }
+}