--- /dev/null
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\DependencyInjection\Compiler;
+
+use Symfony\Component\DependencyInjection\Exception\InvalidArgumentException;
+
+/**
+ * This is a directed graph of your services.
+ *
+ * This information can be used by your compiler passes instead of collecting
+ * it themselves which improves performance quite a lot.
+ *
+ * @author Johannes M. Schmitt <schmittjoh@gmail.com>
+ */
+class ServiceReferenceGraph
+{
+ /**
+ * @var ServiceReferenceGraphNode[]
+ */
+ private $nodes = array();
+
+ /**
+ * Checks if the graph has a specific node.
+ *
+ * @param string $id Id to check
+ *
+ * @return bool
+ */
+ public function hasNode($id)
+ {
+ return isset($this->nodes[$id]);
+ }
+
+ /**
+ * Gets a node by identifier.
+ *
+ * @param string $id The id to retrieve
+ *
+ * @return ServiceReferenceGraphNode
+ *
+ * @throws InvalidArgumentException if no node matches the supplied identifier
+ */
+ public function getNode($id)
+ {
+ if (!isset($this->nodes[$id])) {
+ throw new InvalidArgumentException(sprintf('There is no node with id "%s".', $id));
+ }
+
+ return $this->nodes[$id];
+ }
+
+ /**
+ * Returns all nodes.
+ *
+ * @return ServiceReferenceGraphNode[]
+ */
+ public function getNodes()
+ {
+ return $this->nodes;
+ }
+
+ /**
+ * Clears all nodes.
+ */
+ public function clear()
+ {
+ $this->nodes = array();
+ }
+
+ /**
+ * Connects 2 nodes together in the Graph.
+ *
+ * @param string $sourceId
+ * @param string $sourceValue
+ * @param string $destId
+ * @param string $destValue
+ * @param string $reference
+ */
+ public function connect($sourceId, $sourceValue, $destId, $destValue = null, $reference = null)
+ {
+ $sourceNode = $this->createNode($sourceId, $sourceValue);
+ $destNode = $this->createNode($destId, $destValue);
+ $edge = new ServiceReferenceGraphEdge($sourceNode, $destNode, $reference);
+
+ $sourceNode->addOutEdge($edge);
+ $destNode->addInEdge($edge);
+ }
+
+ /**
+ * Creates a graph node.
+ *
+ * @param string $id
+ * @param string $value
+ *
+ * @return ServiceReferenceGraphNode
+ */
+ private function createNode($id, $value)
+ {
+ if (isset($this->nodes[$id]) && $this->nodes[$id]->getValue() === $value) {
+ return $this->nodes[$id];
+ }
+
+ return $this->nodes[$id] = new ServiceReferenceGraphNode($id, $value);
+ }
+}