// Tarjan's strongly connected components algorithm.
// https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
protected override IList <CircularDependency <T> > FindStronglyConnectedComponents()
{
int index = 0;
var stack = new Stack <T>();
var indexLookup = new Dictionary <T, int>();
var lowLinkLookup = new Dictionary <T, int>();
var circularDependencies = new List <CircularDependency <T> >();
foreach (T id in EdgeIds)
{
indexLookup.Add(id, -1);
lowLinkLookup.Add(id, -1);
}
void StrongConnect(T referenceId)
{
indexLookup[referenceId] = index;
lowLinkLookup[referenceId] = index;
index++;
stack.Push(referenceId);
Edge <T, TActivity> referenceEdge = EdgeLookup[referenceId];
Node <T, TEvent> tailNode = EdgeTailNodeLookup[referenceId];
if (tailNode.NodeType == NodeType.End || tailNode.NodeType == NodeType.Normal)
{
foreach (T incomingEdgeId in tailNode.IncomingEdges)
{
if (indexLookup[incomingEdgeId] < 0)
{
StrongConnect(incomingEdgeId);
lowLinkLookup[referenceId] = Math.Min(lowLinkLookup[referenceId], lowLinkLookup[incomingEdgeId]);
}
else if (stack.Contains(incomingEdgeId))
{
lowLinkLookup[referenceId] = Math.Min(lowLinkLookup[referenceId], indexLookup[incomingEdgeId]);
}
}
}
if (lowLinkLookup[referenceId] == indexLookup[referenceId])
{
var circularDependency = new CircularDependency <T>(Enumerable.Empty <T>());
T currentId;
do
{
currentId = stack.Pop();
Edge <T, TActivity> currentEdge = EdgeLookup[currentId];
if (!currentEdge.Content.CanBeRemoved)
{
circularDependency.Dependencies.Add(currentId);
}
} while (!referenceId.Equals(currentId));
circularDependencies.Add(circularDependency);
}
}
foreach (T id in EdgeIds)
{
if (indexLookup[id] < 0)
{
StrongConnect(id);
}
}
return(circularDependencies);
}
