/// <summary>
/// Orders elements of a linearized directed graph in a dependency order, while preserving the original order
/// between elements with no dependencies.
/// </summary>
public static IEnumerable <T> Order <T>(
IEnumerable <T> itemsToOrder,
TopologicalDependencyFunction <T> dependencyFunction)
{
if (itemsToOrder == null)
{
throw new ArgumentNullException(nameof(itemsToOrder));
}
if (dependencyFunction == null)
{
throw new ArgumentNullException(nameof(dependencyFunction));
}
var itemsToOrderList = itemsToOrder.ToList();
if (itemsToOrderList.Count < 2)
{
return(itemsToOrder);
}
int itemsToOrderCount = itemsToOrderList.Count;
var graph = DependencyGraph <T> .TryCreate(itemsToOrderList, dependencyFunction, EqualityComparer <T> .Default);
if (graph == null)
{
return(itemsToOrder);
}
Restart:
for (int i = 0; i < itemsToOrderCount; ++i)
{
for (int j = 0; j < i; ++j)
{
if (graph.DoesXHaveDirectDependencyOnY(itemsToOrderList[j], itemsToOrderList[i]))
{
bool jDependsOnI = graph.DoesXHaveTransientDependencyOnY(itemsToOrderList[j], itemsToOrderList[i]);
bool iDependsOnJ = graph.DoesXHaveTransientDependencyOnY(itemsToOrderList[i], itemsToOrderList[j]);
bool circularDependency = jDependsOnI && iDependsOnJ;
if (!circularDependency)
{
var t = itemsToOrderList[i];
itemsToOrderList.RemoveAt(i);
itemsToOrderList.Insert(j, t);
goto Restart;
}
}
}
}
return(itemsToOrderList);
}
public static DependencyGraph <T> TryCreate(
IList <T> items,
TopologicalDependencyFunction <T> dependencyFunction,
IEqualityComparer <T> equalityComparer)
{
var graph = new DependencyGraph <T>(equalityComparer, items.Count);
bool hasDependencies = false;
for (int position = 0; position < items.Count; ++position)
{
var element = items[position];
if (!graph.Nodes.TryGetValue(element, out Node node))
{
node = new Node();
graph.Nodes.Add(element, node);
}
foreach (var anotherElement in items)
{
if (equalityComparer.Equals(element, anotherElement))
{
continue;
}
if (dependencyFunction(element, anotherElement))
{
node.Children.Add(anotherElement);
hasDependencies = true;
}
}
}
if (!hasDependencies)
{
return(null);
}
return(graph);
}
