Check footage in use before deleteing

Initial very hacky implementation that checks if the footgae is in
use before deleting it and makes sure all refernences to it are
properly cleaned up.

Also added IsMedia() function to Node to simplify things a bit.

app/widget/projectexplorer/projectexplorer.cpp

@@ -558,6 +558,57 @@ void ProjectExplorer::DeleteSelected()
       }
     }
 
+    if (item_ptr->type() == Item::kFootage) {
+      // Get all sequences
+      QList<ItemPtr> sequences =  model_.project()->get_items_of_type(Item::kSequence);
+
+      // If no sequences exist we don't need to do anything clever here
+      if (!sequences.isEmpty()) {
+        // Footage can contain multiple streams, all of which need to be dealt with
+        foreach (StreamPtr stream, static_cast<Footage*>(item_ptr.get())->streams()) {
+
+          // Check each sequence to see if it contains the footage in question
+          foreach (ItemPtr seq, sequences) {
+
+            Sequence* s = static_cast<Sequence*>(seq.get());
+
+            // Loop through nodes to find our Footage node
+            foreach (Node* node, s->nodes()) {
+
+              // Check if node is of the right type
+              if (node->IsMedia() && static_cast<MediaInput*>(node)->type() == stream.get()->type()) {
+                // Check the streams are the same
+                if (static_cast<MediaInput*>(node)->footage() == stream) {
+                  // Loop through nodes and set any that point to the Footage node to null
+                  foreach (Node* check_node, s->nodes()) {
+                    // Skip itself
+                    if (check_node == node) {
+                      continue;
+                    }
+                    if (check_node->GetImmediateDependencies().contains(node)) {
+                      QList<NodeInput*> inputs = check_node->GetInputsIncludingArrays();
+
+                      foreach (NodeInput* input, inputs) {
+                        foreach (NodeEdgePtr edge, input->edges()) {
+                          Node* connected = edge->output()->parentNode();
+
+                          if (connected == node) {
+                            input->DisconnectEdge(edge);
+                          }
+                        }
+                      }
+                    }
+                  }
+                  static_cast<MediaInput*>(node)->SetFootage(nullptr);
+                  break;
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+
     new ProjectViewModel::RemoveItemCommand(&model_, item_ptr, command);
   }