timeline: reimplemented linking/unlinking functionality

app/node/block/block.cpp

@@ -202,20 +202,25 @@ void Block::LengthInputChanged()
   emit LengthChanged(length());
 }
 
-void Block::Link(Block *a, Block *b)
+bool Block::Link(Block *a, Block *b)
 {
   if (a == b || !a || !b) {
-    return;
+    return false;
   }
 
   // Prevent duplicate link entries (assume that we only need to check one clip since this should be the only function
   // that adds to the linked array)
-  if (a->linked_clips_.contains(b)) {
-    return;
+  if (Block::AreLinked(a, b)) {
+    return false;
   }
 
   a->linked_clips_.append(b);
   b->linked_clips_.append(a);
+
+  emit a->LinksChanged();
+  emit b->LinksChanged();
+
+  return true;
 }
 
 void Block::Link(const QList<Block*>& blocks)
@@ -227,14 +232,23 @@ void Block::Link(const QList<Block*>& blocks)
   }
 }
 
-void Block::Unlink(Block *a, Block *b)
+bool Block::Unlink(Block *a, Block *b)
 {
   if (a == b || !a || !b) {
-    return;
+    return false;
+  }
+
+  if (!Block::AreLinked(a, b)) {
+    return false;
   }
 
   a->linked_clips_.removeOne(b);
   b->linked_clips_.removeOne(a);
+
+  emit a->LinksChanged();
+  emit b->LinksChanged();
+
+  return true;
 }
 
 void Block::Unlink(const QList<Block *> &blocks)

app/node/block/block.h

@@ -76,9 +76,9 @@ public:
   QString block_name() const;
   void set_block_name(const QString& name);
 
-  static void Link(Block* a, Block* b);
+  static bool Link(Block* a, Block* b);
   static void Link(const QList<Block*>& blocks);
-  static void Unlink(Block* a, Block* b);
+  static bool Unlink(Block* a, Block* b);
   static void Unlink(const QList<Block*>& blocks);
   static bool AreLinked(Block* a, Block* b);
   const QVector<Block*>& linked_clips();
@@ -104,6 +104,8 @@ signals:
 
   void LengthChanged(const rational& length);
 
+  void LinksChanged();
+
 protected:
   rational SequenceToMediaTime(const rational& sequence_time) const;