Add ecs ComponentListener

- Add ecs ComponentListener which listens to Component addition and
  removal
- Add RefCounter class used to keep track of moves and copies

CopiumEngine/src/copium/util/RefCounter.cpp

@@ -0,0 +1,72 @@
+#include "copium/util/RefCounter.h"
+
+#include "copium/util/Common.h"
+
+namespace Copium
+{
+  RefCounter::RefCounter()
+    : refCounter{new int{1}}
+  {}
+
+  RefCounter::~RefCounter()
+  {
+    if (Valid())
+    {
+      (*refCounter)--;
+      if (*refCounter == 0)
+      {
+        delete refCounter;
+        refCounter = nullptr;
+      }
+    }
+  }
+
+  RefCounter::RefCounter(RefCounter&& rhs)
+    : refCounter(rhs.refCounter)
+  {
+    CP_ASSERT(Valid(), "RefCounter : Moving a deleted RefCounter");
+    rhs.refCounter = nullptr;
+  }
+
+  RefCounter::RefCounter(const RefCounter& rhs)
+    : refCounter{rhs.refCounter}
+  {
+    CP_ASSERT(Valid(), "RefCounter : Copying a deleted RefCounter");
+    (*refCounter)++;
+  }
+
+  RefCounter& RefCounter::operator=(RefCounter&& rhs)
+  {
+    CP_ASSERT(Valid(), "operator= : Moving a deleted RefCounter");
+
+    refCounter = rhs.refCounter;
+    rhs.refCounter = nullptr;
+    return *this;
+  }
+
+  RefCounter& RefCounter::operator=(const RefCounter& rhs)
+  {
+    CP_ASSERT(Valid(), "operator= : Copying a deleted RefCounter");
+
+    refCounter = rhs.refCounter;
+    (*refCounter)++;
+    return *this;
+  }
+
+  bool RefCounter::Valid() const
+  {
+    return refCounter != nullptr;
+  }
+
+  bool RefCounter::LastRef() const
+  {
+    return Valid() && *refCounter == 1;
+  }
+
+  int RefCounter::Counter() const
+  {
+    CP_ASSERT(Valid(), "Counter : referencing a deleted RefCounter");
+
+    return *refCounter;
+  }
+}