Custom action library, initial version

installer/src/installer-lib/DLL.h

Index: installer/src/installer-lib/DLL.h
===================================================================
new file mode 100644
--- /dev/null
+++ b/installer/src/installer-lib/DLL.h
@@ -0,0 +1,65 @@
+/**
+ * \file DLL.h The DLL as a Windows system module.
+ */
+
+#ifndef DLL_H
+#define DLL_H
+
+#include <memory>
+#include <string>
+
+#include "windows.h"
+
+/**
+ * Singleton representing the DLL module. This class is the source of the file name for the custom action library, used in logging.
+ * The choice to use a singleton reflects the design of the Windows API, which treats the module handle as a global for the DLL instance,
+ * only appearing during the calls that manage the lifetime of the DLL.
+ */
+class DLL_Module
+{
+public:
+  /**
+   * Accessor function for the singleton.
+   */
+  static DLL_Module & module();
+
+  /**
+   * Hook function to call on DLL attach.
+   */
+  static void attach( HINSTANCE handle );
+
+  /**
+   * Hook function to call on DLL detach.
+   */
+  static void detach();
+
+  /**
+   * Textual name of the DLL as an OS module.
+   */
+  std::wstring name();
+
+private:
+  /**
+   * The singleton value.
+   */
+  static std::shared_ptr< DLL_Module > singleton;
+
+  /**
+   * Private constructor ensures use of accessor function only.
+   */
+  DLL_Module( HINSTANCE handle );
+
+  /**
+   * Windows handle for the instance of the DLL.
+   */
+  HINSTANCE handle;
+
+  /**
+   * The text name of the module.
+   *
+   * Implemented as a smart pointer for deferred evaluation of the system call to get the module name.
+   */
+  std::shared_ptr< std::wstring > _name;
+};
+
+#endif