added sqlite db backend progress

include/matador/sql/backend_provider.hpp

@@ -3,29 +3,39 @@
 
 #include "matador/utils/library.hpp"
 
+#include <memory>
 #include <string>
 #include <unordered_map>
 
 namespace matador::sql {
 
 class connection_impl;
+struct connection_info;
 class dialect;
 
 class backend_provider
 {
-public:
-  explicit backend_provider(std::string backends_path);
+private:
+  backend_provider();
 
-  connection_impl* create_connection(const std::string &connection_type);
+public:
+  static backend_provider& instance();
+
+  connection_impl* create_connection(const std::string &connection_type, const connection_info &info);
+  void destroy_connection(const std::string &connection_type, connection_impl *c);
   const dialect& connection_dialect(const std::string &connection_type);
 
 private:
   struct backend_context {
     backend_context(const std::string &connection_type,
                     const std::string &backends_path);
+    backend_context(const backend_context&) = delete;
+    backend_context& operator=(const backend_context&) = delete;
+    backend_context(backend_context&&) noexcept = default;
+    backend_context& operator=(backend_context&&) noexcept = default;
     ~backend_context();
 
-    typedef connection_impl*(*create_func)();
+    typedef connection_impl*(*create_func)(const connection_info&);
     typedef void (*destroy_func)(connection_impl*);
     typedef const dialect*(*dialect_func)();
 
@@ -35,7 +45,7 @@ private:
     utils::library lib;
   };
 private:
-  using backends_t = std::unordered_map<std::string, backend_context>;
+  using backends_t = std::unordered_map<std::string, std::unique_ptr<backend_context>>;
   backends_t backends_;
   std::string backends_path_;
 };