added sqlite connection class (progress)

include/matador/sql/backend_provider.hpp

@@ -0,0 +1,43 @@
+#ifndef QUERY_BACKEND_PROVIDER_HPP
+#define QUERY_BACKEND_PROVIDER_HPP
+
+#include "matador/utils/library.hpp"
+
+#include <string>
+#include <unordered_map>
+
+namespace matador::sql {
+
+class connection_impl;
+class dialect;
+
+class backend_provider
+{
+public:
+  explicit backend_provider(std::string backends_path);
+
+  connection_impl* create_connection(const std::string &connection_type);
+  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();
+
+    typedef connection_impl*(*create_func)();
+    typedef void (*destroy_func)(connection_impl*);
+    typedef const dialect*(*dialect_func)();
+
+    create_func create_connection{};
+    destroy_func destroy_connection{};
+    dialect_func get_dialect{};
+    utils::library lib;
+  };
+private:
+  using backends_t = std::unordered_map<std::string, backend_context>;
+  backends_t backends_;
+  std::string backends_path_;
+};
+}
+#endif //QUERY_BACKEND_PROVIDER_HPP