Added a option to set the style of the selection

include/ftxui/dom/selection.hpp

@@ -5,15 +5,33 @@
 #ifndef FTXUI_DOM_SELECTION_HPP
 #define FTXUI_DOM_SELECTION_HPP
 
+#include <functional>
+
 #include "ftxui/screen/box.hpp"  // for Box
+#include "ftxui/screen/pixel.hpp"  // for Pixel
 
 namespace ftxui {
 
+/// @brief Option for the selection of content.
+/// @ingroup component
+struct SelectionOption {
+  /// @brief Selection is simply inverted:
+  static SelectionOption Simple();
+
+  // Style:
+  std::function<void(Pixel& pixel)> transform ;
+
+  // Observers:
+  /// Called when the selection changed.
+  std::function<void()> on_change = [] {};
+};
+
 /// @brief Represent a selection in the terminal.
 class Selection {
  public:
-  Selection(int start_x, int start_y, int end_x, int end_y);
+  Selection(int start_x, int start_y, int end_x, int end_y, SelectionOption option = SelectionOption::Simple());
   const Box& GetBox() const;
+  const SelectionOption& GetOption() const;
 
   Selection SaturateHorizontal(Box box);
   Selection SaturateVertical(Box box);
@@ -25,6 +43,7 @@ class Selection {
   const int end_x_;
   const int end_y_;
   const Box box_;
+  const SelectionOption option;
 };
 
 }  // namespace ftxui