Feature: the Modal component. (#418)

src/ftxui/component/modal.cpp

@@ -0,0 +1,66 @@
+#include <ftxui/component/event.hpp>  // for Event
+#include <ftxui/dom/elements.hpp>  // for operator|, Element, center, clear_under, dbox
+#include <memory>                  // for __shared_ptr_access, shared_ptr
+#include <utility>                 // for move
+
+#include "ftxui/component/component.hpp"  // for Make, Tab, ComponentDecorator, Modal
+#include "ftxui/component/component_base.hpp"  // for Component, ComponentBase
+
+namespace ftxui {
+
+// Add a |modal| window on top of the |main| component. It is shown one on the
+// top of the other when |show_modal| is true.
+/// @ingroup component
+// NOLINTNEXTLINE
+Component Modal(Component main, Component modal, const bool* show_modal) {
+  class Impl : public ComponentBase {
+   public:
+    explicit Impl(Component main, Component modal, const bool* show_modal)
+        : main_(std::move(main)),
+          modal_(std::move(modal)),
+          show_modal_(show_modal) {
+      selector_ = *show_modal_;
+      Add(Container::Tab({main_, modal_}, &selector_));
+    }
+
+   private:
+    Element Render() override {
+      selector_ = *show_modal_;
+      auto document = main_->Render();
+      if (*show_modal_) {
+        document = dbox({
+            document,
+            modal_->Render() | clear_under | center,
+        });
+      }
+      return document;
+    }
+
+    bool OnEvent(Event event) override {
+      selector_ = *show_modal_;
+      return ComponentBase::OnEvent(event);
+    }
+
+    Component main_;
+    Component modal_;
+    const bool* show_modal_;
+    int selector_ = 0;
+  };
+  return Make<Impl>(main, modal, show_modal);
+}
+
+// Decorate a component. Add a |modal| window on top of it. It is shown one on
+// the top of the other when |show_modal| is true.
+/// @ingroup component
+// NOLINTNEXTLINE
+ComponentDecorator Modal(Component modal, const bool* show_modal) {
+  return [modal, show_modal](Component main) {
+    return Modal(std::move(main), modal, show_modal);
+  };
+}
+
+}  // namespace ftxui
+
+// Copyright 2022 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.