src/ftxui/component/dropdown.cpp

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// Copyright 2021 Arthur Sonzogni. All rights reserved.
// Use of this source code is governed by the MIT license that can be found in
// the LICENSE file.
#include <ftxui/component/event.hpp>
#include <functional>  // for function, less
#include <string>      // for string
 
#include <utility>
#include "ftxui/component/component.hpp"  // for Maybe, Checkbox, Make, Radiobox, Vertical, Dropdown
#include "ftxui/component/component_base.hpp"  // for Component, ComponentBase
#include "ftxui/component/component_options.hpp"  // for CheckboxOption, EntryState
#include "ftxui/dom/elements.hpp"  // for operator|, Element, border, filler, operator|=, separator, size, text, vbox, frame, vscroll_indicator, hbox, HEIGHT, LESS_THAN, bold, inverted
#include "ftxui/screen/util.hpp"   // for clamp
#include "ftxui/util/ref.hpp"      // for ConstStringListRef
 
namespace ftxui {
 
namespace {
// Whether `ref` points to a variable owned by the caller, as opposed to a value
// stored inside `ref` itself.
bool IsExternal(const Ref<bool>& ref) {
  const std::less<const void*> less;
  const void* address = &*ref;
  return less(address, &ref) || !less(address, &ref + 1);
}
}  // namespace
 
/// @brief A dropdown menu.
/// @ingroup component
/// @param entries The list of entries to display.
/// @param selected The index of the selected entry.
Component Dropdown(ConstStringListRef entries, int* selected) {
  DropdownOption option;
  option.radiobox.entries = std::move(entries);
  option.radiobox.selected = selected;
  return Dropdown(option);
}
 
/// @brief A dropdown menu.
/// @ingroup component
/// @param option The options for the dropdown.
// NOLINTNEXTLINE
Component Dropdown(DropdownOption option) {
  class Impl : public ComponentBase, public DropdownOption {
   public:
    explicit Impl(DropdownOption option) : DropdownOption(std::move(option)) {
      FillDefault();
      checkbox_ = Checkbox(checkbox);
      radiobox_ = Radiobox(radiobox);
 
      container_ = Container::Vertical({
          checkbox_,
          Maybe(radiobox_, checkbox.checked),
      });
      Add(container_);
    }
 
    Element OnRender() override {
      selected_ =
          util::clamp(radiobox.selected(), 0, int(radiobox.entries.size()) - 1);
      selected_ = util::clamp(selected_(), 0, int(radiobox.entries.size()) - 1);
 
      if (selected_() >= 0 && selected_() < int(radiobox.entries.size())) {
        title_ = radiobox.entries[selected_()];
      }
 
      // Close the dropdown when another component takes the focus. This can
      // happen without this dropdown receiving any event, e.g. when the user
      // clicks on a sibling dropdown. Move the inner focus back to the
      // checkbox without stealing the focus from the other component.
      if (open() && !Focused()) {
        container_->SetActiveChild(checkbox_);
        *open = false;
      }
 
      return transform(*open, checkbox_->Render(), radiobox_->Render());
    }
 
    // Switch focus in between the checkbox and the radiobox when selecting it.
    bool OnEvent(ftxui::Event event) override {
      const bool open_old = open();
      const int selected_old = selected_();
      bool handled = ComponentBase::OnEvent(event);
 
      // Transfer focus to the radiobox when the dropdown is opened.
      if (!open_old && open()) {
        radiobox_->TakeFocus();
      }
 
      // Auto-close the dropdown when the user selects an item, even if the item
      // it the same as the previous one.
      if (open_old && open()) {
        const bool should_close =
            (selected_() != selected_old) ||     //
            (event == Event::Return) ||          //
            (event == Event::Character(' ')) ||  //
            (event == Event::Escape) ||          //
            (event.is_mouse() && event.mouse().button == Mouse::Left &&
             event.mouse().motion == Mouse::Pressed);
 
        if (should_close) {
          checkbox_->TakeFocus();
          *open = false;
          handled = true;
        }
      }
 
      return handled;
    }
 
    void FillDefault() {
      // Both `open` and `checkbox.checked` can hold the open state. Prefer the
      // one bound to an external variable, then the one set to non-default.
      if (!IsExternal(open) &&
          (IsExternal(checkbox.checked) || checkbox.checked())) {
        open = checkbox.checked;
      }
      selected_ = radiobox.selected;
      checkbox.checked = &*open;
      radiobox.selected = &*selected_;
      checkbox.label = &title_;
 
      if (!checkbox.transform) {
        checkbox.transform = [](const EntryState& s) {
          auto prefix = text(s.state ? "↓ " : "→ ");  // NOLINT
          auto t = text(s.label);
          if (s.active) {
            t |= bold;
          }
          if (s.focused) {
            t |= inverted;
          }
          return hbox({prefix, t});
        };
      }
 
      if (!transform) {
        transform = [](bool is_open, Element checkbox_element,
                       Element radiobox_element) {
          if (is_open) {
            const int max_height = 12;
            return vbox({
                       std::move(checkbox_element),
                       separator(),
                       std::move(radiobox_element) | vscroll_indicator | frame |
                           size(HEIGHT, LESS_THAN, max_height),
                   }) |
                   border;
          }
          return vbox({std::move(checkbox_element), filler()}) | border;
        };
      }
    }
 
   private:
    Ref<int> selected_;
    Component container_;
    Component checkbox_;
    Component radiobox_;
    std::string title_;
  };
 
  return Make<Impl>(option);
}
 
}  // namespace ftxui