#include <algorithm>  // for max
#include <memory>     // for make_shared, __shared_ptr_access
#include <string>     // for string
#include <utility>    // for move
#include <vector>     // for __alloc_traits<>::value_type

#include "ftxui/dom/elements.hpp"        // for Element, vscroll_indicator
#include "ftxui/dom/node.hpp"            // for Node, Elements
#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
#include "ftxui/dom/requirement.hpp"     // for Requirement
#include "ftxui/screen/box.hpp"          // for Box
#include "ftxui/screen/screen.hpp"       // for Screen, Pixel

namespace ftxui {

/// @brief Add a filter that will invert the foreground and the background
/// colors.
/// @ingroup dom
Element vscroll_indicator(Element child) {
  class Impl : public NodeDecorator {
    using NodeDecorator::NodeDecorator;

    void ComputeRequirement() override {
      NodeDecorator::ComputeRequirement();
      requirement_ = children_[0]->requirement();
      requirement_.min_x++;
    }

    void SetBox(Box box) override {
      box_ = box;
      box.x_max--;
      children_[0]->SetBox(box);
    }

    void Render(Screen& screen) final {
      NodeDecorator::Render(screen);

      const Box& stencil = screen.stencil;

      const int size_inner = box_.y_max - box_.y_min;
      if (size_inner <= 0) {
        return;
      }
      const int size_outter = stencil.y_max - stencil.y_min + 1;
      if (size_outter >= size_inner) {
        return;
      }

      int size = 2 * size_outter * size_outter / size_inner;
      size = std::max(size, 1);

      const int start_y =
          2 * stencil.y_min +  //
          2 * (stencil.y_min - box_.y_min) * size_outter / size_inner;

      const int x = stencil.x_max;
      for (int y = stencil.y_min; y <= stencil.y_max; ++y) {
        const int y_up = 2 * y + 0;
        const int y_down = 2 * y + 1;
        const bool up = (start_y <= y_up) && (y_up <= start_y + size);
        const bool down = (start_y <= y_down) && (y_down <= start_y + size);

        const char* c = up ? (down ? "┃" : "╹") : (down ? "╻" : " ");  // NOLINT
        screen.PixelAt(x, y) = Pixel();
        screen.PixelAt(x, y).character = c;
      }
    }
  };
  return std::make_shared<Impl>(std::move(child));
}

}  // namespace ftxui

// 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.