// ----------------------------------------------------------------------------
// -                        Open3D: www.open3d.org                            -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2023 www.open3d.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------

#include "Widget.h"

#include <imgui.h>
#include <imgui_internal.h>

#include "open3d/visualization/gui/Color.h"
#include "open3d/visualization/gui/Events.h"

namespace open3d {
namespace visualization {
namespace gui {

// This should not be Color(0, 0, 0, 0), since transparent is a valid and
// common background color to want.
static const Color DEFAULT_BGCOLOR(0.001f, 0.001f, 0.001f, 0.0f);

struct Widget::Impl {
    Rect frame_;
    Color bg_color_ = DEFAULT_BGCOLOR;
    std::vector<std::shared_ptr<Widget>> children_;
    std::string tooltip_;
    bool is_visible_ = true;
    bool is_enabled_ = true;
    bool pop_disabled_flags_at_end_of_draw_ = false;
};

Widget::Widget() : impl_(new Widget::Impl()) {}

Widget::Widget(const std::vector<std::shared_ptr<Widget>>& children)
    : impl_(new Widget::Impl()) {
    impl_->children_ = children;
}

Widget::~Widget() {}

void Widget::AddChild(std::shared_ptr<Widget> child) {
    impl_->children_.push_back(child);
}

const std::vector<std::shared_ptr<Widget>> Widget::GetChildren() const {
    return impl_->children_;
}

const Rect& Widget::GetFrame() const { return impl_->frame_; }

void Widget::SetFrame(const Rect& f) { impl_->frame_ = f; }

const Color& Widget::GetBackgroundColor() const { return impl_->bg_color_; }

bool Widget::IsDefaultBackgroundColor() const {
    return (impl_->bg_color_ == DEFAULT_BGCOLOR);
}

void Widget::SetBackgroundColor(const Color& color) {
    impl_->bg_color_ = color;
}

bool Widget::IsVisible() const { return impl_->is_visible_; }

void Widget::SetVisible(bool vis) { impl_->is_visible_ = vis; }

bool Widget::IsEnabled() const { return impl_->is_enabled_; }

void Widget::SetEnabled(bool enabled) { impl_->is_enabled_ = enabled; }

void Widget::SetTooltip(const char* text) { impl_->tooltip_ = text; }

const char* Widget::GetTooltip() const { return impl_->tooltip_.c_str(); }

Size Widget::CalcPreferredSize(const LayoutContext&,
                               const Constraints& constraints) const {
    return Size(DIM_GROW, DIM_GROW);
}

Size Widget::CalcMinimumSize(const LayoutContext& context) const {
    return Size(0, 0);
}

void Widget::Layout(const LayoutContext& context) {
    for (auto& child : impl_->children_) {
        child->Layout(context);
    }
}

Widget::DrawResult Widget::Draw(const DrawContext& context) {
    if (!impl_->is_visible_) {
        return DrawResult::NONE;
    }

    DrawResult result = DrawResult::NONE;
    for (auto& child : impl_->children_) {
        if (child->IsVisible()) {
            auto r = child->Draw(context);
            // The mouse can only be over one item, so there should never
            // be multiple items returning non-NONE.
            if (r > result) {
                result = r;
            }
        }
    }
    return result;
}

void Widget::DrawImGuiPushEnabledState() {
    if (!IsEnabled()) {
        ImGui::PushItemFlag(ImGuiItemFlags_Disabled, true);
        ImGui::PushStyleVar(ImGuiStyleVar_Alpha,
                            ImGui::GetStyle().Alpha * 0.5f);
    }
    // As an immediate mode GUI, responses to UI events can happen
    // during a draw. Store what the disabled flag was at the
    // beginning of the draw, so we know how many things to pop
    // to clean up. (An example of when this is needed is a reset
    // button: after clicking it, it will probably disable itself
    // since there is nothing to reset now)
    impl_->pop_disabled_flags_at_end_of_draw_ = !IsEnabled();
}

void Widget::DrawImGuiPopEnabledState() {
    if (impl_->pop_disabled_flags_at_end_of_draw_) {
        ImGui::PopStyleVar();
        ImGui::PopItemFlag();
    }
}

void Widget::DrawImGuiTooltip() {
    if (!impl_->tooltip_.empty() && IsEnabled() &&
        (ImGui::IsItemActive() || ImGui::IsItemHovered())) {
        // The default margins of the tooltips are 0 and rather ugly. It turns
        // out that tooltips are implemented as ImGui Windows, so we need to
        // push WindowPadding, not FramePadding as you might expect.
        // Note: using Push/PopStyleVar() causes problems because we might
        //       already done a Push of the WindowPadding above, and the pushes
        //       seem to get coalesced, so when we pop here, it effectively pops
        //       in calling code, which then crashes because there are too many
        //       pops.
        float border_radius = std::round(0.2f * ImGui::GetFont()->FontSize);
        float margin = 0.25f * ImGui::GetFont()->FontSize;
        float old_radius = ImGui::GetStyle().WindowRounding;
        ImVec2 old_padding = ImGui::GetStyle().WindowPadding;
        ImGui::GetStyle().WindowPadding = ImVec2(2.0f * margin, margin);
        ImGui::GetStyle().WindowRounding = border_radius;

        ImGui::BeginTooltip();
        ImGui::Text("%s", impl_->tooltip_.c_str());
        ImGui::EndTooltip();

        // Pop
        ImGui::GetStyle().WindowPadding = old_padding;
        ImGui::GetStyle().WindowRounding = old_radius;
    }
}

Widget::EventResult Widget::Mouse(const MouseEvent& e) {
    if (!impl_->is_visible_) {
        return EventResult::IGNORED;
    }

    // Iterate backwards so that we send mouse events from the top down.
    for (auto it = impl_->children_.rbegin(); it != impl_->children_.rend();
         ++it) {
        if ((*it)->GetFrame().Contains(e.x, e.y)) {
            auto result = (*it)->Mouse(e);
            if (result != EventResult::IGNORED) {
                return result;
            }
        }
    }

    // If we get here then this event is either for an ImGUI widget,
    // in which case we should not process this event further (ImGUI will
    // do it later), or this is an empty widget like a panel or something,
    // which eats events (it doesn't handle the event [e.g. button down]
    // and nor should anything else).
    return EventResult::DISCARD;
}

Widget::EventResult Widget::Key(const KeyEvent& e) {
    return EventResult::DISCARD;
}

Widget::DrawResult Widget::Tick(const TickEvent& e) {
    auto result = DrawResult::NONE;
    for (auto child : impl_->children_) {
        if (child->Tick(e) == DrawResult::REDRAW) {
            result = DrawResult::REDRAW;
        }
    }
    return result;
}

}  // namespace gui
}  // namespace visualization
}  // namespace open3d