/// TODO:
/// 显然的，原生 QComboBox 的下拉列表样式并不符合 Material Design
/// 规范，未来必须切换成自定义的组件，相关参考：
/// - https://m3.material.io/components/menus/guidelines
/// - https://api.flutter.dev/flutter/material/DropdownMenu-class.html

#pragma once
#include "dropdown-menu.hh"

#include "creeper-qt/utility/animation/animatable.hh"
#include "creeper-qt/utility/animation/state/pid.hh"
#include "creeper-qt/utility/animation/transition.hh"
#include "creeper-qt/utility/material-icon.hh"
#include "creeper-qt/utility/painter/helper.hh"

#include <qabstractitemview.h>
#include <qfontmetrics.h>

using namespace creeper::dropdown_menu::internal;

struct DropdownMenu::Impl {
public:
    explicit Impl(DropdownMenu& self) noexcept
        : animatable(self)
        , self { self } {
        {
            auto state            = std::make_shared<PidState<double>>();
            state->config.kp      = 20.0;
            state->config.ki      = 00.0;
            state->config.kd      = 00.0;
            state->config.epsilon = 1e-2;
            label_position        = make_transition(animatable, std::move(state));
        }

        set_measurements(Measurements {});
    }

    auto set_color_scheme(const ColorScheme& scheme) -> void {
        color_space.enabled.container        = scheme.surface_container_highest;
        color_space.enabled.label_text       = scheme.on_surface_variant;
        color_space.enabled.selected_text    = scheme.on_surface;
        color_space.enabled.leading_icon     = scheme.on_surface_variant;
        color_space.enabled.active_indicator = scheme.on_surface_variant;
        color_space.enabled.supporting_text  = scheme.on_surface_variant;
        color_space.enabled.input_text       = scheme.on_surface;
        color_space.enabled.caret            = scheme.primary;
        color_space.enabled.outline          = scheme.outline;

        color_space.disabled.container = scheme.on_surface;
        color_space.disabled.container.setAlphaF(0.04);
        color_space.disabled.label_text = scheme.on_surface;
        color_space.disabled.label_text.setAlphaF(0.38);
        color_space.disabled.selected_text = scheme.on_surface;
        color_space.disabled.selected_text.setAlphaF(0.38);
        color_space.disabled.leading_icon = scheme.on_surface;
        color_space.disabled.leading_icon.setAlphaF(0.38);
        color_space.disabled.supporting_text = scheme.on_surface;
        color_space.disabled.supporting_text.setAlphaF(0.38);
        color_space.disabled.input_text = scheme.on_surface;
        color_space.disabled.input_text.setAlphaF(0.38);
        color_space.disabled.active_indicator = scheme.on_surface;
        color_space.disabled.active_indicator.setAlphaF(0.38);
        color_space.disabled.outline = scheme.outline;
        color_space.disabled.outline.setAlphaF(0.38);

        color_space.focused.container        = scheme.surface_container_highest;
        color_space.focused.label_text       = scheme.primary;
        color_space.focused.selected_text    = scheme.on_surface;
        color_space.focused.leading_icon     = scheme.on_surface_variant;
        color_space.focused.input_text       = scheme.on_surface;
        color_space.focused.supporting_text  = scheme.on_surface_variant;
        color_space.focused.active_indicator = scheme.primary;
        color_space.focused.outline          = scheme.primary;

        color_space.error.container        = scheme.surface_container_highest;
        color_space.error.active_indicator = scheme.error;
        color_space.error.label_text       = scheme.error;
        color_space.error.selected_text    = scheme.on_surface;
        color_space.error.input_text       = scheme.on_surface;
        color_space.error.supporting_text  = scheme.error;
        color_space.error.leading_icon     = scheme.on_surface_variant;
        color_space.error.caret            = scheme.error;
        color_space.error.outline          = scheme.error;

        color_space.state_layer = scheme.on_surface;
        color_space.state_layer.setAlphaF(0.08);

        const auto& color = get_color_tokens();
        sync_basic_text_style(color.input_text, scheme.surface_container_highest, color.input_text,
            color_space.state_layer);
    }

    auto load_theme_manager(ThemeManager& manager) {
        manager.append_handler(&self,
            [this](const ThemeManager& manager) { set_color_scheme(manager.color_scheme()); });
    }

    auto set_label_text(const QString& text) { label_text = text; }

    auto set_leading_icon(const QString& code, const QString& font) {
        leading_icon_code          = code;
        leading_icon_font          = font;
        is_update_component_status = false;
    }

    auto set_measurements(const Measurements& measurements) -> void {
        this->measurements = measurements;
        self.setFixedHeight(measurements.container_height + measurements.standard_font_height);
        is_update_component_status = false;
    }

    auto paint_filled(QPaintEvent*) -> void {
        const auto widget_rect = self.rect();
        const auto color       = get_color_tokens();

        constexpr auto container_radius = 5;
        update_component_status();

        auto painter = QPainter { &self };

        // Draw container with fixed measurements height and vertically centered
        const auto container_rect = QRect { widget_rect.left(),
            widget_rect.top() + (widget_rect.height() - measurements.container_height) / 2,
            widget_rect.width(), measurements.container_height };

        {
            util::PainterHelper { painter }
                .set_render_hint(QPainter::Antialiasing)
                .rounded_rectangle(color.container, Qt::transparent, 0, container_rect,
                    container_radius, container_radius, 0, 0);
        }

        // Active indicator at container bottom
        {
            const auto p0 = container_rect.bottomLeft();
            const auto p1 = container_rect.bottomRight();
            painter.setBrush(Qt::NoBrush);
            painter.setPen({ color.active_indicator, filled_line_width() });
            painter.drawLine(p0, p1);
        }

        // Icon positioned relative to container_rect
        const auto rect_icon = QRectF {
            container_rect.right() - self.textMargins().right() - measurements.icon_rect_size * 1.,
            container_rect.top() + (container_rect.height() - measurements.icon_rect_size) * 0.5,
            1. * measurements.icon_rect_size,
            1. * measurements.icon_rect_size,
        };
        const auto icon_center = rect_icon.center();
        const bool is_active   = (self.view() && self.view()->isVisible());

        painter.save();
        painter.setBrush(Qt::NoBrush);
        painter.setPen(QPen { color.leading_icon });
        painter.setFont(leading_icon_font);
        painter.translate(icon_center);
        painter.rotate(is_active ? 180.0 : 0.0);
        painter.translate(-icon_center);
        painter.drawText(rect_icon, leading_icon_code, { Qt::AlignCenter });
        painter.restore();

        if (!label_text.isEmpty()) {
            const auto margins = self.textMargins();

            const auto center_label_y = container_rect.top()
                + (measurements.container_height - measurements.label_rect_size) / 2.0;

            const auto rect_center = QRectF {
                QPointF { static_cast<double>(margins.left()), center_label_y },
                QPointF(container_rect.right() - margins.right(),
                    center_label_y + measurements.label_rect_size),
            };

            const auto rect_top = QRectF {
                QPointF(margins.left(), container_rect.top() + measurements.col_padding),
                QPointF(container_rect.right() - margins.right(),
                    container_rect.top() + measurements.col_padding + measurements.label_rect_size),
            };

            const auto position     = self.currentText().isEmpty() ? *label_position : 1.;
            const auto label_rect   = animate::interpolate(rect_center, rect_top, position);
            const auto scale        = 1. - position * 0.25;
            const auto label_anchor = QPointF { label_rect.left(), label_rect.center().y() };

            painter.save();
            painter.translate(label_anchor);
            painter.scale(scale, scale);
            painter.translate(-label_anchor);
            painter.setBrush(Qt::NoBrush);
            painter.setPen(QPen { color.label_text });
            painter.setFont(standard_text_font);
            painter.setRenderHint(QPainter::Antialiasing);
            painter.drawText(label_rect, label_text, { Qt::AlignVCenter | Qt::AlignLeading });
            painter.restore();

            if (self.currentIndex() != -1) {
                painter.save();
                // Place selected text in the input area (below the floating label)
                const auto input_top =
                    container_rect.top() + measurements.col_padding + measurements.label_rect_size;
                const auto input_bottom = container_rect.bottom() - measurements.col_padding;
                const auto rect_center_selected = QRectF {
                    QPointF { static_cast<double>(margins.left()), static_cast<double>(input_top) },
                    QPointF(container_rect.right() - margins.right(),
                        static_cast<double>(input_bottom)),
                };

                // Draw selected text with input text color
                painter.setBrush(Qt::NoBrush);
                painter.setPen(QPen { color.selected_text });
                painter.setFont(standard_text_font);
                painter.setRenderHint(QPainter::Antialiasing);
                painter.drawText(
                    rect_center_selected, self.currentText(), Qt::AlignVCenter | Qt::AlignLeading);

                painter.restore();
            }
        } else if (label_text.isEmpty() && self.currentIndex() != -1) {
            const auto margins   = self.textMargins();
            const auto input_top = container_rect.top()
                + (container_rect.height() - measurements.input_rect_size) / 2.0;
            const auto input_bottom  = input_top + measurements.input_rect_size;
            const auto rect_selected = QRectF {
                QPointF(margins.left(), input_top),
                QPointF(container_rect.right() - margins.right(), input_bottom),
            };

            // Draw selected text
            painter.save();
            painter.setBrush(Qt::NoBrush);
            painter.setPen(QPen { color.selected_text });
            painter.setFont(standard_text_font);
            painter.setRenderHint(QPainter::Antialiasing);
            painter.drawText(
                rect_selected, self.currentText(), Qt::AlignVCenter | Qt::AlignLeading);
            painter.restore();
        }

        if (is_hovered) {
            util::PainterHelper { painter }
                .set_render_hint(QPainter::Antialiasing)
                .rounded_rectangle(color_space.state_layer, Qt::transparent, 0, container_rect,
                    container_radius, container_radius, 0, 0);
        }
    }

    auto enter_event(qt::EnterEvent*) {
        is_hovered = true;
        self.update();
    }

    auto leave_event(QEvent*) {
        is_hovered = false;
        self.update();
    }

    auto focus_in(QFocusEvent*) {
        is_focused = true;
        update_label_position();
        self.update();
    }

    auto focus_out(QFocusEvent*) {
        is_focused = false;
        update_label_position();
        self.update();
    }

    auto show_popup() {
        if (self.count() == 0) {
            return;
        }

        is_active = true;
        self.QComboBox::showPopup();
        update_label_position();
        self.update();
    }

    auto hide_popup() -> void {
        is_active = false;
        self.QComboBox::hidePopup();
        update_label_position();
        self.update();
    }

private:
    auto update_component_status() -> void {
        if (is_update_component_status) {
            return;
        }

        auto font = self.font();
        font.setPixelSize(measurements.standard_font_height);
        self.setFont(font);
        standard_text_font = self.font();
        standard_text_font.setPixelSize(measurements.standard_font_height);

        is_update_component_status = true;
    }

    auto update_label_position() -> void {
        if ((is_focused || is_active) && self.currentIndex() != -1) {
            label_position->transition_to(1.0);
        } else if (is_focused || is_active) {
            label_position->transition_to(1.0);
        } else {
            label_position->transition_to(0.0);
        }
    }

    auto sync_basic_text_style(const QColor& text, const QColor& background,
        const QColor& selection_text, const QColor& selection_background) -> void {

        constexpr auto to_rgba = [](const QColor& color) {
            return QStringLiteral("rgba(%1, %2, %3, %4)")
                .arg(color.red())
                .arg(color.green())
                .arg(color.blue())
                .arg(color.alpha());
        };

        constexpr auto kQComboBoxStyle = R"(
            QComboBox {
                border: none;
                border-radius: 5px;
                selection-color: %3;
                selection-background-color: %4;
            }
            QComboBox QAbstractItemView {
                border: none;
                border-radius: 3px;
                padding-top: 8px;
                padding-bottom: 8px;
                color: %1;
                background-color: %2;
            }
        )";

        self.setStyleSheet(QString { kQComboBoxStyle }
                .arg(to_rgba(text))
                .arg(to_rgba(background))
                .arg(to_rgba(selection_text))
                .arg(to_rgba(selection_background)));
    }

    auto get_color_tokens() const -> ColorSpace::Tokens const& {
        return is_disable ? color_space.disabled
            : is_error    ? color_space.error
            : is_active   ? color_space.focused
            : is_focused  ? color_space.focused
                          : color_space.enabled;
    }

    auto filled_line_width() const -> double { return 1.5; }

    static constexpr auto measure_text(
        const QFont& font, const QString& text, const QTextOption& options) {
        const auto fm   = QFontMetricsF(font);
        const auto size = fm.size(Qt::TextSingleLine, text);
        return size.width();
    }

private:
    Measurements measurements;
    ColorSpace color_space;

    bool is_disable = false;
    bool is_hovered = false;
    bool is_focused = false;
    bool is_error   = false;
    bool is_active  = false;

    bool is_update_component_status = false;

    QString label_text;
    QIcon leading_icon;
    QString leading_icon_code = material::icon::kArrowDropDown;
    QFont leading_icon_font   = material::round::font_1;

    QFont standard_text_font;

    Animatable animatable;
    std::unique_ptr<TransitionValue<PidState<double>>> label_position;

    DropdownMenu& self;
};