//! Display a dropdown list of selectable values.
use crate::core::alignment;
use crate::core::event::{self, Event};
use crate::core::keyboard;
use crate::core::layout;
use crate::core::mouse;
use crate::core::overlay;
use crate::core::renderer;
use crate::core::text::{self, Paragraph as _, Text};
use crate::core::touch;
use crate::core::widget::tree::{self, Tree};
use crate::core::{
    Background, Border, Clipboard, Color, Element, Layout, Length, Padding,
    Pixels, Point, Rectangle, Shell, Size, Theme, Vector, Widget,
};
use crate::overlay::menu::{self, Menu};

use std::borrow::Borrow;
use std::f32;

/// A widget for selecting a single value from a list of options.
#[allow(missing_debug_implementations)]
pub struct PickList<
    'a,
    T,
    L,
    V,
    Message,
    Theme = crate::Theme,
    Renderer = crate::Renderer,
> where
    T: ToString + PartialEq + Clone,
    L: Borrow<[T]> + 'a,
    V: Borrow<T> + 'a,
    Renderer: text::Renderer,
{
    on_select: Box<dyn Fn(T) -> Message + 'a>,
    on_open: Option<Message>,
    on_close: Option<Message>,
    options: L,
    placeholder: Option<String>,
    selected: Option<V>,
    width: Length,
    padding: Padding,
    text_size: Option<Pixels>,
    text_line_height: text::LineHeight,
    text_shaping: text::Shaping,
    font: Option<Renderer::Font>,
    handle: Handle<Renderer::Font>,
    style: Style<'a, Theme>,
}

impl<'a, T, L, V, Message, Theme, Renderer>
    PickList<'a, T, L, V, Message, Theme, Renderer>
where
    T: ToString + PartialEq + Clone,
    L: Borrow<[T]> + 'a,
    V: Borrow<T> + 'a,
    Message: Clone,
    Renderer: text::Renderer,
{
    /// Creates a new [`PickList`] with the given list of options, the current
    /// selected value, and the message to produce when an option is selected.
    pub fn new(
        options: L,
        selected: Option<V>,
        on_select: impl Fn(T) -> Message + 'a,
    ) -> Self
    where
        Theme: DefaultStyle,
    {
        Self {
            on_select: Box::new(on_select),
            on_open: None,
            on_close: None,
            options,
            placeholder: None,
            selected,
            width: Length::Shrink,
            padding: crate::button::DEFAULT_PADDING,
            text_size: None,
            text_line_height: text::LineHeight::default(),
            text_shaping: text::Shaping::Basic,
            font: None,
            handle: Handle::default(),
            style: Theme::default_style(),
        }
    }

    /// Sets the placeholder of the [`PickList`].
    pub fn placeholder(mut self, placeholder: impl Into<String>) -> Self {
        self.placeholder = Some(placeholder.into());
        self
    }

    /// Sets the width of the [`PickList`].
    pub fn width(mut self, width: impl Into<Length>) -> Self {
        self.width = width.into();
        self
    }

    /// Sets the [`Padding`] of the [`PickList`].
    pub fn padding<P: Into<Padding>>(mut self, padding: P) -> Self {
        self.padding = padding.into();
        self
    }

    /// Sets the text size of the [`PickList`].
    pub fn text_size(mut self, size: impl Into<Pixels>) -> Self {
        self.text_size = Some(size.into());
        self
    }

    /// Sets the text [`text::LineHeight`] of the [`PickList`].
    pub fn text_line_height(
        mut self,
        line_height: impl Into<text::LineHeight>,
    ) -> Self {
        self.text_line_height = line_height.into();
        self
    }

    /// Sets the [`text::Shaping`] strategy of the [`PickList`].
    pub fn text_shaping(mut self, shaping: text::Shaping) -> Self {
        self.text_shaping = shaping;
        self
    }

    /// Sets the font of the [`PickList`].
    pub fn font(mut self, font: impl Into<Renderer::Font>) -> Self {
        self.font = Some(font.into());
        self
    }

    /// Sets the [`Handle`] of the [`PickList`].
    pub fn handle(mut self, handle: Handle<Renderer::Font>) -> Self {
        self.handle = handle;
        self
    }

    /// Sets the message that will be produced when the [`PickList`] is opened.
    pub fn on_open(mut self, on_open: Message) -> Self {
        self.on_open = Some(on_open);
        self
    }

    /// Sets the message that will be produced when the [`PickList`] is closed.
    pub fn on_close(mut self, on_close: Message) -> Self {
        self.on_close = Some(on_close);
        self
    }

    /// Sets the style of the [`PickList`].
    pub fn style(mut self, style: impl Into<Style<'a, Theme>>) -> Self {
        self.style = style.into();
        self
    }
}

impl<'a, T, L, V, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
    for PickList<'a, T, L, V, Message, Theme, Renderer>
where
    T: Clone + ToString + PartialEq + 'a,
    L: Borrow<[T]>,
    V: Borrow<T>,
    Message: Clone + 'a,
    Renderer: text::Renderer + 'a,
{
    fn tag(&self) -> tree::Tag {
        tree::Tag::of::<State<Renderer::Paragraph>>()
    }

    fn state(&self) -> tree::State {
        tree::State::new(State::<Renderer::Paragraph>::new())
    }

    fn size(&self) -> Size<Length> {
        Size {
            width: self.width,
            height: Length::Shrink,
        }
    }

    fn layout(
        &self,
        tree: &mut Tree,
        renderer: &Renderer,
        limits: &layout::Limits,
    ) -> layout::Node {
        let state = tree.state.downcast_mut::<State<Renderer::Paragraph>>();

        let font = self.font.unwrap_or_else(|| renderer.default_font());
        let text_size =
            self.text_size.unwrap_or_else(|| renderer.default_size());
        let options = self.options.borrow();

        state.options.resize_with(options.len(), Default::default);

        let option_text = Text {
            content: "",
            bounds: Size::new(
                f32::INFINITY,
                self.text_line_height.to_absolute(text_size).into(),
            ),
            size: text_size,
            line_height: self.text_line_height,
            font,
            horizontal_alignment: alignment::Horizontal::Left,
            vertical_alignment: alignment::Vertical::Center,
            shaping: self.text_shaping,
        };

        for (option, paragraph) in options.iter().zip(state.options.iter_mut())
        {
            let label = option.to_string();

            paragraph.update(Text {
                content: &label,
                ..option_text
            });
        }

        if let Some(placeholder) = &self.placeholder {
            state.placeholder.update(Text {
                content: placeholder,
                ..option_text
            });
        }

        let max_width = match self.width {
            Length::Shrink => {
                let labels_width =
                    state.options.iter().fold(0.0, |width, paragraph| {
                        f32::max(width, paragraph.min_width())
                    });

                labels_width.max(
                    self.placeholder
                        .as_ref()
                        .map(|_| state.placeholder.min_width())
                        .unwrap_or(0.0),
                )
            }
            _ => 0.0,
        };

        let size = {
            let intrinsic = Size::new(
                max_width + text_size.0 + self.padding.left,
                f32::from(self.text_line_height.to_absolute(text_size)),
            );

            limits
                .width(self.width)
                .shrink(self.padding)
                .resolve(self.width, Length::Shrink, intrinsic)
                .expand(self.padding)
        };

        layout::Node::new(size)
    }

    fn on_event(
        &mut self,
        tree: &mut Tree,
        event: Event,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        _renderer: &Renderer,
        _clipboard: &mut dyn Clipboard,
        shell: &mut Shell<'_, Message>,
        _viewport: &Rectangle,
    ) -> event::Status {
        match event {
            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
            | Event::Touch(touch::Event::FingerPressed { .. }) => {
                let state =
                    tree.state.downcast_mut::<State<Renderer::Paragraph>>();

                if state.is_open {
                    // Event wasn't processed by overlay, so cursor was clicked either outside its
                    // bounds or on the drop-down, either way we close the overlay.
                    state.is_open = false;

                    if let Some(on_close) = &self.on_close {
                        shell.publish(on_close.clone());
                    }

                    event::Status::Captured
                } else if cursor.is_over(layout.bounds()) {
                    let selected = self.selected.as_ref().map(Borrow::borrow);

                    state.is_open = true;
                    state.hovered_option = self
                        .options
                        .borrow()
                        .iter()
                        .position(|option| Some(option) == selected);

                    if let Some(on_open) = &self.on_open {
                        shell.publish(on_open.clone());
                    }

                    event::Status::Captured
                } else {
                    event::Status::Ignored
                }
            }
            Event::Mouse(mouse::Event::WheelScrolled {
                delta: mouse::ScrollDelta::Lines { y, .. },
            }) => {
                let state =
                    tree.state.downcast_mut::<State<Renderer::Paragraph>>();

                if state.keyboard_modifiers.command()
                    && cursor.is_over(layout.bounds())
                    && !state.is_open
                {
                    fn find_next<'a, T: PartialEq>(
                        selected: &'a T,
                        mut options: impl Iterator<Item = &'a T>,
                    ) -> Option<&'a T> {
                        let _ = options.find(|&option| option == selected);

                        options.next()
                    }

                    let options = self.options.borrow();
                    let selected = self.selected.as_ref().map(Borrow::borrow);

                    let next_option = if y < 0.0 {
                        if let Some(selected) = selected {
                            find_next(selected, options.iter())
                        } else {
                            options.first()
                        }
                    } else if y > 0.0 {
                        if let Some(selected) = selected {
                            find_next(selected, options.iter().rev())
                        } else {
                            options.last()
                        }
                    } else {
                        None
                    };

                    if let Some(next_option) = next_option {
                        shell.publish((self.on_select)(next_option.clone()));
                    }

                    event::Status::Captured
                } else {
                    event::Status::Ignored
                }
            }
            Event::Keyboard(keyboard::Event::ModifiersChanged(modifiers)) => {
                let state =
                    tree.state.downcast_mut::<State<Renderer::Paragraph>>();

                state.keyboard_modifiers = modifiers;

                event::Status::Ignored
            }
            _ => event::Status::Ignored,
        }
    }

    fn mouse_interaction(
        &self,
        _tree: &Tree,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        _viewport: &Rectangle,
        _renderer: &Renderer,
    ) -> mouse::Interaction {
        let bounds = layout.bounds();
        let is_mouse_over = cursor.is_over(bounds);

        if is_mouse_over {
            mouse::Interaction::Pointer
        } else {
            mouse::Interaction::default()
        }
    }

    fn draw(
        &self,
        tree: &Tree,
        renderer: &mut Renderer,
        theme: &Theme,
        _style: &renderer::Style,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        viewport: &Rectangle,
    ) {
        let font = self.font.unwrap_or_else(|| renderer.default_font());
        let selected = self.selected.as_ref().map(Borrow::borrow);
        let state = tree.state.downcast_ref::<State<Renderer::Paragraph>>();

        let bounds = layout.bounds();
        let is_mouse_over = cursor.is_over(bounds);
        let is_selected = selected.is_some();

        let status = if state.is_open {
            Status::Opened
        } else if is_mouse_over {
            Status::Hovered
        } else {
            Status::Active
        };

        let appearance = (self.style.field)(theme, status);

        renderer.fill_quad(
            renderer::Quad {
                bounds,
                border: appearance.border,
                ..renderer::Quad::default()
            },
            appearance.background,
        );

        let handle = match &self.handle {
            Handle::Arrow { size } => Some((
                Renderer::ICON_FONT,
                Renderer::ARROW_DOWN_ICON,
                *size,
                text::LineHeight::default(),
                text::Shaping::Basic,
            )),
            Handle::Static(Icon {
                font,
                code_point,
                size,
                line_height,
                shaping,
            }) => Some((*font, *code_point, *size, *line_height, *shaping)),
            Handle::Dynamic { open, closed } => {
                if state.is_open {
                    Some((
                        open.font,
                        open.code_point,
                        open.size,
                        open.line_height,
                        open.shaping,
                    ))
                } else {
                    Some((
                        closed.font,
                        closed.code_point,
                        closed.size,
                        closed.line_height,
                        closed.shaping,
                    ))
                }
            }
            Handle::None => None,
        };

        if let Some((font, code_point, size, line_height, shaping)) = handle {
            let size = size.unwrap_or_else(|| renderer.default_size());

            renderer.fill_text(
                Text {
                    content: &code_point.to_string(),
                    size,
                    line_height,
                    font,
                    bounds: Size::new(
                        bounds.width,
                        f32::from(line_height.to_absolute(size)),
                    ),
                    horizontal_alignment: alignment::Horizontal::Right,
                    vertical_alignment: alignment::Vertical::Center,
                    shaping,
                },
                Point::new(
                    bounds.x + bounds.width - self.padding.right,
                    bounds.center_y(),
                ),
                appearance.handle_color,
                *viewport,
            );
        }

        let label = selected.map(ToString::to_string);

        if let Some(label) = label.as_deref().or(self.placeholder.as_deref()) {
            let text_size =
                self.text_size.unwrap_or_else(|| renderer.default_size());

            renderer.fill_text(
                Text {
                    content: label,
                    size: text_size,
                    line_height: self.text_line_height,
                    font,
                    bounds: Size::new(
                        bounds.width - self.padding.horizontal(),
                        f32::from(self.text_line_height.to_absolute(text_size)),
                    ),
                    horizontal_alignment: alignment::Horizontal::Left,
                    vertical_alignment: alignment::Vertical::Center,
                    shaping: self.text_shaping,
                },
                Point::new(bounds.x + self.padding.left, bounds.center_y()),
                if is_selected {
                    appearance.text_color
                } else {
                    appearance.placeholder_color
                },
                *viewport,
            );
        }
    }

    fn overlay<'b>(
        &'b mut self,
        tree: &'b mut Tree,
        layout: Layout<'_>,
        renderer: &Renderer,
        translation: Vector,
    ) -> Option<overlay::Element<'b, Message, Theme, Renderer>> {
        let state = tree.state.downcast_mut::<State<Renderer::Paragraph>>();
        let font = self.font.unwrap_or_else(|| renderer.default_font());

        if state.is_open {
            let bounds = layout.bounds();

            let on_select = &self.on_select;

            let mut menu = Menu::new(
                &mut state.menu,
                self.options.borrow(),
                &mut state.hovered_option,
                |option| {
                    state.is_open = false;

                    (on_select)(option)
                },
                None,
                &self.style.menu,
            )
            .width(bounds.width)
            .padding(self.padding)
            .font(font)
            .text_shaping(self.text_shaping);

            if let Some(text_size) = self.text_size {
                menu = menu.text_size(text_size);
            }

            Some(menu.overlay(layout.position() + translation, bounds.height))
        } else {
            None
        }
    }
}

impl<'a, T, L, V, Message, Theme, Renderer>
    From<PickList<'a, T, L, V, Message, Theme, Renderer>>
    for Element<'a, Message, Theme, Renderer>
where
    T: Clone + ToString + PartialEq + 'a,
    L: Borrow<[T]> + 'a,
    V: Borrow<T> + 'a,
    Message: Clone + 'a,
    Theme: 'a,
    Renderer: text::Renderer + 'a,
{
    fn from(
        pick_list: PickList<'a, T, L, V, Message, Theme, Renderer>,
    ) -> Self {
        Self::new(pick_list)
    }
}

#[derive(Debug)]
struct State<P: text::Paragraph> {
    menu: menu::State,
    keyboard_modifiers: keyboard::Modifiers,
    is_open: bool,
    hovered_option: Option<usize>,
    options: Vec<P>,
    placeholder: P,
}

impl<P: text::Paragraph> State<P> {
    /// Creates a new [`State`] for a [`PickList`].
    fn new() -> Self {
        Self {
            menu: menu::State::default(),
            keyboard_modifiers: keyboard::Modifiers::default(),
            is_open: bool::default(),
            hovered_option: Option::default(),
            options: Vec::new(),
            placeholder: P::default(),
        }
    }
}

impl<P: text::Paragraph> Default for State<P> {
    fn default() -> Self {
        Self::new()
    }
}

/// The handle to the right side of the [`PickList`].
#[derive(Debug, Clone, PartialEq)]
pub enum Handle<Font> {
    /// Displays an arrow icon (▼).
    ///
    /// This is the default.
    Arrow {
        /// Font size of the content.
        size: Option<Pixels>,
    },
    /// A custom static handle.
    Static(Icon<Font>),
    /// A custom dynamic handle.
    Dynamic {
        /// The [`Icon`] used when [`PickList`] is closed.
        closed: Icon<Font>,
        /// The [`Icon`] used when [`PickList`] is open.
        open: Icon<Font>,
    },
    /// No handle will be shown.
    None,
}

impl<Font> Default for Handle<Font> {
    fn default() -> Self {
        Self::Arrow { size: None }
    }
}

/// The icon of a [`Handle`].
#[derive(Debug, Clone, PartialEq)]
pub struct Icon<Font> {
    /// Font that will be used to display the `code_point`,
    pub font: Font,
    /// The unicode code point that will be used as the icon.
    pub code_point: char,
    /// Font size of the content.
    pub size: Option<Pixels>,
    /// Line height of the content.
    pub line_height: text::LineHeight,
    /// The shaping strategy of the icon.
    pub shaping: text::Shaping,
}

/// The possible status of a [`PickList`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Status {
    /// The [`PickList`] can be interacted with.
    Active,
    /// The [`PickList`] is being hovered.
    Hovered,
    /// The [`PickList`] is open.
    Opened,
}

/// The appearance of a pick list.
#[derive(Debug, Clone, Copy)]
pub struct Appearance {
    /// The text [`Color`] of the pick list.
    pub text_color: Color,
    /// The placeholder [`Color`] of the pick list.
    pub placeholder_color: Color,
    /// The handle [`Color`] of the pick list.
    pub handle_color: Color,
    /// The [`Background`] of the pick list.
    pub background: Background,
    /// The [`Border`] of the pick list.
    pub border: Border,
}

/// The styles of the different parts of a [`PickList`].
#[allow(missing_debug_implementations)]
pub struct Style<'a, Theme> {
    /// The style of the [`PickList`] itself.
    pub field: Box<dyn Fn(&Theme, Status) -> Appearance + 'a>,

    /// The style of the [`Menu`] of the pick list.
    pub menu: menu::Style<'a, Theme>,
}

/// The default style of a [`PickList`].
pub trait DefaultStyle: Sized {
    /// Returns the default style of a [`PickList`].
    fn default_style() -> Style<'static, Self>;
}

impl DefaultStyle for Theme {
    fn default_style() -> Style<'static, Self> {
        Style {
            field: Box::new(default),
            menu: menu::DefaultStyle::default_style(),
        }
    }
}

/// The default style of the field of a [`PickList`].
pub fn default(theme: &Theme, status: Status) -> Appearance {
    let palette = theme.extended_palette();

    let active = Appearance {
        text_color: palette.background.weak.text,
        background: palette.background.weak.color.into(),
        placeholder_color: palette.background.strong.color,
        handle_color: palette.background.weak.text,
        border: Border {
            radius: 2.0.into(),
            width: 1.0,
            color: palette.background.strong.color,
        },
    };

    match status {
        Status::Active => active,
        Status::Hovered | Status::Opened => Appearance {
            border: Border {
                color: palette.primary.strong.color,
                ..active.border
            },
            ..active
        },
    }
}