use iced_widget::graphics::text::Paragraph;

use crate::core::alignment;
use crate::core::clipboard;
use crate::core::keyboard;
use crate::core::keyboard::key;
use crate::core::layout;
use crate::core::mouse;
use crate::core::renderer;
use crate::core::text::{Paragraph as _, Span};
use crate::core::touch;
use crate::core::widget::text::{Alignment, LineHeight, Shaping, Wrapping};
use crate::core::widget::tree::{self, Tree};
use crate::core::{
    self, Clipboard, Element, Event, Font, Layout, Length, Pixels, Point,
    Rectangle, Shell, Size, Vector, Widget,
};
use crate::selection::{Selection, SelectionEnd};
use crate::text::{Catalog, Style, StyleFn};

/// A bunch of [`Rich`] text.
pub struct Rich<
    'a,
    Link,
    Message,
    Theme = iced_widget::Theme,
    Renderer = iced_widget::Renderer,
> where
    Link: Clone + 'static,
    Theme: Catalog,
    Renderer: core::text::Renderer,
{
    spans: Box<dyn AsRef<[Span<'a, Link, Renderer::Font>]> + 'a>,
    size: Option<Pixels>,
    line_height: LineHeight,
    width: Length,
    height: Length,
    font: Option<Renderer::Font>,
    align_x: Alignment,
    align_y: alignment::Vertical,
    wrapping: Wrapping,
    class: Theme::Class<'a>,
    hovered_link: Option<usize>,
    on_link_click: Option<Box<dyn Fn(Link) -> Message + 'a>>,
}

impl<'a, Link, Message, Theme, Renderer>
    Rich<'a, Link, Message, Theme, Renderer>
where
    Link: Clone + 'static,
    Theme: Catalog,
    Renderer: core::text::Renderer,
    Renderer::Font: 'a,
{
    /// Creates a new empty [`Rich`] text.
    pub fn new() -> Self {
        Self {
            spans: Box::new([]),
            size: None,
            line_height: LineHeight::default(),
            width: Length::Shrink,
            height: Length::Shrink,
            font: None,
            align_x: Alignment::Default,
            align_y: alignment::Vertical::Top,
            wrapping: Wrapping::default(),
            class: Theme::default(),
            hovered_link: None,
            on_link_click: None,
        }
    }

    /// Creates a new [`Rich`] text with the given text spans.
    pub fn with_spans(
        spans: impl AsRef<[Span<'a, Link, Renderer::Font>]> + 'a,
    ) -> Self {
        Self {
            spans: Box::new(spans),
            ..Self::new()
        }
    }

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

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

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

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

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

    /// Centers the [`Rich`] text, both horizontally and vertically.
    pub fn center(self) -> Self {
        self.align_x(alignment::Horizontal::Center)
            .align_y(alignment::Vertical::Center)
    }

    /// Sets the [`alignment::Horizontal`] of the [`Rich`] text.
    pub fn align_x(mut self, alignment: impl Into<Alignment>) -> Self {
        self.align_x = alignment.into();
        self
    }

    /// Sets the [`alignment::Vertical`] of the [`Rich`] text.
    pub fn align_y(
        mut self,
        alignment: impl Into<alignment::Vertical>,
    ) -> Self {
        self.align_y = alignment.into();
        self
    }

    /// Sets the [`Wrapping`] strategy of the [`Rich`] text.
    pub fn wrapping(mut self, wrapping: Wrapping) -> Self {
        self.wrapping = wrapping;
        self
    }

    /// Sets the message that will be produced when a link of the [`Rich`] text
    /// is clicked.
    pub fn on_link_click(
        mut self,
        on_link_clicked: impl Fn(Link) -> Message + 'a,
    ) -> Self {
        self.on_link_click = Some(Box::new(on_link_clicked));
        self
    }

    /// Sets the default style of the [`Rich`] text.
    #[must_use]
    pub fn style(mut self, style: impl Fn(&Theme) -> Style + 'a) -> Self
    where
        Theme::Class<'a>: From<StyleFn<'a, Theme>>,
    {
        self.class = (Box::new(style) as StyleFn<'a, Theme>).into();
        self
    }

    /// Sets the default style class of the [`Rich`] text.
    #[must_use]
    pub fn class(mut self, class: impl Into<Theme::Class<'a>>) -> Self {
        self.class = class.into();
        self
    }
}

impl<'a, Link, Message, Theme, Renderer> Default
    for Rich<'a, Link, Message, Theme, Renderer>
where
    Link: Clone + 'a,
    Theme: Catalog,
    Renderer: core::text::Renderer<Paragraph = Paragraph, Font = Font>,
    Renderer::Font: 'a,
{
    fn default() -> Self {
        Self::new()
    }
}

struct State<Link> {
    spans: Vec<Span<'static, Link, Font>>,
    span_pressed: Option<usize>,
    paragraph: Paragraph,
    is_hovered: bool,
    selection: Selection,
    is_dragging: bool,
    last_click: Option<mouse::Click>,
    keyboard_modifiers: keyboard::Modifiers,
}

impl<Link> State<Link> {
    fn grapheme_line_and_index(&self, point: Point) -> Option<(usize, usize)> {
        let cursor = self.paragraph.buffer().hit(point.x, point.y)?;
        let value = self.paragraph.buffer().lines[cursor.line].text();

        Some((
            cursor.line,
            unicode_segmentation::UnicodeSegmentation::graphemes(
                &value[..cursor.index.min(value.len())],
                true,
            )
            .count(),
        ))
    }

    fn selection_end_points(&self) -> [Point; 2] {
        let Selection { start, end, .. } = self.selection;

        let start_position = self
            .paragraph
            .grapheme_position(start.line, start.index)
            .unwrap_or(Point::ORIGIN);

        let end_position = self
            .paragraph
            .grapheme_position(end.line, end.index)
            .unwrap_or(Point::ORIGIN);

        [start_position, end_position]
    }
}

impl<Link, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
    for Rich<'_, Link, Message, Theme, Renderer>
where
    Link: Clone + 'static,
    Theme: Catalog,
    Renderer: core::text::Renderer<Paragraph = Paragraph, Font = Font>,
{
    fn tag(&self) -> tree::Tag {
        tree::Tag::of::<State<Link>>()
    }

    fn state(&self) -> tree::State {
        tree::State::new(State::<Link> {
            spans: Vec::new(),
            span_pressed: None,
            paragraph: Paragraph::default(),
            is_hovered: false,
            selection: Selection::default(),
            is_dragging: false,
            last_click: None,
            keyboard_modifiers: keyboard::Modifiers::default(),
        })
    }

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

    fn layout(
        &mut self,
        tree: &mut Tree,
        renderer: &Renderer,
        limits: &layout::Limits,
    ) -> layout::Node {
        layout(
            tree.state.downcast_mut::<State<Link>>(),
            renderer,
            limits,
            self.width,
            self.height,
            self.spans.as_ref().as_ref(),
            self.line_height,
            self.size,
            self.font,
            self.align_x,
            self.align_y,
            self.wrapping,
        )
    }

    fn draw(
        &self,
        tree: &Tree,
        renderer: &mut Renderer,
        theme: &Theme,
        defaults: &renderer::Style,
        layout: Layout<'_>,
        _cursor: mouse::Cursor,
        viewport: &Rectangle,
    ) {
        if !layout.bounds().intersects(viewport) {
            return;
        }

        let state = tree.state.downcast_ref::<State<Link>>();

        let style = theme.style(&self.class);

        for (index, span) in self.spans.as_ref().as_ref().iter().enumerate() {
            let is_hovered_link = self.on_link_click.is_some()
                && Some(index) == self.hovered_link;

            if span.highlight.is_some()
                || span.underline
                || span.strikethrough
                || is_hovered_link
            {
                let translation = layout.position() - Point::ORIGIN;
                let regions = state.paragraph.span_bounds(index);

                if let Some(highlight) = span.highlight {
                    for bounds in &regions {
                        let bounds = Rectangle::new(
                            bounds.position()
                                - Vector::new(
                                    span.padding.left,
                                    span.padding.top,
                                ),
                            bounds.size()
                                + Size::new(
                                    span.padding.horizontal(),
                                    span.padding.vertical(),
                                ),
                        );

                        renderer.fill_quad(
                            renderer::Quad {
                                bounds: bounds + translation,
                                border: highlight.border,
                                ..Default::default()
                            },
                            highlight.background,
                        );
                    }
                }

                if span.underline || span.strikethrough || is_hovered_link {
                    let size = span
                        .size
                        .or(self.size)
                        .unwrap_or(renderer.default_size());

                    let line_height = span
                        .line_height
                        .unwrap_or(self.line_height)
                        .to_absolute(size);

                    let color = span
                        .color
                        .or(style.color)
                        .unwrap_or(defaults.text_color);

                    let baseline = translation
                        + Vector::new(
                            0.0,
                            size.0 + (line_height.0 - size.0) / 2.0,
                        );

                    if span.underline || is_hovered_link {
                        for bounds in &regions {
                            renderer.fill_quad(
                                renderer::Quad {
                                    bounds: Rectangle::new(
                                        bounds.position() + baseline
                                            - Vector::new(0.0, size.0 * 0.08),
                                        Size::new(bounds.width, 1.0),
                                    ),
                                    ..Default::default()
                                },
                                color,
                            );
                        }
                    }

                    if span.strikethrough {
                        for bounds in &regions {
                            renderer.fill_quad(
                                renderer::Quad {
                                    bounds: Rectangle::new(
                                        bounds.position() + baseline
                                            - Vector::new(0.0, size.0 / 2.0),
                                        Size::new(bounds.width, 1.0),
                                    ),
                                    ..Default::default()
                                },
                                color,
                            );
                        }
                    }
                }
            }
        }

        if !state.selection.is_empty() {
            let bounds = layout.bounds();

            let [start, end] = state
                .selection_end_points()
                .map(|pos| pos + Vector::new(bounds.x, bounds.y));

            let line_height = self
                .line_height
                .to_absolute(
                    self.size.unwrap_or_else(|| renderer.default_size()),
                )
                .0;

            let baseline_y = bounds.y
                + ((start.y - bounds.y) / line_height).floor() * line_height;

            // The correct code, uncomment when glyphs report a correct `y` value.
            //
            // let height = end.y - baseline_y - 0.5;
            // let rows = (height / line_height).ceil() as usize;
            //
            // Temporary solution
            let rows =
                state.selection.end.line - state.selection.start.line + 1;

            for row in 0..rows {
                let (x, width) = if row == 0 {
                    (
                        start.x,
                        if rows == 1 {
                            end.x.min(bounds.x + bounds.width) - start.x
                        } else {
                            bounds.x + bounds.width - start.x
                        },
                    )
                } else if row == rows - 1 {
                    (bounds.x, end.x - bounds.x)
                } else {
                    (bounds.x, bounds.width)
                };

                let y = baseline_y + row as f32 * line_height;

                renderer.fill_quad(
                    renderer::Quad {
                        bounds: Rectangle {
                            x,
                            y,
                            width,
                            height: line_height,
                        },
                        snap: true,
                        ..Default::default()
                    },
                    style.selection,
                );
            }
        }

        crate::text::draw(
            renderer,
            defaults,
            layout.bounds(),
            &state.paragraph,
            style,
            viewport,
        );
    }

    fn update(
        &mut self,
        tree: &mut Tree,
        event: &Event,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        _renderer: &Renderer,
        clipboard: &mut dyn Clipboard,
        shell: &mut Shell<'_, Message>,
        viewport: &Rectangle,
    ) {
        let state = tree.state.downcast_mut::<State<Link>>();

        let bounds = layout.bounds();
        let click_position = cursor.position_in(bounds);

        if viewport.intersection(&bounds).is_none()
            && state.selection == Selection::default()
            && !state.is_dragging
        {
            return;
        }

        let link_was_hovered = self.hovered_link.is_some();
        let was_hovered = state.is_hovered;
        let selection_before = state.selection;

        state.is_hovered = click_position.is_some();

        if let Some(position) = click_position {
            self.hovered_link =
                state.paragraph.hit_span(position).and_then(|span| {
                    if self.spans.as_ref().as_ref().get(span)?.link.is_some() {
                        Some(span)
                    } else {
                        None
                    }
                });
        } else {
            self.hovered_link = None;
        }

        match event {
            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
            | Event::Touch(touch::Event::FingerPressed { .. }) => {
                if self.hovered_link.is_some() {
                    state.span_pressed = self.hovered_link;
                    shell.capture_event();
                }

                if let Some(position) = click_position {
                    let click = mouse::Click::new(
                        position,
                        mouse::Button::Left,
                        state.last_click,
                    );

                    let (line, index) = state
                        .grapheme_line_and_index(position)
                        .unwrap_or((0, 0));

                    match click.kind() {
                        mouse::click::Kind::Single => {
                            let new_end = SelectionEnd { line, index };

                            if state.keyboard_modifiers.shift() {
                                state.selection.change_selection(new_end);
                                state.is_dragging = true;
                            } else if state.span_pressed.is_none() {
                                state.selection.select_range(new_end, new_end);
                                state.is_dragging = true;
                            }
                        }
                        mouse::click::Kind::Double => {
                            state.selection.select_word(
                                line,
                                index,
                                &state.paragraph,
                            );
                            state.is_dragging = false;
                        }
                        mouse::click::Kind::Triple => {
                            state.selection.select_line(line, &state.paragraph);
                            state.is_dragging = false;
                        }
                    }
                } else {
                    state.selection = Selection::default();
                }
            }
            Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left))
            | Event::Touch(touch::Event::FingerLifted { .. })
            | Event::Touch(touch::Event::FingerLost { .. }) => {
                state.is_dragging = false;
                if !matches!(
                    event,
                    Event::Touch(touch::Event::FingerLost { .. })
                ) && state.selection.is_empty()
                {
                    match state.span_pressed {
                        Some(span) if Some(span) == self.hovered_link => {
                            if let Some((link, on_link_clicked)) = self
                                .spans
                                .as_ref()
                                .as_ref()
                                .get(span)
                                .and_then(|span| span.link.clone())
                                .zip(self.on_link_click.as_deref())
                            {
                                shell.publish(on_link_clicked(link));
                            }
                        }
                        _ => {}
                    }

                    state.span_pressed = None;
                }
            }
            Event::Mouse(mouse::Event::CursorMoved { .. })
            | Event::Touch(touch::Event::FingerMoved { .. }) => {
                if let Some(position) = click_position
                    && state.is_dragging
                {
                    let (line, index) = state
                        .grapheme_line_and_index(position)
                        .unwrap_or((0, 0));

                    let new_end = SelectionEnd { line, index };

                    state.selection.change_selection(new_end);
                }
            }
            Event::Keyboard(keyboard::Event::KeyPressed { key, .. }) => {
                match key.as_ref() {
                    keyboard::Key::Character("c")
                        if state.keyboard_modifiers.command()
                            && !state.selection.is_empty() =>
                    {
                        clipboard.write(
                            clipboard::Kind::Standard,
                            state.selection.text(&state.paragraph),
                        );

                        shell.capture_event();
                    }
                    keyboard::Key::Character("a")
                        if state.keyboard_modifiers.command()
                            && state.selection != Selection::default() =>
                    {
                        state.selection.select_all(&state.paragraph);

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::Home)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.jump() {
                            state.selection.select_beginning();
                        } else {
                            state.selection.select_line_beginning();
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::End)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.jump() {
                            state.selection.select_end(&state.paragraph);
                        } else {
                            state.selection.select_line_end(&state.paragraph);
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::ArrowLeft)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.macos_command() {
                            state.selection.select_line_beginning();
                        } else if state.keyboard_modifiers.jump() {
                            state
                                .selection
                                .select_left_by_words(&state.paragraph);
                        } else {
                            state.selection.select_left(&state.paragraph);
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::ArrowRight)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.macos_command() {
                            state.selection.select_line_end(&state.paragraph);
                        } else if state.keyboard_modifiers.jump() {
                            state
                                .selection
                                .select_right_by_words(&state.paragraph);
                        } else {
                            state.selection.select_right(&state.paragraph);
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::ArrowUp)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.macos_command() {
                            state.selection.select_beginning();
                        } else if state.keyboard_modifiers.jump() {
                            state.selection.select_line_beginning();
                        } else {
                            state.selection.select_up(&state.paragraph);
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::ArrowDown)
                        if state.keyboard_modifiers.shift()
                            && state.selection != Selection::default() =>
                    {
                        if state.keyboard_modifiers.macos_command() {
                            state.selection.select_end(&state.paragraph);
                        } else if state.keyboard_modifiers.jump() {
                            state.selection.select_line_end(&state.paragraph);
                        } else {
                            state.selection.select_down(&state.paragraph);
                        }

                        shell.capture_event();
                    }
                    keyboard::Key::Named(key::Named::Escape) => {
                        state.is_dragging = false;
                        state.selection = Selection::default();

                        state.keyboard_modifiers =
                            keyboard::Modifiers::default();

                        if state.selection != selection_before {
                            shell.capture_event();
                        }
                    }
                    _ => {}
                }
            }
            Event::Keyboard(keyboard::Event::ModifiersChanged(modifiers)) => {
                state.keyboard_modifiers = *modifiers;
            }
            _ => {}
        }

        if state.is_hovered != was_hovered
            || state.selection != selection_before
            || self.hovered_link.is_some() != link_was_hovered
        {
            shell.request_redraw();
        }
    }

    fn mouse_interaction(
        &self,
        _tree: &Tree,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        _viewport: &Rectangle,
        _renderer: &Renderer,
    ) -> mouse::Interaction {
        if self.hovered_link.is_some() {
            mouse::Interaction::Pointer
        } else if cursor.is_over(layout.bounds()) {
            mouse::Interaction::Text
        } else {
            mouse::Interaction::None
        }
    }
}

#[allow(clippy::too_many_arguments)]
fn layout<Link, Renderer>(
    state: &mut State<Link>,
    renderer: &Renderer,
    limits: &layout::Limits,
    width: Length,
    height: Length,
    spans: &[Span<'_, Link, Renderer::Font>],
    line_height: LineHeight,
    size: Option<Pixels>,
    font: Option<Renderer::Font>,
    align_x: Alignment,
    align_y: alignment::Vertical,
    wrapping: Wrapping,
) -> layout::Node
where
    Link: Clone,
    Renderer: core::text::Renderer<Paragraph = Paragraph, Font = Font>,
{
    layout::sized(limits, width, height, |limits| {
        let bounds = limits.max();

        let size = size.unwrap_or_else(|| renderer.default_size());
        let font = font.unwrap_or_else(|| renderer.default_font());

        let text_with_spans = || core::Text {
            content: spans,
            bounds,
            size,
            line_height,
            font,
            align_x,
            align_y,
            shaping: Shaping::Advanced,
            wrapping,
        };

        if state.spans != spans {
            state.paragraph =
                Renderer::Paragraph::with_spans(text_with_spans());
            state.spans = spans.iter().cloned().map(Span::to_static).collect();
        } else {
            match state.paragraph.compare(core::Text {
                content: (),
                bounds,
                size,
                line_height,
                font,
                align_x,
                align_y,
                shaping: Shaping::Advanced,
                wrapping,
            }) {
                core::text::Difference::None => {}
                core::text::Difference::Bounds => {
                    state.paragraph.resize(bounds);
                }
                core::text::Difference::Shape => {
                    state.paragraph =
                        Renderer::Paragraph::with_spans(text_with_spans());
                }
            }
        }

        state.paragraph.min_bounds()
    })
}

impl<'a, Link, Message, Theme, Renderer>
    FromIterator<Span<'a, Link, Renderer::Font>>
    for Rich<'a, Link, Message, Theme, Renderer>
where
    Link: Clone + 'a,
    Theme: Catalog,
    Renderer: core::text::Renderer<Paragraph = Paragraph, Font = Font>,
    Renderer::Font: 'a,
{
    fn from_iter<T: IntoIterator<Item = Span<'a, Link, Renderer::Font>>>(
        spans: T,
    ) -> Self {
        Self::with_spans(spans.into_iter().collect::<Vec<_>>())
    }
}

impl<'a, Link, Message, Theme, Renderer>
    From<Rich<'a, Link, Message, Theme, Renderer>>
    for Element<'a, Message, Theme, Renderer>
where
    Message: 'a,
    Link: Clone + 'a,
    Theme: Catalog + 'a,
    Renderer: core::text::Renderer<Paragraph = Paragraph, Font = Font> + 'a,
{
    fn from(
        text: Rich<'a, Link, Message, Theme, Renderer>,
    ) -> Element<'a, Message, Theme, Renderer> {
        Element::new(text)
    }
}