use crate::{
    commands::Open,
    compositor::{Callback, Component, Context, Event, EventResult},
    ctrl, key,
};
use tui::{
    buffer::Buffer as Surface,
    widgets::{Block, Borders, Widget},
};

use helix_core::Position;
use helix_view::{
    graphics::{Margin, Rect},
    Editor,
};

// TODO: share logic with Menu, it's essentially Popup(render_fn), but render fn needs to return
// a width/height hint. maybe Popup(Box<Component>)

pub struct Popup<T: Component> {
    contents: T,
    position: Option<Position>,
    margin: Margin,
    size: (u16, u16),
    child_size: (u16, u16),
    position_bias: Open,
    scroll: usize,
    auto_close: bool,
    ignore_escape_key: bool,
    id: &'static str,
    has_scrollbar: bool,
}

impl<T: Component> Popup<T> {
    pub fn new(id: &'static str, contents: T) -> Self {
        Self {
            contents,
            position: None,
            margin: Margin::none(),
            size: (0, 0),
            position_bias: Open::Below,
            child_size: (0, 0),
            scroll: 0,
            auto_close: false,
            ignore_escape_key: false,
            id,
            has_scrollbar: true,
        }
    }

    /// Set the anchor position next to which the popup should be drawn.
    ///
    /// Note that this is not the position of the top-left corner of the rendered popup itself,
    /// but rather the screen-space position of the information to which the popup refers.
    pub fn position(mut self, pos: Option<Position>) -> Self {
        self.position = pos;
        self
    }

    pub fn get_position(&self) -> Option<Position> {
        self.position
    }

    /// Set the popup to prefer to render above or below the anchor position.
    ///
    /// This preference will be ignored if the viewport doesn't have enough space in the
    /// chosen direction.
    pub fn position_bias(mut self, bias: Open) -> Self {
        self.position_bias = bias;
        self
    }

    pub fn margin(mut self, margin: Margin) -> Self {
        self.margin = margin;
        self
    }

    pub fn auto_close(mut self, auto_close: bool) -> Self {
        self.auto_close = auto_close;
        self
    }

    /// Ignores an escape keypress event, letting the outer layer
    /// (usually the editor) handle it. This is useful for popups
    /// in insert mode like completion and signature help where
    /// the popup is closed on the mode change from insert to normal
    /// which is done with the escape key. Otherwise the popup consumes
    /// the escape key event and closes it, and an additional escape
    /// would be required to exit insert mode.
    pub fn ignore_escape_key(mut self, ignore: bool) -> Self {
        self.ignore_escape_key = ignore;
        self
    }

    /// Calculate the position where the popup should be rendered and return the coordinates of the
    /// top left corner.
    pub fn get_rel_position(&mut self, viewport: Rect, editor: &Editor) -> (u16, u16) {
        let position = self
            .position
            .get_or_insert_with(|| editor.cursor().0.unwrap_or_default());

        let (width, height) = self.size;

        // if there's a orientation preference, use that
        // if we're on the top part of the screen, do below
        // if we're on the bottom part, do above

        // -- make sure frame doesn't stick out of bounds
        let mut rel_x = position.col as u16;
        let mut rel_y = position.row as u16;
        if viewport.width <= rel_x + width {
            rel_x = rel_x.saturating_sub((rel_x + width).saturating_sub(viewport.width));
        }

        let can_put_below = viewport.height > rel_y + height;
        let can_put_above = rel_y.checked_sub(height).is_some();
        let final_pos = match self.position_bias {
            Open::Below => match can_put_below {
                true => Open::Below,
                false => Open::Above,
            },
            Open::Above => match can_put_above {
                true => Open::Above,
                false => Open::Below,
            },
        };

        rel_y = match final_pos {
            Open::Above => rel_y.saturating_sub(height),
            Open::Below => rel_y + 1,
        };

        (rel_x, rel_y)
    }

    pub fn get_size(&self) -> (u16, u16) {
        (self.size.0, self.size.1)
    }

    pub fn scroll(&mut self, offset: usize, direction: bool) {
        if direction {
            let max_offset = self.child_size.1.saturating_sub(self.size.1);
            self.scroll = (self.scroll + offset).min(max_offset as usize);
        } else {
            self.scroll = self.scroll.saturating_sub(offset);
        }
    }

    /// Toggles the Popup's scrollbar.
    /// Consider disabling the scrollbar in case the child
    /// already has its own.
    pub fn with_scrollbar(mut self, enable_scrollbar: bool) -> Self {
        self.has_scrollbar = enable_scrollbar;
        self
    }

    pub fn contents(&self) -> &T {
        &self.contents
    }

    pub fn contents_mut(&mut self) -> &mut T {
        &mut self.contents
    }

    pub fn area(&mut self, viewport: Rect, editor: &Editor) -> Rect {
        // trigger required_size so we recalculate if the child changed
        self.required_size((viewport.width, viewport.height));

        let (rel_x, rel_y) = self.get_rel_position(viewport, editor);

        // clip to viewport
        viewport.intersection(Rect::new(rel_x, rel_y, self.size.0, self.size.1))
    }
}

impl<T: Component> Component for Popup<T> {
    fn handle_event(&mut self, event: &Event, cx: &mut Context) -> EventResult {
        let key = match event {
            Event::Key(event) => *event,
            Event::Resize(_, _) => {
                // TODO: calculate inner area, call component's handle_event with that area
                return EventResult::Ignored(None);
            }
            _ => return EventResult::Ignored(None),
        };

        if key!(Esc) == key && self.ignore_escape_key {
            return EventResult::Ignored(None);
        }

        let close_fn: Callback = Box::new(|compositor, _| {
            // remove the layer
            compositor.remove(self.id.as_ref());
        });

        match key {
            // esc or ctrl-c aborts the completion and closes the menu
            key!(Esc) | ctrl!('c') => {
                let _ = self.contents.handle_event(event, cx);
                EventResult::Consumed(Some(close_fn))
            }
            ctrl!('d') => {
                self.scroll(self.size.1 as usize / 2, true);
                EventResult::Consumed(None)
            }
            ctrl!('u') => {
                self.scroll(self.size.1 as usize / 2, false);
                EventResult::Consumed(None)
            }
            _ => {
                let contents_event_result = self.contents.handle_event(event, cx);

                if self.auto_close {
                    if let EventResult::Ignored(None) = contents_event_result {
                        return EventResult::Ignored(Some(close_fn));
                    }
                }

                contents_event_result
            }
        }
        // for some events, we want to process them but send ignore, specifically all input except
        // tab/enter/ctrl-k or whatever will confirm the selection/ ctrl-n/ctrl-p for scroll.
    }

    fn required_size(&mut self, viewport: (u16, u16)) -> Option<(u16, u16)> {
        let max_width = 120.min(viewport.0);
        let max_height = 26.min(viewport.1.saturating_sub(2)); // add some spacing in the viewport

        let inner = Rect::new(0, 0, max_width, max_height).inner(&self.margin);

        let (width, height) = self
            .contents
            .required_size((inner.width, inner.height))
            .expect("Component needs required_size implemented in order to be embedded in a popup");

        self.child_size = (width, height);
        self.size = (
            (width + self.margin.width()).min(max_width),
            (height + self.margin.height()).min(max_height),
        );

        // re-clamp scroll offset
        let max_offset = self.child_size.1.saturating_sub(self.size.1);
        self.scroll = self.scroll.min(max_offset as usize);

        Some(self.size)
    }

    fn render(&mut self, viewport: Rect, surface: &mut Surface, cx: &mut Context) {
        let area = self.area(viewport, cx.editor);
        cx.scroll = Some(self.scroll);

        // clear area
        let background = cx.editor.theme.get("ui.popup");
        surface.clear_with(area, background);

        let render_borders = cx.editor.popup_border();

        let inner = if self
            .contents
            .type_name()
            .starts_with("helix_term::ui::menu::Menu")
        {
            area
        } else {
            area.inner(&self.margin)
        };

        let border = usize::from(render_borders);
        if render_borders {
            Widget::render(Block::default().borders(Borders::ALL), area, surface);
        }

        self.contents.render(inner, surface, cx);

        // render scrollbar if contents do not fit
        if self.has_scrollbar {
            let win_height = (inner.height as usize).saturating_sub(2 * border);
            let len = (self.child_size.1 as usize).saturating_sub(2 * border);
            let fits = len <= win_height;
            let scroll = self.scroll;
            let scroll_style = cx.editor.theme.get("ui.menu.scroll");

            const fn div_ceil(a: usize, b: usize) -> usize {
                (a + b - 1) / b
            }

            if !fits {
                let scroll_height = div_ceil(win_height.pow(2), len).min(win_height);
                let scroll_line = (win_height - scroll_height) * scroll
                    / std::cmp::max(1, len.saturating_sub(win_height));

                let mut cell;
                for i in 0..win_height {
                    cell = &mut surface[(inner.right() - 1, inner.top() + (border + i) as u16)];

                    let half_block = if render_borders { "▌" } else { "▐" };

                    if scroll_line <= i && i < scroll_line + scroll_height {
                        // Draw scroll thumb
                        cell.set_symbol(half_block);
                        cell.set_fg(scroll_style.fg.unwrap_or(helix_view::theme::Color::Reset));
                    } else if !render_borders {
                        // Draw scroll track
                        cell.set_symbol(half_block);
                        cell.set_fg(scroll_style.bg.unwrap_or(helix_view::theme::Color::Reset));
                    }
                }
            }
        }
    }

    fn id(&self) -> Option<&'static str> {
        Some(self.id)
    }
}