// SPDX-License-Identifier: GPL-3.0-only

use std::{
    cell::RefCell,
    io::Read,
    rc::Rc,
    sync::Mutex,
};
use smithay::{
    backend::{
        renderer::{Frame, ImportAll, Renderer, Texture, gles2},
        SwapBuffersError,
    },
    desktop::space::{RenderElement, SpaceOutputTuple, SurfaceTree, DynamicRenderElements},
    reexports::wayland_server::protocol::wl_surface,
    utils::{Logical, Buffer, Point, Rectangle, Size, Transform},
    wayland::{
        compositor::{get_role, with_states},
        seat::{Seat, CursorImageAttributes, CursorImageStatus},
    },
};
use xcursor::{
    parser::{parse_xcursor, Image},
    CursorTheme,
};
use crate::state::get_dnd_icon;

static FALLBACK_CURSOR_DATA: &[u8] = include_bytes!("../../resources/cursor.rgba");

#[derive(Debug, Clone)]
pub struct Cursor {
    icons: Vec<Image>,
    size: u32,
}

impl Cursor {
    pub fn load() -> Cursor {
        let name = std::env::var("XCURSOR_THEME")
            .ok()
            .unwrap_or_else(|| "default".into());
        let size = std::env::var("XCURSOR_SIZE")
            .ok()
            .and_then(|s| s.parse().ok())
            .unwrap_or(24);

        let theme = CursorTheme::load(&name);
        let icons = load_icon(&theme)
            .map_err(|err| slog_scope::warn!("Unable to load xcursor: {}, using fallback cursor", err))
            .unwrap_or_else(|_| {
                vec![Image {
                    size: 32,
                    width: 64,
                    height: 64,
                    xhot: 1,
                    yhot: 1,
                    delay: 1,
                    pixels_rgba: Vec::from(FALLBACK_CURSOR_DATA),
                    pixels_argb: vec![], //unused
                }]
            });

        Cursor { icons, size }
    }

    pub fn get_image(&self, scale: u32, millis: u32) -> Image {
        let size = self.size * scale;
        frame(millis, size, &self.icons)
    }
}

impl Default for Cursor {
    fn default() -> Cursor { Cursor::load() }
}

fn nearest_images(size: u32, images: &[Image]) -> impl Iterator<Item = &Image> {
    // Follow the nominal size of the cursor to choose the nearest
    let nearest_image = images
        .iter()
        .min_by_key(|image| (size as i32 - image.size as i32).abs())
        .unwrap();

    images
        .iter()
        .filter(move |image| image.width == nearest_image.width && image.height == nearest_image.height)
}

fn frame(mut millis: u32, size: u32, images: &[Image]) -> Image {
    let total = nearest_images(size, images).fold(0, |acc, image| acc + image.delay);
    millis %= total;

    for img in nearest_images(size, images) {
        if millis < img.delay {
            return img.clone();
        }
        millis -= img.delay;
    }

    unreachable!()
}

#[derive(thiserror::Error, Debug)]
enum Error {
    #[error("Theme has no default cursor")]
    NoDefaultCursor,
    #[error("Error opening xcursor file: {0}")]
    File(#[from] std::io::Error),
    #[error("Failed to parse XCursor file")]
    Parse,
}

fn load_icon(theme: &CursorTheme) -> Result<Vec<Image>, Error> {
    let icon_path = theme.load_icon("default").ok_or(Error::NoDefaultCursor)?;
    let mut cursor_file = std::fs::File::open(&icon_path)?;
    let mut cursor_data = Vec::new();
    cursor_file.read_to_end(&mut cursor_data)?;
    parse_xcursor(&cursor_data).ok_or(Error::Parse)
}

pub fn draw_surface_cursor<R, F, E, T>(
    surface: wl_surface::WlSurface,
    location: impl Into<Point<i32, Logical>>,
) -> impl RenderElement<R, F, E, T>
where
    R: Renderer<Error = E, TextureId = T, Frame = F> + ImportAll + 'static,
    F: Frame<Error = E, TextureId = T> + 'static,
    E: std::error::Error + Into<SwapBuffersError> + 'static,
    T: Texture + 'static,
{
    let mut position = location.into();
    let ret = with_states(&surface, |states| {
        Some(
            states
                .data_map
                .get::<Mutex<CursorImageAttributes>>()
                .unwrap()
                .lock()
                .unwrap()
                .hotspot,
        )
    })
    .unwrap_or(None);
    position -= match ret {
        Some(h) => h,
        None => {
            slog_scope::warn!("Trying to display as a cursor a surface that does not have the CursorImage role.");
            (0, 0).into()
        }
    };
    SurfaceTree { surface, position }
}

pub fn draw_dnd_icon<R, F, E, T>(
    surface: wl_surface::WlSurface,
    location: impl Into<Point<i32, Logical>>,
) -> impl RenderElement<R, F, E, T>
where
    R: Renderer<Error = E, TextureId = T, Frame = F> + ImportAll + 'static,
    F: Frame<Error = E, TextureId = T> + 'static,
    E: std::error::Error + Into<SwapBuffersError> + 'static,
    T: Texture + 'static,
{
    if get_role(&surface) != Some("dnd_icon") {
        slog_scope::warn!("Trying to display as a dnd icon a surface that does not have the DndIcon role.");
    }
    SurfaceTree {
        surface,
        position: location.into(),
    }
}

pub struct PointerElement<T: Texture> {
    texture: T,
    position: Point<i32, Logical>,
    size: Size<i32, Logical>,
    new_frame: bool,
}

impl<T: Texture> PointerElement<T> {
    pub fn new(texture: T, relative_pointer_pos: Point<i32, Logical>, new_frame: bool) -> PointerElement<T> {
        let size = texture.size().to_logical(1, Transform::Normal);
        PointerElement {
            texture,
            position: relative_pointer_pos,
            size,
            new_frame,
        }
    }
}

impl<R, F, E, T> RenderElement<R, F, E, T> for PointerElement<T>
where
    R: Renderer<Error = E, TextureId = T, Frame = F> + ImportAll + 'static,
    F: Frame<Error = E, TextureId = T> + 'static,
    E: std::error::Error + Into<SwapBuffersError> + 'static,
    T: Texture + 'static,
{
    fn id(&self) -> usize {
        0
    }

    fn geometry(&self) -> Rectangle<i32, Logical> {
        Rectangle::from_loc_and_size(self.position, self.size)
    }

    fn accumulated_damage(&self, _: Option<SpaceOutputTuple<'_, '_>>) -> Vec<Rectangle<i32, Logical>> {
        if self.new_frame { vec![Rectangle::from_loc_and_size((0, 0), self.size)] } else { vec![] }
    }

    fn draw(
        &self,
        _renderer: &mut R,
        frame: &mut F,
        scale: f64,
        position: Point<i32, Logical>,
        damage: &[Rectangle<i32, Logical>],
        _log: &slog::Logger,
    ) -> Result<(), R::Error> {
        frame.render_texture_at(
            &self.texture,
            position.to_f64().to_physical(scale as f64).to_i32_round(),
            1,
            scale as f64,
            Transform::Normal,
            &*damage
                .iter()
                .map(|rect| rect.to_buffer(1, Transform::Normal, &self.size))
                .collect::<Vec<_>>(),
            1.0,
        )?;
        Ok(())
    }
}

#[derive(Debug, Default)]
struct CursorState {
    cursor: Cursor,
    current_image: RefCell<Option<Image>>,
}

pub type Textures = Vec<(Image, gles2::Gles2Texture)>;

pub fn draw_cursor(
    renderer: &mut gles2::Gles2Renderer,
    seat: &Seat,
    start_time: &std::time::Instant,
    draw_default: bool,
) -> Option<DynamicRenderElements<gles2::Gles2Renderer>>
{
    let pointer = match seat.get_pointer() {
        Some(ptr) => ptr,
        None => return None,
    };
    let location = pointer.current_location();

    // draw the dnd icon if applicable
    {
        if let Some(wl_surface) = get_dnd_icon(seat) {
            if wl_surface.as_ref().is_alive() {
                return Some(Box::new(draw_dnd_icon(
                    wl_surface,
                    location.to_i32_round(),
                )));
            }
        }
    }

    // draw the cursor as relevant
    {
        // reset the cursor if the surface is no longer alive
        let cursor_status = seat
            .user_data()
            .get::<RefCell<CursorImageStatus>>()
            .map(|cell| {
                let mut cursor_status = cell.borrow_mut();
                if let CursorImageStatus::Image(ref surface) = *cursor_status {
                    if !surface.as_ref().is_alive() {
                        *cursor_status = CursorImageStatus::Default;
                    }
                }
                cursor_status.clone()
            })
            .unwrap_or(CursorImageStatus::Default);

        if let CursorImageStatus::Image(wl_surface) = cursor_status {
            Some(Box::new(draw_surface_cursor(
                wl_surface.clone(),
                location.to_i32_round(),
            )))
        } else if draw_default {
            let seat_userdata = seat.user_data();
            seat_userdata.insert_if_missing(CursorState::default);
            let state = seat_userdata.get::<CursorState>().unwrap();
            let frame = state.cursor.get_image(1, start_time.elapsed().as_millis() as u32);
            let new_frame = state.current_image.borrow().as_ref() != Some(&frame);

            let egl_userdata = renderer.egl_context().user_data();
            egl_userdata.insert_if_missing(|| Rc::new(RefCell::new(Textures::new())));
            let pointer_images = egl_userdata.get::<Rc<RefCell<Textures>>>().unwrap().clone();
            let pointer_images_ref = &mut *pointer_images.borrow_mut();
            let pointer_image = pointer_images_ref
                .iter()
                .find_map(|(image, texture)| if image == &frame { Some(texture) } else { None })
                .cloned()
                .unwrap_or_else(|| {
                    let texture = import_bitmap(renderer, &frame.pixels_rgba, gles2::ffi::RGBA, (frame.width as i32, frame.height as i32))
                        .expect("Failed to import cursor bitmap");
                    pointer_images_ref.push((frame.clone(), texture.clone()));
                    texture
                });
            let hotspot = Point::<i32, Logical>::from((frame.xhot as i32, frame.yhot as i32));
            *state.current_image.borrow_mut() = Some(frame);

            Some(Box::new(PointerElement::new(
                pointer_image.clone(),
                location.to_i32_round() - hotspot,
                new_frame,
            )))
        } else {
            None
        }
    }
}

pub fn import_bitmap(
    renderer: &mut gles2::Gles2Renderer,
    image: impl std::convert::AsRef<[u8]>,
    format: gles2::ffi::types::GLenum,
    size: impl Into<Size<i32, Buffer>>,
) -> Result<gles2::Gles2Texture, gles2::Gles2Error> {
    use smithay::backend::renderer::gles2::ffi;

    let size = size.into();
    renderer.with_context(|renderer, gl| unsafe {
        let mut tex = 0;
        gl.GenTextures(1, &mut tex);
        gl.BindTexture(ffi::TEXTURE_2D, tex);
        gl.TexParameteri(ffi::TEXTURE_2D, ffi::TEXTURE_WRAP_S, ffi::CLAMP_TO_EDGE as i32);
        gl.TexParameteri(ffi::TEXTURE_2D, ffi::TEXTURE_WRAP_T, ffi::CLAMP_TO_EDGE as i32);
        gl.TexImage2D(
            ffi::TEXTURE_2D,
            0,
            format as i32,
            size.w,
            size.h,
            0,
            format,
            ffi::UNSIGNED_BYTE as u32,
            image.as_ref().as_ptr() as *const _,
        );
        gl.BindTexture(ffi::TEXTURE_2D, 0);

        gles2::Gles2Texture::from_raw(
            renderer,
            tex,
            size,
        )
    })
}