use std::cell::RefCell;
use std::future::{self, Future};
use std::hash::{Hash, Hasher};
use std::mem;
use std::ops::{Deref, DerefMut};
use std::pin::Pin;
use std::rc::Rc;
use std::sync::Arc;
use std::task::{Context, Poll, Waker, ready};
use std::time::Duration;

use cursor_icon::CursorIcon;
use js_sys::{Array, Object};
use wasm_bindgen::JsCast;
use wasm_bindgen::closure::Closure;
use wasm_bindgen::prelude::wasm_bindgen;
use wasm_bindgen_futures::JsFuture;
use web_sys::{
    Blob, Document, DomException, HtmlCanvasElement, HtmlImageElement, ImageBitmap,
    ImageBitmapOptions, ImageBitmapRenderingContext, ImageData, PremultiplyAlpha, Url, Window,
};
use winit_core::cursor::{Cursor, CursorImage, CustomCursorProvider, CustomCursorSource};

use crate::CustomCursorError;
use crate::r#async::{AbortHandle, Abortable, DropAbortHandle, Notified, Notifier};
use crate::backend::Style;
use crate::event_loop::ActiveEventLoop;
use crate::main_thread::{MainThreadMarker, MainThreadSafe};

#[derive(Clone, Debug)]
pub struct CustomCursor {
    pub(crate) animation: bool,
    state: Arc<MainThreadSafe<RefCell<ImageState>>>,
}

impl CustomCursor {
    pub(crate) fn new(event_loop: &ActiveEventLoop, source: CustomCursorSource) -> Self {
        match source {
            CustomCursorSource::Image(image) => Self::build_spawn(
                event_loop,
                from_rgba(event_loop.runner.window(), event_loop.runner.document().clone(), &image),
                false,
            ),
            CustomCursorSource::Url { url, hotspot_x, hotspot_y } => Self::build_spawn(
                event_loop,
                from_url(UrlType::Plain(url), hotspot_x, hotspot_y),
                false,
            ),
            CustomCursorSource::Animation(animation) => {
                let (duration, cursors) = animation.into_raw();
                Self::build_spawn(
                    event_loop,
                    from_animation(event_loop.runner.main_thread(), duration, cursors.into_iter()),
                    true,
                )
            },
            _ => unimplemented!("unknown `CustomCursorSource` variant"),
        }
    }

    fn build_spawn<F, S>(window_target: &ActiveEventLoop, task: F, animation: bool) -> CustomCursor
    where
        F: 'static + Future<Output = Result<S, CustomCursorError>>,
        S: Into<ImageState>,
    {
        let handle = AbortHandle::new();
        let this = CustomCursor {
            animation,
            state: Arc::new(MainThreadSafe::new(
                window_target.runner.main_thread(),
                RefCell::new(ImageState::Loading {
                    notifier: Notifier::new(),
                    _handle: DropAbortHandle::new(handle.clone()),
                }),
            )),
        };
        let weak = Arc::downgrade(&this.state);
        let main_thread = window_target.runner.main_thread();

        let task = Abortable::new(handle, {
            async move {
                let result = task.await;

                let this = weak.upgrade().expect("`CursorHandler` invalidated without aborting");
                let mut this = this.get(main_thread).borrow_mut();

                match result {
                    Ok(new_state) => {
                        let ImageState::Loading { notifier, .. } =
                            mem::replace(this.deref_mut(), new_state.into())
                        else {
                            unreachable!("found invalid state");
                        };
                        notifier.notify(Ok(()));
                    },
                    Err(error) => {
                        let ImageState::Loading { notifier, .. } =
                            mem::replace(this.deref_mut(), ImageState::Failed(error.clone()))
                        else {
                            unreachable!("found invalid state");
                        };
                        notifier.notify(Err(error));
                    },
                }
            }
        });

        wasm_bindgen_futures::spawn_local(async move {
            let _ = task.await;
        });

        this
    }

    pub(crate) fn new_async(
        event_loop: &ActiveEventLoop,
        source: CustomCursorSource,
    ) -> CustomCursorFuture {
        let CustomCursor { animation, state } = Self::new(event_loop, source);
        let binding = state.get(event_loop.runner.main_thread()).borrow();
        let ImageState::Loading { notifier, .. } = binding.deref() else {
            unreachable!("found invalid state")
        };
        let notified = notifier.notified();
        drop(binding);

        CustomCursorFuture { notified, animation, state: Some(state) }
    }
}

impl CustomCursorProvider for CustomCursor {
    fn is_animated(&self) -> bool {
        self.animation
    }
}

impl Hash for CustomCursor {
    fn hash<H: Hasher>(&self, state: &mut H) {
        Arc::as_ptr(&self.state).hash(state);
    }
}

impl PartialEq for CustomCursor {
    fn eq(&self, other: &Self) -> bool {
        Arc::ptr_eq(&self.state, &other.state)
    }
}

impl Eq for CustomCursor {}

#[derive(Debug)]
pub struct CustomCursorFuture {
    notified: Notified<Result<(), CustomCursorError>>,
    animation: bool,
    state: Option<Arc<MainThreadSafe<RefCell<ImageState>>>>,
}

impl Future for CustomCursorFuture {
    type Output = Result<CustomCursor, CustomCursorError>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        if self.state.is_none() {
            panic!("`CustomCursorFuture` polled after completion")
        }

        let result = ready!(Pin::new(&mut self.notified).poll(cx)).unwrap();
        let state = self.state.take().expect("`CustomCursorFuture` polled after completion");

        Poll::Ready(result.map(|_| CustomCursor { animation: self.animation, state }))
    }
}

#[derive(Debug)]
pub struct CursorHandler(Rc<RefCell<Inner>>);

#[derive(Debug)]
struct Inner {
    main_thread: MainThreadMarker,
    canvas: HtmlCanvasElement,
    style: Style,
    visible: bool,
    cursor: SelectedCursor,
}

impl CursorHandler {
    pub(crate) fn new(
        main_thread: MainThreadMarker,
        canvas: HtmlCanvasElement,
        style: Style,
    ) -> Self {
        Self(Rc::new(RefCell::new(Inner {
            main_thread,
            canvas,
            style,
            visible: true,
            cursor: SelectedCursor::default(),
        })))
    }

    pub fn set_cursor(&self, cursor: Cursor) {
        let mut this = self.0.borrow_mut();

        match cursor {
            Cursor::Icon(icon) => {
                if let SelectedCursor::Icon(old_icon)
                | SelectedCursor::Loading { previous: Previous::Icon(old_icon), .. } =
                    &this.cursor
                {
                    if *old_icon == icon {
                        return;
                    }
                }

                this.cursor = SelectedCursor::Icon(icon);
                this.set_style();
            },
            Cursor::Custom(cursor) => {
                let cursor = match cursor.cast_ref::<CustomCursor>() {
                    Some(cursor) => cursor,
                    None => return,
                };

                if let SelectedCursor::Loading { cursor: old_cursor, .. }
                | SelectedCursor::Image(old_cursor)
                | SelectedCursor::Animation { cursor: old_cursor, .. } = &this.cursor
                {
                    if old_cursor == cursor {
                        return;
                    }
                }

                let state = cursor.state.get(this.main_thread).borrow();

                match state.deref() {
                    ImageState::Loading { notifier, .. } => {
                        let notified = notifier.notified();
                        let handle = DropAbortHandle::new(AbortHandle::new());
                        let task = Abortable::new(handle.handle(), {
                            let weak = Rc::downgrade(&self.0);
                            async move {
                                let _ = notified.await;
                                let handler = weak
                                    .upgrade()
                                    .expect("`CursorHandler` invalidated without aborting");
                                handler.borrow_mut().notify();
                            }
                        });
                        wasm_bindgen_futures::spawn_local(async move {
                            let _ = task.await;
                        });

                        drop(state);
                        this.cursor = SelectedCursor::Loading {
                            cursor: cursor.clone(),
                            previous: mem::take(&mut this.cursor).into(),
                            _handle: handle,
                        };
                    },
                    ImageState::Failed(error) => {
                        tracing::error!(
                            "trying to load custom cursor that has failed to load: {error}"
                        )
                    },
                    ImageState::Image(_) => {
                        drop(state);
                        this.cursor = SelectedCursor::Image(cursor.clone());
                        this.set_style();
                    },
                    ImageState::Animation(animation) => {
                        let canvas: &CanvasAnimateExt = this.canvas.unchecked_ref();
                        let animation = canvas.animate_with_keyframe_animation_options(
                            Some(&animation.keyframes),
                            &animation.options,
                        );
                        drop(state);

                        if !this.visible {
                            animation.cancel();
                        }

                        this.cursor = SelectedCursor::Animation {
                            animation: AnimationDropper(animation),
                            cursor: cursor.clone(),
                        };
                        this.set_style();
                    },
                };
            },
        }
    }

    pub fn set_cursor_visible(&self, visible: bool) {
        let mut this = self.0.borrow_mut();

        if !visible && this.visible {
            this.visible = false;
            this.style.set("cursor", "none");

            if let SelectedCursor::Animation { animation, .. } = &this.cursor {
                animation.0.cancel();
            }
        } else if visible && !this.visible {
            this.visible = true;
            this.set_style();
        }
    }
}

impl Inner {
    fn set_style(&self) {
        if self.visible {
            match &self.cursor {
                SelectedCursor::Icon(icon)
                | SelectedCursor::Loading { previous: Previous::Icon(icon), .. } => {
                    if let CursorIcon::Default = icon {
                        self.style.remove("cursor")
                    } else {
                        self.style.set("cursor", icon.name())
                    }
                },
                SelectedCursor::Loading { previous: Previous::Image(cursor), .. }
                | SelectedCursor::Image(cursor) => {
                    match cursor.state.get(self.main_thread).borrow().deref() {
                        ImageState::Image(Image { style, .. }) => self.style.set("cursor", style),
                        _ => unreachable!("found invalid saved state"),
                    }
                },
                SelectedCursor::Loading {
                    previous: Previous::Animation { animation, .. }, ..
                }
                | SelectedCursor::Animation { animation, .. } => {
                    self.style.remove("cursor");
                    animation.0.play()
                },
            }
        }
    }

    fn notify(&mut self) {
        let SelectedCursor::Loading { cursor, previous, .. } = mem::take(&mut self.cursor) else {
            unreachable!("found wrong state")
        };

        let state = cursor.state.get(self.main_thread).borrow();
        match state.deref() {
            ImageState::Image(_) => {
                drop(state);
                self.cursor = SelectedCursor::Image(cursor);
                self.set_style();
            },
            ImageState::Animation(animation) => {
                let canvas: &CanvasAnimateExt = self.canvas.unchecked_ref();
                let animation = canvas.animate_with_keyframe_animation_options(
                    Some(&animation.keyframes),
                    &animation.options,
                );
                drop(state);

                if !self.visible {
                    animation.cancel();
                }

                self.cursor =
                    SelectedCursor::Animation { animation: AnimationDropper(animation), cursor };
                self.set_style();
            },
            ImageState::Failed(error) => {
                tracing::error!("custom cursor failed to load: {error}");
                self.cursor = previous.into()
            },
            ImageState::Loading { .. } => unreachable!("notified without being ready"),
        }
    }
}

#[derive(Debug)]
enum SelectedCursor {
    Icon(CursorIcon),
    Loading { cursor: CustomCursor, previous: Previous, _handle: DropAbortHandle },
    Image(CustomCursor),
    Animation { cursor: CustomCursor, animation: AnimationDropper },
}

impl Default for SelectedCursor {
    fn default() -> Self {
        Self::Icon(Default::default())
    }
}

impl From<Previous> for SelectedCursor {
    fn from(previous: Previous) -> Self {
        match previous {
            Previous::Icon(icon) => Self::Icon(icon),
            Previous::Image(cursor) => Self::Image(cursor),
            Previous::Animation { cursor, animation } => Self::Animation { cursor, animation },
        }
    }
}

#[derive(Debug)]
enum Previous {
    Icon(CursorIcon),
    Image(CustomCursor),
    Animation { cursor: CustomCursor, animation: AnimationDropper },
}

impl From<SelectedCursor> for Previous {
    fn from(value: SelectedCursor) -> Self {
        match value {
            SelectedCursor::Icon(icon) => Self::Icon(icon),
            SelectedCursor::Loading { previous, .. } => previous,
            SelectedCursor::Image(image) => Self::Image(image),
            SelectedCursor::Animation { cursor, animation } => {
                Self::Animation { cursor, animation }
            },
        }
    }
}

#[derive(Debug)]
enum ImageState {
    Loading { notifier: Notifier<Result<(), CustomCursorError>>, _handle: DropAbortHandle },
    Failed(CustomCursorError),
    Image(Image),
    Animation(Animation),
}

#[derive(Debug)]
struct Image {
    style: String,
    _object_url: Option<ObjectUrl>,
    _image: HtmlImageElement,
}

impl From<Image> for ImageState {
    fn from(image: Image) -> Self {
        Self::Image(image)
    }
}

#[derive(Debug)]
struct Animation {
    keyframes: Array,
    options: KeyframeAnimationOptions,
    _images: Vec<CustomCursor>,
}

impl From<Animation> for ImageState {
    fn from(animation: Animation) -> Self {
        Self::Animation(animation)
    }
}

#[derive(Debug)]
enum UrlType {
    Plain(String),
    Object(ObjectUrl),
}

impl UrlType {
    fn url(&self) -> &str {
        match &self {
            UrlType::Plain(url) => url,
            UrlType::Object(object_url) => &object_url.0,
        }
    }
}

#[derive(Debug)]
struct ObjectUrl(String);

impl Drop for ObjectUrl {
    fn drop(&mut self) {
        Url::revoke_object_url(&self.0).expect("unexpected exception in `URL.revokeObjectURL()`");
    }
}

#[derive(Debug)]
struct AnimationDropper(WebAnimation);

impl Drop for AnimationDropper {
    fn drop(&mut self) {
        self.0.cancel()
    }
}

fn from_rgba(
    window: &Window,
    document: Document,
    image: &CursorImage,
) -> impl Future<Output = Result<Image, CustomCursorError>> + use<> {
    // 1. Create an `ImageData` from the RGBA data.
    // 2. Create an `ImageBitmap` from the `ImageData`.
    // 3. Draw `ImageBitmap` on an `HTMLCanvasElement`.
    // 4. Create a `Blob` from the `HTMLCanvasElement`.
    // 5. Create an object URL from the `Blob`.
    // 6. Decode the image on an `HTMLImageElement` from the URL.

    // 1. Create an `ImageData` from the RGBA data.
    // Adapted from https://github.com/rust-windowing/softbuffer/blob/ab7688e2ed2e2eca51b3c4e1863a5bd7fe85800e/src/web.rs#L196-L223
    #[cfg(target_feature = "atomics")]
    // Can't share `SharedArrayBuffer` with `ImageData`.
    let result = {
        use js_sys::{Uint8Array, Uint8ClampedArray};
        use wasm_bindgen::JsValue;

        #[wasm_bindgen]
        extern "C" {
            #[wasm_bindgen(js_namespace = ImageData)]
            type ImageDataExt;
            #[wasm_bindgen(catch, constructor, js_class = ImageData)]
            fn new(array: Uint8ClampedArray, sw: u32) -> Result<ImageDataExt, JsValue>;
        }

        let array = Uint8Array::new_with_length(image.buffer().len() as u32);
        array.copy_from(image.buffer());
        let array = Uint8ClampedArray::new(&array);
        ImageDataExt::new(array, image.width() as u32)
            .map(JsValue::from)
            .map(ImageData::unchecked_from_js)
    };
    #[cfg(not(target_feature = "atomics"))]
    let result = ImageData::new_with_u8_clamped_array(
        wasm_bindgen::Clamped(image.buffer()),
        image.width() as u32,
    );
    let image_data = result.expect("found wrong image size");

    // 2. Create an `ImageBitmap` from the `ImageData`.
    //
    // We call `createImageBitmap()` before spawning the future,
    // to not have to clone the image buffer.
    let options = ImageBitmapOptions::new();
    options.set_premultiply_alpha(PremultiplyAlpha::None);
    let bitmap = JsFuture::from(
        window
            .create_image_bitmap_with_image_data_and_image_bitmap_options(&image_data, &options)
            .expect("unexpected exception in `createImageBitmap()`"),
    );

    let width = image.width();
    let height = image.height();
    let hotspot_x = image.hotspot_x();
    let hotspot_y = image.hotspot_y();
    async move {
        let bitmap: ImageBitmap =
            bitmap.await.expect("found invalid state in `ImageData`").unchecked_into();

        let canvas: HtmlCanvasElement =
            document.create_element("canvas").expect("invalid tag name").unchecked_into();
        #[allow(clippy::disallowed_methods)]
        canvas.set_width(width as u32);
        #[allow(clippy::disallowed_methods)]
        canvas.set_height(height as u32);

        // 3. Draw `ImageBitmap` on an `HTMLCanvasElement`.
        let context: ImageBitmapRenderingContext = canvas
            .get_context("bitmaprenderer")
            .expect("unexpected exception in `HTMLCanvasElement.getContext()`")
            .expect("`bitmaprenderer` context unsupported")
            .unchecked_into();
        context.transfer_from_image_bitmap(&bitmap);
        drop(bitmap);
        drop(context);

        // 4. Create a `Blob` from the `HTMLCanvasElement`.
        //
        // To keep the `Closure` alive until `HTMLCanvasElement.toBlob()` is done,
        // we do the whole `Waker` strategy. Commonly on `Drop` the callback is aborted,
        // but it would increase complexity and isn't possible in this case.
        // Keep in mind that `HTMLCanvasElement.toBlob()` can call the callback immediately.
        let value = Rc::new(RefCell::new(None));
        let waker = Rc::new(RefCell::<Option<Waker>>::new(None));
        let callback = Closure::once({
            let value = value.clone();
            let waker = waker.clone();
            move |blob: Option<Blob>| {
                *value.borrow_mut() = Some(blob);
                if let Some(waker) = waker.borrow_mut().take() {
                    waker.wake();
                }
            }
        });
        canvas
            .to_blob(callback.as_ref().unchecked_ref())
            .expect("failed with `SecurityError` despite only source coming from memory");
        let blob = future::poll_fn(|cx| {
            if let Some(blob) = value.borrow_mut().take() {
                Poll::Ready(blob)
            } else {
                *waker.borrow_mut() = Some(cx.waker().clone());
                Poll::Pending
            }
        })
        .await;
        drop(canvas);

        let Some(blob) = blob else {
            return Err(CustomCursorError::Blob);
        };

        // 5. Create an object URL from the `Blob`.
        let url = Url::create_object_url_with_blob(&blob)
            .expect("unexpected exception in `URL.createObjectURL()`");
        let url = UrlType::Object(ObjectUrl(url));

        from_url(url, hotspot_x, hotspot_y).await
    }
}

async fn from_url(
    url: UrlType,
    hotspot_x: u16,
    hotspot_y: u16,
) -> Result<Image, CustomCursorError> {
    // 6. Decode the image on an `HTMLImageElement` from the URL.
    let image = HtmlImageElement::new().expect("unexpected exception in `new HtmlImageElement`");
    image.set_src(url.url());
    let result = JsFuture::from(image.decode()).await;

    if let Err(error) = result {
        debug_assert!(error.has_type::<DomException>());
        let error: DomException = error.unchecked_into();
        debug_assert_eq!(error.name(), "EncodingError");
        let error = error.message();

        return Err(CustomCursorError::Decode(error));
    }

    Ok(Image {
        style: format!("url({}) {hotspot_x} {hotspot_y}, auto", url.url()),
        _object_url: match url {
            UrlType::Plain(_) => None,
            UrlType::Object(object_url) => Some(object_url),
        },
        _image: image,
    })
}

#[allow(clippy::await_holding_refcell_ref)] // false-positive
async fn from_animation(
    main_thread: MainThreadMarker,
    duration: Duration,
    cursors: impl ExactSizeIterator<Item = winit_core::cursor::CustomCursor>,
) -> Result<Animation, CustomCursorError> {
    let keyframes = Array::new();
    let mut images = Vec::with_capacity(cursors.len());

    for cursor in cursors {
        let cursor = cursor.cast_ref::<CustomCursor>().unwrap();
        let state = cursor.state.get(main_thread).borrow();

        match state.deref() {
            ImageState::Loading { notifier, .. } => {
                let notified = notifier.notified();
                drop(state);
                notified.await.unwrap()?;
            },
            ImageState::Failed(error) => return Err(error.clone()),
            ImageState::Image(_) => drop(state),
            ImageState::Animation(_) => unreachable!("check in `CustomCursorSource` failed"),
        }

        let state = cursor.state.get(main_thread).borrow();
        let style = match state.deref() {
            ImageState::Image(Image { style, .. }) => style,
            _ => unreachable!("found invalid state"),
        };

        let keyframe: Keyframe = Object::new().unchecked_into();
        keyframe.set_cursor(style);
        keyframes.push(&keyframe);
        drop(state);

        images.push(cursor.clone());
    }

    keyframes.push(&keyframes.get(0));

    let options: KeyframeAnimationOptions = Object::new().unchecked_into();
    options.set_duration(duration.as_millis() as f64);
    options.set_iterations(f64::INFINITY);

    Ok(Animation { keyframes, options, _images: images })
}

#[wasm_bindgen]
extern "C" {
    type CanvasAnimateExt;

    #[wasm_bindgen(method, js_name = animate)]
    fn animate_with_keyframe_animation_options(
        this: &CanvasAnimateExt,
        keyframes: Option<&Object>,
        options: &KeyframeAnimationOptions,
    ) -> WebAnimation;

    #[derive(Debug)]
    type WebAnimation;

    #[wasm_bindgen(method)]
    fn cancel(this: &WebAnimation);

    #[wasm_bindgen(method)]
    fn play(this: &WebAnimation);

    #[wasm_bindgen(extends = Object)]
    type Keyframe;

    #[wasm_bindgen(method, setter, js_name = cursor)]
    fn set_cursor(this: &Keyframe, value: &str);

    #[derive(Debug)]
    #[wasm_bindgen(extends = Object)]
    type KeyframeAnimationOptions;

    #[wasm_bindgen(method, setter, js_name = duration)]
    fn set_duration(this: &KeyframeAnimationOptions, value: f64);

    #[wasm_bindgen(method, setter, js_name = iterations)]
    fn set_iterations(this: &KeyframeAnimationOptions, value: f64);
}
