use crate::{
    any_props::VComponentProps,
    arena::ElementId,
    arena::ElementRef,
    diff::DirtyScope,
    factory::RenderReturn,
    innerlude::{Mutations, Scheduler, SchedulerMsg},
    mutations::Mutation,
    nodes::{Template, TemplateId},
    scheduler::{SuspenseBoundary, SuspenseId},
    scopes::{ScopeId, ScopeState},
    Attribute, AttributeValue, Element, EventPriority, Scope, SuspenseContext, UiEvent,
};
use futures_util::{pin_mut, FutureExt, StreamExt};
use slab::Slab;
use std::rc::Rc;
use std::{
    any::Any,
    collections::{BTreeSet, HashMap},
};
use std::{cell::Cell, future::Future};

/// A virtual node system that progresses user events and diffs UI trees.
///
/// ## Guide
///
/// Components are defined as simple functions that take [`Scope`] and return an [`Element`].
///
/// ```rust, ignore
/// #[derive(Props, PartialEq)]
/// struct AppProps {
///     title: String
/// }
///
/// fn App(cx: Scope<AppProps>) -> Element {
///     cx.render(rsx!(
///         div {"hello, {cx.props.title}"}
///     ))
/// }
/// ```
///
/// Components may be composed to make complex apps.
///
/// ```rust, ignore
/// fn App(cx: Scope<AppProps>) -> Element {
///     cx.render(rsx!(
///         NavBar { routes: ROUTES }
///         Title { "{cx.props.title}" }
///         Footer {}
///     ))
/// }
/// ```
///
/// To start an app, create a [`VirtualDom`] and call [`VirtualDom::rebuild`] to get the list of edits required to
/// draw the UI.
///
/// ```rust, ignore
/// let mut vdom = VirtualDom::new(App);
/// let edits = vdom.rebuild();
/// ```
///
/// To call listeners inside the VirtualDom, call [`VirtualDom::handle_event`] with the appropriate event data.
///
/// ```rust, ignore
/// vdom.handle_event(event);
/// ```
///
/// While no events are ready, call [`VirtualDom::wait_for_work`] to poll any futures inside the VirtualDom.
///
/// ```rust, ignore
/// vdom.wait_for_work().await;
/// ```
///
/// Once work is ready, call [`VirtualDom::render_with_deadline`] to compute the differences between the previous and
/// current UI trees. This will return a [`Mutations`] object that contains Edits, Effects, and NodeRefs that need to be
/// handled by the renderer.
///
/// ```rust, ignore
/// let mutations = vdom.work_with_deadline(tokio::time::sleep(Duration::from_millis(100)));
///
/// for edit in mutations.edits {
///     real_dom.apply(edit);
/// }
/// ```
///
/// To not wait for suspense while diffing the VirtualDom, call [`VirtualDom::render_immediate`] or pass an immediately
/// ready future to [`VirtualDom::render_with_deadline`].
///
///
/// ## Building an event loop around Dioxus:
///
/// Putting everything together, you can build an event loop around Dioxus by using the methods outlined above.
/// ```rust
/// fn app(cx: Scope) -> Element {
///     cx.render(rsx!{
///         div { "Hello World" }
///     })
/// }
///
/// let dom = VirtualDom::new(app);
///
/// real_dom.apply(dom.rebuild());
///
/// loop {
///     select! {
///         _ = dom.wait_for_work() => {}
///         evt = real_dom.wait_for_event() => dom.handle_event(evt),
///     }
///
///     real_dom.apply(dom.render_immediate());
/// }
/// ```
///
/// ## Waiting for suspense
///
/// Because Dioxus supports suspense, you can use it for server-side rendering, static site generation, and other usecases
/// where waiting on portions of the UI to finish rendering is important. To wait for suspense, use the
/// [`VirtualDom::render_with_deadline`] method:
///
/// ```rust
/// let dom = VirtualDom::new(app);
///
/// let deadline = tokio::time::sleep(Duration::from_millis(100));
/// let edits = dom.render_with_deadline(deadline).await;
/// ```
///
/// ## Use with streaming
///
/// If not all rendering is done by the deadline, it might be worthwhile to stream the rest later. To do this, we
/// suggest rendering with a deadline, and then looping between [`VirtualDom::wait_for_work`] and render_immediate until
/// no suspended work is left.
///
/// ```
/// let dom = VirtualDom::new(app);
///
/// let deadline = tokio::time::sleep(Duration::from_millis(20));
/// let edits = dom.render_with_deadline(deadline).await;
///
/// real_dom.apply(edits);
///
/// while dom.has_suspended_work() {
///    dom.wait_for_work().await;
///    real_dom.apply(dom.render_immediate());
/// }
/// ```
pub struct VirtualDom {
    pub(crate) templates: HashMap<TemplateId, Template<'static>>,
    pub(crate) scopes: Slab<ScopeState>,
    pub(crate) element_stack: Vec<ElementId>,
    pub(crate) dirty_scopes: BTreeSet<DirtyScope>,
    pub(crate) scheduler: Rc<Scheduler>,

    // Every element is actually a dual reference - one to the template and the other to the dynamic node in that template
    pub(crate) elements: Slab<ElementRef>,

    // While diffing we need some sort of way of breaking off a stream of suspended mutations.
    pub(crate) scope_stack: Vec<ScopeId>,
    pub(crate) collected_leaves: Vec<SuspenseId>,

    // Whenever a suspense tree is finished, we push its boundary onto this stack.
    // When "render_with_deadline" is called, we pop the stack and return the mutations
    pub(crate) finished_fibers: Vec<ScopeId>,

    pub(crate) rx: futures_channel::mpsc::UnboundedReceiver<SchedulerMsg>,
}

impl VirtualDom {
    /// Create a new VirtualDom with a component that does not have special props.
    ///
    /// # Description
    ///
    /// Later, the props can be updated by calling "update" with a new set of props, causing a set of re-renders.
    ///
    /// This is useful when a component tree can be driven by external state (IE SSR) but it would be too expensive
    /// to toss out the entire tree.
    ///
    ///
    /// # Example
    /// ```rust, ignore
    /// fn Example(cx: Scope) -> Element  {
    ///     cx.render(rsx!( div { "hello world" } ))
    /// }
    ///
    /// let dom = VirtualDom::new(Example);
    /// ```
    ///
    /// Note: the VirtualDom is not progressed, you must either "run_with_deadline" or use "rebuild" to progress it.
    pub fn new(app: fn(Scope) -> Element) -> Self {
        Self::new_with_props(app, ())
    }

    /// Create a new VirtualDom with the given properties for the root component.
    ///
    /// # Description
    ///
    /// Later, the props can be updated by calling "update" with a new set of props, causing a set of re-renders.
    ///
    /// This is useful when a component tree can be driven by external state (IE SSR) but it would be too expensive
    /// to toss out the entire tree.
    ///
    ///
    /// # Example
    /// ```rust, ignore
    /// #[derive(PartialEq, Props)]
    /// struct SomeProps {
    ///     name: &'static str
    /// }
    ///
    /// fn Example(cx: Scope<SomeProps>) -> Element  {
    ///     cx.render(rsx!{ div{ "hello {cx.props.name}" } })
    /// }
    ///
    /// let dom = VirtualDom::new(Example);
    /// ```
    ///
    /// Note: the VirtualDom is not progressed on creation. You must either "run_with_deadline" or use "rebuild" to progress it.
    ///
    /// ```rust, ignore
    /// let mut dom = VirtualDom::new_with_props(Example, SomeProps { name: "jane" });
    /// let mutations = dom.rebuild();
    /// ```
    pub fn new_with_props<P>(root: fn(Scope<P>) -> Element, root_props: P) -> Self
    where
        P: 'static,
    {
        let (tx, rx) = futures_channel::mpsc::unbounded();
        let mut dom = Self {
            rx,
            scheduler: Scheduler::new(tx),
            templates: Default::default(),
            scopes: Slab::default(),
            elements: Default::default(),
            scope_stack: Vec::new(),
            element_stack: vec![ElementId(0)],
            dirty_scopes: BTreeSet::new(),
            collected_leaves: Vec::new(),
            finished_fibers: Vec::new(),
        };

        let root = dom.new_scope(Box::into_raw(Box::new(VComponentProps::new(
            root,
            |_, _| unreachable!(),
            root_props,
        ))));

        // The root component is always a suspense boundary for any async children
        // This could be unexpected, so we might rethink this behavior
        root.provide_context(SuspenseBoundary::new(ScopeId(0)));

        // the root element is always given element 0
        dom.elements.insert(ElementRef::null());

        dom
    }

    pub fn get_scope(&self, id: ScopeId) -> Option<&ScopeState> {
        self.scopes.get(id.0)
    }

    pub fn base_scope(&self) -> &ScopeState {
        self.scopes.get(0).unwrap()
    }

    /// Build the virtualdom with a global context inserted into the base scope
    pub fn with_root_context<T: Clone + 'static>(self, context: T) -> Self {
        self.base_scope().provide_context(context);
        self
    }

    fn mark_dirty_scope(&mut self, id: ScopeId) {
        let height = self.scopes[id.0].height;
        self.dirty_scopes.insert(DirtyScope { height, id });
    }

    fn is_scope_suspended(&self, id: ScopeId) -> bool {
        !self.scopes[id.0]
            .consume_context::<SuspenseContext>()
            .unwrap()
            .waiting_on
            .borrow()
            .is_empty()
    }

    /// Returns true if there is any suspended work left to be done.
    pub fn has_suspended_work(&self) -> bool {
        !self.scheduler.leaves.borrow().is_empty()
    }

    /// Call a listener inside the VirtualDom with data from outside the VirtualDom.
    ///
    /// This method will identify the appropriate element
    ///
    ///
    ///
    ///
    ///
    ///
    ///
    pub fn handle_event(
        &mut self,
        name: &str,
        data: Rc<dyn Any>,
        element: ElementId,
        bubbles: bool,
        // todo: priority is helpful when scheduling work around suspense, but we don't currently use it
        _priority: EventPriority,
    ) {
        let uievent = UiEvent {
            bubbles: Rc::new(Cell::new(bubbles)),
            data,
        };

        /*
        ------------------------
        The algorithm works by walking through the list of dynamic attributes, checking their paths, and breaking when
        we find the target path.

        With the target path, we try and move up to the parent until there is no parent.
        Due to how bubbling works, we call the listeners before walking to the parent.

        If we wanted to do capturing, then we would accumulate all the listeners and call them in reverse order.
        ----------------------
        |           <-- yes (is ascendant)
        | | |       <-- no  (is not ascendant)
        | |         <-- yes (is ascendant)
        | | | | |   <--- target element, break early
        | | |       <-- no, broke early
        |           <-- no, broke early
        */
        let mut parent_path = self.elements.get(element.0);
        let mut listeners = vec![];

        while let Some(el_ref) = parent_path {
            let template = unsafe { &*el_ref.template };
            let target_path = el_ref.path;

            let mut attrs = template.dynamic_attrs.iter().enumerate();

            while let Some((idx, attr)) = attrs.next() {
                pub fn is_path_ascendant(small: &[u8], big: &[u8]) -> bool {
                    small.len() >= big.len() && small == &big[..small.len()]
                }

                let this_path = template.template.attr_paths[idx];

                println!(
                    "is {:?} ascendant of {:?} ? {}",
                    this_path,
                    target_path,
                    is_path_ascendant(this_path, target_path)
                );

                println!("{ } - {name}, - {}", attr.name, &attr.name[2..]);

                if &attr.name[2..] == name && is_path_ascendant(&target_path, &this_path) {
                    listeners.push(&attr.value);

                    // Break if the event doesn't bubble anyways
                    if !bubbles {
                        break;
                    }

                    // Break if this is the exact target element
                    if this_path == target_path {
                        break;
                    }
                }
            }

            for listener in listeners.drain(..).rev() {
                if let AttributeValue::Listener(listener) = listener {
                    listener.borrow_mut()(uievent.clone());

                    // Break if the event doesn't bubble
                    if !uievent.bubbles.get() {
                        return;
                    }
                }
            }

            parent_path = template.parent.and_then(|id| self.elements.get(id.0));
        }
    }

    /// Wait for the scheduler to have any work.
    ///
    /// This method polls the internal future queue, waiting for suspense nodes, tasks, or other work. This completes when
    /// any work is ready. If multiple scopes are marked dirty from a task or a suspense tree is finished, this method
    /// will exit.
    ///
    /// This method is cancel-safe, so you're fine to discard the future in a select block.
    ///
    /// This lets us poll async tasks during idle periods without blocking the main thread.
    ///
    /// # Example
    ///
    /// ```rust, ignore
    /// let dom = VirtualDom::new(App);
    /// let sender = dom.get_scheduler_channel();
    /// ```
    pub async fn wait_for_work(&mut self) {
        let mut some_msg = None;

        loop {
            match some_msg.take() {
                // If a bunch of messages are ready in a sequence, try to pop them off synchronously
                Some(msg) => match msg {
                    SchedulerMsg::Immediate(id) => self.mark_dirty_scope(id),
                    SchedulerMsg::TaskNotified(task) => self.handle_task_wakeup(task),
                    SchedulerMsg::SuspenseNotified(id) => self.handle_suspense_wakeup(id),
                },

                // If they're not ready, then we should wait for them to be ready
                None => {
                    match self.rx.try_next() {
                        Ok(Some(val)) => some_msg = Some(val),
                        Ok(None) => return,
                        Err(_) => {
                            // If we have any dirty scopes, or finished fiber trees then we should exit
                            if !self.dirty_scopes.is_empty() || !self.finished_fibers.is_empty() {
                                return;
                            }

                            some_msg = self.rx.next().await
                        }
                    }
                }
            }
        }
    }

    /// Performs a *full* rebuild of the virtual dom, returning every edit required to generate the actual dom from scratch.
    ///
    /// The diff machine expects the RealDom's stack to be the root of the application.
    ///
    /// Tasks will not be polled with this method, nor will any events be processed from the event queue. Instead, the
    /// root component will be ran once and then diffed. All updates will flow out as mutations.
    ///
    /// All state stored in components will be completely wiped away.
    ///
    /// Any templates previously registered will remain.
    ///
    /// # Example
    /// ```rust, ignore
    /// static App: Component = |cx|  cx.render(rsx!{ "hello world" });
    ///
    /// let mut dom = VirtualDom::new();
    /// let edits = dom.rebuild();
    ///
    /// apply_edits(edits);
    /// ```
    pub fn rebuild<'a>(&'a mut self) -> Mutations<'a> {
        let mut mutations = Mutations::new(0);

        let root_node = unsafe { self.run_scope_extend(ScopeId(0)) };
        match root_node {
            RenderReturn::Sync(Some(node)) => {
                let m = self.create_scope(ScopeId(0), &mut mutations, node);
                mutations.push(Mutation::AppendChildren { m });
            }
            RenderReturn::Sync(None) => {}
            RenderReturn::Async(_) => unreachable!("Root scope cannot be an async component"),
        }

        mutations
    }

    /// Render whatever the VirtualDom has ready as fast as possible without requiring an executor to progress
    /// suspended subtrees.
    pub fn render_immediate(&mut self) -> Mutations {
        // Build a waker that won't wake up since our deadline is already expired when it's polled
        let waker = futures_util::task::noop_waker();
        let mut cx = std::task::Context::from_waker(&waker);

        // Now run render with deadline but dont even try to poll any async tasks
        let fut = self.render_with_deadline(std::future::ready(()));
        pin_mut!(fut);
        match fut.poll_unpin(&mut cx) {
            std::task::Poll::Ready(mutations) => mutations,
            std::task::Poll::Pending => panic!("render_immediate should never return pending"),
        }
    }

    /// Render what you can given the timeline and then move on
    ///
    /// It's generally a good idea to put some sort of limit on the suspense process in case a future is having issues.
    ///
    /// If no suspense trees are present
    pub async fn render_with_deadline<'a>(
        &'a mut self,
        deadline: impl Future<Output = ()>,
    ) -> Mutations<'a> {
        use futures_util::future::{select, Either};

        let mut mutations = Mutations::new(0);
        pin_mut!(deadline);

        loop {
            // first, unload any complete suspense trees
            for finished_fiber in self.finished_fibers.drain(..) {
                let scope = &mut self.scopes[finished_fiber.0];
                let context = scope.has_context::<SuspenseContext>().unwrap();
                println!("unloading suspense tree {:?}", context.mutations);

                mutations.extend(context.mutations.borrow_mut().template_mutations.drain(..));
                mutations.extend(context.mutations.borrow_mut().drain(..));

                mutations.push(Mutation::ReplaceWith {
                    id: context.placeholder.get().unwrap(),
                    m: 1,
                })
            }

            // Next, diff any dirty scopes
            // We choose not to poll the deadline since we complete pretty quickly anyways
            if let Some(dirty) = self.dirty_scopes.iter().next().cloned() {
                self.dirty_scopes.remove(&dirty);

                // if the scope is currently suspended, then we should skip it, ignoring any tasks calling for an update
                if !self.is_scope_suspended(dirty.id) {
                    self.run_scope(dirty.id);
                    self.diff_scope(&mut mutations, dirty.id);
                }
            }

            // Wait for suspense, or a deadline
            if self.dirty_scopes.is_empty() {
                if self.scheduler.leaves.borrow().is_empty() {
                    return mutations;
                }

                let (work, deadline) = (self.wait_for_work(), &mut deadline);
                pin_mut!(work);

                if let Either::Left((_, _)) = select(deadline, work).await {
                    return mutations;
                }
            }
        }
    }

    // fn mark_dirty_scope(&mut self, scope_id: ScopeId) {
    //     let scopes = &self.scopes;
    //     if let Some(scope) = scopes.get_scope(scope_id) {
    //         let height = scope.height;
    //         let id = scope_id.0;
    //         if let Err(index) = self.dirty_scopes.binary_search_by(|new| {
    //             let scope = scopes.get_scope(*new).unwrap();
    //             let new_height = scope.height;
    //             let new_id = &scope.scope_id();
    //             height.cmp(&new_height).then(new_id.0.cmp(&id))
    //         }) {
    //             self.dirty_scopes.insert(index, scope_id);
    //             log::info!("mark_dirty_scope: {:?}", self.dirty_scopes);
    //         }
    //     }
    // }
}

impl Drop for VirtualDom {
    fn drop(&mut self) {
        // self.drop_scope(ScopeId(0));
    }
}