//! # VirtualDOM Implementation for Rust
//! This module provides the primary mechanics to create a hook-based, concurrent VDOM for Rust.
//!
//! In this file, multiple items are defined. This file is big, but should be documented well to
//! navigate the innerworkings of the Dom. We try to keep these main mechanics in this file to limit
//! the possible exposed API surface (keep fields private). This particular implementation of VDOM
//! is extremely efficient, but relies on some unsafety under the hood to do things like manage
//! micro-heaps for components. We are currently working on refactoring the safety out into safe(r)
//! abstractions, but current tests (MIRI and otherwise) show no issues with the current implementation.
//!
//! Included is:
//! - The [`VirtualDom`] itself
//! - The [`Scope`] object for mangning component lifecycle
//! - The [`ActiveFrame`] object for managing the Scope`s microheap
//! - The [`Context`] object for exposing VirtualDOM API to components
//! - The [`NodeFactory`] object for lazyily exposing the `Context` API to the nodebuilder API
//! - The [`Hook`] object for exposing state management in components.
//!
//! This module includes just the barebones for a complete VirtualDOM API.
//! Additional functionality is defined in the respective files.
#![allow(unreachable_code)]
use futures_util::StreamExt;
use fxhash::FxHashMap;

use crate::hooks::{SuspendedContext, SuspenseHook};
use crate::{arena::SharedResources, innerlude::*};

use std::any::Any;

use std::any::TypeId;
use std::cell::{Ref, RefCell, RefMut};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap};
use std::pin::Pin;

/// An integrated virtual node system that progresses events and diffs UI trees.
/// Differences are converted into patches which a renderer can use to draw the UI.
///
///
///
///
///
///
///
pub struct VirtualDom {
    /// All mounted components are arena allocated to make additions, removals, and references easy to work with
    /// A generational arena is used to re-use slots of deleted scopes without having to resize the underlying arena.
    ///
    /// This is wrapped in an UnsafeCell because we will need to get mutable access to unique values in unique bump arenas
    /// and rusts's guartnees cannot prove that this is safe. We will need to maintain the safety guarantees manually.
    pub shared: SharedResources,

    /// The index of the root component
    /// Should always be the first (gen=0, id=0)
    pub base_scope: ScopeId,

    pending_events: BTreeMap<EventKey, EventTrigger>,

    // for managing the props that were used to create the dom
    #[doc(hidden)]
    _root_prop_type: std::any::TypeId,

    #[doc(hidden)]
    _root_props: std::pin::Pin<Box<dyn std::any::Any>>,
}

impl VirtualDom {
    /// Create a new instance of the Dioxus Virtual Dom with no properties for the root component.
    ///
    /// This means that the root component must either consumes its own context, or statics are used to generate the page.
    /// The root component can access things like routing in its context.
    ///
    /// As an end-user, you'll want to use the Renderer's "new" method instead of this method.
    /// Directly creating the VirtualDOM is only useful when implementing a new renderer.
    ///
    ///
    /// ```ignore
    /// // Directly from a closure
    ///
    /// let dom = VirtualDom::new(|cx| cx.render(rsx!{ div {"hello world"} }));
    ///
    /// // or pass in...
    ///
    /// let root = |cx| {
    ///     cx.render(rsx!{
    ///         div {"hello world"}
    ///     })
    /// }
    /// let dom = VirtualDom::new(root);
    ///
    /// // or directly from a fn
    ///
    /// fn Example(cx: Context<()>) -> DomTree  {
    ///     cx.render(rsx!{ div{"hello world"} })
    /// }
    ///
    /// let dom = VirtualDom::new(Example);
    /// ```
    pub fn new(root: FC<()>) -> Self {
        Self::new_with_props(root, ())
    }

    /// Start a new VirtualDom instance with a dependent cx.
    /// 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.
    ///
    /// ```ignore
    /// // Directly from a closure
    ///
    /// let dom = VirtualDom::new(|cx| cx.render(rsx!{ div {"hello world"} }));
    ///
    /// // or pass in...
    ///
    /// let root = |cx| {
    ///     cx.render(rsx!{
    ///         div {"hello world"}
    ///     })
    /// }
    /// let dom = VirtualDom::new(root);
    ///
    /// // or directly from a fn
    ///
    /// fn Example(cx: Context, props: &SomeProps) -> VNode  {
    ///     cx.render(rsx!{ div{"hello world"} })
    /// }
    ///
    /// let dom = VirtualDom::new(Example);
    /// ```
    pub fn new_with_props<P: Properties + 'static>(root: FC<P>, root_props: P) -> Self {
        let components = SharedResources::new();

        let root_props: Pin<Box<dyn Any>> = Box::pin(root_props);
        let props_ptr = root_props.as_ref().downcast_ref::<P>().unwrap() as *const P;

        let link = components.clone();

        let base_scope = components.insert_scope_with_key(move |myidx| {
            let caller = NodeFactory::create_component_caller(root, props_ptr as *const _);
            Scope::new(caller, myidx, None, 0, ScopeChildren(&[]), link)
        });

        Self {
            base_scope,
            _root_props: root_props,
            shared: components,
            pending_events: BTreeMap::new(),
            _root_prop_type: TypeId::of::<P>(),
        }
    }

    pub fn launch_in_place(root: FC<()>) -> Self {
        let mut s = Self::new(root);
        s.rebuild_in_place().unwrap();
        s
    }

    /// Creates a new virtualdom and immediately rebuilds it in place, not caring about the RealDom to write into.
    ///
    pub fn launch_with_props_in_place<P: Properties + 'static>(root: FC<P>, root_props: P) -> Self {
        let mut s = Self::new_with_props(root, root_props);
        s.rebuild_in_place().unwrap();
        s
    }

    pub fn base_scope(&self) -> &Scope {
        unsafe { self.shared.get_scope(self.base_scope).unwrap() }
    }

    pub fn get_scope(&self, id: ScopeId) -> Option<&Scope> {
        unsafe { self.shared.get_scope(id) }
    }

    /// Rebuilds the VirtualDOM from scratch, but uses a "dummy" RealDom.
    ///
    /// Used in contexts where a real copy of the  structure doesn't matter, and the VirtualDOM is the source of truth.
    ///
    /// ## Why?
    ///
    /// This method uses the `DebugDom` under the hood - essentially making the VirtualDOM's diffing patches a "no-op".
    ///
    /// SSR takes advantage of this by using Dioxus itself as the source of truth, and rendering from the tree directly.
    pub fn rebuild_in_place(&mut self) -> Result<Vec<DomEdit>> {
        todo!();
        // let mut realdom = DebugDom::new();
        // let mut edits = Vec::new();
        // self.rebuild(&mut realdom, &mut edits)?;
        // Ok(edits)
    }

    /// Performs a *full* rebuild of the virtual dom, returning every edit required to generate the actual dom rom scratch
    ///
    /// The diff machine expects the RealDom's stack to be the root of the application
    ///
    /// Events like garabge collection, application of refs, etc are not handled by this method and can only be progressed
    /// through "run"
    ///
    pub fn rebuild<'s>(&'s mut self, edits: &'_ mut Vec<DomEdit<'s>>) -> Result<()> {
        let mut diff_machine = DiffMachine::new(edits, self.base_scope, &self.shared);

        let cur_component = diff_machine
            .get_scope_mut(&self.base_scope)
            .expect("The base scope should never be moved");

        // We run the component. If it succeeds, then we can diff it and add the changes to the dom.
        if cur_component.run_scope().is_ok() {
            let meta = diff_machine.create_vnode(cur_component.frames.fin_head());
            diff_machine.edit_append_children(meta.added_to_stack);
        } else {
            // todo: should this be a hard error?
            log::warn!(
                "Component failed to run succesfully during rebuild.
                This does not result in a failed rebuild, but indicates a logic failure within your app."
            );
        }

        Ok(())
    }

    async fn select_next_event(&mut self) -> Option<EventTrigger> {
        let mut receiver = self.shared.task_receiver.borrow_mut();

        // drain the in-flight events so that we can sort them out with the current events
        while let Ok(Some(trigger)) = receiver.try_next() {
            log::info!("scooping event from receiver");
            self.pending_events.insert(trigger.make_key(), trigger);
        }

        if self.pending_events.is_empty() {
            // Continuously poll the future pool and the event receiver for work
            let mut tasks = self.shared.async_tasks.borrow_mut();
            let tasks_tasks = tasks.next();

            let mut receiver = self.shared.task_receiver.borrow_mut();
            let reciv_task = receiver.next();

            futures_util::pin_mut!(tasks_tasks);
            futures_util::pin_mut!(reciv_task);

            let trigger = match futures_util::future::select(tasks_tasks, reciv_task).await {
                futures_util::future::Either::Left((trigger, _)) => trigger,
                futures_util::future::Either::Right((trigger, _)) => trigger,
            }
            .unwrap();
            self.pending_events.insert(trigger.make_key(), trigger);
        }

        todo!()

        // let trigger = self.select_next_event().unwrap();
        // trigger
    }

    // the cooperartive, fiber-based scheduler
    // is "awaited" and will always return some edits for the real dom to apply
    //
    // Right now, we'll happily partially render component trees
    //
    // Normally, you would descend through the tree depth-first, but we actually descend breadth-first.
    pub async fn run(&mut self, realdom: &mut dyn RealDom) -> Result<()> {
        let cur_component = self.base_scope;
        let mut edits = Vec::new();
        let resources = self.shared.clone();

        let mut diff_machine = DiffMachine::new(&mut edits, cur_component, &resources);

        loop {
            let trigger = self.select_next_event().await.unwrap();

            match &trigger.event {
                // Collecting garabge is not currently interruptible.
                //
                // In the future, it could be though
                VirtualEvent::GarbageCollection => {
                    let scope = diff_machine.get_scope_mut(&trigger.originator).unwrap();

                    let mut garbage_list = scope.consume_garbage();

                    let mut scopes_to_kill = Vec::new();
                    while let Some(node) = garbage_list.pop() {
                        match &node.kind {
                            VNodeKind::Text(_) => {
                                self.shared.collect_garbage(node.direct_id());
                            }
                            VNodeKind::Anchor(_) => {
                                self.shared.collect_garbage(node.direct_id());
                            }
                            VNodeKind::Suspended(_) => {
                                self.shared.collect_garbage(node.direct_id());
                            }

                            VNodeKind::Element(el) => {
                                self.shared.collect_garbage(node.direct_id());
                                for child in el.children {
                                    garbage_list.push(child);
                                }
                            }

                            VNodeKind::Fragment(frag) => {
                                for child in frag.children {
                                    garbage_list.push(child);
                                }
                            }

                            VNodeKind::Component(comp) => {
                                // TODO: run the hook destructors and then even delete the scope
                                // TODO: allow interruption here
                                if !realdom.must_commit() {
                                    let scope_id = comp.ass_scope.get().unwrap();
                                    let scope = self.get_scope(scope_id).unwrap();
                                    let root = scope.root();
                                    garbage_list.push(root);
                                    scopes_to_kill.push(scope_id);
                                }
                            }
                        }
                    }

                    for scope in scopes_to_kill {
                        // oy kill em
                        log::debug!("should be removing scope {:#?}", scope);
                    }
                }

                VirtualEvent::AsyncEvent { .. } => {
                    // we want to progress these events
                    // However, there's nothing we can do for these events, they must generate their own events.
                }

                // Suspense Events! A component's suspended node is updated
                VirtualEvent::SuspenseEvent { hook_idx, domnode } => {
                    // Safety: this handler is the only thing that can mutate shared items at this moment in tim
                    let scope = diff_machine.get_scope_mut(&trigger.originator).unwrap();

                    // safety: we are sure that there are no other references to the inner content of suspense hooks
                    let hook = unsafe { scope.hooks.get_mut::<SuspenseHook>(*hook_idx) }.unwrap();

                    let cx = Context { scope, props: &() };
                    let scx = SuspendedContext { inner: cx };

                    // generate the new node!
                    let nodes: Option<VNode> = (&hook.callback)(scx);
                    match nodes {
                        None => {
                            log::warn!(
                            "Suspense event came through, but there were no generated nodes >:(."
                        );
                        }
                        Some(nodes) => {
                            // allocate inside the finished frame - not the WIP frame
                            let nodes = scope.frames.finished_frame().bump.alloc(nodes);

                            // push the old node's root onto the stack
                            let real_id = domnode.get().ok_or(Error::NotMounted)?;
                            diff_machine.edit_push_root(real_id);

                            // push these new nodes onto the diff machines stack
                            let meta = diff_machine.create_vnode(&*nodes);

                            // replace the placeholder with the new nodes we just pushed on the stack
                            diff_machine.edit_replace_with(1, meta.added_to_stack);
                        }
                    }
                }

                // Run the component
                VirtualEvent::ScheduledUpdate { height: u32 } => {
                    let scope = diff_machine.get_scope_mut(&trigger.originator).unwrap();

                    match scope.run_scope() {
                        Ok(_) => {
                            let event = VirtualEvent::DiffComponent;
                            let trigger = EventTrigger {
                                event,
                                originator: trigger.originator,
                                priority: EventPriority::High,
                                real_node_id: None,
                            };
                            self.shared.task_sender.unbounded_send(trigger);
                        }
                        Err(_) => {
                            log::error!("failed to run this component!");
                        }
                    }
                }

                VirtualEvent::DiffComponent => {
                    diff_machine.diff_scope(trigger.originator)?;
                }

                // Process any user-facing events just by calling their listeners
                // This performs no actual work - but the listeners themselves will cause insert new work
                VirtualEvent::ClipboardEvent(_)
                | VirtualEvent::CompositionEvent(_)
                | VirtualEvent::KeyboardEvent(_)
                | VirtualEvent::FocusEvent(_)
                | VirtualEvent::FormEvent(_)
                | VirtualEvent::SelectionEvent(_)
                | VirtualEvent::TouchEvent(_)
                | VirtualEvent::UIEvent(_)
                | VirtualEvent::WheelEvent(_)
                | VirtualEvent::MediaEvent(_)
                | VirtualEvent::AnimationEvent(_)
                | VirtualEvent::TransitionEvent(_)
                | VirtualEvent::ToggleEvent(_)
                | VirtualEvent::MouseEvent(_)
                | VirtualEvent::PointerEvent(_) => {
                    let scope_id = &trigger.originator;
                    let scope = unsafe { self.shared.get_scope_mut(*scope_id) };
                    match scope {
                        Some(scope) => scope.call_listener(trigger)?,
                        None => {
                            log::warn!("No scope found for event: {:#?}", scope_id);
                        }
                    }
                }
            }

            if realdom.must_commit() || self.pending_events.is_empty() {
                realdom.commit_edits(&mut diff_machine.edits);
                realdom.wait_until_ready().await;
            }
        }

        Ok(())
    }

    pub fn get_event_sender(&self) -> futures_channel::mpsc::UnboundedSender<EventTrigger> {
        todo!()
        // std::rc::Rc::new(move |_| {
        //     //
        // })
        // todo()
    }
}

// TODO!
// These impls are actually wrong. The DOM needs to have a mutex implemented.
unsafe impl Sync for VirtualDom {}
unsafe impl Send for VirtualDom {}

fn select_next_event(
    pending_events: &mut BTreeMap<EventKey, EventTrigger>,
) -> Option<EventTrigger> {
    None
}