//! Internal and external event system
//!
//!
//! This is all kinda WIP, but the bones are there.

use crate::{ElementId, ScopeId};
use std::{any::Any, cell::Cell, fmt::Debug, rc::Rc, sync::Arc};

pub(crate) struct BubbleState {
    pub canceled: Cell<bool>,
}

impl BubbleState {
    pub fn new() -> Self {
        Self {
            canceled: Cell::new(false),
        }
    }
}

/// User Events are events that are shuttled from the renderer into the [`VirtualDom`] through the scheduler channel.
///
/// These events will be passed to the appropriate Element given by `mounted_dom_id` and then bubbled up through the tree
/// where each listener is checked and fired if the event name matches.
///
/// It is the expectation that the event name matches the corresponding event listener, otherwise Dioxus will panic in
/// attempting to downcast the event data.
///
/// Because Event Data is sent across threads, it must be `Send + Sync`. We are hoping to lift the `Sync` restriction but
/// `Send` will not be lifted. The entire `UserEvent` must also be `Send + Sync` due to its use in the scheduler channel.
///
/// # Example
/// ```rust, ignore
/// fn App(cx: Scope) -> Element {
///     render!(div {
///         onclick: move |_| println!("Clicked!")
///     })
/// }
///
/// let mut dom = VirtualDom::new(App);
/// let mut scheduler = dom.get_scheduler_channel();
/// scheduler.unbounded_send(SchedulerMsg::UiEvent(
///     UserEvent {
///         scope_id: None,
///         priority: EventPriority::Medium,
///         name: "click",
///         element: Some(ElementId(0)),
///         data: Arc::new(ClickEvent { .. })
///     }
/// )).unwrap();
/// ```
#[derive(Debug, Clone)]
pub struct UserEvent {
    /// The originator of the event trigger if available
    pub scope_id: Option<ScopeId>,

    /// The priority of the event to be scheduled around ongoing work
    pub priority: EventPriority,

    /// The optional real node associated with the trigger
    pub element: Option<ElementId>,

    /// The event type IE "onclick" or "onmouseover"
    pub name: &'static str,

    /// If the event is bubbles up through the vdom
    pub bubbles: bool,

    /// The event data to be passed onto the event handler
    pub data: Arc<dyn Any + Send + Sync>,
}

/// Priority of Event Triggers.
///
/// Internally, Dioxus will abort work that's taking too long if new, more important work arrives. Unlike React, Dioxus
/// won't be afraid to pause work or flush changes to the Real Dom. This is called "cooperative scheduling". Some Renderers
/// implement this form of scheduling internally, however Dioxus will perform its own scheduling as well.
///
/// The ultimate goal of the scheduler is to manage latency of changes, prioritizing "flashier" changes over "subtler" changes.
///
/// React has a 5-tier priority system. However, they break things into "Continuous" and "Discrete" priority. For now,
/// we keep it simple, and just use a 3-tier priority system.
///
/// - `NoPriority` = 0
/// - `LowPriority` = 1
/// - `NormalPriority` = 2
/// - `UserBlocking` = 3
/// - `HighPriority` = 4
/// - `ImmediatePriority` = 5
///
/// We still have a concept of discrete vs continuous though - discrete events won't be batched, but continuous events will.
/// This means that multiple "scroll" events will be processed in a single frame, but multiple "click" events will be
/// flushed before proceeding. Multiple discrete events is highly unlikely, though.
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, PartialOrd, Ord)]
pub enum EventPriority {
    /// Work that must be completed during the EventHandler phase.
    ///
    /// Currently this is reserved for controlled inputs.
    Immediate = 3,

    /// "High Priority" work will not interrupt other high priority work, but will interrupt medium and low priority work.
    ///
    /// This is typically reserved for things like user interaction.
    ///
    /// React calls these "discrete" events, but with an extra category of "user-blocking" (Immediate).
    High = 2,

    /// "Medium priority" work is generated by page events not triggered by the user. These types of events are less important
    /// than "High Priority" events and will take precedence over low priority events.
    ///
    /// This is typically reserved for VirtualEvents that are not related to keyboard or mouse input.
    ///
    /// React calls these "continuous" events (e.g. mouse move, mouse wheel, touch move, etc).
    Medium = 1,

    /// "Low Priority" work will always be preempted unless the work is significantly delayed, in which case it will be
    /// advanced to the front of the work queue until completed.
    ///
    /// The primary user of Low Priority work is the asynchronous work system (Suspense).
    ///
    /// This is considered "idle" work or "background" work.
    Low = 0,
}

/// The internal Dioxus type that carries any event data to the relevant handler.

pub struct AnyEvent {
    pub(crate) bubble_state: Rc<BubbleState>,
    pub(crate) data: Arc<dyn Any + Send + Sync>,
}

impl AnyEvent {
    /// Convert this [`AnyEvent`] into a specific [`UiEvent`] with [`EventData`].
    ///
    /// ```rust, ignore
    /// let evt: FormEvent = evvt.downcast().unwrap();
    /// ```
    #[must_use]
    pub fn downcast<T: Send + Sync + 'static>(self) -> Option<UiEvent<T>> {
        let AnyEvent { data, bubble_state } = self;

        data.downcast::<T>()
            .ok()
            .map(|data| UiEvent { data, bubble_state })
    }
}

/// A [`UiEvent`] is a type that wraps various [`EventData`].
///
/// You should prefer to use the name of the event directly, rather than
/// the [`UiEvent`]<T> generic type.
///
/// For the HTML crate, this would include `MouseEvent`, `FormEvent` etc.
pub struct UiEvent<T> {
    /// The internal data of the event
    /// This is wrapped in an Arc so that it can be sent across threads
    pub data: Arc<T>,

    #[allow(unused)]
    bubble_state: Rc<BubbleState>,
}

impl<T: Debug> std::fmt::Debug for UiEvent<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("UiEvent").field("data", &self.data).finish()
    }
}

impl<T> std::ops::Deref for UiEvent<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        self.data.as_ref()
    }
}

impl<T> UiEvent<T> {
    /// Prevent this event from bubbling up the tree.
    pub fn cancel_bubble(&self) {
        self.bubble_state.canceled.set(true);
    }
}