//! App event and commands API.

use std::{
    any::Any,
    fmt,
    marker::PhantomData,
    mem,
    ops::Deref,
    sync::{
        atomic::{AtomicBool, Ordering},
        Arc,
    },
    time::Instant,
};

mod args;
pub use args::*;

mod command;
pub use command::*;

mod events;
pub use events::*;

mod channel;
pub use channel::*;

use crate::{
    handler::{AppHandler, AppHandlerArgs},
    update::{EventUpdate, UpdateDeliveryList, UpdateSubscribers},
    widget::WidgetId,
};
use parking_lot::Mutex;
use zng_app_context::AppLocal;
use zng_clone_move::clmv;
use zng_unique_id::{IdEntry, IdMap, IdSet};

///<span data-del-macro-root></span> Declares new [`Event<A>`] static items.
///
/// Event static items represent external, app or widget events. You can also use [`command!`]
/// to declare events specialized for commanding widgets and services.
///
/// [`AppExtension`]: crate::AppExtension
///
/// # Conventions
///
/// Command events have the `_EVENT` suffix, for example an event representing a click is called `CLICK_EVENT`.
///
/// # Properties
///
/// If the event targets widgets you can use `event_property!` to declare properties that setup event handlers for the event.
///
/// # Examples
///
/// The example defines two events with the same arguments type.
///
/// ```
/// # use zng_app::event::*;
/// # event_args! { pub struct ClickArgs { .. fn delivery_list(&self, _l: &mut UpdateDeliveryList) { } } }
/// event! {
///     /// Event docs.
///     pub static CLICK_EVENT: ClickArgs;
///
///     /// Other event docs.
///     pub static DOUBLE_CLICK_EVENT: ClickArgs;
/// }
/// ```
#[macro_export]
macro_rules! event_macro {
    ($(
        $(#[$attr:meta])*
        $vis:vis static $EVENT:ident: $Args:path;
    )+) => {
        $(
            $(#[$attr])*
            $vis static $EVENT: $crate::event::Event<$Args> = {
                $crate::event::app_local! {
                    static LOCAL: $crate::event::EventData = const { $crate::event::EventData::new(std::stringify!($EVENT)) };
                }
                $crate::event::Event::new(&LOCAL)
            };
        )+
    }
}
#[doc(inline)]
pub use crate::event_macro as event;

#[doc(hidden)]
pub struct EventData {
    name: &'static str,
    widget_subs: IdMap<WidgetId, EventHandle>,
    hooks: Vec<EventHook>,
}
impl EventData {
    #[doc(hidden)]
    pub const fn new(name: &'static str) -> Self {
        EventData {
            name,
            widget_subs: IdMap::new(),
            hooks: vec![],
        }
    }
}

/// Represents an event.
///
/// Use the [`event!`] macro to declare events.
pub struct Event<A: EventArgs> {
    local: &'static AppLocal<EventData>,
    _args: PhantomData<fn(A)>,
}
impl<A: EventArgs> fmt::Debug for Event<A> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if f.alternate() {
            write!(f, "Event({})", self.name())
        } else {
            write!(f, "{}", self.name())
        }
    }
}
impl<A: EventArgs> Event<A> {
    #[doc(hidden)]
    pub const fn new(local: &'static AppLocal<EventData>) -> Self {
        Event { local, _args: PhantomData }
    }

    /// Gets the event without the args type.
    pub fn as_any(&self) -> AnyEvent {
        AnyEvent { local: self.local }
    }

    /// Register the widget to receive targeted events from this event.
    ///
    /// Widgets only receive events if they are in the delivery list generated by the event args and are
    /// subscribers to the event. App extensions receive all events.
    pub fn subscribe(&self, widget_id: WidgetId) -> EventHandle {
        self.as_any().subscribe(widget_id)
    }

    /// Returns `true` if the widget is subscribed to this event.
    pub fn is_subscriber(&self, widget_id: WidgetId) -> bool {
        self.as_any().is_subscriber(widget_id)
    }

    /// Returns `true` if at least one widget is subscribed to this event.
    pub fn has_subscribers(&self) -> bool {
        self.as_any().has_subscribers()
    }

    /// Calls `visit` for each widget subscribed to this event.
    ///
    /// Note that trying to subscribe or add hook inside `visit` will deadlock. Inside `visit` you can notify the event and
    /// generate event updates.
    pub fn visit_subscribers(&self, visit: impl FnMut(WidgetId)) {
        self.as_any().visit_subscribers(visit)
    }

    /// Name of the event static item.
    pub fn name(&self) -> &'static str {
        self.local.read().name
    }

    /// Returns `true` if the update is for this event.
    pub fn has(&self, update: &EventUpdate) -> bool {
        *self == update.event
    }

    /// Get the event update args if the update is for this event.
    pub fn on<'a>(&self, update: &'a EventUpdate) -> Option<&'a A> {
        if *self == update.event {
            update.args.as_any().downcast_ref()
        } else {
            None
        }
    }

    /// Get the event update args if the update is for this event and propagation is not stopped.
    pub fn on_unhandled<'a>(&self, update: &'a EventUpdate) -> Option<&'a A> {
        self.on(update).filter(|a| !a.propagation().is_stopped())
    }

    /// Calls `handler` if the update is for this event and propagation is not stopped, after the handler is called propagation is stopped.
    pub fn handle<R>(&self, update: &EventUpdate, handler: impl FnOnce(&A) -> R) -> Option<R> {
        if let Some(args) = self.on(update) {
            args.handle(handler)
        } else {
            None
        }
    }

    /// Create an event update for this event with delivery list filtered by the event subscribers.
    pub fn new_update(&self, args: A) -> EventUpdate {
        self.new_update_custom(args, UpdateDeliveryList::new(Box::new(self.as_any())))
    }

    /// Create and event update for this event with a custom delivery list.
    pub fn new_update_custom(&self, args: A, mut delivery_list: UpdateDeliveryList) -> EventUpdate {
        args.delivery_list(&mut delivery_list);
        EventUpdate {
            event: self.as_any(),
            delivery_list,
            args: Box::new(args),
            pre_actions: Mutex::new(vec![]),
            pos_actions: Mutex::new(vec![]),
        }
    }

    /// Schedule an event update.
    pub fn notify(&self, args: A) {
        let update = self.new_update(args);
        EVENTS.notify(update);
    }

    /// Creates a preview event handler.
    ///
    /// The event `handler` is called for every update that has not stopped [`propagation`](AnyEventArgs::propagation).
    /// The handler is called before widget handlers and [`on_event`](Self::on_event) handlers. The handler is called
    /// after all previous registered preview handlers.
    ///
    /// Returns an [`EventHandle`] that can be dropped to unsubscribe, you can also unsubscribe from inside the handler by calling
    /// [`unsubscribe`](crate::handler::AppWeakHandle::unsubscribe) in the third parameter of [`app_hn!`] or [`async_app_hn!`].
    ///
    /// # Examples
    ///
    /// ```
    /// # use zng_app::event::*;
    /// # use zng_app::APP;
    /// # use zng_app::handler::app_hn;
    /// # event_args! { pub struct FocusChangedArgs { pub new_focus: bool, .. fn delivery_list(&self, _l: &mut UpdateDeliveryList) {} } }
    /// # event! { pub static FOCUS_CHANGED_EVENT: FocusChangedArgs; }
    /// # let _scope = APP.minimal();
    /// let handle = FOCUS_CHANGED_EVENT.on_pre_event(app_hn!(|args: &FocusChangedArgs, _| {
    ///     println!("focused: {:?}", args.new_focus);
    /// }));
    /// ```
    /// The example listens to all `FOCUS_CHANGED_EVENT` events, independent of widget context and before all UI handlers.
    ///
    /// # Handlers
    ///
    /// the event handler can be any type that implements [`AppHandler`], there are multiple flavors of handlers, including
    /// async handlers that allow calling `.await`. The handler closures can be declared using [`app_hn!`], [`async_app_hn!`],
    /// [`app_hn_once!`] and [`async_app_hn_once!`].
    ///
    /// ## Async
    ///
    /// Note that for async handlers only the code before the first `.await` is called in the *preview* moment, code after runs in
    /// subsequent event updates, after the event has already propagated, so stopping [`propagation`](AnyEventArgs::propagation)
    /// only causes the desired effect before the first `.await`.
    ///
    /// [`app_hn!`]: crate::handler::app_hn!
    /// [`async_app_hn!`]: crate::handler::async_app_hn!
    /// [`app_hn_once!`]: crate::handler::app_hn_once!
    /// [`async_app_hn_once!`]: crate::handler::async_app_hn_once!
    pub fn on_pre_event<H>(&self, handler: H) -> EventHandle
    where
        H: AppHandler<A>,
    {
        self.on_event_impl(handler, true)
    }

    /// Creates an event handler.
    ///
    /// The event `handler` is called for every update that has not stopped [`propagation`](AnyEventArgs::propagation).
    /// The handler is called after all [`on_pre_event`](Self::on_pre_event) all widget handlers and all [`on_event`](Self::on_event)
    /// handlers registered before this one.
    ///
    /// Returns an [`EventHandle`] that can be dropped to unsubscribe, you can also unsubscribe from inside the handler by calling
    /// [`unsubscribe`](crate::handler::AppWeakHandle::unsubscribe) in the third parameter of [`app_hn!`] or [`async_app_hn!`].
    ///
    /// # Examples
    ///
    /// ```
    /// # use zng_app::event::*;
    /// # use zng_app::APP;
    /// # use zng_app::handler::app_hn;
    /// # event_args! { pub struct FocusChangedArgs { pub new_focus: bool, .. fn delivery_list(&self, _l: &mut UpdateDeliveryList) {} } }
    /// # event! { pub static FOCUS_CHANGED_EVENT: FocusChangedArgs; }
    /// # let _scope = APP.minimal();
    /// let handle = FOCUS_CHANGED_EVENT.on_event(app_hn!(|args: &FocusChangedArgs, _| {
    ///     println!("focused: {:?}", args.new_focus);
    /// }));
    /// ```
    /// The example listens to all `FOCUS_CHANGED_EVENT` events, independent of widget context, after the UI was notified.
    ///
    /// # Handlers
    ///
    /// the event handler can be any type that implements [`AppHandler`], there are multiple flavors of handlers, including
    /// async handlers that allow calling `.await`. The handler closures can be declared using [`app_hn!`], [`async_app_hn!`],
    /// [`app_hn_once!`] and [`async_app_hn_once!`].
    ///
    /// ## Async
    ///
    /// Note that for async handlers only the code before the first `.await` is called in the *preview* moment, code after runs in
    /// subsequent event updates, after the event has already propagated, so stopping [`propagation`](AnyEventArgs::propagation)
    /// only causes the desired effect before the first `.await`.
    ///
    /// [`app_hn!`]: crate::handler::app_hn!
    /// [`async_app_hn!`]: crate::handler::async_app_hn!
    /// [`app_hn_once!`]: crate::handler::app_hn_once!
    /// [`async_app_hn_once!`]: crate::handler::async_app_hn_once!
    pub fn on_event(&self, handler: impl AppHandler<A>) -> EventHandle {
        self.on_event_impl(handler, false)
    }

    fn on_event_impl(&self, handler: impl AppHandler<A>, is_preview: bool) -> EventHandle {
        let handler = Arc::new(Mutex::new(handler));
        let (inner_handle_owner, inner_handle) = zng_handle::Handle::new(());
        self.as_any().hook(move |update| {
            if inner_handle_owner.is_dropped() {
                return false;
            }

            let handle = inner_handle.downgrade();
            update.push_once_action(
                Box::new(clmv!(handler, |update| {
                    let args = update.args().as_any().downcast_ref::<A>().unwrap();
                    if !args.propagation().is_stopped() {
                        handler.lock().event(
                            args,
                            &AppHandlerArgs {
                                handle: &handle,
                                is_preview,
                            },
                        );
                    }
                })),
                is_preview,
            );

            true
        })
    }

    /// Creates a receiver channel for the event. The event updates are send on hook, before even preview handlers.
    /// The receiver is unbounded, it will fill indefinitely if not drained. The receiver can be used in any thread,
    /// including non-app threads.
    ///
    /// Drop the receiver to stop listening.
    pub fn receiver(&self) -> EventReceiver<A>
    where
        A: Send,
    {
        let (sender, receiver) = flume::unbounded();

        self.as_any()
            .hook(move |update| sender.send(update.args().as_any().downcast_ref::<A>().unwrap().clone()).is_ok())
            .perm();

        EventReceiver { receiver, event: *self }
    }

    /// Creates a sender channel that can notify the event.
    ///
    /// Events can notify from any app thread, this sender can notify other threads too.
    pub fn sender(&self) -> EventSender<A>
    where
        A: Send,
    {
        EVENTS_SV.write().sender(*self)
    }

    /// Returns `true` if any app level callback is registered for this event.
    ///
    /// This includes [`AnyEvent::hook`], [`Event::on_pre_event`], [`Event::on_event`] and [`Event::receiver`].
    pub fn has_hooks(&self) -> bool {
        self.as_any().has_hooks()
    }
}
impl<A: EventArgs> Clone for Event<A> {
    fn clone(&self) -> Self {
        *self
    }
}
impl<A: EventArgs> Copy for Event<A> {}
impl<A: EventArgs> PartialEq for Event<A> {
    fn eq(&self, other: &Self) -> bool {
        self.local == other.local
    }
}
impl<A: EventArgs> Eq for Event<A> {}

/// Represents an [`Event`] without the args type.
#[derive(Clone, Copy)]
pub struct AnyEvent {
    local: &'static AppLocal<EventData>,
}
impl fmt::Debug for AnyEvent {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if f.alternate() {
            write!(f, "AnyEvent({})", self.name())
        } else {
            write!(f, "{}", self.name())
        }
    }
}
impl AnyEvent {
    /// Name of the event static item.
    pub fn name(&self) -> &'static str {
        self.local.read().name
    }

    /// Returns `true` if `self` is the type erased `event`.
    pub fn is<A: EventArgs>(&self, event: &Event<A>) -> bool {
        self == event
    }

    /// Returns `true` if the update is for this event.
    pub fn has(&self, update: &EventUpdate) -> bool {
        *self == update.event
    }

    /// Register a callback that is called just before an event begins notifying.
    pub fn hook(&self, hook: impl Fn(&mut EventUpdate) -> bool + Send + Sync + 'static) -> EventHandle {
        self.hook_impl(Box::new(hook))
    }
    fn hook_impl(&self, hook: Box<dyn Fn(&mut EventUpdate) -> bool + Send + Sync>) -> EventHandle {
        let (handle, hook) = EventHandle::new(hook);
        self.local.write().hooks.push(hook);
        handle
    }

    /// Register the widget to receive targeted events from this event.
    ///
    /// Widgets only receive events if they are in the delivery list generated by the event args and are
    /// subscribers to the event. App extensions receive all events.
    pub fn subscribe(&self, widget_id: WidgetId) -> EventHandle {
        self.local
            .write()
            .widget_subs
            .entry(widget_id)
            .or_insert_with(EventHandle::new_none)
            .clone()
    }

    /// Returns `true` if the widget is subscribed to this event.
    pub fn is_subscriber(&self, widget_id: WidgetId) -> bool {
        self.local.read().widget_subs.contains_key(&widget_id)
    }

    /// Returns `true` if at least one widget is subscribed to this event.
    pub fn has_subscribers(&self) -> bool {
        !self.local.read().widget_subs.is_empty()
    }

    /// Calls `visit` for each widget subscribed to this event.
    ///
    /// Note that trying to subscribe or add hook inside `visit` will deadlock. Inside `visit` you can notify the event and
    /// generate event updates.
    pub fn visit_subscribers(&self, mut visit: impl FnMut(WidgetId)) {
        for sub in self.local.read().widget_subs.keys() {
            visit(*sub);
        }
    }

    /// Returns `true` if any app level callback is registered for this event.
    ///
    /// This includes [`AnyEvent::hook`], [`Event::on_pre_event`], [`Event::on_event`] and [`Event::receiver`].
    pub fn has_hooks(&self) -> bool {
        !self.local.read().hooks.is_empty()
    }

    pub(crate) fn on_update(&self, update: &mut EventUpdate) {
        let mut hooks = mem::take(&mut self.local.write().hooks);
        hooks.retain(|h| h.call(update));

        let mut write = self.local.write();
        hooks.append(&mut write.hooks);
        write.hooks = hooks;
    }
}
impl PartialEq for AnyEvent {
    fn eq(&self, other: &Self) -> bool {
        self.local == other.local
    }
}
impl Eq for AnyEvent {}
impl<A: EventArgs> PartialEq<AnyEvent> for Event<A> {
    fn eq(&self, other: &AnyEvent) -> bool {
        self.local == other.local
    }
}
impl<A: EventArgs> PartialEq<Event<A>> for AnyEvent {
    fn eq(&self, other: &Event<A>) -> bool {
        self.local == other.local
    }
}

impl UpdateSubscribers for AnyEvent {
    fn contains(&self, widget_id: WidgetId) -> bool {
        if let Some(mut write) = self.local.try_write() {
            match write.widget_subs.entry(widget_id) {
                IdEntry::Occupied(e) => {
                    let t = e.get().retain();
                    if !t {
                        let _ = e.remove();
                    }
                    t
                }
                IdEntry::Vacant(_) => false,
            }
        } else {
            // fallback without cleanup
            match self.local.read().widget_subs.get(&widget_id) {
                Some(e) => e.retain(),
                None => false,
            }
        }
    }

    fn to_set(&self) -> IdSet<WidgetId> {
        self.local.read().widget_subs.keys().copied().collect()
    }
}

/// Represents a collection of event handles.
#[must_use = "the event subscriptions or handlers are dropped if the handle is dropped"]
#[derive(Clone, Default)]
pub struct EventHandles(pub Vec<EventHandle>);
impl EventHandles {
    /// Empty collection.
    pub const fn dummy() -> Self {
        EventHandles(vec![])
    }

    /// Returns `true` if empty or all handles are dummy.
    pub fn is_dummy(&self) -> bool {
        self.0.is_empty() || self.0.iter().all(EventHandle::is_dummy)
    }

    /// Drop all handles without stopping their behavior.
    pub fn perm(self) {
        for handle in self.0 {
            handle.perm()
        }
    }

    /// Add `other` handle to the collection.
    pub fn push(&mut self, other: EventHandle) -> &mut Self {
        if !other.is_dummy() {
            self.0.push(other);
        }
        self
    }

    /// Drop all handles.
    pub fn clear(&mut self) {
        self.0.clear();
    }
}
impl FromIterator<EventHandle> for EventHandles {
    fn from_iter<T: IntoIterator<Item = EventHandle>>(iter: T) -> Self {
        EventHandles(iter.into_iter().filter(|h| !h.is_dummy()).collect())
    }
}
impl<const N: usize> From<[EventHandle; N]> for EventHandles {
    fn from(handles: [EventHandle; N]) -> Self {
        handles.into_iter().filter(|h| !h.is_dummy()).collect()
    }
}
impl Extend<EventHandle> for EventHandles {
    fn extend<T: IntoIterator<Item = EventHandle>>(&mut self, iter: T) {
        for handle in iter {
            self.push(handle);
        }
    }
}
impl IntoIterator for EventHandles {
    type Item = EventHandle;

    type IntoIter = std::vec::IntoIter<EventHandle>;

    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter()
    }
}

struct EventHandleData {
    perm: AtomicBool,
    hook: Option<Box<dyn Fn(&mut EventUpdate) -> bool + Send + Sync>>,
}

/// Represents an event widget subscription, handler callback or hook.
#[derive(Clone)]
#[must_use = "the event subscription or handler is dropped if the handle is dropped"]
pub struct EventHandle(Option<Arc<EventHandleData>>);
impl PartialEq for EventHandle {
    fn eq(&self, other: &Self) -> bool {
        match (&self.0, &other.0) {
            (None, None) => true,
            (None, Some(_)) | (Some(_), None) => false,
            (Some(a), Some(b)) => Arc::ptr_eq(a, b),
        }
    }
}
impl Eq for EventHandle {}
impl std::hash::Hash for EventHandle {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        let i = match &self.0 {
            Some(rc) => Arc::as_ptr(rc) as usize,
            None => 0,
        };
        state.write_usize(i);
    }
}
impl fmt::Debug for EventHandle {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let i = match &self.0 {
            Some(rc) => Arc::as_ptr(rc) as usize,
            None => 0,
        };
        f.debug_tuple("EventHandle").field(&i).finish()
    }
}
/// Dummy
impl Default for EventHandle {
    fn default() -> Self {
        Self::dummy()
    }
}
impl EventHandle {
    fn new(hook: Box<dyn Fn(&mut EventUpdate) -> bool + Send + Sync>) -> (Self, EventHook) {
        let rc = Arc::new(EventHandleData {
            perm: AtomicBool::new(false),
            hook: Some(hook),
        });
        (Self(Some(rc.clone())), EventHook(rc))
    }

    fn new_none() -> Self {
        Self(Some(Arc::new(EventHandleData {
            perm: AtomicBool::new(false),
            hook: None,
        })))
    }

    /// Handle to no event.
    pub fn dummy() -> Self {
        EventHandle(None)
    }

    /// If the handle is not actually registered in an event.
    pub fn is_dummy(&self) -> bool {
        self.0.is_none()
    }

    /// Drop the handle without un-registering it, the resource it represents will remain registered in the event for the duration of
    /// the process.
    pub fn perm(self) {
        if let Some(rc) = self.0 {
            rc.perm.store(true, Ordering::Relaxed);
        }
    }

    /// Create an [`EventHandles`] collection with `self` and `other`.
    pub fn with(self, other: Self) -> EventHandles {
        [self, other].into()
    }

    fn retain(&self) -> bool {
        let rc = self.0.as_ref().unwrap();
        Arc::strong_count(rc) > 1 || rc.perm.load(Ordering::Relaxed)
    }
}

struct EventHook(Arc<EventHandleData>);
impl EventHook {
    /// Callback, returns `true` if the handle must be retained.
    fn call(&self, update: &mut EventUpdate) -> bool {
        (Arc::strong_count(&self.0) > 1 || self.0.perm.load(Ordering::Relaxed)) && (self.0.hook.as_ref().unwrap())(update)
    }
}