use crate::{global_context::current_scope_id, Runtime, ScopeId};
use generational_box::GenerationalBox;
use std::{cell::Cell, rc::Rc};

/// A wrapper around some generic data that handles the event's state
///
///
/// Prevent this event from continuing to bubble up the tree to parent elements.
///
/// # Example
///
/// ```rust, ignore
/// rsx! {
///     button {
///         onclick: move |evt: Event<MouseData>| {
///             evt.cancel_bubble();
///
///         }
///     }
/// }
/// ```
pub struct Event<T: 'static + ?Sized> {
    /// The data associated with this event
    pub data: Rc<T>,
    pub(crate) propagates: Rc<Cell<bool>>,
}

impl<T: ?Sized + 'static> Event<T> {
    pub(crate) fn new(data: Rc<T>, bubbles: bool) -> Self {
        Self {
            data,
            propagates: Rc::new(Cell::new(bubbles)),
        }
    }
}

impl<T> Event<T> {
    /// Map the event data to a new type
    ///
    /// # Example
    ///
    /// ```rust, ignore
    /// rsx! {
    ///    button {
    ///       onclick: move |evt: Event<FormData>| {
    ///          let data = evt.map(|data| data.value());
    ///          assert_eq!(data.inner(), "hello world");
    ///       }
    ///    }
    /// }
    /// ```
    pub fn map<U: 'static, F: FnOnce(&T) -> U>(&self, f: F) -> Event<U> {
        Event {
            data: Rc::new(f(&self.data)),
            propagates: self.propagates.clone(),
        }
    }

    /// Prevent this event from continuing to bubble up the tree to parent elements.
    ///
    /// # Example
    ///
    /// ```rust, ignore
    /// rsx! {
    ///     button {
    ///         onclick: move |evt: Event<MouseData>| {
    ///             evt.cancel_bubble();
    ///         }
    ///     }
    /// }
    /// ```
    #[deprecated = "use stop_propagation instead"]
    pub fn cancel_bubble(&self) {
        self.propagates.set(false);
    }

    /// Prevent this event from continuing to bubble up the tree to parent elements.
    ///
    /// # Example
    ///
    /// ```rust, ignore
    /// rsx! {
    ///     button {
    ///         onclick: move |evt: Event<MouseData>| {
    ///             evt.stop_propagation();
    ///         }
    ///     }
    /// }
    /// ```
    pub fn stop_propagation(&self) {
        self.propagates.set(false);
    }

    /// Get a reference to the inner data from this event
    ///
    /// ```rust, ignore
    /// rsx! {
    ///     button {
    ///         onclick: move |evt: Event<MouseData>| {
    ///             let data = evt.inner.clone();
    ///             cx.spawn(async move {
    ///                 println!("{:?}", data);
    ///             });
    ///         }
    ///     }
    /// }
    /// ```
    pub fn data(&self) -> Rc<T> {
        self.data.clone()
    }
}

impl<T: ?Sized> Clone for Event<T> {
    fn clone(&self) -> Self {
        Self {
            propagates: self.propagates.clone(),
            data: self.data.clone(),
        }
    }
}

impl<T> std::ops::Deref for Event<T> {
    type Target = Rc<T>;
    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

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

/// The callback type generated by the `rsx!` macro when an `on` field is specified for components.
///
/// This makes it possible to pass `move |evt| {}` style closures into components as property fields.
///
///
/// # Example
///
/// ```rust, ignore
/// rsx!{
///     MyComponent { onclick: move |evt| tracing::debug!("clicked") }
/// }
///
/// #[derive(Props)]
/// struct MyProps {
///     onclick: EventHandler<MouseEvent>,
/// }
///
/// fn MyComponent(cx: MyProps) -> Element {
///     rsx!{
///         button {
///             onclick: move |evt| cx.onclick.call(evt),
///         }
///     }
/// }
///
/// ```
pub struct EventHandler<T = ()> {
    pub(crate) origin: ScopeId,
    pub(super) callback: GenerationalBox<Option<ExternalListenerCallback<T>>>,
}

impl<T: 'static> Default for EventHandler<T> {
    fn default() -> Self {
        EventHandler::new(|_| {})
    }
}

impl<F: FnMut(T) + 'static, T: 'static> From<F> for EventHandler<T> {
    fn from(f: F) -> Self {
        EventHandler::new(f)
    }
}

impl<T> Copy for EventHandler<T> {}

impl<T> Clone for EventHandler<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: 'static> PartialEq for EventHandler<T> {
    fn eq(&self, _: &Self) -> bool {
        true
    }
}

type ExternalListenerCallback<T> = Box<dyn FnMut(T)>;

impl<T: 'static> EventHandler<T> {
    /// Create a new [`EventHandler`] from an [`FnMut`]
    #[track_caller]
    pub fn new(mut f: impl FnMut(T) + 'static) -> EventHandler<T> {
        let callback = GenerationalBox::leak(Some(Box::new(move |event: T| {
            f(event);
        }) as Box<dyn FnMut(T)>));
        EventHandler {
            callback,
            origin: current_scope_id().expect("to be in a dioxus runtime"),
        }
    }

    /// Call this event handler with the appropriate event type
    ///
    /// This borrows the event using a RefCell. Recursively calling a listener will cause a panic.
    pub fn call(&self, event: T) {
        if let Some(callback) = self.callback.write().as_mut() {
            Runtime::with(|rt| rt.scope_stack.borrow_mut().push(self.origin));
            callback(event);
            Runtime::with(|rt| rt.scope_stack.borrow_mut().pop());
        }
    }

    /// Forcibly drop the internal handler callback, releasing memory
    ///
    /// This will force any future calls to "call" to not doing anything
    pub fn release(&self) {
        self.callback.set(None);
    }

    #[doc(hidden)]
    /// This should only be used by the `rsx!` macro.
    pub fn __set(&mut self, value: impl FnMut(T) + 'static) {
        self.callback.set(Some(Box::new(value)));
    }

    #[doc(hidden)]
    /// This should only be used by the `rsx!` macro.
    pub fn __take(&self) -> ExternalListenerCallback<T> {
        self.callback
            .manually_drop()
            .expect("Signal has already been dropped")
            .expect("EventHandler was manually dropped")
    }
}

impl<T: 'static> std::ops::Deref for EventHandler<T> {
    type Target = dyn Fn(T) + 'static;

    fn deref(&self) -> &Self::Target {
        // https://github.com/dtolnay/case-studies/tree/master/callable-types

        // First we create a closure that captures something with the Same in memory layout as Self (MaybeUninit<Self>).
        let uninit_callable = std::mem::MaybeUninit::<Self>::uninit();
        // Then move that value into the closure. We assume that the closure now has a in memory layout of Self.
        let uninit_closure = move |t| Self::call(unsafe { &*uninit_callable.as_ptr() }, t);

        // Check that the size of the closure is the same as the size of Self in case the compiler changed the layout of the closure.
        let size_of_closure = std::mem::size_of_val(&uninit_closure);
        assert_eq!(size_of_closure, std::mem::size_of::<Self>());

        // Then cast the lifetime of the closure to the lifetime of &self.
        fn cast_lifetime<'a, T>(_a: &T, b: &'a T) -> &'a T {
            b
        }
        let reference_to_closure = cast_lifetime(
            {
                // The real closure that we will never use.
                &uninit_closure
            },
            // We transmute self into a reference to the closure. This is safe because we know that the closure has the same memory layout as Self so &Closure == &Self.
            unsafe { std::mem::transmute(self) },
        );

        // Cast the closure to a trait object.
        reference_to_closure as &_
    }
}