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use std::{
    convert::Into,
    fmt,
    rc::Rc,
};

/// A generic sized representation of a function that can be
/// attached to a Node. The callback will essentially be owned by the element
pub struct Callback<EVENT, MSG>(Rc<dyn Fn(EVENT) -> MSG>);

impl<EVENT, F, MSG> From<F> for Callback<EVENT, MSG>
where
    F: Fn(EVENT) -> MSG,
    F: 'static,
{
    fn from(func: F) -> Self {
        Callback(Rc::new(func))
    }
}
impl<EVENT, MSG> fmt::Debug for Callback<EVENT, MSG> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "||{{..}}")
    }
}

impl<EVENT, MSG> Callback<EVENT, MSG>
where
    EVENT: 'static,
    MSG: 'static,
{
    /// This method calls the actual callback.
    pub fn emit<T: Into<EVENT>>(&self, value: T) -> MSG {
        (self.0)(value.into())
    }

    /// Changes input type of the callback to another.
    /// Works like common `map` method but in an opposite direction.
    pub fn reform<F, EVENT2>(self, func: F) -> Callback<EVENT2, MSG>
    where
        F: Fn(EVENT2) -> EVENT,
        F: 'static,
    {
        let func_wrap = move |input| {
            let output = func(input);
            self.emit(output)
        };
        Callback::from(func_wrap)
    }

    /// Map the output of this callback to return a different type
    pub fn map<F, MSG2>(self, func: F) -> Callback<EVENT, MSG2>
    where
        F: Fn(MSG) -> MSG2,
        F: 'static,
    {
        let func_wrap = move |input| {
            let out = self.emit(input);
            func(out)
        };
        Callback::from(func_wrap)
    }

    pub fn map_callback<MSG2>(
        self,
        cb: Callback<MSG, MSG2>,
    ) -> Callback<EVENT, MSG2>
    where
        MSG2: 'static,
    {
        let func_wrap = move |input| {
            let out = self.emit(input);
            cb.emit(out)
        };
        Callback::from(func_wrap)
    }
}

impl<EVENT, MSG> Clone for Callback<EVENT, MSG> {
    fn clone(&self) -> Self {
        Callback(Rc::clone(&self.0))
    }
}

impl<EVENT, MSG> PartialEq for Callback<EVENT, MSG> {
    fn eq(&self, rhs: &Self) -> bool {
        // Comparing the callback is only applicable
        // when they are a clone to each other.
        // This defeats the purpose in logically comparing for the
        // diffing algorthmn since all callbacks are effectively called with the closure.into()
        // which are essentially not the same Callback even when they are derived from the same
        // function.
        Rc::ptr_eq(&self.0, &rhs.0)
    }
}