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use std::cell::UnsafeCell;
use std::rc::Rc;
use std::os::raw::c_void;
use std::marker::PhantomData;

use crate::Sender;
use crate::priv_traits::*;

pub struct Fold<'a, T1, T2, F: FnMut(T2,T1) -> T2>{
    func: F,
    fold: Option<T2>,
    sender: Sender<'a,T2>,
    _marker: PhantomData<T1>,
}

impl<'a,T1, T2, F: FnMut(T2,T1) -> T2> Fold<'a,T1,T2,F>{
    pub fn new(f: F, fold: T2) -> Fold<'a,T1,T2,F>{
        Fold{
            func: f,
            fold: Some(fold),
            sender: Sender::new(),
            _marker: PhantomData,
        }
    }
}

impl<'a,T1, T2, F: FnMut(T2,T1) -> T2> StreamInner<'a,T2> for Fold<'a,T1,T2,F>{
    #[inline]
    fn push(&mut self, st: Rc<UnsafeCell<dyn SinkInner<'a,T2>+'a>>){
        self.sender.push(st)
    }

    #[inline]
    fn send(&mut self, t: T2){
        self.sender.send(t)
    }
}

impl<'a,T1, T2, F: FnMut(T2,T1) -> T2> Remove for Fold<'a,T1,T2,F>{
    fn remove_raw(&mut self, st: *const c_void){
        self.sender.remove_raw(st)
    }
}

impl<'a,T1, T2: Clone, F: FnMut(T2,T1) -> T2> SinkInner<'a, T1> for Fold<'a,T1,T2,F>{
    #[inline]
    fn call(&mut self, t: T1) -> Result<(),()>{
        let fold = (self.func)(self.fold.take().unwrap(), t);
        self.fold = Some(fold.clone());
        self.sender.send(fold);
        Ok(())
    }

    #[inline]
    fn is_alive(&self) -> bool {
        true
    }
}