use std::marker::PhantomData;

use super::*;

pub struct ControlFlowInstance<C>(ControlFlow<(), C>);

impl<C> WeakFunctor for ControlFlowInstance<C> {
    type F<'a, A: 'a> =  ControlFlow<A, C>
    where
        Self: 'a;
}

impl<'a, C: 'a> Functor<'a> for ControlFlowInstance<C> {
    fn fmap<A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B> {
        match fa {
            ControlFlow::Continue(c) => ControlFlow::Continue(c),
            ControlFlow::Break(a) => ControlFlow::Break(f(a)),
        }
    }
}

impl<'a, C: 'a> Pure<'a> for ControlFlowInstance<C> {
    fn pure<A: 'a>(a: A) -> Self::F<'a, A> {
        ControlFlow::Break(a)
    }
}

pub struct BindableMut<T: ?Sized, A, B, F>(A, F, PhantomData<B>, PhantomData<T>);

impl<
        'a,
        T: ?Sized + Functor<'a>,
        A: 'a,
        B: 'a,
        F: 'a + FnMut(A) -> T::F<'a, ControlFlow<B, A>>,
    > BindableMut<T, A, B, F>
{
    pub fn new(a: A, f: F) -> Self {
        BindableMut(a, f, PhantomData, PhantomData)
    }
}

impl<
        'a,
        T: ?Sized + Functor<'a>,
        A: 'a,
        B: 'a,
        F: 'a + FnMut(A) -> T::F<'a, ControlFlow<B, A>>,
    > Iterative<'a> for BindableMut<T, A, B, F>
{
    type B = B;
    type T = T;

    fn next(mut self) -> IterativeWrapped<'a, Self> {
        let fstate = self.1(self.0);
        T::fmap(
            move |state| match state {
                ControlFlow::Continue(next_a) => {
                    ControlFlow::Continue(BindableMut::new(next_a, self.1))
                }
                ControlFlow::Break(b) => ControlFlow::Break(b),
            },
            fstate,
        )
    }
}

/// Next [Iterative] state, wrapped.
pub type IterativeWrapped<'a, F> =
    Wrap<'a, ControlFlow<<F as Iterative<'a>>::B, F>, <F as Iterative<'a>>::T>;

/// Value passed to [`Monad::iterate`].
pub trait Iterative<'a>: 'a + Sized {
    /// [`ControlFlow::Break`].
    type B: 'a;
    /// Corresponding [`WeakFunctor`].
    type T: 'a + ?Sized + WeakFunctor;
    /// Get next state.
    fn next(self) -> IterativeWrapped<'a, Self>;
}