pub mod classes;
pub mod clone_func;
pub mod copy_func;
#[cfg(test)]
pub mod test_suite;
#[cfg(test)]
pub mod tests;

pub trait WeakFunctor {
    type F<'a, A: 'a> : 'a;
}

/// Rust-specific implementation of [Functor], respecting `move` semantics.
///
/// Cannot insantiate for e.g. multi-element collections:
/// ```compile_fail
/// use radn_rs::func::*;
///
/// struct VecClass;
///
/// impl WeakFunctor for VecClass {
///     type F<'a, A> = Vec<A>;
/// }
///
/// impl Functor for VecClass {
///     fn fmap<'a, A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B>
///         fa.into_iter().map(f).collect()
///     }
/// }
/// ```
/// Why does it fail to compile? `.map` expects `FnMut` (or we can think of it being `Fn`, doesn't matter here). But what we provide it (`f`) is
///
/// For Haskell-style Functors, use [clone_func::CloneFunctor] instead.
/// ```
/// use radn_rs::func::clone_func::*;
///
/// struct VecClass;
///
/// impl CloneWeakFunctor for VecClass {
///     type ClF<'a, A: Clone> = Vec<A>;
/// }
///
/// impl CloneFunctor for VecClass {
///     fn clone_fmap<'a, A: 'a + Clone, B: 'a + Clone>(
///         f: impl 'a + Fn(A) -> B,
///         fa: Self::ClF<'a, A>,
///     ) -> Self::ClF<'a, B> {
///         fa.into_iter().map(f).collect()
///     }
/// }
/// ```

pub trait Functor: WeakFunctor {
    fn fmap<'a, A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B>
    where
        Self: 'a;

    fn replace<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, b: B) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Self::fmap(|_| b, fa)
    }

    fn void<'a, A: 'a>(fa: Self::F<'a, A>) -> Self::F<'a, ()>
    where
        Self: 'a,
    {
        Self::replace(fa, ())
    }
}

pub fn fmap<'a, T: 'a + Functor, A: 'a, B: 'a>(
    f: impl 'a + FnOnce(A) -> B,
) -> impl FnOnce(T::F<'a, A>) -> T::F<'a, B> {
    move |fa| T::fmap(f, fa)
}

pub trait ApplicativeSeq: Functor {
    fn seq<'a, A: 'a, B: 'a>(
        ff: Self::F<'a, impl 'a + FnOnce(A) -> B>,
        fa: Self::F<'a, A>,
    ) -> Self::F<'a, B>
    where
        Self: 'a;
    fn _la2<'a, A: 'a, B: 'a, C: 'a>(
        f: impl 'a + FnOnce(A, B) -> C,
        fa: Self::F<'a, A>,
        fb: Self::F<'a, B>,
    ) -> Self::F<'a, C>
    where
        Self: 'a,
    {
        Self::seq(Self::fmap(|a| |b| f(a, b), fa), fb)
    }
}

pub trait ApplicativeLA2: Functor {
    fn la2<'a, A: 'a, B: 'a, C: 'a>(
        f: impl 'a + FnOnce(A, B) -> C,
        fa: Self::F<'a, A>,
        fb: Self::F<'a, B>,
    ) -> Self::F<'a, C>
    where
        Self: 'a;
    fn _seq<'a, A: 'a, B: 'a>(
        ff: Self::F<'a, impl 'a + FnOnce(A) -> B>,
        fa: Self::F<'a, A>,
    ) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Self::la2(|f, a| f(a), ff, fa)
    }
}

pub trait Applicative: Functor + ApplicativeSeq + ApplicativeLA2 {
    fn pure<'a, A: 'a>(a: A) -> Self::F<'a, A>;

    fn discard_first<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, fb: Self::F<'a, B>) -> Self::F<'a, B>
    where
        Self: 'a,
    {
        Self::seq(Self::replace(fa, |b| b), fb)
    }

    fn discard_second<'a, A: 'a, B: 'a>(fa: Self::F<'a, A>, fb: Self::F<'a, B>) -> Self::F<'a, A>
    where
        Self: 'a,
    {
        Self::la2(|a, _| a, fa, fb)
    }
}

pub trait Monad: Applicative {
    fn bind<'a, A: 'a, B: 'a>(
        fa: Self::F<'a, A>,
        f: impl 'a + FnOnce(A) -> Self::F<'a, B>,
    ) -> Self::F<'a, B>
    where
        Self: 'a;

    fn join<'a, A: 'a>(ffa: Self::F<'a, Self::F<'a, A>>) -> Self::F<'a, A>
    where
        Self::F<'a, A>: 'a,
        Self: 'a,
    {
        Self::bind(ffa, |fa| fa)
    }
}

pub trait MonadFail<E>: Monad {
    fn fail<'a, A>(e: E) -> Self::F<'a, A>;
}

pub trait Alternative: Applicative {
    fn empty<'a, A>() -> Self::F<'a, A>;

    fn add<'a, A>(fa: Self::F<'a, A>, fb: Self::F<'a, A>) -> Self::F<'a, A>;
}