bulks 0.11.3

use core::{marker::Destruct, ops::Try};

use array_trait::{AsArray, length};
use currying::Curry;

use crate::{Bulk, DoubleEndedBulk, IntoBulk, IntoContained, StaticBulk};

/// A bulk that maps each element to an iterator, and yields the elements
/// of the produced bulks.
///
/// This `struct` is created by [`Bulk::flat_map`]. See its documentation
/// for more.
#[must_use = "bulks are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct FlatMap<I, F>
where
    I: Bulk,
    F: FnMut<(I::Item,), Output: IntoBulk<IntoBulk: StaticBulk>>
{
    bulk: I,
    map: F
}

impl<I, U, F> FlatMap<I, F>
where
    I: Bulk,
    F: FnMut(I::Item) -> U,
    U: IntoBulk<IntoBulk: StaticBulk>
{
    pub(crate) const fn new(bulk: I, map: F) -> Self
    {
        Self { bulk, map }
    }

    const fn chunk() -> usize
    {
        <<<U as IntoBulk>::IntoBulk as StaticBulk>::Array<U::Item> as AsArray>::LENGTH
    }
}

impl<I, U, F> IntoIterator for FlatMap<I, F>
where
    I: Bulk,
    F: FnMut(I::Item) -> U,
    U: IntoBulk<IntoBulk: StaticBulk>
{
    type IntoIter = <<core::iter::FlatMap<I::IntoIter, U, F> as IntoContained>::IntoContained as IntoIterator>::IntoIter;
    type Item = U::Item;

    fn into_iter(self) -> Self::IntoIter
    {
        let Self { bulk, map } = self;
        unsafe { bulk.into_iter().flat_map(map).into_contained().into_iter() }
    }
}
const impl<I, U, F> Bulk for FlatMap<I, F>
where
    I: [const] Bulk<Item: [const] Destruct>,
    F: [const] FnMut(I::Item) -> U + [const] Destruct,
    U: [const] IntoBulk<IntoBulk: StaticBulk + [const] Bulk>
{
    type MaxLength = length::Mul<I::MaxLength, <U::IntoBulk as StaticBulk>::Array<()>>;
    type MinLength = length::Mul<I::MinLength, <U::IntoBulk as StaticBulk>::Array<()>>;

    fn len(&self) -> usize
    {
        let Self { bulk, map: _ } = self;
        bulk.len() * Self::chunk()
    }

    fn is_empty(&self) -> bool
    {
        let Self { bulk, map: _ } = self;
        Self::chunk() == 0 || bulk.is_empty()
    }

    fn first(self) -> Option<Self::Item>
    where
        Self::Item: [const] Destruct,
        Self: Sized
    {
        const fn into_first<F, T, U>(f: F, x: T) -> Option<U::Item>
        where
            F: [const] FnOnce(T) -> U,
            U: [const] IntoBulk<Item: [const] Destruct>
        {
            f(x).into_bulk().first()
        }

        let Self { bulk, mut map } = self;
        bulk.first().and_then(into_first.curry(&mut map))
    }

    fn for_each<FF>(self, f: FF)
    where
        Self: Sized,
        FF: [const] FnMut(Self::Item) + [const] Destruct
    {
        struct Closure<F, FF>
        {
            map: F,
            f: FF
        }
        const impl<F, FF, U, T> FnOnce<(T,)> for Closure<F, FF>
        where
            F: [const] FnOnce(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] Bulk>,
            FF: [const] FnMut(U::Item) + [const] Destruct
        {
            type Output = ();

            extern "rust-call" fn call_once(self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().for_each(self.f)
            }
        }
        const impl<F, FF, U, T> FnMut<(T,)> for Closure<F, FF>
        where
            F: [const] FnMut(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] Bulk>,
            FF: [const] FnMut(U::Item) + [const] Destruct
        {
            extern "rust-call" fn call_mut(&mut self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().for_each(&mut self.f)
            }
        }

        let Self { bulk, map } = self;
        bulk.for_each(Closure { map, f })
    }

    fn try_for_each<FF, R>(self, f: FF) -> R
    where
        Self: Sized,
        Self::Item: [const] Destruct,
        FF: [const] FnMut(Self::Item) -> R + [const] Destruct,
        R: [const] Try<Output = ()>
    {
        struct Closure<F, FF>
        {
            map: F,
            f: FF
        }
        const impl<F, FF, U, T, R> FnOnce<(T,)> for Closure<F, FF>
        where
            F: [const] FnOnce(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] Bulk, Item: [const] Destruct>,
            FF: [const] FnMut(U::Item) -> R + [const] Destruct,
            R: [const] Try<Output = ()>
        {
            type Output = R;

            extern "rust-call" fn call_once(self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().try_for_each(self.f)
            }
        }
        const impl<F, FF, U, T, R> FnMut<(T,)> for Closure<F, FF>
        where
            F: [const] FnMut(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] Bulk, Item: [const] Destruct>,
            FF: [const] FnMut(U::Item) -> R + [const] Destruct,
            R: [const] Try<Output = ()>
        {
            extern "rust-call" fn call_mut(&mut self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().try_for_each(&mut self.f)
            }
        }

        let Self { bulk, map } = self;
        bulk.try_for_each(Closure { map, f })
    }
}
const impl<I, U, F> DoubleEndedBulk for FlatMap<I, F>
where
    I: [const] DoubleEndedBulk<Item: [const] Destruct>,
    F: [const] FnMut(I::Item) -> U + [const] Destruct,
    U: [const] IntoBulk<IntoBulk: StaticBulk + [const] DoubleEndedBulk>,
    Self::IntoIter: DoubleEndedIterator
{
    fn rev_for_each<FF>(self, f: FF)
    where
        Self: Sized,
        FF: [const] FnMut(Self::Item) + [const] Destruct
    {
        struct Closure<F, FF>
        {
            map: F,
            f: FF
        }
        const impl<F, FF, U, T> FnOnce<(T,)> for Closure<F, FF>
        where
            F: [const] FnOnce(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] DoubleEndedBulk>,
            FF: [const] FnMut(U::Item) + [const] Destruct
        {
            type Output = ();

            extern "rust-call" fn call_once(self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().rev_for_each(self.f)
            }
        }
        const impl<F, FF, U, T> FnMut<(T,)> for Closure<F, FF>
        where
            F: [const] FnMut(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] DoubleEndedBulk>,
            FF: [const] FnMut(U::Item) + [const] Destruct
        {
            extern "rust-call" fn call_mut(&mut self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().rev_for_each(&mut self.f)
            }
        }

        let Self { bulk, map } = self;
        bulk.rev_for_each(Closure { map, f })
    }

    fn try_rev_for_each<FF, R>(self, f: FF) -> R
    where
        Self: Sized,
        Self::Item: [const] Destruct,
        FF: [const] FnMut(Self::Item) -> R + [const] Destruct,
        R: [const] Try<Output = ()>
    {
        struct Closure<F, FF>
        {
            map: F,
            f: FF
        }
        const impl<F, FF, U, T, R> FnOnce<(T,)> for Closure<F, FF>
        where
            F: [const] FnOnce(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] DoubleEndedBulk, Item: [const] Destruct>,
            FF: [const] FnMut(U::Item) -> R + [const] Destruct,
            R: [const] Try<Output = ()>
        {
            type Output = R;

            extern "rust-call" fn call_once(self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().try_rev_for_each(self.f)
            }
        }
        const impl<F, FF, U, T, R> FnMut<(T,)> for Closure<F, FF>
        where
            F: [const] FnMut(T) -> U,
            U: [const] IntoBulk<IntoBulk: StaticBulk + [const] DoubleEndedBulk, Item: [const] Destruct>,
            FF: [const] FnMut(U::Item) -> R + [const] Destruct,
            R: [const] Try<Output = ()>
        {
            extern "rust-call" fn call_mut(&mut self, (x,): (T,)) -> Self::Output
            {
                (self.map)(x).into_bulk().try_rev_for_each(&mut self.f)
            }
        }

        let Self { bulk, map } = self;
        bulk.try_rev_for_each(Closure { map, f })
    }
}

#[cfg(test)]
mod test
{
    use crate::*;

    #[test]
    fn it_works()
    {
        let a = [1, 2, 3];
        let b = a.into_bulk().flat_map(|x| [x, -x]).collect::<[_; _], _>();

        println!("{b:?}")
    }
}