treaty -


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use core::{mem::MaybeUninit, ops::ControlFlow};

use crate::{
    any_trait,
    protocol::{
        visitor::{Sequence, SequenceScope, Status},
        ControlFlowFor, Effect, Ready,
    },
};

#[cfg(feature = "alloc")]
use crate::protocol::AsyncEffect;

#[cfg(all(feature = "alloc", not(feature = "std")))]
use alloc::boxed::Box;

impl<'ctx, T, const N: usize> crate::Build<'ctx> for [T; N]
where
    T: crate::Build<'ctx>,
{
    type Builder = Builder<'ctx, T::Builder, N>;
}

#[derive(Debug)]
pub enum ArrayError<E> {
    Incomplete,
    Item(usize, E),
}

pub struct Builder<'ctx, B: crate::Builder<'ctx>, const N: usize> {
    array: MaybeUninit<[B::Value; N]>,
    index: usize,
    item_err: Option<(usize, B::Error)>,
}

impl<'ctx, B: crate::Builder<'ctx>, const N: usize> Default for Builder<'ctx, B, N> {
    fn default() -> Self {
        Self {
            array: MaybeUninit::uninit(),
            index: 0,
            item_err: None,
        }
    }
}

impl<'ctx, B: crate::Builder<'ctx>, const N: usize> crate::Builder<'ctx> for Builder<'ctx, B, N> {
    type Error = ArrayError<B::Error>;

    type Value = [B::Value; N];

    fn as_visitor(&mut self) -> &mut crate::protocol::Visitor<'_, 'ctx> {
        self
    }

    fn build(self) -> Result<Self::Value, Self::Error> {
        if let Some((index, err)) = self.item_err {
            return Err(ArrayError::Item(index, err));
        }

        if self.index < N {
            Err(ArrayError::Incomplete)
        } else {
            Ok(unsafe { self.array.assume_init() })
        }
    }
}

#[cfg(not(feature = "alloc"))]
any_trait! {
    impl['a, 'ctx, B: crate::Builder<'ctx>, const N: usize] Builder<'ctx, B, N> = [
        dyn Sequence<'ctx> + 'a,
    ];
}

#[cfg(feature = "alloc")]
any_trait! {
    impl['a, 'ctx, B: crate::Builder<'ctx>, const N: usize] Builder<'ctx, B, N> = [
        dyn Sequence<'ctx> + 'a,
        dyn Sequence<'ctx, AsyncEffect> + 'a,
    ];
}

impl<'ctx, B: crate::Builder<'ctx>, const N: usize, E: Effect> Sequence<'ctx, E>
    for Builder<'ctx, B, N>
{
    #[inline]
    fn visit<'a>(&'a mut self, scope: &'a mut dyn SequenceScope<'ctx, E>) -> ControlFlowFor<'a, E> {
        E::wrap(async {
            loop {
                // Check if the array is full.
                if self.index >= N {
                    return ControlFlow::Continue(());
                }

                // Try to build the next value.
                let mut builder = B::default();
                match scope.next(builder.as_visitor()).await {
                    ControlFlow::Continue(Status::Done) => {
                        // The sequence is done so the builder wasn't given a value.
                        // We just throw away the empty builder.
                        return ControlFlow::Continue(());
                    }
                    ControlFlow::Continue(Status::Continue) => match builder.build() {
                        Ok(value) => {
                            // Put the value in the array, and move to the next one.
                            unsafe { maybe_uninit_array(&mut self.array).get_unchecked_mut(self.index).write(value) };
                            self.index += 1;
                        }
                        Err(err) => {
                            // Record the item error and return a stop signal.
                            self.item_err = Some((self.index, err));
                            return ControlFlow::Break(());
                        }
                    },
                    ControlFlow::Break(()) => {
                        return ControlFlow::Break(());
                    }
                }
            }
        })
    }
}

fn maybe_uninit_array<T, const N: usize>(
    array: &mut MaybeUninit<[T; N]>,
) -> &mut [MaybeUninit<T>; N] {
    unsafe { &mut *(array as *mut _ as *mut [MaybeUninit<T>; N]) }
}