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use crate::{builder::Builder, traits::*, Cursor, Offset};
use core::mem::MaybeUninit;

impl<T, P, const N: usize> WriteAsOffset<[P]> for [T; N]
where
    P: Primitive,
    T: VectorWrite<P>,
{
    fn prepare(&self, builder: &mut Builder) -> Offset<[P]> {
        let mut tmp: [MaybeUninit<T::Value>; N] = unsafe { MaybeUninit::uninit().assume_init() };
        for (t, v) in tmp.iter_mut().zip(self.iter()) {
            t.write(v.prepare(builder));
        }
        // TODO: replace with std::mem::MaybeUninit::array_assume_init when it becomes stable
        //       https://github.com/rust-lang/rust/issues/80908
        let tmp =
            unsafe { (&tmp as *const [MaybeUninit<T::Value>; N] as *const [T::Value; N]).read() };
        unsafe {
            builder.write_with(
                4 + T::STRIDE.checked_mul(self.len()).unwrap(),
                P::ALIGNMENT_MASK.max(3),
                |buffer_position, bytes| {
                    let bytes = bytes.as_mut_ptr();

                    (self.len() as u32).write(
                        Cursor::new(&mut *(bytes as *mut [MaybeUninit<u8>; 4])),
                        buffer_position,
                    );

                    T::write_values(&tmp, bytes.add(4), buffer_position - 4);
                },
            )
        };
        builder.current_offset()
    }
}

impl<T, P, const N: usize> WriteAs<Offset<[P]>> for [T; N]
where
    P: Primitive,
    T: VectorWrite<P>,
{
    type Prepared = Offset<[P]>;

    fn prepare(&self, builder: &mut Builder) -> Offset<[P]> {
        WriteAsOffset::prepare(self, builder)
    }
}

impl<T, P, const N: usize> WriteAsOptional<Offset<[P]>> for [T; N]
where
    P: Primitive,
    T: VectorWrite<P>,
{
    type Prepared = Offset<[P]>;

    #[inline]
    fn prepare(&self, builder: &mut Builder) -> Option<Offset<[P]>> {
        Some(WriteAsOffset::prepare(self, builder))
    }
}