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use crate::{
    consumer::Consumer,
    producer::Producer,
    ring_buffer::{RbRead, RbRef, RbWrite},
};

/// Moves at most `count` items from the `src` consumer to the `dst` producer.
///
/// Consumer and producer may be of different buffers as well as of the same one.
/// `count` is the number of items being moved, if `None` - as much as possible items will be moved.
///
/// Returns number of items been moved.
pub fn transfer<T, Rs: RbRef, Rd: RbRef>(
    src: &mut Consumer<T, Rs>,
    dst: &mut Producer<T, Rd>,
    count: Option<usize>,
) -> usize
where
    Rs::Rb: RbRead<T>,
    Rd::Rb: RbWrite<T>,
{
    let (src_left, src_right) = unsafe { src.as_uninit_slices() };
    let (dst_left, dst_right) = unsafe { dst.free_space_as_slices() };
    let src_iter = src_left.iter().chain(src_right.iter());
    let dst_iter = dst_left.iter_mut().chain(dst_right.iter_mut());

    let mut actual_count = 0;
    for (src_elem, dst_place) in src_iter.zip(dst_iter) {
        if let Some(count) = count {
            if actual_count >= count {
                break;
            }
        }
        unsafe { dst_place.write(src_elem.as_ptr().read()) };
        actual_count += 1;
    }
    unsafe { src.advance(actual_count) };
    unsafe { dst.advance(actual_count) };
    actual_count
}