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use super::BitChunk;

/// An iterator over mutable slices of bytes of exact size.
///
/// # Safety
/// The slices returned by this iterator are guaranteed to have length equal to
/// `std::mem::size_of::<T>()`.
#[derive(Debug)]
pub struct BitChunksExactMut<'a, T: BitChunk> {
    chunks: std::slice::ChunksExactMut<'a, u8>,
    remainder: &'a mut [u8],
    remainder_len: usize,
    marker: std::marker::PhantomData<T>,
}

impl<'a, T: BitChunk> BitChunksExactMut<'a, T> {
    /// Returns a new [`BitChunksExactMut`]
    #[inline]
    pub fn new(bitmap: &'a mut [u8], length: usize) -> Self {
        assert!(length <= bitmap.len() * 8);
        let size_of = std::mem::size_of::<T>();

        let bitmap = &mut bitmap[..length.saturating_add(7) / 8];

        let split = (length / 8 / size_of) * size_of;
        let (chunks, remainder) = bitmap.split_at_mut(split);
        let remainder_len = length - chunks.len() * 8;

        let chunks = chunks.chunks_exact_mut(size_of);
        Self {
            chunks,
            remainder,
            remainder_len,
            marker: std::marker::PhantomData,
        }
    }

    /// The remainder slice
    #[inline]
    pub fn remainder(&mut self) -> &mut [u8] {
        self.remainder
    }

    /// The length of the remainder slice in bits.
    #[inline]
    pub fn remainder_len(&mut self) -> usize {
        self.remainder_len
    }
}

impl<'a, T: BitChunk> Iterator for BitChunksExactMut<'a, T> {
    type Item = &'a mut [u8];

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        self.chunks.next()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.chunks.size_hint()
    }
}