use core::iter::ExactSizeIterator;
use core::iter::FusedIterator;
use core::mem::MaybeUninit;

pub(crate) struct ArrayVec<T, const N: usize> {
    len: usize,
    array: [MaybeUninit<T>; N],
}

impl<T, const N: usize> Clone for ArrayVec<T, N>
where
    T: Copy,
{
    #[inline]
    fn clone(&self) -> Self {
        Self {
            len: self.len,
            array: self.array.clone(),
        }
    }
}

impl<T, const N: usize> ArrayVec<T, N> {
    #[inline]
    pub(crate) fn new() -> Self {
        Self {
            len: 0,
            array: [const { MaybeUninit::uninit() }; N],
        }
    }
    #[inline]
    pub(crate) unsafe fn push_unchecked(&mut self, m: T) {
        debug_assert!(self.len < N);
        unsafe {
            self.array.get_unchecked_mut(self.len).write(m);
            self.len = self.len.unchecked_add(1);
        }
    }
    #[inline]
    pub(crate) fn len(&self) -> usize {
        self.len
    }
    #[inline]
    pub(crate) fn get(&self, index: usize) -> Option<&T> {
        if index < self.len {
            Some(unsafe { self.array.as_slice().get_unchecked(index).assume_init_ref() })
        } else {
            None
        }
    }
    #[inline]
    pub(crate) fn as_slice(&self) -> &[T] {
        unsafe { core::mem::transmute::<_, &[T]>(self.array.get_unchecked(0..self.len)) }
    }
    #[inline]
    pub(crate) fn as_mut_slice(&mut self) -> &mut [T] {
        unsafe { core::mem::transmute::<_, &mut [T]>(self.array.get_unchecked_mut(0..self.len)) }
    }
}

impl<T, const N: usize> IntoIterator for ArrayVec<T, N> {
    type Item = T;
    type IntoIter = ArrayVecIntoIter<T, N>;
    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        ArrayVecIntoIter {
            array: self,
            index: 0,
        }
    }
}

pub(crate) struct ArrayVecIntoIter<T, const N: usize> {
    array: ArrayVec<T, N>,
    index: usize,
}
impl<T, const N: usize> Iterator for ArrayVecIntoIter<T, N> {
    type Item = T;
    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.index < self.array.len {
            unsafe {
                let item = self
                    .array
                    .array
                    .get_unchecked(self.index)
                    .assume_init_read();
                self.index = self.index.unchecked_add(1);
                Some(item)
            }
        } else {
            None
        }
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let len = self.len();
        (len, Some(len))
    }
}
impl<T, const N: usize> FusedIterator for ArrayVecIntoIter<T, N> {}
impl<T, const N: usize> ExactSizeIterator for ArrayVecIntoIter<T, N> {
    #[inline]
    fn len(&self) -> usize {
        unsafe { self.array.len().unchecked_sub(self.index) }
    }
}