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#[derive(Debug, Clone, Eq, PartialEq, Hash)]
pub struct RingBuffer<T> {
    elements: Vec<T>,
    pos: usize,
}

impl<T> RingBuffer<T> {
    pub fn new(size: usize) -> RingBuffer<T> {
        assert!(size > 0);

        RingBuffer {
            elements: Vec::with_capacity(size),
            pos: 0,
        }
    }

    #[inline]
    pub fn capacity(&self) -> usize {
        self.elements.capacity()
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.elements.len()
    }

    #[inline]
    pub fn pos(&self) -> usize {
        self.pos
    }

    #[inline]
    pub fn next(&mut self) -> Option<&mut T> {
        let idx = self.advance();
        let el = self.elements.get_mut(idx);
        el
    }

    #[inline]
    pub fn peek(&self) -> Option<&T> {
        self.elements.get(self.pos)
    }

    #[inline]
    pub fn peek_mut(&mut self) -> Option<&mut T> {
        self.elements.get_mut(self.pos)
    }

    #[inline]
    pub fn push(&mut self, mut v: T) -> Option<T> {
        if self.len() < self.capacity() {
            self.elements.push(v);
            self.advance();
            None
        } else {
            std::mem::swap(&mut self.elements[self.pos], &mut v);
            self.advance();
            Some(v)
        }
    }

    #[inline]
    fn advance(&mut self) -> usize {
        let old = self.pos;
        self.pos = (self.pos + 1) % self.len();
        old
    }
}