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    use generic_array::{sequence::GenericSequence, ArrayLength, GenericArray};

    /// A "history buffer", similar to a write-only ring buffer of fixed length.
    ///
    /// This buffer keeps a fixed number of elements.  On write, the oldest element
    /// is overwritten. Thus, the buffer is useful to keep a history of values with
    /// some desired depth, and for example calculate a rolling average.
    ///
    /// The buffer is always fully initialized; depending on the constructor, the
    /// initial value is either the default value for the element type or a supplied
    /// initial value. This simplifies the API and is mostly irrelevant for the
    /// intended use case.
    ///
    /// # Examples
    /// ```
    /// use heapless::HistoryBuffer;
    /// use heapless::consts::*;
    ///
    /// // Initialize a new buffer with 8 elements, all initially zero.
    /// let mut buf = HistoryBuffer::<_, U8>::new();
    ///
    /// buf.write(3);
    /// buf.write(5);
    /// buf.extend(&[4, 4]);
    ///
    /// // The most recent written element is a four.
    /// assert_eq!(buf.recent(), &4);
    ///
    /// // To access all elements in an unspecified order, use `as_slice()`.
    /// for el in buf.as_slice() { println!("{:?}", el); }
    ///
    /// // Now we can prepare an average of all values, which comes out to 2.
    /// let avg = buf.as_slice().iter().sum::<usize>() / buf.len();
    /// assert_eq!(avg, 2);
    /// ```
    #[derive(Clone)]
    pub struct HistoryBuffer<T, N>
    where
        N: ArrayLength<T>,
    {
        data: GenericArray<T, N>,
        write_at: usize,
    }

    impl<T, N> HistoryBuffer<T, N>
    where
        N: ArrayLength<T>,
        T: Default,
    {
        /// Constructs a new history buffer, where every element is filled with the
        /// default value of the type `T`.
        ///
        /// `HistoryBuffer` currently cannot be constructed in `const` context.
        ///
        /// # Examples
        ///
        /// ```
        /// use heapless::HistoryBuffer;
        /// use heapless::consts::*;
        ///
        /// // Allocate a 16-element buffer on the stack
        /// let mut x: HistoryBuffer<u8, U16> = HistoryBuffer::new();
        /// // All elements are zero
        /// assert_eq!(x.as_slice(), [0; 16]);
        /// ```
        pub fn new() -> Self {
            Self {
                data: Default::default(),
                write_at: 0,
            }
        }

        /// Clears the buffer, replacing every element with the default value of
        /// type `T`.
        pub fn clear(&mut self) {
            *self = Self::new();
        }
    }

    impl<T, N> HistoryBuffer<T, N>
    where
        N: ArrayLength<T>,
        T: Clone,
    {
        /// Constructs a new history buffer, where every element is the given value.
        ///
        /// # Examples
        ///
        /// ```
        /// use heapless::HistoryBuffer;
        /// use heapless::consts::*;
        ///
        /// // Allocate a 16-element buffer on the stack
        /// let mut x: HistoryBuffer<u8, U16> = HistoryBuffer::new_with(4);
        /// // All elements are four
        /// assert_eq!(x.as_slice(), [4; 16]);
        /// ```
        pub fn new_with(t: T) -> Self {
            Self {
                data: GenericArray::generate(|_| t.clone()),
                write_at: 0,
            }
        }

        /// Clears the buffer, replacing every element with the given value.
        pub fn clear_with(&mut self, t: T) {
            *self = Self::new_with(t);
        }
    }

    impl<T, N> HistoryBuffer<T, N>
    where
        N: ArrayLength<T>,
    {
        /// Returns the capacity of the buffer, which is the length of the
        /// underlying backing array.
        pub fn len(&self) -> usize {
            self.data.len()
        }

        /// Writes an element to the buffer, overwriting the oldest value.
        pub fn write(&mut self, t: T) {
            self.data[self.write_at] = t;
            self.write_at += 1;
            if self.write_at == self.len() {
                self.write_at = 0;
            }
        }

        /// Clones and writes all elements in a slice to the buffer.
        ///
        /// If the slice is longer than the buffer, only the last `self.len()`
        /// elements will actually be stored.
        pub fn extend_from_slice(&mut self, other: &[T])
        where
            T: Clone,
        {
            for item in other {
                self.write(item.clone());
            }
        }

        /// Returns a reference to the most recently written value.
        ///
        /// # Examples
        ///
        /// ```
        /// use heapless::HistoryBuffer;
        /// use heapless::consts::*;
        ///
        /// let mut x: HistoryBuffer<u8, U16> = HistoryBuffer::new();
        /// x.write(4);
        /// x.write(10);
        /// assert_eq!(x.recent(), &10);
        /// ```
        pub fn recent(&self) -> &T {
            if self.write_at == 0 {
                &self.data[self.len() - 1]
            } else {
                &self.data[self.write_at - 1]
            }
        }

        /// Returns the array slice backing the buffer, without keeping track
        /// of the write position. Therefore, the element order is unspecified.
        pub fn as_slice(&self) -> &[T] {
            &self.data
        }
    }

    impl<T, N> Extend<T> for HistoryBuffer<T, N>
    where
        N: ArrayLength<T>,
    {
        fn extend<I>(&mut self, iter: I)
        where
            I: IntoIterator<Item = T>,
        {
            for item in iter.into_iter() {
                self.write(item);
            }
        }
    }

    impl<'a, T, N> Extend<&'a T> for HistoryBuffer<T, N>
    where
        T: 'a + Clone,
        N: ArrayLength<T>,
    {
        fn extend<I>(&mut self, iter: I)
        where
            I: IntoIterator<Item = &'a T>,
        {
            self.extend(iter.into_iter().cloned())
        }
    }

    #[cfg(test)]
    mod tests {
        use crate::{consts::*, HistoryBuffer};

        #[test]
        fn new() {
            let x: HistoryBuffer<u8, U4> = HistoryBuffer::new_with(1);
            assert_eq!(x.len(), 4);
            assert_eq!(x.as_slice(), [1; 4]);

            let x: HistoryBuffer<u8, U4> = HistoryBuffer::new();
            assert_eq!(x.as_slice(), [0; 4]);
        }

        #[test]
        fn write() {
            let mut x: HistoryBuffer<u8, U4> = HistoryBuffer::new();
            x.write(1);
            x.write(4);
            assert_eq!(x.as_slice(), [1, 4, 0, 0]);

            x.write(5);
            x.write(6);
            x.write(10);
            assert_eq!(x.as_slice(), [10, 4, 5, 6]);

            x.extend([11, 12].iter());
            assert_eq!(x.as_slice(), [10, 11, 12, 6]);
        }

        #[test]
        fn clear() {
            let mut x: HistoryBuffer<u8, U4> = HistoryBuffer::new_with(1);
            x.clear();
            assert_eq!(x.as_slice(), [0; 4]);

            let mut x: HistoryBuffer<u8, U4> = HistoryBuffer::new();
            x.clear_with(1);
            assert_eq!(x.as_slice(), [1; 4]);
        }

        #[test]
        fn recent() {
            let mut x: HistoryBuffer<u8, U4> = HistoryBuffer::new();
            assert_eq!(x.recent(), &0);

            x.write(1);
            x.write(4);
            assert_eq!(x.recent(), &4);

            x.write(5);
            x.write(6);
            x.write(10);
            assert_eq!(x.recent(), &10);
        }

        #[test]
        fn as_slice() {
            let mut x: HistoryBuffer<u8, U4> = HistoryBuffer::new();

            x.extend([1, 2, 3, 4, 5].iter());

            assert_eq!(x.as_slice(), [5, 2, 3, 4]);
        }
    }