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    use std::cmp;

    use chained_hash_table::WINDOW_SIZE;
    use huffman_table;

    const MAX_MATCH: usize = huffman_table::MAX_MATCH as usize;

    /// The maximum size of the buffer.
    pub const BUFFER_SIZE: usize = (WINDOW_SIZE * 2) + MAX_MATCH;

    pub struct InputBuffer {
        buffer: Vec<u8>,
    }

    impl InputBuffer {
        #[cfg(test)]
        pub fn new<'a>(data: &'a [u8]) -> (InputBuffer, Option<&[u8]>) {
            let mut b = InputBuffer::empty();
            let rem = b.add_data(data);
            (b, rem)
        }

        pub fn empty() -> InputBuffer {
            InputBuffer {
                buffer: Vec::with_capacity(BUFFER_SIZE),
            }
        }

        /// Add data to the buffer.
        ///
        /// Returns a slice of the data that was not added (including the lookahead if any).
        pub fn add_data<'a>(&mut self, data: &'a [u8]) -> Option<&'a [u8]> {
            debug_assert!(self.current_end() <= BUFFER_SIZE);
            if self.current_end() + data.len() > BUFFER_SIZE {
                // Add data and return how much was left.
                let consumed = {
                    let space_left = BUFFER_SIZE - self.buffer.len();
                    self.buffer.extend_from_slice(&data[..space_left]);
                    space_left
                };
                Some(&data[consumed..])
            } else {
                // There's space for all of the data.
                self.buffer.extend_from_slice(data);
                None
            }
        }

        /// Get the current amount of data in the buffer.
        pub fn current_end(&self) -> usize {
            self.buffer.len()
        }

        /// Slide the input window and add new data.
        ///
        /// Returns a slice containing the data that did not fit, or None if all data was consumed.
        pub fn slide<'a>(&mut self, data: &'a [u8]) -> Option<&'a [u8]> {
            // This should only be used when the buffer is full
            assert!(self.buffer.len() > WINDOW_SIZE * 2);

            // Do this in a closure to to end the borrow of buffer.
            let (final_len, upper_len, end) = {
                // Split into lower window and upper window + lookahead
                let (lower, upper) = self.buffer.split_at_mut(WINDOW_SIZE);
                // Copy the upper window to the lower window
                lower.copy_from_slice(&upper[..WINDOW_SIZE]);
                let lookahead_len = {
                    // Copy the lookahead to the start of the upper window
                    let (upper_2, lookahead) = upper.split_at_mut(WINDOW_SIZE);
                    let lookahead_len = lookahead.len();
                    debug_assert!(lookahead_len <= MAX_MATCH);
                    upper_2[..lookahead_len].copy_from_slice(lookahead);
                    lookahead_len
                };

                // Length of the upper window minus the lookahead bytes
                let upper_len = upper.len() - lookahead_len;
                let end = cmp::min(data.len(), upper_len);
                upper[lookahead_len..lookahead_len + end].copy_from_slice(&data[..end]);
                // Remove unused data if any.
                (lower.len() + lookahead_len + end, upper_len, end)
            };
            // Remove unused space.
            self.buffer.truncate(final_len);

            if data.len() > upper_len {
                // Return a slice of the data that was not added
                Some(&data[end..])
            } else {
                None
            }
        }

        /// Get a mutable slice of the used part of the buffer.
        pub fn get_buffer(&mut self) -> &mut [u8] {
            &mut self.buffer
        }
    }

    #[cfg(test)]
    mod test {
        use super::MAX_MATCH;
        use chained_hash_table::WINDOW_SIZE;
        use super::*;
        #[test]
        pub fn buffer_add_full() {
            let data = [10u8; BUFFER_SIZE + 10];
            let (mut buf, extra) = InputBuffer::new(&data[..]);
            assert!(extra.unwrap() == &[10; 10]);
            let to_add = [2, 5, 3];
            let not_added = buf.add_data(&to_add);
            assert_eq!(not_added.unwrap(), to_add);
        }

        #[test]
        pub fn buffer_add_not_full() {
            let data = [10u8; BUFFER_SIZE - 5];
            let (mut buf, extra) = InputBuffer::new(&data[..]);
            assert_eq!(buf.current_end(), data.len());
            assert_eq!(extra, None);
            let to_add = [2, 5, 3];
            {
                let not_added = buf.add_data(&to_add);
                assert!(not_added.is_none());
            }
            let not_added = buf.add_data(&to_add);
            assert_eq!(not_added.unwrap()[0], 3);
        }

        #[test]
        fn slide() {
            let data = [10u8; BUFFER_SIZE];
            let (mut buf, extra) = InputBuffer::new(&data[..]);
            assert_eq!(extra, None);
            let to_add = [5; 5];
            let rem = buf.slide(&to_add);
            assert!(rem.is_none());
            {
                let slice = buf.get_buffer();
                assert!(slice[..WINDOW_SIZE + MAX_MATCH] == data[WINDOW_SIZE..]);
                assert_eq!(
                    slice[WINDOW_SIZE + MAX_MATCH..WINDOW_SIZE + MAX_MATCH + 5],
                    to_add
                );
            }
            assert_eq!(buf.current_end(), WINDOW_SIZE + MAX_MATCH + to_add.len());
        }
    }

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