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    use std::io::Write;
    use std::{thread, io};

    use byteorder::{WriteBytesExt, BigEndian};

    use checksum::{Adler32Checksum, RollingChecksum};
    use compress::compress_data_dynamic_n;
    use compress::Flush;
    use deflate_state::DeflateState;
    use compression_options::CompressionOptions;
    use zlib::{write_zlib_header, CompressionLevel};

    const ERR_STR: &'static str = "Error! The wrapped writer is missing.\
                                   This is a bug, please file an issue.";

    /// Keep compressing until all the input has been compressed and output or the writer returns `Err`.
    pub fn compress_until_done<W: Write>(
        mut input: &[u8],
        deflate_state: &mut DeflateState<W>,
        flush_mode: Flush,
    ) -> io::Result<()> {
        // This should only be used for flushing.
        assert!(flush_mode != Flush::None);
        loop {
            match compress_data_dynamic_n(input, deflate_state, flush_mode) {
                Ok(0) => {
                    if deflate_state.output_buf().is_empty() {
                        break;
                    } else {
                        // If the output buffer isn't empty, keep going until it is, as there is still
                        // data to be flushed.
                        input = &[];
                    }
                }
                Ok(n) => {
                    if n < input.len() {
                        input = &input[n..]
                    } else {
                        input = &[];
                    }
                }
                Err(e) => {
                    match e.kind() {
                        // This error means that there may still be data to flush.
                        // This could possibly get stuck if the underlying writer keeps returning this
                        // error.
                        io::ErrorKind::Interrupted => (),
                        _ => return Err(e),
                    }
                }
            }
        }

        debug_assert_eq!(
            deflate_state.bytes_written,
            deflate_state.bytes_written_control.get()
        );

        Ok(())
    }

    /// A DEFLATE encoder/compressor.
    ///
    /// A struct implementing a [`Write`] interface that takes unencoded data and compresses it to
    /// the provided writer using DEFLATE compression.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use std::io;
    /// #
    /// # fn try_main() -> io::Result<Vec<u8>> {
    /// #
    /// use std::io::Write;
    ///
    /// use deflate::Compression;
    /// use deflate::write::DeflateEncoder;
    ///
    /// let data = b"This is some test data";
    /// let mut encoder = DeflateEncoder::new(Vec::new(), Compression::Default);
    /// encoder.write_all(data)?;
    /// let compressed_data = encoder.finish()?;
    /// # Ok(compressed_data)
    /// #
    /// # }
    /// # fn main() {
    /// #     try_main().unwrap();
    /// # }
    /// ```
    /// [`Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
    pub struct DeflateEncoder<W: Write> {
        deflate_state: DeflateState<W>,
    }

    impl<W: Write> DeflateEncoder<W> {
        /// Creates a new encoder using the provided compression options.
        pub fn new<O: Into<CompressionOptions>>(writer: W, options: O) -> DeflateEncoder<W> {
            DeflateEncoder {
                deflate_state: DeflateState::new(options.into(), writer),
            }
        }

        /// Encode all pending data to the contained writer, consume this `DeflateEncoder`,
        /// and return the contained writer if writing succeeds.
        pub fn finish(mut self) -> io::Result<W> {
            self.output_all()?;
            // We have to move the inner writer out of the encoder, and replace it with `None`
            // to let the `DeflateEncoder` drop safely.
            Ok(self.deflate_state.inner.take().expect(ERR_STR))
        }

        /// Resets the encoder (except the compression options), replacing the current writer
        /// with a new one, returning the old one.
        pub fn reset(&mut self, w: W) -> io::Result<W> {
            self.output_all()?;
            self.deflate_state.reset(w)
        }

        /// Output all pending data as if encoding is done, but without resetting anything
        fn output_all(&mut self) -> io::Result<()> {
            compress_until_done(&[], &mut self.deflate_state, Flush::Finish)
        }
    }

    impl<W: Write> io::Write for DeflateEncoder<W> {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            let flush_mode = self.deflate_state.flush_mode;
            compress_data_dynamic_n(buf, &mut self.deflate_state, flush_mode)
        }

        /// Flush the encoder.
        ///
        /// This will flush the encoder, emulating the Sync flush method from Zlib.
        /// This essentially finishes the current block, and sends an additional empty stored block to
        /// the writer.
        fn flush(&mut self) -> io::Result<()> {
            compress_until_done(&[], &mut self.deflate_state, Flush::Sync)
        }
    }

    impl<W: Write> Drop for DeflateEncoder<W> {
        /// When the encoder is dropped, output the rest of the data.
        ///
        /// WARNING: This may silently fail if writing fails, so using this to finish encoding
        /// for writers where writing might fail is not recommended, for that call
        /// [`finish()`](#method.finish) instead.
        fn drop(&mut self) {
            // Not sure if implementing drop is a good idea or not, but we follow flate2 for now.
            // We only do this if we are not panicking, to avoid a double panic.
            if self.deflate_state.inner.is_some() && !thread::panicking() {
                let _ = self.output_all();
            }
        }
    }

    /// A Zlib encoder/compressor.
    ///
    /// A struct implementing a [`Write`] interface that takes unencoded data and compresses it to
    /// the provided writer using DEFLATE compression with Zlib headers and trailers.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use std::io;
    /// #
    /// # fn try_main() -> io::Result<Vec<u8>> {
    /// #
    /// use std::io::Write;
    ///
    /// use deflate::Compression;
    /// use deflate::write::ZlibEncoder;
    ///
    /// let data = b"This is some test data";
    /// let mut encoder = ZlibEncoder::new(Vec::new(), Compression::Default);
    /// encoder.write_all(data)?;
    /// let compressed_data = encoder.finish()?;
    /// # Ok(compressed_data)
    /// #
    /// # }
    /// # fn main() {
    /// #     try_main().unwrap();
    /// # }
    /// ```
    /// [`Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
    pub struct ZlibEncoder<W: Write> {
        deflate_state: DeflateState<W>,
        checksum: Adler32Checksum,
        header_written: bool,
    }

    impl<W: Write> ZlibEncoder<W> {
        /// Create a new `ZlibEncoder` using the provided compression options.
        pub fn new<O: Into<CompressionOptions>>(writer: W, options: O) -> ZlibEncoder<W> {
            ZlibEncoder {
                deflate_state: DeflateState::new(options.into(), writer),
                checksum: Adler32Checksum::new(),
                header_written: false,
            }
        }

        /// Output all pending data ,including the trailer(checksum) as if encoding is done,
        /// but without resetting anything.
        fn output_all(&mut self) -> io::Result<()> {
            self.check_write_header()?;
            compress_until_done(&[], &mut self.deflate_state, Flush::Finish)?;
            self.write_trailer()
        }

        /// Encode all pending data to the contained writer, consume this `ZlibEncoder`,
        /// and return the contained writer if writing succeeds.
        pub fn finish(mut self) -> io::Result<W> {
            self.output_all()?;
            // We have to move the inner writer out of the encoder, and replace it with `None`
            // to let the `DeflateEncoder` drop safely.
            Ok(self.deflate_state.inner.take().expect(ERR_STR))
        }

        /// Resets the encoder (except the compression options), replacing the current writer
        /// with a new one, returning the old one.
        pub fn reset(&mut self, writer: W) -> io::Result<W> {
            self.output_all()?;
            self.header_written = false;
            self.checksum = Adler32Checksum::new();
            self.deflate_state.reset(writer)
        }

        /// Check if a zlib header should be written.
        fn check_write_header(&mut self) -> io::Result<()> {
            if !self.header_written {
                write_zlib_header(self.deflate_state.output_buf(), CompressionLevel::Default)?;
                self.header_written = true;
            }
            Ok(())
        }

        /// Write the trailer, which for zlib is the Adler32 checksum.
        fn write_trailer(&mut self) -> io::Result<()> {
            let hash = self.checksum.current_hash();

            self.deflate_state
                .inner
                .as_mut()
                .expect(ERR_STR)
                .write_u32::<BigEndian>(hash)
        }

        /// Return the adler32 checksum of the currently consumed data.
        pub fn checksum(&self) -> u32 {
            self.checksum.current_hash()
        }
    }

    impl<W: Write> io::Write for ZlibEncoder<W> {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.check_write_header()?;
            let flush_mode = self.deflate_state.flush_mode;
            let res = compress_data_dynamic_n(buf, &mut self.deflate_state, flush_mode);
            match res {
                // If this is returned, the whole buffer was consumed
                Ok(0) => self.checksum.update_from_slice(buf),
                // Otherwise, only part of it was consumed, so only that part
                // added to the checksum.
                Ok(n) => self.checksum.update_from_slice(&buf[0..n]),
                _ => (),
            };
            res
        }

        /// Flush the encoder.
        ///
        /// This will flush the encoder, emulating the Sync flush method from Zlib.
        /// This essentially finishes the current block, and sends an additional empty stored block to
        /// the writer.
        fn flush(&mut self) -> io::Result<()> {
            compress_until_done(&[], &mut self.deflate_state, Flush::Sync)
        }
    }

    impl<W: Write> Drop for ZlibEncoder<W> {
        /// When the encoder is dropped, output the rest of the data.
        ///
        /// WARNING: This may silently fail if writing fails, so using this to finish encoding
        /// for writers where writing might fail is not recommended, for that call
        /// [`finish()`](#method.finish) instead.
        fn drop(&mut self) {
            if self.deflate_state.inner.is_some() && !thread::panicking() {
                let _ = self.output_all();
            }
        }
    }

    #[cfg(feature = "gzip")]
    pub mod gzip {

        use std::io::{Write, Cursor};
        use std::{thread, io};

        use super::*;

        use byteorder::{WriteBytesExt, LittleEndian};
        use gzip_header::{Crc, GzBuilder};

        /// A Gzip encoder/compressor.
        ///
        /// A struct implementing a [`Write`] interface that takes unencoded data and compresses it to
        /// the provided writer using DEFLATE compression with Gzip headers and trailers.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use std::io;
        /// #
        /// # fn try_main() -> io::Result<Vec<u8>> {
        /// #
        /// use std::io::Write;
        ///
        /// use deflate::Compression;
        /// use deflate::write::GzEncoder;
        ///
        /// let data = b"This is some test data";
        /// let mut encoder = GzEncoder::new(Vec::new(), Compression::Default);
        /// encoder.write_all(data)?;
        /// let compressed_data = encoder.finish()?;
        /// # Ok(compressed_data)
        /// #
        /// # }
        /// # fn main() {
        /// #     try_main().unwrap();
        /// # }
        /// ```
        /// [`Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
        pub struct GzEncoder<W: Write> {
            inner: DeflateEncoder<W>,
            checksum: Crc,
            header: Vec<u8>,
        }

        impl<W: Write> GzEncoder<W> {
            /// Create a new `GzEncoder` writing deflate-compressed data to the underlying writer when
            /// written to, wrapped in a gzip header and trailer. The header details will be blank.
            pub fn new<O: Into<CompressionOptions>>(writer: W, options: O) -> GzEncoder<W> {
                GzEncoder::from_builder(GzBuilder::new(), writer, options)
            }

            /// Create a new GzEncoder from the provided `GzBuilder`. This allows customising
            /// the detalis of the header, such as the filename and comment fields.
            pub fn from_builder<O: Into<CompressionOptions>>(
                builder: GzBuilder,
                writer: W,
                options: O,
            ) -> GzEncoder<W> {
                GzEncoder {
                    inner: DeflateEncoder::new(writer, options),
                    checksum: Crc::new(),
                    header: builder.into_header(),
                }
            }

            /// Write header to the output buffer if it hasn't been done yet.
            fn check_write_header(&mut self) {
                if !self.header.is_empty() {
                    self.inner
                        .deflate_state
                        .output_buf()
                        .extend_from_slice(&self.header);
                    self.header.clear();
                }
            }

            /// Output all pending data ,including the trailer(checksum + count) as if encoding is done.
            /// but without resetting anything.
            fn output_all(&mut self) -> io::Result<()> {
                self.check_write_header();
                self.inner.output_all()?;
                self.write_trailer()
            }

            /// Encode all pending data to the contained writer, consume this `GzEncoder`,
            /// and return the contained writer if writing succeeds.
            pub fn finish(mut self) -> io::Result<W> {
                self.output_all()?;
                // We have to move the inner writer out of the encoder, and replace it with `None`
                // to let the `DeflateEncoder` drop safely.
                Ok(self.inner.deflate_state.inner.take().expect(ERR_STR))
            }

            fn reset_no_header(&mut self, writer: W) -> io::Result<W> {
                self.output_all()?;
                self.checksum = Crc::new();
                self.inner.deflate_state.reset(writer)
            }

            /// Resets the encoder (except the compression options), replacing the current writer
            /// with a new one, returning the old one. (Using a blank header).
            pub fn reset(&mut self, writer: W) -> io::Result<W> {
                let w = self.reset_no_header(writer);
                self.header = GzBuilder::new().into_header();
                w
            }

            /// Resets the encoder (excelt the compression options), replacing the current writer
            /// with a new one, returning the old one, and using the provided `GzBuilder` to
            /// create the header.
            pub fn reset_with_builder(&mut self, writer: W, builder: GzBuilder) -> io::Result<W> {
                let w = self.reset_no_header(writer);
                self.header = builder.into_header();
                w
            }

            /// Write the checksum and number of bytes mod 2^32 to the output writer.
            fn write_trailer(&mut self) -> io::Result<()> {
                let crc = self.checksum.sum();
                let amount = self.checksum.amt_as_u32();

                // We use a buffer here to make sure we don't end up writing only half the header if
                // writing fails.
                let mut buf = [0u8; 8];
                let mut temp = Cursor::new(&mut buf[..]);
                temp.write_u32::<LittleEndian>(crc).unwrap();
                temp.write_u32::<LittleEndian>(amount).unwrap();
                self.inner
                    .deflate_state
                    .inner
                    .as_mut()
                    .expect(ERR_STR)
                    .write_all(temp.into_inner())
            }

            /// Get the crc32 checksum of the data comsumed so far.
            pub fn checksum(&self) -> u32 {
                self.checksum.sum()
            }
        }

        impl<W: Write> io::Write for GzEncoder<W> {
            fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
                self.check_write_header();
                let res = self.inner.write(buf);
                match res {
                    Ok(0) => self.checksum.update(buf),
                    Ok(n) => self.checksum.update(&buf[0..n]),
                    _ => (),
                };
                res
            }

            /// Flush the encoder.
            ///
            /// This will flush the encoder, emulating the Sync flush method from Zlib.
            /// This essentially finishes the current block, and sends an additional empty stored
            /// block to the writer.
            fn flush(&mut self) -> io::Result<()> {
                self.inner.flush()
            }
        }

        impl<W: Write> Drop for GzEncoder<W> {
            /// When the encoder is dropped, output the rest of the data.
            ///
            /// WARNING: This may silently fail if writing fails, so using this to finish encoding
            /// for writers where writing might fail is not recommended, for that call
            /// [`finish()`](#method.finish) instead.
            fn drop(&mut self) {
                if self.inner.deflate_state.inner.is_some() && !thread::panicking() {
                    let _ = self.output_all();
                }
            }
        }

        #[cfg(test)]
        mod test {
            use super::*;
            use test_utils::{get_test_data, decompress_gzip};
            #[test]
            fn gzip_writer() {
                let data = get_test_data();
                let comment = b"Comment";
                let compressed = {
                    let mut compressor = GzEncoder::from_builder(
                        GzBuilder::new().comment(&comment[..]),
                        Vec::with_capacity(data.len() / 3),
                        CompressionOptions::default(),
                    );
                    compressor.write_all(&data[0..data.len() / 2]).unwrap();
                    compressor.write_all(&data[data.len() / 2..]).unwrap();
                    compressor.finish().unwrap()
                };

                let (dec, res) = decompress_gzip(&compressed);
                assert_eq!(dec.header().comment().unwrap(), comment);
                assert!(res == data);
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use test_utils::{get_test_data, decompress_to_end, decompress_zlib};
        use compression_options::CompressionOptions;
        use std::io::Write;

        #[test]
        fn deflate_writer() {
            let data = get_test_data();
            let compressed = {
                let mut compressor = DeflateEncoder::new(
                    Vec::with_capacity(data.len() / 3),
                    CompressionOptions::high(),
                );
                // Write in multiple steps to see if this works as it's supposed to.
                compressor.write_all(&data[0..data.len() / 2]).unwrap();
                compressor.write_all(&data[data.len() / 2..]).unwrap();
                compressor.finish().unwrap()
            };

            let res = decompress_to_end(&compressed);
            assert!(res == data);
        }

        #[test]
        fn zlib_writer() {
            let data = get_test_data();
            let compressed = {
                let mut compressor = ZlibEncoder::new(
                    Vec::with_capacity(data.len() / 3),
                    CompressionOptions::high(),
                );
                compressor.write_all(&data[0..data.len() / 2]).unwrap();
                compressor.write_all(&data[data.len() / 2..]).unwrap();
                compressor.finish().unwrap()
            };

            let res = decompress_zlib(&compressed);
            assert!(res == data);
        }

        #[test]
        /// Check if the the result of compressing after resetting is the same as before.
        fn writer_reset() {
            let data = get_test_data();
            let mut compressor = DeflateEncoder::new(
                Vec::with_capacity(data.len() / 3),
                CompressionOptions::default(),
            );
            compressor.write_all(&data).unwrap();
            let res1 = compressor
                .reset(Vec::with_capacity(data.len() / 3))
                .unwrap();
            compressor.write_all(&data).unwrap();
            let res2 = compressor.finish().unwrap();
            assert!(res1 == res2);
        }

        #[test]
        fn writer_reset_zlib() {
            let data = get_test_data();
            let mut compressor = ZlibEncoder::new(
                Vec::with_capacity(data.len() / 3),
                CompressionOptions::default(),
            );
            compressor.write_all(&data).unwrap();
            let res1 = compressor
                .reset(Vec::with_capacity(data.len() / 3))
                .unwrap();
            compressor.write_all(&data).unwrap();
            let res2 = compressor.finish().unwrap();
            assert!(res1 == res2);
        }

        #[test]
        fn writer_sync() {
            let data = get_test_data();
            let compressed = {
                let mut compressor = DeflateEncoder::new(
                    Vec::with_capacity(data.len() / 3),
                    CompressionOptions::default(),
                );
                let split = data.len() / 2;
                compressor.write_all(&data[..split]).unwrap();
                compressor.flush().unwrap();
                {
                    let buf = &mut compressor.deflate_state.inner.as_mut().unwrap();
                    let buf_len = buf.len();
                    // Check for the sync marker. (excluding the header as it might not line
                    // up with the byte boundary.)
                    assert_eq!(buf[buf_len - 4..], [0, 0, 255, 255]);
                }
                compressor.write_all(&data[split..]).unwrap();
                compressor.finish().unwrap()
            };

            let decompressed = decompress_to_end(&compressed);

            assert!(decompressed == data);
        }

        #[test]
        /// Make sure compression works with the writer when the input is between 1 and 2 window sizes.
        fn issue_18() {
            use compression_options::Compression;
            let data = vec![0; 61000];
            let compressed = {
                let mut compressor = ZlibEncoder::new(Vec::new(), Compression::Default);
                compressor.write_all(&data[..]).unwrap();
                compressor.finish().unwrap()
            };
            let decompressed = decompress_zlib(&compressed);
            assert!(decompressed == data);
        }

        #[test]
        fn writer_sync_multiple() {
            use std::cmp;
            let data = get_test_data();
            let compressed = {
                let mut compressor = DeflateEncoder::new(
                    Vec::with_capacity(data.len() / 3),
                    CompressionOptions::default(),
                );
                let split = data.len() / 2;
                compressor.write_all(&data[..split]).unwrap();
                compressor.flush().unwrap();
                compressor.flush().unwrap();
                {
                    let buf = &mut compressor.deflate_state.inner.as_mut().unwrap();
                    let buf_len = buf.len();
                    // Check for the sync marker. (excluding the header as it might not line
                    // up with the byte boundary.)
                    assert_eq!(buf[buf_len - 4..], [0, 0, 255, 255]);
                }
                compressor
                    .write_all(&data[split..cmp::min(split + 2, data.len())])
                    .unwrap();
                compressor.flush().unwrap();
                compressor
                    .write_all(&data[cmp::min(split + 2, data.len())..])
                    .unwrap();
                compressor.finish().unwrap()
            };

            let decompressed = decompress_to_end(&compressed);

            assert!(decompressed == data);

            let mut compressor = DeflateEncoder::new(
                Vec::with_capacity(data.len() / 3),
                CompressionOptions::default(),
            );

            compressor.flush().unwrap();
            compressor.write_all(&[1, 2]).unwrap();
            compressor.flush().unwrap();
            compressor.write_all(&[3]).unwrap();
            compressor.flush().unwrap();
            let compressed = compressor.finish().unwrap();

            let decompressed = decompress_to_end(&compressed);

            assert_eq!(decompressed, [1, 2, 3]);
        }
    }

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