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    use crate::frame::{util, Error, Frame, Head, Kind, StreamId};
    use bytes::{Buf, BufMut, Bytes};

    use std::fmt;

    /// Data frame
    ///
    /// Data frames convey arbitrary, variable-length sequences of octets associated
    /// with a stream. One or more DATA frames are used, for instance, to carry HTTP
    /// request or response payloads.
    #[derive(Eq, PartialEq)]
    pub struct Data<T = Bytes> {
        stream_id: StreamId,
        data: T,
        flags: DataFlags,
        pad_len: Option<u8>,
    }

    #[derive(Copy, Clone, Eq, PartialEq)]
    struct DataFlags(u8);

    const END_STREAM: u8 = 0x1;
    const PADDED: u8 = 0x8;
    const ALL: u8 = END_STREAM | PADDED;

    impl<T> Data<T> {
        /// Creates a new DATA frame.
        pub fn new(stream_id: StreamId, payload: T) -> Self {
            assert!(!stream_id.is_zero());

            Data {
                stream_id,
                data: payload,
                flags: DataFlags::default(),
                pad_len: None,
            }
        }

        /// Returns the stream identifier that this frame is associated with.
        ///
        /// This cannot be a zero stream identifier.
        pub fn stream_id(&self) -> StreamId {
            self.stream_id
        }

        /// Gets the value of the `END_STREAM` flag for this frame.
        ///
        /// If true, this frame is the last that the endpoint will send for the
        /// identified stream.
        ///
        /// Setting this flag causes the stream to enter one of the "half-closed"
        /// states or the "closed" state (Section 5.1).
        pub fn is_end_stream(&self) -> bool {
            self.flags.is_end_stream()
        }

        /// Sets the value for the `END_STREAM` flag on this frame.
        pub fn set_end_stream(&mut self, val: bool) {
            if val {
                self.flags.set_end_stream();
            } else {
                self.flags.unset_end_stream();
            }
        }

        /// Returns whether the `PADDED` flag is set on this frame.
        #[cfg(feature = "unstable")]
        pub fn is_padded(&self) -> bool {
            self.flags.is_padded()
        }

        /// Sets the value for the `PADDED` flag on this frame.
        #[cfg(feature = "unstable")]
        pub fn set_padded(&mut self) {
            self.flags.set_padded();
        }

        /// Returns a reference to this frame's payload.
        ///
        /// This does **not** include any padding that might have been originally
        /// included.
        pub fn payload(&self) -> &T {
            &self.data
        }

        /// Returns a mutable reference to this frame's payload.
        ///
        /// This does **not** include any padding that might have been originally
        /// included.
        pub fn payload_mut(&mut self) -> &mut T {
            &mut self.data
        }

        /// Consumes `self` and returns the frame's payload.
        ///
        /// This does **not** include any padding that might have been originally
        /// included.
        pub fn into_payload(self) -> T {
            self.data
        }

        pub(crate) fn head(&self) -> Head {
            Head::new(Kind::Data, self.flags.into(), self.stream_id)
        }

        pub(crate) fn map<F, U>(self, f: F) -> Data<U>
        where
            F: FnOnce(T) -> U,
        {
            Data {
                stream_id: self.stream_id,
                data: f(self.data),
                flags: self.flags,
                pad_len: self.pad_len,
            }
        }
    }

    impl Data<Bytes> {
        pub(crate) fn load(head: Head, mut payload: Bytes) -> Result<Self, Error> {
            let flags = DataFlags::load(head.flag());

            // The stream identifier must not be zero
            if head.stream_id().is_zero() {
                return Err(Error::InvalidStreamId);
            }

            let pad_len = if flags.is_padded() {
                let len = util::strip_padding(&mut payload)?;
                Some(len)
            } else {
                None
            };

            Ok(Data {
                stream_id: head.stream_id(),
                data: payload,
                flags,
                pad_len,
            })
        }
    }

    impl<T: Buf> Data<T> {
        /// Encode the data frame into the `dst` buffer.
        ///
        /// # Panics
        ///
        /// Panics if `dst` cannot contain the data frame.
        pub(crate) fn encode_chunk<U: BufMut>(&mut self, dst: &mut U) {
            let len = self.data.remaining() as usize;

            assert!(dst.remaining_mut() >= len);

            self.head().encode(len, dst);
            dst.put(&mut self.data);
        }
    }

    impl<T> From<Data<T>> for Frame<T> {
        fn from(src: Data<T>) -> Self {
            Frame::Data(src)
        }
    }

    impl<T> fmt::Debug for Data<T> {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            let mut f = fmt.debug_struct("Data");
            f.field("stream_id", &self.stream_id);
            if !self.flags.is_empty() {
                f.field("flags", &self.flags);
            }
            if let Some(ref pad_len) = self.pad_len {
                f.field("pad_len", pad_len);
            }
            // `data` bytes purposefully excluded
            f.finish()
        }
    }

    // ===== impl DataFlags =====

    impl DataFlags {
        fn load(bits: u8) -> DataFlags {
            DataFlags(bits & ALL)
        }

        fn is_empty(&self) -> bool {
            self.0 == 0
        }

        fn is_end_stream(&self) -> bool {
            self.0 & END_STREAM == END_STREAM
        }

        fn set_end_stream(&mut self) {
            self.0 |= END_STREAM
        }

        fn unset_end_stream(&mut self) {
            self.0 &= !END_STREAM
        }

        fn is_padded(&self) -> bool {
            self.0 & PADDED == PADDED
        }

        #[cfg(feature = "unstable")]
        fn set_padded(&mut self) {
            self.0 |= PADDED
        }
    }

    impl Default for DataFlags {
        fn default() -> Self {
            DataFlags(0)
        }
    }

    impl From<DataFlags> for u8 {
        fn from(src: DataFlags) -> u8 {
            src.0
        }
    }

    impl fmt::Debug for DataFlags {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            util::debug_flags(fmt, self.0)
                .flag_if(self.is_end_stream(), "END_STREAM")
                .flag_if(self.is_padded(), "PADDED")
                .finish()
        }
    }