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use std::{
    error::Error as StdError,
    fmt,
    pin::Pin,
    task::{ready, Context, Poll},
};

use bytes::Bytes;
use futures::stream::Stream;
use http_body::{Body as HttpBody, Frame};
use http_body_util::{combinators::UnsyncBoxBody, BodyExt};
use pin_project::pin_project;

/// A request body.
pub struct Body {
    kind: Kind,
}

impl fmt::Debug for Body {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Body").finish()
    }
}

enum Kind {
    Once(Option<Bytes>),
    Wrap(UnsyncBoxBody<Bytes, Box<dyn StdError + Send + Sync>>),
}

impl Body {
    fn new(kind: Kind) -> Self {
        Body { kind }
    }

    pub(crate) fn empty() -> Self {
        Self::new(Kind::Once(None))
    }

    pub(crate) fn wrap_body<B>(body: B) -> Self
    where
        B: HttpBody<Data = Bytes> + Send + 'static,
        B::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
    {
        Body::new(Kind::Wrap(body.map_err(Into::into).boxed_unsync()))
    }
}

impl From<Bytes> for Body {
    fn from(bytes: Bytes) -> Self {
        if bytes.is_empty() {
            Self::empty()
        } else {
            Self::new(Kind::Once(Some(bytes)))
        }
    }
}

impl From<Vec<u8>> for Body {
    fn from(vec: Vec<u8>) -> Self {
        Self::from(Bytes::from(vec))
    }
}

impl HttpBody for Body {
    type Data = Bytes;
    type Error = crate::Error;

    fn poll_frame(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Result<http_body::Frame<Self::Data>, Self::Error>>> {
        match self.kind {
            Kind::Once(ref mut val) => {
                if let Some(data) = val.take() {
                    Poll::Ready(Some(Ok(Frame::data(data))))
                } else {
                    Poll::Ready(None)
                }
            }
            Kind::Wrap(ref mut stream) => Poll::Ready(
                ready!(Pin::new(stream).poll_frame(cx))
                    .map(|opt_chunk| opt_chunk.map_err(crate::Error::Service)),
            ),
        }
    }
}

// Wrap `http_body::Body` to implement `Stream`.
#[pin_project]
pub struct BodyDataStream<B> {
    #[pin]
    body: B,
}

impl<B> BodyDataStream<B> {
    pub(crate) fn new(body: B) -> Self {
        Self { body }
    }
}

impl<B> Stream for BodyDataStream<B>
where
    B: HttpBody<Data = Bytes>,
{
    type Item = Result<B::Data, B::Error>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        loop {
            return match ready!(self.as_mut().project().body.poll_frame(cx)) {
                Some(Ok(frame)) => {
                    let Ok(bytes) = frame.into_data() else {
                        continue;
                    };
                    Poll::Ready(Some(Ok(bytes)))
                }
                Some(Err(err)) => Poll::Ready(Some(Err(err))),
                None => Poll::Ready(None),
            };
        }
    }
}

pub trait IntoBodyDataStream: HttpBody {
    fn into_stream(self) -> BodyDataStream<Self>
    where
        Self: Sized,
    {
        BodyDataStream::new(self)
    }
}

impl<T> IntoBodyDataStream for T where T: HttpBody {}