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use std::{
    mem,
    pin::Pin,
    task::{Context, Poll},
};

use bytes::Bytes;
use futures_core::{ready, Stream};
use pin_project::pin_project;

use crate::error::Error;

use super::{Body, BodySize, MessageBody};

#[pin_project(project = ResponseBodyProj)]
pub enum ResponseBody<B> {
    Body(#[pin] B),
    Other(Body),
}

impl ResponseBody<Body> {
    pub fn into_body<B>(self) -> ResponseBody<B> {
        match self {
            ResponseBody::Body(b) => ResponseBody::Other(b),
            ResponseBody::Other(b) => ResponseBody::Other(b),
        }
    }
}

impl<B> ResponseBody<B> {
    pub fn take_body(&mut self) -> ResponseBody<B> {
        mem::replace(self, ResponseBody::Other(Body::None))
    }
}

impl<B: MessageBody> ResponseBody<B> {
    pub fn as_ref(&self) -> Option<&B> {
        if let ResponseBody::Body(ref b) = self {
            Some(b)
        } else {
            None
        }
    }
}

impl<B> MessageBody for ResponseBody<B>
where
    B: MessageBody,
    B::Error: Into<Error>,
{
    type Error = Error;

    fn size(&self) -> BodySize {
        match self {
            ResponseBody::Body(ref body) => body.size(),
            ResponseBody::Other(ref body) => body.size(),
        }
    }

    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Result<Bytes, Self::Error>>> {
        Stream::poll_next(self, cx)
    }
}

impl<B> Stream for ResponseBody<B>
where
    B: MessageBody,
    B::Error: Into<Error>,
{
    type Item = Result<Bytes, Error>;

    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Self::Item>> {
        match self.project() {
            // TODO: MSRV 1.51: poll_map_err
            ResponseBodyProj::Body(body) => match ready!(body.poll_next(cx)) {
                Some(Err(err)) => Poll::Ready(Some(Err(err.into()))),
                Some(Ok(val)) => Poll::Ready(Some(Ok(val))),
                None => Poll::Ready(None),
            },
            ResponseBodyProj::Other(body) => Pin::new(body).poll_next(cx),
        }
    }
}