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use super::super::handle::BodyHandle;
use crate::abi;
use std::io::Write;

/// A low-level interface to a streaming HTTP body.
///
/// The interface to this type is very similar to [`BodyHandle`], however it is write-only, and can
/// only be created as a result of calling
/// [`ResponseHandle::send_to_client()`][`crate::handle::ResponseHandle::send_to_client()`] or
/// [`RequestHandle::send_async_streaming()`][`crate::handle::RequestHandle::send_async_streaming()`].
///
/// This type implements [`Write`] to write to the end of a body. Note that these operations are
/// unbuffered, unlike the same operations on the higher-level [`Body`][`crate::Body`] type.
///
/// A streaming body will be automatically closed when it goes out of scope, or when it is passed to
/// [`drop()`].
#[derive(Debug, Eq, Hash, PartialEq)]
#[repr(transparent)]
pub struct StreamingBodyHandle {
    handle: u32,
}

impl StreamingBodyHandle {
    /// Make a streaming body handle from a non-streaming handle.
    ///
    /// This should only be used when calling the raw ABI directly, and care should be taken not to
    /// reuse or alias handle values.
    pub(crate) fn from_body_handle(body_handle: &BodyHandle) -> Self {
        Self {
            handle: body_handle.handle,
        }
    }

    /// Get a non-streaming body handle from a streaming handle.
    ///
    /// This should only be used when calling the raw ABI directly, and care should be taken not to
    /// reuse or alias handle values, or to use the returned value in contexts where a streaming
    /// handle is not valid.
    fn as_body_handle(&self) -> BodyHandle {
        BodyHandle {
            handle: self.handle,
        }
    }

    /// Append another body onto the end of this body.
    ///
    /// This operation is performed in amortized constant time, and so should always be preferred to
    /// reading an entire body and then writing the same contents to another body.
    ///
    /// The other body will no longer be valid after this call.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # use fastly::handle::{BodyHandle, ResponseHandle};
    /// # let response_handle = ResponseHandle::new();
    /// # let other_body = BodyHandle::new();
    /// let mut streaming_body = response_handle.stream_to_client(BodyHandle::new());
    /// streaming_body.append(other_body);
    /// ```
    pub fn append(&mut self, other: BodyHandle) {
        self.as_body_handle().append(other)
    }

    /// Write a slice of bytes to the end of this streaming body, and return the number of bytes written.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # use fastly::handle::{BodyHandle, ResponseHandle};
    /// # let response_handle = ResponseHandle::new();
    /// let mut streaming_body = response_handle.stream_to_client(BodyHandle::new());
    /// streaming_body.write_bytes(&[0, 1, 2, 3]);
    /// ```
    pub fn write_bytes(&mut self, bytes: &[u8]) -> usize {
        self.as_body_handle().write_bytes(bytes)
    }

    /// Write a string slice to the end of this streaming body, and return the number of bytes written.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # use fastly::handle::{BodyHandle, ResponseHandle};
    /// # let response_handle = ResponseHandle::new();
    /// let mut streaming_body = response_handle.stream_to_client(BodyHandle::new());
    /// streaming_body.write_str("woof woof");
    /// ```
    pub fn write_str(&mut self, string: &str) -> usize {
        self.write_bytes(string.as_bytes())
    }
}

impl Drop for StreamingBodyHandle {
    fn drop(&mut self) {
        unsafe { abi::fastly_http_body::close(self.as_body_handle().as_u32()) }
            .result()
            .expect("fastly_http_body::close failed");
    }
}

impl Write for StreamingBodyHandle {
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        Ok(self.write_bytes(buf))
    }

    fn flush(&mut self) -> std::io::Result<()> {
        Ok(())
    }
}