use crate::response::{AppResponse, AppResponseError};
use app_error::ErrorCode;
use bytes::{Buf, Bytes, BytesMut};
use futures::{ready, Stream, TryStreamExt};

use pin_project::pin_project;
use serde::de::DeserializeOwned;
use serde_json::de::SliceRead;
use serde_json::StreamDeserializer;

use crate::dto::ai_dto::StringOrMessage;
use futures::stream::StreamExt;
use infra::reqwest::{JsonStream, NewlineStream};
use std::pin::Pin;
use std::task::{Context, Poll};

impl<T> AppResponse<T>
where
  T: DeserializeOwned + 'static,
{
  pub async fn json_response_stream(
    resp: reqwest::Response,
  ) -> Result<impl Stream<Item = Result<T, AppResponseError>>, AppResponseError> {
    let status_code = resp.status();
    if !status_code.is_success() {
      let body = resp.text().await?;
      return Err(AppResponseError::new(ErrorCode::Internal, body));
    }

    let stream = resp.bytes_stream().map_err(AppResponseError::from);
    let stream = check_first_item_response_error(stream).await?;
    Ok(JsonStream::<T, _, AppResponseError>::new(stream))
  }

  pub async fn new_line_response_stream(
    resp: reqwest::Response,
  ) -> Result<impl Stream<Item = Result<String, AppResponseError>>, AppResponseError> {
    let status_code = resp.status();
    if !status_code.is_success() {
      let body = resp.text().await?;
      return Err(AppResponseError::new(ErrorCode::Internal, body));
    }

    let stream = resp.bytes_stream().map_err(AppResponseError::from);
    let stream = check_first_item_response_error(stream).await?;
    Ok(NewlineStream::new(stream))
  }

  pub async fn answer_response_stream(
    resp: reqwest::Response,
  ) -> Result<impl Stream<Item = Result<Bytes, AppResponseError>>, AppResponseError> {
    let status_code = resp.status();
    if !status_code.is_success() {
      let body = resp.text().await?;
      return Err(AppResponseError::new(ErrorCode::Internal, body));
    }

    let stream = resp.bytes_stream().map_err(AppResponseError::from);
    let stream = check_first_item_response_error(stream).await?;
    Ok(stream)
  }
}

/// AnswerStream is a custom stream handler designed to process incoming byte streams.
/// It alternates between handling text strings and JSON objects based on specific delimiters.
///
/// - When in `ReceivingStrings` state:
///   - It accumulates bytes into `string_buffer`.
///   - It splits the buffer at newline characters (`\n`) to extract complete text strings.
///   - If a null byte (`\0`) delimiter is encountered, it switches to `ReceivingJson` state.
///
/// - When in `ReceivingJson` state:
///   - It accumulates bytes into `json_buffer`.
///   - It attempts to deserialize the accumulated bytes into JSON objects.
///   - If deserialization is successful, it returns the JSON object and removes the processed bytes from the buffer.
///
/// This stream returns either text strings or deserialized JSON objects as `EitherStringOrChatMessage`,
/// and handles errors appropriately during the conversion and deserialization processes.
#[pin_project]
pub struct AnswerStream {
  #[pin]
  stream: Pin<Box<dyn Stream<Item = Result<Bytes, AppResponseError>> + Send>>,
  json_buffer: BytesMut,
  finished: bool,
}

impl AnswerStream {
  pub fn new<S>(stream: S) -> Self
  where
    S: Stream<Item = Result<Bytes, AppResponseError>> + Send + 'static,
  {
    AnswerStream {
      stream: Box::pin(stream),
      json_buffer: BytesMut::new(),
      finished: false,
    }
  }
}

impl Stream for AnswerStream {
  type Item = Result<StringOrMessage, AppResponseError>;

  fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
    let mut this = self.project();

    if *this.finished {
      return Poll::Ready(None);
    }

    loop {
      match ready!(this.stream.as_mut().poll_next(cx)) {
        Some(Ok(bytes)) => {
          // Each stream bytes if it comes with a newline character it will be a string. it's
          // guaranteed by the server
          const NEW_LINE: &[u8; 1] = b"\n";
          if bytes.ends_with(NEW_LINE) {
            let bytes = &bytes[..bytes.len() - NEW_LINE.len()];
            return match String::from_utf8(bytes.to_vec()) {
              Ok(value) => Poll::Ready(Some(Ok(StringOrMessage::Left(value)))),
              Err(err) => Poll::Ready(Some(Err(AppResponseError::from(err)))),
            };
          } else {
            this.json_buffer.extend_from_slice(&bytes);
            let slice_read = SliceRead::new(&this.json_buffer[..]);
            let deserializer = StreamDeserializer::new(slice_read);
            let mut iter = deserializer.into_iter();
            if let Some(result) = iter.next() {
              match result {
                Ok(value) => {
                  // Get the byte offset of the remaining unprocessed bytes
                  let remaining = iter.byte_offset();

                  // Advance the json_buffer to remove processed bytes
                  this.json_buffer.advance(remaining);
                  return Poll::Ready(Some(Ok(StringOrMessage::Right(value))));
                },
                Err(err) => {
                  if err.is_eof() {
                    continue;
                  } else {
                    return Poll::Ready(Some(Err(AppResponseError::from(err))));
                  }
                },
              }
            }
          }
        },
        Some(Err(err)) => return Poll::Ready(Some(Err(err))),
        None => {
          return Poll::Ready(None);
        },
      }
    }
  }
}

async fn check_first_item_response_error(
  stream: impl Stream<Item = Result<Bytes, AppResponseError>> + Unpin,
) -> Result<impl Stream<Item = Result<Bytes, AppResponseError>>, AppResponseError> {
  let mut stream = stream.peekable();
  if let Some(first_item) = Pin::new(&mut stream).peek().await {
    let first_item = first_item.as_ref().map_err(|e| e.clone())?;
    if let Ok(app_err) = serde_json::from_slice::<AppResponseError>(first_item) {
      if app_err.code != ErrorCode::Ok {
        return Err(app_err);
      }
    };
  }
  Ok(stream)
}