use std::process::Stdio;

use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio::process::Command;
use tokio_stream::StreamExt;
use tokio_stream::wrappers::ReceiverStream;

use crate::bare::GitBare;
use crate::pb::UploadPackResponse;

impl GitBare {
    /// Upload pack data using git-upload-pack with true concurrent streaming.
    ///
    /// Client-streaming input → server-streaming output.
    /// Stdin packets are forwarded to the child process as they arrive from the client,
    /// while stdout is concurrently read and streamed back via a channel.
    pub async fn upload_pack(
        &self,
        input: impl tokio_stream::Stream<Item = Result<crate::pb::UploadPackRequest, tonic::Status>>
        + Send
        + 'static,
    ) -> Result<ReceiverStream<Result<UploadPackResponse, tonic::Status>>, tonic::Status> {
        let bare_dir = self.bare_dir.to_string_lossy().into_owned();

        let (tx, rx) = tokio::sync::mpsc::channel(16);

        // Move input into the spawned task to make it 'static
        let stream = Box::pin(input);
        tokio::spawn(async move {
            let stream = stream;
            let mut child = match Command::new("git")
                .arg("--git-dir")
                .arg(&bare_dir)
                .arg("upload-pack")
                .arg(&bare_dir)
                .stdin(Stdio::piped())
                .stdout(Stdio::piped())
                .stderr(Stdio::piped())
                .spawn()
            {
                Ok(c) => c,
                Err(e) => {
                    let _ = tx
                        .send(Err(tonic::Status::internal(format!(
                            "failed to spawn git upload-pack: {e}"
                        ))))
                        .await;
                    return;
                }
            };

            let mut stdin = child.stdin.take();
            let mut stdout = child.stdout.take();
            let mut stderr = child.stderr.take();

            // Concurrent: write stdin packets, read stdout chunks, read stderr
            let stdin_task = {
                let mut stream = stream;
                async move {
                    if let Some(mut stdin) = stdin.take() {
                        while let Some(result) = stream.next().await {
                            match result {
                                Ok(req) => {
                                    if stdin.write_all(&req.packet).await.is_err() {
                                        break;
                                    }
                                    if req.done {
                                        break;
                                    }
                                }
                                Err(_) => break,
                            }
                        }
                        // Close stdin to signal end-of-input
                        drop(stdin);
                    }
                }
            };

            let stdout_task = {
                let tx = tx.clone();
                async move {
                    if let Some(mut stdout) = stdout.take() {
                        let mut buf = vec![0u8; 65536];
                        loop {
                            match stdout.read(&mut buf).await {
                                Ok(0) => break,
                                Ok(n) => {
                                    if tx
                                        .send(Ok(UploadPackResponse {
                                            packet: buf[..n].to_vec(),
                                            stderr: String::new(),
                                        }))
                                        .await
                                        .is_err()
                                    {
                                        break;
                                    }
                                }
                                Err(_) => break,
                            }
                        }
                    }
                }
            };

            let stderr_task = {
                let tx = tx.clone();
                async move {
                    if let Some(mut stderr) = stderr.take() {
                        let mut s = String::new();
                        if stderr.read_to_string(&mut s).await.is_ok() && !s.is_empty() {
                            let _ = tx
                                .send(Ok(UploadPackResponse {
                                    packet: Vec::new(),
                                    stderr: s,
                                }))
                                .await;
                        }
                    }
                }
            };

            // Run all three concurrently
            tokio::join!(stdin_task, stdout_task, stderr_task);

            // Wait for child exit
            match child.wait().await {
                Ok(status) if !status.success() => {
                    let _ = tx
                        .send(Err(tonic::Status::internal(
                            "git upload-pack exited with error",
                        )))
                        .await;
                }
                Err(e) => {
                    let _ = tx
                        .send(Err(tonic::Status::internal(format!("wait error: {e}"))))
                        .await;
                }
                _ => {}
            }
        });

        Ok(ReceiverStream::new(rx))
    }
}