use std::process::Stdio;

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

use crate::bare::GitBare;
use crate::pb::PackfileChunk;

const MAX_PACK_OBJECTS_STDERR_BYTES: u64 = 64 * 1024;

impl GitBare {
    /// Pack objects using git-pack-objects --stdout.
    ///
    /// Unary request → server-streaming response.
    /// The returned stream yields `PackfileChunk` chunks as pack data is produced.
    pub async fn pack_objects(
        &self,
        request: crate::pb::PackObjectsRequest,
    ) -> Result<ReceiverStream<Result<PackfileChunk, tonic::Status>>, tonic::Status> {
        let bare_dir = self.bare_dir.clone();
        let bare_dir_str = bare_dir.to_string_lossy().into_owned();
        tracing::info!(
            repo = %bare_dir_str,
            "spawning git pack-objects subprocess"
        );

        let (tx, rx) = tokio::sync::mpsc::channel(8);

        tokio::spawn(async move {
            let opts = request.options.as_ref();
            let has_wants = opts.is_some_and(|o| !o.wants.is_empty());

            let mut args = vec![
                "--git-dir".to_string(),
                bare_dir_str,
                "pack-objects".to_string(),
                "--stdout".to_string(),
            ];

            // --all is mutually exclusive with explicit revision selection.
            if !has_wants {
                args.push("--all".into());
            } else {
                args.push("--revs".into());
            }

            if opts.is_some_and(|o| o.thin_pack) {
                args.push("--thin".into());
            }
            if opts.is_some_and(|o| !o.use_bitmaps) {
                args.push("--no-use-bitmaps".into());
            }
            if opts.is_some_and(|o| o.delta_base_offset) {
                args.push("--delta-base-offset".into());
            }
            let stdin_data = match generate_pack_input(&request) {
                Ok(data) => data,
                Err(err) => {
                    let _ = tx
                        .send(Err(tonic::Status::invalid_argument(err.to_string())))
                        .await;
                    return;
                }
            };

            let mut child = match Command::new("git")
                .args(&args)
                .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 pack-objects: {e}"
                        ))))
                        .await;
                    return;
                }
            };

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

            let stdin_task = async move {
                if let Some(mut stdin) = stdin.take() {
                    let _ = stdin.write_all(&stdin_data).await;
                }
            };

            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(PackfileChunk {
                                            data: buf[..n].to_vec(),
                                        }))
                                        .await
                                        .is_err()
                                    {
                                        break;
                                    }
                                }
                                Err(e) => {
                                    let _ = tx
                                        .send(Err(tonic::Status::internal(format!(
                                            "read error: {e}"
                                        ))))
                                        .await;
                                    break;
                                }
                            }
                        }
                    }
                }
            };

            let stderr_task = {
                let tx = tx.clone();
                async move {
                    if let Some(stderr) = stderr.take() {
                        let mut stderr = stderr.take(MAX_PACK_OBJECTS_STDERR_BYTES);
                        let mut s = String::new();
                        if stderr.read_to_string(&mut s).await.is_ok() && !s.is_empty() {
                            let _ = tx.send(Err(tonic::Status::internal(s))).await;
                        }
                    }
                }
            };

            tokio::join!(stdin_task, stdout_task, stderr_task);

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

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

fn generate_pack_input(
    req: &crate::pb::PackObjectsRequest,
) -> Result<Vec<u8>, crate::error::GitError> {
    let mut input = String::new();
    if let Some(opts) = req.options.as_ref() {
        for want in &opts.wants {
            crate::sanitize::validate_oid_hex(&want.hex)?;
            input.push_str(&format!("{}\n", want.hex));
        }
        for have in &opts.haves {
            crate::sanitize::validate_oid_hex(&have.hex)?;
            input.push_str(&format!("^{}\n", have.hex));
        }
    }
    Ok(input.into_bytes())
}