//! Shared subprocess helpers: a TTY-detached async runner with a wall-clock
//! timeout and concurrent pipe draining, plus the hermetic `git` binary path.

use std::env;
use std::ffi::OsString;
use std::path::PathBuf;
use std::process::Output;
use std::process::Stdio;
use std::time::Duration;
use std::time::Instant;

use tokio::io::AsyncRead;
use tokio::io::AsyncReadExt;
use tokio::process::Child;
use tokio::process::Command;
use tokio::sync::mpsc;
use tracing::debug;
use tracing::warn;
use xai_tty_utils::ProcessGroup;

const MAX_CAPTURE_BYTES: usize = 1024 * 1024;

const READ_CHUNK_SIZE: usize = 8192;

/// Quiet lull ending the post-exit drain (backgrounded grandchildren may hold
/// the pipes open).
const POST_EXIT_QUIET: Duration = Duration::from_millis(250);

/// Hard cap on the whole post-exit drain (`POST_EXIT_QUIET` is per-chunk, so a
/// grandchild that keeps writing could otherwise reach the deadline).
const POST_EXIT_BUDGET: Duration = Duration::from_secs(2);

/// Grace between SIGTERM and SIGKILL when tearing down a timed-out process
/// group, so a signal-aware child can exit cleanly before it is force-killed.
const TERM_GRACE: Duration = Duration::from_millis(500);

/// Resolve the `git` binary: `GIT_BIN_PATH` (Bazel's hermetic-git data dep;
/// runfiles-relative, so resolved against the cwd) or bare `git` on `PATH`.
pub(crate) fn git_bin() -> OsString {
    let Some(raw) = env::var_os("GIT_BIN_PATH") else {
        return OsString::from("git");
    };
    let path = PathBuf::from(&raw);
    if path.is_relative() {
        match env::current_dir() {
            Ok(cwd) => cwd.join(&path).into_os_string(),
            Err(_) => raw,
        }
    } else {
        raw
    }
}

/// A `sh -c <script>` command: the portable shell escape hatch shared by the
/// identity and auth providers.
pub(crate) fn sh_c(script: &str) -> Command {
    let mut cmd = Command::new("sh");
    cmd.args(["-c", script]);
    cmd
}

/// Whether the command text may appear in spawn-failure/timeout logs.
/// `Redacted` (the safe default) keeps it out for commands whose text may
/// embed secrets; `Shown` includes it for diagnostics.
#[derive(Clone, Copy)]
pub(crate) enum CommandLog<'a> {
    Redacted,
    Shown(&'a str),
}

impl std::fmt::Display for CommandLog<'_> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match *self {
            Self::Shown(cmd) => f.write_str(cmd),
            Self::Redacted => f.write_str("<redacted>"),
        }
    }
}

pub(crate) struct RunOptions<'a> {
    pub label: &'a str,
    pub command_log: CommandLog<'a>,
}

/// Why [`run_detached_with_timeout`] produced no `Output`. A nonzero exit is
/// not one of these; it comes back as `Ok`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum RunError {
    SpawnFailed,
    TimedOut,
    WaitFailed,
}

/// Run `cmd` detached from the TTY with a wall-clock `timeout`, killing the
/// whole process group on timeout and capping capture per stream. A nonzero
/// exit comes back as `Ok`; [`RunError`] covers the no-output cases.
pub(crate) async fn run_detached_with_timeout(
    mut cmd: Command,
    timeout: Duration,
    opts: RunOptions<'_>,
) -> Result<Output, RunError> {
    let RunOptions { label, command_log } = opts;

    cmd.stdin(Stdio::null())
        .stdout(Stdio::piped())
        // Pipe stderr; inherit would corrupt the TUI alternate screen.
        .stderr(Stdio::piped())
        .kill_on_drop(true);
    xai_grok_tools::util::detach_command(&mut cmd);
    cmd.envs(xai_grok_tools::util::pager_env());

    let mut child = match cmd.spawn() {
        Ok(child) => child,
        Err(e) => {
            warn!(error = %e, label, cmd = %command_log, "failed to start the command");
            return Err(RunError::SpawnFailed);
        }
    };

    // Enroll the child's process group so a timeout kill reaches grandchildren;
    // on failure only the direct child is killed.
    let group = ProcessGroup::new()
        .and_then(|mut group| group.attach(&child).map(|()| group))
        .inspect_err(|e| {
            debug!(error = %e, label, "process-group enrollment failed; a timeout kill covers the direct child only");
        })
        .ok();

    let stdout_rx = child.stdout.take().map(spawn_pipe_reader);
    let stderr_rx = child.stderr.take().map(spawn_pipe_reader);

    let status = match tokio::time::timeout(timeout, child.wait()).await {
        Ok(Ok(status)) => status,
        Ok(Err(e)) => {
            warn!(error = %e, label, "error while waiting for the command");
            terminate_child(&mut child, group.as_ref()).await;
            return Err(RunError::WaitFailed);
        }
        Err(_elapsed) => {
            warn!(
                label,
                cmd = %command_log,
                timeout_secs = timeout.as_secs(),
                "command timed out; terminating"
            );
            terminate_child(&mut child, group.as_ref()).await;
            return Err(RunError::TimedOut);
        }
    };

    // Both streams drain concurrently under one budget measured fresh from the
    // child's exit, so a near-deadline exit still captures its buffered output
    // in full.
    let drain_deadline = Instant::now() + POST_EXIT_BUDGET;
    let (stdout, stderr) = tokio::join!(
        drain_reader(stdout_rx, drain_deadline),
        drain_reader(stderr_rx, drain_deadline),
    );
    if !status.success() {
        // Debug, not warn: some callers run secret-bearing commands (auth
        // tokens, resolved identities), so stderr stays out of routine logs;
        // callers that need louder reporting inspect the returned stderr.
        debug!(status = %status, label, "command exited with a nonzero status");
    }
    Ok(Output {
        status,
        stdout,
        stderr,
    })
}

/// Tear down a timed-out or errored run: SIGTERM the process group, wait
/// [`TERM_GRACE`], then SIGKILL survivors. Always reaps the direct child too,
/// so an absent group signal can't leave it unwaited.
async fn terminate_child(child: &mut Child, group: Option<&ProcessGroup>) {
    if let Some(group) = group {
        let _ = group.terminate();
        let _ = tokio::time::timeout(TERM_GRACE, child.wait()).await;
        let _ = group.kill();
    }
    let _ = child.start_kill();
    // Bounded reap: a wedged (uninterruptible) child must not park the runner;
    // `kill_on_drop` reaps it later if this wait gives up.
    let _ = tokio::time::timeout(TERM_GRACE, child.wait()).await;
}

/// Stream a child pipe over an unbounded channel, capped at
/// [`MAX_CAPTURE_BYTES`]; a closed receiver (the drain gave up) stops the
/// reader so it never parks in `read()` forever.
fn spawn_pipe_reader<R>(mut pipe: R) -> mpsc::UnboundedReceiver<Vec<u8>>
where
    R: AsyncRead + Unpin + Send + 'static,
{
    let (tx, rx) = mpsc::unbounded_channel();
    tokio::spawn(async move {
        let mut sent = 0usize;
        let mut chunk = [0u8; READ_CHUNK_SIZE];
        loop {
            let n = tokio::select! {
                biased;
                () = tx.closed() => break,
                result = pipe.read(&mut chunk) => match result {
                    Ok(0) | Err(_) => break,
                    Ok(n) => n,
                },
            };
            let keep = n.min(MAX_CAPTURE_BYTES.saturating_sub(sent));
            if keep > 0 {
                if tx.send(chunk[..keep].to_vec()).is_err() {
                    break;
                }
                sent += keep;
            }
            // Past the cap: keep reading to drain the pipe (never block the child),
            // discarding the excess.
        }
    });
    rx
}

async fn drain_reader(
    rx: Option<mpsc::UnboundedReceiver<Vec<u8>>>,
    drain_deadline: Instant,
) -> Vec<u8> {
    let Some(mut rx) = rx else {
        return Vec::new();
    };
    let mut buf = Vec::new();
    loop {
        let Some(remaining) = drain_deadline.checked_duration_since(Instant::now()) else {
            break;
        };
        let wait = POST_EXIT_QUIET.min(remaining);
        match tokio::time::timeout(wait, rx.recv()).await {
            Ok(Some(chunk)) => buf.extend_from_slice(&chunk),
            // A closed channel is EOF; an elapsed wait is a quiet lull (a
            // grandchild may still hold the pipe).
            Ok(None) | Err(_) => break,
        }
    }
    buf
}

#[cfg(test)]
mod tests {
    use super::*;

    fn sh(script: &str) -> Command {
        sh_c(script)
    }

    fn opts(label: &str) -> RunOptions<'_> {
        RunOptions {
            label,
            command_log: CommandLog::Redacted,
        }
    }

    const TIMEOUT: Duration = Duration::from_secs(10);

    #[tokio::test]
    async fn large_stderr_is_streamed_and_capped() {
        let out = run_detached_with_timeout(
            sh("yes 0123456789abcdef | head -c 2097152 >&2; echo done"),
            TIMEOUT,
            opts("test large stderr"),
        )
        .await
        .expect("must complete without hitting the timeout");
        assert!(out.status.success());
        assert_eq!(String::from_utf8_lossy(&out.stdout).trim(), "done");
        assert_eq!(out.stderr.len(), MAX_CAPTURE_BYTES);
    }

    #[tokio::test]
    async fn backgrounded_grandchild_does_not_block_the_drain() {
        let start = Instant::now();
        let out = run_detached_with_timeout(
            sh("sleep 5 & echo hi"),
            TIMEOUT,
            opts("test grandchild drain"),
        )
        .await
        .expect("must return promptly, not at the grandchild's exit");
        assert!(out.status.success());
        assert_eq!(String::from_utf8_lossy(&out.stdout).trim(), "hi");
        assert!(
            start.elapsed() < Duration::from_secs(3),
            "drain must not wait for the grandchild (took {:?})",
            start.elapsed()
        );
    }

    #[tokio::test]
    async fn nonzero_exit_returns_output_to_caller() {
        let out = run_detached_with_timeout(
            sh("echo partial; echo diagnostics >&2; exit 3"),
            TIMEOUT,
            opts("test nonzero"),
        )
        .await
        .expect("nonzero exit is the caller's call, not a runner failure");
        assert_eq!(out.status.code(), Some(3));
        assert_eq!(String::from_utf8_lossy(&out.stdout).trim(), "partial");
        assert_eq!(String::from_utf8_lossy(&out.stderr).trim(), "diagnostics");
    }

    #[tokio::test]
    async fn timeout_with_grandchild_reports_timeout_promptly() {
        let start = Instant::now();
        let out = run_detached_with_timeout(
            sh("sleep 30 & sleep 30"),
            Duration::from_secs(1),
            opts("test group kill"),
        )
        .await;
        assert!(matches!(out, Err(RunError::TimedOut)));
        assert!(
            start.elapsed() < Duration::from_secs(5),
            "group kill must not wait for the grandchild (took {:?})",
            start.elapsed()
        );
    }

    #[tokio::test]
    async fn timeout_escalates_past_a_sigterm_trap() {
        let start = Instant::now();
        let out = run_detached_with_timeout(
            sh("trap '' TERM; while :; do sleep 0.2; done"),
            Duration::from_secs(1),
            opts("test sigterm trap"),
        )
        .await;
        assert!(matches!(out, Err(RunError::TimedOut)));
        assert!(
            start.elapsed() < Duration::from_secs(5),
            "escalation must bound teardown of a SIGTERM-ignoring child (took {:?})",
            start.elapsed()
        );
    }

    #[tokio::test]
    async fn spawn_failure_reports_spawn_error() {
        let cmd = Command::new("/nonexistent/grok-test-binary");
        let out = run_detached_with_timeout(cmd, TIMEOUT, opts("test spawn failure")).await;
        assert!(matches!(out, Err(RunError::SpawnFailed)));
    }

    #[tokio::test]
    async fn post_exit_budget_is_shared_across_streams() {
        let start = Instant::now();
        let out = run_detached_with_timeout(
            sh("(i=0; while [ $i -lt 100 ]; do echo out; echo err >&2; sleep 0.1; i=$((i+1)); done) & echo hi"),
            TIMEOUT,
            opts("test shared drain budget"),
        )
        .await
        .expect("must return at the shared budget, not the timeout");
        assert!(out.status.success());
        assert!(String::from_utf8_lossy(&out.stdout).contains("hi"));
        assert!(
            start.elapsed() < POST_EXIT_BUDGET + Duration::from_millis(1500),
            "drain must be bounded by ONE shared budget (took {:?})",
            start.elapsed()
        );
    }
}