//! Harness-internal async bash task runner for `get_loose_ends`-compatible
//! background execution. An MCP tool call writes a task request file to
//! `harness_dir()/bash-tasks/<id>.json`; this background loop picks it up,
//! runs `sh -c <cmd>` with a timeout, writes stdout/stderr to sibling files,
//! and fires a `Wake` via the broker socket on completion. The agent's next
//! turn finds the result via `bash_status(<id>)`.
//!
//! Files under `harness_dir()/bash-tasks/`:
//! - `<id>.json`  — task metadata + status (pending → running → done)
//! - `<id>.out`   — captured stdout (appended while running)
//! - `<id>.err`   — captured stderr (appended while running)
//!
//! Tasks with status `running` on harness boot are marked `interrupted`
//! (the process died with the previous harness). Best-effort wake is still
//! sent so the agent is not silently blocked waiting forever.
//!
//! The runner kills the child process on timeout — `tokio::process::Child::drop()`
//! does not kill children, so we explicitly call `child.kill().await` before
//! collecting the copy tasks.

use std::collections::HashSet;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use std::time::Duration;

use anyhow::Result;
use serde::{Deserialize, Serialize};
use tokio::io::AsyncWriteExt;

const POLL_INTERVAL: Duration = Duration::from_millis(200);
/// Soft cap on stdout/stderr captured in the done JSON summary.
/// Full output always lives in the .out/.err files.
const SUMMARY_BYTES: usize = 4096;
/// Default timeout for tasks that don't specify one.
pub const DEFAULT_TIMEOUT_SECS: u64 = 180;

static TASK_SEQ: AtomicU64 = AtomicU64::new(0);

/// Generate a task ID: `<timestamp_hex><seq_hex>` — unique within a
/// harness session; collision chance across sessions negligible for our
/// volume.
#[must_use]
pub fn new_task_id() -> String {
    use std::time::{SystemTime, UNIX_EPOCH};
    let t = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_millis();
    let seq = TASK_SEQ.fetch_add(1, Ordering::Relaxed);
    format!("{t:013x}{seq:04x}")
}

/// Base directory for task files. Uses `HYPERHIVE_HARNESS_DIR` if set
/// (injected by hive-c0re meta flake after the harness/state split);
/// falls back to a sibling of `state_dir()` for pre-split deployments.
fn tasks_dir() -> PathBuf {
    let base = if let Some(p) = std::env::var_os("HYPERHIVE_HARNESS_DIR") {
        PathBuf::from(p)
    } else {
        // Pre-split fallback: derive harness/ as a sibling of state/.
        let state = crate::paths::state_dir();
        state.parent().map(|p| p.join("harness")).unwrap_or(state)
    };
    base.join("bash-tasks")
}

fn task_json(id: &str) -> PathBuf {
    tasks_dir().join(format!("{id}.json"))
}

fn task_out(id: &str) -> PathBuf {
    tasks_dir().join(format!("{id}.out"))
}

fn task_err(id: &str) -> PathBuf {
    tasks_dir().join(format!("{id}.err"))
}

// ---------------------------------------------------------------------------
// Wire types (shared between MCP tool writers and runner readers)
// ---------------------------------------------------------------------------

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "snake_case")]
pub enum TaskStatus {
    Pending,
    Running,
    Done,
    TimedOut,
    /// Harness was restarted while the task was running; process is gone.
    Interrupted,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TaskFile {
    pub id: String,
    pub cmd: String,
    pub timeout_secs: u64,
    pub status: TaskStatus,
    pub created_at: i64,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub started_at: Option<i64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub completed_at: Option<i64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub exit_code: Option<i32>,
    /// Last `SUMMARY_BYTES` of stdout (full output in `<id>.out`).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub stdout_tail: Option<String>,
    /// Last `SUMMARY_BYTES` of stderr (full output in `<id>.err`).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub stderr_tail: Option<String>,
}

impl TaskFile {
    #[must_use]
    pub fn new(id: String, cmd: String, timeout_secs: u64) -> Self {
        Self {
            id,
            cmd,
            timeout_secs,
            status: TaskStatus::Pending,
            created_at: crate::serve_common::now_unix(),
            started_at: None,
            completed_at: None,
            exit_code: None,
            stdout_tail: None,
            stderr_tail: None,
        }
    }
}

/// Write a task file atomically (tmp + rename).
fn write_task(task: &TaskFile) -> std::io::Result<()> {
    let json = serde_json::to_string_pretty(task)
        .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
    let dest = task_json(&task.id);
    let tmp = dest.with_extension("json.tmp");
    std::fs::write(&tmp, json)?;
    std::fs::rename(&tmp, &dest)
}

/// Read a task file. Returns `None` if the file doesn't exist or is
/// unparseable.
#[must_use]
pub fn read_task(id: &str) -> Option<TaskFile> {
    let s = std::fs::read_to_string(task_json(id)).ok()?;
    serde_json::from_str(&s).ok()
}

// ---------------------------------------------------------------------------
// Public API used by MCP tools
// ---------------------------------------------------------------------------

/// Return all tasks in `Pending` or `Running` state. Used by the
/// `get_loose_ends` tool to surface active background work alongside
/// broker-side items (questions, reminders). Silently skips unreadable
/// or unparseable files.
#[must_use]
pub fn active_tasks() -> Vec<TaskFile> {
    let Ok(rd) = std::fs::read_dir(tasks_dir()) else {
        return Vec::new();
    };
    let mut out = Vec::new();
    for entry in rd.flatten() {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }
        let Some(id) = path.file_stem().and_then(|s| s.to_str()).map(str::to_owned) else {
            continue;
        };
        let Some(task) = read_task(&id) else { continue };
        if matches!(task.status, TaskStatus::Pending | TaskStatus::Running) {
            out.push(task);
        }
    }
    out
}

/// Create a new pending task and write it to disk. Returns the task ID
/// the MCP tool should return to claude. The runner will pick it up
/// within the next poll interval (~200ms).
///
/// # Errors
///
/// Returns an error if the tasks directory cannot be created or the task
/// file cannot be written.
pub fn submit_task(cmd: String, timeout_secs: Option<u64>) -> Result<String> {
    std::fs::create_dir_all(tasks_dir())?;
    let id = new_task_id();
    let task = TaskFile::new(
        id.clone(),
        cmd,
        timeout_secs.unwrap_or(DEFAULT_TIMEOUT_SECS),
    );
    write_task(&task)?;
    Ok(id)
}

// ---------------------------------------------------------------------------
// Runner background loop
// ---------------------------------------------------------------------------

/// Spawn the background runner loop as a detached tokio task. `socket` is
/// the path to the per-agent broker socket, used to deliver the completion
/// `Wake`. Call once at harness startup from `serve_main`.
pub fn spawn(socket: PathBuf) {
    tokio::spawn(async move {
        run_loop(socket).await;
    });
}

async fn run_loop(socket: PathBuf) {
    if let Err(e) = std::fs::create_dir_all(tasks_dir()) {
        tracing::warn!(error = ?e, "bash_runner: create tasks dir failed");
    }
    // Mark any tasks left in "running" state from a previous harness
    // session as interrupted so agents waiting on them get unblocked.
    mark_interrupted(&socket).await;

    // In-memory set of task IDs we have already claimed this session
    // so we don't re-spawn on each poll iteration.
    let claimed: Arc<Mutex<HashSet<String>>> = Arc::new(Mutex::new(HashSet::new()));

    loop {
        poll_once(&socket, &claimed).await;
        tokio::time::sleep(POLL_INTERVAL).await;
    }
}

/// On boot, find any task files in `running` state and flip them to
/// `interrupted`, then fire a wake so the agent unblocks.
async fn mark_interrupted(socket: &Path) {
    let Ok(rd) = std::fs::read_dir(tasks_dir()) else {
        return;
    };
    for entry in rd.flatten() {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }
        let Some(id) = path.file_stem().and_then(|s| s.to_str()).map(str::to_owned) else {
            continue;
        };
        let Some(mut task) = read_task(&id) else {
            continue;
        };
        if task.status != TaskStatus::Running {
            continue;
        }
        tracing::warn!(id = %id, "bash_runner: marking interrupted task");
        task.status = TaskStatus::Interrupted;
        task.completed_at = Some(crate::serve_common::now_unix());
        if let Err(e) = write_task(&task) {
            tracing::warn!(id = %id, error = ?e, "bash_runner: write interrupted task failed");
        }
        send_wake(socket, &id, "interrupted (harness restarted)", None).await;
    }
}

async fn poll_once(socket: &Path, claimed: &Arc<Mutex<HashSet<String>>>) {
    let Ok(rd) = std::fs::read_dir(tasks_dir()) else {
        return;
    };
    for entry in rd.flatten() {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }
        let Some(id) = path.file_stem().and_then(|s| s.to_str()).map(str::to_owned) else {
            continue;
        };
        {
            let guard = claimed.lock().unwrap();
            if guard.contains(&id) {
                continue;
            }
        }
        let Some(task) = read_task(&id) else { continue };
        if task.status != TaskStatus::Pending {
            continue;
        }
        // Claim before spawning to avoid double-spawn across poll iterations.
        claimed.lock().unwrap().insert(id.clone());
        let socket = socket.to_path_buf();
        let claimed = claimed.clone();
        tokio::spawn(async move {
            run_task(task, &socket).await;
            // Remove from claimed so a resubmitted ID (rare) could be
            // picked up again. In practice each ID is unique.
            claimed.lock().unwrap().remove(&id);
        });
    }
}

// ---------------------------------------------------------------------------
// Task execution
// ---------------------------------------------------------------------------

async fn run_task(mut task: TaskFile, socket: &Path) {
    let id = task.id.clone();
    tracing::info!(id = %id, cmd = %task.cmd, "bash_runner: starting task");

    task.status = TaskStatus::Running;
    task.started_at = Some(crate::serve_common::now_unix());
    if let Err(e) = write_task(&task) {
        tracing::warn!(id = %id, error = ?e, "bash_runner: write running state failed");
    }

    let out_path = task_out(&id);
    let err_path = task_err(&id);
    let timeout = Duration::from_secs(task.timeout_secs);

    let (timed_out, exit_code) = match exec_cmd(&task.cmd, &out_path, &err_path, timeout).await {
        Ok((code, false)) => (false, Some(code)),
        Ok((_, true)) => {
            tracing::warn!(id = %id, "bash_runner: task timed out");
            (true, None)
        }
        Err(e) => {
            tracing::warn!(id = %id, error = ?e, "bash_runner: exec error");
            (false, None)
        }
    };

    let stdout_tail = tail_file(&out_path, SUMMARY_BYTES);
    let stderr_tail = tail_file(&err_path, SUMMARY_BYTES);

    task.status = if timed_out {
        TaskStatus::TimedOut
    } else {
        TaskStatus::Done
    };
    task.completed_at = Some(crate::serve_common::now_unix());
    task.exit_code = exit_code;
    task.stdout_tail = stdout_tail.clone().filter(|s| !s.is_empty());
    task.stderr_tail = stderr_tail.clone().filter(|s| !s.is_empty());

    if let Err(e) = write_task(&task) {
        tracing::warn!(id = %id, error = ?e, "bash_runner: write done state failed");
    }

    let summary = if timed_out {
        format!("timed out after {}s", task.timeout_secs)
    } else {
        format!("exit={}", exit_code.unwrap_or(-1))
    };
    let output_snippet = stdout_tail.as_deref().unwrap_or("").trim();
    let err_snippet = stderr_tail.as_deref().unwrap_or("").trim();
    send_wake(socket, &id, &summary, Some((output_snippet, err_snippet))).await;
}

/// Run `sh -c cmd`, streaming output to files. Returns `(exit_code, timed_out)`.
/// On timeout the child process is explicitly killed before returning.
async fn exec_cmd(
    cmd: &str,
    out_path: &Path,
    err_path: &Path,
    timeout: Duration,
) -> Result<(i32, bool)> {
    use tokio::process::Command;
    let mut child = Command::new("sh")
        .arg("-c")
        .arg(cmd)
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped())
        .spawn()?;

    let stdout = child.stdout.take().expect("stdout piped");
    let stderr = child.stderr.take().expect("stderr piped");

    let out_path = out_path.to_path_buf();
    let err_path = err_path.to_path_buf();

    // Stream stdout and stderr to files concurrently.
    let copy_stdout = tokio::spawn(copy_stream_to_file(
        tokio::io::BufReader::new(stdout),
        out_path,
    ));
    let copy_stderr = tokio::spawn(copy_stream_to_file(
        tokio::io::BufReader::new(stderr),
        err_path,
    ));

    match tokio::time::timeout(timeout, child.wait()).await {
        Ok(Ok(status)) => {
            let _ = copy_stdout.await;
            let _ = copy_stderr.await;
            Ok((status.code().unwrap_or(-1), false))
        }
        Ok(Err(e)) => Err(e.into()),
        Err(_elapsed) => {
            // Kill the child so it doesn't linger after timeout.
            let _ = child.kill().await;
            let _ = child.wait().await; // reap zombie
            let _ = copy_stdout.await;
            let _ = copy_stderr.await;
            Ok((-1, true))
        }
    }
}

async fn copy_stream_to_file<R>(mut reader: R, path: PathBuf)
where
    R: tokio::io::AsyncRead + Unpin,
{
    match tokio::fs::File::create(&path).await {
        Ok(mut f) => {
            let _ = tokio::io::copy(&mut reader, &mut f).await;
            let _ = f.flush().await;
        }
        Err(e) => {
            tracing::warn!(path = %path.display(), error = ?e, "bash_runner: open output file failed")
        }
    }
}

/// Read the last `max_bytes` of a file as a UTF-8 string.
fn tail_file(path: &Path, max_bytes: usize) -> Option<String> {
    let data = std::fs::read(path).ok()?;
    let slice = if data.len() > max_bytes {
        &data[data.len() - max_bytes..]
    } else {
        &data
    };
    Some(String::from_utf8_lossy(slice).into_owned())
}

// ---------------------------------------------------------------------------
// Wake delivery
// ---------------------------------------------------------------------------

async fn send_wake(socket: &Path, id: &str, summary: &str, output: Option<(&str, &str)>) {
    let mut body = format!("bash task `{id}` finished: {summary}");
    if let Some((stdout, stderr)) = output {
        if !stdout.is_empty() {
            body.push_str("\n\nstdout:\n```\n");
            body.push_str(stdout);
            body.push_str("\n```");
        }
        if !stderr.is_empty() {
            body.push_str("\n\nstderr:\n```\n");
            body.push_str(stderr);
            body.push_str("\n```");
        }
    }
    let req = hive_sh4re::AgentRequest::Wake {
        from: format!("bash-task-{id}"),
        body,
    };
    match crate::client::request::<_, hive_sh4re::AgentResponse>(socket, &req).await {
        Ok(_) => tracing::info!(id = %id, "bash_runner: wake delivered"),
        Err(e) => tracing::warn!(id = %id, error = ?e, "bash_runner: wake delivery failed"),
    }
}