//! Process management: detached background start, PID bookkeeping, stop
//! with a graceful signal followed by a forceful kill after a timeout.

use crate::app::App;
use anyhow::{bail, Context, Result};
use std::collections::BTreeMap;
use std::path::{Path, PathBuf};
use std::process::{Command, Stdio};
use std::time::{Duration, Instant};

/// Log file for a background agent.
pub fn agent_log_path(app: &App, agent_name: &str) -> PathBuf {
    app.log.log_dir().join(format!("{agent_name}.log"))
}

/// Is a process with this PID alive?
pub fn is_running(pid: u32) -> bool {
    #[cfg(windows)]
    {
        let out = Command::new("tasklist")
            .args(["/FI", &format!("PID eq {pid}"), "/NH"])
            .output();
        match out {
            Ok(o) => String::from_utf8_lossy(&o.stdout)
                .split_whitespace()
                .any(|w| w == pid.to_string()),
            Err(_) => false,
        }
    }
    #[cfg(not(windows))]
    {
        Command::new("kill")
            .args(["-0", &pid.to_string()])
            .status()
            .map(|s| s.success())
            .unwrap_or(false)
    }
}

/// Send SIGTERM/SIGKILL (or taskkill / taskkill /F on Windows).
fn signal(pid: u32, force: bool) -> bool {
    #[cfg(windows)]
    {
        let mut cmd = Command::new("taskkill");
        cmd.arg("/PID").arg(pid.to_string());
        if force {
            cmd.arg("/T").arg("/F");
        }
        cmd.status().map(|s| s.success()).unwrap_or(false)
    }
    #[cfg(not(windows))]
    {
        let sig = if force { "-KILL" } else { "-TERM" };
        Command::new("kill")
            .arg(sig)
            .arg(pid.to_string())
            .status()
            .map(|s| s.success())
            .unwrap_or(false)
    }
}

/// Stop a process: TERM first, then KILL after the timeout. Returns whether
/// the process was running when the call started.
pub fn stop_pid(pid: u32, force: bool, timeout_secs: u64) -> bool {
    if !is_running(pid) {
        return false;
    }
    if force {
        signal(pid, true);
    } else {
        signal(pid, false);
        let deadline = Instant::now() + Duration::from_secs(timeout_secs);
        while Instant::now() < deadline {
            if !is_running(pid) {
                return true;
            }
            std::thread::sleep(Duration::from_millis(200));
        }
        if is_running(pid) {
            signal(pid, true);
        }
    }
    for _ in 0..50 {
        if !is_running(pid) {
            return true;
        }
        std::thread::sleep(Duration::from_millis(100));
    }
    !is_running(pid)
}

/// Kill a process and its whole tree (process group on unix, taskkill /T on
/// Windows). Used by the plugin runner and the lab benchmark to stop
/// runaway scripts and timed-out task runs.
pub fn kill_tree(pid: u32) {
    #[cfg(unix)]
    {
        use std::os::unix::process::CommandExt;
        let _ = Command::new("kill")
            .arg("-KILL")
            .arg(format!("-{pid}")) // negative pid = the process group
            .status();
        let _ = Command::new("kill").arg("-KILL").arg(pid.to_string()).status();
    }
    #[cfg(windows)]
    {
        let _ = Command::new("taskkill")
            .args(["/PID", &pid.to_string(), "/T", "/F"])
            .status();
    }
}

/// Start a program detached: stdout/stderr are redirected to the agent log
/// file. Returns the PID. Fails when the process exits immediately.
pub fn spawn_background(
    app: &App,
    agent_name: &str,
    program: &Path,
    args: &[String],
    env: &BTreeMap<String, String>,
    cwd: Option<&Path>,
) -> Result<u32> {
    let log = agent_log_path(app, agent_name);
    if app.dry_run() {
        app.log.dry(format!(
            "would start {} (detached, log: {})",
            program.display(),
            log.display()
        ));
        return Ok(0);
    }
    if let Some(parent) = log.parent() {
        std::fs::create_dir_all(parent)?;
    }
    let file = std::fs::File::create(&log)
        .with_context(|| format!("cannot create log file {}", log.display()))?;
    let (prog, prefix) = crate::runner::resolve_program(&program.display().to_string());
    let mut full_args = prefix;
    full_args.extend(args.iter().cloned());
    let mut cmd = Command::new(&prog);
    cmd.args(&full_args)
        .envs(env)
        .stdout(Stdio::from(file.try_clone()?))
        .stderr(Stdio::from(file));
    if let Some(dir) = cwd {
        cmd.current_dir(dir);
    }
    #[cfg(unix)]
    {
        use std::os::unix::process::CommandExt;
        cmd.process_group(0);
    }
    #[cfg(windows)]
    {
        use std::os::windows::process::CommandExt;
        const CREATE_NEW_PROCESS_GROUP: u32 = 0x0000_0200;
        cmd.creation_flags(CREATE_NEW_PROCESS_GROUP);
    }
    app.log
        .cmd(&format!("{} {}", program.display(), args.join(" ")));
    let mut child = cmd
        .spawn()
        .with_context(|| format!("failed to start {}", program.display()))?;
    let pid = child.id();
    // Give the process a moment: some agents crash at startup.
    std::thread::sleep(Duration::from_millis(400));
    match child.try_wait() {
        Ok(Some(status)) => {
            let tail = last_lines(&log, 8);
            bail!(
                "agent '{agent_name}' exited immediately after start (status {status}); log: {}
{}",
                log.display(),
                tail
            );
        }
        Ok(None) => {}
        Err(_) => {}
    }
    Ok(pid)
}

/// Tail of a text file (last n lines).
pub fn last_lines(path: &Path, n: usize) -> String {
    let Ok(text) = std::fs::read_to_string(path) else {
        return String::new();
    };
    let lines: Vec<&str> = text.lines().collect();
    let start = lines.len().saturating_sub(n);
    lines[start..].join("
")
}

/// Best-effort desktop notification once an agent has started.
pub fn desktop_notify(title: &str, body: &str) {
    #[cfg(target_os = "linux")]
    {
        let _ = Command::new("notify-send")
            .args(["-a", "agent-manager", title, body])
            .spawn();
    }
    #[cfg(target_os = "macos")]
    {
        let _ = Command::new("osascript")
            .args([
                "-e",
                &format!("display notification \"{body}\" with title \"{title}\""),
            ])
            .spawn();
    }
    #[cfg(windows)]
    {
        // No built-in non-blocking toast without extra tooling; log instead.
        let _ = (title, body);
    }
}

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

    fn sleep_cmd() -> (&'static str, Vec<String>) {
        if cfg!(windows) {
            ("ping", vec!["-n".to_string(), "30".to_string(), "127.0.0.1".to_string()])
        } else {
            ("sleep", vec!["30".to_string()])
        }
    }

    #[test]
    fn pid_lifecycle() {
        let (prog, args) = sleep_cmd();
        let mut child = Command::new(prog).args(&args).spawn().unwrap();
        let pid = child.id();
        assert!(is_running(pid));
        assert!(stop_pid(pid, true, 5));
        assert!(!is_running(pid));
        let _ = child.wait();
    }

    #[test]
    fn stop_non_running_is_false() {
        assert!(!stop_pid(u32::MAX - 1, true, 1));
    }
}