use std::fs::{self, File, OpenOptions};
use std::io::{ErrorKind, Write};
#[cfg(unix)]
use std::os::unix::net::UnixStream as StdUnixStream;
use std::path::{Path, PathBuf};
use std::process::{Command, Stdio};
use std::time::{Duration, Instant};

use crate::atuin_client::{
    database::Sqlite, history::History, record::sqlite_store::SqliteStore, settings::Settings,
};
use crate::atuin_daemon::DaemonEvent;
use crate::atuin_daemon::client::{
    ControlClient, DaemonClientErrorKind, HistoryClient, classify_error,
};
use clap::Subcommand;
#[cfg(unix)]
use daemonize::Daemonize;
use eyre::{Result, WrapErr, bail, eyre};
use fs4::fs_std::FileExt;
use tokio::time::sleep;

#[derive(clap::Args, Debug)]
pub struct Cmd {
    /// Internal flag for daemonization
    #[arg(long, hide = true)]
    daemonize: bool,

    /// Also write daemon logs to the console (useful for debugging)
    #[arg(long)]
    show_logs: bool,

    #[command(subcommand)]
    subcmd: Option<SubCmd>,
}

#[derive(Subcommand, Debug)]
#[command(infer_subcommands = true)]
pub enum SubCmd {
    /// Start the daemon server
    Start {
        #[arg(long, hide = true)]
        daemonize: bool,

        /// Also write daemon logs to the console (useful for debugging)
        #[arg(long)]
        show_logs: bool,

        /// Force start: kill existing daemon process and reset the socket
        #[arg(long)]
        force: bool,
    },

    /// Show the daemon's current status
    Status,

    /// Stop the daemon gracefully
    Stop,

    /// Restart the daemon (stop, then start in background)
    Restart,
}

impl Cmd {
    /// Returns `true` when the process should daemonize before creating the
    /// async runtime or opening any database connections.
    #[cfg(unix)]
    pub fn should_daemonize(&self) -> bool {
        match &self.subcmd {
            Some(SubCmd::Start { daemonize, .. }) => *daemonize,
            None => self.daemonize,
            _ => false,
        }
    }

    /// Returns `true` when logs should also be written to the console.
    pub fn show_logs(&self) -> bool {
        match &self.subcmd {
            Some(SubCmd::Start { show_logs, .. }) => *show_logs,
            None => self.show_logs,
            _ => false,
        }
    }

    pub async fn run(
        self,
        settings: Settings,
        store: SqliteStore,
        history_db: Sqlite,
    ) -> Result<()> {
        match self.subcmd {
            None => {
                eprintln!("Warning: `atuin daemon` is deprecated, use `atuin daemon start`");
                run(settings, store, history_db, false).await
            }
            Some(SubCmd::Start { force, .. }) => run(settings, store, history_db, force).await,
            Some(SubCmd::Status) => status_cmd(&settings).await,
            Some(SubCmd::Stop) => stop_cmd(&settings).await,
            Some(SubCmd::Restart) => restart_cmd(&settings).await,
        }
    }
}

const DAEMON_VERSION: &str = env!("CARGO_PKG_VERSION");
const DAEMON_PROTOCOL_VERSION: u32 = 1;
const STARTUP_POLL: Duration = Duration::from_millis(40);
const LOCK_POLL: Duration = Duration::from_millis(20);
const LEGACY_DAEMON_RESTART_MESSAGE: &str = "legacy daemon detected; restart daemon manually";

struct PidfileGuard {
    file: File,
}

impl PidfileGuard {
    fn acquire(path: &Path) -> Result<Self> {
        let mut file = open_lock_file(path)?;

        if !file.try_lock_exclusive()? {
            bail!(
                "daemon already running (pidfile lock busy at {})",
                path.display()
            );
        }

        file.set_len(0)
            .wrap_err_with(|| format!("could not truncate daemon pidfile {}", path.display()))?;
        writeln!(file, "{}", std::process::id())
            .and_then(|()| writeln!(file, "{DAEMON_VERSION}"))
            .wrap_err_with(|| format!("could not write daemon pidfile {}", path.display()))?;

        Ok(Self { file })
    }
}

impl Drop for PidfileGuard {
    fn drop(&mut self) {
        let _ = self.file.unlock();
    }
}

enum Probe {
    Ready(HistoryClient),
    NeedsRestart(String),
    Unreachable(eyre::Report),
}

fn daemon_matches_expected(version: &str, protocol: u32) -> bool {
    version == DAEMON_VERSION && protocol == DAEMON_PROTOCOL_VERSION
}

fn daemon_mismatch_message(version: &str, protocol: u32) -> String {
    if protocol == DAEMON_PROTOCOL_VERSION {
        format!("daemon is out of date: expected {DAEMON_VERSION}, got {version}")
    } else {
        format!("daemon protocol mismatch: expected {DAEMON_PROTOCOL_VERSION}, got {protocol}")
    }
}

fn is_legacy_daemon_error(err: &eyre::Report) -> bool {
    matches!(classify_error(err), DaemonClientErrorKind::Unimplemented)
}

fn should_retry_after_error(err: &eyre::Report) -> bool {
    matches!(
        classify_error(err),
        DaemonClientErrorKind::Connect
            | DaemonClientErrorKind::Unavailable
            | DaemonClientErrorKind::Unimplemented
    )
}

fn daemon_startup_lock_path(pidfile_path: &Path) -> PathBuf {
    let mut os = pidfile_path.as_os_str().to_os_string();
    os.push(".startup.lock");
    PathBuf::from(os)
}

fn open_lock_file(path: &Path) -> Result<File> {
    if let Some(parent) = path.parent() {
        fs::create_dir_all(parent)
            .wrap_err_with(|| format!("could not create lock directory {}", parent.display()))?;
    }

    OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .truncate(false)
        .open(path)
        .wrap_err_with(|| format!("could not open lock file {}", path.display()))
}

async fn wait_for_lock(path: &Path, timeout: Duration) -> Result<File> {
    let file = open_lock_file(path)?;
    let start = Instant::now();

    loop {
        match file.try_lock_exclusive() {
            Ok(true) => return Ok(file),
            Ok(false) => {
                if start.elapsed() >= timeout {
                    bail!("timed out waiting for lock at {}", path.display());
                }

                sleep(LOCK_POLL).await;
            }
            Err(err) => {
                return Err(eyre!("could not lock {}: {err}", path.display()));
            }
        }
    }
}

async fn wait_for_pidfile_available(path: &Path, timeout: Duration) -> Result<()> {
    let file = wait_for_lock(path, timeout).await?;
    file.unlock()
        .wrap_err_with(|| format!("failed to unlock {}", path.display()))?;
    Ok(())
}

async fn connect_client(settings: &Settings) -> Result<HistoryClient> {
    HistoryClient::new(
        #[cfg(unix)]
        settings.daemon.socket_path.clone(),
    )
    .await
}

async fn probe(settings: &Settings) -> Probe {
    let mut client = match connect_client(settings).await {
        Ok(client) => client,
        Err(err) => return Probe::Unreachable(err),
    };

    match client.status().await {
        Ok(status) => {
            if daemon_matches_expected(&status.version, status.protocol) {
                Probe::Ready(client)
            } else {
                Probe::NeedsRestart(daemon_mismatch_message(&status.version, status.protocol))
            }
        }
        Err(err) => Probe::Unreachable(err),
    }
}

async fn request_shutdown(settings: &Settings) {
    if let Ok(mut client) = connect_client(settings).await {
        let _ = client.shutdown().await;
    }
}

fn spawn_daemon_process() -> Result<()> {
    let exe = std::env::current_exe().wrap_err("could not locate atuin executable")?;

    let mut cmd = Command::new(exe);
    cmd.arg("daemon")
        .arg("start")
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null());

    #[cfg(unix)]
    cmd.arg("--daemonize");

    cmd.spawn().wrap_err("failed to spawn daemon process")?;

    Ok(())
}

fn startup_timeout(settings: &Settings) -> Duration {
    Duration::from_secs_f64(settings.local_timeout.max(0.5) + 2.0)
}

#[cfg(unix)]
fn remove_stale_socket_if_present(settings: &Settings) -> Result<()> {
    if settings.daemon.systemd_socket {
        return Ok(());
    }

    let socket_path = Path::new(&settings.daemon.socket_path);
    if !socket_path.exists() {
        return Ok(());
    }

    match StdUnixStream::connect(socket_path) {
        Ok(stream) => {
            drop(stream);
            Ok(())
        }
        Err(err) if err.kind() == ErrorKind::ConnectionRefused => {
            fs::remove_file(socket_path).wrap_err_with(|| {
                format!(
                    "failed to remove stale daemon socket {}",
                    socket_path.display()
                )
            })?;
            Ok(())
        }
        Err(err) if err.kind() == ErrorKind::NotFound => Ok(()),
        Err(_) => Ok(()),
    }
}

async fn wait_until_ready(settings: &Settings, timeout: Duration) -> Result<HistoryClient> {
    let start = Instant::now();
    let mut last_error = eyre!("daemon did not become ready");

    loop {
        match probe(settings).await {
            Probe::Ready(client) => return Ok(client),
            Probe::NeedsRestart(reason) => {
                last_error = eyre!(reason);
            }
            Probe::Unreachable(err) => {
                if is_legacy_daemon_error(&err) {
                    return Err(err.wrap_err(LEGACY_DAEMON_RESTART_MESSAGE));
                }
                last_error = err;
            }
        }

        if start.elapsed() >= timeout {
            return Err(last_error.wrap_err(format!(
                "timed out waiting for daemon startup after {}ms",
                timeout.as_millis()
            )));
        }

        sleep(STARTUP_POLL).await;
    }
}

#[expect(clippy::unnecessary_wraps)]
fn ensure_autostart_supported(settings: &Settings) -> Result<()> {
    #[cfg(unix)]
    if settings.daemon.systemd_socket {
        bail!(
            "daemon autostart is incompatible with `daemon.systemd_socket = true`; use systemd to manage the daemon"
        );
    }

    Ok(())
}

/// Ensure the daemon is running, starting it if necessary.
///
/// If the daemon is already running and up-to-date, this is a no-op.
/// If it is not running or needs a restart, this will spawn a new daemon
/// process and wait for it to become ready.
///
/// Returns an error if the daemon could not be started.
pub async fn ensure_daemon_running(settings: &Settings) -> Result<()> {
    ensure_autostart_supported(settings)?;

    let timeout = startup_timeout(settings);
    let pidfile_path = PathBuf::from(&settings.daemon.pidfile_path);
    let startup_lock_path = daemon_startup_lock_path(&pidfile_path);
    let startup_lock = wait_for_lock(&startup_lock_path, timeout).await?;

    match probe(settings).await {
        Probe::Ready(_) => {
            drop(startup_lock);
            return Ok(());
        }
        Probe::NeedsRestart(_) => {
            request_shutdown(settings).await;
        }
        Probe::Unreachable(err) => {
            if is_legacy_daemon_error(&err) {
                return Err(err.wrap_err(LEGACY_DAEMON_RESTART_MESSAGE));
            }
        }
    }

    // This prevents rapid-fire hook invocations from racing daemon restart.
    wait_for_pidfile_available(&pidfile_path, timeout).await?;

    #[cfg(unix)]
    remove_stale_socket_if_present(settings)?;

    spawn_daemon_process()?;
    let _ = wait_until_ready(settings, timeout).await?;

    drop(startup_lock);
    Ok(())
}

async fn restart_daemon(settings: &Settings) -> Result<HistoryClient> {
    ensure_daemon_running(settings).await?;
    connect_client(settings).await
}

fn ensure_reply_compatible(settings: &Settings, version: &str, protocol: u32) -> Result<()> {
    if daemon_matches_expected(version, protocol) {
        return Ok(());
    }

    let message = daemon_mismatch_message(version, protocol);
    if settings.daemon.autostart {
        bail!("{message}");
    }

    bail!("{message}. Enable `daemon.autostart = true` or restart the daemon manually");
}

pub async fn start_history(settings: &Settings, history: History) -> Result<String> {
    match async {
        connect_client(settings)
            .await?
            .start_history(history.clone())
            .await
    }
    .await
    {
        Ok(resp) => {
            if daemon_matches_expected(&resp.version, resp.protocol) {
                return Ok(resp.id);
            }

            if !settings.daemon.autostart {
                return Err(eyre!(
                    "{}. Enable `daemon.autostart = true` or restart the daemon manually",
                    daemon_mismatch_message(&resp.version, resp.protocol)
                ));
            }
        }
        Err(err) if !settings.daemon.autostart => return Err(err),
        Err(err) if !should_retry_after_error(&err) => return Err(err),
        Err(_) => {}
    }

    let resp = restart_daemon(settings)
        .await?
        .start_history(history)
        .await?;
    ensure_reply_compatible(settings, &resp.version, resp.protocol)?;
    Ok(resp.id)
}

pub async fn end_history(settings: &Settings, id: String, duration: u64, exit: i64) -> Result<()> {
    match async {
        connect_client(settings)
            .await?
            .end_history(id.clone(), duration, exit)
            .await
    }
    .await
    {
        Ok(resp) => {
            if daemon_matches_expected(&resp.version, resp.protocol) {
                return Ok(());
            }

            if !settings.daemon.autostart {
                return Err(eyre!(
                    "{}. Enable `daemon.autostart = true` or restart the daemon manually",
                    daemon_mismatch_message(&resp.version, resp.protocol)
                ));
            }

            // End succeeded on the running daemon, so avoid replaying it.
            // We only restart to make subsequent hook calls target the expected version.
            let _ = restart_daemon(settings).await;
            return Ok(());
        }
        Err(err) if !settings.daemon.autostart => return Err(err),
        Err(err) if !should_retry_after_error(&err) => return Err(err),
        Err(_) => {}
    }

    let resp = restart_daemon(settings)
        .await?
        .end_history(id, duration, exit)
        .await?;
    ensure_reply_compatible(settings, &resp.version, resp.protocol)?;
    Ok(())
}

/// Emit a daemon event, auto-starting the daemon if it is not running.
///
/// If the daemon is not reachable and `daemon.autostart` is enabled, this
/// will start the daemon and retry the event. If the daemon cannot be
/// started or the retry fails, a warning is printed to stderr.
pub async fn emit_event(settings: &Settings, event: DaemonEvent) {
    // Try to connect and send
    match ControlClient::from_settings(settings).await {
        Ok(mut client) => {
            if let Err(e) = client.send_event(event).await {
                tracing::debug!(?e, "failed to send event to daemon");
            }
            return;
        }
        Err(e) if !settings.daemon.autostart || !should_retry_after_error(&e) => {
            tracing::debug!(?e, "daemon not available, skipping event emission");
            return;
        }
        Err(_) => {}
    }

    // Auto-start the daemon and retry
    if let Err(e) = ensure_daemon_running(settings).await {
        eprintln!("Could not start daemon: {e}");
        return;
    }

    match ControlClient::from_settings(settings).await {
        Ok(mut client) => {
            if let Err(e) = client.send_event(event).await {
                eprintln!("Daemon started but failed to send event: {e}");
            }
        }
        Err(e) => {
            eprintln!("Daemon started but failed to connect: {e}");
        }
    }
}

pub async fn tail_client(settings: &Settings) -> Result<HistoryClient> {
    match probe(settings).await {
        Probe::Ready(client) => return Ok(client),
        Probe::NeedsRestart(reason) if !settings.daemon.autostart => {
            bail!("{reason}. Enable `daemon.autostart = true` or restart the daemon manually");
        }
        Probe::Unreachable(err) if is_legacy_daemon_error(&err) => {
            return Err(err.wrap_err(LEGACY_DAEMON_RESTART_MESSAGE));
        }
        Probe::Unreachable(err) if !settings.daemon.autostart => return Err(err),
        Probe::Unreachable(err) if !should_retry_after_error(&err) => return Err(err),
        Probe::NeedsRestart(_) | Probe::Unreachable(_) => {}
    }

    restart_daemon(settings).await
}

async fn status_cmd(settings: &Settings) -> Result<()> {
    match probe(settings).await {
        Probe::Ready(mut client) => {
            let status = client.status().await?;
            println!("Daemon running");
            println!("  PID:      {}", status.pid);
            println!("  Version:  {}", status.version);
            println!("  Protocol: {}", status.protocol);
            println!("  Healthy:  {}", status.healthy);
            #[cfg(unix)]
            println!("  Socket:   {}", settings.daemon.socket_path);
        }
        Probe::NeedsRestart(reason) => {
            println!("Daemon running (needs restart)");
            println!("  Reason: {reason}");
        }
        Probe::Unreachable(_) => {
            println!("Daemon is not running");
        }
    }

    Ok(())
}

async fn stop_cmd(settings: &Settings) -> Result<()> {
    let Ok(mut client) = connect_client(settings).await else {
        println!("Daemon is not running");
        return Ok(());
    };

    match client.shutdown().await {
        Ok(true) => {
            println!("Shutdown requested");

            let pidfile_path = PathBuf::from(&settings.daemon.pidfile_path);
            let timeout = Duration::from_secs(5);
            match wait_for_pidfile_available(&pidfile_path, timeout).await {
                Ok(()) => println!("Daemon stopped"),
                Err(_) => println!("Daemon may still be shutting down"),
            }

            Ok(())
        }
        Ok(false) => bail!("Daemon rejected shutdown request"),
        Err(err) => Err(err.wrap_err("Failed to send shutdown request")),
    }
}

async fn restart_cmd(settings: &Settings) -> Result<()> {
    // Stop if running
    match probe(settings).await {
        Probe::Ready(_) | Probe::NeedsRestart(_) => {
            request_shutdown(settings).await;
            println!("Stopping daemon...");

            let pidfile_path = PathBuf::from(&settings.daemon.pidfile_path);
            let timeout = Duration::from_secs(5);
            wait_for_pidfile_available(&pidfile_path, timeout)
                .await
                .wrap_err("Timed out waiting for old daemon to stop")?;
        }
        Probe::Unreachable(_) => {
            println!("No daemon running");
        }
    }

    #[cfg(unix)]
    remove_stale_socket_if_present(settings)?;

    spawn_daemon_process()?;
    println!("Starting daemon...");

    let timeout = startup_timeout(settings);
    let status = wait_until_ready(settings, timeout).await?.status().await?;

    println!("Daemon restarted");
    println!("  PID:      {}", status.pid);
    println!("  Version:  {}", status.version);

    Ok(())
}

/// Daemonize the current process. Must be called before creating the tokio
/// runtime or opening database connections, since `fork()` inside an async
/// runtime corrupts its internal state.
#[cfg(unix)]
pub fn daemonize_current_process() -> Result<()> {
    let cwd =
        std::env::current_dir().wrap_err("could not determine current directory for daemon")?;

    Daemonize::new()
        .working_directory(cwd)
        .start()
        .wrap_err("failed to daemonize process")?;

    Ok(())
}

async fn run(
    settings: Settings,
    store: SqliteStore,
    history_db: Sqlite,
    force: bool,
) -> Result<()> {
    if force {
        force_cleanup(&settings);
    }

    let pidfile_path = PathBuf::from(&settings.daemon.pidfile_path);
    let _pidfile_guard = PidfileGuard::acquire(&pidfile_path)?;

    crate::atuin_daemon::boot(settings, store, history_db).await?;

    Ok(())
}

/// Force cleanup: kill existing daemon process and remove socket.
fn force_cleanup(settings: &Settings) {
    let pidfile_path = Path::new(&settings.daemon.pidfile_path);

    // Read and kill the existing process if pidfile exists
    if pidfile_path.exists() {
        if let Ok(contents) = fs::read_to_string(pidfile_path)
            && let Some(pid_str) = contents.lines().next()
            && let Ok(pid) = pid_str.parse::<u32>()
        {
            kill_process(pid);
            // Give it a moment to release resources
            std::thread::sleep(Duration::from_millis(100));
        }

        // Remove the pidfile
        if let Err(e) = fs::remove_file(pidfile_path)
            && e.kind() != ErrorKind::NotFound
        {
            tracing::warn!("failed to remove pidfile: {e}");
        }
    }

    // Remove the socket file
    #[cfg(unix)]
    {
        let socket_path = Path::new(&settings.daemon.socket_path);
        if socket_path.exists()
            && let Err(e) = fs::remove_file(socket_path)
            && e.kind() != ErrorKind::NotFound
        {
            tracing::warn!("failed to remove socket: {e}");
        }
    }
}

/// Kill a process by PID.
#[cfg(unix)]
fn kill_process(pid: u32) {
    // Use kill command to send SIGTERM for graceful shutdown
    let _ = Command::new("kill")
        .args(["-TERM", &pid.to_string()])
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .status();
}

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

    #[test]
    fn test_version_matches() {
        assert!(daemon_matches_expected(
            DAEMON_VERSION,
            DAEMON_PROTOCOL_VERSION
        ));
    }

    #[test]
    fn test_version_mismatch() {
        assert!(!daemon_matches_expected("0.0.0", DAEMON_PROTOCOL_VERSION));
        assert!(!daemon_matches_expected(DAEMON_VERSION, 999));
        assert!(!daemon_matches_expected("0.0.0", 999));
    }

    #[test]
    fn test_mismatch_message_version() {
        let msg = daemon_mismatch_message("0.0.0", DAEMON_PROTOCOL_VERSION);
        assert!(msg.contains("out of date"), "got: {msg}");
        assert!(msg.contains("0.0.0"));
        assert!(msg.contains(DAEMON_VERSION));
    }

    #[test]
    fn test_mismatch_message_protocol() {
        let msg = daemon_mismatch_message(DAEMON_VERSION, 999);
        assert!(msg.contains("protocol mismatch"), "got: {msg}");
    }

    #[test]
    fn test_startup_lock_path() {
        let pidfile = Path::new("/tmp/atuin-daemon.pid");
        let lock = daemon_startup_lock_path(pidfile);
        assert_eq!(lock, PathBuf::from("/tmp/atuin-daemon.pid.startup.lock"));
    }

    #[test]
    fn test_pidfile_guard_acquire_and_drop() {
        let tmp = tempfile::tempdir().unwrap();
        let pidfile = tmp.path().join("daemon.pid");

        {
            let _guard = PidfileGuard::acquire(&pidfile).unwrap();
            // Guard holds an exclusive lock — on Windows other handles cannot
            // read the file, so we verify contents after the guard is dropped.
        }

        let contents = std::fs::read_to_string(&pidfile).unwrap();
        let lines: Vec<&str> = contents.lines().collect();
        assert_eq!(lines.len(), 2);
        assert_eq!(lines[0], std::process::id().to_string());
        assert_eq!(lines[1], DAEMON_VERSION);

        // After guard is dropped, lock should be released — acquiring again must succeed.
        let _guard2 = PidfileGuard::acquire(&pidfile).unwrap();
    }

    #[test]
    fn test_pidfile_guard_prevents_double_acquire() {
        let tmp = tempfile::tempdir().unwrap();
        let pidfile = tmp.path().join("daemon.pid");

        let _guard = PidfileGuard::acquire(&pidfile).unwrap();
        let result = PidfileGuard::acquire(&pidfile);
        assert!(result.is_err());
    }
}