//! `warpgate run` — single-process supervisor for all services.
//!
//! Manages rclone mount + protocol services in one process tree with
//! coordinated startup and shutdown. Designed to run as a systemd unit
//! or standalone (Docker-friendly).

use std::os::unix::process::CommandExt;
use std::process::{Child, Command};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::thread;
use std::time::{Duration, Instant};

use anyhow::{Context, Result};

use crate::config::Config;
use crate::rclone::mount::{build_mount_args, is_mounted};
use crate::services::{nfs, samba, webdav};

/// Mount ready timeout.
const MOUNT_TIMEOUT: Duration = Duration::from_secs(30);
/// Supervision loop poll interval.
const POLL_INTERVAL: Duration = Duration::from_secs(2);
/// Grace period for SIGTERM before escalating to SIGKILL.
const SIGTERM_GRACE: Duration = Duration::from_secs(3);
/// Max restart attempts before giving up on a protocol service.
const MAX_RESTARTS: u32 = 3;
/// Reset restart counter after this period of stable running.
const RESTART_STABLE_PERIOD: Duration = Duration::from_secs(300);
/// Max time to wait for write-back queue to drain on shutdown.
const WRITEBACK_DRAIN_TIMEOUT: Duration = Duration::from_secs(300);
/// Poll interval when waiting for write-back drain.
const WRITEBACK_POLL_INTERVAL: Duration = Duration::from_secs(2);

/// Tracks restart attempts for a supervised child process.
struct RestartTracker {
    count: u32,
    last_restart: Option<Instant>,
}

impl RestartTracker {
    fn new() -> Self {
        Self {
            count: 0,
            last_restart: None,
        }
    }

    /// Returns true if another restart is allowed. Resets counter if the
    /// service has been stable for `RESTART_STABLE_PERIOD`.
    fn can_restart(&mut self) -> bool {
        if let Some(last) = self.last_restart
            && last.elapsed() >= RESTART_STABLE_PERIOD
        {
            self.count = 0;
        }
        self.count < MAX_RESTARTS
    }

    fn record_restart(&mut self) {
        self.count += 1;
        self.last_restart = Some(Instant::now());
    }
}

/// Child processes for protocol servers managed by the supervisor.
///
/// Implements `Drop` to kill any spawned children — prevents orphaned
/// processes if startup fails partway through `start_protocols()`.
struct ProtocolChildren {
    smbd: Option<Child>,
    webdav: Option<Child>,
}

impl Drop for ProtocolChildren {
    fn drop(&mut self) {
        for child in [&mut self.smbd, &mut self.webdav].into_iter().flatten() {
            graceful_kill(child);
        }
    }
}

/// Entry point — called from main.rs for `warpgate run`.
pub fn run(config: &Config) -> Result<()> {
    let shutdown = Arc::new(AtomicBool::new(false));

    // Install signal handler (SIGTERM + SIGINT)
    let shutdown_flag = Arc::clone(&shutdown);
    ctrlc::set_handler(move || {
        eprintln!("Signal received, shutting down...");
        shutdown_flag.store(true, Ordering::SeqCst);
    })
    .context("Failed to set signal handler")?;

    // Phase 1: Preflight — generate configs, create dirs
    println!("Preflight checks...");
    preflight(config)?;

    // Phase 2: Start rclone mount and wait for it to become ready
    println!("Starting rclone mount...");
    let mut mount_child = start_and_wait_mount(config, &shutdown)?;
    println!("Mount ready at {}", config.mount.point.display());

    // Phase 3: Start protocol services
    if shutdown.load(Ordering::SeqCst) {
        println!("Shutdown signal received during mount.");
        let _ = mount_child.kill();
        let _ = mount_child.wait();
        return Ok(());
    }
    println!("Starting protocol services...");
    let mut protocols = start_protocols(config)?;

    // Phase 3.5: Auto-warmup (non-blocking, best-effort)
    if !config.warmup.rules.is_empty() && config.warmup.auto {
        println!("Running auto-warmup...");
        for rule in &config.warmup.rules {
            if shutdown.load(Ordering::SeqCst) {
                break;
            }
            if let Err(e) =
                crate::cli::warmup::run(config, &rule.path, rule.newer_than.as_deref())
            {
                eprintln!("Warmup warning: {e}");
            }
        }
    }

    // Phase 4: Supervision loop
    println!("Supervision active. Press Ctrl+C to stop.");
    let result = supervise(config, &mut mount_child, &mut protocols, Arc::clone(&shutdown));

    // Phase 5: Teardown (always runs)
    println!("Shutting down...");
    shutdown_services(config, &mut mount_child, &mut protocols);

    result
}

/// Write configs and create directories. Reuses existing modules.
fn preflight(config: &Config) -> Result<()> {
    // Ensure mount point exists
    std::fs::create_dir_all(&config.mount.point).with_context(|| {
        format!(
            "Failed to create mount point: {}",
            config.mount.point.display()
        )
    })?;

    // Ensure cache directory exists
    std::fs::create_dir_all(&config.cache.dir).with_context(|| {
        format!(
            "Failed to create cache dir: {}",
            config.cache.dir.display()
        )
    })?;

    // Generate rclone config
    crate::rclone::config::write_config(config)?;

    // Generate protocol configs
    if config.protocols.enable_smb {
        samba::write_config(config)?;
    }
    if config.protocols.enable_nfs {
        nfs::write_config(config)?;
    }

    Ok(())
}

/// Spawn rclone mount process and poll until the FUSE mount appears.
fn start_and_wait_mount(config: &Config, shutdown: &AtomicBool) -> Result<Child> {
    let args = build_mount_args(config);

    let mut child = Command::new("rclone")
        .args(&args)
        .process_group(0) // isolate from terminal SIGINT
        .spawn()
        .context("Failed to spawn rclone mount")?;

    // Poll for mount readiness
    let deadline = Instant::now() + MOUNT_TIMEOUT;
    loop {
        // Check for shutdown signal (e.g. Ctrl+C during mount wait)
        if shutdown.load(Ordering::SeqCst) {
            let _ = child.kill();
            let _ = child.wait();
            anyhow::bail!("Interrupted while waiting for mount");
        }

        if Instant::now() > deadline {
            let _ = child.kill();
            let _ = child.wait();
            anyhow::bail!(
                "Timed out waiting for mount at {} ({}s)",
                config.mount.point.display(),
                MOUNT_TIMEOUT.as_secs()
            );
        }

        // Detect early rclone exit (e.g. bad config, auth failure)
        match child.try_wait() {
            Ok(Some(status)) => {
                anyhow::bail!("rclone mount exited immediately ({status}). Check remote/auth config.");
            }
            Ok(None) => {} // still running, good
            Err(e) => {
                anyhow::bail!("Failed to check rclone mount status: {e}");
            }
        }

        match is_mounted(config) {
            Ok(true) => break,
            Ok(false) => {}
            Err(e) => eprintln!("Warning: mount check failed: {e}"),
        }

        thread::sleep(Duration::from_millis(500));
    }

    Ok(child)
}

/// Spawn smbd as a foreground child process.
fn spawn_smbd() -> Result<Child> {
    Command::new("smbd")
        .args(["--foreground", "--debug-stdout", "--no-process-group",
               "--configfile", samba::SMB_CONF_PATH])
        .process_group(0)
        .spawn()
        .context("Failed to spawn smbd")
}

/// Start protocol services after the mount is ready.
///
/// - SMB: spawn `smbd -F` as a child process
/// - NFS: `exportfs -ra`
/// - WebDAV: spawn `rclone serve webdav` as a child process
fn start_protocols(config: &Config) -> Result<ProtocolChildren> {
    let smbd = if config.protocols.enable_smb {
        let child = spawn_smbd()?;
        println!("  SMB: started");
        Some(child)
    } else {
        None
    };

    if config.protocols.enable_nfs {
        let status = Command::new("exportfs")
            .arg("-ra")
            .status()
            .context("Failed to run exportfs -ra")?;
        if !status.success() {
            anyhow::bail!("exportfs -ra failed: {status}");
        }
        println!("  NFS: exported");
    }

    let webdav = if config.protocols.enable_webdav {
        let child = spawn_webdav(config)?;
        println!("  WebDAV: started");
        Some(child)
    } else {
        None
    };

    Ok(ProtocolChildren { smbd, webdav })
}

/// Spawn a `rclone serve webdav` child process.
fn spawn_webdav(config: &Config) -> Result<Child> {
    let args = webdav::build_serve_args(config);
    Command::new("rclone")
        .args(&args)
        .process_group(0)
        .spawn()
        .context("Failed to spawn rclone serve webdav")
}

/// Main supervision loop. Polls child processes every 2s.
///
/// - If rclone mount dies → full shutdown (data safety: dirty files may be in flight).
/// - If smbd/WebDAV dies → restart up to 3 times (counter resets after 5 min stable).
/// - Checks shutdown flag set by signal handler.
fn supervise(
    config: &Config,
    mount: &mut Child,
    protocols: &mut ProtocolChildren,
    shutdown: Arc<AtomicBool>,
) -> Result<()> {
    let mut smbd_tracker = RestartTracker::new();
    let mut webdav_tracker = RestartTracker::new();

    loop {
        // Check for shutdown signal
        if shutdown.load(Ordering::SeqCst) {
            println!("Shutdown signal received.");
            return Ok(());
        }

        // Check rclone mount process
        match mount.try_wait() {
            Ok(Some(status)) => {
                anyhow::bail!(
                    "rclone mount exited unexpectedly ({}). Initiating full shutdown for data safety.",
                    status
                );
            }
            Ok(None) => {} // still running
            Err(e) => {
                anyhow::bail!("Failed to check rclone mount status: {e}");
            }
        }

        // Check smbd process (if enabled)
        if let Some(child) = &mut protocols.smbd {
            match child.try_wait() {
                Ok(Some(status)) => {
                    eprintln!("smbd exited ({status}).");
                    if smbd_tracker.can_restart() {
                        smbd_tracker.record_restart();
                        let delay = smbd_tracker.count * 2;
                        eprintln!(
                            "Restarting smbd in {delay}s ({}/{MAX_RESTARTS})...",
                            smbd_tracker.count,
                        );
                        thread::sleep(Duration::from_secs(delay.into()));
                        match spawn_smbd() {
                            Ok(new_child) => *child = new_child,
                            Err(e) => {
                                eprintln!("Failed to restart smbd: {e}");
                                protocols.smbd = None;
                            }
                        }
                    } else {
                        eprintln!(
                            "smbd exceeded max restarts ({MAX_RESTARTS}), giving up."
                        );
                        protocols.smbd = None;
                    }
                }
                Ok(None) => {} // still running
                Err(e) => eprintln!("Warning: failed to check smbd status: {e}"),
            }
        }

        // Check WebDAV process (if enabled)
        if let Some(child) = &mut protocols.webdav {
            match child.try_wait() {
                Ok(Some(status)) => {
                    eprintln!("WebDAV exited ({status}).");
                    if webdav_tracker.can_restart() {
                        webdav_tracker.record_restart();
                        let delay = webdav_tracker.count * 2;
                        eprintln!(
                            "Restarting WebDAV in {delay}s ({}/{MAX_RESTARTS})...",
                            webdav_tracker.count,
                        );
                        thread::sleep(Duration::from_secs(delay.into()));
                        match spawn_webdav(config) {
                            Ok(new_child) => *child = new_child,
                            Err(e) => {
                                eprintln!("Failed to restart WebDAV: {e}");
                                protocols.webdav = None;
                            }
                        }
                    } else {
                        eprintln!(
                            "WebDAV exceeded max restarts ({MAX_RESTARTS}), giving up."
                        );
                        protocols.webdav = None;
                    }
                }
                Ok(None) => {} // still running
                Err(e) => eprintln!("Warning: failed to check WebDAV status: {e}"),
            }
        }

        thread::sleep(POLL_INTERVAL);
    }
}

/// Send SIGTERM, wait up to `SIGTERM_GRACE`, then SIGKILL if still alive.
///
/// smbd forks worker processes per client connection — SIGTERM lets
/// the parent signal its children to exit cleanly. SIGKILL would
/// orphan those workers.
fn graceful_kill(child: &mut Child) {
    let pid = child.id() as i32;
    // SAFETY: sending a signal to a known child PID is safe.
    unsafe { libc::kill(pid, libc::SIGTERM) };

    let deadline = Instant::now() + SIGTERM_GRACE;
    loop {
        match child.try_wait() {
            Ok(Some(_)) => return, // exited cleanly
            Ok(None) => {}
            Err(_) => break,
        }
        if Instant::now() > deadline {
            break;
        }
        thread::sleep(Duration::from_millis(100));
    }

    // Still alive after grace period — escalate
    let _ = child.kill(); // SIGKILL
    let _ = child.wait();
}

/// Wait for rclone VFS write-back queue to drain.
///
/// Polls `vfs/stats` every 2s. Exits when uploads_in_progress + uploads_queued
/// reaches 0, or after 5 minutes (safety cap to avoid hanging forever).
fn wait_writeback_drain() {
    use crate::rclone::rc;

    let deadline = Instant::now() + WRITEBACK_DRAIN_TIMEOUT;
    let mut first = true;

    loop {
        match rc::vfs_stats() {
            Ok(vfs) => {
                if let Some(dc) = &vfs.disk_cache {
                    let pending = dc.uploads_in_progress + dc.uploads_queued;
                    if pending == 0 {
                        if !first {
                            println!("  Write-back queue drained.");
                        }
                        return;
                    }
                    if first {
                        println!(
                            "  Waiting for write-back queue ({pending} files pending)..."
                        );
                        first = false;
                    } else {
                        eprint!("\r  Write-back: {pending} files remaining...  ");
                    }
                } else {
                    return; // no cache info → nothing to wait for
                }
            }
            Err(_) => return, // RC API unavailable → rclone already gone
        }

        if Instant::now() > deadline {
            eprintln!();
            eprintln!(
                "  Warning: write-back drain timed out after {}s, proceeding with shutdown.",
                WRITEBACK_DRAIN_TIMEOUT.as_secs()
            );
            return;
        }

        thread::sleep(WRITEBACK_POLL_INTERVAL);
    }
}

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

    #[test]
    fn test_restart_tracker_new() {
        let tracker = RestartTracker::new();
        assert_eq!(tracker.count, 0);
        assert!(tracker.last_restart.is_none());
    }

    #[test]
    fn test_restart_tracker_record_restart() {
        let mut tracker = RestartTracker::new();
        tracker.record_restart();
        assert_eq!(tracker.count, 1);
        assert!(tracker.last_restart.is_some());
    }

    #[test]
    fn test_restart_tracker_can_restart_under_max() {
        let mut tracker = RestartTracker::new();
        assert!(tracker.can_restart());

        tracker.record_restart();
        assert!(tracker.can_restart()); // count = 1

        tracker.record_restart();
        assert!(tracker.can_restart()); // count = 2
    }

    #[test]
    fn test_restart_tracker_cannot_restart_at_max() {
        let mut tracker = RestartTracker::new();
        for _ in 0..MAX_RESTARTS {
            tracker.record_restart();
        }
        assert!(!tracker.can_restart()); // count = 3 = MAX_RESTARTS
    }

    #[test]
    fn test_restart_tracker_backoff_delay() {
        let mut tracker = RestartTracker::new();

        tracker.record_restart();
        assert_eq!(tracker.count * 2, 2); // 2s delay

        tracker.record_restart();
        assert_eq!(tracker.count * 2, 4); // 4s delay

        tracker.record_restart();
        assert_eq!(tracker.count * 2, 6); // 6s delay
    }

    #[test]
    fn test_restart_tracker_multiple_record() {
        let mut tracker = RestartTracker::new();
        tracker.record_restart();
        tracker.record_restart();
        tracker.record_restart();
        assert_eq!(tracker.count, 3);
        assert!(!tracker.can_restart());
    }

    #[test]
    fn test_constants() {
        assert_eq!(MOUNT_TIMEOUT, Duration::from_secs(30));
        assert_eq!(POLL_INTERVAL, Duration::from_secs(2));
        assert_eq!(SIGTERM_GRACE, Duration::from_secs(3));
        assert_eq!(MAX_RESTARTS, 3);
        assert_eq!(RESTART_STABLE_PERIOD, Duration::from_secs(300));
        assert_eq!(WRITEBACK_DRAIN_TIMEOUT, Duration::from_secs(300));
        assert_eq!(WRITEBACK_POLL_INTERVAL, Duration::from_secs(2));
    }
}

/// Reverse-order teardown of all services.
///
/// Order: stop smbd → unexport NFS → kill WebDAV → unmount FUSE → kill rclone.
fn shutdown_services(config: &Config, mount: &mut Child, protocols: &mut ProtocolChildren) {
    // Stop SMB
    if let Some(child) = &mut protocols.smbd {
        graceful_kill(child);
        println!("  SMB: stopped");
    }

    // Unexport NFS
    if config.protocols.enable_nfs {
        let _ = Command::new("exportfs").arg("-ua").status();
        println!("  NFS: unexported");
    }

    // Kill WebDAV
    if let Some(child) = &mut protocols.webdav {
        graceful_kill(child);
        println!("  WebDAV: stopped");
    }

    // Wait for write-back queue to drain before unmounting
    wait_writeback_drain();

    // Lazy unmount FUSE (skip if rclone already unmounted on signal)
    if is_mounted(config).unwrap_or(false) {
        let mount_point = config.mount.point.display().to_string();
        let unmounted = Command::new("fusermount3")
            .args(["-uz", &mount_point])
            .status()
            .map(|s| s.success())
            .unwrap_or(false);
        if !unmounted {
            let _ = Command::new("fusermount")
                .args(["-uz", &mount_point])
                .status();
        }
    }
    println!("  FUSE: unmounted");

    // Gracefully stop rclone
    graceful_kill(mount);
    println!("  rclone: stopped");
}