//! Shutdown and signal handling for telemt.
//!
//! Handles graceful shutdown on various signals:
//! - SIGINT (Ctrl+C) / SIGTERM: Graceful shutdown
//! - SIGQUIT: Graceful shutdown with stats dump
//! - SIGUSR1: Reserved for log rotation (logs acknowledgment)
//! - SIGUSR2: Dump runtime status to log
//!
//! SIGHUP is handled separately in config/hot_reload.rs for config reload.

use std::sync::Arc;
use std::time::{Duration, Instant};

#[cfg(unix)]
use tokio::signal::unix::{SignalKind, signal};
#[cfg(not(unix))]
use tokio::signal;
use tracing::{info, warn};

use crate::stats::Stats;
use crate::transport::middle_proxy::MePool;

use super::helpers::{format_uptime, unit_label};

/// Signal that triggered shutdown.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ShutdownSignal {
    /// SIGINT (Ctrl+C)
    Interrupt,
    /// SIGTERM
    Terminate,
    /// SIGQUIT (with stats dump)
    Quit,
}

impl std::fmt::Display for ShutdownSignal {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ShutdownSignal::Interrupt => write!(f, "SIGINT"),
            ShutdownSignal::Terminate => write!(f, "SIGTERM"),
            ShutdownSignal::Quit => write!(f, "SIGQUIT"),
        }
    }
}

/// Waits for a shutdown signal and performs graceful shutdown.
pub(crate) async fn wait_for_shutdown(
    process_started_at: Instant,
    me_pool: Option<Arc<MePool>>,
    stats: Arc<Stats>,
) {
    let signal = wait_for_shutdown_signal().await;
    perform_shutdown(signal, process_started_at, me_pool, &stats).await;
}

/// Waits for any shutdown signal (SIGINT, SIGTERM, SIGQUIT).
#[cfg(unix)]
async fn wait_for_shutdown_signal() -> ShutdownSignal {
    let mut sigint = signal(SignalKind::interrupt()).expect("Failed to register SIGINT handler");
    let mut sigterm = signal(SignalKind::terminate()).expect("Failed to register SIGTERM handler");
    let mut sigquit = signal(SignalKind::quit()).expect("Failed to register SIGQUIT handler");

    tokio::select! {
        _ = sigint.recv() => ShutdownSignal::Interrupt,
        _ = sigterm.recv() => ShutdownSignal::Terminate,
        _ = sigquit.recv() => ShutdownSignal::Quit,
    }
}

#[cfg(not(unix))]
async fn wait_for_shutdown_signal() -> ShutdownSignal {
    signal::ctrl_c().await.expect("Failed to listen for Ctrl+C");
    ShutdownSignal::Interrupt
}

/// Performs graceful shutdown sequence.
async fn perform_shutdown(
    signal: ShutdownSignal,
    process_started_at: Instant,
    me_pool: Option<Arc<MePool>>,
    stats: &Stats,
) {
    let shutdown_started_at = Instant::now();
    info!(signal = %signal, "Received shutdown signal");

    // Dump stats if SIGQUIT
    if signal == ShutdownSignal::Quit {
        dump_stats(stats, process_started_at);
    }

    info!("Shutting down...");
    let uptime_secs = process_started_at.elapsed().as_secs();
    info!("Uptime: {}", format_uptime(uptime_secs));

    // Graceful ME pool shutdown
    if let Some(pool) = &me_pool {
        match tokio::time::timeout(Duration::from_secs(2), pool.shutdown_send_close_conn_all()).await
        {
            Ok(total) => {
                info!(
                    close_conn_sent = total,
                    "ME shutdown: RPC_CLOSE_CONN broadcast completed"
                );
            }
            Err(_) => {
                warn!("ME shutdown: RPC_CLOSE_CONN broadcast timed out");
            }
        }
    }

    let shutdown_secs = shutdown_started_at.elapsed().as_secs();
    info!(
        "Shutdown completed successfully in {} {}.",
        shutdown_secs,
        unit_label(shutdown_secs, "second", "seconds")
    );
}

/// Dumps runtime statistics to the log.
fn dump_stats(stats: &Stats, process_started_at: Instant) {
    let uptime_secs = process_started_at.elapsed().as_secs();

    info!("=== Runtime Statistics Dump ===");
    info!("Uptime: {}", format_uptime(uptime_secs));

    // Connection stats
    info!(
        "Connections: total={}, current={} (direct={}, me={}), bad={}",
        stats.get_connects_all(),
        stats.get_current_connections_total(),
        stats.get_current_connections_direct(),
        stats.get_current_connections_me(),
        stats.get_connects_bad(),
    );

    // ME pool stats
    info!(
        "ME keepalive: sent={}, pong={}, failed={}, timeout={}",
        stats.get_me_keepalive_sent(),
        stats.get_me_keepalive_pong(),
        stats.get_me_keepalive_failed(),
        stats.get_me_keepalive_timeout(),
    );

    // Relay stats
    info!(
        "Relay adaptive: promotions={}, demotions={}, hard_promotions={}",
        stats.get_relay_adaptive_promotions_total(),
        stats.get_relay_adaptive_demotions_total(),
        stats.get_relay_adaptive_hard_promotions_total(),
    );

    info!("=== End Statistics Dump ===");
}

/// Spawns a background task to handle operational signals (SIGUSR1, SIGUSR2).
///
/// These signals don't trigger shutdown but perform specific actions:
/// - SIGUSR1: Log rotation acknowledgment (for external log rotation tools)
/// - SIGUSR2: Dump runtime status to log
#[cfg(unix)]
pub(crate) fn spawn_signal_handlers(
    stats: Arc<Stats>,
    process_started_at: Instant,
) {
    tokio::spawn(async move {
        let mut sigusr1 = signal(SignalKind::user_defined1())
            .expect("Failed to register SIGUSR1 handler");
        let mut sigusr2 = signal(SignalKind::user_defined2())
            .expect("Failed to register SIGUSR2 handler");

        loop {
            tokio::select! {
                _ = sigusr1.recv() => {
                    handle_sigusr1();
                }
                _ = sigusr2.recv() => {
                    handle_sigusr2(&stats, process_started_at);
                }
            }
        }
    });
}

/// No-op on non-Unix platforms.
#[cfg(not(unix))]
pub(crate) fn spawn_signal_handlers(
    _stats: Arc<Stats>,
    _process_started_at: Instant,
) {
    // No SIGUSR1/SIGUSR2 on non-Unix
}

/// Handles SIGUSR1 - log rotation signal.
///
/// This signal is typically sent by logrotate or similar tools after
/// rotating log files. Since tracing-subscriber doesn't natively support
/// reopening files, we just acknowledge the signal. If file logging is
/// added in the future, this would reopen log file handles.
#[cfg(unix)]
fn handle_sigusr1() {
    info!("SIGUSR1 received - log rotation acknowledged");
    // Future: If using file-based logging, reopen file handles here
}

/// Handles SIGUSR2 - dump runtime status.
#[cfg(unix)]
fn handle_sigusr2(stats: &Stats, process_started_at: Instant) {
    info!("SIGUSR2 received - dumping runtime status");
    dump_stats(stats, process_started_at);
}