use crate::agents::AgentPool;
use crate::slog;
use matrix_sdk::{Client, LoopCtrl, config::SyncSettings};
use matrix_sdk::ruma::OwnedRoomId;
use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
use std::collections::{HashMap, HashSet};
use std::path::PathBuf;
use std::sync::Arc;
use tokio::sync::Mutex as TokioMutex;
use tokio::sync::{mpsc, watch};

use super::context::BotContext;
use super::format::{format_startup_announcement, markdown_to_html};
use super::history::load_history;
use super::messages::on_room_message;
use super::verification::{on_room_verification_request, on_to_device_verification_request};

/// Connect to the Matrix homeserver, join all configured rooms, and start
/// listening for messages. Runs the full Matrix sync loop — call from a
/// `tokio::spawn` task so it doesn't block the main thread.
pub async fn run_bot(
    config: super::super::config::BotConfig,
    project_root: PathBuf,
    watcher_rx: tokio::sync::broadcast::Receiver<crate::io::watcher::WatcherEvent>,
    watcher_rx_auto: tokio::sync::broadcast::Receiver<crate::io::watcher::WatcherEvent>,
    perm_rx: Arc<TokioMutex<mpsc::UnboundedReceiver<crate::http::context::PermissionForward>>>,
    agents: Arc<AgentPool>,
    shutdown_rx: watch::Receiver<Option<crate::rebuild::ShutdownReason>>,
) -> Result<(), String> {
    let store_path = project_root.join(".huskies").join("matrix_store");
    let client = Client::builder()
        .homeserver_url(config.homeserver.as_deref().unwrap_or_default())
        .sqlite_store(&store_path, None)
        .build()
        .await
        .map_err(|e| format!("Failed to build Matrix client: {e}"))?;

    // Persist device ID so E2EE crypto state survives restarts.
    let device_id_path = project_root.join(".huskies").join("matrix_device_id");
    let saved_device_id: Option<String> = std::fs::read_to_string(&device_id_path)
        .ok()
        .map(|s| s.trim().to_string())
        .filter(|s| !s.is_empty());

    let mut login_builder = client
        .matrix_auth()
        .login_username(
            config.username.as_deref().unwrap_or_default(),
            config.password.as_deref().unwrap_or_default(),
        )
        .initial_device_display_name("Huskies Bot");

    if let Some(ref device_id) = saved_device_id {
        login_builder = login_builder.device_id(device_id);
    }

    let login_response = login_builder
        .await
        .map_err(|e| format!("Matrix login failed: {e}"))?;

    // Save device ID on first login so subsequent restarts reuse the same device.
    if saved_device_id.is_none() {
        let _ = std::fs::write(&device_id_path, &login_response.device_id);
        slog!(
            "[matrix-bot] Saved device ID {} for future restarts",
            login_response.device_id
        );
    }

    let bot_user_id = client
        .user_id()
        .ok_or_else(|| "No user ID after login".to_string())?
        .to_owned();

    slog!("[matrix-bot] Logged in as {bot_user_id} (device: {})", login_response.device_id);

    // Bootstrap cross-signing keys for E2EE verification support.
    // Pass the bot's password for UIA (User-Interactive Authentication) —
    // the homeserver requires proof of identity before accepting cross-signing keys.
    {
        use matrix_sdk::ruma::api::client::uiaa;
        let password_auth = uiaa::AuthData::Password(uiaa::Password::new(
            uiaa::UserIdentifier::UserIdOrLocalpart(
                config.username.clone().unwrap_or_default(),
            ),
            config.password.clone().unwrap_or_default(),
        ));
        if let Err(e) = client
            .encryption()
            .bootstrap_cross_signing(Some(password_auth))
            .await
        {
            slog!("[matrix-bot] Cross-signing bootstrap note: {e}");
        }
    }

    // Self-sign own device keys so other clients don't show
    // "encrypted by a device not verified by its owner" warnings.
    match client.encryption().get_own_device().await {
        Ok(Some(own_device)) => {
            if own_device.is_cross_signed_by_owner() {
                slog!("[matrix-bot] Device already self-signed");
            } else {
                slog!("[matrix-bot] Device not self-signed, signing now...");
                match own_device.verify().await {
                    Ok(()) => slog!("[matrix-bot] Successfully self-signed device keys"),
                    Err(e) => slog!("[matrix-bot] Failed to self-sign device keys: {e}"),
                }
            }
        }
        Ok(None) => slog!("[matrix-bot] Could not find own device in crypto store"),
        Err(e) => slog!("[matrix-bot] Error retrieving own device: {e}"),
    }

    if config.allowed_users.is_empty() {
        return Err(
            "allowed_users is empty in bot.toml — refusing to start (fail-closed). \
             Add at least one Matrix user ID to allowed_users."
                .to_string(),
        );
    }

    slog!("[matrix-bot] Allowed users: {:?}", config.allowed_users);

    // Parse and join all configured rooms.
    let mut target_room_ids: Vec<OwnedRoomId> = Vec::new();
    for room_id_str in config.effective_room_ids() {
        let room_id: OwnedRoomId = room_id_str
            .parse()
            .map_err(|_| format!("Invalid room ID '{room_id_str}'"))?;

        // Try to join with a timeout. Conduit sometimes hangs or returns
        // errors on join if the bot is already a member.
        match tokio::time::timeout(
            std::time::Duration::from_secs(10),
            client.join_room_by_id(&room_id),
        )
        .await
        {
            Ok(Ok(_)) => slog!("[matrix-bot] Joined room {room_id}"),
            Ok(Err(e)) => {
                slog!("[matrix-bot] Join room error (may already be a member): {e}")
            }
            Err(_) => slog!("[matrix-bot] Join room timed out (may already be a member)"),
        }

        target_room_ids.push(room_id);
    }

    if target_room_ids.is_empty() {
        return Err("No valid room IDs configured — cannot start".to_string());
    }

    slog!(
        "[matrix-bot] Listening in {} room(s): {:?}",
        target_room_ids.len(),
        target_room_ids
    );

    // Clone values needed by the notification listener and startup announcement
    // before they are moved into BotContext.
    let notif_room_ids = target_room_ids.clone();
    let notif_project_root = project_root.clone();
    let announce_room_ids = target_room_ids.clone();

    let persisted = load_history(&project_root);
    slog!(
        "[matrix-bot] Loaded persisted conversation history for {} room(s)",
        persisted.len()
    );

    // Restore persisted ambient rooms from config.
    let persisted_ambient: HashSet<String> = config
        .ambient_rooms
        .iter()
        .cloned()
        .collect();
    if !persisted_ambient.is_empty() {
        slog!(
            "[matrix-bot] Restored ambient mode for {} room(s): {:?}",
            persisted_ambient.len(),
            persisted_ambient
        );
    }

    // Create the transport abstraction based on the configured transport type.
    let transport: Arc<dyn crate::chat::ChatTransport> = match config.transport.as_str() {
        "whatsapp" => {
            if config.whatsapp_provider == "twilio" {
                slog!("[matrix-bot] Using WhatsApp/Twilio transport");
                Arc::new(crate::chat::transport::whatsapp::TwilioWhatsAppTransport::new(
                    config.twilio_account_sid.clone().unwrap_or_default(),
                    config.twilio_auth_token.clone().unwrap_or_default(),
                    config.twilio_whatsapp_number.clone().unwrap_or_default(),
                ))
            } else {
                slog!("[matrix-bot] Using WhatsApp/Meta transport");
                Arc::new(crate::chat::transport::whatsapp::WhatsAppTransport::new(
                    config.whatsapp_phone_number_id.clone().unwrap_or_default(),
                    config.whatsapp_access_token.clone().unwrap_or_default(),
                    config
                        .whatsapp_notification_template
                        .clone()
                        .unwrap_or_else(|| "pipeline_notification".to_string()),
                ))
            }
        }
        _ => {
            slog!("[matrix-bot] Using Matrix transport");
            Arc::new(super::super::transport_impl::MatrixTransport::new(client.clone()))
        }
    };

    let bot_name = config
        .display_name
        .clone()
        .unwrap_or_else(|| "Assistant".to_string());
    let announce_bot_name = bot_name.clone();

    let timer_store = Arc::new(crate::chat::timer::TimerStore::load(
        project_root.join(".huskies").join("timers.json"),
    ));
    crate::chat::timer::spawn_timer_tick_loop(
        Arc::clone(&timer_store),
        Arc::clone(&agents),
        project_root.clone(),
    );
    // Auto-schedule timers when an agent hits a hard rate limit.
    crate::chat::timer::spawn_rate_limit_auto_scheduler(
        Arc::clone(&timer_store),
        watcher_rx_auto,
    );

    let ctx = BotContext {
        bot_user_id,
        target_room_ids,
        project_root,
        allowed_users: config.allowed_users,
        history: Arc::new(TokioMutex::new(persisted)),
        history_size: config.history_size,
        bot_sent_event_ids: Arc::new(TokioMutex::new(HashSet::new())),
        perm_rx,
        pending_perm_replies: Arc::new(TokioMutex::new(HashMap::new())),
        permission_timeout_secs: config.permission_timeout_secs,
        bot_name,
        ambient_rooms: Arc::new(std::sync::Mutex::new(persisted_ambient)),
        agents,
        htop_sessions: Arc::new(TokioMutex::new(HashMap::new())),
        transport: Arc::clone(&transport),
        timer_store,
    };

    slog!("[matrix-bot] Cryptographic identity verification is always ON — commands from unencrypted rooms or unverified devices are rejected");

    // Register event handlers and inject shared context.
    client.add_event_handler_context(ctx);
    client.add_event_handler(on_room_message);
    client.add_event_handler(on_to_device_verification_request);
    client.add_event_handler(on_room_verification_request);

    // Spawn the stage-transition notification listener before entering the
    // sync loop so it starts receiving watcher events immediately.
    let notif_room_id_strings: Vec<String> =
        notif_room_ids.iter().map(|r| r.to_string()).collect();
    super::super::notifications::spawn_notification_listener(
        Arc::clone(&transport),
        move || notif_room_id_strings.clone(),
        watcher_rx,
        notif_project_root,
    );

    // Spawn a shutdown watcher that sends a best-effort goodbye message to all
    // configured rooms when the server is about to stop (SIGINT/SIGTERM or rebuild).
    {
        let shutdown_transport = Arc::clone(&transport);
        let shutdown_rooms: Vec<String> =
            announce_room_ids.iter().map(|r| r.to_string()).collect();
        let shutdown_bot_name = announce_bot_name.clone();
        let mut rx = shutdown_rx;
        tokio::spawn(async move {
            // Wait until the channel holds Some(reason).
            if rx.wait_for(|v| v.is_some()).await.is_ok() {
                let reason = rx.borrow().clone();
                let notifier = crate::rebuild::BotShutdownNotifier::new(
                    shutdown_transport,
                    shutdown_rooms,
                    shutdown_bot_name,
                );
                if let Some(r) = reason {
                    notifier.notify(r).await;
                }
            }
        });
    }

    // Send a startup announcement to each configured room so users know the
    // bot is online.  This runs once per process start — the sync loop handles
    // reconnects internally so this code is never reached again on a network
    // blip or sync resumption.
    let announce_msg = format_startup_announcement(&announce_bot_name);
    let announce_html = markdown_to_html(&announce_msg);
    slog!("[matrix-bot] Sending startup announcement: {announce_msg}");
    for room_id in &announce_room_ids {
        let room_id_str = room_id.to_string();
        if let Err(e) = transport
            .send_message(&room_id_str, &announce_msg, &announce_html)
            .await
        {
            slog!("[matrix-bot] Failed to send startup announcement to {room_id}: {e}");
        }
    }

    slog!("[matrix-bot] Starting Matrix sync loop");

    // Retry state — shared across `Fn` closure invocations via Arc atomics.
    const MAX_BACKOFF_SECS: u64 = 300;
    const INITIAL_BACKOFF_SECS: u64 = 5;
    let backoff = Arc::new(AtomicU64::new(INITIAL_BACKOFF_SECS));
    let was_disconnected = Arc::new(AtomicBool::new(false));

    let sync_transport = Arc::clone(&transport);
    let sync_rooms: Vec<String> = announce_room_ids.iter().map(|r| r.to_string()).collect();
    let sync_bot_name = announce_bot_name.clone();

    let backoff_cb = Arc::clone(&backoff);
    let was_disconnected_cb = Arc::clone(&was_disconnected);

    // Use sync_with_result_callback so transient errors (network blips, DNS
    // hiccups, temporary homeserver outages) are handled in the callback
    // rather than bubbling up as fatal errors.  Fatal errors (HTTP 401/403)
    // still terminate the loop and propagate to the caller.
    client
        .sync_with_result_callback(SyncSettings::default(), move |result| {
            let backoff = Arc::clone(&backoff_cb);
            let was_disconnected = Arc::clone(&was_disconnected_cb);
            let recovery_transport = Arc::clone(&sync_transport);
            let recovery_rooms = sync_rooms.clone();
            let recovery_bot_name = sync_bot_name.clone();
            async move {
                match result {
                    Ok(_) => {
                        // If we previously lost the connection, announce recovery.
                        if was_disconnected.swap(false, Ordering::Relaxed) {
                            backoff.store(INITIAL_BACKOFF_SECS, Ordering::Relaxed);
                            slog!("[matrix-bot] Reconnected to homeserver — resuming normal operation");
                            let msg = format!(
                                "⚡ **{recovery_bot_name}** reconnected to homeserver."
                            );
                            let html = format!(
                                "<p>⚡ <strong>{recovery_bot_name}</strong> reconnected to homeserver.</p>"
                            );
                            for room_id in &recovery_rooms {
                                if let Err(e) = recovery_transport
                                    .send_message(room_id, &msg, &html)
                                    .await
                                {
                                    slog!(
                                        "[matrix-bot] Failed to send recovery notification to {room_id}: {e}"
                                    );
                                }
                            }
                        }
                        Ok(LoopCtrl::Continue)
                    }
                    Err(e) if is_fatal_sync_error(&e) => Err(e),
                    Err(e) => {
                        // Transient error: log, back off, and let the stream retry.
                        let delay = backoff.load(Ordering::Relaxed);
                        slog!("[matrix-bot] Sync warning (retrying in {delay}s): {e}");
                        was_disconnected.store(true, Ordering::Relaxed);
                        tokio::time::sleep(std::time::Duration::from_secs(delay)).await;
                        let new_delay = (delay * 2).min(MAX_BACKOFF_SECS);
                        backoff.store(new_delay, Ordering::Relaxed);
                        Ok(LoopCtrl::Continue)
                    }
                }
            }
        })
        .await
        .map_err(|e| format!("Matrix sync error: {e}"))?;

    Ok(())
}

/// Returns `true` for errors that indicate the bot's session is permanently
/// invalid (HTTP 401 Unauthorized or 403 Forbidden).  All other errors —
/// network failures, timeouts, transient 5xx responses — are considered
/// recoverable and should be retried with exponential back-off.
fn is_fatal_sync_error(e: &matrix_sdk::Error) -> bool {
    e.as_client_api_error()
        .map(|api_err| {
            let code = api_err.status_code.as_u16();
            code == 401 || code == 403
        })
        .unwrap_or(false)
}

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

    /// An I/O error (e.g. connection refused) must NOT be treated as fatal so
    /// that the sync loop retries rather than shutting the bot down.
    #[test]
    fn io_error_is_not_fatal() {
        let e: matrix_sdk::Error =
            std::io::Error::new(std::io::ErrorKind::ConnectionRefused, "connection refused")
                .into();
        assert!(!is_fatal_sync_error(&e));
    }

    /// Exponential back-off must clamp at MAX_BACKOFF_SECS (300 s) regardless
    /// of how many consecutive failures occur.
    #[test]
    fn backoff_clamps_at_max() {
        const MAX_BACKOFF_SECS: u64 = 300;
        let mut delay = 5u64;
        for _ in 0..20 {
            delay = (delay * 2).min(MAX_BACKOFF_SECS);
        }
        assert_eq!(delay, MAX_BACKOFF_SECS);
    }

    /// Back-off must at least double each step before clamping.
    #[test]
    fn backoff_doubles_each_step() {
        const MAX_BACKOFF_SECS: u64 = 300;
        let steps: Vec<u64> = std::iter::successors(Some(5u64), |&d| {
            let next = (d * 2).min(MAX_BACKOFF_SECS);
            if next < MAX_BACKOFF_SECS { Some(next) } else { None }
        })
        .collect();
        // First few steps: 5, 10, 20, 40, 80, 160
        assert_eq!(steps[0], 5);
        assert_eq!(steps[1], 10);
        assert_eq!(steps[2], 20);
        assert_eq!(steps[3], 40);
    }
}