use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::sync::RwLock;
use tauri::{AppHandle, Emitter};
use serde::{Serialize, Deserialize};

use crate::jellyfin::http_client::HttpClient;

// Offline recovery probe interval.
// Reachability while online is driven by real repository traffic, so there is
// no online polling. While offline we probe quickly to detect the server
// returning even when no user traffic is flowing.
const RETRY_CHECK_INTERVAL_MS: u64 = 5000; // 5 seconds when offline

// Time-window debounce for declaring the server offline.
// A single dropped request must not trip the banner: we only flip to offline
// once network failures have persisted continuously for this window with no
// intervening success. Recovery (online) is instant on the first success.
const OFFLINE_CONFIRM_WINDOW: Duration = Duration::from_secs(5);

/// Connectivity status
#[derive(specta::Type, Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ConnectivityStatus {
    /// Whether the Jellyfin server is reachable
    pub is_server_reachable: bool,
    /// Last time we checked server reachability (ISO 8601 string)
    pub last_checked: Option<String>,
    /// Error message from last connectivity check
    pub connection_error: Option<String>,
    /// Whether we're currently checking connectivity
    pub is_checking: bool,
}

impl Default for ConnectivityStatus {
    fn default() -> Self {
        Self {
            // Start optimistic - assume online until proven otherwise
            // This prevents the app from appearing offline on startup
            is_server_reachable: true,
            last_checked: None,
            connection_error: None,
            is_checking: false,
        }
    }
}

/// Connectivity change event emitted to frontend
#[derive(specta::Type, Debug, Clone, Serialize)]
#[serde(rename_all = "camelCase")]
struct ConnectivityChangeEvent {
    is_reachable: bool,
}

/// Shared reachability state and transition logic.
///
/// This is the single place that mutates reachability and emits events. It is
/// cheap to clone (all fields are `Arc`/`Option`) and is shared by:
/// - the `ConnectivityMonitor` (commands, offline recovery probe), and
/// - `OnlineRepository`, which reports the outcome of every server request.
///
/// Reachability is therefore driven by real traffic; the probe only fills the
/// gap while offline.
#[derive(Clone)]
pub struct ConnectivityReporter {
    status: Arc<RwLock<ConnectivityStatus>>,
    /// Timestamp of the first network failure in the current failure streak.
    /// Used to debounce the transition to offline (see `OFFLINE_CONFIRM_WINDOW`).
    first_failure_at: Arc<RwLock<Option<Instant>>>,
    app_handle: Option<AppHandle>,
}

impl ConnectivityReporter {
    fn new(status: Arc<RwLock<ConnectivityStatus>>, app_handle: Option<AppHandle>) -> Self {
        Self {
            status,
            first_failure_at: Arc::new(RwLock::new(None)),
            app_handle,
        }
    }

    /// Current reachability as seen by this reporter (shared with the monitor
    /// and the UI). Useful for callers that want to branch on connectivity.
    #[allow(dead_code)] // public API; currently only exercised by cross-module tests
    pub async fn is_reachable(&self) -> bool {
        self.status.read().await.is_server_reachable
    }

    /// Test-only: force the reporter into the offline state without going through
    /// the debounce, so other modules' tests can set up an "offline" precondition.
    #[cfg(test)]
    pub async fn mark_unreachable_for_test(&self) {
        self.apply_probe_result(false, Some("forced offline (test)".to_string()))
            .await;
    }

    /// Report that a real server request succeeded (or that the server answered
    /// at all, e.g. with 401/404/5xx). The server is up — recover instantly.
    pub async fn report_success(&self) {
        *self.first_failure_at.write().await = None;
        self.set_reachable(true, None).await;
    }

    /// Report that a real server request failed with a network-level error
    /// (connection refused, timeout, DNS). Subject to the time-window debounce:
    /// we only flip to offline once failures have persisted for
    /// `OFFLINE_CONFIRM_WINDOW` with no intervening success.
    pub async fn report_network_failure(&self, error: Option<String>) {
        // If already offline, nothing to debounce.
        if !self.status.read().await.is_server_reachable {
            return;
        }

        let now = Instant::now();
        let streak_start = {
            let mut first = self.first_failure_at.write().await;
            *first.get_or_insert(now)
        };

        if now.duration_since(streak_start) >= OFFLINE_CONFIRM_WINDOW {
            log::warn!(
                "[ConnectivityMonitor] Network failures sustained for {:?}; declaring offline",
                OFFLINE_CONFIRM_WINDOW
            );
            self.set_reachable(false, error).await;
        } else {
            log::debug!(
                "[ConnectivityMonitor] Network failure within debounce window; not yet offline"
            );
        }
    }

    /// Apply a deliberate reachability probe result (offline recovery probe or a
    /// manual check). Unlike `report_network_failure`, a probe is an explicit
    /// reachability test, so its result is applied immediately without debounce.
    async fn apply_probe_result(&self, is_reachable: bool, error: Option<String>) {
        if is_reachable {
            *self.first_failure_at.write().await = None;
        }
        self.set_reachable(is_reachable, error).await;
    }

    /// Core transition: update status and emit events only on an actual change.
    async fn set_reachable(&self, is_reachable: bool, error: Option<String>) {
        let was_reachable = {
            let mut status = self.status.write().await;
            let was = status.is_server_reachable;
            status.is_server_reachable = is_reachable;
            status.last_checked = Some(chrono::Utc::now().to_rfc3339());
            status.connection_error = if is_reachable {
                None
            } else {
                Some(error.unwrap_or_else(|| "Server unreachable".to_string()))
            };
            status.is_checking = false;
            was
        };

        if is_reachable != was_reachable {
            self.emit_connectivity_change(is_reachable).await;
            if is_reachable {
                self.emit_server_reconnected().await;
            }
        }
    }

    /// Emit connectivity change event to frontend
    async fn emit_connectivity_change(&self, is_reachable: bool) {
        if let Some(app_handle) = &self.app_handle {
            let event = ConnectivityChangeEvent { is_reachable };
            if let Err(e) = app_handle.emit("connectivity:changed", event) {
                log::error!("[ConnectivityMonitor] Failed to emit connectivity change event: {}", e);
            } else {
                log::info!("[ConnectivityMonitor] Emitted connectivity change: {}", is_reachable);
            }
        }
    }

    /// Emit server reconnected event to frontend
    async fn emit_server_reconnected(&self) {
        if let Some(app_handle) = &self.app_handle {
            if let Err(e) = app_handle.emit("connectivity:reconnected", ()) {
                log::error!("[ConnectivityMonitor] Failed to emit reconnection event: {}", e);
            } else {
                log::info!("[ConnectivityMonitor] Emitted server reconnected event");
            }
        }
    }
}

/// Connectivity monitor for tracking server reachability.
///
/// Reachability is driven primarily by real repository traffic via the shared
/// [`ConnectivityReporter`]. The monitor itself only runs an offline recovery
/// probe (see `start_monitoring`) and serves the connectivity Tauri commands.
pub struct ConnectivityMonitor {
    server_url: Arc<RwLock<Option<String>>>,
    http_client: Arc<HttpClient>,
    reporter: ConnectivityReporter,
    is_monitoring: Arc<AtomicBool>,
}

impl ConnectivityMonitor {
    /// Create a new connectivity monitor
    pub fn new(http_client: HttpClient) -> Self {
        let status = Arc::new(RwLock::new(ConnectivityStatus::default()));
        Self {
            server_url: Arc::new(RwLock::new(None)),
            http_client: Arc::new(http_client),
            reporter: ConnectivityReporter::new(status, None),
            is_monitoring: Arc::new(AtomicBool::new(false)),
        }
    }

    /// Set the Tauri app handle for event emission.
    /// Must be called before the reporter is shared with the repository.
    pub fn set_app_handle(&mut self, app_handle: AppHandle) {
        self.reporter.app_handle = Some(app_handle);
    }

    /// Get a cheap, cloneable reporter so the repository can feed server
    /// outcomes into the same reachability state the UI observes.
    pub fn reporter(&self) -> ConnectivityReporter {
        self.reporter.clone()
    }

    /// Update the server URL
    pub async fn set_server_url(&self, url: String) {
        log::info!("[ConnectivityMonitor] Setting server URL: {}", url);
        *self.server_url.write().await = Some(url);

        // Check new server immediately
        log::info!("[ConnectivityMonitor] Checking reachability of new server...");
        let is_reachable = self.check_reachability().await;
        log::info!("[ConnectivityMonitor] New server is {}", if is_reachable { "REACHABLE" } else { "UNREACHABLE" });
    }

    /// Get current connectivity status
    pub async fn get_status(&self) -> ConnectivityStatus {
        self.reporter.status.read().await.clone()
    }

    /// Deliberately probe the server's reachability (manual check / recovery probe).
    /// The result is applied immediately (no debounce) since this is an explicit test.
    pub async fn check_reachability(&self) -> bool {
        {
            let mut status = self.reporter.status.write().await;
            status.is_checking = true;
        }

        let server_url = self.server_url.read().await.clone();

        let Some(url) = server_url else {
            log::warn!("[ConnectivityMonitor] Cannot check reachability: No server URL configured");
            self.reporter
                .apply_probe_result(false, Some("No server URL configured".to_string()))
                .await;
            return false;
        };

        let ping_url = format!("{}/System/Info/Public", url);
        log::debug!("[ConnectivityMonitor] Pinging server: {}", ping_url);

        let is_reachable = self.http_client.ping(&ping_url).await;
        log::debug!(
            "[ConnectivityMonitor] Ping result: {}",
            if is_reachable { "SUCCESS" } else { "FAILED" }
        );

        self.reporter.apply_probe_result(is_reachable, None).await;
        is_reachable
    }

    /// Mark server as reachable (called after successful API call / login)
    pub async fn mark_reachable(&self) {
        self.reporter.report_success().await;
    }

    /// Mark server as unreachable directly.
    ///
    /// Used by deliberate signals (e.g. a failed login/connect) where the caller
    /// knows the server is unreachable now. Repository traffic should prefer
    /// `reporter().report_network_failure()` so the debounce applies.
    pub async fn mark_unreachable(&self, error: Option<String>) {
        self.reporter.apply_probe_result(false, error).await;
    }

    /// Start the offline recovery probe.
    ///
    /// While **online**, reachability is kept fresh by real traffic, so the probe
    /// idles. While **offline**, it polls `/System/Info/Public` every
    /// `RETRY_CHECK_INTERVAL_MS` to detect the server returning even when no user
    /// traffic is flowing.
    pub async fn start_monitoring(&self) {
        if self.is_monitoring.swap(true, Ordering::SeqCst) {
            log::info!("[ConnectivityMonitor] Already monitoring");
            return;
        }

        log::info!("[ConnectivityMonitor] Starting connectivity monitoring (offline recovery probe)");

        // Perform an immediate check so startup reflects reality quickly.
        let is_reachable = self.check_reachability().await;
        log::info!("[ConnectivityMonitor] Initial connectivity check: {}", if is_reachable { "ONLINE" } else { "OFFLINE" });

        let is_monitoring = Arc::clone(&self.is_monitoring);
        let server_url = Arc::clone(&self.server_url);
        let http_client = Arc::clone(&self.http_client);
        let reporter = self.reporter.clone();

        tokio::spawn(async move {
            while is_monitoring.load(Ordering::SeqCst) {
                tokio::time::sleep(Duration::from_millis(RETRY_CHECK_INTERVAL_MS)).await;

                if !is_monitoring.load(Ordering::SeqCst) {
                    break;
                }

                // Only probe while offline — real traffic is the signal when online.
                if reporter.status.read().await.is_server_reachable {
                    continue;
                }

                let Some(url) = server_url.read().await.clone() else {
                    continue;
                };
                let ping_url = format!("{}/System/Info/Public", url);
                let is_reachable = http_client.ping(&ping_url).await;

                // Probe only ever recovers us to online; a failed probe leaves us
                // offline without re-emitting (no change).
                if is_reachable {
                    reporter.apply_probe_result(true, None).await;
                }
            }

            log::info!("[ConnectivityMonitor] Stopped monitoring");
        });
    }

    /// Stop monitoring connectivity
    pub fn stop_monitoring(&self) {
        log::info!("[ConnectivityMonitor] Stopping connectivity monitoring");
        self.is_monitoring.store(false, Ordering::SeqCst);
    }
}

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

    /// Build a reporter backed by a fresh (optimistic) status, with no app handle.
    /// Event emission is a no-op without a handle, which is exactly what we want
    /// for unit-testing the reachability state transitions.
    fn test_reporter() -> ConnectivityReporter {
        ConnectivityReporter::new(Arc::new(RwLock::new(ConnectivityStatus::default())), None)
    }

    async fn is_reachable(reporter: &ConnectivityReporter) -> bool {
        reporter.status.read().await.is_server_reachable
    }

    #[test]
    fn test_intervals() {
        // Offline recovery probe interval (online has no polling).
        assert_eq!(RETRY_CHECK_INTERVAL_MS, 5000);
        assert_eq!(OFFLINE_CONFIRM_WINDOW, Duration::from_secs(5));
    }

    #[tokio::test]
    async fn test_default_status() {
        let status = ConnectivityStatus::default();
        // Default is now optimistic (assume online until proven otherwise)
        assert!(status.is_server_reachable);
        assert!(status.last_checked.is_none());
        assert!(status.connection_error.is_none());
        assert!(!status.is_checking);
    }

    /// A single (or brief) network failure must NOT flip the app offline:
    /// the time-window debounce keeps us online until the failure persists.
    ///
    /// @req-test: UR-002 - Access media when online or offline
    #[tokio::test]
    async fn test_single_network_failure_does_not_go_offline() {
        let reporter = test_reporter();
        assert!(is_reachable(&reporter).await, "starts online");

        reporter
            .report_network_failure(Some("timeout".to_string()))
            .await;

        assert!(
            is_reachable(&reporter).await,
            "one network failure within the debounce window stays online"
        );
        // But the failure streak is now being tracked.
        assert!(reporter.first_failure_at.read().await.is_some());
    }

    /// Once failures persist past OFFLINE_CONFIRM_WINDOW, we flip offline.
    /// We simulate elapsed time by backdating the streak start.
    ///
    /// @req-test: UR-002 - Access media when online or offline
    #[tokio::test]
    async fn test_sustained_network_failure_goes_offline() {
        let reporter = test_reporter();

        // First failure starts the streak.
        reporter.report_network_failure(None).await;
        assert!(is_reachable(&reporter).await);

        // Backdate the streak start to before the window.
        {
            let mut first = reporter.first_failure_at.write().await;
            *first = Some(Instant::now() - OFFLINE_CONFIRM_WINDOW - Duration::from_secs(1));
        }

        // Next failure now exceeds the window → offline.
        reporter
            .report_network_failure(Some("connection refused".to_string()))
            .await;
        assert!(
            !is_reachable(&reporter).await,
            "sustained network failure flips to offline"
        );
    }

    /// A success during a failure streak clears the streak and keeps us online —
    /// recovery is instant and never trips the banner.
    #[tokio::test]
    async fn test_success_clears_failure_streak() {
        let reporter = test_reporter();

        reporter.report_network_failure(None).await;
        assert!(reporter.first_failure_at.read().await.is_some());

        reporter.report_success().await;

        assert!(is_reachable(&reporter).await);
        assert!(
            reporter.first_failure_at.read().await.is_none(),
            "success resets the debounce streak"
        );
    }

    /// First success after being offline recovers instantly (no debounce on the
    /// way back up).
    #[tokio::test]
    async fn test_recovery_is_instant() {
        let reporter = test_reporter();

        // Force offline.
        reporter.apply_probe_result(false, Some("down".to_string())).await;
        assert!(!is_reachable(&reporter).await);

        // A single success brings us straight back online.
        reporter.report_success().await;
        assert!(is_reachable(&reporter).await);
        let status = reporter.status.read().await;
        assert!(status.connection_error.is_none());
    }

    /// Server-answered errors (401/404/5xx) are reported via report_success
    /// by the repository, because the server is demonstrably reachable. This
    /// test documents that contract: report_success means "server is up".
    #[tokio::test]
    async fn test_server_answered_error_counts_as_reachable() {
        let reporter = test_reporter();

        // Simulate being offline, then the server answers (even with an error).
        reporter.apply_probe_result(false, None).await;
        assert!(!is_reachable(&reporter).await);

        // Repository maps Authentication/NotFound/Server errors to report_success.
        reporter.report_success().await;
        assert!(
            is_reachable(&reporter).await,
            "a server that answers (even with 4xx/5xx) is reachable"
        );
    }

    /// report_network_failure is a no-op once already offline (nothing to debounce,
    /// no duplicate events).
    #[tokio::test]
    async fn test_network_failure_noop_when_already_offline() {
        let reporter = test_reporter();
        reporter.apply_probe_result(false, None).await;
        assert!(!is_reachable(&reporter).await);

        // Should not panic or change state.
        reporter.report_network_failure(Some("still down".to_string())).await;
        assert!(!is_reachable(&reporter).await);
    }
}