//! Proactive Sync Module - GRASP-02 v4 Implementation
//!
//! This module implements proactive synchronization of repository data from external
//! relays based on relay URLs listed in 30617 repository announcements.
//!
//! ## Architecture
//!
//! The sync system uses three index structures:
//! - `RepoSyncIndex` - What we WANT to sync (source of truth from self-subscription)
//! - `RelaySyncIndex` - What we have CONFIRMED syncing + connection state
//! - `PendingSyncIndex` - In-flight batches awaiting EOSE confirmation
//!
//! See `docs/explanation/grasp-02-proactive-sync-v4.md` for full design details.

pub mod algorithms;
pub mod filters;
pub mod health;
pub mod relay_connection;
pub mod self_subscriber;

// Re-export core algorithm types
pub use algorithms::{AddFilters, RelaySyncNeeds};

// Re-export relay connection types
pub use relay_connection::{RelayConnection, RelayEvent};

// Re-export self-subscriber types
pub use self_subscriber::{RelayAction, SelfSubscriber};

// Re-export health tracking types
pub use health::RelayHealthTracker;

use std::collections::{HashMap, HashSet};
use std::sync::Arc;

use nostr_sdk::prelude::*;
use prometheus::{IntCounterVec, IntGauge, IntGaugeVec, Opts, Registry};
use tokio::sync::RwLock;

use crate::config::Config;
use crate::nostr::builder::{Nip34WritePolicy, SharedDatabase};

// =============================================================================
// Type Aliases for Index Structures
// =============================================================================

/// What we WANT to sync - derived from events received via self-subscription.
/// Updated immediately when self-subscriber batch fires.
/// Key: repo addressable ref - 30617:pubkey:identifier
pub type RepoSyncIndex = Arc<RwLock<HashMap<String, RepoSyncNeeds>>>;

/// What we have CONFIRMED syncing - includes connection state for integrated lifecycle.
/// Key: relay URL
pub type RelaySyncIndex = Arc<RwLock<HashMap<String, RelayState>>>;

/// Tracks batches of subscriptions that are in-flight, awaiting EOSE.
/// Each batch has its own ID and can confirm independently.
/// Key: relay URL
pub type PendingSyncIndex = Arc<RwLock<HashMap<String, Vec<PendingBatch>>>>;

// =============================================================================
// Supporting Data Structures
// =============================================================================

/// What repos and root events need to be synced
#[derive(Debug, Clone, Default)]
pub struct RepoSyncNeeds {
    /// Relay URLs listed in this repo's 30617 announcement
    pub relays: HashSet<String>,
    /// Root event IDs - 1617/1618/1619/1621 - that reference this repo
    pub root_events: HashSet<EventId>,
}

/// Connection status for a relay
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum ConnectionStatus {
    /// Not currently connected
    #[default]
    Disconnected,
    /// Connection attempt in progress
    Connecting,
    /// Successfully connected and subscribed
    Connected,
}

/// Complete state for a single relay - combines sync needs with connection lifecycle
#[derive(Debug)]
pub struct RelayState {
    /// Repos we have confirmed syncing from this relay
    pub repos: HashSet<String>,
    /// Root events we have confirmed tracking
    pub root_events: HashSet<EventId>,
    /// If true, never disconnect this relay
    pub is_bootstrap: bool,
    /// Current connection status
    pub connection_status: ConnectionStatus,
    /// When we last successfully connected - used for since filter on reconnect
    pub last_connected: Option<Timestamp>,
    /// When we disconnected - for 15-minute state retention rule
    pub disconnected_at: Option<Timestamp>,
    // The active connection - will be added in Phase 4
    // pub connection: Option<RelayConnection>,
}

impl Default for RelayState {
    fn default() -> Self {
        Self {
            repos: HashSet::new(),
            root_events: HashSet::new(),
            is_bootstrap: false,
            connection_status: ConnectionStatus::Disconnected,
            last_connected: None,
            disconnected_at: None,
        }
    }
}

impl RelayState {
    /// Check if state should be cleared based on 15-minute rule
    pub fn should_clear_state(&self) -> bool {
        match self.disconnected_at {
            Some(disconnected) => {
                let now = Timestamp::now();
                now.as_secs().saturating_sub(disconnected.as_secs()) > 900 // 15 minutes
            }
            None => false, // Still connected or never connected
        }
    }

    /// Clear repos and root_events - called when reconnect takes > 15 minutes
    pub fn clear_sync_state(&mut self) {
        self.repos.clear();
        self.root_events.clear();
    }
}

/// A batch of items pending EOSE confirmation
#[derive(Debug, Clone)]
pub struct PendingBatch {
    /// Unique ID for this batch - for debugging/logging
    pub batch_id: u64,
    /// The items this batch is syncing
    pub items: PendingItems,
    /// Subscription IDs that must ALL receive EOSE before confirming
    pub outstanding_subs: HashSet<SubscriptionId>,
}

/// Items included in a pending batch
#[derive(Debug, Clone, Default)]
pub struct PendingItems {
    /// Repos being synced in this batch
    pub repos: HashSet<String>,
    /// Root events being synced in this batch
    pub root_events: HashSet<EventId>,
}

// =============================================================================
// SyncMetrics - Prometheus Metrics for Sync System
// =============================================================================

/// Prometheus metrics for the proactive sync system.
///
/// Tracks relay connections, sync progress, and operational statistics.
/// Following the comprehensive v3 metrics design.
#[derive(Clone)]
pub struct SyncMetrics {
    // === Connection metrics ===
    /// Per-relay connection status (1=connected, 0=disconnected)
    relay_connected: IntGaugeVec,
    /// Connection attempts by relay and result (success/failure)
    connection_attempts_total: IntCounterVec,

    // === Event metrics ===
    /// Events synced by source (live/startup/reconnect/daily)
    events_total: IntCounterVec,

    // === Summary metrics ===
    /// Total relays discovered and tracked
    relays_tracked_total: IntGauge,
    /// Currently connected relay count
    relays_connected_total: IntGauge,
}

impl SyncMetrics {
    /// Register sync metrics with a Prometheus registry.
    ///
    /// Returns an error if metrics are already registered (e.g., in tests).
    pub fn register(registry: &Registry) -> Result<Self, prometheus::Error> {
        // Connection metrics
        let relay_connected = IntGaugeVec::new(
            Opts::new(
                "ngit_sync_relay_connected",
                "Relay connection status (1=connected, 0=disconnected)",
            ),
            &["relay"],
        )?;
        registry.register(Box::new(relay_connected.clone()))?;

        let connection_attempts_total = IntCounterVec::new(
            Opts::new(
                "ngit_sync_connection_attempts_total",
                "Total connection attempts by relay and result",
            ),
            &["relay", "result"],
        )?;
        registry.register(Box::new(connection_attempts_total.clone()))?;

        // Event metrics
        let events_total = IntCounterVec::new(
            Opts::new(
                "ngit_sync_events_total",
                "Total events synced by source type",
            ),
            &["source"],
        )?;
        registry.register(Box::new(events_total.clone()))?;

        // Summary metrics
        let relays_tracked_total = IntGauge::with_opts(Opts::new(
            "ngit_sync_relays_tracked_total",
            "Total number of relays discovered and tracked",
        ))?;
        registry.register(Box::new(relays_tracked_total.clone()))?;

        let relays_connected_total = IntGauge::with_opts(Opts::new(
            "ngit_sync_relays_connected_total",
            "Number of currently connected relays",
        ))?;
        registry.register(Box::new(relays_connected_total.clone()))?;

        Ok(Self {
            relay_connected,
            connection_attempts_total,
            events_total,
            relays_tracked_total,
            relays_connected_total,
        })
    }

    // === Connection Recording Methods ===

    /// Record a connection attempt (success or failure)
    pub fn record_connection_attempt(&self, relay: &str, success: bool) {
        let result = if success { "success" } else { "failure" };
        self.connection_attempts_total
            .with_label_values(&[relay, result])
            .inc();
    }

    /// Set relay connection status
    pub fn set_relay_connected(&self, relay: &str, connected: bool) {
        self.relay_connected
            .with_label_values(&[relay])
            .set(if connected { 1 } else { 0 });
    }

    /// Increment connected count
    pub fn inc_connected_count(&self) {
        self.relays_connected_total.inc();
    }

    /// Decrement connected count
    pub fn dec_connected_count(&self) {
        self.relays_connected_total.dec();
    }

    // === Event Recording Methods ===

    /// Record a synced event by source type
    ///
    /// Source types:
    /// - "live" - Real-time subscription events
    /// - "startup" - Events from startup catchup
    /// - "reconnect" - Events from reconnection catchup
    pub fn record_event(&self, source: &str) {
        self.events_total.with_label_values(&[source]).inc();
    }

    /// Record multiple events synced by source type
    pub fn record_events(&self, source: &str, count: u64) {
        self.events_total
            .with_label_values(&[source])
            .inc_by(count);
    }

    // === Summary Recording Methods ===

    /// Set the total tracked relay count
    pub fn set_tracked_count(&self, count: i64) {
        self.relays_tracked_total.set(count);
    }

    /// Increment tracked relay count
    pub fn inc_tracked_count(&self) {
        self.relays_tracked_total.inc();
    }

    /// Get current tracked relay count
    pub fn get_tracked_count(&self) -> i64 {
        self.relays_tracked_total.get()
    }

    /// Get current connected relay count
    pub fn get_connected_count(&self) -> i64 {
        self.relays_connected_total.get()
    }
}

/// Event source types for metrics tracking
pub mod event_source {
    /// Real-time subscription events
    pub const LIVE: &str = "live";
    /// Events from startup catchup
    pub const STARTUP: &str = "startup";
    /// Events from reconnection catchup
    pub const RECONNECT: &str = "reconnect";
}

// =============================================================================
// SyncManager - Main Entry Point
// =============================================================================

/// Manages proactive synchronization with external relays
///
/// The SyncManager runs as a background task, subscribing to repository
/// announcements on the local relay and syncing data from external relays
/// listed in those announcements.
#[allow(dead_code)] // Fields will be used in later phases
pub struct SyncManager {
    /// Bootstrap relay URL for initial sync (optional)
    bootstrap_relay_url: Option<String>,
    /// Our service domain - used for filtering relevant repos
    service_domain: String,
    /// Database for event storage and queries
    database: SharedDatabase,
    /// Write policy for validating incoming events
    write_policy: Nip34WritePolicy,
    /// Configuration reference for sync settings
    config: Config,
    /// What we want to sync (source of truth)
    repo_sync_index: RepoSyncIndex,
    /// What we've confirmed syncing + connection state
    relay_sync_index: RelaySyncIndex,
    /// In-flight subscription batches
    pending_sync_index: PendingSyncIndex,
    /// Active relay connections - keyed by relay URL
    connections: HashMap<String, RelayConnection>,
    /// Health tracker for relay connection state
    health_tracker: Arc<RelayHealthTracker>,
    /// Counter for generating unique batch IDs
    next_batch_id: u64,
}

impl SyncManager {
    /// Create a new SyncManager
    ///
    /// # Arguments
    /// * `bootstrap_relay_url` - Optional relay URL for initial historical sync
    /// * `service_domain` - The domain this relay serves (for filtering repos)
    /// * `database` - Shared database for event storage
    /// * `write_policy` - Policy for validating events before storage
    /// * `config` - Configuration for sync settings
    pub fn new(
        bootstrap_relay_url: Option<String>,
        service_domain: String,
        database: SharedDatabase,
        write_policy: Nip34WritePolicy,
        config: &Config,
    ) -> Self {
        Self {
            bootstrap_relay_url,
            service_domain,
            database,
            write_policy,
            config: config.clone(),
            repo_sync_index: Arc::new(RwLock::new(HashMap::new())),
            relay_sync_index: Arc::new(RwLock::new(HashMap::new())),
            pending_sync_index: Arc::new(RwLock::new(HashMap::new())),
            connections: HashMap::new(),
            health_tracker: Arc::new(RelayHealthTracker::new(config)),
            next_batch_id: 0,
        }
    }

    /// Run the sync manager
    ///
    /// Coordinates all sync components:
    /// 1. Spawns self-subscriber to monitor own relay for announcements
    /// 2. Connects to bootstrap relay if configured
    /// 3. Handles relay actions from self-subscriber
    pub async fn run(self) {
        use tokio::sync::mpsc;

        tracing::info!(
            bootstrap_relay = ?self.bootstrap_relay_url,
            service_domain = %self.service_domain,
            "SyncManager starting"
        );

        // 1. Create action channel for self-subscriber -> manager communication
        let (action_tx, mut action_rx) = mpsc::channel::<RelayAction>(100);

        // 2. Spawn self-subscriber
        let self_subscriber = SelfSubscriber::new(
            format!("ws://{}", self.service_domain),
            self.service_domain.clone(),
            Arc::clone(&self.repo_sync_index),
            action_tx,
        );
        tokio::spawn(async move { self_subscriber.run().await });

        // 3. Connect to bootstrap relay if configured
        if let Some(ref bootstrap_url) = self.bootstrap_relay_url {
            self.spawn_relay_connection(bootstrap_url.clone()).await;
        }

        // 4. Main loop - handle actions from self-subscriber
        loop {
            tokio::select! {
                action = action_rx.recv() => {
                    match action {
                        Some(RelayAction::SpawnRelay { relay_url, repos }) => {
                            // Check if relay already exists
                            let relay_index = self.relay_sync_index.read().await;
                            let exists = relay_index.contains_key(&relay_url);
                            drop(relay_index);

                            if !exists {
                                tracing::info!(relay = %relay_url, "Spawning new relay connection");
                                self.spawn_relay_with_layer2(relay_url, repos).await;
                            } else {
                                tracing::debug!(
                                    relay = %relay_url,
                                    "Relay already exists, considering AddFilters"
                                );
                                // For MVP, we don't handle AddFilters - just log
                                // Full implementation would call subscribe_filters on existing connection
                            }
                        }
                        Some(RelayAction::AddFilters { relay_url, repos }) => {
                            tracing::debug!(
                                relay = %relay_url,
                                repo_count = repos.len(),
                                "AddFilters action (MVP: not implemented)"
                            );
                            // For MVP, not implemented - full version would add Layer 2 filters
                            // to existing relay connection
                        }
                        None => break,
                    }
                }
            }
        }
    }

    /// Spawn relay connection with Layer 2 filters for specific repos
    ///
    /// Used when discovering relays from announcements. Connects to the relay,
    /// subscribes to Layer 1 (announcements) AND Layer 2+3 filters for the
    /// specific repos we want to sync.
    async fn spawn_relay_with_layer2(
        &self,
        relay_url: String,
        repos: HashMap<String, HashSet<EventId>>,
    ) {
        use crate::sync::filters::build_layer2_and_layer3_filters;
        use tokio::sync::mpsc;

        let database = Arc::clone(&self.database);
        let write_policy = self.write_policy.clone();
        let relay_sync_index = Arc::clone(&self.relay_sync_index);

        // Create relay connection
        let connection = RelayConnection::new(relay_url.clone());

        // Connect and subscribe to Layer 1 (announcements)
        if let Err(e) = connection.connect_and_subscribe(None).await {
            tracing::error!(relay = %relay_url, error = %e, "Failed to connect to relay");
            return;
        }

        // Mark as connected in relay sync index
        {
            let mut index = relay_sync_index.write().await;
            index.insert(
                relay_url.clone(),
                RelayState {
                    repos: repos.keys().cloned().collect(),
                    root_events: repos.values().flatten().cloned().collect(),
                    is_bootstrap: false,
                    connection_status: ConnectionStatus::Connected,
                    last_connected: Some(Timestamp::now()),
                    disconnected_at: None,
                },
            );
        }

        // Subscribe to Layer 2+3 filters for the repos
        let repo_ids: HashSet<String> = repos.keys().cloned().collect();
        let root_events: HashSet<EventId> = repos.values().flatten().cloned().collect();
        let filters = build_layer2_and_layer3_filters(&repo_ids, &root_events, None);

        for filter in filters {
            if let Err(e) = connection.subscribe_filter(filter).await {
                tracing::error!(
                    relay = %relay_url,
                    error = %e,
                    "Failed to subscribe to Layer 2 filter"
                );
            }
        }

        tracing::info!(
            relay = %relay_url,
            repo_count = repos.len(),
            "Connected to discovered relay with Layer 2+3 filters"
        );

        // Create event channel
        let (event_tx, mut event_rx) = mpsc::channel::<RelayEvent>(1000);

        // Spawn event loop
        tokio::spawn(async move {
            connection.run_event_loop(event_tx).await;
        });

        // Spawn event processor
        let relay_url_clone = relay_url.clone();
        tokio::spawn(async move {
            while let Some(relay_event) = event_rx.recv().await {
                match relay_event {
                    RelayEvent::Event(event) => {
                        Self::process_event_static(
                            &event,
                            &relay_url_clone,
                            &database,
                            &write_policy,
                        )
                        .await;
                    }
                    RelayEvent::EndOfStoredEvents(_) => {
                        tracing::debug!(relay = %relay_url_clone, "EOSE received");
                    }
                    RelayEvent::Closed(_) | RelayEvent::Shutdown => {
                        tracing::info!(relay = %relay_url_clone, "Relay disconnected");
                        break;
                    }
                }
            }
        });
    }

    /// Spawn a relay connection and start its event loop
    async fn spawn_relay_connection(&self, relay_url: String) {
        use tokio::sync::mpsc;

        let database = Arc::clone(&self.database);
        let write_policy = self.write_policy.clone();
        let relay_sync_index = Arc::clone(&self.relay_sync_index);

        // Create relay connection
        let connection = RelayConnection::new(relay_url.clone());

        // Connect and subscribe to Layer 1
        if let Err(e) = connection.connect_and_subscribe(None).await {
            tracing::error!("Failed to connect to relay {}: {}", relay_url, e);
            return;
        }

        // Mark as connected in relay sync index
        {
            let mut index = relay_sync_index.write().await;
            index.insert(
                relay_url.clone(),
                RelayState {
                    repos: HashSet::new(),
                    root_events: HashSet::new(),
                    is_bootstrap: true,
                    connection_status: ConnectionStatus::Connected,
                    last_connected: Some(Timestamp::now()),
                    disconnected_at: None,
                },
            );
        }

        // Create event channel
        let (event_tx, mut event_rx) = mpsc::channel::<RelayEvent>(1000);

        // Spawn event loop
        tokio::spawn(async move {
            connection.run_event_loop(event_tx).await;
        });

        // Spawn event processor
        let relay_url_clone = relay_url.clone();
        tokio::spawn(async move {
            while let Some(relay_event) = event_rx.recv().await {
                match relay_event {
                    RelayEvent::Event(event) => {
                        Self::process_event_static(&event, &relay_url_clone, &database, &write_policy)
                            .await;
                    }
                    RelayEvent::EndOfStoredEvents(_) => {
                        tracing::debug!("EOSE from {}", relay_url_clone);
                    }
                    RelayEvent::Closed(_) | RelayEvent::Shutdown => {
                        tracing::info!("Relay {} disconnected", relay_url_clone);
                        break;
                    }
                }
            }
        });
    }

    /// Process a single event from a relay (static version for spawned tasks)
    async fn process_event_static(
        event: &Event,
        relay_url: &str,
        database: &SharedDatabase,
        write_policy: &Nip34WritePolicy,
    ) {
        use nostr_relay_builder::prelude::{PolicyResult, WritePolicy};
        use std::net::{IpAddr, Ipv4Addr, SocketAddr};

        // Check if event already exists
        match database.event_by_id(&event.id).await {
            Ok(Some(_)) => {
                tracing::trace!(event_id = %event.id, "Event already exists, skipping");
                return;
            }
            Err(e) => {
                tracing::warn!(event_id = %event.id, error = %e, "Database error checking event");
                return;
            }
            Ok(None) => {} // Continue processing
        }

        // Apply write policy using a dummy address (sync events aren't from network clients)
        let dummy_addr = SocketAddr::new(IpAddr::V4(Ipv4Addr::LOCALHOST), 0);
        let result = write_policy.admit_event(event, &dummy_addr).await;

        match result {
            PolicyResult::Accept => {
                // Save event
                if let Err(e) = database.save_event(event).await {
                    tracing::error!(
                        event_id = %event.id,
                        relay = %relay_url,
                        error = %e,
                        "Failed to save synced event"
                    );
                } else {
                    tracing::debug!(
                        event_id = %event.id,
                        relay = %relay_url,
                        kind = %event.kind.as_u16(),
                        "Saved synced event"
                    );
                }
            }
            PolicyResult::Reject(reason) => {
                tracing::debug!(
                    event_id = %event.id,
                    relay = %relay_url,
                    reason = %reason,
                    "Event rejected by write policy"
                );
            }
        }
    }
}