//! Prometheus Metrics for Proactive Sync (GRASP-02)
//!
//! This module provides comprehensive sync monitoring metrics including:
//! - Connection status and attempts per relay
//! - Health state tracking (Healthy/Degraded/Dead)
//! - Event sync tracking by source (live/startup/reconnect/daily catchup)
//! - Gap events filled during catchup operations
//!
//! All metrics follow the `ngit_sync_` prefix convention.

use prometheus::{IntCounterVec, IntGauge, IntGaugeVec, Opts, Registry};

use super::health::HealthState;

/// Prometheus metrics for the proactive sync system.
///
/// Tracks relay connections, sync progress, health states, and operational statistics.
/// Designed for comprehensive monitoring of GRASP-02 proactive sync operations.
#[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,

    // === Health metrics ===
    /// Per-relay health status (healthy=1, degraded=2, dead=3)
    relay_status: IntGaugeVec,
    /// Per-relay consecutive failure count
    relay_failures: IntGaugeVec,

    // === Event metrics ===
    /// Events synced by source (live/startup/reconnect/daily)
    events_total: IntCounterVec,
    /// Gap events filled during catchup, by relay
    gap_events_total: IntCounterVec,

    // === Summary metrics ===
    /// Total relays discovered and tracked
    relays_tracked_total: IntGauge,
    /// Currently connected relay count
    relays_connected_total: IntGauge,
    /// Relays marked as dead
    relays_dead_total: IntGauge,
}

impl SyncMetrics {
    /// Register all sync metrics with the provided Prometheus registry.
    ///
    /// # Errors
    ///
    /// 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()))?;

        // Health metrics
        let relay_status = IntGaugeVec::new(
            Opts::new(
                "ngit_sync_relay_status",
                "Relay health status (1=healthy, 2=degraded, 3=dead)",
            ),
            &["relay"],
        )?;
        registry.register(Box::new(relay_status.clone()))?;

        let relay_failures = IntGaugeVec::new(
            Opts::new(
                "ngit_sync_relay_failures",
                "Consecutive failure count per relay",
            ),
            &["relay"],
        )?;
        registry.register(Box::new(relay_failures.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()))?;

        let gap_events_total = IntCounterVec::new(
            Opts::new(
                "ngit_sync_gap_events_total",
                "Gap events filled during catchup by relay",
            ),
            &["relay"],
        )?;
        registry.register(Box::new(gap_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()))?;

        let relays_dead_total = IntGauge::with_opts(Opts::new(
            "ngit_sync_relays_dead_total",
            "Number of relays marked as dead",
        ))?;
        registry.register(Box::new(relays_dead_total.clone()))?;

        Ok(Self {
            relay_connected,
            connection_attempts_total,
            relay_status,
            relay_failures,
            events_total,
            gap_events_total,
            relays_tracked_total,
            relays_connected_total,
            relays_dead_total,
        })
    }

    // === Connection Recording Methods ===

    /// Record a connection attempt (success or failure).
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL
    /// * `success` - Whether the connection attempt succeeded
    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.
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL
    /// * `connected` - Whether the relay is currently connected
    pub fn set_relay_connected(&self, relay: &str, connected: bool) {
        self.relay_connected
            .with_label_values(&[relay])
            .set(if connected { 1 } else { 0 });

        // Note: Connected count should be updated via update_connected_count() for accuracy
    }

    /// Update the total connected relay count.
    ///
    /// This directly sets the count rather than deriving it from individual relay states,
    /// which is more accurate when relay connection states are managed elsewhere.
    pub fn update_connected_count(&self, count: i64) {
        self.relays_connected_total.set(count);
    }

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

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

    // === Health Recording Methods ===

    /// Record relay health state change.
    ///
    /// Maps health states to numeric values for Prometheus:
    /// - Healthy = 1
    /// - Degraded = 2
    /// - Dead = 3
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL
    /// * `state` - The current health state
    pub fn record_health_state(&self, relay: &str, state: HealthState) {
        let state_value = match state {
            HealthState::Healthy => 1,
            HealthState::Degraded => 2,
            HealthState::Dead => 3,
        };
        self.relay_status
            .with_label_values(&[relay])
            .set(state_value);
    }

    /// Record relay failure count.
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL
    /// * `count` - The number of consecutive failures
    pub fn record_failure_count(&self, relay: &str, count: u32) {
        self.relay_failures
            .with_label_values(&[relay])
            .set(count as i64);
    }

    /// Update dead relay count.
    pub fn update_dead_count(&self, count: i64) {
        self.relays_dead_total.set(count);
    }

    /// Increment dead relay count by one.
    pub fn inc_dead_count(&self) {
        self.relays_dead_total.inc();
    }

    /// Decrement dead relay count by one.
    pub fn dec_dead_count(&self) {
        self.relays_dead_total.dec();
    }

    // === Event Recording Methods ===

    /// Record a synced event by source type.
    ///
    /// # Arguments
    ///
    /// * `source` - The event source type. Use constants from [`event_source`]:
    ///   - [`event_source::LIVE`] - Real-time subscription events
    ///   - [`event_source::STARTUP`] - Events from startup catchup
    ///   - [`event_source::RECONNECT`] - Events from reconnection catchup
    ///   - [`event_source::DAILY`] - Events from daily catchup
    pub fn record_event(&self, source: &str) {
        self.events_total.with_label_values(&[source]).inc();
    }

    /// Record multiple events synced by source type.
    ///
    /// # Arguments
    ///
    /// * `source` - The event source type (see [`record_event`](Self::record_event))
    /// * `count` - Number of events to record
    pub fn record_events(&self, source: &str, count: u64) {
        self.events_total.with_label_values(&[source]).inc_by(count);
    }

    /// Record a gap event filled during catchup.
    ///
    /// Gap events are historical events discovered during catchup that weren't
    /// received during live sync.
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL from which the gap event was received
    pub fn record_gap_event(&self, relay: &str) {
        self.gap_events_total.with_label_values(&[relay]).inc();
    }

    /// Record multiple gap events filled during catchup.
    ///
    /// # Arguments
    ///
    /// * `relay` - The relay URL from which the gap events were received
    /// * `count` - Number of gap events to record
    pub fn record_gap_events(&self, relay: &str, count: u64) {
        self.gap_events_total
            .with_label_values(&[relay])
            .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 by one.
    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()
    }

    /// Get current dead relay count.
    pub fn get_dead_count(&self) -> i64 {
        self.relays_dead_total.get()
    }
}

/// Event source types for metrics tracking.
///
/// These constants are used as labels for the `ngit_sync_events_total` metric
/// to categorize events by how they were discovered.
pub mod event_source {
    /// Real-time subscription events received during live sync.
    pub const LIVE: &str = "live";

    /// Events from startup catchup when the relay first starts.
    pub const STARTUP: &str = "startup";

    /// Events from reconnection catchup after a relay reconnects.
    pub const RECONNECT: &str = "reconnect";

    /// Events from daily catchup for drift detection.
    pub const DAILY: &str = "daily";
}

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

    fn create_test_registry() -> Registry {
        Registry::new()
    }

    #[test]
    fn test_metrics_registration() {
        let registry = create_test_registry();
        let metrics = SyncMetrics::register(&registry);
        assert!(metrics.is_ok());
    }

    #[test]
    fn test_connection_metrics() {
        let registry = create_test_registry();
        let metrics = SyncMetrics::register(&registry).unwrap();

        // Record connection attempts
        metrics.record_connection_attempt("wss://relay1.example.com", true);
        metrics.record_connection_attempt("wss://relay1.example.com", false);
        metrics.record_connection_attempt("wss://relay2.example.com", true);

        // Set relay connection status
        metrics.set_relay_connected("wss://relay1.example.com", true);
        metrics.inc_connected_count();

        assert_eq!(metrics.get_connected_count(), 1);

        // Test decrement
        metrics.dec_connected_count();
        assert_eq!(metrics.get_connected_count(), 0);
    }

    #[test]
    fn test_health_metrics() {
        let registry = create_test_registry();
        let metrics = SyncMetrics::register(&registry).unwrap();

        // Record health states
        metrics.record_health_state("wss://relay1.example.com", HealthState::Healthy);
        metrics.record_health_state("wss://relay2.example.com", HealthState::Degraded);
        metrics.record_health_state("wss://relay3.example.com", HealthState::Dead);

        // Record failure count
        metrics.record_failure_count("wss://relay2.example.com", 5);

        // Test dead count tracking
        metrics.update_dead_count(1);
        assert_eq!(metrics.get_dead_count(), 1);

        metrics.inc_dead_count();
        assert_eq!(metrics.get_dead_count(), 2);

        metrics.dec_dead_count();
        assert_eq!(metrics.get_dead_count(), 1);
    }

    #[test]
    fn test_event_metrics() {
        let registry = create_test_registry();
        let metrics = SyncMetrics::register(&registry).unwrap();

        // Record single events
        metrics.record_event(event_source::LIVE);
        metrics.record_event(event_source::STARTUP);
        metrics.record_event(event_source::RECONNECT);
        metrics.record_event(event_source::DAILY);

        // Record multiple events
        metrics.record_events(event_source::STARTUP, 10);

        // Record gap events
        metrics.record_gap_event("wss://relay1.example.com");
        metrics.record_gap_events("wss://relay2.example.com", 5);
    }

    #[test]
    fn test_summary_metrics() {
        let registry = create_test_registry();
        let metrics = SyncMetrics::register(&registry).unwrap();

        // Test tracked count
        metrics.set_tracked_count(5);
        assert_eq!(metrics.get_tracked_count(), 5);

        metrics.inc_tracked_count();
        assert_eq!(metrics.get_tracked_count(), 6);

        // Test connected count
        metrics.update_connected_count(3);
        assert_eq!(metrics.get_connected_count(), 3);
    }

    #[test]
    fn test_event_source_constants() {
        // Verify constants have expected values
        assert_eq!(event_source::LIVE, "live");
        assert_eq!(event_source::STARTUP, "startup");
        assert_eq!(event_source::RECONNECT, "reconnect");
        assert_eq!(event_source::DAILY, "daily");
    }

    #[test]
    fn test_duplicate_registration_fails() {
        let registry = create_test_registry();

        // First registration should succeed
        let metrics1 = SyncMetrics::register(&registry);
        assert!(metrics1.is_ok());

        // Second registration should fail (metrics already registered)
        let metrics2 = SyncMetrics::register(&registry);
        assert!(metrics2.is_err());
    }
}