oxirs-cluster 0.2.4

//! # Advanced Federation Features
//!
//! This module implements advanced federation capabilities for cross-cluster
//! communication, intelligent load balancing, and adaptive query routing.

use anyhow::{anyhow, Result};
use dashmap::DashMap;
use serde::{Deserialize, Serialize};
use std::collections::{HashMap, HashSet};
use std::sync::Arc;
use std::time::{Duration, Instant, SystemTime};
use tokio::sync::{RwLock, Semaphore};
use tracing::{debug, info, warn};

/// Cross-cluster federation manager
#[derive(Debug)]
pub struct CrossClusterFederation {
    /// Local cluster ID
    #[allow(dead_code)]
    cluster_id: String,
    /// Remote cluster registry
    remote_clusters: Arc<RwLock<HashMap<String, RemoteCluster>>>,
    /// Load balancer for federated queries
    load_balancer: Arc<FederatedLoadBalancer>,
    /// Cross-cluster query cache
    query_cache: Arc<DashMap<String, CachedFederatedResult>>,
    /// Network client pool
    client_pool: Arc<ClientPool>,
    /// Federation statistics
    stats: Arc<RwLock<FederationStats>>,
}

/// Information about a remote cluster
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RemoteCluster {
    pub cluster_id: String,
    pub name: String,
    pub gateway_endpoints: Vec<String>,
    pub capabilities: ClusterCapabilities,
    pub authentication: ClusterAuth,
    pub health_status: ClusterHealth,
    pub last_contact: SystemTime,
    pub network_metrics: NetworkMetrics,
}

/// Capabilities of a remote cluster
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ClusterCapabilities {
    pub sparql_version: String,
    pub supports_federation: bool,
    pub supports_transactions: bool,
    pub max_query_complexity: Option<u32>,
    pub supported_formats: HashSet<String>,
    pub data_sources: Vec<DataSourceInfo>,
    pub specialized_domains: Vec<String>,
}

/// Information about data sources in a cluster
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DataSourceInfo {
    pub source_id: String,
    pub source_type: String,
    pub estimated_size: Option<u64>,
    pub vocabularies: Vec<String>,
    pub temporal_coverage: Option<TemporalRange>,
    pub geographic_coverage: Option<GeographicBounds>,
}

/// Temporal coverage information
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TemporalRange {
    pub start: Option<chrono::DateTime<chrono::Utc>>,
    pub end: Option<chrono::DateTime<chrono::Utc>>,
    pub granularity: String,
}

/// Geographic coverage bounds
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct GeographicBounds {
    pub north: f64,
    pub south: f64,
    pub east: f64,
    pub west: f64,
}

/// Authentication configuration for cluster access
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum ClusterAuth {
    None,
    ApiKey {
        key: String,
    },
    OAuth2 {
        client_id: String,
        client_secret: String,
        token_url: String,
    },
    MutualTLS {
        cert_path: String,
        key_path: String,
        ca_path: String,
    },
    ClusterToken {
        token: String,
        refresh_token: Option<String>,
    },
}

/// Health status of a cluster
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ClusterHealth {
    pub status: HealthStatus,
    pub available_nodes: u32,
    pub total_nodes: u32,
    pub load_average: f64,
    pub response_time_ms: f64,
    pub error_rate: f64,
    pub last_health_check: SystemTime,
}

/// Health status enumeration
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
pub enum HealthStatus {
    Healthy,
    Degraded,
    Critical,
    Unavailable,
}

/// Network performance metrics
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct NetworkMetrics {
    pub latency_ms: f64,
    pub bandwidth_mbps: f64,
    pub packet_loss_rate: f64,
    pub throughput_qps: f64,
    pub connection_quality: ConnectionQuality,
}

/// Connection quality assessment
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub enum ConnectionQuality {
    Excellent,
    Good,
    Fair,
    Poor,
    Critical,
}

/// Federated load balancer
#[derive(Debug)]
pub struct FederatedLoadBalancer {
    /// Load balancing strategy
    #[allow(dead_code)]
    strategy: LoadBalancingStrategy,
    /// Node performance tracking
    #[allow(dead_code)]
    node_metrics: Arc<DashMap<String, NodePerformanceMetrics>>,
    /// Request routing history
    #[allow(dead_code)]
    routing_history: Arc<RwLock<Vec<RoutingDecision>>>,
    /// Adaptive learning model
    #[allow(dead_code)]
    ml_predictor: Arc<RwLock<Option<PerformancePredictor>>>,
}

/// Load balancing strategies
#[derive(Debug, Clone)]
pub enum LoadBalancingStrategy {
    RoundRobin,
    WeightedRoundRobin,
    LeastConnections,
    ResponseTimeBased,
    CapabilityBased,
    AdaptiveMachineLearning,
    GeographicProximity,
    DataLocalityAware,
}

/// Performance metrics for a cluster node
#[derive(Debug, Clone)]
pub struct NodePerformanceMetrics {
    pub node_id: String,
    pub cluster_id: String,
    pub current_load: f64,
    pub average_response_time: f64,
    pub success_rate: f64,
    pub active_connections: u32,
    pub capabilities_score: f64,
    pub last_updated: Instant,
    pub prediction_confidence: f64,
}

/// Routing decision record
#[derive(Debug, Clone)]
pub struct RoutingDecision {
    pub timestamp: Instant,
    pub query_hash: String,
    pub chosen_cluster: String,
    pub chosen_node: String,
    pub decision_factors: Vec<DecisionFactor>,
    pub actual_performance: Option<ActualPerformance>,
}

/// Factors that influenced routing decision
#[derive(Debug, Clone)]
pub struct DecisionFactor {
    pub factor_name: String,
    pub weight: f64,
    pub value: f64,
    pub reasoning: String,
}

/// Actual performance after routing
#[derive(Debug, Clone)]
pub struct ActualPerformance {
    pub response_time_ms: f64,
    pub success: bool,
    pub result_count: usize,
    pub error_type: Option<String>,
}

/// Machine learning predictor for performance
#[derive(Debug)]
pub struct PerformancePredictor {
    /// Training data history
    #[allow(dead_code)]
    training_data: Vec<TrainingExample>,
    /// Feature weights (simple linear model)
    #[allow(dead_code)]
    feature_weights: HashMap<String, f64>,
    /// Model accuracy metrics
    #[allow(dead_code)]
    accuracy_metrics: AccuracyMetrics,
}

/// Training example for ML model
#[derive(Debug, Clone)]
pub struct TrainingExample {
    pub features: HashMap<String, f64>,
    pub target_performance: f64,
    pub actual_performance: f64,
}

/// Accuracy metrics for the ML model
#[derive(Debug, Clone)]
pub struct AccuracyMetrics {
    pub mean_absolute_error: f64,
    pub root_mean_square_error: f64,
    pub correlation_coefficient: f64,
    pub prediction_count: u64,
}

/// Cached federated query result
#[derive(Debug, Clone)]
pub struct CachedFederatedResult {
    pub result_data: Vec<HashMap<String, String>>,
    pub metadata: FederationResultMetadata,
    pub cached_at: Instant,
    pub ttl: Duration,
    pub source_clusters: Vec<String>,
}

/// Metadata about federated result
#[derive(Debug, Clone)]
pub struct FederationResultMetadata {
    pub total_execution_time: Duration,
    pub clusters_queried: u32,
    pub partial_results: bool,
    pub result_confidence: f64,
}

/// HTTP client pool for federation
#[derive(Debug)]
pub struct ClientPool {
    clients: DashMap<String, reqwest::Client>,
    semaphore: Arc<Semaphore>,
    #[allow(dead_code)]
    max_connections_per_cluster: usize,
}

/// Federation statistics
#[derive(Debug, Clone)]
pub struct FederationStats {
    pub total_federated_queries: u64,
    pub successful_queries: u64,
    pub cross_cluster_queries: u64,
    pub cache_hit_rate: f64,
    pub average_response_time: f64,
    pub clusters_discovered: u32,
    pub data_transferred_bytes: u64,
}

impl CrossClusterFederation {
    /// Create a new cross-cluster federation manager
    pub fn new(cluster_id: String) -> Self {
        Self {
            cluster_id,
            remote_clusters: Arc::new(RwLock::new(HashMap::new())),
            load_balancer: Arc::new(FederatedLoadBalancer::new()),
            query_cache: Arc::new(DashMap::new()),
            client_pool: Arc::new(ClientPool::new(100)),
            stats: Arc::new(RwLock::new(FederationStats::default())),
        }
    }

    /// Discover and register remote clusters
    pub async fn discover_remote_clusters(&self) -> Result<Vec<RemoteCluster>> {
        info!("Starting remote cluster discovery");

        let discovery_mechanisms = vec![
            self.discover_via_dns().await,
            self.discover_via_multicast().await,
            self.discover_via_registry().await,
        ];

        let mut discovered_clusters = Vec::new();

        for mechanism_result in discovery_mechanisms {
            match mechanism_result {
                Ok(mut clusters) => discovered_clusters.append(&mut clusters),
                Err(e) => warn!("Discovery mechanism failed: {}", e),
            }
        }

        // Register discovered clusters
        let mut remote_clusters = self.remote_clusters.write().await;
        for cluster in &discovered_clusters {
            remote_clusters.insert(cluster.cluster_id.clone(), cluster.clone());
            info!("Registered remote cluster: {}", cluster.cluster_id);
        }

        // Update statistics
        let mut stats = self.stats.write().await;
        stats.clusters_discovered = remote_clusters.len() as u32;

        Ok(discovered_clusters)
    }

    /// Execute a federated query across multiple clusters
    pub async fn execute_federated_query(
        &self,
        query: &str,
        target_clusters: Option<Vec<String>>,
    ) -> Result<CachedFederatedResult> {
        let start_time = Instant::now();
        let query_hash = self.calculate_query_hash(query);

        // Check cache first
        if let Some(cached) = self.query_cache.get(&query_hash) {
            if !self.is_cache_expired(&cached) {
                info!("Returning cached result for query hash: {}", query_hash);
                return Ok(cached.clone());
            }
        }

        // Determine target clusters
        let clusters_to_query = if let Some(targets) = target_clusters {
            targets
        } else {
            self.select_optimal_clusters(query).await?
        };

        // Route queries using load balancer
        let routing_plan = self
            .load_balancer
            .create_routing_plan(query, &clusters_to_query)
            .await?;

        // Execute queries in parallel
        let mut query_futures = Vec::new();
        for route in routing_plan {
            let client = self.client_pool.get_client(&route.cluster_id).await?;
            let query_str = query.to_string();
            let query_future = self.execute_cluster_query(client, route, query_str);
            query_futures.push(query_future);
        }

        // Collect results and track successes/failures
        let mut successful_results = Vec::new();
        let mut failed_count = 0;
        let total_queries = query_futures.len();

        // Try to collect all results, but continue on failure
        for future in query_futures {
            match future.await {
                Ok(result) => successful_results.push(result),
                Err(e) => {
                    warn!("Cluster query failed: {}", e);
                    failed_count += 1;
                }
            }
        }

        // If all queries failed, return error
        if successful_results.is_empty() {
            return Err(anyhow!(
                "All federated queries failed ({} failures)",
                failed_count
            ));
        }

        // Calculate metrics before integrating results
        let success_count = successful_results.len();
        let partial_results = failed_count > 0 || success_count < total_queries;

        // Calculate result confidence based on multiple factors:
        // 1. Success rate (70% weight)
        // 2. Result consistency (20% weight)
        // 3. Completeness (10% weight)
        let success_rate = success_count as f64 / total_queries as f64;
        let consistency_score = self.calculate_result_consistency(&successful_results);
        let completeness_score = if partial_results { 0.8 } else { 1.0 };

        // Integrate results
        let integrated_result = self.integrate_federated_results(successful_results).await?;

        let result_confidence =
            (success_rate * 0.7) + (consistency_score * 0.2) + (completeness_score * 0.1);

        debug!(
            "Federation confidence: {:.2} (success_rate={:.2}, consistency={:.2}, completeness={:.2})",
            result_confidence, success_rate, consistency_score, completeness_score
        );

        // Cache the result
        let cached_result = CachedFederatedResult {
            result_data: integrated_result,
            metadata: FederationResultMetadata {
                total_execution_time: start_time.elapsed(),
                clusters_queried: clusters_to_query.len() as u32,
                partial_results,
                result_confidence,
            },
            cached_at: Instant::now(),
            ttl: Duration::from_secs(300), // 5 minutes default TTL
            source_clusters: clusters_to_query,
        };

        self.query_cache.insert(query_hash, cached_result.clone());

        // Update statistics
        let mut stats = self.stats.write().await;
        stats.total_federated_queries += 1;
        stats.successful_queries += 1;
        stats.cross_cluster_queries += 1;
        stats.average_response_time = (stats.average_response_time
            * (stats.total_federated_queries - 1) as f64
            + start_time.elapsed().as_millis() as f64)
            / stats.total_federated_queries as f64;

        Ok(cached_result)
    }

    /// Perform health check on all registered clusters
    pub async fn health_check_all_clusters(&self) -> Result<HashMap<String, ClusterHealth>> {
        let clusters = self.remote_clusters.read().await;
        let mut health_results = HashMap::new();

        let mut health_checks = Vec::new();
        for (cluster_id, cluster) in clusters.iter() {
            let cluster_clone = cluster.clone();
            let client = self.client_pool.get_client(cluster_id).await?;

            health_checks.push(async move {
                let health = Self::check_cluster_health(client, &cluster_clone).await;
                (cluster_id.clone(), health)
            });
        }

        let health_results_vec = futures::future::join_all(health_checks).await;

        for (cluster_id, health_result) in health_results_vec {
            match health_result {
                Ok(health) => {
                    health_results.insert(cluster_id, health);
                }
                Err(e) => {
                    warn!("Health check failed for cluster {}: {}", cluster_id, e);
                    health_results.insert(
                        cluster_id,
                        ClusterHealth {
                            status: HealthStatus::Unavailable,
                            available_nodes: 0,
                            total_nodes: 0,
                            load_average: 0.0,
                            response_time_ms: f64::INFINITY,
                            error_rate: 1.0,
                            last_health_check: SystemTime::now(),
                        },
                    );
                }
            }
        }

        Ok(health_results)
    }

    /// Get federation statistics
    pub async fn get_federation_stats(&self) -> FederationStats {
        self.stats.read().await.clone()
    }

    // Private helper methods

    async fn discover_via_dns(&self) -> Result<Vec<RemoteCluster>> {
        // DNS-based cluster discovery using TXT records
        debug!("Discovering clusters via DNS");

        // In a real implementation, this would query DNS TXT records
        // for cluster information in a standardized format
        Ok(vec![])
    }

    async fn discover_via_multicast(&self) -> Result<Vec<RemoteCluster>> {
        // Multicast-based cluster discovery
        debug!("Discovering clusters via multicast");

        // In a real implementation, this would use UDP multicast
        // to discover clusters on the local network
        Ok(vec![])
    }

    async fn discover_via_registry(&self) -> Result<Vec<RemoteCluster>> {
        // Registry-based cluster discovery
        debug!("Discovering clusters via central registry");

        // In a real implementation, this would query a central
        // cluster registry service
        Ok(vec![])
    }

    async fn select_optimal_clusters(&self, query: &str) -> Result<Vec<String>> {
        let clusters = self.remote_clusters.read().await;

        // Analyze query to determine which clusters might have relevant data
        let mut relevant_clusters = Vec::new();

        for (cluster_id, cluster) in clusters.iter() {
            if cluster.health_status.status == HealthStatus::Healthy {
                // Simple heuristic: check if query contains vocabulary terms
                // that this cluster specializes in
                if self.query_matches_cluster_capabilities(query, cluster) {
                    relevant_clusters.push(cluster_id.clone());
                }
            }
        }

        if relevant_clusters.is_empty() {
            // Fallback: use all healthy clusters
            relevant_clusters = clusters
                .iter()
                .filter(|(_, cluster)| cluster.health_status.status == HealthStatus::Healthy)
                .map(|(id, _)| id.clone())
                .collect();
        }

        Ok(relevant_clusters)
    }

    fn query_matches_cluster_capabilities(&self, query: &str, cluster: &RemoteCluster) -> bool {
        // Simple keyword matching with cluster specializations
        for domain in &cluster.capabilities.specialized_domains {
            if query.to_lowercase().contains(&domain.to_lowercase()) {
                return true;
            }
        }

        // Check vocabularies
        for source in &cluster.capabilities.data_sources {
            for vocab in &source.vocabularies {
                if query.contains(vocab) {
                    return true;
                }
            }
        }

        false
    }

    async fn execute_cluster_query(
        &self,
        client: reqwest::Client,
        route: RoutingPlan,
        query: String,
    ) -> Result<HashMap<String, String>> {
        let response = client
            .post(&route.endpoint_url)
            .header("Content-Type", "application/sparql-query")
            .header("Accept", "application/sparql-results+json")
            .body(query)
            .send()
            .await?;

        if response.status().is_success() {
            let result_text = response.text().await?;
            // Simplified result processing
            Ok(HashMap::from([("result".to_string(), result_text)]))
        } else {
            Err(anyhow!("Query failed with status: {}", response.status()))
        }
    }

    async fn integrate_federated_results(
        &self,
        results: Vec<HashMap<String, String>>,
    ) -> Result<Vec<HashMap<String, String>>> {
        // Simple integration - in a real implementation this would be more sophisticated
        Ok(results)
    }

    /// Calculate consistency score for federated results
    /// Returns a value between 0.0 and 1.0 indicating result consistency
    fn calculate_result_consistency(&self, results: &[HashMap<String, String>]) -> f64 {
        if results.is_empty() {
            return 0.0;
        }

        if results.len() == 1 {
            // Single result is always consistent
            return 1.0;
        }

        // Calculate consistency based on result overlap
        // For each key in results, check how many results have the same value
        let mut total_keys = 0;
        let mut consistent_keys = 0;

        // Collect all unique keys
        let mut all_keys = std::collections::HashSet::new();
        for result in results {
            for key in result.keys() {
                all_keys.insert(key.clone());
            }
        }

        for key in all_keys {
            total_keys += 1;

            // Count unique values for this key across results
            let mut value_counts: HashMap<String, usize> = HashMap::new();
            let mut present_count = 0;

            for result in results {
                if let Some(value) = result.get(&key) {
                    *value_counts.entry(value.clone()).or_insert(0) += 1;
                    present_count += 1;
                }
            }

            // If the key appears in most results with the same value, consider it consistent
            if let Some((&_, &max_count)) = value_counts.iter().max_by_key(|(_, &count)| count) {
                if max_count >= results.len() / 2 && present_count >= results.len() / 2 {
                    consistent_keys += 1;
                }
            }
        }

        if total_keys == 0 {
            return 1.0; // No keys means trivially consistent
        }

        // Return ratio of consistent keys to total keys
        consistent_keys as f64 / total_keys as f64
    }

    async fn check_cluster_health(
        client: reqwest::Client,
        cluster: &RemoteCluster,
    ) -> Result<ClusterHealth> {
        let start_time = Instant::now();

        // Try to reach the cluster's health endpoint
        let health_url = format!("{}/health", cluster.gateway_endpoints[0]);
        let response = client.get(&health_url).send().await;

        let response_time = start_time.elapsed().as_millis() as f64;

        match response {
            Ok(resp) if resp.status().is_success() => {
                Ok(ClusterHealth {
                    status: HealthStatus::Healthy,
                    available_nodes: 1, // Simplified
                    total_nodes: 1,
                    load_average: 0.5,
                    response_time_ms: response_time,
                    error_rate: 0.0,
                    last_health_check: SystemTime::now(),
                })
            }
            _ => Ok(ClusterHealth {
                status: HealthStatus::Unavailable,
                available_nodes: 0,
                total_nodes: 1,
                load_average: 0.0,
                response_time_ms: response_time,
                error_rate: 1.0,
                last_health_check: SystemTime::now(),
            }),
        }
    }

    fn calculate_query_hash(&self, query: &str) -> String {
        use std::collections::hash_map::DefaultHasher;
        use std::hash::{Hash, Hasher};

        let mut hasher = DefaultHasher::new();
        query.hash(&mut hasher);
        format!("{:x}", hasher.finish())
    }

    fn is_cache_expired(&self, cached: &CachedFederatedResult) -> bool {
        cached.cached_at.elapsed() > cached.ttl
    }
}

/// Routing plan for federated queries
#[derive(Debug, Clone)]
pub struct RoutingPlan {
    pub cluster_id: String,
    pub node_id: String,
    pub endpoint_url: String,
    pub estimated_cost: f64,
    pub confidence: f64,
}

impl Default for FederatedLoadBalancer {
    fn default() -> Self {
        Self::new()
    }
}

impl FederatedLoadBalancer {
    pub fn new() -> Self {
        Self {
            strategy: LoadBalancingStrategy::AdaptiveMachineLearning,
            node_metrics: Arc::new(DashMap::new()),
            routing_history: Arc::new(RwLock::new(Vec::new())),
            ml_predictor: Arc::new(RwLock::new(None)),
        }
    }

    pub async fn create_routing_plan(
        &self,
        _query: &str,
        clusters: &[String],
    ) -> Result<Vec<RoutingPlan>> {
        let mut routing_plans = Vec::new();

        for cluster_id in clusters {
            // For now, create a simple routing plan
            routing_plans.push(RoutingPlan {
                cluster_id: cluster_id.clone(),
                node_id: format!("{cluster_id}-node-1"),
                endpoint_url: format!("http://{cluster_id}.cluster.local/sparql"),
                estimated_cost: 1.0,
                confidence: 0.8,
            });
        }

        Ok(routing_plans)
    }
}

impl ClientPool {
    pub fn new(max_connections: usize) -> Self {
        Self {
            clients: DashMap::new(),
            semaphore: Arc::new(Semaphore::new(max_connections)),
            max_connections_per_cluster: max_connections / 10, // Conservative estimate
        }
    }

    pub async fn get_client(&self, cluster_id: &str) -> Result<reqwest::Client> {
        if let Some(client) = self.clients.get(cluster_id) {
            return Ok(client.clone());
        }

        let _permit = self
            .semaphore
            .acquire()
            .await
            .map_err(|_| anyhow!("Failed to acquire connection permit"))?;

        let client = reqwest::Client::builder()
            .timeout(Duration::from_secs(30))
            .build()?;

        self.clients.insert(cluster_id.to_string(), client.clone());
        Ok(client)
    }
}

impl Default for FederationStats {
    fn default() -> Self {
        Self {
            total_federated_queries: 0,
            successful_queries: 0,
            cross_cluster_queries: 0,
            cache_hit_rate: 0.0,
            average_response_time: 0.0,
            clusters_discovered: 0,
            data_transferred_bytes: 0,
        }
    }
}

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

    #[tokio::test]
    async fn test_cross_cluster_federation_creation() {
        let federation = CrossClusterFederation::new("test-cluster".to_string());
        let stats = federation.get_federation_stats().await;
        assert_eq!(stats.total_federated_queries, 0);
    }

    #[tokio::test]
    async fn test_client_pool() {
        let pool = ClientPool::new(10);
        let client1 = pool.get_client("cluster1").await.unwrap();
        let client2 = pool.get_client("cluster1").await.unwrap();

        // Should reuse the same client instance (comparing by pointer won't work for non-Arc types)
        // For now, just verify we got valid clients
        // Note: danger_accept_invalid_certs() method doesn't exist in current reqwest version
        // assert!(!client1.danger_accept_invalid_certs());
        // assert!(!client2.danger_accept_invalid_certs());

        // Just verify we have valid clients
        assert!(format!("{client1:?}").contains("Client"));
        assert!(format!("{client2:?}").contains("Client"));
    }

    #[tokio::test]
    async fn test_query_hash_consistency() {
        let federation = CrossClusterFederation::new("test".to_string());
        let query = "SELECT ?s ?p ?o WHERE { ?s ?p ?o }";

        let hash1 = federation.calculate_query_hash(query);
        let hash2 = federation.calculate_query_hash(query);

        assert_eq!(hash1, hash2);
    }
}