oxirs-fuseki 0.2.4

//! Advanced Federated Query Optimization for SPARQL 1.2
//!
//! This module implements sophisticated federated query processing with:
//! - SERVICE clause optimization and delegation
//! - Remote endpoint discovery and health monitoring
//! - Query decomposition and distributed planning
//! - Cost-based optimization for federation
//! - Parallel execution strategies
//! - Intelligent result merging

use crate::{
    error::{FusekiError, FusekiResult},
    metrics::MetricsService,
};
use async_trait::async_trait;
use dashmap::DashMap;
use futures::{stream::FuturesUnordered, StreamExt};
use metrics::{counter, histogram};
use reqwest::{Client, ClientBuilder, StatusCode};
use serde::{Deserialize, Serialize};
use std::{
    collections::{HashMap, HashSet},
    sync::Arc,
    time::{Duration, Instant},
};
use tokio::{
    sync::{RwLock, Semaphore},
    time::timeout,
};

/// Type alias for query decomposition function
type QueryDecomposeFn = Box<dyn Fn(&str) -> Vec<QueryFragment> + Send + Sync>;

/// Federated query optimizer for distributed SPARQL execution
pub struct FederatedQueryOptimizer {
    /// Remote endpoint registry
    pub endpoints: Arc<RwLock<EndpointRegistry>>,
    /// Query planner for federation
    pub planner: Arc<QueryPlanner>,
    /// Cost estimator for distributed queries
    pub cost_estimator: Arc<CostEstimator>,
    /// Execution engine for federated queries
    pub executor: Arc<FederatedExecutor>,
    /// Result merger for combining distributed results
    pub merger: Arc<ResultMerger>,
    /// Metrics service
    pub metrics: Arc<MetricsService>,
}

/// Registry for managing remote SPARQL endpoints
pub struct EndpointRegistry {
    /// Registered endpoints with metadata
    endpoints: HashMap<String, EndpointInfo>,
    /// Health status cache
    health_cache: DashMap<String, HealthStatus>,
    /// Discovery service
    discovery: Arc<EndpointDiscovery>,
}

/// Information about a remote SPARQL endpoint
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EndpointInfo {
    pub url: String,
    pub name: String,
    pub description: Option<String>,
    pub capabilities: EndpointCapabilities,
    pub authentication: Option<EndpointAuth>,
    pub timeout_ms: u64,
    pub max_retries: u32,
    pub priority: u32,
}

/// Capabilities of a remote endpoint
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EndpointCapabilities {
    pub sparql_version: String,
    pub supports_update: bool,
    pub supports_graph_store: bool,
    pub supports_service_description: bool,
    pub max_query_size: Option<usize>,
    pub rate_limit: Option<RateLimit>,
    pub features: HashSet<String>,
}

/// Rate limiting configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RateLimit {
    pub requests_per_second: u32,
    pub burst_size: u32,
}

/// Authentication configuration for endpoints
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum EndpointAuth {
    Basic {
        username: String,
        password: String,
    },
    Bearer {
        token: String,
    },
    ApiKey {
        key: String,
        header_name: String,
    },
    OAuth2 {
        client_id: String,
        client_secret: String,
        token_url: String,
    },
}

/// Health status of an endpoint
#[derive(Debug, Clone)]
pub struct HealthStatus {
    pub is_healthy: bool,
    pub last_check: Instant,
    pub response_time_ms: u64,
    pub error_count: u32,
    pub success_count: u32,
}

/// Endpoint discovery service
pub struct EndpointDiscovery {
    /// HTTP client for discovery
    client: Client,
    /// Known endpoint catalogs
    catalogs: Vec<String>,
}

/// Query planner for federated execution
pub struct QueryPlanner {
    /// Query decomposition rules
    decomposition_rules: Vec<DecompositionRule>,
    /// Join order optimizer
    join_optimizer: Arc<JoinOrderOptimizer>,
    /// Statistics cache
    statistics: Arc<RwLock<FederationStatistics>>,
}

/// Rule for decomposing queries
pub struct DecompositionRule {
    pub name: String,
    pub pattern: String,
    pub applicability_check: Box<dyn Fn(&str) -> bool + Send + Sync>,
    pub decompose: QueryDecomposeFn,
}

/// Fragment of a decomposed query
#[derive(Debug, Clone)]
pub struct QueryFragment {
    pub fragment_id: String,
    pub sparql: String,
    pub target_endpoints: Vec<String>,
    pub dependencies: Vec<String>,
    pub estimated_cost: f64,
    pub is_optional: bool,
}

/// Join order optimizer for distributed queries
pub struct JoinOrderOptimizer {
    /// Cost model for joins
    cost_model: Arc<JoinCostModel>,
    /// Dynamic programming cache
    dp_cache: DashMap<String, JoinPlan>,
}

/// Cost model for distributed joins
pub struct JoinCostModel {
    /// Network latency estimates
    latency_map: DashMap<(String, String), Duration>,
    /// Bandwidth estimates
    bandwidth_map: DashMap<String, f64>,
}

/// Optimized join plan
#[derive(Debug, Clone)]
pub struct JoinPlan {
    pub steps: Vec<JoinStep>,
    pub estimated_cost: f64,
    pub estimated_time_ms: u64,
}

/// Single step in a join plan
#[derive(Debug, Clone)]
pub struct JoinStep {
    pub operation: JoinOperation,
    pub left_source: String,
    pub right_source: String,
    pub output_destination: String,
}

/// Join operation type
#[derive(Debug, Clone)]
pub enum JoinOperation {
    HashJoin,
    SortMergeJoin,
    NestedLoopJoin,
    BroadcastJoin,
    IndexJoin,
}

/// Cost estimator for federated queries
pub struct CostEstimator {
    /// Historical query statistics
    history: Arc<RwLock<QueryHistory>>,
    /// Machine learning model for cost prediction
    ml_model: Option<Arc<CostPredictionModel>>,
    /// Cardinality estimator
    cardinality: Arc<CardinalityEstimator>,
}

/// Historical query execution data
pub struct QueryHistory {
    /// Past query executions
    executions: Vec<QueryExecution>,
    /// Pattern statistics
    patterns: HashMap<String, PatternStats>,
}

/// Single query execution record
#[derive(Debug, Clone)]
pub struct QueryExecution {
    pub query_hash: String,
    pub fragments: Vec<String>,
    pub endpoints: Vec<String>,
    pub execution_time_ms: u64,
    pub result_count: usize,
    pub timestamp: Instant,
}

/// Statistics for query patterns
#[derive(Debug, Clone)]
pub struct PatternStats {
    pub pattern: String,
    pub avg_execution_time: f64,
    pub avg_result_count: f64,
    pub execution_count: u32,
}

/// Machine learning model for cost prediction
pub struct CostPredictionModel {
    // Placeholder for ML model implementation
    _model_data: Vec<u8>,
}

/// Cardinality estimator for distributed queries
pub struct CardinalityEstimator {
    /// Endpoint statistics
    endpoint_stats: DashMap<String, EndpointStatistics>,
    /// Histogram cache
    histograms: DashMap<String, Histogram>,
}

/// Statistics for an endpoint
#[derive(Debug, Clone)]
pub struct EndpointStatistics {
    pub triple_count: u64,
    pub distinct_subjects: u64,
    pub distinct_predicates: u64,
    pub distinct_objects: u64,
    pub last_updated: Instant,
}

impl Default for EndpointStatistics {
    fn default() -> Self {
        Self {
            triple_count: 0,
            distinct_subjects: 0,
            distinct_predicates: 0,
            distinct_objects: 0,
            last_updated: Instant::now(),
        }
    }
}

/// Histogram for selectivity estimation
#[derive(Debug, Clone)]
pub struct Histogram {
    pub buckets: Vec<HistogramBucket>,
    pub total_count: u64,
}

/// Single histogram bucket
#[derive(Debug, Clone)]
pub struct HistogramBucket {
    pub min_value: String,
    pub max_value: String,
    pub count: u64,
}

/// Federation statistics
pub struct FederationStatistics {
    /// Query execution stats
    query_stats: HashMap<String, QueryStats>,
    /// Endpoint performance stats
    endpoint_stats: HashMap<String, EndpointPerformance>,
}

/// Query execution statistics
#[derive(Debug, Clone)]
pub struct QueryStats {
    pub total_executions: u64,
    pub avg_execution_time: f64,
    pub success_rate: f64,
}

/// Endpoint performance metrics
#[derive(Debug, Clone)]
pub struct EndpointPerformance {
    pub avg_response_time: f64,
    pub availability: f64,
    pub throughput: f64,
}

/// Federated query executor
pub struct FederatedExecutor {
    /// HTTP client pool
    client_pool: Arc<ClientPool>,
    /// Execution strategies
    strategies: Vec<Arc<dyn ExecutionStrategy>>,
    /// Parallel execution limiter
    semaphore: Arc<Semaphore>,
    /// Retry policy
    retry_policy: Arc<RetryPolicy>,
}

/// HTTP client pool for endpoint connections
pub struct ClientPool {
    /// Clients per endpoint
    clients: DashMap<String, Client>,
    /// Connection limits
    max_connections_per_endpoint: usize,
}

/// Execution strategy trait
#[async_trait]
pub trait ExecutionStrategy: Send + Sync {
    fn name(&self) -> &str;
    fn applicable(&self, plan: &ExecutionPlan) -> bool;
    async fn execute(
        &self,
        plan: &ExecutionPlan,
        executor: &FederatedExecutor,
    ) -> FusekiResult<QueryResults>;
}

/// Execution plan for federated query
#[derive(Debug, Clone)]
pub struct ExecutionPlan {
    pub query_id: String,
    pub fragments: Vec<QueryFragment>,
    pub join_plan: JoinPlan,
    pub timeout_ms: u64,
    pub optimization_hints: HashMap<String, String>,
    /// Execution steps for performance testing
    pub execution_steps: Vec<String>,
    /// Estimated cost of execution
    pub estimated_cost: f64,
    /// Resource requirements for the execution plan
    pub resource_requirements: ResourceRequirements,
}

/// Resource requirements for execution plan
#[derive(Debug, Clone)]
pub struct ResourceRequirements {
    /// Required service endpoints
    pub required_endpoints: Vec<String>,
    /// Estimated memory requirements in MB
    pub estimated_memory_mb: f64,
    /// Estimated CPU requirements
    pub estimated_cpu_cores: f64,
}

/// Results from federated query execution
#[derive(Debug, Clone)]
pub struct QueryResults {
    pub bindings: Vec<HashMap<String, serde_json::Value>>,
    pub metadata: ResultMetadata,
}

/// Metadata about query results
#[derive(Debug, Clone)]
pub struct ResultMetadata {
    pub total_execution_time_ms: u64,
    pub endpoint_times: HashMap<String, u64>,
    pub result_count: usize,
    pub partial_results: bool,
}

/// Retry policy for failed requests
pub struct RetryPolicy {
    pub max_retries: u32,
    pub initial_backoff_ms: u64,
    pub max_backoff_ms: u64,
    pub exponential_base: f64,
}

/// Service pattern extracted from SPARQL query
#[derive(Debug, Clone)]
pub struct ServicePattern {
    pub service_url: String,
    pub pattern: String,
    pub is_silent: bool,
    pub is_optional: bool,
}

/// Merge strategy trait for combining results
#[async_trait]
pub trait MergeStrategy: Send + Sync {
    fn name(&self) -> &str;
    async fn merge(&self, results: Vec<QueryResults>) -> FusekiResult<QueryResults>;
}

/// Result merger for combining distributed results
pub struct ResultMerger {
    /// Merge strategies
    pub strategies: HashMap<String, Arc<dyn MergeStrategy>>,
    /// Deduplication cache
    dedup_cache: Arc<RwLock<HashSet<u64>>>,
}

impl FederatedQueryOptimizer {
    pub fn new(metrics: Arc<MetricsService>) -> Self {
        Self {
            endpoints: Arc::new(RwLock::new(EndpointRegistry::new())),
            planner: Arc::new(QueryPlanner::new()),
            cost_estimator: Arc::new(CostEstimator::new()),
            executor: Arc::new(FederatedExecutor::new()),
            merger: Arc::new(ResultMerger::new()),
            metrics,
        }
    }

    /// Process a federated SPARQL query
    pub async fn process_federated_query(
        &self,
        query: &str,
        timeout_ms: u64,
    ) -> FusekiResult<QueryResults> {
        let start = Instant::now();

        // Extract SERVICE clauses
        let service_patterns = self.extract_service_patterns(query)?;
        if service_patterns.is_empty() {
            return Err(FusekiError::bad_request("No SERVICE patterns found"));
        }

        // Check endpoint health
        self.check_endpoint_health(&service_patterns).await?;

        // Plan query execution
        let plan = self
            .planner
            .create_execution_plan(query, &service_patterns)
            .await?;

        // Estimate costs
        let cost_estimate = self.cost_estimator.estimate_cost(&plan).await?;
        histogram!("federated_query.estimated_cost").record(cost_estimate);

        // Execute with timeout
        let results = timeout(
            Duration::from_millis(timeout_ms),
            self.executor.execute_plan(&plan),
        )
        .await
        .map_err(|_| FusekiError::TimeoutWithMessage("Federated query timeout".into()))??;

        // Record metrics
        let duration = start.elapsed();
        histogram!("federated_query.execution_time").record(duration.as_millis() as f64);
        counter!("federated_query.total").increment(1);

        Ok(results)
    }

    /// Extract SERVICE patterns from query
    pub fn extract_service_patterns(&self, query: &str) -> FusekiResult<Vec<ServicePattern>> {
        let mut patterns = Vec::new();
        let mut in_service = false;
        let mut current_service = String::new();
        let mut brace_count = 0;
        let mut service_url = String::new();

        for line in query.lines() {
            let trimmed = line.trim();

            if trimmed.starts_with("SERVICE") {
                in_service = true;
                // Extract URL from SERVICE <url> or SERVICE SILENT <url>
                if let Some(url_start) = trimmed.find('<') {
                    if let Some(url_end) = trimmed.find('>') {
                        service_url = trimmed[url_start + 1..url_end].to_string();
                    }
                }
            }

            if in_service {
                current_service.push_str(line);
                current_service.push('\n');

                for ch in trimmed.chars() {
                    match ch {
                        '{' => brace_count += 1,
                        '}' => {
                            brace_count -= 1;
                            if brace_count == 0 {
                                patterns.push(ServicePattern {
                                    service_url: service_url.clone(),
                                    pattern: current_service.clone(),
                                    is_silent: current_service.contains("SILENT"),
                                    is_optional: false,
                                });
                                in_service = false;
                                current_service.clear();
                                service_url.clear();
                            }
                        }
                        _ => {}
                    }
                }
            }
        }

        Ok(patterns)
    }

    /// Check health of required endpoints
    async fn check_endpoint_health(&self, patterns: &[ServicePattern]) -> FusekiResult<()> {
        let endpoints = self.endpoints.read().await;
        let mut futures = FuturesUnordered::new();

        for pattern in patterns {
            let endpoint_url = pattern.service_url.clone();
            if let Some(endpoint) = endpoints.endpoints.get(&endpoint_url) {
                let health_check = endpoints.check_endpoint_health(endpoint.clone());
                futures.push(health_check);
            } else if !pattern.is_silent {
                return Err(FusekiError::bad_request(format!(
                    "Unknown endpoint: {endpoint_url}"
                )));
            }
        }

        // Wait for all health checks
        while let Some(result) = futures.next().await {
            result?;
        }

        Ok(())
    }
}

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

impl EndpointRegistry {
    pub fn new() -> Self {
        Self {
            endpoints: HashMap::new(),
            health_cache: DashMap::new(),
            discovery: Arc::new(EndpointDiscovery::new()),
        }
    }

    /// Register a new endpoint
    pub fn register_endpoint(&mut self, endpoint: EndpointInfo) {
        self.endpoints.insert(endpoint.url.clone(), endpoint);
    }

    /// Check endpoint health
    pub async fn check_endpoint_health(&self, endpoint: EndpointInfo) -> FusekiResult<()> {
        let client = ClientBuilder::new()
            .timeout(Duration::from_millis(5000))
            .build()
            .map_err(|e| FusekiError::internal(format!("Client error: {e}")))?;

        let start = Instant::now();
        let response = client
            .get(&endpoint.url)
            .header("Accept", "application/sparql-results+json")
            .query(&[("query", "ASK { ?s ?p ?o } LIMIT 1")])
            .send()
            .await;

        let response_time = start.elapsed().as_millis() as u64;

        match response {
            Ok(resp) if resp.status() == StatusCode::OK => {
                self.health_cache.insert(
                    endpoint.url.clone(),
                    HealthStatus {
                        is_healthy: true,
                        last_check: Instant::now(),
                        response_time_ms: response_time,
                        error_count: 0,
                        success_count: 1,
                    },
                );
                Ok(())
            }
            Ok(resp) => Err(FusekiError::bad_request(format!(
                "Endpoint returned status: {}",
                resp.status()
            ))),
            Err(e) => {
                self.health_cache.insert(
                    endpoint.url.clone(),
                    HealthStatus {
                        is_healthy: false,
                        last_check: Instant::now(),
                        response_time_ms: response_time,
                        error_count: 1,
                        success_count: 0,
                    },
                );
                Err(FusekiError::internal(format!("Health check failed: {e}")))
            }
        }
    }

    /// Discover endpoints from catalogs
    pub async fn discover_endpoints(&self) -> FusekiResult<Vec<EndpointInfo>> {
        self.discovery.discover_from_catalogs().await
    }
}

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

impl EndpointDiscovery {
    pub fn new() -> Self {
        Self {
            client: Client::new(),
            catalogs: vec![
                "https://www.w3.org/wiki/SparqlEndpoints".to_string(),
                "https://lod-cloud.net/endpoints".to_string(),
            ],
        }
    }

    /// Discover endpoints from known catalogs
    pub async fn discover_from_catalogs(&self) -> FusekiResult<Vec<EndpointInfo>> {
        // Placeholder for actual discovery implementation
        // Would parse VOID descriptions, SPARQL Service Descriptions, etc.
        Ok(vec![])
    }
}

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

impl QueryPlanner {
    pub fn new() -> Self {
        Self {
            decomposition_rules: Self::create_decomposition_rules(),
            join_optimizer: Arc::new(JoinOrderOptimizer::new()),
            statistics: Arc::new(RwLock::new(FederationStatistics::new())),
        }
    }

    /// Create standard decomposition rules
    fn create_decomposition_rules() -> Vec<DecompositionRule> {
        vec![
            // Triple pattern decomposition
            DecompositionRule {
                name: "TriplePatternDecomposition".to_string(),
                pattern: "triple_pattern".to_string(),
                applicability_check: Box::new(|query| {
                    query.contains("?s") && query.contains("?p") && query.contains("?o")
                }),
                decompose: Box::new(|_query| {
                    // Decompose triple patterns across endpoints
                    vec![]
                }),
            },
            // UNION decomposition
            DecompositionRule {
                name: "UnionDecomposition".to_string(),
                pattern: "union".to_string(),
                applicability_check: Box::new(|query| query.to_uppercase().contains("UNION")),
                decompose: Box::new(|_query| {
                    // Split UNION branches for parallel execution
                    vec![]
                }),
            },
            // OPTIONAL decomposition
            DecompositionRule {
                name: "OptionalDecomposition".to_string(),
                pattern: "optional".to_string(),
                applicability_check: Box::new(|query| query.to_uppercase().contains("OPTIONAL")),
                decompose: Box::new(|_query| {
                    // Handle OPTIONAL patterns
                    vec![]
                }),
            },
        ]
    }

    /// Create execution plan for federated query
    pub async fn create_execution_plan(
        &self,
        query: &str,
        service_patterns: &[ServicePattern],
    ) -> FusekiResult<ExecutionPlan> {
        // Decompose query into fragments
        let fragments = self.decompose_query(query, service_patterns)?;

        // Optimize join order
        let join_plan = self.join_optimizer.optimize_joins(&fragments).await?;

        // Create execution plan
        let required_endpoints: Vec<String> = service_patterns
            .iter()
            .map(|p| p.service_url.clone())
            .collect();

        let execution_steps: Vec<String> = fragments
            .iter()
            .enumerate()
            .map(|(i, f)| {
                format!(
                    "Execute fragment {} ({}) at {:?}",
                    i, f.sparql, f.target_endpoints
                )
            })
            .collect();

        let estimated_cost = fragments.iter().map(|f| f.estimated_cost).sum::<f64>(); // Sum of fragment costs

        Ok(ExecutionPlan {
            query_id: uuid::Uuid::new_v4().to_string(),
            fragments: fragments.clone(),
            join_plan,
            timeout_ms: 30000,
            optimization_hints: HashMap::new(),
            execution_steps,
            estimated_cost,
            resource_requirements: ResourceRequirements {
                required_endpoints,
                estimated_memory_mb: fragments.len() as f64 * 5.0,
                estimated_cpu_cores: (fragments.len() as f64 / 2.0).max(1.0),
            },
        })
    }

    /// Decompose query into executable fragments
    fn decompose_query(
        &self,
        query: &str,
        service_patterns: &[ServicePattern],
    ) -> FusekiResult<Vec<QueryFragment>> {
        let mut fragments = Vec::new();

        // Create fragments for each SERVICE pattern
        for (idx, pattern) in service_patterns.iter().enumerate() {
            fragments.push(QueryFragment {
                fragment_id: format!("service_{idx}"),
                sparql: pattern.pattern.clone(),
                target_endpoints: vec![pattern.service_url.clone()],
                dependencies: vec![],
                estimated_cost: 1.0,
                is_optional: pattern.is_optional,
            });
        }

        // Apply decomposition rules
        for rule in &self.decomposition_rules {
            if (rule.applicability_check)(query) {
                let decomposed = (rule.decompose)(query);
                fragments.extend(decomposed);
            }
        }

        Ok(fragments)
    }
}

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

impl JoinOrderOptimizer {
    pub fn new() -> Self {
        Self {
            cost_model: Arc::new(JoinCostModel::new()),
            dp_cache: DashMap::new(),
        }
    }

    /// Optimize join order for fragments
    pub async fn optimize_joins(&self, fragments: &[QueryFragment]) -> FusekiResult<JoinPlan> {
        // Use dynamic programming to find optimal join order
        let cache_key = self.compute_cache_key(fragments);

        if let Some(cached_plan) = self.dp_cache.get(&cache_key) {
            return Ok(cached_plan.clone());
        }

        // Compute optimal plan
        let plan = self.compute_optimal_plan(fragments).await?;

        // Cache the result
        self.dp_cache.insert(cache_key, plan.clone());

        Ok(plan)
    }

    /// Compute cache key for fragments
    fn compute_cache_key(&self, fragments: &[QueryFragment]) -> String {
        let mut hasher = std::collections::hash_map::DefaultHasher::new();
        for fragment in fragments {
            std::hash::Hash::hash(&fragment.fragment_id, &mut hasher);
        }
        format!("{:x}", std::hash::Hasher::finish(&hasher))
    }

    /// Compute optimal join plan
    async fn compute_optimal_plan(&self, fragments: &[QueryFragment]) -> FusekiResult<JoinPlan> {
        // Simplified join planning
        let mut steps = Vec::new();

        if fragments.len() > 1 {
            // Create pairwise joins
            for i in 0..fragments.len() - 1 {
                steps.push(JoinStep {
                    operation: JoinOperation::HashJoin,
                    left_source: fragments[i].fragment_id.clone(),
                    right_source: fragments[i + 1].fragment_id.clone(),
                    output_destination: format!("join_{i}"),
                });
            }
        }

        Ok(JoinPlan {
            steps,
            estimated_cost: fragments.len() as f64,
            estimated_time_ms: fragments.len() as u64 * 100,
        })
    }
}

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

impl JoinCostModel {
    pub fn new() -> Self {
        Self {
            latency_map: DashMap::new(),
            bandwidth_map: DashMap::new(),
        }
    }
}

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

impl CostEstimator {
    pub fn new() -> Self {
        Self {
            history: Arc::new(RwLock::new(QueryHistory::new())),
            ml_model: None,
            cardinality: Arc::new(CardinalityEstimator::new()),
        }
    }

    /// Estimate cost of execution plan
    pub async fn estimate_cost(&self, plan: &ExecutionPlan) -> FusekiResult<f64> {
        let mut total_cost = 0.0;

        // Estimate fragment costs
        for fragment in &plan.fragments {
            let fragment_cost = self.estimate_fragment_cost(fragment).await?;
            total_cost += fragment_cost;
        }

        // Add join costs
        for step in &plan.join_plan.steps {
            let join_cost = self.estimate_join_cost(step).await?;
            total_cost += join_cost;
        }

        Ok(total_cost)
    }

    /// Estimate cost of a query fragment
    async fn estimate_fragment_cost(&self, fragment: &QueryFragment) -> FusekiResult<f64> {
        // Use historical data if available
        let history = self.history.read().await;
        if let Some(stats) = history.patterns.get(&fragment.fragment_id) {
            return Ok(stats.avg_execution_time);
        }

        // Otherwise use cardinality estimation
        let cardinality = self
            .cardinality
            .estimate_cardinality(&fragment.sparql)
            .await?;
        Ok(cardinality as f64 * 0.001) // 1ms per 1000 results
    }

    /// Estimate cost of a join operation
    async fn estimate_join_cost(&self, step: &JoinStep) -> FusekiResult<f64> {
        match step.operation {
            JoinOperation::HashJoin => Ok(10.0),
            JoinOperation::SortMergeJoin => Ok(20.0),
            JoinOperation::NestedLoopJoin => Ok(100.0),
            JoinOperation::BroadcastJoin => Ok(5.0),
            JoinOperation::IndexJoin => Ok(2.0),
        }
    }
}

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

impl QueryHistory {
    pub fn new() -> Self {
        Self {
            executions: Vec::new(),
            patterns: HashMap::new(),
        }
    }
}

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

impl CardinalityEstimator {
    pub fn new() -> Self {
        Self {
            endpoint_stats: DashMap::new(),
            histograms: DashMap::new(),
        }
    }

    /// Estimate result cardinality
    pub async fn estimate_cardinality(&self, query: &str) -> FusekiResult<u64> {
        // Simplified cardinality estimation
        if query.contains("LIMIT") {
            if let Some(limit_pos) = query.find("LIMIT") {
                let limit_str = &query[limit_pos + 5..].trim();

                // Extract the limit value (handle both cases: with space after or at end of query)
                let limit_val = if let Some(space_pos) = limit_str.find(' ') {
                    &limit_str[..space_pos]
                } else {
                    // No space found, use the entire remaining string
                    limit_str
                };

                if let Ok(limit) = limit_val.parse::<u64>() {
                    return Ok(limit);
                }
            }
        }

        // Default estimate
        Ok(1000)
    }
}

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

impl FederationStatistics {
    pub fn new() -> Self {
        Self {
            query_stats: HashMap::new(),
            endpoint_stats: HashMap::new(),
        }
    }
}

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

impl FederatedExecutor {
    pub fn new() -> Self {
        Self {
            client_pool: Arc::new(ClientPool::new()),
            strategies: Self::create_execution_strategies(),
            semaphore: Arc::new(Semaphore::new(10)),
            retry_policy: Arc::new(RetryPolicy::default()),
        }
    }

    /// Create execution strategies
    fn create_execution_strategies() -> Vec<Arc<dyn ExecutionStrategy>> {
        vec![
            Arc::new(ParallelExecutionStrategy),
            Arc::new(SequentialExecutionStrategy),
            Arc::new(AdaptiveExecutionStrategy),
        ]
    }

    /// Execute a federated query plan
    pub async fn execute_plan(&self, plan: &ExecutionPlan) -> FusekiResult<QueryResults> {
        // Select appropriate strategy
        let strategy = self.select_strategy(plan);

        // Execute with selected strategy
        strategy.execute(plan, self).await
    }

    /// Select execution strategy
    fn select_strategy(&self, plan: &ExecutionPlan) -> Arc<dyn ExecutionStrategy> {
        for strategy in &self.strategies {
            if strategy.applicable(plan) {
                return strategy.clone();
            }
        }

        // Default to sequential
        self.strategies[1].clone()
    }

    /// Execute a single fragment
    pub async fn execute_fragment(
        &self,
        fragment: &QueryFragment,
        endpoint_url: &str,
    ) -> FusekiResult<QueryResults> {
        let _permit = self
            .semaphore
            .acquire()
            .await
            .map_err(|_| FusekiError::internal("Semaphore error"))?;

        let client = self.client_pool.get_client(endpoint_url).await?;

        let mut retries = 0;
        loop {
            match self
                .send_query(&client, endpoint_url, &fragment.sparql)
                .await
            {
                Ok(results) => return Ok(results),
                Err(_e) if retries < self.retry_policy.max_retries => {
                    retries += 1;
                    let backoff = self.calculate_backoff(retries);
                    tokio::time::sleep(backoff).await;
                }
                Err(e) => return Err(e),
            }
        }
    }

    /// Send query to endpoint
    async fn send_query(
        &self,
        client: &Client,
        endpoint_url: &str,
        query: &str,
    ) -> FusekiResult<QueryResults> {
        let response = client
            .post(endpoint_url)
            .header("Content-Type", "application/sparql-query")
            .header("Accept", "application/sparql-results+json")
            .body(query.to_string())
            .send()
            .await
            .map_err(|e| FusekiError::internal(format!("Request failed: {e}")))?;

        if !response.status().is_success() {
            return Err(FusekiError::bad_request(format!(
                "Endpoint returned status: {}",
                response.status()
            )));
        }

        let json: serde_json::Value = response
            .json()
            .await
            .map_err(|e| FusekiError::internal(format!("JSON parse error: {e}")))?;

        // Parse SPARQL results
        let bindings = self.parse_sparql_results(json)?;

        Ok(QueryResults {
            bindings: bindings.clone(),
            metadata: ResultMetadata {
                total_execution_time_ms: 0,
                endpoint_times: HashMap::new(),
                result_count: bindings.len(),
                partial_results: false,
            },
        })
    }

    /// Parse SPARQL JSON results
    fn parse_sparql_results(
        &self,
        json: serde_json::Value,
    ) -> FusekiResult<Vec<HashMap<String, serde_json::Value>>> {
        let results = json
            .get("results")
            .and_then(|r| r.get("bindings"))
            .and_then(|b| b.as_array())
            .ok_or_else(|| FusekiError::internal("Invalid SPARQL results format"))?;

        let mut bindings = Vec::new();
        for result in results {
            if let Some(obj) = result.as_object() {
                let mut binding = HashMap::new();
                for (var, value) in obj {
                    binding.insert(var.clone(), value.clone());
                }
                bindings.push(binding);
            }
        }

        Ok(bindings)
    }

    /// Calculate backoff duration
    pub fn calculate_backoff(&self, attempt: u32) -> Duration {
        let backoff_ms = (self.retry_policy.initial_backoff_ms as f64
            * self.retry_policy.exponential_base.powi(attempt as i32))
            as u64;

        Duration::from_millis(backoff_ms.min(self.retry_policy.max_backoff_ms))
    }
}

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

impl ClientPool {
    pub fn new() -> Self {
        Self {
            clients: DashMap::new(),
            max_connections_per_endpoint: 10,
        }
    }

    /// Get or create client for endpoint
    pub async fn get_client(&self, endpoint_url: &str) -> FusekiResult<Client> {
        if let Some(client) = self.clients.get(endpoint_url) {
            return Ok(client.clone());
        }

        let client = ClientBuilder::new()
            .pool_max_idle_per_host(self.max_connections_per_endpoint)
            .timeout(Duration::from_secs(30))
            .build()
            .map_err(|e| FusekiError::internal(format!("Client creation failed: {e}")))?;

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

impl Default for RetryPolicy {
    fn default() -> Self {
        Self {
            max_retries: 3,
            initial_backoff_ms: 100,
            max_backoff_ms: 5000,
            exponential_base: 2.0,
        }
    }
}

/// Parallel execution strategy
struct ParallelExecutionStrategy;

#[async_trait]
impl ExecutionStrategy for ParallelExecutionStrategy {
    fn name(&self) -> &str {
        "ParallelExecution"
    }

    fn applicable(&self, plan: &ExecutionPlan) -> bool {
        plan.fragments.len() > 1 && plan.fragments.iter().all(|f| f.dependencies.is_empty())
    }

    async fn execute(
        &self,
        plan: &ExecutionPlan,
        executor: &FederatedExecutor,
    ) -> FusekiResult<QueryResults> {
        let mut futures = FuturesUnordered::new();

        // Execute all fragments in parallel
        for fragment in &plan.fragments {
            for endpoint in &fragment.target_endpoints {
                let fragment_clone = fragment.clone();
                let endpoint_clone = endpoint.clone();
                let executor_clone = executor;

                futures.push(async move {
                    executor_clone
                        .execute_fragment(&fragment_clone, &endpoint_clone)
                        .await
                });
            }
        }

        // Collect results
        let mut all_results = Vec::new();
        while let Some(result) = futures.next().await {
            all_results.push(result?);
        }

        // Merge results
        ResultMerger::new().merge_results(all_results).await
    }
}

/// Sequential execution strategy
struct SequentialExecutionStrategy;

#[async_trait]
impl ExecutionStrategy for SequentialExecutionStrategy {
    fn name(&self) -> &str {
        "SequentialExecution"
    }

    fn applicable(&self, _plan: &ExecutionPlan) -> bool {
        true // Always applicable as fallback
    }

    async fn execute(
        &self,
        plan: &ExecutionPlan,
        executor: &FederatedExecutor,
    ) -> FusekiResult<QueryResults> {
        let mut all_results = Vec::new();

        // Execute fragments sequentially
        for fragment in &plan.fragments {
            for endpoint in &fragment.target_endpoints {
                let result = executor.execute_fragment(fragment, endpoint).await?;
                all_results.push(result);
            }
        }

        // Merge results
        ResultMerger::new().merge_results(all_results).await
    }
}

/// Adaptive execution strategy
struct AdaptiveExecutionStrategy;

#[async_trait]
impl ExecutionStrategy for AdaptiveExecutionStrategy {
    fn name(&self) -> &str {
        "AdaptiveExecution"
    }

    fn applicable(&self, plan: &ExecutionPlan) -> bool {
        plan.fragments.len() > 2
    }

    async fn execute(
        &self,
        plan: &ExecutionPlan,
        executor: &FederatedExecutor,
    ) -> FusekiResult<QueryResults> {
        // Group fragments by dependencies
        let independent: Vec<_> = plan
            .fragments
            .iter()
            .filter(|f| f.dependencies.is_empty())
            .collect();

        let dependent: Vec<_> = plan
            .fragments
            .iter()
            .filter(|f| !f.dependencies.is_empty())
            .collect();

        let mut all_results = Vec::new();

        // Execute independent fragments in parallel
        if !independent.is_empty() {
            let mut futures = FuturesUnordered::new();
            for fragment in independent {
                for endpoint in &fragment.target_endpoints {
                    let fragment_clone = fragment.clone();
                    let endpoint_clone = endpoint.clone();
                    let executor_clone = executor;

                    futures.push(async move {
                        executor_clone
                            .execute_fragment(&fragment_clone, &endpoint_clone)
                            .await
                    });
                }
            }

            while let Some(result) = futures.next().await {
                all_results.push(result?);
            }
        }

        // Execute dependent fragments sequentially
        for fragment in dependent {
            for endpoint in &fragment.target_endpoints {
                let result = executor.execute_fragment(fragment, endpoint).await?;
                all_results.push(result);
            }
        }

        // Merge results
        ResultMerger::new().merge_results(all_results).await
    }
}

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

impl ResultMerger {
    pub fn new() -> Self {
        Self {
            strategies: Self::create_merge_strategies(),
            dedup_cache: Arc::new(RwLock::new(HashSet::new())),
        }
    }

    /// Create merge strategies
    fn create_merge_strategies() -> HashMap<String, Arc<dyn MergeStrategy>> {
        let mut strategies = HashMap::new();
        strategies.insert(
            "union".to_string(),
            Arc::new(UnionMergeStrategy) as Arc<dyn MergeStrategy>,
        );
        strategies.insert(
            "join".to_string(),
            Arc::new(JoinMergeStrategy) as Arc<dyn MergeStrategy>,
        );
        strategies.insert(
            "distinct".to_string(),
            Arc::new(DistinctMergeStrategy) as Arc<dyn MergeStrategy>,
        );
        strategies
    }

    /// Merge multiple query results
    pub async fn merge_results(&self, results: Vec<QueryResults>) -> FusekiResult<QueryResults> {
        if results.is_empty() {
            return Ok(QueryResults {
                bindings: vec![],
                metadata: ResultMetadata {
                    total_execution_time_ms: 0,
                    endpoint_times: HashMap::new(),
                    result_count: 0,
                    partial_results: false,
                },
            });
        }

        if results.len() == 1 {
            return Ok(results
                .into_iter()
                .next()
                .expect("results should not be empty after check"));
        }

        // Default to union merge
        let strategy = self
            .strategies
            .get("union")
            .expect("union strategy should be registered");
        strategy.merge(results).await
    }
}

/// Union merge strategy
struct UnionMergeStrategy;

#[async_trait]
impl MergeStrategy for UnionMergeStrategy {
    fn name(&self) -> &str {
        "UnionMerge"
    }

    async fn merge(&self, results: Vec<QueryResults>) -> FusekiResult<QueryResults> {
        let mut merged_bindings = Vec::new();
        let mut total_time = 0;
        let mut endpoint_times = HashMap::new();

        for result in results {
            merged_bindings.extend(result.bindings);
            total_time += result.metadata.total_execution_time_ms;
            endpoint_times.extend(result.metadata.endpoint_times);
        }

        let result_count = merged_bindings.len();
        Ok(QueryResults {
            bindings: merged_bindings,
            metadata: ResultMetadata {
                total_execution_time_ms: total_time,
                endpoint_times,
                result_count,
                partial_results: false,
            },
        })
    }
}

/// Join merge strategy
struct JoinMergeStrategy;

#[async_trait]
impl MergeStrategy for JoinMergeStrategy {
    fn name(&self) -> &str {
        "JoinMerge"
    }

    async fn merge(&self, results: Vec<QueryResults>) -> FusekiResult<QueryResults> {
        if results.len() != 2 {
            return Err(FusekiError::internal("Join requires exactly 2 result sets"));
        }

        let left = &results[0];
        let right = &results[1];
        let mut joined_bindings = Vec::new();

        // Simple nested loop join
        for left_binding in &left.bindings {
            for right_binding in &right.bindings {
                // Find common variables
                let common_vars: Vec<_> = left_binding
                    .keys()
                    .filter(|k| right_binding.contains_key(*k))
                    .collect();

                // Check if common variables have same values
                let mut match_found = true;
                for var in &common_vars {
                    if left_binding.get(*var) != right_binding.get(*var) {
                        match_found = false;
                        break;
                    }
                }

                if match_found {
                    // Merge bindings
                    let mut merged = left_binding.clone();
                    for (k, v) in right_binding {
                        merged.entry(k.clone()).or_insert(v.clone());
                    }
                    joined_bindings.push(merged);
                }
            }
        }

        let result_count = joined_bindings.len();
        Ok(QueryResults {
            bindings: joined_bindings,
            metadata: ResultMetadata {
                total_execution_time_ms: left.metadata.total_execution_time_ms
                    + right.metadata.total_execution_time_ms,
                endpoint_times: {
                    let mut times = left.metadata.endpoint_times.clone();
                    times.extend(right.metadata.endpoint_times.clone());
                    times
                },
                result_count,
                partial_results: false,
            },
        })
    }
}

/// Distinct merge strategy
struct DistinctMergeStrategy;

#[async_trait]
impl MergeStrategy for DistinctMergeStrategy {
    fn name(&self) -> &str {
        "DistinctMerge"
    }

    async fn merge(&self, results: Vec<QueryResults>) -> FusekiResult<QueryResults> {
        let mut seen = HashSet::new();
        let mut distinct_bindings = Vec::new();
        let mut total_time = 0;
        let mut endpoint_times = HashMap::new();

        for result in results {
            for binding in result.bindings {
                let hash = Self::hash_binding(&binding);
                if seen.insert(hash) {
                    distinct_bindings.push(binding);
                }
            }
            total_time += result.metadata.total_execution_time_ms;
            endpoint_times.extend(result.metadata.endpoint_times);
        }

        let result_count = distinct_bindings.len();
        Ok(QueryResults {
            bindings: distinct_bindings,
            metadata: ResultMetadata {
                total_execution_time_ms: total_time,
                endpoint_times,
                result_count,
                partial_results: false,
            },
        })
    }
}

impl DistinctMergeStrategy {
    fn hash_binding(binding: &HashMap<String, serde_json::Value>) -> u64 {
        use std::hash::{Hash, Hasher};
        let mut hasher = std::collections::hash_map::DefaultHasher::new();

        let mut items: Vec<_> = binding.iter().collect();
        items.sort_by_key(|(k, _)| k.as_str());

        for (k, v) in items {
            k.hash(&mut hasher);
            v.to_string().hash(&mut hasher);
        }

        hasher.finish()
    }
}

/// UUID generation for query IDs
mod uuid {
    pub struct Uuid;

    impl Uuid {
        pub fn new_v4() -> Self {
            Uuid
        }
    }

    impl std::fmt::Display for Uuid {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            use scirs2_core::random::{Random, Rng};
            let mut rng = Random::seed(42);
            write!(
                f,
                "{:x}-{:x}-{:x}-{:x}",
                rng.random_range(0..u32::MAX),
                rng.random_range(0..u16::MAX),
                rng.random_range(0..u16::MAX),
                rng.random_range(0..u32::MAX)
            )
        }
    }
}

/// Random number generation
mod rand {
    pub fn random<T>() -> T
    where
        T: From<u32>,
    {
        T::from(
            std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .expect("SystemTime should be after UNIX_EPOCH")
                .as_nanos() as u32,
        )
    }
}

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

    #[tokio::test]
    async fn test_extract_service_patterns() {
        let config = crate::config::MonitoringConfig {
            metrics: crate::config::MetricsConfig {
                enabled: false,
                endpoint: "/metrics".to_string(),
                port: Some(9000),
                namespace: "oxirs_fuseki".to_string(),
                collect_system_metrics: true,
                histogram_buckets: vec![
                    0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
                ],
            },
            health_checks: crate::config::HealthCheckConfig {
                enabled: false,
                interval_secs: 30,
                timeout_secs: 5,
                checks: vec!["store".to_string(), "memory".to_string()],
            },
            tracing: crate::config::TracingConfig {
                enabled: false,
                endpoint: None,
                service_name: "oxirs-fuseki".to_string(),
                sample_rate: 0.1,
                output: crate::config::TracingOutput::Stdout,
            },
            prometheus: Some(crate::config::PrometheusConfig {
                enabled: false,
                endpoint: "/metrics".to_string(),
                port: Some(9090),
                namespace: "oxirs_fuseki".to_string(),
                job_name: "oxirs-fuseki".to_string(),
                instance: "localhost:3030".to_string(),
                scrape_interval_secs: 15,
                timeout_secs: 10,
            }),
        };
        let optimizer =
            FederatedQueryOptimizer::new(Arc::new(MetricsService::new(config).unwrap()));

        let query = r#"
            PREFIX foaf: <http://xmlns.com/foaf/0.1/>
            SELECT ?person ?name ?friend
            WHERE {
                ?person foaf:name ?name .
                SERVICE <http://example.org/sparql> {
                    ?person foaf:knows ?friend .
                }
            }
        "#;

        let patterns = optimizer.extract_service_patterns(query).unwrap();
        assert_eq!(patterns.len(), 1);
        assert_eq!(patterns[0].service_url, "http://example.org/sparql");
        assert!(!patterns[0].is_silent);
    }

    #[tokio::test]
    async fn test_multiple_service_patterns() {
        let config = crate::config::MonitoringConfig {
            metrics: crate::config::MetricsConfig {
                enabled: false,
                endpoint: "/metrics".to_string(),
                port: Some(9000),
                namespace: "oxirs_fuseki".to_string(),
                collect_system_metrics: true,
                histogram_buckets: vec![
                    0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
                ],
            },
            health_checks: crate::config::HealthCheckConfig {
                enabled: false,
                interval_secs: 30,
                timeout_secs: 5,
                checks: vec!["store".to_string(), "memory".to_string()],
            },
            tracing: crate::config::TracingConfig {
                enabled: false,
                endpoint: None,
                service_name: "oxirs-fuseki".to_string(),
                sample_rate: 0.1,
                output: crate::config::TracingOutput::Stdout,
            },
            prometheus: Some(crate::config::PrometheusConfig {
                enabled: false,
                endpoint: "/metrics".to_string(),
                port: Some(9090),
                namespace: "oxirs_fuseki".to_string(),
                job_name: "oxirs-fuseki".to_string(),
                instance: "localhost:3030".to_string(),
                scrape_interval_secs: 15,
                timeout_secs: 10,
            }),
        };
        let optimizer =
            FederatedQueryOptimizer::new(Arc::new(MetricsService::new(config).unwrap()));

        let query = r#"
            SELECT ?s ?p ?o
            WHERE {
                SERVICE <http://endpoint1.org/sparql> {
                    ?s ?p ?o
                }
                SERVICE SILENT <http://endpoint2.org/sparql> {
                    ?s ?p2 ?o2
                }
            }
        "#;

        let patterns = optimizer.extract_service_patterns(query).unwrap();
        assert_eq!(patterns.len(), 2);
        assert!(!patterns[0].is_silent);
        assert!(patterns[1].is_silent);
    }

    #[tokio::test]
    async fn test_query_planner() {
        let planner = QueryPlanner::new();
        let service_patterns = vec![ServicePattern {
            service_url: "http://test.org/sparql".to_string(),
            pattern: "?s ?p ?o".to_string(),
            is_silent: false,
            is_optional: false,
        }];

        let plan = planner
            .create_execution_plan("SELECT * WHERE { ?s ?p ?o }", &service_patterns)
            .await
            .unwrap();
        assert!(!plan.fragments.is_empty());
    }

    #[tokio::test]
    async fn test_result_merger_union() {
        let merger = ResultMerger::new();

        let results = vec![
            QueryResults {
                bindings: vec![HashMap::from([(
                    "x".to_string(),
                    serde_json::json!("value1"),
                )])],
                metadata: ResultMetadata {
                    total_execution_time_ms: 100,
                    endpoint_times: HashMap::new(),
                    result_count: 1,
                    partial_results: false,
                },
            },
            QueryResults {
                bindings: vec![HashMap::from([(
                    "x".to_string(),
                    serde_json::json!("value2"),
                )])],
                metadata: ResultMetadata {
                    total_execution_time_ms: 150,
                    endpoint_times: HashMap::new(),
                    result_count: 1,
                    partial_results: false,
                },
            },
        ];

        let merged = merger.merge_results(results).await.unwrap();
        assert_eq!(merged.bindings.len(), 2);
        assert_eq!(merged.metadata.total_execution_time_ms, 250);
    }
}