oxirs-gql 0.2.4

//! RDF Dataset Federation for SPARQL endpoint integration

use anyhow::{Context, Result};
use futures_util::future;
use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::time::{Duration, Instant};

/// RDF dataset federation manager
pub struct DatasetFederation {
    endpoints: Vec<SparqlEndpoint>,
    join_optimizer: JoinOptimizer,
}

/// SPARQL endpoint configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SparqlEndpoint {
    pub id: String,
    pub url: String,
    pub auth_header: Option<String>,
    pub timeout_secs: u64,
    pub max_concurrent_queries: usize,
    pub supported_features: HashSet<String>,
    pub statistics: Option<EndpointStatistics>,
}

/// Statistics about a SPARQL endpoint
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct EndpointStatistics {
    #[serde(with = "duration_serde")]
    pub avg_response_time: Duration,
    pub triple_count: Option<u64>,
    pub indexes: Vec<String>,
    #[serde(with = "instant_serde")]
    pub last_updated: Instant,
}

impl Default for EndpointStatistics {
    fn default() -> Self {
        Self {
            avg_response_time: Duration::from_millis(100),
            triple_count: None,
            indexes: Vec::new(),
            last_updated: Instant::now(),
        }
    }
}

mod duration_serde {
    use serde::{Deserialize, Deserializer, Serializer};
    use std::time::Duration;

    pub fn serialize<S>(duration: &Duration, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u64(duration.as_millis() as u64)
    }

    pub fn deserialize<'de, D>(deserializer: D) -> Result<Duration, D::Error>
    where
        D: Deserializer<'de>,
    {
        let millis = u64::deserialize(deserializer)?;
        Ok(Duration::from_millis(millis))
    }
}

mod instant_serde {
    use serde::{Deserializer, Serializer};
    use std::time::{Instant, SystemTime, UNIX_EPOCH};

    pub fn serialize<S>(_instant: &Instant, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        // Convert to timestamp relative to Unix epoch
        let now = SystemTime::now();
        let epoch_duration = now.duration_since(UNIX_EPOCH).unwrap_or_default();
        let instant_timestamp = epoch_duration.as_secs();
        serializer.serialize_u64(instant_timestamp)
    }

    pub fn deserialize<'de, D>(_deserializer: D) -> Result<Instant, D::Error>
    where
        D: Deserializer<'de>,
    {
        // Just return current instant for deserialization
        Ok(Instant::now())
    }
}

/// Join optimization for federated queries
pub struct JoinOptimizer {
    #[allow(dead_code)]
    cost_model: CostModel,
}

/// Cost model for query planning
#[derive(Debug, Clone)]
pub struct CostModel {
    #[allow(dead_code)]
    network_latency_ms: f64,
    #[allow(dead_code)]
    transfer_cost_per_mb: f64,
    #[allow(dead_code)]
    local_processing_cost: f64,
}

/// Federated query execution step
#[derive(Debug, Clone)]
pub struct FederatedStep {
    pub endpoint_id: String,
    pub sparql_query: String,
    pub expected_result_size: Option<u64>,
}

/// Join pattern for optimization
#[derive(Debug, Clone)]
pub struct JoinPattern {
    pub left_step: usize,
    pub right_step: usize,
    pub join_variables: Vec<String>,
}

impl DatasetFederation {
    pub fn new() -> Self {
        Self {
            endpoints: Vec::new(),
            join_optimizer: JoinOptimizer::new(),
        }
    }

    pub fn add_endpoint(&mut self, endpoint: SparqlEndpoint) {
        self.endpoints.push(endpoint);
    }

    /// Federate a SPARQL query across multiple endpoints
    pub async fn federate_sparql_query(&self, query: &str) -> Result<serde_json::Value> {
        // Parse and analyze the query
        let query_plan = self.plan_federated_query(query).await?;

        // Execute the plan
        self.execute_federated_plan(&query_plan).await
    }

    /// Plan execution across multiple SPARQL endpoints
    async fn plan_federated_query(&self, query: &str) -> Result<Vec<FederatedStep>> {
        let mut steps = Vec::new();

        // Simple implementation: determine which endpoints can contribute
        for endpoint in &self.endpoints {
            if self.endpoint_can_contribute(endpoint, query).await? {
                let adapted_query = self.adapt_query_for_endpoint(query, endpoint)?;
                steps.push(FederatedStep {
                    endpoint_id: endpoint.id.clone(),
                    sparql_query: adapted_query,
                    expected_result_size: None,
                });
            }
        }

        // Optimize join order
        self.join_optimizer.optimize_joins(&mut steps);

        Ok(steps)
    }

    /// Check if an endpoint can contribute to the query
    async fn endpoint_can_contribute(
        &self,
        endpoint: &SparqlEndpoint,
        query: &str,
    ) -> Result<bool> {
        // Simple heuristic: check if endpoint supports required features
        // In practice, this would involve more sophisticated capability assessment

        if query.contains("FILTER") && !endpoint.supported_features.contains("filters") {
            return Ok(false);
        }

        if query.contains("GROUP BY") && !endpoint.supported_features.contains("aggregation") {
            return Ok(false);
        }

        Ok(true)
    }

    /// Adapt a query for a specific endpoint
    fn adapt_query_for_endpoint(&self, query: &str, endpoint: &SparqlEndpoint) -> Result<String> {
        // Simple adaptation - in practice this would be much more sophisticated
        let mut adapted = query.to_string();

        // Add SERVICE clause if needed
        if !adapted.contains("SERVICE") {
            adapted = format!(
                "SELECT * WHERE {{ SERVICE <{}> {{ {} }} }}",
                endpoint.url, adapted
            );
        }

        Ok(adapted)
    }

    /// Execute a federated query plan
    async fn execute_federated_plan(&self, plan: &[FederatedStep]) -> Result<serde_json::Value> {
        // Execute steps in parallel where possible
        let futures: Vec<_> = plan
            .iter()
            .map(|step| self.execute_federated_step(step))
            .collect();

        let step_results = future::try_join_all(futures).await?;

        // Merge results
        self.merge_federated_results(&step_results)
    }

    /// Execute a single federated step
    async fn execute_federated_step(&self, step: &FederatedStep) -> Result<serde_json::Value> {
        let endpoint = self
            .endpoints
            .iter()
            .find(|ep| ep.id == step.endpoint_id)
            .ok_or_else(|| anyhow::anyhow!("Endpoint not found: {}", step.endpoint_id))?;

        let client = reqwest::Client::new();

        let mut request = client
            .post(&endpoint.url)
            .header("Content-Type", "application/sparql-query")
            .body(step.sparql_query.clone());

        if let Some(auth) = &endpoint.auth_header {
            request = request.header("Authorization", auth);
        }

        let response = request
            .timeout(Duration::from_secs(endpoint.timeout_secs))
            .send()
            .await
            .context("Failed to execute SPARQL query")?;

        if !response.status().is_success() {
            return Err(anyhow::anyhow!(
                "SPARQL query failed with status: {}",
                response.status()
            ));
        }

        let result = response
            .json()
            .await
            .context("Failed to parse SPARQL response")?;

        Ok(result)
    }

    /// Merge results from federated execution
    fn merge_federated_results(&self, results: &[serde_json::Value]) -> Result<serde_json::Value> {
        // Simple merge - combine all bindings
        let mut merged_bindings = Vec::new();

        for result in results {
            if let Some(result_obj) = result.as_object() {
                if let Some(results_obj) = result_obj.get("results") {
                    if let Some(bindings) = results_obj.get("bindings").and_then(|b| b.as_array()) {
                        merged_bindings.extend(bindings.iter().cloned());
                    }
                }
            }
        }

        Ok(serde_json::json!({
            "head": {
                "vars": []
            },
            "results": {
                "bindings": merged_bindings
            }
        }))
    }

    /// Update endpoint statistics
    pub async fn update_endpoint_statistics(&mut self, endpoint_id: &str) -> Result<()> {
        let endpoint_idx = self
            .endpoints
            .iter()
            .position(|ep| ep.id == endpoint_id)
            .ok_or_else(|| anyhow::anyhow!("Endpoint not found: {}", endpoint_id))?;

        // Perform capability assessment
        let stats = self
            .assess_endpoint_capabilities(&self.endpoints[endpoint_idx])
            .await?;
        self.endpoints[endpoint_idx].statistics = Some(stats);

        Ok(())
    }

    /// Assess endpoint capabilities and performance
    async fn assess_endpoint_capabilities(
        &self,
        endpoint: &SparqlEndpoint,
    ) -> Result<EndpointStatistics> {
        let start_time = Instant::now();

        // Simple capability test query
        let test_query = "SELECT (COUNT(*) as ?count) WHERE { ?s ?p ?o }";

        let client = reqwest::Client::new();
        let mut request = client
            .post(&endpoint.url)
            .header("Content-Type", "application/sparql-query")
            .body(test_query);

        if let Some(auth) = &endpoint.auth_header {
            request = request.header("Authorization", auth);
        }

        let response = request
            .timeout(Duration::from_secs(endpoint.timeout_secs))
            .send()
            .await
            .context("Failed to assess endpoint capabilities")?;

        let response_time = start_time.elapsed();

        let mut triple_count = None;
        if response.status().is_success() {
            if let Ok(result) = response.json::<serde_json::Value>().await {
                if let Some(bindings) = result.pointer("/results/bindings/0/count/value") {
                    if let Some(count_str) = bindings.as_str() {
                        triple_count = count_str.parse().ok();
                    }
                }
            }
        }

        Ok(EndpointStatistics {
            avg_response_time: response_time,
            triple_count,
            indexes: vec!["spo".to_string()], // Default assumption
            last_updated: Instant::now(),
        })
    }
}

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

impl JoinOptimizer {
    pub fn new() -> Self {
        Self {
            cost_model: CostModel {
                network_latency_ms: 50.0,
                transfer_cost_per_mb: 1.0,
                local_processing_cost: 0.1,
            },
        }
    }

    /// Optimize join order for federated steps
    pub fn optimize_joins(&self, steps: &mut [FederatedStep]) {
        // Simple optimization: prioritize endpoints with better statistics
        steps.sort_by(|a, b| {
            // Prefer steps with smaller expected result sizes
            match (a.expected_result_size, b.expected_result_size) {
                (Some(size_a), Some(size_b)) => size_a.cmp(&size_b),
                (Some(_), None) => std::cmp::Ordering::Less,
                (None, Some(_)) => std::cmp::Ordering::Greater,
                (None, None) => std::cmp::Ordering::Equal,
            }
        });
    }

    /// Identify potential join patterns
    pub fn identify_join_patterns(&self, steps: &[FederatedStep]) -> Vec<JoinPattern> {
        let mut patterns = Vec::new();

        // Simple pattern detection: look for common variables in queries
        for (i, step_a) in steps.iter().enumerate() {
            for (j, step_b) in steps.iter().enumerate().skip(i + 1) {
                let common_vars =
                    self.find_common_variables(&step_a.sparql_query, &step_b.sparql_query);
                if !common_vars.is_empty() {
                    patterns.push(JoinPattern {
                        left_step: i,
                        right_step: j,
                        join_variables: common_vars,
                    });
                }
            }
        }

        patterns
    }

    /// Find common variables between two SPARQL queries
    fn find_common_variables(&self, query_a: &str, query_b: &str) -> Vec<String> {
        // Simple regex-based variable extraction
        let var_regex =
            regex::Regex::new(r"\?(\w+)").expect("parse should succeed for valid input");

        let vars_a: HashSet<String> = var_regex
            .captures_iter(query_a)
            .map(|cap| cap[1].to_string())
            .collect();

        let vars_b: HashSet<String> = var_regex
            .captures_iter(query_b)
            .map(|cap| cap[1].to_string())
            .collect();

        vars_a.intersection(&vars_b).cloned().collect()
    }
}

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