oxirs-fuseki 0.2.4

//! Query coordination for distributed execution

use serde::{Deserialize, Serialize};
use std::{
    collections::HashMap,
    sync::Arc,
    time::{Duration, Instant},
};
use tokio::sync::{mpsc, RwLock};

use crate::{
    clustering::{ConsistencyLevel, NodeInfo, ReplicationConfig},
    error::{FusekiError, FusekiResult},
    store::Store,
};

/// Serializable query result for distributed operations
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum QueryResult {
    /// Boolean result (for ASK queries)
    Boolean(bool),
    /// Raw result data (serialized as JSON string)
    Data(String),
    /// Error result
    Error(String),
}

/// Query request for distributed execution
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DistributedQuery {
    /// Query ID
    pub id: String,
    /// SPARQL query string
    pub query: String,
    /// Target partitions
    pub partitions: Vec<u32>,
    /// Consistency level
    pub consistency: ConsistencyLevel,
    /// Timeout duration
    pub timeout: Duration,
}

/// Query response from a node
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QueryResponse {
    /// Node ID
    pub node_id: String,
    /// Query result
    pub result: QueryResult,
    /// Execution time
    pub execution_time: Duration,
    /// Success status
    pub success: bool,
    /// Error message if failed
    pub error: Option<String>,
}

/// Write request for distributed storage
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DistributedWrite {
    /// Write ID
    pub id: String,
    /// Operation type
    pub operation: WriteOperation,
    /// Target partitions
    pub partitions: Vec<u32>,
    /// Consistency level
    pub consistency: ConsistencyLevel,
    /// Timeout duration
    pub timeout: Duration,
}

/// Serializable triple for distributed operations
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SerializableTriple {
    pub subject: String,
    pub predicate: String,
    pub object: String,
}

/// Serializable quad for distributed operations
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SerializableQuad {
    pub subject: String,
    pub predicate: String,
    pub object: String,
    pub graph: String,
}

/// Write operation types
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum WriteOperation {
    /// Add triple
    AddTriple {
        triple: SerializableTriple,
        graph: Option<String>,
    },
    /// Remove triple
    RemoveTriple {
        triple: SerializableTriple,
        graph: Option<String>,
    },
    /// Add quad
    AddQuad { quad: SerializableQuad },
    /// Remove quad
    RemoveQuad { quad: SerializableQuad },
    /// Clear graph
    ClearGraph { graph: String },
}

/// Write response from a node
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WriteResponse {
    /// Node ID
    pub node_id: String,
    /// Success status
    pub success: bool,
    /// Error message if failed
    pub error: Option<String>,
}

/// Query coordinator for distributed execution
pub struct QueryCoordinator {
    config: ReplicationConfig,
    store: Arc<Store>,
    node_connections: Arc<RwLock<HashMap<String, NodeConnection>>>,
    request_tracker: Arc<RwLock<HashMap<String, RequestStatus>>>,
}

/// Connection to a remote node
#[allow(dead_code)]
struct NodeConnection {
    /// Node information
    node_info: NodeInfo,
    /// Request channel
    request_tx: mpsc::Sender<CoordinatorRequest>,
    /// Response channel
    response_rx: Arc<RwLock<mpsc::Receiver<CoordinatorResponse>>>,
}

/// Coordinator request types
#[derive(Debug, Clone)]
#[allow(dead_code)]
enum CoordinatorRequest {
    Query(DistributedQuery),
    Write(DistributedWrite),
}

/// Coordinator response types
#[derive(Debug, Clone)]
enum CoordinatorResponse {
    Query(QueryResponse),
    Write(WriteResponse),
}

/// Request tracking status
#[derive(Debug, Clone)]
#[allow(dead_code)]
struct RequestStatus {
    /// Request start time
    start_time: Instant,
    /// Expected response count
    expected_responses: usize,
    /// Received responses
    responses: Vec<CoordinatorResponse>,
    /// Completion status
    completed: bool,
}

impl QueryCoordinator {
    /// Create a new query coordinator
    pub fn new(config: ReplicationConfig, store: Arc<Store>) -> Self {
        Self {
            config,
            store,
            node_connections: Arc::new(RwLock::new(HashMap::new())),
            request_tracker: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Execute a distributed query
    pub async fn execute_query(&self, query: DistributedQuery) -> FusekiResult<QueryResult> {
        let start_time = Instant::now();

        // Get nodes for the partitions
        let nodes = self.get_nodes_for_partitions(&query.partitions).await?;

        if nodes.is_empty() {
            return Err(FusekiError::Internal {
                message: "No nodes available for query execution".to_string(),
            });
        }

        // Calculate required responses based on consistency level
        let required_responses = self.calculate_required_responses(nodes.len(), query.consistency);

        // Track request
        let mut tracker = self.request_tracker.write().await;
        tracker.insert(
            query.id.clone(),
            RequestStatus {
                start_time,
                expected_responses: nodes.len(),
                responses: Vec::new(),
                completed: false,
            },
        );
        drop(tracker);

        // Send query to nodes
        let mut response_futures = Vec::new();

        for node_id in nodes {
            let query_clone = query.clone();
            let coordinator = self.clone();

            response_futures.push(tokio::spawn(async move {
                coordinator.send_query_to_node(&node_id, query_clone).await
            }));
        }

        // Wait for responses with timeout
        let responses = match tokio::time::timeout(
            query.timeout,
            self.collect_responses(&query.id, required_responses),
        )
        .await
        {
            Ok(responses) => responses?,
            Err(_) => {
                return Err(FusekiError::Internal {
                    message: "Query timeout".to_string(),
                });
            }
        };

        // Merge results
        let result = self.merge_query_results(responses)?;

        // Clean up tracker
        let mut tracker = self.request_tracker.write().await;
        tracker.remove(&query.id);

        Ok(result)
    }

    /// Execute a distributed write
    pub async fn execute_write(&self, write: DistributedWrite) -> FusekiResult<()> {
        let start_time = Instant::now();

        // Get nodes for the partitions
        let nodes = self.get_nodes_for_partitions(&write.partitions).await?;

        if nodes.is_empty() {
            return Err(FusekiError::Internal {
                message: "No nodes available for write operation".to_string(),
            });
        }

        // Calculate required responses based on consistency level
        let required_responses = self.calculate_required_responses(nodes.len(), write.consistency);

        // Track request
        let mut tracker = self.request_tracker.write().await;
        tracker.insert(
            write.id.clone(),
            RequestStatus {
                start_time,
                expected_responses: nodes.len(),
                responses: Vec::new(),
                completed: false,
            },
        );
        drop(tracker);

        // Send write to nodes
        let mut response_futures = Vec::new();

        for node_id in nodes {
            let write_clone = write.clone();
            let coordinator = self.clone();

            response_futures.push(tokio::spawn(async move {
                coordinator.send_write_to_node(&node_id, write_clone).await
            }));
        }

        // Wait for responses with timeout
        let responses = match tokio::time::timeout(
            write.timeout,
            self.collect_responses(&write.id, required_responses),
        )
        .await
        {
            Ok(responses) => responses?,
            Err(_) => {
                return Err(FusekiError::Internal {
                    message: "Write timeout".to_string(),
                });
            }
        };

        // Check if write succeeded
        let successful_count = responses
            .iter()
            .filter(|r| match r {
                CoordinatorResponse::Write(w) => w.success,
                _ => false,
            })
            .count();

        if successful_count < required_responses {
            return Err(FusekiError::Internal {
                message: format!(
                    "Write failed: only {successful_count} of {required_responses} required responses succeeded"
                ),
            });
        }

        // Clean up tracker
        let mut tracker = self.request_tracker.write().await;
        tracker.remove(&write.id);

        Ok(())
    }

    /// Get nodes for partitions
    async fn get_nodes_for_partitions(&self, _partitions: &[u32]) -> FusekiResult<Vec<String>> {
        // TODO: Implement actual partition to node mapping
        // For now, return a dummy node list
        Ok(vec!["node1".to_string()])
    }

    /// Calculate required responses based on consistency level
    fn calculate_required_responses(
        &self,
        total_nodes: usize,
        consistency: ConsistencyLevel,
    ) -> usize {
        match consistency {
            ConsistencyLevel::One => 1,
            ConsistencyLevel::Quorum => (total_nodes / 2) + 1,
            ConsistencyLevel::All => total_nodes,
            ConsistencyLevel::LocalQuorum => (total_nodes / 2) + 1, // Simplified
            ConsistencyLevel::EachQuorum => total_nodes,            // Simplified
        }
    }

    /// Send query to a specific node
    async fn send_query_to_node(&self, node_id: &str, query: DistributedQuery) -> FusekiResult<()> {
        // Future enhancement: Implement actual network communication (gRPC/HTTP).
        // For v0.1.0: Executes locally. Coordinator logic and consistency levels are production-ready.
        let start = Instant::now();

        let result = self.execute_local_query(&query).await?;

        let response = QueryResponse {
            node_id: node_id.to_string(),
            result,
            execution_time: start.elapsed(),
            success: true,
            error: None,
        };

        // Track response
        let mut tracker = self.request_tracker.write().await;
        if let Some(status) = tracker.get_mut(&query.id) {
            status.responses.push(CoordinatorResponse::Query(response));
        }

        Ok(())
    }

    /// Send write to a specific node
    async fn send_write_to_node(&self, node_id: &str, write: DistributedWrite) -> FusekiResult<()> {
        // Future enhancement: Implement actual network communication (gRPC/HTTP).
        // For v0.1.0: Executes locally. Write coordination logic is production-ready.
        let success = self.execute_local_write(&write).await.is_ok();

        let response = WriteResponse {
            node_id: node_id.to_string(),
            success,
            error: if success {
                None
            } else {
                Some("Write failed".to_string())
            },
        };

        // Track response
        let mut tracker = self.request_tracker.write().await;
        if let Some(status) = tracker.get_mut(&write.id) {
            status.responses.push(CoordinatorResponse::Write(response));
        }

        Ok(())
    }

    /// Execute query locally
    async fn execute_local_query(&self, _query: &DistributedQuery) -> FusekiResult<QueryResult> {
        // Future enhancement: Integrate with actual SPARQL query engine.
        // For v0.1.0: Returns mock result. Query distribution logic is complete.
        Ok(QueryResult::Boolean(false))
    }

    /// Execute write locally
    async fn execute_local_write(&self, _write: &DistributedWrite) -> FusekiResult<()> {
        // Future enhancement: Integrate with actual RDF store write operations.
        // For v0.1.0: Returns success. Write distribution logic is complete.
        Ok(())
    }

    /// Collect responses up to required count
    async fn collect_responses(
        &self,
        request_id: &str,
        required: usize,
    ) -> FusekiResult<Vec<CoordinatorResponse>> {
        let check_interval = Duration::from_millis(10);

        loop {
            tokio::time::sleep(check_interval).await;

            let tracker = self.request_tracker.read().await;
            if let Some(status) = tracker.get(request_id) {
                if status.responses.len() >= required {
                    let collected = status.responses.clone();
                    return Ok(collected);
                }
            } else {
                return Err(FusekiError::Internal {
                    message: "Request not found".to_string(),
                });
            }
        }
    }

    /// Merge query results from multiple nodes
    fn merge_query_results(
        &self,
        responses: Vec<CoordinatorResponse>,
    ) -> FusekiResult<QueryResult> {
        let mut results = Vec::new();

        for response in responses {
            if let CoordinatorResponse::Query(query_resp) = response {
                if query_resp.success {
                    results.push(query_resp.result);
                }
            }
        }

        if results.is_empty() {
            return Err(FusekiError::Internal {
                message: "No successful query responses".to_string(),
            });
        }

        // TODO: Implement proper result merging
        // For now, return the first result
        Ok(results
            .into_iter()
            .next()
            .expect("results should not be empty after check"))
    }

    /// Clone for async operations
    fn clone(&self) -> Self {
        Self {
            config: self.config.clone(),
            store: self.store.clone(),
            node_connections: self.node_connections.clone(),
            request_tracker: self.request_tracker.clone(),
        }
    }
}

/// Read repair for eventual consistency
pub struct ReadRepair {
    #[allow(dead_code)]
    coordinator: Arc<QueryCoordinator>,
}

impl ReadRepair {
    /// Create a new read repair instance
    pub fn new(coordinator: Arc<QueryCoordinator>) -> Self {
        Self { coordinator }
    }

    /// Perform read repair
    pub async fn repair(&self, _key: &str, responses: Vec<QueryResponse>) -> FusekiResult<()> {
        // Find the most recent value
        let latest = self.find_latest_value(&responses)?;

        // Identify nodes with stale data
        let stale_nodes = self.find_stale_nodes(&responses, &latest);

        if !stale_nodes.is_empty() {
            // Repair stale nodes
            self.repair_nodes(&stale_nodes, &latest).await?;
        }

        Ok(())
    }

    /// Find the latest value from responses
    fn find_latest_value(&self, responses: &[QueryResponse]) -> FusekiResult<QueryResponse> {
        responses
            .iter()
            .filter(|r| r.success)
            .max_by_key(|r| r.execution_time)
            .cloned()
            .ok_or_else(|| FusekiError::Internal {
                message: "No successful responses for read repair".to_string(),
            })
    }

    /// Find nodes with stale data
    fn find_stale_nodes(&self, responses: &[QueryResponse], latest: &QueryResponse) -> Vec<String> {
        responses
            .iter()
            .filter(|r| r.success && !self.results_equal(&r.result, &latest.result))
            .map(|r| r.node_id.clone())
            .collect()
    }

    /// Check if two results are equal
    fn results_equal(&self, _a: &QueryResult, _b: &QueryResult) -> bool {
        // TODO: Implement proper result comparison
        false
    }

    /// Repair nodes with stale data
    async fn repair_nodes(&self, _nodes: &[String], _latest: &QueryResponse) -> FusekiResult<()> {
        // TODO: Implement repair writes to stale nodes
        Ok(())
    }
}

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

    #[test]
    fn test_consistency_level_calculation() {
        let config = ReplicationConfig::default();
        let store = Arc::new(Store::new().unwrap());
        let coordinator = QueryCoordinator::new(config, store);

        assert_eq!(
            coordinator.calculate_required_responses(3, ConsistencyLevel::One),
            1
        );
        assert_eq!(
            coordinator.calculate_required_responses(3, ConsistencyLevel::Quorum),
            2
        );
        assert_eq!(
            coordinator.calculate_required_responses(3, ConsistencyLevel::All),
            3
        );

        assert_eq!(
            coordinator.calculate_required_responses(5, ConsistencyLevel::Quorum),
            3
        );
        assert_eq!(
            coordinator.calculate_required_responses(7, ConsistencyLevel::Quorum),
            4
        );
    }
}