kotoba_db_cluster/

replication.rs

//! # Data Replication
//!
//! Replication mechanisms for KotobaDB cluster.
//! Provides data redundancy, fault tolerance, and read scaling.

use crate::*;
use std::collections::{HashMap, HashSet};
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::sync::{RwLock, mpsc};
use tokio::time::{self, MissedTickBehavior};

/// Replication manager for data redundancy
pub struct ReplicationManager {
    /// Cluster state
    cluster_state: Arc<ClusterState>,
    /// Replication configuration
    config: ReplicationConfig,
    /// Replication queues for each node
    replication_queues: Arc<RwLock<HashMap<NodeId, ReplicationQueue>>>,
    /// Replication status tracking
    status: Arc<RwLock<ReplicationStatus>>,
    /// Command channel
    command_tx: mpsc::Sender<ReplicationCommand>,
    command_rx: mpsc::Receiver<ReplicationCommand>,
}

impl ReplicationManager {
    /// Create a new replication manager
    pub fn new(cluster_state: Arc<ClusterState>, config: ReplicationConfig) -> Self {
        let (command_tx, command_rx) = mpsc::channel(1000);

        Self {
            cluster_state,
            config,
            replication_queues: Arc::new(RwLock::new(HashMap::new())),
            status: Arc::new(RwLock::new(ReplicationStatus::new())),
            command_tx,
            command_rx,
        }
    }

    /// Start replication processes
    pub async fn start(&mut self) -> Result<(), ReplicationError> {
        // TODO: Implement replication startup
        // For now, just return Ok to allow compilation
        Ok(())
    }

    /// Queue an operation for replication
    pub async fn replicate_operation(&self, operation: Operation, primary_node: &NodeId) -> Result<(), ReplicationError> {
        let mut queues = self.replication_queues.write().await;

        // Get replica nodes for this operation
        let key = self.get_operation_key(&operation);
        let replica_nodes = self.cluster_state.get_nodes_for_key(&key).await;

        // Queue operation on replica nodes (excluding primary)
        for node_id in replica_nodes {
            if &node_id != primary_node {
                let queue = queues.entry(node_id.clone()).or_insert_with(ReplicationQueue::new);
                queue.push(ReplicationItem {
                    operation: operation.clone(),
                    timestamp: Instant::now(),
                    retries: 0,
                });
            }
        }

        Ok(())
    }

    /// Synchronize data with a specific node
    pub async fn sync_with_node(&self, node_id: &NodeId) -> Result<(), ReplicationError> {
        let config = self.cluster_state.config.read().await;
        let partitions = config.nodes.get(node_id)
            .map(|info| info.partitions.clone())
            .unwrap_or_default();

        // TODO: Implement full partition synchronization
        println!("Synchronizing {} partitions with node {}", partitions.len(), node_id.0);

        Ok(())
    }

    /// Handle node failure and promote replica
    pub async fn handle_node_failure(&self, failed_node: &NodeId) -> Result<(), ReplicationError> {
        println!("Handling failure of node {}", failed_node.0);

        // Find partitions owned by failed node
        let partitions = self.cluster_state.get_partitions_for_node(failed_node).await;

        // Redistribute partitions to remaining nodes
        for partition in partitions {
            self.redistribute_partition(&partition).await?;
        }

        // Update replication status
        let mut status = self.status.write().await;
        status.mark_node_failed(failed_node);

        Ok(())
    }

    /// Check replication health
    pub async fn check_health(&self) -> ReplicationHealth {
        let status = self.status.read().await;
        let queues = self.replication_queues.read().await;

        let total_queued = queues.values().map(|q| q.len()).sum();
        let failed_nodes = status.failed_nodes.len();

        ReplicationHealth {
            total_queued_operations: total_queued,
            failed_nodes_count: failed_nodes,
            replication_lag: status.get_average_lag(),
            is_healthy: failed_nodes == 0 && total_queued < 1000, // Arbitrary threshold
        }
    }

    /// Get replication status
    pub async fn get_status(&self) -> ReplicationStatusSnapshot {
        let status = self.status.read().await;
        let queues = self.replication_queues.read().await;

        let node_statuses: HashMap<NodeId, NodeReplicationStatus> = queues.iter()
            .map(|(node_id, queue)| {
                let node_status = status.node_status.get(node_id)
                    .cloned()
                    .unwrap_or_default();

                (node_id.clone(), NodeReplicationStatus {
                    queued_operations: queue.len(),
                    last_sync: node_status.last_sync,
                    replication_lag: node_status.replication_lag,
                    is_synced: node_status.is_synced,
                })
            })
            .collect();

        ReplicationStatusSnapshot {
            node_statuses,
            total_operations_processed: status.total_operations_processed,
            total_operations_failed: status.total_operations_failed,
        }
    }

    // Internal methods

    async fn start_status_monitor(&self, cluster_state: Arc<ClusterState>) -> Result<(), ReplicationError> {
        let status = Arc::clone(&self.status);
        let queues = Arc::clone(&self.replication_queues);
        let config = self.config.clone();

        tokio::spawn(async move {
            let mut interval = time::interval(config.status_check_interval);
            interval.set_missed_tick_behavior(MissedTickBehavior::Delay);

            loop {
                interval.tick().await;

                let mut status = status.write().await;
                let queues = queues.read().await;

                // Update replication lag for each node
                for (node_id, queue) in queues.iter() {
                    if let Some(oldest) = queue.oldest_item() {
                        let lag = oldest.timestamp.elapsed();
                        status.update_node_lag(node_id, lag);
                    }
                }

                // Check for failed nodes (no sync for too long)
                let timeout = config.node_failure_timeout;
                let mut failed_nodes = Vec::new();

                for (node_id, node_status) in &status.node_status {
                    if let Some(last_sync) = node_status.last_sync {
                        if last_sync.elapsed() > timeout {
                            failed_nodes.push(node_id.clone());
                        }
                    }
                }

                for node_id in failed_nodes {
                    status.mark_node_failed(&node_id);
                    println!("Node {} marked as failed due to timeout", node_id.0);
                }
            }
        });

        Ok(())
    }

    async fn start_queue_processor(&self, cluster_state: Arc<ClusterState>) -> Result<(), ReplicationError> {
        let queues = Arc::clone(&self.replication_queues);
        let status = Arc::clone(&self.status);
        let config = self.config.clone();

        tokio::spawn(async move {
            loop {
                let mut queues = queues.write().await;
                let mut status = status.write().await;

                // Process replication queues
                for (node_id, queue) in queues.iter_mut() {
                    while let Some(item) = queue.pop() {
                        match Self::replicate_item_to_node(&item, node_id, &config).await {
                            Ok(_) => {
                                status.record_operation_success(node_id);
                            }
                            Err(e) => {
                                status.record_operation_failure(node_id);
                                println!("Replication failed for node {}: {}", node_id.0, e);

                                // Re-queue with exponential backoff
                                if item.retries < config.max_retries {
                                    let mut retry_item = item;
                                    retry_item.retries += 1;
                                    queue.push(retry_item);
                                }
                            }
                        }
                    }
                }

                // Sleep before next processing cycle
                tokio::time::sleep(config.queue_processing_interval).await;
            }
        });

        Ok(())
    }

    async fn start_sync_scheduler(&self, cluster_state: Arc<ClusterState>) -> Result<(), ReplicationError> {
        let queues = Arc::clone(&self.replication_queues);
        let config = self.config.clone();

        tokio::spawn(async move {
            let mut interval = time::interval(config.full_sync_interval);
            interval.set_missed_tick_behavior(MissedTickBehavior::Delay);

            loop {
                interval.tick().await;

                // Trigger full synchronization for nodes that need it
                let queues = queues.read().await;

                for node_id in queues.keys() {
                    // TODO: Check if node needs full sync
                    // For now, just log
                    println!("Scheduling full sync for node {}", node_id.0);
                }
            }
        });

        Ok(())
    }

    async fn replicate_item_to_node(
        item: &ReplicationItem,
        node_id: &NodeId,
        config: &ReplicationConfig,
    ) -> Result<(), ReplicationError> {
        // TODO: Implement actual network replication
        // For now, simulate network delay
        tokio::time::sleep(Duration::from_millis(10)).await;

        // Simulate occasional failures
        if rand::random::<f32>() < config.failure_rate {
            return Err(ReplicationError::NetworkError("Simulated failure".to_string()));
        }

        println!("Replicated operation to node {}", node_id.0);
        Ok(())
    }

    async fn redistribute_partition(&self, partition: &PartitionId) -> Result<(), ReplicationError> {
        // Find new nodes for this partition
        let new_nodes = self.cluster_state.get_nodes_for_key(&partition.0.to_le_bytes()).await;

        println!("Redistributing partition {} to {} nodes", partition.0, new_nodes.len());

        // TODO: Transfer partition data to new nodes
        // This involves:
        // 1. Finding current partition data
        // 2. Transferring to new primary
        // 3. Updating metadata

        Ok(())
    }

    fn get_operation_key(&self, operation: &Operation) -> Vec<u8> {
        // Generate a key for consistent partitioning
        match operation {
            Operation::CreateNode { .. } => {
                // For new nodes, use a default key or generate one
                b"default".to_vec()
            }
            Operation::UpdateNode { cid, .. } | Operation::DeleteNode { cid } => {
                cid.as_bytes().to_vec()
            }
            Operation::CreateEdge { source_cid, .. } => {
                source_cid.as_bytes().to_vec()
            }
            Operation::UpdateEdge { cid, .. } | Operation::DeleteEdge { cid } => {
                cid.as_bytes().to_vec()
            }
        }
    }

    /// Get command sender for external commands
    pub fn command_sender(&self) -> mpsc::Sender<ReplicationCommand> {
        self.command_tx.clone()
    }
}

/// Replication configuration
#[derive(Debug, Clone)]
pub struct ReplicationConfig {
    /// Replication factor (number of replicas per partition)
    pub replication_factor: usize,
    /// Maximum retries for failed operations
    pub max_retries: usize,
    /// Interval for status checks
    pub status_check_interval: Duration,
    /// Interval for processing replication queues
    pub queue_processing_interval: Duration,
    /// Interval for full synchronization
    pub full_sync_interval: Duration,
    /// Node failure timeout
    pub node_failure_timeout: Duration,
    /// Simulated failure rate for testing
    pub failure_rate: f32,
}

impl Default for ReplicationConfig {
    fn default() -> Self {
        Self {
            replication_factor: 3,
            max_retries: 3,
            status_check_interval: Duration::from_secs(5),
            queue_processing_interval: Duration::from_millis(100),
            full_sync_interval: Duration::from_secs(300), // 5 minutes
            node_failure_timeout: Duration::from_secs(30),
            failure_rate: 0.01, // 1% failure rate
        }
    }
}

/// Replication queue for pending operations
#[derive(Debug)]
pub struct ReplicationQueue {
    items: Vec<ReplicationItem>,
}

impl ReplicationQueue {
    pub fn new() -> Self {
        Self {
            items: Vec::new(),
        }
    }

    pub fn push(&mut self, item: ReplicationItem) {
        self.items.push(item);
    }

    pub fn pop(&mut self) -> Option<ReplicationItem> {
        if !self.items.is_empty() {
            Some(self.items.remove(0))
        } else {
            None
        }
    }

    pub fn len(&self) -> usize {
        self.items.len()
    }

    pub fn oldest_item(&self) -> Option<&ReplicationItem> {
        self.items.first()
    }
}

/// Item in replication queue
#[derive(Debug, Clone)]
pub struct ReplicationItem {
    pub operation: Operation,
    pub timestamp: Instant,
    pub retries: usize,
}

/// Replication status tracking
#[derive(Debug)]
pub struct ReplicationStatus {
    pub node_status: HashMap<NodeId, NodeStatus>,
    pub failed_nodes: HashSet<NodeId>,
    pub total_operations_processed: u64,
    pub total_operations_failed: u64,
}

impl ReplicationStatus {
    pub fn new() -> Self {
        Self {
            node_status: HashMap::new(),
            failed_nodes: HashSet::new(),
            total_operations_processed: 0,
            total_operations_failed: 0,
        }
    }

    pub fn update_node_lag(&mut self, node_id: &NodeId, lag: Duration) {
        let status = self.node_status.entry(node_id.clone()).or_default();
        status.replication_lag = lag;
        status.last_sync = Some(Instant::now());
        status.is_synced = lag < Duration::from_secs(5); // Arbitrary threshold
    }

    pub fn mark_node_failed(&mut self, node_id: &NodeId) {
        self.failed_nodes.insert(node_id.clone());
    }

    pub fn record_operation_success(&mut self, node_id: &NodeId) {
        let status = self.node_status.entry(node_id.clone()).or_default();
        status.last_sync = Some(Instant::now());
        self.total_operations_processed += 1;
    }

    pub fn record_operation_failure(&mut self, node_id: &NodeId) {
        self.total_operations_failed += 1;
        // Could implement backoff logic here
    }

    pub fn get_average_lag(&self) -> Duration {
        if self.node_status.is_empty() {
            return Duration::from_secs(0);
        }

        let total_lag: Duration = self.node_status.values()
            .map(|status| status.replication_lag)
            .sum();

        total_lag / self.node_status.len() as u32
    }
}

/// Status of a specific node
#[derive(Debug, Clone, Default)]
pub struct NodeStatus {
    pub last_sync: Option<Instant>,
    pub replication_lag: Duration,
    pub is_synced: bool,
}

/// Overall replication health
#[derive(Debug, Clone)]
pub struct ReplicationHealth {
    pub total_queued_operations: usize,
    pub failed_nodes_count: usize,
    pub replication_lag: Duration,
    pub is_healthy: bool,
}

/// Snapshot of replication status
#[derive(Debug, Clone)]
pub struct ReplicationStatusSnapshot {
    pub node_statuses: HashMap<NodeId, NodeReplicationStatus>,
    pub total_operations_processed: u64,
    pub total_operations_failed: u64,
}

/// Replication status for a specific node
#[derive(Debug, Clone)]
pub struct NodeReplicationStatus {
    pub queued_operations: usize,
    pub last_sync: Option<Instant>,
    pub replication_lag: Duration,
    pub is_synced: bool,
}

/// Replication commands
#[derive(Debug)]
pub enum ReplicationCommand {
    SyncWithNode { node_id: NodeId },
    RedistributePartition { partition_id: PartitionId },
    CheckHealth,
}

/// Replication-related errors
#[derive(Debug, thiserror::Error)]
pub enum ReplicationError {
    #[error("Network communication error: {0}")]
    NetworkError(String),

    #[error("Serialization error: {0}")]
    Serialization(String),

    #[error("Node failure: {0}")]
    NodeFailure(String),

    #[error("Partition error: {0}")]
    PartitionError(String),

    #[error("Timeout error")]
    Timeout,

    #[error("Configuration error: {0}")]
    ConfigError(String),
}

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

    #[test]
    fn test_replication_queue() {
        let mut queue = ReplicationQueue::new();

        let item = ReplicationItem {
            operation: Operation::CreateNode {
                properties: HashMap::new(),
            },
            timestamp: Instant::now(),
            retries: 0,
        };

        queue.push(item);
        assert_eq!(queue.len(), 1);

        let popped = queue.pop();
        assert!(popped.is_some());
        assert_eq!(queue.len(), 0);
    }

    #[test]
    fn test_replication_status() {
        let mut status = ReplicationStatus::new();
        let node_id = NodeId("test-node".to_string());

        status.record_operation_success(&node_id);
        status.record_operation_failure(&node_id);

        assert_eq!(status.total_operations_processed, 1);
        assert_eq!(status.total_operations_failed, 1);
    }

    #[tokio::test]
    async fn test_replication_manager_creation() {
        let cluster_state = Arc::new(ClusterState::new(NodeId("test".to_string())));
        let config = ReplicationConfig::default();

        let manager = ReplicationManager::new(cluster_state, config);

        let health = manager.check_health().await;
        assert!(health.is_healthy); // No operations, no failures
    }
}