anya_core/infrastructure/high_availability/

replication.rs

use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, info, instrument, warn};

use crate::infrastructure::high_availability::config::{HighAvailabilityConfig, ReplicationMode};
use crate::infrastructure::high_availability::HaError;

/// Manager for data replication across cluster nodes
/// Implements Write-Ahead Log pattern and Leader-Follower replication
/// [AIR-3][AIS-3][RES-3][SCL-3]
pub struct ReplicationManager {
    config: Arc<HighAvailabilityConfig>,
    replication_active: Arc<RwLock<bool>>,
    replication_state: Arc<RwLock<ReplicationState>>,
    pending_writes: Arc<Mutex<Vec<WriteOperation>>>,
    node_status: Arc<RwLock<HashMap<String, NodeReplicationStatus>>>,
    write_ahead_log: Arc<Mutex<Vec<LogEntry>>>,
    #[allow(dead_code)]
    // Required for future WAL/consensus extensions (see docs/INDEX_CORRECTED.md)
    last_applied_index: Arc<RwLock<u64>>,
    #[allow(dead_code)]
    // Required for future WAL/consensus extensions (see docs/INDEX_CORRECTED.md)
    commit_index: Arc<RwLock<u64>>,
}

/// Current state of replication system
#[derive(Debug, Clone)]
pub struct ReplicationState {
    pub mode: ReplicationMode,
    pub is_leader: bool,
    pub leader_node: Option<String>,
    pub follower_nodes: Vec<String>,
    pub lag_metrics: HashMap<String, Duration>,
    pub last_sync_time: Option<Instant>,
}

/// Status of replication for a specific node
#[derive(Debug, Clone)]
pub struct NodeReplicationStatus {
    pub node_id: String,
    pub is_healthy: bool,
    pub last_heartbeat: Option<Instant>,
    pub replication_lag: Duration,
    pub bytes_behind: u64,
    pub last_ack_time: Option<Instant>,
}

/// A write operation to be replicated
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WriteOperation {
    pub id: String,
    pub operation_type: OperationType,
    pub data: Vec<u8>,
    pub timestamp: u64,
    pub checksum: String,
}

/// Types of operations that can be replicated
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum OperationType {
    Create { key: String },
    Update { key: String },
    Delete { key: String },
    Batch { operations: Vec<WriteOperation> },
}

/// Entry in the write-ahead log
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LogEntry {
    pub index: u64,
    pub term: u64,
    pub operation: WriteOperation,
    pub committed: bool,
}

/// Result of a replication operation
#[derive(Debug, Clone)]
pub struct ReplicationResult {
    pub success: bool,
    pub replicated_nodes: Vec<String>,
    pub failed_nodes: Vec<String>,
    pub total_time: Duration,
}

impl ReplicationManager {
    /// Creates a new replication manager
    pub fn new(config: &HighAvailabilityConfig) -> Self {
        Self {
            config: Arc::new(config.clone()),
            replication_active: Arc::new(RwLock::new(false)),
            replication_state: Arc::new(RwLock::new(ReplicationState {
                mode: config.replication.mode,
                is_leader: false,
                leader_node: None,
                follower_nodes: Vec::new(),
                lag_metrics: HashMap::new(),
                last_sync_time: None,
            })),
            pending_writes: Arc::new(Mutex::new(Vec::new())),
            node_status: Arc::new(RwLock::new(HashMap::new())),
            write_ahead_log: Arc::new(Mutex::new(Vec::new())),
            last_applied_index: Arc::new(RwLock::new(0)),
            commit_index: Arc::new(RwLock::new(0)),
        }
    }

    /// Initializes the replication manager
    #[instrument(skip(self))]
    pub async fn initialize(&mut self) -> Result<(), HaError> {
        info!("Initializing replication manager");

        // Initialize write-ahead log
        self.initialize_wal().await?;

        // Set up replication topology
        self.setup_replication_topology().await?;

        info!("Replication manager initialized successfully");
        Ok(())
    }

    /// Starts replication services
    #[instrument(skip(self))]
    pub async fn start_replication(&mut self) -> Result<(), HaError> {
        info!("Starting replication services");

        *self.replication_active.write().await = true;

        // Start background tasks
        self.start_replication_loop().await?;
        self.start_heartbeat_monitoring().await?;
        self.start_lag_monitoring().await?;

        info!("Replication services started");
        Ok(())
    }

    /// Stops replication services
    #[instrument(skip(self))]
    pub async fn stop_replication(&mut self) -> Result<(), HaError> {
        info!("Stopping replication services");

        *self.replication_active.write().await = false;

        // Flush pending writes
        self.flush_pending_writes().await?;

        info!("Replication services stopped");
        Ok(())
    }

    /// Replicates a write operation
    #[instrument(skip(self, operation))]
    pub async fn replicate_write(
        &self,
        operation: WriteOperation,
    ) -> Result<ReplicationResult, HaError> {
        let _start_time = Instant::now();

        // Add to write-ahead log first (durability)
        self.append_to_wal(&operation).await?;

        match self.config.replication.mode {
            ReplicationMode::Synchronous => self.replicate_synchronously(operation).await,
            ReplicationMode::SemiSynchronous => self.replicate_semi_synchronously(operation).await,
            ReplicationMode::Asynchronous => self.replicate_asynchronously(operation).await,
        }
    }

    /// Handles leader promotion for this node
    #[instrument(skip(self))]
    pub async fn promote_to_leader(&mut self) -> Result<(), HaError> {
        info!("Promoting node to replication leader");

        let mut state = self.replication_state.write().await;
        state.is_leader = true;
        state.leader_node = Some("self".to_string()); // In real implementation, use actual node ID

        // Initialize leader-specific tasks
        self.initialize_leader_tasks().await?;

        info!("Node promoted to replication leader");
        Ok(())
    }

    /// Handles demotion from leader role
    #[instrument(skip(self))]
    pub async fn demote_from_leader(&mut self) -> Result<(), HaError> {
        info!("Demoting node from replication leader");

        let mut state = self.replication_state.write().await;
        state.is_leader = false;
        state.leader_node = None;

        // Stop leader-specific tasks
        self.stop_leader_tasks().await?;

        info!("Node demoted from replication leader");
        Ok(())
    }

    /// Gets current replication status
    #[instrument(skip(self))]
    pub async fn get_replication_status(&self) -> Result<ReplicationState, HaError> {
        let state = self.replication_state.read().await;
        Ok(state.clone())
    }

    /// Updates configuration
    #[instrument(skip(self, config))]
    pub async fn update_config(&mut self, config: &HighAvailabilityConfig) -> Result<(), HaError> {
        info!("Updating replication manager configuration");
        self.config = Arc::new(config.clone());

        // Update replication mode if changed
        let mut state = self.replication_state.write().await;
        state.mode = config.replication.mode;

        Ok(())
    }

    /// Private methods for implementation details
    async fn initialize_wal(&self) -> Result<(), HaError> {
        debug!("Initializing write-ahead log");

        // In a real implementation, this would:
        // 1. Load existing WAL from disk
        // 2. Replay uncommitted entries
        // 3. Initialize log rotation

        Ok(())
    }

    async fn setup_replication_topology(&self) -> Result<(), HaError> {
        debug!("Setting up replication topology");

        // In a real implementation, this would:
        // 1. Discover other nodes in cluster
        // 2. Establish replication connections
        // 3. Negotiate replication parameters

        Ok(())
    }

    async fn start_replication_loop(&self) -> Result<(), HaError> {
        let pending_writes = Arc::clone(&self.pending_writes);
        let replication_active = Arc::clone(&self.replication_active);
        let config = Arc::clone(&self.config);

        tokio::spawn(async move {
            Self::replication_loop(pending_writes, replication_active, config).await;
        });

        Ok(())
    }

    async fn start_heartbeat_monitoring(&self) -> Result<(), HaError> {
        let node_status = Arc::clone(&self.node_status);
        let replication_active = Arc::clone(&self.replication_active);

        tokio::spawn(async move {
            Self::heartbeat_monitoring_loop(node_status, replication_active).await;
        });

        Ok(())
    }

    async fn start_lag_monitoring(&self) -> Result<(), HaError> {
        let replication_state = Arc::clone(&self.replication_state);
        let replication_active = Arc::clone(&self.replication_active);

        tokio::spawn(async move {
            Self::lag_monitoring_loop(replication_state, replication_active).await;
        });

        Ok(())
    }

    async fn append_to_wal(&self, operation: &WriteOperation) -> Result<(), HaError> {
        let mut wal = self.write_ahead_log.lock().await;
        let index = wal.len() as u64 + 1;

        let entry = LogEntry {
            index,
            term: 1, // In real implementation, use current term
            operation: operation.clone(),
            committed: false,
        };

        wal.push(entry);
        debug!(
            "Appended operation {} to WAL at index {}",
            operation.id, index
        );

        Ok(())
    }

    async fn replicate_synchronously(
        &self,
        operation: WriteOperation,
    ) -> Result<ReplicationResult, HaError> {
        let start_time = Instant::now();

        // In synchronous replication, all followers must acknowledge before returning
        debug!(
            "Performing synchronous replication for operation {}",
            operation.id
        );

        // Simulate replication to followers
        let followers = self.get_follower_nodes().await;
        let mut replicated_nodes = Vec::new();
        let mut failed_nodes = Vec::new();

        for follower in followers {
            match self.replicate_to_node(&follower, &operation).await {
                Ok(_) => replicated_nodes.push(follower),
                Err(_) => failed_nodes.push(follower),
            }
        }

        // Synchronous mode requires all nodes to succeed
        let success = failed_nodes.is_empty();

        Ok(ReplicationResult {
            success,
            replicated_nodes,
            failed_nodes,
            total_time: start_time.elapsed(),
        })
    }

    async fn replicate_semi_synchronously(
        &self,
        operation: WriteOperation,
    ) -> Result<ReplicationResult, HaError> {
        let start_time = Instant::now();

        debug!(
            "Performing semi-synchronous replication for operation {}",
            operation.id
        );

        let followers = self.get_follower_nodes().await;
        let required_acks = self.config.replication.ack_count.unwrap_or(1);
        let mut replicated_nodes = Vec::new();
        let mut failed_nodes = Vec::new();

        for follower in followers {
            match self.replicate_to_node(&follower, &operation).await {
                Ok(_) => replicated_nodes.push(follower),
                Err(_) => failed_nodes.push(follower),
            }

            // Check if we have enough acknowledgments
            if replicated_nodes.len() >= required_acks {
                break;
            }
        }

        let success = replicated_nodes.len() >= required_acks;

        Ok(ReplicationResult {
            success,
            replicated_nodes,
            failed_nodes,
            total_time: start_time.elapsed(),
        })
    }

    async fn replicate_asynchronously(
        &self,
        operation: WriteOperation,
    ) -> Result<ReplicationResult, HaError> {
        let start_time = Instant::now();

        debug!(
            "Performing asynchronous replication for operation {}",
            operation.id
        );

        // Add to pending writes for background processing
        let mut pending = self.pending_writes.lock().await;
        pending.push(operation.clone());

        Ok(ReplicationResult {
            success: true,
            replicated_nodes: vec!["pending".to_string()],
            failed_nodes: Vec::new(),
            total_time: start_time.elapsed(),
        })
    }

    async fn replicate_to_node(
        &self,
        node: &str,
        operation: &WriteOperation,
    ) -> Result<(), HaError> {
        debug!("Replicating operation {} to node {}", operation.id, node);

        // In a real implementation, this would:
        // 1. Send the operation over the network
        // 2. Wait for acknowledgment
        // 3. Handle timeouts and retries

        // Simulate network delay
        tokio::time::sleep(Duration::from_millis(10)).await;

        Ok(())
    }

    async fn get_follower_nodes(&self) -> Vec<String> {
        let state = self.replication_state.read().await;
        state.follower_nodes.clone()
    }

    async fn flush_pending_writes(&self) -> Result<(), HaError> {
        debug!("Flushing pending writes");

        let mut pending = self.pending_writes.lock().await;
        let operations = std::mem::take(&mut *pending);

        for operation in operations {
            // Process each pending operation
            self.replicate_to_all_followers(&operation).await?;
        }

        Ok(())
    }

    async fn replicate_to_all_followers(&self, operation: &WriteOperation) -> Result<(), HaError> {
        let followers = self.get_follower_nodes().await;

        for follower in followers {
            if let Err(e) = self.replicate_to_node(&follower, operation).await {
                warn!("Failed to replicate to {}: {}", follower, e);
            }
        }

        Ok(())
    }

    async fn initialize_leader_tasks(&self) -> Result<(), HaError> {
        debug!("Initializing leader-specific replication tasks");
        // In real implementation: start log compaction, follower monitoring, etc.
        Ok(())
    }

    async fn stop_leader_tasks(&self) -> Result<(), HaError> {
        debug!("Stopping leader-specific replication tasks");
        Ok(())
    }

    // Background monitoring loops

    async fn replication_loop(
        pending_writes: Arc<Mutex<Vec<WriteOperation>>>,
        replication_active: Arc<RwLock<bool>>,
        _config: Arc<HighAvailabilityConfig>,
    ) {
        info!("Starting replication background loop");

        while *replication_active.read().await {
            // Process pending writes
            let mut pending = pending_writes.lock().await;
            if !pending.is_empty() {
                debug!("Processing {} pending writes", pending.len());
                // In real implementation: process each write
                pending.clear();
            }
            drop(pending);

            tokio::time::sleep(Duration::from_millis(100)).await;
        }

        info!("Replication background loop ended");
    }

    async fn heartbeat_monitoring_loop(
        node_status: Arc<RwLock<HashMap<String, NodeReplicationStatus>>>,
        replication_active: Arc<RwLock<bool>>,
    ) {
        info!("Starting heartbeat monitoring loop");

        while *replication_active.read().await {
            // Check heartbeats from all nodes
            let mut status_map = node_status.write().await;
            let now = Instant::now();

            for (node_id, status) in status_map.iter_mut() {
                if let Some(last_heartbeat) = status.last_heartbeat {
                    if now.duration_since(last_heartbeat) > Duration::from_secs(30) {
                        warn!("Node {} heartbeat timeout", node_id);
                        status.is_healthy = false;
                    }
                }
            }
            drop(status_map);

            tokio::time::sleep(Duration::from_secs(5)).await;
        }

        info!("Heartbeat monitoring loop ended");
    }

    async fn lag_monitoring_loop(
        replication_state: Arc<RwLock<ReplicationState>>,
        replication_active: Arc<RwLock<bool>>,
    ) {
        info!("Starting lag monitoring loop");

        while *replication_active.read().await {
            // Monitor replication lag
            let mut state = replication_state.write().await;

            // In real implementation: calculate actual lag metrics
            state.last_sync_time = Some(Instant::now());
            drop(state);

            tokio::time::sleep(Duration::from_secs(10)).await;
        }

        info!("Lag monitoring loop ended");
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::infrastructure::high_availability::config::ReplicationConfig;
    use uuid::Uuid;

    fn create_test_config() -> HighAvailabilityConfig {
        HighAvailabilityConfig {
            replication: ReplicationConfig {
                mode: ReplicationMode::SemiSynchronous,
                sync_timeout: Duration::from_secs(5),
                max_lag: Duration::from_millis(500),
                ack_count: Some(2),
                compression_enabled: true,
                encryption_enabled: true,
            },
            ..Default::default()
        }
    }

    #[tokio::test]
    async fn test_replication_manager_creation() {
        let config = create_test_config();
        let manager = ReplicationManager::new(&config);

        assert!(!*manager.replication_active.read().await);
    }

    #[tokio::test]
    async fn test_replication_initialization() {
        let config = create_test_config();
        let mut manager = ReplicationManager::new(&config);

        let result = manager.initialize().await;
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_write_operation_creation() {
        let operation = WriteOperation {
            id: Uuid::new_v4().to_string(),
            operation_type: OperationType::Create {
                key: "test_key".to_string(),
            },
            data: b"test_data".to_vec(),
            timestamp: 123456789,
            checksum: "abc123".to_string(),
        };

        assert_eq!(operation.data, b"test_data");
    }

    #[tokio::test]
    async fn test_leader_promotion() {
        let config = create_test_config();
        let mut manager = ReplicationManager::new(&config);

        manager.promote_to_leader().await.unwrap();

        let state = manager.get_replication_status().await.unwrap();
        assert!(state.is_leader);
    }
}