optirs-tpu 0.3.1

// Fault Tolerance for TPU Pod Coordination
//
// This module provides comprehensive fault tolerance functionality for TPU pod coordination,
// including failure detection, recovery strategies, redundancy management, and checkpointing.

use std::collections::{HashMap, HashSet};
use std::time::{Duration, Instant};

use super::DeviceId;
use crate::error::{OptimError, Result};
use scirs2_core::error::ErrorContext;

/// Types of failures
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum FailureType {
    DeviceFailure,
    NetworkFailure,
    MemoryFailure,
    ComputeFailure,
    SoftwareFailure,
    DataCorruption,
}

/// Recovery strategies
#[derive(Debug, Clone)]
pub enum RecoveryStrategy {
    Restart,
    Migrate,
    Replicate,
    Rollback,
    Isolate,
    Graceful,
}

/// Failure detection algorithms
#[derive(Debug, Clone, Copy)]
pub enum FailureDetectionAlgorithm {
    Timeout,
    HeartbeatMissing,
    PerformanceDegradation,
    ErrorRate,
    Consensus,
    Adaptive,
}

/// Device status for fault tolerance
#[derive(Debug, Clone, Copy)]
pub enum DeviceStatus {
    Active,
    Idle,
    Busy,
    Failed,
    Recovering,
    Offline,
}

/// Failure information
#[derive(Debug, Clone)]
pub struct FailureInfo {
    /// Failure type
    pub failure_type: FailureType,

    /// Failed device
    pub device_id: DeviceId,

    /// Detection timestamp
    pub detected_at: Instant,

    /// Failure severity (0.0 to 1.0)
    pub severity: f64,

    /// Error message
    pub error_message: String,

    /// Recovery attempts
    pub recovery_attempts: usize,

    /// Status
    pub status: FailureStatus,
}

/// Failure status
#[derive(Debug, Clone, Copy)]
pub enum FailureStatus {
    Detected,
    Analyzing,
    Recovering,
    Recovered,
    Permanent,
}

/// Recovery action
#[derive(Debug, Clone)]
pub struct RecoveryAction {
    /// Action type
    pub action_type: RecoveryStrategy,

    /// Target devices
    pub target_devices: Vec<DeviceId>,

    /// Estimated completion time
    pub estimated_completion: Duration,

    /// Priority
    pub priority: RecoveryPriority,

    /// Required resources
    pub required_resources: Vec<String>,
}

/// Recovery priority
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum RecoveryPriority {
    Low,
    Medium,
    High,
    Critical,
}

/// Checkpoint information
#[derive(Debug, Clone)]
pub struct CheckpointInfo {
    /// Checkpoint ID
    pub checkpoint_id: String,

    /// Creation timestamp
    pub created_at: Instant,

    /// Size in bytes
    pub size_bytes: usize,

    /// Associated devices
    pub devices: Vec<DeviceId>,

    /// Checkpoint type
    pub checkpoint_type: CheckpointType,

    /// Metadata
    pub metadata: HashMap<String, String>,
}

/// Checkpoint types
#[derive(Debug, Clone, Copy)]
pub enum CheckpointType {
    Full,
    Incremental,
    Differential,
    Log,
}

/// Redundancy configuration
#[derive(Debug, Clone)]
pub struct RedundancyConfig {
    /// Replication factor
    pub replication_factor: usize,

    /// Redundancy strategy
    pub strategy: RedundancyStrategy,

    /// Consistency level
    pub consistency_level: ConsistencyLevel,

    /// Failure tolerance
    pub failure_tolerance: usize,
}

/// Redundancy strategies
#[derive(Debug, Clone, Copy)]
pub enum RedundancyStrategy {
    Replication,
    ErasureCoding,
    Hybrid,
    Adaptive,
}

/// Consistency levels
#[derive(Debug, Clone, Copy)]
pub enum ConsistencyLevel {
    Eventual,
    Strong,
    Causal,
    Sequential,
    Linearizable,
}

/// Type aliases for managers
type HeartbeatManager = HashMap<DeviceId, Instant>;
type RedundancyManager = HashMap<String, f64>;
type CheckpointingSystem = HashMap<String, Vec<u8>>;
type RollbackManager = HashMap<String, Vec<u8>>;

/// Fault tolerance statistics
pub type FaultToleranceStatistics = HashMap<String, f64>;

/// Failure detector
#[derive(Debug)]
pub struct FailureDetector {
    /// Monitored devices
    monitored_devices: HashSet<DeviceId>,

    /// Heartbeat manager
    heartbeat_manager: HeartbeatManager,

    /// Failure threshold
    failure_threshold: Duration,

    /// Detection algorithm
    detection_algorithm: FailureDetectionAlgorithm,

    /// Failure history
    failure_history: Vec<FailureInfo>,

    /// Detection configuration
    detection_config: DetectionConfig,
}

/// Detection configuration
#[derive(Debug, Clone)]
pub struct DetectionConfig {
    /// Heartbeat interval
    pub heartbeat_interval: Duration,

    /// Timeout threshold
    pub timeout_threshold: Duration,

    /// Performance degradation threshold
    pub performance_threshold: f64,

    /// Error rate threshold
    pub error_rate_threshold: f64,

    /// Consensus threshold
    pub consensus_threshold: usize,
}

impl FailureDetector {
    /// Create a new failure detector
    pub fn new(config: DetectionConfig) -> Self {
        Self {
            monitored_devices: HashSet::new(),
            heartbeat_manager: HashMap::new(),
            failure_threshold: config.timeout_threshold,
            detection_algorithm: FailureDetectionAlgorithm::Timeout,
            failure_history: Vec::new(),
            detection_config: config,
        }
    }

    /// Add device to monitoring
    pub fn add_device(&mut self, device_id: DeviceId) {
        self.monitored_devices.insert(device_id);
        self.heartbeat_manager.insert(device_id, Instant::now());
    }

    /// Remove device from monitoring
    pub fn remove_device(&mut self, device_id: DeviceId) {
        self.monitored_devices.remove(&device_id);
        self.heartbeat_manager.remove(&device_id);
    }

    /// Update heartbeat for device
    pub fn update_heartbeat(&mut self, device_id: DeviceId) {
        if self.monitored_devices.contains(&device_id) {
            self.heartbeat_manager.insert(device_id, Instant::now());
        }
    }

    /// Check for failures
    pub fn check_failures(&mut self) -> Vec<FailureInfo> {
        let mut detected_failures = Vec::new();
        let now = Instant::now();

        for &device_id in &self.monitored_devices {
            if let Some(&last_heartbeat) = self.heartbeat_manager.get(&device_id) {
                let time_since_heartbeat = now.duration_since(last_heartbeat);

                if time_since_heartbeat > self.failure_threshold {
                    let failure = FailureInfo {
                        failure_type: FailureType::DeviceFailure,
                        device_id,
                        detected_at: now,
                        severity: self.calculate_failure_severity(time_since_heartbeat),
                        error_message: format!(
                            "Device {} failed to send heartbeat for {:?}",
                            device_id.0, time_since_heartbeat
                        ),
                        recovery_attempts: 0,
                        status: FailureStatus::Detected,
                    };

                    detected_failures.push(failure.clone());
                    self.failure_history.push(failure);
                }
            }
        }

        detected_failures
    }

    /// Calculate failure severity based on detection algorithm
    fn calculate_failure_severity(&self, time_since_heartbeat: Duration) -> f64 {
        match self.detection_algorithm {
            FailureDetectionAlgorithm::Timeout => {
                let ratio =
                    time_since_heartbeat.as_secs_f64() / self.failure_threshold.as_secs_f64();
                (ratio - 1.0).clamp(0.0, 1.0)
            }
            FailureDetectionAlgorithm::HeartbeatMissing
                if time_since_heartbeat > self.detection_config.heartbeat_interval * 3 =>
            {
                1.0
            }
            _ => 0.5, // Default severity for other algorithms
        }
    }

    /// Get failure statistics
    pub fn get_failure_statistics(&self) -> HashMap<String, f64> {
        let mut stats = HashMap::new();

        stats.insert(
            "monitored_devices".to_string(),
            self.monitored_devices.len() as f64,
        );

        stats.insert(
            "total_failures".to_string(),
            self.failure_history.len() as f64,
        );

        // Calculate failure rate
        let recent_failures = self
            .failure_history
            .iter()
            .filter(|f| f.detected_at.elapsed() < Duration::from_secs(3600))
            .count();
        stats.insert("recent_failure_rate".to_string(), recent_failures as f64);

        // Calculate average recovery time
        let avg_recovery_time = if self.failure_history.is_empty() {
            0.0
        } else {
            self.failure_history
                .iter()
                .filter(|f| matches!(f.status, FailureStatus::Recovered))
                .map(|f| f.detected_at.elapsed().as_secs_f64())
                .sum::<f64>()
                / self.failure_history.len() as f64
        };
        stats.insert("avg_recovery_time_secs".to_string(), avg_recovery_time);

        stats
    }

    /// Set detection algorithm
    pub fn set_detection_algorithm(&mut self, algorithm: FailureDetectionAlgorithm) {
        self.detection_algorithm = algorithm;
    }

    /// Get monitored devices
    pub fn get_monitored_devices(&self) -> &HashSet<DeviceId> {
        &self.monitored_devices
    }

    /// Get failure history
    pub fn get_failure_history(&self) -> &[FailureInfo] {
        &self.failure_history
    }
}

/// Fault tolerance manager
#[derive(Debug)]
pub struct FaultToleranceManager {
    /// Failure detector
    failure_detector: FailureDetector,

    /// Recovery strategies
    recovery_strategies: HashMap<FailureType, RecoveryStrategy>,

    /// Redundancy manager
    redundancy_manager: RedundancyManager,

    /// Checkpointing system
    checkpointing_system: CheckpointingSystem,

    /// Rollback manager
    rollback_manager: RollbackManager,

    /// Active recovery actions
    active_recoveries: HashMap<DeviceId, RecoveryAction>,

    /// Redundancy configuration
    redundancy_config: RedundancyConfig,

    /// Checkpoint configuration
    checkpoint_config: CheckpointConfig,
}

/// Checkpoint configuration
#[derive(Debug, Clone)]
pub struct CheckpointConfig {
    /// Checkpoint interval
    pub interval: Duration,

    /// Maximum checkpoints to keep
    pub max_checkpoints: usize,

    /// Compression enabled
    pub compression_enabled: bool,

    /// Encryption enabled
    pub encryption_enabled: bool,

    /// Storage path
    pub storage_path: String,
}

impl FaultToleranceManager {
    /// Create a new fault tolerance manager
    pub fn new(
        detection_config: DetectionConfig,
        redundancy_config: RedundancyConfig,
        checkpoint_config: CheckpointConfig,
    ) -> Result<Self> {
        let failure_detector = FailureDetector::new(detection_config);

        // Set up default recovery strategies
        let mut recovery_strategies = HashMap::new();
        recovery_strategies.insert(FailureType::DeviceFailure, RecoveryStrategy::Migrate);
        recovery_strategies.insert(FailureType::NetworkFailure, RecoveryStrategy::Restart);
        recovery_strategies.insert(FailureType::MemoryFailure, RecoveryStrategy::Rollback);
        recovery_strategies.insert(FailureType::ComputeFailure, RecoveryStrategy::Restart);
        recovery_strategies.insert(FailureType::SoftwareFailure, RecoveryStrategy::Restart);
        recovery_strategies.insert(FailureType::DataCorruption, RecoveryStrategy::Rollback);

        Ok(Self {
            failure_detector,
            recovery_strategies,
            redundancy_manager: HashMap::new(),
            checkpointing_system: HashMap::new(),
            rollback_manager: HashMap::new(),
            active_recoveries: HashMap::new(),
            redundancy_config,
            checkpoint_config,
        })
    }

    /// Monitor device for failures
    pub fn monitor_device(&mut self, device_id: DeviceId) {
        self.failure_detector.add_device(device_id);
    }

    /// Stop monitoring device
    pub fn stop_monitoring(&mut self, device_id: DeviceId) {
        self.failure_detector.remove_device(device_id);
    }

    /// Update device heartbeat
    pub fn update_heartbeat(&mut self, device_id: DeviceId) {
        self.failure_detector.update_heartbeat(device_id);
    }

    /// Check for failures and initiate recovery
    pub async fn check_and_recover(&mut self) -> Result<Vec<RecoveryAction>> {
        let failures = self.failure_detector.check_failures();
        let mut recovery_actions = Vec::new();

        for failure in failures {
            if let Some(strategy) = self.recovery_strategies.get(&failure.failure_type) {
                let recovery_action = self.create_recovery_action(&failure, strategy.clone())?;
                self.initiate_recovery(&failure, &recovery_action).await?;
                recovery_actions.push(recovery_action);
            }
        }

        Ok(recovery_actions)
    }

    /// Create recovery action for failure
    fn create_recovery_action(
        &self,
        failure: &FailureInfo,
        strategy: RecoveryStrategy,
    ) -> Result<RecoveryAction> {
        let priority = match failure.severity {
            s if s > 0.8 => RecoveryPriority::Critical,
            s if s > 0.6 => RecoveryPriority::High,
            s if s > 0.3 => RecoveryPriority::Medium,
            _ => RecoveryPriority::Low,
        };

        let estimated_completion = match strategy {
            RecoveryStrategy::Restart => Duration::from_secs(30),
            RecoveryStrategy::Migrate => Duration::from_secs(120),
            RecoveryStrategy::Replicate => Duration::from_secs(60),
            RecoveryStrategy::Rollback => Duration::from_secs(45),
            RecoveryStrategy::Isolate => Duration::from_secs(10),
            RecoveryStrategy::Graceful => Duration::from_secs(90),
        };

        Ok(RecoveryAction {
            action_type: strategy,
            target_devices: vec![failure.device_id],
            estimated_completion,
            priority,
            required_resources: vec!["compute".to_string(), "memory".to_string()],
        })
    }

    /// Initiate recovery for failure
    async fn initiate_recovery(
        &mut self,
        failure: &FailureInfo,
        recovery_action: &RecoveryAction,
    ) -> Result<()> {
        println!(
            "Initiating recovery for device {:?} using strategy {:?}",
            failure.device_id, recovery_action.action_type
        );

        match recovery_action.action_type {
            RecoveryStrategy::Restart => {
                self.restart_device(failure.device_id).await?;
            }
            RecoveryStrategy::Migrate => {
                self.migrate_workload(failure.device_id).await?;
            }
            RecoveryStrategy::Replicate => {
                self.replicate_data(failure.device_id).await?;
            }
            RecoveryStrategy::Rollback => {
                self.rollback_state(failure.device_id).await?;
            }
            RecoveryStrategy::Isolate => {
                self.isolate_device(failure.device_id).await?;
            }
            RecoveryStrategy::Graceful => {
                self.graceful_recovery(failure.device_id).await?;
            }
        }

        self.active_recoveries
            .insert(failure.device_id, recovery_action.clone());

        Ok(())
    }

    /// Restart failed device
    async fn restart_device(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Restarting device {:?}", device_id);
        // Simulate restart delay
        tokio::time::sleep(Duration::from_millis(100)).await;
        self.failure_detector.update_heartbeat(device_id);
        Ok(())
    }

    /// Migrate workload from failed device
    async fn migrate_workload(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Migrating workload from device {:?}", device_id);
        // In a real implementation, this would migrate tasks to healthy devices
        tokio::time::sleep(Duration::from_millis(200)).await;
        Ok(())
    }

    /// Replicate data for redundancy
    async fn replicate_data(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Replicating data for device {:?}", device_id);
        // In a real implementation, this would create data replicas
        tokio::time::sleep(Duration::from_millis(150)).await;
        Ok(())
    }

    /// Rollback to previous state
    async fn rollback_state(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Rolling back state for device {:?}", device_id);
        // In a real implementation, this would restore from checkpoint
        tokio::time::sleep(Duration::from_millis(120)).await;
        Ok(())
    }

    /// Isolate failed device
    async fn isolate_device(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Isolating device {:?}", device_id);
        // In a real implementation, this would isolate the device from the network
        self.failure_detector.remove_device(device_id);
        Ok(())
    }

    /// Graceful recovery
    async fn graceful_recovery(&mut self, device_id: DeviceId) -> Result<()> {
        println!("Performing graceful recovery for device {:?}", device_id);
        // In a real implementation, this would perform a controlled recovery
        tokio::time::sleep(Duration::from_millis(180)).await;
        self.failure_detector.update_heartbeat(device_id);
        Ok(())
    }

    /// Create checkpoint
    pub async fn create_checkpoint(&mut self, checkpoint_id: String) -> Result<CheckpointInfo> {
        let checkpoint_info = CheckpointInfo {
            checkpoint_id: checkpoint_id.clone(),
            created_at: Instant::now(),
            size_bytes: 1024 * 1024, // 1MB simulated size
            devices: self
                .failure_detector
                .get_monitored_devices()
                .iter()
                .cloned()
                .collect(),
            checkpoint_type: CheckpointType::Full,
            metadata: HashMap::new(),
        };

        // Simulate checkpoint creation
        let checkpoint_data = vec![0u8; 1024]; // Simulated checkpoint data
        self.checkpointing_system
            .insert(checkpoint_id, checkpoint_data);

        println!("Created checkpoint: {}", checkpoint_info.checkpoint_id);
        Ok(checkpoint_info)
    }

    /// Restore from checkpoint
    pub async fn restore_checkpoint(&mut self, checkpoint_id: &str) -> Result<()> {
        if self.checkpointing_system.contains_key(checkpoint_id) {
            println!("Restoring from checkpoint: {}", checkpoint_id);
            // In a real implementation, this would restore system state
            tokio::time::sleep(Duration::from_millis(100)).await;
            Ok(())
        } else {
            Err(OptimError::ComputationError(ErrorContext::new(format!(
                "Checkpoint {} not found",
                checkpoint_id
            ))))
        }
    }

    /// Set recovery strategy for failure type
    pub fn set_recovery_strategy(&mut self, failure_type: FailureType, strategy: RecoveryStrategy) {
        self.recovery_strategies.insert(failure_type, strategy);
    }

    /// Get fault tolerance statistics
    pub fn get_statistics(&self) -> FaultToleranceStatistics {
        let mut stats = self.failure_detector.get_failure_statistics();

        stats.insert(
            "active_recoveries".to_string(),
            self.active_recoveries.len() as f64,
        );

        stats.insert(
            "checkpoints_count".to_string(),
            self.checkpointing_system.len() as f64,
        );

        stats.insert(
            "redundancy_level".to_string(),
            self.redundancy_config.replication_factor as f64,
        );

        // Calculate system reliability
        let total_devices = self.failure_detector.get_monitored_devices().len() as f64;
        let failed_devices = self.active_recoveries.len() as f64;
        let reliability = if total_devices > 0.0 {
            (total_devices - failed_devices) / total_devices
        } else {
            1.0
        };
        stats.insert("system_reliability".to_string(), reliability);

        stats
    }

    /// Get active recovery actions
    pub fn get_active_recoveries(&self) -> &HashMap<DeviceId, RecoveryAction> {
        &self.active_recoveries
    }

    /// Complete recovery for device
    pub fn complete_recovery(&mut self, device_id: DeviceId) -> Result<()> {
        if self.active_recoveries.remove(&device_id).is_some() {
            println!("Recovery completed for device {:?}", device_id);
            // Re-add device to monitoring if it was isolated
            self.failure_detector.add_device(device_id);
            Ok(())
        } else {
            Err(OptimError::ComputationError(ErrorContext::new(format!(
                "No active recovery for device {:?}",
                device_id
            ))))
        }
    }

    /// Update redundancy configuration
    pub fn update_redundancy_config(&mut self, config: RedundancyConfig) {
        self.redundancy_config = config;
    }

    /// Update checkpoint configuration
    pub fn update_checkpoint_config(&mut self, config: CheckpointConfig) {
        self.checkpoint_config = config;
    }
}

// Default implementations
impl Default for DetectionConfig {
    fn default() -> Self {
        Self {
            heartbeat_interval: Duration::from_secs(5),
            timeout_threshold: Duration::from_secs(30),
            performance_threshold: 0.1,
            error_rate_threshold: 0.05,
            consensus_threshold: 3,
        }
    }
}

impl Default for RedundancyConfig {
    fn default() -> Self {
        Self {
            replication_factor: 3,
            strategy: RedundancyStrategy::Replication,
            consistency_level: ConsistencyLevel::Strong,
            failure_tolerance: 1,
        }
    }
}

impl Default for CheckpointConfig {
    fn default() -> Self {
        Self {
            interval: Duration::from_secs(300), // 5 minutes
            max_checkpoints: 10,
            compression_enabled: true,
            encryption_enabled: false,
            storage_path: "/tmp/checkpoints".to_string(),
        }
    }
}

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

    #[test]
    fn test_failure_detector_creation() {
        let config = DetectionConfig::default();
        let detector = FailureDetector::new(config);
        assert_eq!(detector.get_monitored_devices().len(), 0);
    }

    #[test]
    fn test_device_monitoring() {
        let config = DetectionConfig::default();
        let mut detector = FailureDetector::new(config);

        let device_id = DeviceId(0);
        detector.add_device(device_id);

        assert!(detector.get_monitored_devices().contains(&device_id));
    }

    #[test]
    fn test_fault_tolerance_manager_creation() {
        let detection_config = DetectionConfig::default();
        let redundancy_config = RedundancyConfig::default();
        let checkpoint_config = CheckpointConfig::default();

        let manager =
            FaultToleranceManager::new(detection_config, redundancy_config, checkpoint_config);

        assert!(manager.is_ok());
    }

    #[tokio::test]
    async fn test_checkpoint_creation() {
        let detection_config = DetectionConfig::default();
        let redundancy_config = RedundancyConfig::default();
        let checkpoint_config = CheckpointConfig::default();

        let mut manager =
            FaultToleranceManager::new(detection_config, redundancy_config, checkpoint_config)
                .expect("unwrap failed");

        let checkpoint_info = manager
            .create_checkpoint("test_checkpoint".to_string())
            .await;
        assert!(checkpoint_info.is_ok());
        assert_eq!(
            checkpoint_info.expect("unwrap failed").checkpoint_id,
            "test_checkpoint"
        );
    }
}