scirs2-linalg 0.4.2

//! Fault tolerance management for distributed operations

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

/// Advanced fault tolerance manager
#[derive(Debug)]
pub struct FaultToleranceManager {
    /// Node health monitoring
    health_monitor: NodeHealthMonitor,
    /// Checkpointing system
    checkpoint_manager: CheckpointManager,
    /// Recovery strategies
    recovery_strategies: HashMap<FaultType, RecoveryStrategy>,
    /// Redundancy manager
    redundancy_manager: crate::distributed::redundancy::RedundancyManager,
}

/// Node health monitoring system
#[derive(Debug)]
pub struct NodeHealthMonitor {
    /// Health status of each node
    node_health: HashMap<usize, NodeHealthStatus>,
    /// Health check intervals
    check_intervals: HashMap<usize, Duration>,
    /// Failure prediction model
    failure_predictor: FailurePredictionModel,
}

/// Health status of a compute node
#[derive(Debug, Clone)]
pub struct NodeHealthStatus {
    node_id: usize,
    is_healthy: bool,
    last_heartbeat: Instant,
    response_time: f64,
    error_rate: f64,
    resource_utilization: ResourceUtilization,
    predicted_failure_probability: f64,
}

/// Resource utilization metrics
#[derive(Debug, Clone, Default)]
pub struct ResourceUtilization {
    cpu_usage: f64,
    memory_usage: f64,
    disk_usage: f64,
    network_usage: f64,
    gpu_usage: Option<f64>,
    temperature: Option<f64>,
}

/// Failure prediction model
#[derive(Debug)]
pub struct FailurePredictionModel {
    /// Time series analysis for failure patterns
    failure_patterns: Vec<FailurePattern>,
    /// Anomaly detection thresholds
    anomaly_thresholds: AnomalyThresholds,
    /// Prediction horizon (time ahead to predict)
    prediction_horizon: Duration,
}

/// Pattern of node failures
#[derive(Debug, Clone)]
pub struct FailurePattern {
    pattern_type: FailurePatternType,
    indicators: Vec<HealthIndicator>,
    confidence: f64,
    time_to_failure: Duration,
}

/// Types of failure patterns
#[derive(Debug, Clone, Copy)]
pub enum FailurePatternType {
    GradualDegradation,
    SuddenFailure,
    PeriodicIssues,
    ResourceExhaustion,
    NetworkIsolation,
}

/// Health indicator for failure prediction
#[derive(Debug, Clone)]
pub struct HealthIndicator {
    metric_name: String,
    threshold: f64,
    trend: TrendDirection,
    severity: IndicatorSeverity,
}

/// Trend direction for health indicators
#[derive(Debug, Clone, Copy)]
pub enum TrendDirection {
    Increasing,
    Decreasing,
    Stable,
    Oscillating,
}

/// Severity of health indicators
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum IndicatorSeverity {
    Low,
    Medium,
    High,
    Critical,
}

/// Anomaly detection thresholds
#[derive(Debug, Clone)]
pub struct AnomalyThresholds {
    cpu_threshold: f64,
    memory_threshold: f64,
    response_time_threshold: f64,
    error_rate_threshold: f64,
    temperature_threshold: Option<f64>,
}

/// Checkpointing system for fault recovery
#[derive(Debug)]
pub struct CheckpointManager {
    /// Checkpoint storage locations
    storage_locations: Vec<CheckpointStorage>,
    /// Checkpoint frequency configuration
    checkpoint_config: CheckpointConfig,
    /// Active checkpoints
    active_checkpoints: HashMap<String, CheckpointMetadata>,
}

/// Checkpoint storage backend
#[derive(Debug, Clone)]
pub enum CheckpointStorage {
    LocalFileSystem { path: PathBuf },
    DistributedFileSystem { endpoint: String },
    ObjectStorage { bucket: String, credentials: String },
    InMemory { maxsize: usize },
}

/// Configuration for checkpointing
#[derive(Debug, Clone)]
pub struct CheckpointConfig {
    /// Frequency of checkpoints (operations)
    frequency: usize,
    /// Compression for checkpoint data
    compression: bool,
    /// Async checkpointing
    async_checkpointing: bool,
    /// Maximum checkpoint age before cleanup
    max_age: Duration,
    /// Verification of checkpoint integrity
    verify_integrity: bool,
}

/// Metadata for checkpoint
#[derive(Debug, Clone)]
pub struct CheckpointMetadata {
    checkpoint_id: String,
    timestamp: Instant,
    operation_state: String,
    datasize: usize,
    compression_ratio: f64,
    integrity_hash: String,
    recovery_instructions: RecoveryInstructions,
}

/// Instructions for recovery from checkpoint
#[derive(Debug, Clone)]
pub struct RecoveryInstructions {
    required_nodes: Vec<usize>,
    data_redistribution: HashMap<usize, DataRedistributionPlan>,
    computation_restart_point: String,
    dependencies: Vec<String>,
}

/// Plan for redistributing data during recovery
#[derive(Debug, Clone)]
pub struct DataRedistributionPlan {
    source_nodes: Vec<usize>,
    target_node: usize,
    data_ranges: Vec<DataRange>,
    priority: RecoveryPriority,
}

/// Range of data for redistribution
#[derive(Debug, Clone)]
pub struct DataRange {
    start_offset: usize,
    end_offset: usize,
    data_type: String,
    size_bytes: usize,
}

/// Priority for recovery operations
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum RecoveryPriority {
    Low,
    Normal,
    High,
    Critical,
}

/// Fault types for recovery strategies
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum FaultType {
    NodeFailure,
    NetworkPartition,
    DataCorruption,
    ResourceExhaustion,
    SoftwareError,
    HardwareFailure,
}

/// Recovery strategy for different fault types
#[derive(Debug, Clone)]
pub struct RecoveryStrategy {
    strategy_type: RecoveryStrategyType,
    estimated_recovery_time: Duration,
    resource_requirements: HashMap<String, f64>,
    success_probability: f64,
    fallback_strategies: Vec<RecoveryStrategyType>,
}

/// Types of recovery strategies
#[derive(Debug, Clone, Copy)]
pub enum RecoveryStrategyType {
    Restart,
    Migrate,
    Replicate,
    Rollback,
    PartialRecovery,
    GracefulDegradation,
}

impl FaultToleranceManager {
    /// Create a new fault tolerance manager
    pub fn new() -> Self {
        Self {
            health_monitor: NodeHealthMonitor::new(),
            checkpoint_manager: CheckpointManager::new(),
            recovery_strategies: HashMap::new(),
            redundancy_manager: crate::distributed::redundancy::RedundancyManager::new(),
        }
    }

    /// Monitor node health
    pub fn monitor_node_health(&mut self, node_id: usize) -> &NodeHealthStatus {
        self.health_monitor.check_node_health(node_id)
    }

    /// Create a checkpoint
    pub fn create_checkpoint(&mut self, operation_state: String) -> Result<String, String> {
        self.checkpoint_manager.create_checkpoint(operation_state)
    }

    /// Recover from checkpoint
    pub fn recover_from_checkpoint(&self, checkpoint_id: &str) -> Result<(), String> {
        self.checkpoint_manager.recover_from_checkpoint(checkpoint_id)
    }

    /// Handle node failure
    pub fn handle_node_failure(&mut self, node_id: usize, fault_type: FaultType) -> Result<(), String> {
        // Get recovery strategy for this fault type
        if let Some(strategy) = self.recovery_strategies.get(&fault_type) {
            self.execute_recovery_strategy(node_id, strategy)
        } else {
            Err(format!("No recovery strategy found for fault type: {:?}", fault_type))
        }
    }

    /// Execute recovery strategy
    fn execute_recovery_strategy(&self, _node_id: usize, _strategy: &RecoveryStrategy) -> Result<(), String> {
        // Implementation would depend on the specific strategy
        Ok(())
    }
}

impl NodeHealthMonitor {
    fn new() -> Self {
        Self {
            node_health: HashMap::new(),
            check_intervals: HashMap::new(),
            failure_predictor: FailurePredictionModel::new(),
        }
    }

    fn check_node_health(&mut self, node_id: usize) -> &NodeHealthStatus {
        // Update health status for the node
        let status = NodeHealthStatus {
            node_id,
            is_healthy: true,
            last_heartbeat: Instant::now(),
            response_time: 0.0,
            error_rate: 0.0,
            resource_utilization: ResourceUtilization::default(),
            predicted_failure_probability: 0.0,
        };

        self.node_health.entry(node_id).or_insert(status);
        self.node_health.get(&node_id).expect("Operation failed")
    }
}

impl CheckpointManager {
    fn new() -> Self {
        Self {
            storage_locations: Vec::new(),
            checkpoint_config: CheckpointConfig::default(),
            active_checkpoints: HashMap::new(),
        }
    }

    fn create_checkpoint(&mut self, operation_state: String) -> Result<String, String> {
        let checkpoint_id = format!("checkpoint_{}", Instant::now().elapsed().as_millis());
        let metadata = CheckpointMetadata {
            checkpoint_id: checkpoint_id.clone(),
            timestamp: Instant::now(),
            operation_state,
            datasize: 0,
            compression_ratio: 1.0,
            integrity_hash: String::new(),
            recovery_instructions: RecoveryInstructions {
                required_nodes: Vec::new(),
                data_redistribution: HashMap::new(),
                computation_restart_point: String::new(),
                dependencies: Vec::new(),
            },
        };

        self.active_checkpoints.insert(checkpoint_id.clone(), metadata);
        Ok(checkpoint_id)
    }

    fn recover_from_checkpoint(&self, _checkpoint_id: &str) -> Result<(), String> {
        // Implementation would load checkpoint data and restore state
        Ok(())
    }
}

impl FailurePredictionModel {
    fn new() -> Self {
        Self {
            failure_patterns: Vec::new(),
            anomaly_thresholds: AnomalyThresholds {
                cpu_threshold: 0.9,
                memory_threshold: 0.95,
                response_time_threshold: 1000.0,
                error_rate_threshold: 0.1,
                temperature_threshold: Some(80.0),
            },
            prediction_horizon: Duration::from_secs(3600),
        }
    }
}

impl Default for CheckpointConfig {
    fn default() -> Self {
        Self {
            frequency: 100,
            compression: true,
            async_checkpointing: true,
            max_age: Duration::from_secs(3600),
            verify_integrity: true,
        }
    }
}