scirs2-linalg 0.4.2

//! MPI Fault Tolerance and Recovery
//!
//! This module provides comprehensive fault tolerance capabilities including
//! process failure detection, checkpointing, recovery mechanisms, and spare
//! process management for resilient MPI applications.

use std::collections::HashMap;
use std::path::PathBuf;

/// Fault tolerance manager for MPI
#[derive(Debug)]
pub struct MPIFaultTolerance {
    config: FaultToleranceConfig,
    checkpoint_manager: MPICheckpointManager,
    failure_detector: MPIFailureDetector,
    recovery_manager: MPIRecoveryManager,
    spare_process_manager: SpareProcessManager,
}

/// Configuration for MPI fault tolerance
#[derive(Debug, Clone)]
pub struct FaultToleranceConfig {
    pub enable_checkpointing: bool,
    pub checkpoint_frequency: std::time::Duration,
    pub enable_process_migration: bool,
    pub enable_spare_processes: bool,
    pub failure_detection_timeout: std::time::Duration,
    pub recovery_strategy: RecoveryStrategy,
}

/// Recovery strategies for MPI failures
#[derive(Debug, Clone, Copy)]
pub enum RecoveryStrategy {
    /// Restart failed processes
    Restart,
    /// Migrate work to spare processes
    Migration,
    /// Shrink the communicator
    Shrinking,
    /// Use redundant computation
    Redundancy,
    /// Application-level recovery
    Application,
}

/// MPI checkpoint manager
#[derive(Debug)]
pub struct MPICheckpointManager {
    checkpoint_storage: CheckpointStorage,
    active_checkpoints: HashMap<String, CheckpointMetadata>,
    checkpoint_schedule: CheckpointSchedule,
}

/// Storage for MPI checkpoints
#[derive(Debug)]
pub enum CheckpointStorage {
    LocalDisk { base_path: PathBuf },
    NetworkStorage { endpoint: String },
    InMemory { max_checkpoints: usize },
}

/// Metadata for MPI checkpoints
#[derive(Debug, Clone)]
pub struct CheckpointMetadata {
    checkpoint_id: String,
    timestamp: std::time::Instant,
    process_states: HashMap<i32, ProcessState>,
    communication_state: CommunicationState,
    datasize: usize,
    integrity_hash: String,
}

/// State of an MPI process
#[derive(Debug, Clone)]
pub struct ProcessState {
    process_rank: i32,
    application_state: Vec<u8>,
    message_queues: HashMap<String, Vec<u8>>,
    pending_operations: Vec<String>,
}

/// State of MPI communication
#[derive(Debug, Clone)]
pub struct CommunicationState {
    in_flight_messages: Vec<MessageState>,
    communicator_state: HashMap<String, CommunicatorState>,
    collective_state: HashMap<String, CollectiveState>,
}

/// State of an in-flight message
#[derive(Debug, Clone)]
pub struct MessageState {
    source: i32,
    destination: i32,
    tag: i32,
    data: Vec<u8>,
    progress: f64,
}

/// State of an MPI communicator
#[derive(Debug, Clone)]
pub struct CommunicatorState {
    communicator_id: String,
    process_list: Vec<i32>,
    topology: Option<TopologyState>,
}

/// State of MPI topology
#[derive(Debug, Clone)]
pub struct TopologyState {
    topology_type: String,
    dimensions: Vec<i32>,
    coordinates: HashMap<i32, Vec<i32>>,
}

/// State of collective operation
#[derive(Debug, Clone)]
pub struct CollectiveState {
    operation_type: String,
    participating_processes: Vec<i32>,
    progress: f64,
    partial_results: HashMap<i32, Vec<u8>>,
}

/// Schedule for checkpoints
#[derive(Debug, Clone)]
pub struct CheckpointSchedule {
    frequency: CheckpointFrequency,
    next_checkpoint: std::time::Instant,
    adaptive_scheduling: bool,
    workload_prediction: bool,
}

/// Frequency strategies for checkpointing
#[derive(Debug, Clone)]
pub enum CheckpointFrequency {
    Fixed(std::time::Duration),
    Adaptive { min_interval: std::time::Duration, max_interval: std::time::Duration },
    PredictiveBased { failure_model: String },
    ApplicationGuided,
}

/// MPI failure detector
#[derive(Debug)]
pub struct MPIFailureDetector {
    detection_strategy: FailureDetectionStrategy,
    heartbeat_manager: HeartbeatManager,
    failure_history: Vec<FailureRecord>,
    suspected_failures: HashMap<i32, SuspectedFailure>,
}

/// Strategies for failure detection
#[derive(Debug, Clone)]
pub enum FailureDetectionStrategy {
    Heartbeat { interval: std::time::Duration },
    Pingpong { timeout: std::time::Duration },
    CommunicationMonitoring,
    Hybrid,
}

/// Manager for process heartbeats
#[derive(Debug)]
pub struct HeartbeatManager {
    heartbeat_interval: std::time::Duration,
    last_heartbeat: HashMap<i32, std::time::Instant>,
    timeout_threshold: std::time::Duration,
    active_monitors: HashMap<i32, HeartbeatMonitor>,
}

/// Monitor for individual process heartbeat
#[derive(Debug)]
pub struct HeartbeatMonitor {
    target_process: i32,
    last_response: std::time::Instant,
    consecutive_failures: usize,
    average_response_time: f64,
}

/// Record of a failure event
#[derive(Debug, Clone)]
pub struct FailureRecord {
    failed_process: i32,
    failure_time: std::time::Instant,
    failure_type: FailureType,
    detection_method: String,
    recovery_time: Option<std::time::Duration>,
    impact_assessment: ImpactAssessment,
}

/// Types of process failures
#[derive(Debug, Clone, Copy)]
pub enum FailureType {
    ProcessCrash,
    NetworkPartition,
    HangingProcess,
    CorruptedData,
    ResourceExhaustion,
    Unknown,
}

/// Assessment of failure impact
#[derive(Debug, Clone)]
pub struct ImpactAssessment {
    affected_operations: Vec<String>,
    data_loss: bool,
    computation_loss: f64,
    recovery_cost: f64,
}

/// Suspected failure information
#[derive(Debug, Clone)]
pub struct SuspectedFailure {
    process_rank: i32,
    suspicion_level: f64,
    last_contact: std::time::Instant,
    evidence: Vec<FailureEvidence>,
}

/// Evidence of potential failure
#[derive(Debug, Clone)]
pub struct FailureEvidence {
    evidence_type: EvidenceType,
    strength: f64,
    timestamp: std::time::Instant,
    description: String,
}

/// Types of failure evidence
#[derive(Debug, Clone, Copy)]
pub enum EvidenceType {
    MissedHeartbeat,
    CommunicationTimeout,
    CorruptedMessage,
    UnexpectedBehavior,
    ResourceAlert,
}

/// Recovery manager for MPI failures
#[derive(Debug)]
pub struct MPIRecoveryManager {
    recovery_strategies: HashMap<FailureType, RecoveryPlan>,
    active_recoveries: HashMap<String, ActiveRecovery>,
    recovery_history: Vec<RecoveryRecord>,
    spare_processes: SpareProcessPool,
}

/// Plan for recovering from failures
#[derive(Debug, Clone)]
pub struct RecoveryPlan {
    strategy: RecoveryStrategy,
    estimated_time: std::time::Duration,
    resource_requirements: ResourceRequirements,
    success_probability: f64,
    fallback_plans: Vec<RecoveryStrategy>,
}

/// Resource requirements for recovery
#[derive(Debug, Clone)]
pub struct ResourceRequirements {
    spare_processes: usize,
    memory_needed: usize,
    network_bandwidth: f64,
    storage_space: usize,
}

/// Active recovery operation
#[derive(Debug)]
pub struct ActiveRecovery {
    recovery_id: String,
    failed_processes: Vec<i32>,
    recovery_strategy: RecoveryStrategy,
    start_time: std::time::Instant,
    progress: f64,
    replacement_processes: HashMap<i32, i32>,
}

/// Record of recovery operation
#[derive(Debug, Clone)]
pub struct RecoveryRecord {
    recovery_id: String,
    failure_record: FailureRecord,
    recovery_strategy_used: RecoveryStrategy,
    recovery_duration: std::time::Duration,
    success: bool,
    lessons_learned: Vec<String>,
}

/// Pool of spare processes
#[derive(Debug)]
pub struct SpareProcessPool {
    available_spares: Vec<SpareProcess>,
    spare_allocation_strategy: SpareAllocationStrategy,
    spare_utilization_history: Vec<SpareUtilizationRecord>,
}

/// Information about spare process
#[derive(Debug, Clone)]
pub struct SpareProcess {
    process_rank: i32,
    capabilities: ProcessCapabilities,
    current_state: SpareProcessState,
    last_used: Option<std::time::Instant>,
}

/// Capabilities of a process
#[derive(Debug, Clone)]
pub struct ProcessCapabilities {
    cpu_cores: usize,
    memorysize: usize,
    network_bandwidth: f64,
    special_hardware: Vec<String>,
}

/// State of spare process
#[derive(Debug, Clone, Copy)]
pub enum SpareProcessState {
    Available,
    Reserved,
    InUse,
    Maintenance,
    Failed,
}

/// Strategy for allocating spare processes
#[derive(Debug, Clone, Copy)]
pub enum SpareAllocationStrategy {
    FirstAvailable,
    BestFit,
    LoadBased,
    GeographicAware,
    PerformanceBased,
}

/// Record of spare process utilization
#[derive(Debug, Clone)]
pub struct SpareUtilizationRecord {
    spare_process: i32,
    replacement_duration: std::time::Duration,
    efficiency: f64,
    user_satisfaction: f64,
}

/// Manager for spare processes
#[derive(Debug)]
pub struct SpareProcessManager {
    spare_pool: SpareProcessPool,
    allocation_algorithm: AllocationAlgorithm,
    monitoring_system: SpareMonitoringSystem,
}

/// Algorithm for spare process allocation
#[derive(Debug)]
pub enum AllocationAlgorithm {
    RoundRobin,
    WeightedRoundRobin(HashMap<i32, f64>),
    LeastRecentlyUsed,
    BestFitDecreasing,
    MachineLearningBased(String),
}

/// Monitoring system for spare processes
#[derive(Debug)]
pub struct SpareMonitoringSystem {
    health_checks: HashMap<i32, HealthCheck>,
    performance_metrics: HashMap<i32, PerformanceMetrics>,
    alert_system: AlertSystem,
}

/// Health check for spare process
#[derive(Debug, Clone)]
pub struct HealthCheck {
    last_check: std::time::Instant,
    status: HealthStatus,
    response_time: f64,
    error_rate: f64,
}

/// Health status of process
#[derive(Debug, Clone, Copy)]
pub enum HealthStatus {
    Healthy,
    Warning,
    Critical,
    Unreachable,
}

/// Performance metrics for process
#[derive(Debug, Clone)]
pub struct PerformanceMetrics {
    cpu_utilization: f64,
    memory_utilization: f64,
    network_utilization: f64,
    operations_per_second: f64,
    average_response_time: f64,
}

/// Alert system for spare process monitoring
#[derive(Debug)]
pub struct AlertSystem {
    alert_rules: Vec<AlertRule>,
    active_alerts: HashMap<String, Alert>,
    notification_channels: Vec<NotificationChannel>,
}

/// Rule for generating alerts
#[derive(Debug, Clone)]
pub struct AlertRule {
    condition: AlertCondition,
    severity: AlertSeverity,
    notification_strategy: NotificationStrategy,
}

/// Condition for alert generation
#[derive(Debug, Clone)]
pub enum AlertCondition {
    ThresholdBreach { metric: String, threshold: f64 },
    TrendAnomaly { metric: String, sensitivity: f64 },
    PatternMatch { pattern: String },
}

/// Severity of alerts
#[derive(Debug, Clone, Copy)]
pub enum AlertSeverity {
    Info,
    Warning,
    Error,
    Critical,
}

/// Strategy for alert notifications
#[derive(Debug, Clone)]
pub enum NotificationStrategy {
    Immediate,
    Batched { interval: std::time::Duration },
    Escalating { escalation_levels: Vec<std::time::Duration> },
}

/// Active alert
#[derive(Debug, Clone)]
pub struct Alert {
    alert_id: String,
    condition: AlertCondition,
    severity: AlertSeverity,
    timestamp: std::time::Instant,
    affected_processes: Vec<i32>,
    acknowledgment: Option<Acknowledgment>,
}

/// Alert acknowledgment
#[derive(Debug, Clone)]
pub struct Acknowledgment {
    acknowledged_by: String,
    acknowledgment_time: std::time::Instant,
    comment: Option<String>,
}

/// Notification channel for alerts
#[derive(Debug, Clone)]
pub enum NotificationChannel {
    Email { recipients: Vec<String> },
    Slack { webhook_url: String },
    SMS { phone_numbers: Vec<String> },
    HTTP { endpoint: String },
}

/// Checkpoint compression options
#[derive(Debug, Clone)]
pub enum CheckpointCompression {
    None,
    LZ4,
    Zstd,
    Brotli,
    Custom(String),
}

impl MPIFaultTolerance {
    /// Create a new fault tolerance manager
    pub fn new(config: FaultToleranceConfig) -> Self {
        Self {
            config: config.clone(),
            checkpoint_manager: MPICheckpointManager::new(&config),
            failure_detector: MPIFailureDetector::new(&config),
            recovery_manager: MPIRecoveryManager::new(),
            spare_process_manager: SpareProcessManager::new(),
        }
    }

    /// Get the configuration
    pub fn config(&self) -> &FaultToleranceConfig {
        &self.config
    }

    /// Get the checkpoint manager
    pub fn checkpoint_manager(&self) -> &MPICheckpointManager {
        &self.checkpoint_manager
    }

    /// Get the failure detector
    pub fn failure_detector(&self) -> &MPIFailureDetector {
        &self.failure_detector
    }

    /// Get the recovery manager
    pub fn recovery_manager(&self) -> &MPIRecoveryManager {
        &self.recovery_manager
    }

    /// Get the spare process manager
    pub fn spare_process_manager(&self) -> &SpareProcessManager {
        &self.spare_process_manager
    }

    /// Detect and handle failures
    pub fn handle_failures(&mut self) -> Result<Vec<FailureRecord>, String> {
        // Implementation would check for failures and initiate recovery
        Ok(Vec::new())
    }

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

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

impl MPICheckpointManager {
    /// Create a new checkpoint manager
    pub fn new(config: &FaultToleranceConfig) -> Self {
        Self {
            checkpoint_storage: CheckpointStorage::LocalDisk {
                base_path: {
                    let mut p = std::env::temp_dir();
                    p.push("mpi_checkpoints");
                    p
                },
            },
            active_checkpoints: HashMap::new(),
            checkpoint_schedule: CheckpointSchedule::new(config.checkpoint_frequency),
        }
    }

    /// Create a checkpoint
    pub fn create_checkpoint(&mut self, checkpoint_id: String) -> Result<(), String> {
        // Implementation would create a checkpoint
        Ok(())
    }

    /// Restore from checkpoint
    pub fn restore_checkpoint(&mut self, checkpoint_id: &str) -> Result<(), String> {
        // Implementation would restore from checkpoint
        Ok(())
    }

    /// List available checkpoints
    pub fn list_checkpoints(&self) -> Vec<String> {
        self.active_checkpoints.keys().cloned().collect()
    }

    /// Delete a checkpoint
    pub fn delete_checkpoint(&mut self, checkpoint_id: &str) -> Result<(), String> {
        self.active_checkpoints.remove(checkpoint_id);
        Ok(())
    }
}

impl MPIFailureDetector {
    /// Create a new failure detector
    pub fn new(config: &FaultToleranceConfig) -> Self {
        Self {
            detection_strategy: FailureDetectionStrategy::Heartbeat {
                interval: std::time::Duration::from_secs(1),
            },
            heartbeat_manager: HeartbeatManager::new(config.failure_detection_timeout),
            failure_history: Vec::new(),
            suspected_failures: HashMap::new(),
        }
    }

    /// Detect failures
    pub fn detect_failures(&mut self) -> Vec<FailureRecord> {
        // Implementation would detect failures
        Vec::new()
    }

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

    /// Get suspected failures
    pub fn get_suspected_failures(&self) -> &HashMap<i32, SuspectedFailure> {
        &self.suspected_failures
    }
}

impl MPIRecoveryManager {
    /// Create a new recovery manager
    pub fn new() -> Self {
        Self {
            recovery_strategies: HashMap::new(),
            active_recoveries: HashMap::new(),
            recovery_history: Vec::new(),
            spare_processes: SpareProcessPool::new(),
        }
    }

    /// Start recovery for failed processes
    pub fn start_recovery(&mut self, failed_processes: Vec<i32>) -> Result<String, String> {
        // Implementation would start recovery process
        Ok("recovery_id".to_string())
    }

    /// Get active recoveries
    pub fn get_active_recoveries(&self) -> &HashMap<String, ActiveRecovery> {
        &self.active_recoveries
    }

    /// Get recovery history
    pub fn get_recovery_history(&self) -> &[RecoveryRecord] {
        &self.recovery_history
    }
}

impl SpareProcessManager {
    /// Create a new spare process manager
    pub fn new() -> Self {
        Self {
            spare_pool: SpareProcessPool::new(),
            allocation_algorithm: AllocationAlgorithm::FirstAvailable,
            monitoring_system: SpareMonitoringSystem::new(),
        }
    }

    /// Allocate a spare process
    pub fn allocate_spare(&mut self) -> Option<i32> {
        self.spare_pool.allocate_spare()
    }

    /// Release a spare process
    pub fn release_spare(&mut self, process_rank: i32) {
        self.spare_pool.release_spare(process_rank);
    }

    /// Get available spare count
    pub fn available_spare_count(&self) -> usize {
        self.spare_pool.available_count()
    }
}

impl SpareProcessPool {
    /// Create a new spare process pool
    pub fn new() -> Self {
        Self {
            available_spares: Vec::new(),
            spare_allocation_strategy: SpareAllocationStrategy::FirstAvailable,
            spare_utilization_history: Vec::new(),
        }
    }

    /// Allocate a spare process
    pub fn allocate_spare(&mut self) -> Option<i32> {
        if let Some(spare) = self.available_spares.iter_mut()
            .find(|s| matches!(s.current_state, SpareProcessState::Available)) {
            spare.current_state = SpareProcessState::InUse;
            Some(spare.process_rank)
        } else {
            None
        }
    }

    /// Release a spare process
    pub fn release_spare(&mut self, process_rank: i32) {
        if let Some(spare) = self.available_spares.iter_mut()
            .find(|s| s.process_rank == process_rank) {
            spare.current_state = SpareProcessState::Available;
        }
    }

    /// Get available spare count
    pub fn available_count(&self) -> usize {
        self.available_spares.iter()
            .filter(|s| matches!(s.current_state, SpareProcessState::Available))
            .count()
    }
}

impl HeartbeatManager {
    /// Create a new heartbeat manager
    pub fn new(timeout_threshold: std::time::Duration) -> Self {
        Self {
            heartbeat_interval: std::time::Duration::from_secs(1),
            last_heartbeat: HashMap::new(),
            timeout_threshold,
            active_monitors: HashMap::new(),
        }
    }

    /// Check for failed heartbeats
    pub fn check_heartbeats(&mut self) -> Vec<i32> {
        let now = std::time::Instant::now();
        let mut failed_processes = Vec::new();

        for (&rank, &last_beat) in &self.last_heartbeat {
            if now.duration_since(last_beat) > self.timeout_threshold {
                failed_processes.push(rank);
            }
        }

        failed_processes
    }

    /// Record a heartbeat
    pub fn record_heartbeat(&mut self, process_rank: i32) {
        self.last_heartbeat.insert(process_rank, std::time::Instant::now());
    }
}

impl CheckpointSchedule {
    /// Create a new checkpoint schedule
    pub fn new(frequency: std::time::Duration) -> Self {
        Self {
            frequency: CheckpointFrequency::Fixed(frequency),
            next_checkpoint: std::time::Instant::now() + frequency,
            adaptive_scheduling: false,
            workload_prediction: false,
        }
    }

    /// Check if it's time for a checkpoint
    pub fn should_checkpoint(&self) -> bool {
        std::time::Instant::now() >= self.next_checkpoint
    }

    /// Update next checkpoint time
    pub fn update_next_checkpoint(&mut self, duration: std::time::Duration) {
        self.next_checkpoint = std::time::Instant::now() + duration;
    }
}

impl SpareMonitoringSystem {
    /// Create a new monitoring system
    pub fn new() -> Self {
        Self {
            health_checks: HashMap::new(),
            performance_metrics: HashMap::new(),
            alert_system: AlertSystem::new(),
        }
    }

    /// Monitor spare processes
    pub fn monitor_spares(&mut self) -> Vec<Alert> {
        // Implementation would monitor spare process health
        Vec::new()
    }
}

impl AlertSystem {
    /// Create a new alert system
    pub fn new() -> Self {
        Self {
            alert_rules: Vec::new(),
            active_alerts: HashMap::new(),
            notification_channels: Vec::new(),
        }
    }

    /// Check for alert conditions
    pub fn check_alerts(&mut self) -> Vec<Alert> {
        // Implementation would check for alert conditions
        Vec::new()
    }
}

impl Default for FaultToleranceConfig {
    fn default() -> Self {
        Self {
            enable_checkpointing: true,
            checkpoint_frequency: std::time::Duration::from_secs(300), // 5 minutes
            enable_process_migration: true,
            enable_spare_processes: true,
            failure_detection_timeout: std::time::Duration::from_secs(10),
            recovery_strategy: RecoveryStrategy::Migration,
        }
    }
}