//! Fault Tolerance and Retry Management Module
//!
//! This module provides comprehensive fault tolerance capabilities for the CUDA
//! optimization execution engine, including failure detection, retry strategies,
//! circuit breakers, recovery mechanisms, health monitoring, and system resilience
//! to ensure robust execution in the presence of hardware and software failures.

use serde::{Deserialize, Serialize};
use std::collections::{HashMap, VecDeque};
use std::sync::{
    atomic::{AtomicUsize, Ordering},
    Arc, Mutex, RwLock,
};
use std::time::{Duration, Instant, SystemTime};
use uuid;

use super::config::{CheckpointConfig, FaultToleranceConfig, RetryConfig};
use super::task_management::{TaskError, TaskId};

/// Comprehensive fault tolerance manager for CUDA execution
///
/// Manages all aspects of fault tolerance including failure detection, retry logic,
/// recovery strategies, health monitoring, and system resilience mechanisms.
#[derive(Debug)]
pub struct FaultToleranceManager {
    /// Failure detection system
    failure_detector: Arc<Mutex<FailureDetector>>,

    /// Retry management system
    retry_manager: Arc<Mutex<RetryManager>>,

    /// Circuit breaker management
    circuit_breaker_manager: Arc<Mutex<CircuitBreakerManager>>,

    /// Recovery orchestrator
    recovery_orchestrator: Arc<Mutex<RecoveryOrchestrator>>,

    /// Health monitoring system
    health_monitor: Arc<Mutex<HealthMonitor>>,

    /// Checkpointing system
    checkpoint_manager: Arc<Mutex<CheckpointManager>>,

    /// Fault tolerance metrics
    metrics_collector: Arc<Mutex<FaultToleranceMetricsCollector>>,

    /// Resilience engine
    resilience_engine: Arc<Mutex<ResilienceEngine>>,

    /// Configuration
    config: FaultToleranceConfig,

    /// System state tracking
    system_state: Arc<RwLock<SystemState>>,

    /// Fault tolerance statistics
    statistics: Arc<Mutex<FaultToleranceStatistics>>,
}

/// Failure detection system with advanced monitoring
#[derive(Debug)]
pub struct FailureDetector {
    /// Active failure monitors
    active_monitors: HashMap<MonitorId, FailureMonitor>,

    /// Failure pattern analyzer
    pattern_analyzer: FailurePatternAnalyzer,

    /// Anomaly detection engine
    anomaly_detector: AnomalyDetector,

    /// Failure classification system
    classifier: FailureClassifier,

    /// Detection configuration
    detection_config: FailureDetectionConfig,

    /// Historical failure data
    failure_history: VecDeque<FailureRecord>,

    /// Real-time failure metrics
    failure_metrics: FailureMetrics,
}

/// Retry management system with sophisticated strategies
#[derive(Debug)]
pub struct RetryManager {
    /// Active retry contexts
    active_retries: HashMap<TaskId, RetryContext>,

    /// Retry strategy engine
    strategy_engine: RetryStrategyEngine,

    /// Retry policy enforcer
    policy_enforcer: RetryPolicyEnforcer,

    /// Backoff calculator
    backoff_calculator: BackoffCalculator,

    /// Retry attempt tracker
    attempt_tracker: RetryAttemptTracker,

    /// Retry statistics
    retry_statistics: RetryStatistics,

    /// Configuration
    config: RetryConfig,
}

/// Circuit breaker management for preventing cascade failures
#[derive(Debug)]
pub struct CircuitBreakerManager {
    /// Circuit breakers by component
    circuit_breakers: HashMap<String, CircuitBreaker>,

    /// Circuit breaker state monitor
    state_monitor: CircuitBreakerStateMonitor,

    /// Failure threshold calculator
    threshold_calculator: FailureThresholdCalculator,

    /// Recovery condition checker
    recovery_checker: RecoveryConditionChecker,

    /// Circuit breaker configuration
    config: CircuitBreakerConfig,

    /// Performance metrics
    performance_metrics: CircuitBreakerMetrics,
}

/// Recovery orchestrator for system recovery operations
#[derive(Debug)]
pub struct RecoveryOrchestrator {
    /// Recovery strategies by failure type
    recovery_strategies: HashMap<FailureType, Vec<RecoveryStrategy>>,

    /// Recovery execution engine
    execution_engine: RecoveryExecutionEngine,

    /// Recovery state machine
    state_machine: RecoveryStateMachine,

    /// Resource recovery manager
    resource_recovery: ResourceRecoveryManager,

    /// Recovery validation system
    validation_system: RecoveryValidationSystem,

    /// Recovery configuration
    config: RecoveryConfig,

    /// Recovery history
    recovery_history: VecDeque<RecoveryRecord>,
}

/// Health monitoring system for proactive failure prevention
#[derive(Debug)]
pub struct HealthMonitor {
    /// System health checkers
    health_checkers: HashMap<String, HealthChecker>,

    /// Health metrics collector
    metrics_collector: HealthMetricsCollector,

    /// Health trend analyzer
    trend_analyzer: HealthTrendAnalyzer,

    /// Predictive health model
    predictive_model: Option<PredictiveHealthModel>,

    /// Alert system
    alert_system: HealthAlertSystem,

    /// Health monitoring configuration
    config: HealthMonitoringConfig,

    /// Current system health status
    system_health: SystemHealthStatus,
}

/// Checkpointing system for state preservation
#[derive(Debug)]
pub struct CheckpointManager {
    /// Active checkpoints
    active_checkpoints: HashMap<TaskId, Vec<Checkpoint>>,

    /// Checkpoint storage backend
    storage_backend: CheckpointStorageBackend,

    /// Checkpoint creation engine
    creation_engine: CheckpointCreationEngine,

    /// Checkpoint restoration engine
    restoration_engine: CheckpointRestorationEngine,

    /// Checkpoint validation system
    validation_system: CheckpointValidationSystem,

    /// Checkpoint configuration
    config: CheckpointConfig,

    /// Checkpoint statistics
    statistics: CheckpointStatistics,
}

/// Resilience engine for system-wide resilience management
#[derive(Debug)]
pub struct ResilienceEngine {
    /// Resilience strategies
    resilience_strategies: Vec<ResilienceStrategy>,

    /// Adaptation engine
    adaptation_engine: AdaptationEngine,

    /// Load shedding controller
    load_shedding: LoadSheddingController,

    /// Graceful degradation manager
    degradation_manager: GracefulDegradationManager,

    /// Resilience metrics
    resilience_metrics: ResilienceMetrics,

    /// Configuration
    config: ResilienceConfig,
}

// === Core Types and Structures ===

/// Failure monitor for detecting specific types of failures
#[derive(Debug, Clone)]
pub struct FailureMonitor {
    /// Monitor identifier
    pub monitor_id: MonitorId,

    /// Monitor type
    pub monitor_type: MonitorType,

    /// Monitored component
    pub component: String,

    /// Detection thresholds
    pub thresholds: DetectionThresholds,

    /// Monitoring window
    pub monitoring_window: Duration,

    /// Current status
    pub status: MonitorStatus,

    /// Last check timestamp
    pub last_check: Instant,

    /// Detection history
    pub detection_history: VecDeque<DetectionEvent>,
}

/// Retry context for managing retry attempts
#[derive(Debug, Clone)]
pub struct RetryContext {
    /// Task being retried
    pub task_id: TaskId,

    /// Retry strategy
    pub strategy: RetryStrategy,

    /// Current attempt number
    pub attempt_number: usize,

    /// Maximum attempts allowed
    pub max_attempts: usize,

    /// Next retry time
    pub next_retry_at: Instant,

    /// Retry delay progression
    pub delay_progression: Vec<Duration>,

    /// Failure reasons
    pub failure_reasons: Vec<FailureReason>,

    /// Retry metadata
    pub metadata: HashMap<String, String>,

    /// Context creation time
    pub created_at: Instant,
}

/// Circuit breaker for preventing cascade failures
#[derive(Debug, Clone)]
pub struct CircuitBreaker {
    /// Circuit breaker name
    pub name: String,

    /// Current state
    pub state: CircuitBreakerState,

    /// Failure count in current window (simplified for Clone)
    pub failure_count: usize,

    /// Success count in current window (simplified for Clone)
    pub success_count: usize,

    /// Failure threshold
    pub failure_threshold: usize,

    /// Success threshold for recovery
    pub success_threshold: usize,

    /// Monitoring window duration
    pub window_duration: Duration,

    /// Current window start time
    pub window_start: Instant,

    /// Last state change time
    pub last_state_change: Instant,

    /// Half-open test count (simplified for Clone)
    pub half_open_test_count: usize,

    /// Configuration
    pub config: CircuitBreakerConfiguration,
}

/// Recovery strategy for handling specific failure types
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RecoveryStrategy {
    /// Strategy name
    pub name: String,

    /// Applicable failure types
    pub applicable_failures: Vec<FailureType>,

    /// Recovery actions
    pub recovery_actions: Vec<RecoveryAction>,

    /// Recovery priority
    pub priority: RecoveryPriority,

    /// Maximum recovery time
    pub max_recovery_time: Duration,

    /// Success criteria
    pub success_criteria: Vec<RecoverySuccessCriterion>,

    /// Rollback strategy
    pub rollback_strategy: Option<RollbackStrategy>,

    /// Resource requirements
    pub resource_requirements: RecoveryResourceRequirements,
}

/// Health checker for monitoring system health
#[derive(Debug)]
pub struct HealthChecker {
    /// Checker name
    pub name: String,

    /// Check type
    pub check_type: HealthCheckType,

    /// Check interval
    pub check_interval: Duration,

    /// Health check function
    pub check_function: Box<dyn Fn() -> HealthCheckResult + Send + Sync>,

    /// Timeout for health checks
    pub timeout: Duration,

    /// Last check result
    pub last_result: Option<HealthCheckResult>,

    /// Last check time
    pub last_check_time: Option<Instant>,

    /// Health history
    pub health_history: VecDeque<HealthCheckRecord>,
}

/// Checkpoint for preserving task state
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Checkpoint {
    /// Checkpoint identifier
    pub checkpoint_id: String,

    /// Associated task
    pub task_id: TaskId,

    /// Checkpoint timestamp
    pub timestamp: SystemTime,

    /// Task state data
    pub state_data: Vec<u8>,

    /// Resource state
    pub resource_state: ResourceState,

    /// Checkpoint metadata
    pub metadata: CheckpointMetadata,

    /// Validation checksum
    pub checksum: String,

    /// Compression used
    pub compression: CompressionType,

    /// Storage location
    pub storage_location: String,
}

// === Enumerations and Configuration Types ===

/// Types of failure monitors
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum MonitorType {
    /// Hardware failure monitoring
    Hardware,
    /// Software failure monitoring
    Software,
    /// Performance degradation monitoring
    Performance,
    /// Resource exhaustion monitoring
    Resource,
    /// Network failure monitoring
    Network,
    /// Memory failure monitoring
    Memory,
    /// GPU failure monitoring
    GPU,
    /// Custom failure monitoring
    Custom,
}

/// Circuit breaker states
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum CircuitBreakerState {
    /// Circuit is closed - normal operation
    Closed,
    /// Circuit is open - failing fast
    Open,
    /// Circuit is half-open - testing recovery
    HalfOpen,
}

/// Types of failures
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum FailureType {
    /// Hardware failure
    Hardware(HardwareFailureType),
    /// Software failure
    Software(SoftwareFailureType),
    /// Resource failure
    Resource(ResourceFailureType),
    /// Network failure
    Network(NetworkFailureType),
    /// Timeout failure
    Timeout(TimeoutFailureType),
    /// Configuration failure
    Configuration(ConfigurationFailureType),
    /// Custom failure
    Custom(String),
}

/// Hardware failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum HardwareFailureType {
    GPUFailure,
    MemoryFailure,
    CPUFailure,
    StorageFailure,
    ThermalFailure,
    PowerFailure,
}

/// Software failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum SoftwareFailureType {
    CrashFailure,
    HangFailure,
    CorruptionFailure,
    LogicFailure,
    APIFailure,
}

/// Resource failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum ResourceFailureType {
    OutOfMemory,
    OutOfStorage,
    OutOfCPU,
    OutOfGPU,
    ResourceDeadlock,
}

/// Network failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum NetworkFailureType {
    ConnectionFailure,
    TimeoutFailure,
    BandwidthFailure,
    LatencyFailure,
}

/// Timeout failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum TimeoutFailureType {
    ExecutionTimeout,
    ResponseTimeout,
    ResourceTimeout,
    NetworkTimeout,
}

/// Configuration failure subtypes
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum ConfigurationFailureType {
    InvalidConfiguration,
    MissingConfiguration,
    ConflictingConfiguration,
}

/// Retry strategies
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum RetryStrategy {
    /// Fixed delay between retries
    FixedDelay(Duration),
    /// Exponential backoff
    ExponentialBackoff {
        initial_delay: Duration,
        multiplier: f64,
        max_delay: Duration,
        jitter: bool,
    },
    /// Linear backoff
    LinearBackoff {
        initial_delay: Duration,
        increment: Duration,
        max_delay: Duration,
    },
    /// Fibonacci backoff
    FibonacciBackoff {
        initial_delay: Duration,
        max_delay: Duration,
    },
    /// Custom retry strategy
    Custom {
        name: String,
        parameters: HashMap<String, String>,
    },
}

/// Recovery actions
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum RecoveryAction {
    /// Restart component
    RestartComponent(String),
    /// Reset resource state
    ResetResource(String),
    /// Reallocate resources
    ReallocateResources,
    /// Switch to backup system
    SwitchToBackup,
    /// Reduce resource usage
    ReduceResourceUsage(f64),
    /// Clear cache/memory
    ClearCache,
    /// Reinitialize system
    ReinitializeSystem,
    /// Execute custom recovery
    CustomRecovery {
        name: String,
        parameters: HashMap<String, String>,
    },
}

/// Recovery priorities
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
pub enum RecoveryPriority {
    Critical = 0,
    High = 1,
    Medium = 2,
    Low = 3,
}

/// Health check types
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum HealthCheckType {
    Heartbeat,
    ResourceCheck,
    PerformanceCheck,
    ConnectivityCheck,
    FunctionalCheck,
    Custom,
}

/// Compression types for checkpoints
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum CompressionType {
    None,
    Gzip,
    Lz4,
    Zstd,
}

// === Configuration Structures ===

/// Failure detection configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FailureDetectionConfig {
    /// Enable anomaly detection
    pub enable_anomaly_detection: bool,

    /// Detection sensitivity level
    pub sensitivity_level: DetectionSensitivity,

    /// Monitoring intervals
    pub monitoring_intervals: HashMap<MonitorType, Duration>,

    /// Detection thresholds
    pub detection_thresholds: HashMap<MonitorType, DetectionThresholds>,

    /// Pattern analysis configuration
    pub pattern_analysis_config: PatternAnalysisConfig,

    /// False positive reduction settings
    pub false_positive_reduction: FalsePositiveReductionConfig,
}

/// Circuit breaker configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CircuitBreakerConfig {
    /// Default failure threshold
    pub default_failure_threshold: usize,

    /// Default success threshold
    pub default_success_threshold: usize,

    /// Default window duration
    pub default_window_duration: Duration,

    /// Half-open test limit
    pub half_open_test_limit: usize,

    /// Component-specific configurations
    pub component_configs: HashMap<String, CircuitBreakerConfiguration>,
}

/// Recovery configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RecoveryConfig {
    /// Maximum concurrent recoveries
    pub max_concurrent_recoveries: usize,

    /// Recovery timeout
    pub recovery_timeout: Duration,

    /// Enable automatic recovery
    pub enable_automatic_recovery: bool,

    /// Recovery strategy selection
    pub strategy_selection: RecoveryStrategySelection,

    /// Rollback configuration
    pub rollback_config: RollbackConfig,
}

/// Health monitoring configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct HealthMonitoringConfig {
    /// Health check intervals
    pub check_intervals: HashMap<HealthCheckType, Duration>,

    /// Health check timeouts
    pub check_timeouts: HashMap<HealthCheckType, Duration>,

    /// Enable predictive health modeling
    pub enable_predictive_modeling: bool,

    /// Alert thresholds
    pub alert_thresholds: HashMap<String, f64>,

    /// Health history retention
    pub history_retention_period: Duration,
}

/// Resilience configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ResilienceConfig {
    /// Enable adaptive resilience
    pub enable_adaptive_resilience: bool,

    /// Load shedding thresholds
    pub load_shedding_thresholds: LoadSheddingThresholds,

    /// Graceful degradation settings
    pub degradation_settings: GracefulDegradationSettings,

    /// Resilience strategy weights
    pub strategy_weights: HashMap<String, f64>,
}

// === Implementation ===

impl FaultToleranceManager {
    /// Create a new fault tolerance manager
    pub fn new(config: FaultToleranceConfig) -> Self {
        Self {
            failure_detector: Arc::new(Mutex::new(FailureDetector::new(&config))),
            retry_manager: Arc::new(Mutex::new(RetryManager::new(&config.retry))),
            circuit_breaker_manager: Arc::new(Mutex::new(CircuitBreakerManager::new(&config))),
            recovery_orchestrator: Arc::new(Mutex::new(RecoveryOrchestrator::new(&config))),
            health_monitor: Arc::new(Mutex::new(HealthMonitor::new(&config))),
            checkpoint_manager: Arc::new(Mutex::new(CheckpointManager::new(&config.checkpointing))),
            metrics_collector: Arc::new(Mutex::new(FaultToleranceMetricsCollector::new())),
            resilience_engine: Arc::new(Mutex::new(ResilienceEngine::new(&config))),
            config,
            system_state: Arc::new(RwLock::new(SystemState::new())),
            statistics: Arc::new(Mutex::new(FaultToleranceStatistics::new())),
        }
    }

    /// Handle a task failure
    pub fn handle_failure(
        &self,
        task_id: TaskId,
        failure: TaskError,
    ) -> Result<FailureHandlingResult, FaultToleranceError> {
        // Detect and classify the failure
        let failure_classification = {
            let mut detector = self.failure_detector.lock().expect("lock should not be poisoned");
            detector.classify_failure(&failure)?
        };

        // Check if retry is appropriate
        let retry_decision = {
            let mut retry_manager = self.retry_manager.lock().expect("lock should not be poisoned");
            retry_manager.should_retry(task_id, &failure_classification)?
        };

        match retry_decision {
            RetryDecision::Retry(retry_delay) => {
                // Schedule retry
                self.schedule_retry(task_id, retry_delay)?;
                Ok(FailureHandlingResult::Retry(retry_delay))
            }
            RetryDecision::NoRetry(reason) => {
                // Initiate recovery if possible
                let recovery_result = {
                    let mut recovery = self.recovery_orchestrator.lock().expect("lock should not be poisoned");
                    recovery.attempt_recovery(&failure_classification)?
                };

                match recovery_result {
                    RecoveryResult::Success => Ok(FailureHandlingResult::Recovered),
                    RecoveryResult::Failed => {
                        // Update circuit breakers
                        self.update_circuit_breakers(&failure_classification)?;
                        Ok(FailureHandlingResult::Failed(reason))
                    }
                    RecoveryResult::Partial => Ok(FailureHandlingResult::PartialRecovery),
                }
            }
        }
    }

    /// Create a checkpoint for a task
    pub fn create_checkpoint(
        &self,
        task_id: TaskId,
        state_data: Vec<u8>,
    ) -> Result<String, FaultToleranceError> {
        let mut checkpoint_manager = self.checkpoint_manager.lock().expect("lock should not be poisoned");
        let checkpoint_id = checkpoint_manager.create_checkpoint(task_id, state_data)?;

        // Update statistics
        {
            let mut stats = self.statistics.lock().expect("lock should not be poisoned");
            stats.checkpoints_created += 1;
        }

        Ok(checkpoint_id)
    }

    /// Restore a task from checkpoint
    pub fn restore_from_checkpoint(
        &self,
        task_id: TaskId,
        checkpoint_id: &str,
    ) -> Result<Vec<u8>, FaultToleranceError> {
        let mut checkpoint_manager = self.checkpoint_manager.lock().expect("lock should not be poisoned");
        let state_data = checkpoint_manager.restore_checkpoint(task_id, checkpoint_id)?;

        // Update statistics
        {
            let mut stats = self.statistics.lock().expect("lock should not be poisoned");
            stats.checkpoints_restored += 1;
        }

        Ok(state_data)
    }

    /// Get current system health status
    pub fn get_system_health(&self) -> SystemHealthStatus {
        let health_monitor = self.health_monitor.lock().expect("lock should not be poisoned");
        health_monitor.get_current_health_status()
    }

    /// Get fault tolerance statistics
    pub fn get_statistics(&self) -> FaultToleranceStatistics {
        let stats = self.statistics.lock().expect("lock should not be poisoned");
        stats.clone()
    }

    // === Private Helper Methods ===

    fn schedule_retry(&self, task_id: TaskId, delay: Duration) -> Result<(), FaultToleranceError> {
        // Implementation would schedule the retry with appropriate delay
        Ok(())
    }

    fn update_circuit_breakers(
        &self,
        failure: &FailureClassification,
    ) -> Result<(), FaultToleranceError> {
        let mut circuit_breakers = self.circuit_breaker_manager.lock().expect("lock should not be poisoned");
        circuit_breakers.record_failure(&failure.component, &failure.failure_type)?;
        Ok(())
    }
}

impl FailureDetector {
    fn new(config: &FaultToleranceConfig) -> Self {
        Self {
            active_monitors: HashMap::new(),
            pattern_analyzer: FailurePatternAnalyzer::new(),
            anomaly_detector: AnomalyDetector::new(),
            classifier: FailureClassifier::new(),
            detection_config: config.detection.clone().unwrap_or_default(),
            failure_history: VecDeque::new(),
            failure_metrics: FailureMetrics::new(),
        }
    }

    fn classify_failure(
        &mut self,
        failure: &TaskError,
    ) -> Result<FailureClassification, FaultToleranceError> {
        let failure_type = self.classifier.classify(failure);
        let component = self.identify_component(failure);
        let severity = self.assess_severity(failure);

        let classification = FailureClassification {
            failure_type,
            component,
            severity,
            timestamp: Instant::now(),
            context: HashMap::new(),
        };

        // Record for pattern analysis
        self.record_failure(&classification);

        Ok(classification)
    }

    fn record_failure(&mut self, classification: &FailureClassification) {
        let record = FailureRecord {
            classification: classification.clone(),
            recorded_at: Instant::now(),
        };

        self.failure_history.push_back(record);

        // Limit history size
        if self.failure_history.len() > 1000 {
            self.failure_history.pop_front();
        }

        // Update metrics
        self.failure_metrics.record_failure(classification);
    }

    fn identify_component(&self, failure: &TaskError) -> String {
        match failure {
            TaskError::ResourceAllocationFailed(_) => "resource_manager".to_string(),
            TaskError::ExecutionFailed(_) => "execution_engine".to_string(),
            TaskError::DependencyResolutionFailed(_) => "dependency_manager".to_string(),
            _ => "unknown".to_string(),
        }
    }

    fn assess_severity(&self, failure: &TaskError) -> FailureSeverity {
        match failure {
            TaskError::TaskNotFound(_) => FailureSeverity::Low,
            TaskError::InvalidTask(_) => FailureSeverity::Medium,
            TaskError::ResourceAllocationFailed(_) => FailureSeverity::High,
            TaskError::ExecutionFailed(_) => FailureSeverity::Critical,
            _ => FailureSeverity::Medium,
        }
    }
}

impl RetryManager {
    fn new(config: &RetryConfig) -> Self {
        Self {
            active_retries: HashMap::new(),
            strategy_engine: RetryStrategyEngine::new(),
            policy_enforcer: RetryPolicyEnforcer::new(config),
            backoff_calculator: BackoffCalculator::new(),
            attempt_tracker: RetryAttemptTracker::new(),
            retry_statistics: RetryStatistics::new(),
            config: config.clone(),
        }
    }

    fn should_retry(
        &mut self,
        task_id: TaskId,
        failure: &FailureClassification,
    ) -> Result<RetryDecision, FaultToleranceError> {
        // Check if retry is enabled for this failure type
        if !self.is_retryable_failure(&failure.failure_type) {
            return Ok(RetryDecision::NoRetry(
                "Non-retryable failure type".to_string(),
            ));
        }

        // Get or create retry context
        let retry_context = self
            .active_retries
            .entry(task_id)
            .or_insert_with(|| RetryContext {
                task_id,
                strategy: self.determine_retry_strategy(&failure.failure_type),
                attempt_number: 0,
                max_attempts: self.config.max_retries,
                next_retry_at: Instant::now(),
                delay_progression: Vec::new(),
                failure_reasons: Vec::new(),
                metadata: HashMap::new(),
                created_at: Instant::now(),
            });

        // Check if we've exceeded maximum attempts
        if retry_context.attempt_number >= retry_context.max_attempts {
            return Ok(RetryDecision::NoRetry(
                "Maximum retry attempts exceeded".to_string(),
            ));
        }

        // Calculate next retry delay
        let retry_delay = self
            .backoff_calculator
            .calculate_delay(&retry_context.strategy, retry_context.attempt_number);

        // Update retry context
        retry_context.attempt_number += 1;
        retry_context.next_retry_at = Instant::now() + retry_delay;
        retry_context.failure_reasons.push(FailureReason {
            failure_type: failure.failure_type.clone(),
            timestamp: failure.timestamp,
            details: "Failure recorded for retry decision".to_string(),
        });

        // Record retry attempt
        self.attempt_tracker
            .record_attempt(task_id, retry_context.attempt_number, retry_delay);

        Ok(RetryDecision::Retry(retry_delay))
    }

    fn is_retryable_failure(&self, failure_type: &FailureType) -> bool {
        match failure_type {
            FailureType::Hardware(_) => false, // Hardware failures typically not retryable
            FailureType::Software(SoftwareFailureType::CrashFailure) => true,
            FailureType::Resource(ResourceFailureType::OutOfMemory) => true,
            FailureType::Network(_) => true,
            FailureType::Timeout(_) => true,
            _ => false,
        }
    }

    fn determine_retry_strategy(&self, failure_type: &FailureType) -> RetryStrategy {
        match failure_type {
            FailureType::Network(_) => RetryStrategy::ExponentialBackoff {
                initial_delay: Duration::from_millis(100),
                multiplier: 2.0,
                max_delay: Duration::from_secs(30),
                jitter: true,
            },
            FailureType::Resource(_) => RetryStrategy::LinearBackoff {
                initial_delay: Duration::from_millis(500),
                increment: Duration::from_millis(500),
                max_delay: Duration::from_secs(60),
            },
            _ => RetryStrategy::FixedDelay(Duration::from_secs(1)),
        }
    }
}

impl CircuitBreakerManager {
    fn new(config: &FaultToleranceConfig) -> Self {
        Self {
            circuit_breakers: HashMap::new(),
            state_monitor: CircuitBreakerStateMonitor::new(),
            threshold_calculator: FailureThresholdCalculator::new(),
            recovery_checker: RecoveryConditionChecker::new(),
            config: config.circuit_breaker.clone().unwrap_or_default(),
            performance_metrics: CircuitBreakerMetrics::new(),
        }
    }

    fn record_failure(
        &mut self,
        component: &str,
        failure_type: &FailureType,
    ) -> Result<(), FaultToleranceError> {
        let circuit_breaker = self
            .circuit_breakers
            .entry(component.to_string())
            .or_insert_with(|| self.create_circuit_breaker(component));

        // Record failure
        circuit_breaker
            .failure_count
            .fetch_add(1, Ordering::Relaxed);

        // Check if circuit breaker should trip
        self.check_circuit_breaker_state(circuit_breaker)?;

        Ok(())
    }

    fn create_circuit_breaker(&self, component: &str) -> CircuitBreaker {
        let component_config = self
            .config
            .component_configs
            .get(component)
            .cloned()
            .unwrap_or_default();

        CircuitBreaker {
            name: component.to_string(),
            state: CircuitBreakerState::Closed,
            failure_count: 0,
            success_count: 0,
            failure_threshold: component_config.failure_threshold,
            success_threshold: component_config.success_threshold,
            window_duration: component_config.window_duration,
            window_start: Instant::now(),
            last_state_change: Instant::now(),
            half_open_test_count: 0,
            config: component_config,
        }
    }

    fn check_circuit_breaker_state(
        &mut self,
        circuit_breaker: &mut CircuitBreaker,
    ) -> Result<(), FaultToleranceError> {
        let failure_count = circuit_breaker.failure_count;
        let success_count = circuit_breaker.success_count;

        match circuit_breaker.state {
            CircuitBreakerState::Closed => {
                if failure_count >= circuit_breaker.failure_threshold {
                    circuit_breaker.state = CircuitBreakerState::Open;
                    circuit_breaker.last_state_change = Instant::now();
                    self.performance_metrics
                        .record_state_change(&circuit_breaker.name, CircuitBreakerState::Open);
                }
            }
            CircuitBreakerState::Open => {
                // Check if enough time has passed to try recovery
                if circuit_breaker.last_state_change.elapsed()
                    > circuit_breaker.config.recovery_timeout
                {
                    circuit_breaker.state = CircuitBreakerState::HalfOpen;
                    circuit_breaker.last_state_change = Instant::now();
                    circuit_breaker.half_open_test_count = 0;
                    self.performance_metrics
                        .record_state_change(&circuit_breaker.name, CircuitBreakerState::HalfOpen);
                }
            }
            CircuitBreakerState::HalfOpen => {
                if success_count >= circuit_breaker.success_threshold {
                    circuit_breaker.state = CircuitBreakerState::Closed;
                    circuit_breaker.last_state_change = Instant::now();
                    circuit_breaker.failure_count = 0;
                    circuit_breaker.success_count = 0;
                    self.performance_metrics
                        .record_state_change(&circuit_breaker.name, CircuitBreakerState::Closed);
                } else if failure_count > 0 {
                    circuit_breaker.state = CircuitBreakerState::Open;
                    circuit_breaker.last_state_change = Instant::now();
                    self.performance_metrics
                        .record_state_change(&circuit_breaker.name, CircuitBreakerState::Open);
                }
            }
        }

        Ok(())
    }
}

impl CheckpointManager {
    fn new(config: &CheckpointConfig) -> Self {
        Self {
            active_checkpoints: HashMap::new(),
            storage_backend: CheckpointStorageBackend::new(&config.storage_location),
            creation_engine: CheckpointCreationEngine::new(),
            restoration_engine: CheckpointRestorationEngine::new(),
            validation_system: CheckpointValidationSystem::new(),
            config: config.clone(),
            statistics: CheckpointStatistics::new(),
        }
    }

    fn create_checkpoint(
        &mut self,
        task_id: TaskId,
        state_data: Vec<u8>,
    ) -> Result<String, FaultToleranceError> {
        let checkpoint_id = uuid::Uuid::new_v4().to_string();

        let checkpoint = Checkpoint {
            checkpoint_id: checkpoint_id.clone(),
            task_id,
            timestamp: SystemTime::now(),
            state_data: if self.config.compression_enabled {
                self.compress_data(&state_data)?
            } else {
                state_data
            },
            resource_state: ResourceState::default(),
            metadata: CheckpointMetadata::new(),
            checksum: self.calculate_checksum(&state_data),
            compression: if self.config.compression_enabled {
                CompressionType::Gzip
            } else {
                CompressionType::None
            },
            storage_location: self.config.storage_location.clone(),
        };

        // Store checkpoint
        self.storage_backend.store_checkpoint(&checkpoint)?;

        // Add to active checkpoints
        self.active_checkpoints
            .entry(task_id)
            .or_insert_with(Vec::new)
            .push(checkpoint);

        // Cleanup old checkpoints if needed
        self.cleanup_old_checkpoints(task_id)?;

        Ok(checkpoint_id)
    }

    fn restore_checkpoint(
        &mut self,
        task_id: TaskId,
        checkpoint_id: &str,
    ) -> Result<Vec<u8>, FaultToleranceError> {
        let checkpoint = self.storage_backend.load_checkpoint(checkpoint_id)?;

        // Validate checkpoint
        if self.config.validation_enabled {
            self.validation_system.validate_checkpoint(&checkpoint)?;
        }

        // Decompress if needed
        let state_data = if checkpoint.compression != CompressionType::None {
            self.decompress_data(&checkpoint.state_data)?
        } else {
            checkpoint.state_data
        };

        Ok(state_data)
    }

    fn cleanup_old_checkpoints(&mut self, task_id: TaskId) -> Result<(), FaultToleranceError> {
        if let Some(checkpoints) = self.active_checkpoints.get_mut(&task_id) {
            // Keep only the most recent N checkpoints
            if checkpoints.len() > self.config.max_checkpoints {
                checkpoints.sort_by(|a, b| b.timestamp.cmp(&a.timestamp));
                checkpoints.truncate(self.config.max_checkpoints);
            }
        }
        Ok(())
    }

    fn compress_data(&self, data: &[u8]) -> Result<Vec<u8>, FaultToleranceError> {
        // Implementation would use actual compression library
        Ok(data.to_vec()) // Placeholder
    }

    fn decompress_data(&self, data: &[u8]) -> Result<Vec<u8>, FaultToleranceError> {
        // Implementation would use actual decompression library
        Ok(data.to_vec()) // Placeholder
    }

    fn calculate_checksum(&self, data: &[u8]) -> String {
        // Implementation would use actual hashing
        format!("checksum_{}", data.len()) // Placeholder
    }
}

// === Error Handling ===

/// Fault tolerance errors
#[derive(Debug, Clone)]
pub enum FaultToleranceError {
    /// Failure detection error
    FailureDetectionError(String),
    /// Retry management error
    RetryError(String),
    /// Circuit breaker error
    CircuitBreakerError(String),
    /// Recovery error
    RecoveryError(String),
    /// Health monitoring error
    HealthMonitoringError(String),
    /// Checkpoint error
    CheckpointError(String),
    /// Configuration error
    ConfigurationError(String),
    /// System state error
    SystemStateError(String),
}

/// Results of failure handling
#[derive(Debug, Clone)]
pub enum FailureHandlingResult {
    /// Task should be retried after delay
    Retry(Duration),
    /// Task was recovered successfully
    Recovered,
    /// Partial recovery achieved
    PartialRecovery,
    /// Task failed and cannot be recovered
    Failed(String),
}

/// Retry decision enumeration
#[derive(Debug, Clone)]
pub enum RetryDecision {
    /// Retry with specified delay
    Retry(Duration),
    /// Do not retry with reason
    NoRetry(String),
}

/// Recovery results
#[derive(Debug, Clone)]
pub enum RecoveryResult {
    /// Recovery succeeded
    Success,
    /// Recovery failed
    Failed,
    /// Partial recovery achieved
    Partial,
}

// === Placeholder Types and Default Implementations ===

macro_rules! default_placeholder_type {
    ($name:ident) => {
        #[derive(Debug, Clone, Default, PartialEq, Eq, Hash, Serialize, Deserialize)]
        pub struct $name {
            pub placeholder: bool,
        }
    };
}

default_placeholder_type!(MonitorId);
default_placeholder_type!(MonitorStatus);
default_placeholder_type!(DetectionEvent);
default_placeholder_type!(DetectionThresholds);
default_placeholder_type!(FailureReason);
default_placeholder_type!(CircuitBreakerConfiguration);
default_placeholder_type!(RecoverySuccessCriterion);
default_placeholder_type!(RollbackStrategy);
default_placeholder_type!(RecoveryResourceRequirements);
default_placeholder_type!(HealthCheckResult);
default_placeholder_type!(HealthCheckRecord);
default_placeholder_type!(ResourceState);
default_placeholder_type!(CheckpointMetadata);
default_placeholder_type!(DetectionSensitivity);
default_placeholder_type!(PatternAnalysisConfig);
default_placeholder_type!(FalsePositiveReductionConfig);
default_placeholder_type!(RecoveryStrategySelection);
default_placeholder_type!(RollbackConfig);
default_placeholder_type!(LoadSheddingThresholds);
default_placeholder_type!(GracefulDegradationSettings);
default_placeholder_type!(FailurePatternAnalyzer);
default_placeholder_type!(AnomalyDetector);
default_placeholder_type!(FailureClassifier);
default_placeholder_type!(FailureMetrics);
default_placeholder_type!(FailureRecord);
/// Failure classification for fault tolerance analysis
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FailureClassification {
    /// Type of failure
    pub failure_type: FailureType,
    /// Component where failure occurred
    pub component: String,
    /// Severity level
    pub severity: FailureSeverity,
    /// When the failure occurred
    #[serde(skip)]
    pub timestamp: Instant,
    /// Additional context
    pub context: HashMap<String, String>,
}
default_placeholder_type!(FailureSeverity);
default_placeholder_type!(RetryStrategyEngine);
default_placeholder_type!(RetryPolicyEnforcer);
default_placeholder_type!(BackoffCalculator);
default_placeholder_type!(RetryAttemptTracker);
default_placeholder_type!(RetryStatistics);
default_placeholder_type!(CircuitBreakerStateMonitor);
default_placeholder_type!(FailureThresholdCalculator);
default_placeholder_type!(RecoveryConditionChecker);
default_placeholder_type!(CircuitBreakerMetrics);

impl CircuitBreakerMetrics {
    /// Record a state change in the circuit breaker
    pub fn record_state_change(&mut self, _name: &str, _state: CircuitBreakerState) {
        // Placeholder implementation - would record metrics in production
    }
}
default_placeholder_type!(RecoveryExecutionEngine);
default_placeholder_type!(RecoveryStateMachine);
default_placeholder_type!(ResourceRecoveryManager);
default_placeholder_type!(RecoveryValidationSystem);
default_placeholder_type!(RecoveryRecord);
default_placeholder_type!(HealthMetricsCollector);
default_placeholder_type!(HealthTrendAnalyzer);
default_placeholder_type!(PredictiveHealthModel);
default_placeholder_type!(HealthAlertSystem);
default_placeholder_type!(SystemHealthStatus);
default_placeholder_type!(CheckpointStorageBackend);
default_placeholder_type!(CheckpointCreationEngine);
default_placeholder_type!(CheckpointRestorationEngine);
default_placeholder_type!(CheckpointValidationSystem);
default_placeholder_type!(CheckpointStatistics);
default_placeholder_type!(ResilienceStrategy);
default_placeholder_type!(AdaptationEngine);
default_placeholder_type!(LoadSheddingController);
default_placeholder_type!(GracefulDegradationManager);
default_placeholder_type!(ResilienceMetrics);
default_placeholder_type!(FaultToleranceMetricsCollector);
default_placeholder_type!(SystemState);

// Implement necessary methods
impl FaultToleranceStatistics {
    fn new() -> Self {
        Self {
            checkpoints_created: 0,
            checkpoints_restored: 0,
            ..Default::default()
        }
    }
}

// Override the default FaultToleranceStatistics to include actual fields
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FaultToleranceStatistics {
    pub checkpoints_created: u64,
    pub checkpoints_restored: u64,
    pub failures_detected: u64,
    pub retries_attempted: u64,
    pub recoveries_successful: u64,
    pub circuit_breakers_tripped: u64,
}

impl CheckpointStorageBackend {
    fn new(storage_location: &str) -> Self {
        Self::default()
    }

    fn store_checkpoint(&self, checkpoint: &Checkpoint) -> Result<(), FaultToleranceError> {
        Ok(())
    }

    fn load_checkpoint(&self, checkpoint_id: &str) -> Result<Checkpoint, FaultToleranceError> {
        Err(FaultToleranceError::CheckpointError(
            "Checkpoint not found".to_string(),
        ))
    }
}

impl CheckpointCreationEngine {
    fn new() -> Self {
        Self::default()
    }
}

impl CheckpointRestorationEngine {
    fn new() -> Self {
        Self::default()
    }
}

impl CheckpointValidationSystem {
    fn new() -> Self {
        Self::default()
    }

    fn validate_checkpoint(&self, checkpoint: &Checkpoint) -> Result<(), FaultToleranceError> {
        Ok(())
    }
}

impl CheckpointStatistics {
    fn new() -> Self {
        Self::default()
    }
}

impl CheckpointMetadata {
    fn new() -> Self {
        Self::default()
    }
}

impl SystemState {
    fn new() -> Self {
        Self::default()
    }
}

impl FailurePatternAnalyzer {
    fn new() -> Self {
        Self::default()
    }
}

impl AnomalyDetector {
    fn new() -> Self {
        Self::default()
    }
}

impl FailureClassifier {
    fn new() -> Self {
        Self::default()
    }

    fn classify(&self, failure: &TaskError) -> FailureType {
        match failure {
            TaskError::ResourceAllocationFailed(_) => {
                FailureType::Resource(ResourceFailureType::OutOfMemory)
            }
            TaskError::ExecutionFailed(_) => {
                FailureType::Software(SoftwareFailureType::CrashFailure)
            }
            _ => FailureType::Custom("Unknown".to_string()),
        }
    }
}

impl FailureMetrics {
    fn new() -> Self {
        Self::default()
    }

    fn record_failure(&mut self, classification: &FailureClassification) {
        // Implementation would update metrics
    }
}

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

    #[test]
    fn test_fault_tolerance_manager_creation() {
        let config = FaultToleranceConfig::default();
        let manager = FaultToleranceManager::new(config);
        let stats = manager.get_statistics();
        assert_eq!(stats.checkpoints_created, 0);
    }

    #[test]
    fn test_circuit_breaker_state_transitions() {
        let config = FaultToleranceConfig::default();
        let mut manager = CircuitBreakerManager::new(&config);

        // Create a circuit breaker
        let breaker = manager.create_circuit_breaker("test_component");
        assert_eq!(breaker.state, CircuitBreakerState::Closed);
    }

    #[test]
    fn test_retry_strategy_selection() {
        let config = RetryConfig::default();
        let retry_manager = RetryManager::new(&config);

        let network_strategy = retry_manager
            .determine_retry_strategy(&FailureType::Network(NetworkFailureType::ConnectionFailure));
        match network_strategy {
            RetryStrategy::ExponentialBackoff { .. } => {}
            _ => panic!("Expected exponential backoff for network failures"),
        }
    }

    #[test]
    fn test_checkpoint_creation() {
        let config = CheckpointConfig::default();
        let mut manager = CheckpointManager::new(&config);

        let task_id = TaskId::new();
        let state_data = vec![1, 2, 3, 4, 5];

        let checkpoint_id = manager.create_checkpoint(task_id, state_data).unwrap();
        assert!(!checkpoint_id.is_empty());
    }
}
