//! Load Balancing Module
//!
//! This module provides comprehensive load balancing capabilities for the CUDA
//! optimization execution engine, including dynamic load distribution, resource
//! allocation optimization, workload balancing, adaptive scheduling, and
//! performance optimization across multiple GPUs and compute resources.

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

use super::config::{LoadBalancingConfig, SchedulingConfig};
use super::task_management::{ResourceType, TaskId};

/// Unique identifier for a resource
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct ResourceId(pub u64);

/// Comprehensive load balancing manager for CUDA execution
///
/// Manages all aspects of load balancing including workload distribution,
/// resource allocation optimization, dynamic scheduling, performance optimization,
/// and adaptive load balancing strategies to ensure optimal resource utilization
/// and system performance across multiple compute resources.
#[derive(Debug)]
pub struct LoadBalancingManager {
    /// Workload distribution system
    workload_distributor: Arc<Mutex<WorkloadDistributor>>,

    /// Resource load monitor
    resource_monitor: Arc<Mutex<ResourceLoadMonitor>>,

    /// Dynamic scheduler
    dynamic_scheduler: Arc<Mutex<DynamicScheduler>>,

    /// Load balancing strategy engine
    strategy_engine: Arc<Mutex<LoadBalancingStrategyEngine>>,

    /// Performance optimizer
    performance_optimizer: Arc<Mutex<PerformanceOptimizer>>,

    /// Adaptive load balancer
    adaptive_balancer: Arc<Mutex<AdaptiveLoadBalancer>>,

    /// Load migration system
    migration_system: Arc<Mutex<LoadMigrationSystem>>,

    /// Load balancing metrics collector
    metrics_collector: Arc<Mutex<LoadBalancingMetricsCollector>>,

    /// Configuration
    config: LoadBalancingConfig,

    /// System load state
    system_load_state: Arc<RwLock<SystemLoadState>>,

    /// Load balancing statistics
    statistics: Arc<Mutex<LoadBalancingStatistics>>,

    /// Active load balancing sessions
    active_sessions: Arc<Mutex<HashMap<String, LoadBalancingSession>>>,
}

/// Workload distribution system for optimal task allocation
#[derive(Debug)]
pub struct WorkloadDistributor {
    /// Distribution strategies
    distribution_strategies: HashMap<String, DistributionStrategy>,

    /// Workload analyzer
    workload_analyzer: WorkloadAnalyzer,

    /// Task assignment engine
    task_assignment_engine: TaskAssignmentEngine,

    /// Load distribution predictor
    distribution_predictor: LoadDistributionPredictor,

    /// Resource capacity tracker
    capacity_tracker: ResourceCapacityTracker,

    /// Distribution configuration
    config: WorkloadDistributionConfig,

    /// Distribution history
    distribution_history: VecDeque<DistributionRecord>,
}

/// Resource load monitoring system
#[derive(Debug)]
pub struct ResourceLoadMonitor {
    /// Resource load trackers by resource type
    load_trackers: HashMap<ResourceType, ResourceLoadTracker>,

    /// Real-time load metrics collector
    metrics_collector: LoadMetricsCollector,

    /// Load trend analyzer
    trend_analyzer: LoadTrendAnalyzer,

    /// Load threshold monitor
    threshold_monitor: LoadThresholdMonitor,

    /// Load prediction engine
    prediction_engine: LoadPredictionEngine,

    /// Monitoring configuration
    config: LoadMonitoringConfig,

    /// Current system load snapshot
    current_load_snapshot: SystemLoadSnapshot,
}

/// Dynamic scheduling system for adaptive task scheduling
#[derive(Debug)]
pub struct DynamicScheduler {
    /// Scheduling algorithms
    scheduling_algorithms: HashMap<String, SchedulingAlgorithm>,

    /// Priority queue manager
    priority_queue_manager: PriorityQueueManager,

    /// Scheduling decision engine
    decision_engine: SchedulingDecisionEngine,

    /// Preemption manager
    preemption_manager: PreemptionManager,

    /// Scheduling policy enforcer
    policy_enforcer: SchedulingPolicyEnforcer,

    /// Configuration
    config: SchedulingConfig,

    /// Scheduling statistics
    scheduling_stats: SchedulingStatistics,
}

/// Load balancing strategy engine
#[derive(Debug)]
pub struct LoadBalancingStrategyEngine {
    /// Available strategies
    available_strategies: HashMap<StrategyType, LoadBalancingStrategy>,

    /// Strategy selector
    strategy_selector: StrategySelector,

    /// Strategy effectiveness tracker
    effectiveness_tracker: StrategyEffectivenessTracker,

    /// Strategy adaptation engine
    adaptation_engine: StrategyAdaptationEngine,

    /// Configuration
    config: StrategyEngineConfig,

    /// Current active strategy
    current_strategy: Option<StrategyType>,
}

/// Performance optimizer for load balancing efficiency
#[derive(Debug)]
pub struct PerformanceOptimizer {
    /// Performance models
    performance_models: HashMap<String, PerformanceModel>,

    /// Optimization algorithms
    optimization_algorithms: HashMap<String, OptimizationAlgorithm>,

    /// Performance predictor
    performance_predictor: PerformancePredictor,

    /// Bottleneck analyzer
    bottleneck_analyzer: BottleneckAnalyzer,

    /// Optimization recommendation engine
    recommendation_engine: OptimizationRecommendationEngine,

    /// Configuration
    config: PerformanceOptimizationConfig,
}

/// Adaptive load balancer for self-adjusting strategies
#[derive(Debug)]
pub struct AdaptiveLoadBalancer {
    /// Adaptation algorithms
    adaptation_algorithms: HashMap<String, AdaptationAlgorithm>,

    /// Learning system for strategy improvement
    learning_system: LoadBalancingLearningSystem,

    /// Feedback system
    feedback_system: LoadBalancingFeedbackSystem,

    /// Adaptation trigger system
    trigger_system: AdaptationTriggerSystem,

    /// Configuration
    config: AdaptiveBalancingConfig,

    /// Adaptation history
    adaptation_history: VecDeque<AdaptationRecord>,
}

/// Load migration system for moving tasks between resources
#[derive(Debug)]
pub struct LoadMigrationSystem {
    /// Migration strategies
    migration_strategies: HashMap<String, MigrationStrategy>,

    /// Migration cost calculator
    cost_calculator: MigrationCostCalculator,

    /// Migration executor
    migration_executor: MigrationExecutor,

    /// Migration validator
    migration_validator: MigrationValidator,

    /// Migration rollback system
    rollback_system: MigrationRollbackSystem,

    /// Configuration
    config: MigrationConfig,

    /// Active migrations
    active_migrations: HashMap<String, MigrationContext>,
}

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

/// Load balancing session for tracking balancing operations
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LoadBalancingSession {
    /// Session identifier
    pub session_id: String,

    /// Session type
    pub session_type: SessionType,

    /// Start timestamp
    pub start_time: SystemTime,

    /// Session duration
    pub duration: Duration,

    /// Participating resources
    pub resources: Vec<ResourceId>,

    /// Balancing strategy used
    pub strategy: StrategyType,

    /// Session configuration
    pub config: SessionConfig,

    /// Session status
    pub status: SessionStatus,

    /// Performance metrics
    pub performance_metrics: SessionPerformanceMetrics,
}

/// Distribution strategy for workload allocation
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DistributionStrategy {
    /// Strategy name
    pub name: String,

    /// Strategy type
    pub strategy_type: DistributionStrategyType,

    /// Distribution algorithm
    pub algorithm: DistributionAlgorithm,

    /// Strategy parameters
    pub parameters: HashMap<String, f64>,

    /// Strategy effectiveness metrics
    pub effectiveness_metrics: EffectivenessMetrics,

    /// Strategy constraints
    pub constraints: Vec<DistributionConstraint>,
}

/// Resource load tracker for monitoring individual resources
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ResourceLoadTracker {
    /// Resource identifier
    pub resource_id: ResourceId,

    /// Resource type
    pub resource_type: ResourceType,

    /// Current load level
    pub current_load: LoadLevel,

    /// Load history
    pub load_history: VecDeque<LoadMeasurement>,

    /// Load capacity
    pub capacity: ResourceCapacity,

    /// Load thresholds
    pub thresholds: LoadThresholds,

    /// Tracker status
    pub status: TrackerStatus,
}

/// System load snapshot for overall system status
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SystemLoadSnapshot {
    /// Snapshot timestamp
    pub timestamp: SystemTime,

    /// Overall system load
    pub overall_load: LoadLevel,

    /// Per-resource load breakdown
    pub resource_loads: HashMap<ResourceId, LoadLevel>,

    /// Load distribution metrics
    pub distribution_metrics: LoadDistributionMetrics,

    /// System performance indicators
    pub performance_indicators: SystemPerformanceIndicators,

    /// Load imbalance indicators
    pub imbalance_indicators: LoadImbalanceIndicators,
}

/// Load balancing strategy for different balancing approaches
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LoadBalancingStrategy {
    /// Strategy identifier
    pub strategy_id: String,

    /// Strategy type
    pub strategy_type: StrategyType,

    /// Strategy implementation
    pub implementation: StrategyImplementation,

    /// Strategy parameters
    pub parameters: StrategyParameters,

    /// Performance characteristics
    pub performance_characteristics: PerformanceCharacteristics,

    /// Applicability conditions
    pub applicability_conditions: ApplicabilityConditions,
}

/// Migration context for task migration operations
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MigrationContext {
    /// Migration identifier
    pub migration_id: String,

    /// Source resource
    pub source_resource: ResourceId,

    /// Target resource
    pub target_resource: ResourceId,

    /// Tasks to migrate
    pub tasks: Vec<TaskId>,

    /// Migration strategy
    pub strategy: MigrationStrategy,

    /// Migration status
    pub status: MigrationStatus,

    /// Migration start time
    pub start_time: SystemTime,

    /// Expected completion time
    pub expected_completion: SystemTime,

    /// Migration cost estimate
    pub cost_estimate: MigrationCost,
}

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

/// Session types for load balancing operations
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum SessionType {
    /// Continuous load balancing
    Continuous,
    /// Periodic rebalancing
    Periodic,
    /// Event-triggered balancing
    EventTriggered,
    /// Manual balancing
    Manual,
    /// Emergency rebalancing
    Emergency,
}

/// Load balancing strategy types
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum StrategyType {
    /// Round-robin distribution
    RoundRobin,
    /// Weighted round-robin
    WeightedRoundRobin,
    /// Least connections strategy
    LeastConnections,
    /// Least load strategy
    LeastLoad,
    /// Random distribution
    Random,
    /// Consistent hashing
    ConsistentHashing,
    /// Performance-based routing
    PerformanceBased,
    /// Adaptive strategy
    Adaptive,
    /// Machine learning based
    MLBased,
    /// Custom strategy
    Custom(String),
}

/// Distribution strategy types
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum DistributionStrategyType {
    /// Static distribution
    Static,
    /// Dynamic distribution
    Dynamic,
    /// Predictive distribution
    Predictive,
    /// Reactive distribution
    Reactive,
    /// Hybrid distribution
    Hybrid,
}

/// Load levels for resource utilization
#[derive(Debug, Clone, Copy, PartialEq, PartialOrd, Serialize, Deserialize)]
pub enum LoadLevel {
    /// Very low load (0-20%)
    VeryLow,
    /// Low load (20-40%)
    Low,
    /// Medium load (40-60%)
    Medium,
    /// High load (60-80%)
    High,
    /// Very high load (80-95%)
    VeryHigh,
    /// Overloaded (95-100%)
    Overloaded,
}

/// Session status enumeration
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum SessionStatus {
    Starting,
    Active,
    Paused,
    Completed,
    Failed,
    Cancelled,
}

/// Migration status for task migrations
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum MigrationStatus {
    Planned,
    Preparing,
    InProgress,
    Completed,
    Failed,
    RolledBack,
    Cancelled,
}

/// Tracker status for resource monitoring
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum TrackerStatus {
    Active,
    Inactive,
    Error,
    Calibrating,
}

// === Configuration Structures ===

/// Workload distribution configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WorkloadDistributionConfig {
    /// Default distribution strategy
    pub default_strategy: DistributionStrategyType,

    /// Enable dynamic strategy switching
    pub enable_dynamic_switching: bool,

    /// Distribution update interval
    pub update_interval: Duration,

    /// Minimum tasks per resource
    pub min_tasks_per_resource: usize,

    /// Maximum tasks per resource
    pub max_tasks_per_resource: Option<usize>,

    /// Load balancing threshold
    pub load_balancing_threshold: f64,
}

/// Load monitoring configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LoadMonitoringConfig {
    /// Monitoring interval
    pub monitoring_interval: Duration,

    /// Load history retention period
    pub history_retention: Duration,

    /// Load threshold levels
    pub threshold_levels: HashMap<LoadLevel, f64>,

    /// Enable load prediction
    pub enable_load_prediction: bool,

    /// Prediction horizon
    pub prediction_horizon: Duration,
}

/// Strategy engine configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct StrategyEngineConfig {
    /// Strategy evaluation interval
    pub evaluation_interval: Duration,

    /// Strategy switching threshold
    pub switching_threshold: f64,

    /// Enable strategy learning
    pub enable_strategy_learning: bool,

    /// Performance history window
    pub performance_history_window: Duration,
}

/// Performance optimization configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PerformanceOptimizationConfig {
    /// Optimization interval
    pub optimization_interval: Duration,

    /// Performance target SLA
    pub performance_targets: PerformanceTargets,

    /// Enable bottleneck detection
    pub enable_bottleneck_detection: bool,

    /// Optimization aggressiveness level
    pub optimization_aggressiveness: f64,
}

/// Adaptive balancing configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AdaptiveBalancingConfig {
    /// Learning rate for adaptation
    pub learning_rate: f64,

    /// Adaptation sensitivity
    pub adaptation_sensitivity: f64,

    /// Minimum adaptation interval
    pub min_adaptation_interval: Duration,

    /// Maximum adaptation interval
    pub max_adaptation_interval: Duration,

    /// Enable feedback learning
    pub enable_feedback_learning: bool,
}

/// Migration configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MigrationConfig {
    /// Enable automatic migration
    pub enable_auto_migration: bool,

    /// Migration cost threshold
    pub cost_threshold: f64,

    /// Maximum concurrent migrations
    pub max_concurrent_migrations: usize,

    /// Migration timeout
    pub migration_timeout: Duration,

    /// Enable migration rollback
    pub enable_rollback: bool,
}

// === Implementation ===

impl LoadBalancingManager {
    /// Create a new load balancing manager
    pub fn new(config: LoadBalancingConfig) -> Self {
        Self {
            workload_distributor: Arc::new(Mutex::new(WorkloadDistributor::new(&config))),
            resource_monitor: Arc::new(Mutex::new(ResourceLoadMonitor::new(&config))),
            dynamic_scheduler: Arc::new(Mutex::new(DynamicScheduler::new(&config.scheduling))),
            strategy_engine: Arc::new(Mutex::new(LoadBalancingStrategyEngine::new(&config))),
            performance_optimizer: Arc::new(Mutex::new(PerformanceOptimizer::new(&config))),
            adaptive_balancer: Arc::new(Mutex::new(AdaptiveLoadBalancer::new(&config))),
            migration_system: Arc::new(Mutex::new(LoadMigrationSystem::new(&config))),
            metrics_collector: Arc::new(Mutex::new(LoadBalancingMetricsCollector::new())),
            config,
            system_load_state: Arc::new(RwLock::new(SystemLoadState::new())),
            statistics: Arc::new(Mutex::new(LoadBalancingStatistics::new())),
            active_sessions: Arc::new(Mutex::new(HashMap::new())),
        }
    }

    /// Start load balancing operations
    pub fn start_load_balancing(&self) -> Result<String, LoadBalancingError> {
        let session_id = uuid::Uuid::new_v4().to_string();

        // Start monitoring
        {
            let mut monitor = self.resource_monitor.lock().expect("lock should not be poisoned");
            monitor.start_monitoring()?;
        }

        // Initialize load balancing session
        let session = LoadBalancingSession {
            session_id: session_id.clone(),
            session_type: SessionType::Continuous,
            start_time: SystemTime::now(),
            duration: Duration::from_secs(24 * 60 * 60), // Default 24 hour session
            resources: vec![],                           // Would be populated with actual resources
            strategy: StrategyType::Adaptive,
            config: SessionConfig::default(),
            status: SessionStatus::Starting,
            performance_metrics: SessionPerformanceMetrics::default(),
        };

        {
            let mut sessions = self.active_sessions.lock().expect("lock should not be poisoned");
            sessions.insert(session_id.clone(), session);
        }

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

        Ok(session_id)
    }

    /// Distribute workload across resources
    pub fn distribute_workload(
        &self,
        tasks: Vec<TaskId>,
    ) -> Result<WorkloadDistribution, LoadBalancingError> {
        let mut distributor = self.workload_distributor.lock().expect("lock should not be poisoned");
        let distribution = distributor.distribute_tasks(tasks)?;

        // Update statistics
        {
            let mut stats = self.statistics.lock().expect("lock should not be poisoned");
            stats.tasks_distributed += distribution.task_assignments.len() as u64;
        }

        Ok(distribution)
    }

    /// Get current system load status
    pub fn get_system_load(&self) -> SystemLoadSnapshot {
        let monitor = self.resource_monitor.lock().expect("lock should not be poisoned");
        monitor.get_current_snapshot()
    }

    /// Optimize load balancing performance
    pub fn optimize_performance(&self) -> Result<OptimizationResult, LoadBalancingError> {
        let mut optimizer = self.performance_optimizer.lock().expect("lock should not be poisoned");
        let result = optimizer.optimize_current_load_distribution()?;

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

        Ok(result)
    }

    /// Migrate tasks between resources
    pub fn migrate_tasks(
        &self,
        migration_request: MigrationRequest,
    ) -> Result<String, LoadBalancingError> {
        let mut migration_system = self.migration_system.lock().expect("lock should not be poisoned");
        let migration_id = migration_system.initiate_migration(migration_request)?;

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

        Ok(migration_id)
    }

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

    /// Adapt load balancing strategy
    pub fn adapt_strategy(&self) -> Result<StrategyType, LoadBalancingError> {
        let mut adaptive_balancer = self.adaptive_balancer.lock().expect("lock should not be poisoned");
        let new_strategy = adaptive_balancer.adapt_strategy()?;

        // Update strategy engine
        {
            let mut strategy_engine = self.strategy_engine.lock().expect("lock should not be poisoned");
            strategy_engine.switch_strategy(new_strategy.clone())?;
        }

        Ok(new_strategy)
    }
}

impl WorkloadDistributor {
    fn new(config: &LoadBalancingConfig) -> Self {
        Self {
            distribution_strategies: HashMap::new(),
            workload_analyzer: WorkloadAnalyzer::new(),
            task_assignment_engine: TaskAssignmentEngine::new(),
            distribution_predictor: LoadDistributionPredictor::new(),
            capacity_tracker: ResourceCapacityTracker::new(),
            config: config.workload_distribution.clone().unwrap_or_default(),
            distribution_history: VecDeque::new(),
        }
    }

    fn distribute_tasks(
        &mut self,
        tasks: Vec<TaskId>,
    ) -> Result<WorkloadDistribution, LoadBalancingError> {
        // Analyze workload characteristics
        let workload_analysis = self.workload_analyzer.analyze_workload(&tasks)?;

        // Select appropriate distribution strategy
        let strategy = self.select_distribution_strategy(&workload_analysis)?;

        // Assign tasks to resources
        let task_assignments = self.task_assignment_engine.assign_tasks(tasks, &strategy)?;

        let distribution = WorkloadDistribution {
            distribution_id: uuid::Uuid::new_v4().to_string(),
            strategy_used: strategy.strategy_type,
            task_assignments,
            timestamp: SystemTime::now(),
            performance_prediction: self
                .distribution_predictor
                .predict_performance(&workload_analysis)?,
        };

        // Record distribution for history
        let record = DistributionRecord {
            distribution_id: distribution.distribution_id.clone(),
            timestamp: distribution.timestamp,
            tasks_distributed: distribution.task_assignments.len(),
            strategy_used: distribution.strategy_used.clone(),
            performance_metrics: DistributionPerformanceMetrics::default(),
        };

        self.distribution_history.push_back(record);

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

        Ok(distribution)
    }

    fn select_distribution_strategy(
        &self,
        analysis: &WorkloadAnalysis,
    ) -> Result<DistributionStrategy, LoadBalancingError> {
        // For now, return a default strategy
        // In reality, would select based on workload characteristics
        Ok(DistributionStrategy {
            name: "default".to_string(),
            strategy_type: DistributionStrategyType::Dynamic,
            algorithm: DistributionAlgorithm::default(),
            parameters: HashMap::new(),
            effectiveness_metrics: EffectivenessMetrics::default(),
            constraints: vec![],
        })
    }
}

impl ResourceLoadMonitor {
    fn new(config: &LoadBalancingConfig) -> Self {
        Self {
            load_trackers: HashMap::new(),
            metrics_collector: LoadMetricsCollector::new(),
            trend_analyzer: LoadTrendAnalyzer::new(),
            threshold_monitor: LoadThresholdMonitor::new(),
            prediction_engine: LoadPredictionEngine::new(),
            config: config.load_monitoring.clone().unwrap_or_default(),
            current_load_snapshot: SystemLoadSnapshot::default(),
        }
    }

    fn start_monitoring(&mut self) -> Result<(), LoadBalancingError> {
        // Initialize load trackers for each resource type
        for resource_type in [ResourceType::GPU, ResourceType::CPU, ResourceType::Memory].iter() {
            let tracker = ResourceLoadTracker {
                resource_id: ResourceId::new(),
                resource_type: *resource_type,
                current_load: LoadLevel::Low,
                load_history: VecDeque::new(),
                capacity: ResourceCapacity::default(),
                thresholds: LoadThresholds::default(),
                status: TrackerStatus::Active,
            };

            self.load_trackers.insert(*resource_type, tracker);
        }

        Ok(())
    }

    fn get_current_snapshot(&self) -> SystemLoadSnapshot {
        self.current_load_snapshot.clone()
    }
}

impl DynamicScheduler {
    fn new(config: &SchedulingConfig) -> Self {
        Self {
            scheduling_algorithms: HashMap::new(),
            priority_queue_manager: PriorityQueueManager::new(),
            decision_engine: SchedulingDecisionEngine::new(),
            preemption_manager: PreemptionManager::new(),
            policy_enforcer: SchedulingPolicyEnforcer::new(),
            config: config.clone(),
            scheduling_stats: SchedulingStatistics::new(),
        }
    }
}

impl LoadBalancingStrategyEngine {
    fn new(config: &LoadBalancingConfig) -> Self {
        let mut engine = Self {
            available_strategies: HashMap::new(),
            strategy_selector: StrategySelector::new(),
            effectiveness_tracker: StrategyEffectivenessTracker::new(),
            adaptation_engine: StrategyAdaptationEngine::new(),
            config: config.strategy_engine.clone().unwrap_or_default(),
            current_strategy: Some(StrategyType::RoundRobin),
        };

        // Initialize default strategies
        engine.initialize_strategies();
        engine
    }

    fn initialize_strategies(&mut self) {
        // Add round-robin strategy
        self.available_strategies.insert(
            StrategyType::RoundRobin,
            LoadBalancingStrategy {
                strategy_id: "round_robin".to_string(),
                strategy_type: StrategyType::RoundRobin,
                implementation: StrategyImplementation::default(),
                parameters: StrategyParameters::default(),
                performance_characteristics: PerformanceCharacteristics::default(),
                applicability_conditions: ApplicabilityConditions::default(),
            },
        );

        // Add adaptive strategy
        self.available_strategies.insert(
            StrategyType::Adaptive,
            LoadBalancingStrategy {
                strategy_id: "adaptive".to_string(),
                strategy_type: StrategyType::Adaptive,
                implementation: StrategyImplementation::default(),
                parameters: StrategyParameters::default(),
                performance_characteristics: PerformanceCharacteristics::default(),
                applicability_conditions: ApplicabilityConditions::default(),
            },
        );
    }

    fn switch_strategy(&mut self, new_strategy: StrategyType) -> Result<(), LoadBalancingError> {
        if self.available_strategies.contains_key(&new_strategy) {
            self.current_strategy = Some(new_strategy);
            Ok(())
        } else {
            Err(LoadBalancingError::StrategyNotFound(format!(
                "{:?}",
                new_strategy
            )))
        }
    }
}

impl PerformanceOptimizer {
    fn new(config: &LoadBalancingConfig) -> Self {
        Self {
            performance_models: HashMap::new(),
            optimization_algorithms: HashMap::new(),
            performance_predictor: PerformancePredictor::new(),
            bottleneck_analyzer: BottleneckAnalyzer::new(),
            recommendation_engine: OptimizationRecommendationEngine::new(),
            config: config.performance_optimization.clone().unwrap_or_default(),
        }
    }

    fn optimize_current_load_distribution(
        &mut self,
    ) -> Result<OptimizationResult, LoadBalancingError> {
        // Analyze current performance
        let current_performance = self.performance_predictor.get_current_performance()?;

        // Identify bottlenecks
        let bottlenecks = self
            .bottleneck_analyzer
            .identify_bottlenecks(&current_performance)?;

        // Generate optimization recommendations
        let recommendations = self
            .recommendation_engine
            .generate_recommendations(&bottlenecks)?;

        Ok(OptimizationResult {
            optimization_id: uuid::Uuid::new_v4().to_string(),
            current_performance,
            bottlenecks,
            recommendations,
            expected_improvement: 15.0, // Placeholder
            timestamp: SystemTime::now(),
        })
    }
}

impl AdaptiveLoadBalancer {
    fn new(config: &LoadBalancingConfig) -> Self {
        Self {
            adaptation_algorithms: HashMap::new(),
            learning_system: LoadBalancingLearningSystem::new(),
            feedback_system: LoadBalancingFeedbackSystem::new(),
            trigger_system: AdaptationTriggerSystem::new(),
            config: config.adaptive_balancing.clone().unwrap_or_default(),
            adaptation_history: VecDeque::new(),
        }
    }

    fn adapt_strategy(&mut self) -> Result<StrategyType, LoadBalancingError> {
        // Check if adaptation is needed
        if self.trigger_system.should_adapt()? {
            // Use learning system to determine best strategy
            let new_strategy = self.learning_system.recommend_strategy()?;

            // Record adaptation
            let record = AdaptationRecord {
                timestamp: SystemTime::now(),
                previous_strategy: StrategyType::RoundRobin, // Placeholder
                new_strategy: new_strategy.clone(),
                adaptation_reason: "Performance optimization".to_string(),
                expected_improvement: 10.0,
            };

            self.adaptation_history.push_back(record);

            Ok(new_strategy)
        } else {
            Ok(StrategyType::RoundRobin) // No adaptation needed
        }
    }
}

impl LoadMigrationSystem {
    fn new(config: &LoadBalancingConfig) -> Self {
        Self {
            migration_strategies: HashMap::new(),
            cost_calculator: MigrationCostCalculator::new(),
            migration_executor: MigrationExecutor::new(),
            migration_validator: MigrationValidator::new(),
            rollback_system: MigrationRollbackSystem::new(),
            config: config.migration.clone().unwrap_or_default(),
            active_migrations: HashMap::new(),
        }
    }

    fn initiate_migration(
        &mut self,
        request: MigrationRequest,
    ) -> Result<String, LoadBalancingError> {
        let migration_id = uuid::Uuid::new_v4().to_string();

        // Calculate migration cost
        let cost = self.cost_calculator.calculate_cost(&request)?;

        // Create migration context
        let context = MigrationContext {
            migration_id: migration_id.clone(),
            source_resource: request.source_resource,
            target_resource: request.target_resource,
            tasks: request.tasks,
            strategy: request
                .strategy
                .unwrap_or_else(|| MigrationStrategy::default()),
            status: MigrationStatus::Planned,
            start_time: SystemTime::now(),
            expected_completion: SystemTime::now() + Duration::from_secs(30 * 60),
            cost_estimate: cost,
        };

        self.active_migrations.insert(migration_id.clone(), context);

        Ok(migration_id)
    }
}

// === Error Handling ===

/// Load balancing errors
#[derive(Debug, Clone)]
pub enum LoadBalancingError {
    /// Resource not found
    ResourceNotFound(String),
    /// Strategy not found
    StrategyNotFound(String),
    /// Invalid configuration
    InvalidConfiguration(String),
    /// Load monitoring error
    LoadMonitoringError(String),
    /// Distribution error
    DistributionError(String),
    /// Migration error
    MigrationError(String),
    /// Performance optimization error
    OptimizationError(String),
    /// System error
    SystemError(String),
}

// === 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,
        }
    };
}

// Core types
default_placeholder_type!(WorkloadAnalyzer);
default_placeholder_type!(TaskAssignmentEngine);
default_placeholder_type!(LoadDistributionPredictor);
default_placeholder_type!(ResourceCapacityTracker);
default_placeholder_type!(LoadMetricsCollector);
default_placeholder_type!(LoadTrendAnalyzer);
default_placeholder_type!(LoadThresholdMonitor);
default_placeholder_type!(LoadPredictionEngine);
default_placeholder_type!(SchedulingAlgorithm);
default_placeholder_type!(PriorityQueueManager);
default_placeholder_type!(SchedulingDecisionEngine);
default_placeholder_type!(PreemptionManager);
default_placeholder_type!(SchedulingPolicyEnforcer);
default_placeholder_type!(SchedulingStatistics);
default_placeholder_type!(StrategySelector);
default_placeholder_type!(StrategyEffectivenessTracker);
default_placeholder_type!(StrategyAdaptationEngine);
default_placeholder_type!(PerformanceModel);
default_placeholder_type!(OptimizationAlgorithm);
default_placeholder_type!(PerformancePredictor);
default_placeholder_type!(BottleneckAnalyzer);
default_placeholder_type!(OptimizationRecommendationEngine);
default_placeholder_type!(AdaptationAlgorithm);
default_placeholder_type!(LoadBalancingLearningSystem);
default_placeholder_type!(LoadBalancingFeedbackSystem);
default_placeholder_type!(AdaptationTriggerSystem);
default_placeholder_type!(MigrationCostCalculator);
default_placeholder_type!(MigrationExecutor);
default_placeholder_type!(MigrationValidator);
default_placeholder_type!(MigrationRollbackSystem);
default_placeholder_type!(LoadBalancingMetricsCollector);
default_placeholder_type!(SystemLoadState);

// Configuration types
default_placeholder_type!(SessionConfig);
default_placeholder_type!(PerformanceTargets);

// Data structures
default_placeholder_type!(SessionPerformanceMetrics);
default_placeholder_type!(DistributionAlgorithm);
default_placeholder_type!(EffectivenessMetrics);
default_placeholder_type!(DistributionConstraint);
default_placeholder_type!(LoadMeasurement);
default_placeholder_type!(ResourceCapacity);
default_placeholder_type!(LoadThresholds);
default_placeholder_type!(LoadDistributionMetrics);
default_placeholder_type!(SystemPerformanceIndicators);
default_placeholder_type!(LoadImbalanceIndicators);
default_placeholder_type!(StrategyImplementation);
default_placeholder_type!(StrategyParameters);
default_placeholder_type!(PerformanceCharacteristics);
default_placeholder_type!(ApplicabilityConditions);
default_placeholder_type!(MigrationStrategy);
default_placeholder_type!(MigrationCost);
default_placeholder_type!(WorkloadAnalysis);
default_placeholder_type!(DistributionRecord);
default_placeholder_type!(DistributionPerformanceMetrics);
default_placeholder_type!(AdaptationRecord);

// Results and requests
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WorkloadDistribution {
    pub distribution_id: String,
    pub strategy_used: DistributionStrategyType,
    pub task_assignments: Vec<TaskAssignment>,
    pub timestamp: SystemTime,
    pub performance_prediction: PerformancePrediction,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OptimizationResult {
    pub optimization_id: String,
    pub current_performance: CurrentPerformance,
    pub bottlenecks: Vec<PerformanceBottleneck>,
    pub recommendations: Vec<OptimizationRecommendation>,
    pub expected_improvement: f64,
    pub timestamp: SystemTime,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MigrationRequest {
    pub source_resource: ResourceId,
    pub target_resource: ResourceId,
    pub tasks: Vec<TaskId>,
    pub strategy: Option<MigrationStrategy>,
    pub priority: MigrationPriority,
}

// Additional types
default_placeholder_type!(TaskAssignment);
default_placeholder_type!(PerformancePrediction);
default_placeholder_type!(CurrentPerformance);
default_placeholder_type!(PerformanceBottleneck);
default_placeholder_type!(OptimizationRecommendation);

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum MigrationPriority {
    Low,
    Medium,
    High,
    Critical,
}

// Statistics with actual fields
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LoadBalancingStatistics {
    pub sessions_started: u64,
    pub tasks_distributed: u64,
    pub optimizations_performed: u64,
    pub migrations_initiated: u64,
    pub strategy_adaptations: u64,
    pub average_load_balance: f64,
    pub system_efficiency: f64,
}

// Implement constructors
impl WorkloadAnalyzer {
    fn new() -> Self {
        Self::default()
    }

    fn analyze_workload(&self, tasks: &[TaskId]) -> Result<WorkloadAnalysis, LoadBalancingError> {
        Ok(WorkloadAnalysis::default())
    }
}

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

    fn assign_tasks(
        &self,
        tasks: Vec<TaskId>,
        strategy: &DistributionStrategy,
    ) -> Result<Vec<TaskAssignment>, LoadBalancingError> {
        Ok(vec![TaskAssignment::default(); tasks.len()])
    }
}

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

    fn predict_performance(
        &self,
        analysis: &WorkloadAnalysis,
    ) -> Result<PerformancePrediction, LoadBalancingError> {
        Ok(PerformancePrediction::default())
    }
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    fn get_current_performance(&self) -> Result<CurrentPerformance, LoadBalancingError> {
        Ok(CurrentPerformance::default())
    }
}

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

    fn identify_bottlenecks(
        &self,
        performance: &CurrentPerformance,
    ) -> Result<Vec<PerformanceBottleneck>, LoadBalancingError> {
        Ok(vec![])
    }
}

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

    fn generate_recommendations(
        &self,
        bottlenecks: &[PerformanceBottleneck],
    ) -> Result<Vec<OptimizationRecommendation>, LoadBalancingError> {
        Ok(vec![])
    }
}

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

    fn recommend_strategy(&self) -> Result<StrategyType, LoadBalancingError> {
        Ok(StrategyType::Adaptive)
    }
}

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

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

    fn should_adapt(&self) -> Result<bool, LoadBalancingError> {
        Ok(false) // Placeholder
    }
}

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

    fn calculate_cost(
        &self,
        request: &MigrationRequest,
    ) -> Result<MigrationCost, LoadBalancingError> {
        Ok(MigrationCost::default())
    }
}

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

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

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

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

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

impl LoadBalancingStatistics {
    fn new() -> Self {
        Self {
            sessions_started: 0,
            tasks_distributed: 0,
            optimizations_performed: 0,
            migrations_initiated: 0,
            strategy_adaptations: 0,
            average_load_balance: 0.0,
            system_efficiency: 0.0,
        }
    }
}

impl Default for SystemLoadSnapshot {
    fn default() -> Self {
        Self {
            timestamp: SystemTime::now(),
            overall_load: LoadLevel::Low,
            resource_loads: HashMap::new(),
            distribution_metrics: LoadDistributionMetrics::default(),
            performance_indicators: SystemPerformanceIndicators::default(),
            imbalance_indicators: LoadImbalanceIndicators::default(),
        }
    }
}

// Default configurations
impl Default for WorkloadDistributionConfig {
    fn default() -> Self {
        Self {
            default_strategy: DistributionStrategyType::Dynamic,
            enable_dynamic_switching: true,
            update_interval: Duration::from_secs(30),
            min_tasks_per_resource: 1,
            max_tasks_per_resource: Some(100),
            load_balancing_threshold: 0.8,
        }
    }
}

impl Default for LoadMonitoringConfig {
    fn default() -> Self {
        Self {
            monitoring_interval: Duration::from_secs(5),
            history_retention: Duration::from_secs(24 * 60 * 60),
            threshold_levels: HashMap::new(),
            enable_load_prediction: true,
            prediction_horizon: Duration::from_secs(15 * 60),
        }
    }
}

impl Default for StrategyEngineConfig {
    fn default() -> Self {
        Self {
            evaluation_interval: Duration::from_secs(5 * 60),
            switching_threshold: 0.1,
            enable_strategy_learning: true,
            performance_history_window: Duration::from_secs(1 * 60 * 60),
        }
    }
}

impl Default for PerformanceOptimizationConfig {
    fn default() -> Self {
        Self {
            optimization_interval: Duration::from_secs(10 * 60),
            performance_targets: PerformanceTargets::default(),
            enable_bottleneck_detection: true,
            optimization_aggressiveness: 0.7,
        }
    }
}

impl Default for AdaptiveBalancingConfig {
    fn default() -> Self {
        Self {
            learning_rate: 0.1,
            adaptation_sensitivity: 0.2,
            min_adaptation_interval: Duration::from_secs(5 * 60),
            max_adaptation_interval: Duration::from_secs(2 * 60 * 60),
            enable_feedback_learning: true,
        }
    }
}

impl Default for MigrationConfig {
    fn default() -> Self {
        Self {
            enable_auto_migration: false,
            cost_threshold: 0.5,
            max_concurrent_migrations: 3,
            migration_timeout: Duration::from_secs(30 * 60),
            enable_rollback: true,
        }
    }
}

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

    #[test]
    fn test_load_balancing_manager_creation() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);
        let stats = manager.get_statistics();
        assert_eq!(stats.sessions_started, 0);
    }

    #[test]
    fn test_start_load_balancing() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);

        let session_id = manager.start_load_balancing().unwrap();
        assert!(!session_id.is_empty());
    }

    #[test]
    fn test_workload_distribution() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);

        let tasks = vec![TaskId::new(), TaskId::new(), TaskId::new()];
        let distribution = manager.distribute_workload(tasks).unwrap();
        assert!(!distribution.distribution_id.is_empty());
    }

    #[test]
    fn test_system_load_monitoring() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);

        let load_snapshot = manager.get_system_load();
        assert_eq!(load_snapshot.overall_load, LoadLevel::Low);
    }

    #[test]
    fn test_performance_optimization() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);

        let optimization_result = manager.optimize_performance().unwrap();
        assert!(!optimization_result.optimization_id.is_empty());
    }

    #[test]
    fn test_strategy_adaptation() {
        let config = LoadBalancingConfig::default();
        let manager = LoadBalancingManager::new(config);

        let new_strategy = manager.adapt_strategy().unwrap();
        assert_eq!(new_strategy, StrategyType::RoundRobin);
    }
}
