//! Long-term stability guarantees and API contracts for SciRS2
//!
//! This module provides comprehensive stability guarantees, API contracts,
//! and compatibility assurance for production environments requiring
//! long-term stability commitments.
//!
//! ## Stability Levels
//!
//! - **Stable**: No breaking changes allowed
//! - **Evolving**: Minor breaking changes with migration path
//! - **Experimental**: May break without notice
//! - **Deprecated**: Scheduled for removal
//!
//! ## API Contracts
//!
//! API contracts define behavioral guarantees beyond just signature stability:
//! - Performance contracts (complexity guarantees)
//! - Numerical contracts (precision and accuracy)
//! - Concurrency contracts (thread-safety)
//! - Memory contracts (allocation patterns)

use crate::apiversioning::Version;
use crate::error::{CoreError, CoreResult, ErrorContext};
use crate::performance_optimization::PerformanceMetrics;
use std::collections::HashMap;
use std::hash::Hash;
use std::sync::mpsc::{self, Receiver, Sender};
use std::sync::{Arc, Mutex, RwLock};
use std::time::{Duration, Instant, SystemTime};

#[cfg(feature = "serialization")]
use serde::{Deserialize, Serialize};

// Advanced implementations
mod advanced_implementations;
pub use advanced_implementations::*;

/// Stability level for APIs and components
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum StabilityLevel {
    /// Stable APIs - no breaking changes allowed
    Stable,
    /// Evolving APIs - minor breaking changes with migration path
    Evolving,
    /// Experimental APIs - may break without notice
    Experimental,
    /// Deprecated APIs - scheduled for removal
    Deprecated,
}

impl StabilityLevel {
    /// Check if this stability level is compatible with another
    pub fn is_compatible_with(self, other: StabilityLevel) -> bool {
        match (self, other) {
            (StabilityLevel::Stable, StabilityLevel::Stable) => true,
            (StabilityLevel::Evolving, StabilityLevel::Stable) => true,
            (StabilityLevel::Evolving, StabilityLevel::Experimental) => false,
            (StabilityLevel::Experimental, StabilityLevel::Evolving) => true,
            (StabilityLevel::Experimental, StabilityLevel::Experimental) => true,
            (StabilityLevel::Deprecated, _) | (_, StabilityLevel::Deprecated) => false,
            // Missing patterns
            (StabilityLevel::Stable, StabilityLevel::Evolving) => false,
            (StabilityLevel::Stable, StabilityLevel::Experimental) => false,
            (StabilityLevel::Evolving, StabilityLevel::Evolving) => true,
            (StabilityLevel::Experimental, StabilityLevel::Stable) => false,
        }
    }

    /// Get the minimum supported version for this stability level
    pub fn min_support_duration(self) -> Duration {
        match self {
            StabilityLevel::Stable => Duration::from_secs(365 * 24 * 3600 * 5), // 5 years
            StabilityLevel::Evolving => Duration::from_secs(365 * 24 * 3600 * 2), // 2 years
            StabilityLevel::Experimental => Duration::from_secs(90 * 24 * 3600), // 90 days
            StabilityLevel::Deprecated => Duration::from_secs(365 * 24 * 3600), // 1 year deprecation period
        }
    }
}

/// API contract definition
#[derive(Debug, Clone)]
pub struct ApiContract {
    /// API identifier
    pub apiname: String,
    /// Module name
    pub module: String,
    /// Cryptographic hash of the contract for immutability
    pub contract_hash: String,
    /// Timestamp when contract was created
    pub created_at: SystemTime,
    /// Formal verification status
    pub verification_status: VerificationStatus,
    /// Stability level
    pub stability: StabilityLevel,
    /// Version when contract was established
    pub since_version: Version,
    /// Performance contract
    pub performance: PerformanceContract,
    /// Numerical contract
    pub numerical: NumericalContract,
    /// Concurrency contract
    pub concurrency: ConcurrencyContract,
    /// Memory contract
    pub memory: MemoryContract,
    /// Deprecation information
    pub deprecation: Option<DeprecationInfo>,
}

/// Performance contract guarantees
#[derive(Debug, Clone)]
pub struct PerformanceContract {
    /// Algorithmic complexity (time)
    pub time_complexity: ComplexityBound,
    /// Space complexity
    pub space_complexity: ComplexityBound,
    /// Maximum execution time for typical inputs
    pub maxexecution_time: Option<Duration>,
    /// Minimum throughput guarantee
    pub min_throughput: Option<f64>,
    /// Memory bandwidth utilization
    pub memorybandwidth: Option<f64>,
}

/// Numerical contract guarantees
#[derive(Debug, Clone)]
pub struct NumericalContract {
    /// Precision guarantee (ULPs or relative error)
    pub precision: PrecisionGuarantee,
    /// Numerical stability characteristics
    pub stability: NumericalStability,
    /// Input domain constraints
    pub input_domain: InputDomain,
    /// Output range guarantees
    pub output_range: OutputRange,
}

/// Concurrency contract guarantees
#[derive(Debug, Clone)]
pub struct ConcurrencyContract {
    /// Thread safety level
    pub thread_safety: ThreadSafety,
    /// Atomic operation guarantees
    pub atomicity: AtomicityGuarantee,
    /// Lock-free guarantees
    pub lock_free: bool,
    /// Wait-free guarantees
    pub wait_free: bool,
    /// Memory ordering constraints
    pub memory_ordering: MemoryOrdering,
}

/// Memory contract guarantees
#[derive(Debug, Clone)]
pub struct MemoryContract {
    /// Memory allocation pattern
    pub allocation_pattern: AllocationPattern,
    /// Maximum memory usage
    pub max_memory: Option<usize>,
    /// Memory alignment requirements
    pub alignment: Option<usize>,
    /// Memory locality guarantees
    pub locality: LocalityGuarantee,
    /// Garbage collection behavior
    pub gc_behavior: GcBehavior,
}

/// Deprecation information
#[derive(Debug, Clone)]
pub struct DeprecationInfo {
    /// Version when deprecation was announced
    pub announced_version: Version,
    /// Version when removal is planned
    pub removal_version: Version,
    /// Reason for deprecation
    pub reason: String,
    /// Migration path to replacement
    pub migration_path: Option<String>,
    /// Replacement API recommendation
    pub replacement: Option<String>,
}

/// Complexity bounds for performance contracts
#[derive(Debug, Clone)]
pub enum ComplexityBound {
    /// O(1) - constant time
    Constant,
    /// O(log n) - logarithmic
    Logarithmic,
    /// O(n) - linear
    Linear,
    /// O(n log n) - linearithmic
    Linearithmic,
    /// O(n²) - quadratic
    Quadratic,
    /// O(n³) - cubic
    Cubic,
    /// O(2^n) - exponential
    Exponential,
    /// Custom complexity expression
    Custom(String),
}

/// Precision guarantees for numerical operations
#[derive(Debug, Clone)]
pub enum PrecisionGuarantee {
    /// Exact computation (no rounding errors)
    Exact,
    /// Machine precision (within floating-point epsilon)
    MachinePrecision,
    /// Relative error bound
    RelativeError(f64),
    /// Absolute error bound
    AbsoluteError(f64),
    /// ULP (Units in the Last Place) bound
    UlpBound(u64),
    /// Custom precision specification
    Custom(String),
}

/// Numerical stability characteristics
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum NumericalStability {
    /// Stable algorithm - small input changes produce small output changes
    Stable,
    /// Conditionally stable - stability depends on input characteristics
    ConditionallyStable,
    /// Unstable - may amplify small input errors significantly
    Unstable,
}

/// Input domain constraints
#[derive(Debug, Clone)]
pub struct InputDomain {
    /// Valid input ranges
    pub ranges: Vec<(f64, f64)>,
    /// Excluded values or ranges
    pub exclusions: Vec<f64>,
    /// Special value handling (NaN, Inf)
    pub special_values: SpecialValueHandling,
}

/// Output range guarantees
#[derive(Debug, Clone)]
pub struct OutputRange {
    /// Guaranteed output bounds
    pub bounds: Option<(f64, f64)>,
    /// Monotonicity guarantee
    pub monotonic: Option<Monotonicity>,
    /// Continuity guarantee
    pub continuous: bool,
}

/// Special value handling in numerical operations
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SpecialValueHandling {
    /// Propagate special values (IEEE 754 standard)
    Propagate,
    /// Error on special values
    Error,
    /// Replace with default values
    Replace,
    /// Custom handling
    Custom,
}

/// Monotonicity characteristics
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Monotonicity {
    /// Strictly increasing
    StrictlyIncreasing,
    /// Non-decreasing
    NonDecreasing,
    /// Strictly decreasing
    StrictlyDecreasing,
    /// Non-increasing
    NonIncreasing,
}

/// Thread safety levels
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ThreadSafety {
    /// Thread-safe for all operations
    ThreadSafe,
    /// Thread-safe for read operations only
    ReadSafe,
    /// Not thread-safe - requires external synchronization
    NotThreadSafe,
    /// Immutable - inherently thread-safe
    Immutable,
}

/// Atomicity guarantees
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum AtomicityGuarantee {
    /// All operations are atomic
    FullyAtomic,
    /// Individual operations are atomic, but sequences are not
    OperationAtomic,
    /// No atomicity guarantees
    NonAtomic,
}

/// Memory ordering constraints
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MemoryOrdering {
    /// Sequentially consistent
    SequentiallyConsistent,
    /// Acquire-release
    AcquireRelease,
    /// Relaxed ordering
    Relaxed,
}

/// Memory allocation patterns
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum AllocationPattern {
    /// No heap allocations
    NoAllocation,
    /// Single allocation at initialization
    SingleAllocation,
    /// Bounded number of allocations
    BoundedAllocations,
    /// Unbounded allocations possible
    UnboundedAllocations,
}

/// Memory locality guarantees
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum LocalityGuarantee {
    /// Excellent spatial locality
    ExcellentSpatial,
    /// Good spatial locality
    GoodSpatial,
    /// Poor spatial locality
    PoorSpatial,
    /// Random access pattern
    RandomAccess,
}

/// Garbage collection behavior
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum GcBehavior {
    /// No garbage collection impact
    NoGc,
    /// Minimal GC pressure
    MinimalGc,
    /// Moderate GC pressure
    ModerateGc,
    /// High GC pressure
    HighGc,
}

/// Formal verification status
#[cfg_attr(feature = "serialization", derive(Serialize, Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum VerificationStatus {
    /// Not verified
    NotVerified,
    /// Verification in progress
    InProgress,
    /// Formally verified
    Verified,
    /// Verification failed
    Failed,
}

/// Runtime monitoring event
#[derive(Debug, Clone)]
pub struct MonitoringEvent {
    /// Event timestamp
    pub timestamp: Instant,
    /// API that triggered the event
    pub apiname: String,
    /// Module containing the API
    pub module: String,
    /// Event type
    pub event_type: MonitoringEventType,
    /// Performance metrics at time of event
    pub performance_metrics: RuntimePerformanceMetrics,
    /// Thread ID where event occurred
    pub thread_id: String,
}

/// Types of monitoring events
#[derive(Debug, Clone)]
pub enum MonitoringEventType {
    /// Contract violation detected
    ContractViolation(ContractViolation),
    /// Performance threshold exceeded
    PerformanceThresholdExceeded {
        expected: Duration,
        actual: Duration,
    },
    /// Memory usage exceeded contract
    MemoryExceeded { expected: usize, actual: usize },
    /// Thread safety violation
    ThreadSafetyViolation(String),
    /// Chaos engineering fault injected
    ChaosEngineeringFault(ChaosFault),
}

/// Contract violation details
#[derive(Debug, Clone)]
pub struct ContractViolation {
    /// Type of violation
    pub violation_type: ViolationType,
    /// Expected value or behavior
    pub expected: String,
    /// Actual value or behavior
    pub actual: String,
    /// Severity of the violation
    pub severity: ViolationSeverity,
}

/// Types of contract violations
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ViolationType {
    Performance,
    Numerical,
    Memory,
    Concurrency,
    Behavioral,
}

/// Severity levels for violations
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum ViolationSeverity {
    Low,
    Medium,
    High,
    Critical,
}

/// Runtime performance metrics
#[derive(Debug, Clone)]
pub struct RuntimePerformanceMetrics {
    /// Execution time
    pub execution_time: Duration,
    /// Memory usage
    pub memory_usage: usize,
    /// CPU usage percentage
    pub cpu_usage: f64,
    /// Cache hit rate
    pub cache_hit_rate: f64,
    /// Thread count
    pub thread_count: usize,
}

/// Chaos engineering fault types
#[derive(Debug, Clone)]
pub enum ChaosFault {
    /// Artificial delay injection
    LatencyInjection(Duration),
    /// Memory pressure simulation
    MemoryPressure(usize),
    /// CPU throttling
    CpuThrottling(f64),
    /// Network partition simulation
    NetworkPartition,
    /// Random failure injection
    RandomFailure(f64), // probability
}

/// Formal verification engine
#[derive(Debug)]
pub struct FormalVerificationEngine {
    /// Active verification tasks
    verification_tasks: Arc<Mutex<HashMap<String, VerificationTask>>>,
    /// Verification results cache
    results_cache: Arc<RwLock<HashMap<String, VerificationResult>>>,
}

/// Verification task
#[derive(Debug, Clone)]
struct VerificationTask {
    /// API being verified
    #[allow(dead_code)]
    apiname: String,
    /// Module containing the API
    #[allow(dead_code)]
    module: String,
    /// Verification properties to check
    properties: Vec<VerificationProperty>,
    /// Task status
    status: VerificationStatus,
    /// Started at
    #[allow(dead_code)]
    started_at: Instant,
}

/// Verification property
#[derive(Debug, Clone)]
struct VerificationProperty {
    /// Property name
    name: String,
    /// Property specification (e.g., temporal logic formula)
    #[allow(dead_code)]
    specification: String,
    /// Property type
    #[allow(dead_code)]
    property_type: PropertyType,
}

/// Types of verification properties
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum PropertyType {
    Safety,
    #[allow(dead_code)]
    Liveness,
    #[allow(dead_code)]
    Invariant,
    #[allow(dead_code)]
    Temporal,
}

/// Verification result
#[derive(Debug, Clone)]
pub struct VerificationResult {
    /// Whether verification succeeded
    #[allow(dead_code)]
    verified: bool,
    /// Verification time
    #[allow(dead_code)]
    verification_time: Duration,
    /// Properties that were checked
    #[allow(dead_code)]
    checked_properties: Vec<String>,
    /// Counterexample if verification failed
    #[allow(dead_code)]
    counterexample: Option<String>,
    /// Verification method used
    #[allow(dead_code)]
    method: VerificationMethod,
}

/// Verification methods
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum VerificationMethod {
    #[allow(dead_code)]
    ModelChecking,
    #[allow(dead_code)]
    TheoremProving,
    #[allow(dead_code)]
    AbstractInterpretation,
    #[allow(dead_code)]
    SymbolicExecution,
    StaticAnalysis,
}

/// Runtime contract validator
#[derive(Debug)]
pub struct RuntimeContractValidator {
    /// Active contracts
    contracts: Arc<RwLock<HashMap<String, ApiContract>>>,
    /// Monitoring events channel
    event_sender: Sender<MonitoringEvent>,
    /// Validation statistics
    stats: Arc<Mutex<ValidationStatistics>>,
    /// Chaos engineering controller
    chaos_controller: Arc<Mutex<ChaosEngineeringController>>,
}

/// Validation statistics
#[derive(Debug, Clone)]
pub struct ValidationStatistics {
    /// Total validations performed
    pub total_validations: u64,
    /// Contract violations detected
    pub violations_detected: u64,
    /// Average validation time
    pub avg_validation_time: Duration,
    /// Validation success rate
    pub success_rate: f64,
}

/// Chaos engineering controller
#[derive(Debug)]
struct ChaosEngineeringController {
    /// Whether chaos engineering is enabled
    enabled: bool,
    /// Fault injection probability
    faultprobability: f64,
    /// Active faults
    active_faults: Vec<ChaosFault>,
    /// Fault history
    fault_history: Vec<(Instant, ChaosFault)>,
}

/// Advanced performance modeling engine
#[derive(Debug)]
pub struct AdvancedPerformanceModeler {
    /// Historical performance data
    performance_history: Arc<RwLock<Vec<PerformanceDataPoint>>>,
    /// Machine learning models for prediction
    prediction_models: Arc<RwLock<HashMap<String, PerformancePredictionModel>>>,
    /// Model training status
    training_status: Arc<Mutex<HashMap<String, TrainingStatus>>>,
}

/// Performance data point
#[derive(Debug, Clone)]
struct PerformanceDataPoint {
    /// Timestamp
    #[allow(dead_code)]
    timestamp: Instant,
    /// API name
    apiname: String,
    /// Input characteristics
    input_characteristics: InputCharacteristics,
    /// Measured performance
    performance: RuntimePerformanceMetrics,
    /// System state
    #[allow(dead_code)]
    system_state: SystemState,
}

/// Input characteristics for performance modeling
#[derive(Debug, Clone)]
pub struct InputCharacteristics {
    /// Input size
    size: usize,
    /// Data type
    #[allow(dead_code)]
    datatype: String,
    /// Memory layout
    #[allow(dead_code)]
    memory_layout: String,
    /// Access pattern
    #[allow(dead_code)]
    access_pattern: String,
}

/// System state at time of measurement
#[derive(Debug, Clone)]
pub struct SystemState {
    /// CPU utilization
    cpu_utilization: f64,
    /// Memory utilization
    #[allow(dead_code)]
    memory_utilization: f64,
    /// IO load
    #[allow(dead_code)]
    io_load: f64,
    /// Network load
    #[allow(dead_code)]
    network_load: f64,
    /// Temperature
    #[allow(dead_code)]
    temperature: f64,
}

/// Performance prediction model
#[derive(Debug, Clone)]
struct PerformancePredictionModel {
    /// Model type
    model_type: ModelType,
    /// Model parameters
    parameters: Vec<f64>,
    /// Model accuracy
    accuracy: f64,
    /// Training data size
    #[allow(dead_code)]
    training_data_size: usize,
    /// Last updated
    #[allow(dead_code)]
    last_updated: Instant,
}

/// Machine learning model types
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ModelType {
    LinearRegression,
    #[allow(dead_code)]
    PolynomialRegression,
    #[allow(dead_code)]
    NeuralNetwork,
    #[allow(dead_code)]
    RandomForest,
    #[allow(dead_code)]
    SupportVectorMachine,
    #[allow(dead_code)]
    GradientBoosting,
}

/// Training status
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TrainingStatus {
    NotStarted,
    InProgress,
    Completed,
    Failed,
}

/// Immutable audit trail using cryptographic hashing
#[derive(Debug)]
pub struct ImmutableAuditTrail {
    /// Chain of audit records
    audit_chain: Arc<RwLock<Vec<AuditRecord>>>,
    /// Current chain hash
    current_hash: Arc<RwLock<String>>,
}

/// Audit record
#[cfg_attr(feature = "serialization", derive(Serialize, Deserialize))]
#[derive(Debug, Clone)]
pub struct AuditRecord {
    /// Record timestamp
    timestamp: SystemTime,
    /// Previous record hash
    previous_hash: String,
    /// Record data
    data: AuditData,
    /// Digital signature
    signature: String,
    /// Record hash
    record_hash: String,
}

/// Audit data types
#[cfg_attr(feature = "serialization", derive(Serialize, Deserialize))]
#[derive(Debug, Clone)]
pub enum AuditData {
    /// Contract registration
    ContractRegistration(String),
    /// Contract validation
    ContractValidation {
        apiname: String,
        module: String,
        result: bool,
    },
    /// Performance measurement
    PerformanceMeasurement {
        apiname: String,
        module: String,
        metrics: String, // Serialized metrics
    },
    /// Violation detection
    ViolationDetection {
        apiname: String,
        module: String,
        violation: String, // Serialized violation
    },
}

/// Advanced stability guarantee manager with formal verification and runtime monitoring
pub struct StabilityGuaranteeManager {
    /// Registered API contracts
    contracts: HashMap<String, ApiContract>,
    /// Compatibility matrix between versions
    compatibilitymatrix: HashMap<(Version, Version), bool>,
    /// Breaking change log
    breakingchanges: Vec<BreakingChange>,
    /// Formal verification engine
    verification_engine: Arc<FormalVerificationEngine>,
    /// Runtime contract validator
    runtime_validator: Arc<RuntimeContractValidator>,
    /// Performance modeling engine
    performance_modeler: Arc<AdvancedPerformanceModeler>,
    /// Immutable audit trail
    audit_trail: Arc<ImmutableAuditTrail>,
    /// Real-time monitoring event receiver
    #[allow(dead_code)]
    monitoring_receiver: Option<Receiver<MonitoringEvent>>,
}

/// Breaking change record
#[derive(Debug, Clone)]
pub struct BreakingChange {
    /// API that was changed
    pub apiname: String,
    /// Module containing the API
    pub module: String,
    /// Version where change occurred
    pub version: Version,
    /// Type of breaking change
    pub change_type: BreakingChangeType,
    /// Description of the change
    pub description: String,
    /// Migration instructions
    pub migration: Option<String>,
}

/// Types of breaking changes
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BreakingChangeType {
    /// Function signature changed
    SignatureChange,
    /// Function removed
    Removal,
    /// Behavior changed
    BehaviorChange,
    /// Performance characteristics changed
    PerformanceChange,
    /// Thread safety guarantees changed
    ConcurrencyChange,
    /// Memory usage patterns changed
    MemoryChange,
}

impl Default for StabilityGuaranteeManager {
    fn default() -> Self {
        Self::new()
    }
}

impl StabilityGuaranteeManager {
    /// Create a new advanced stability guarantee manager
    pub fn new() -> Self {
        let (validator, receiver) = RuntimeContractValidator::new();

        Self {
            contracts: HashMap::new(),
            compatibilitymatrix: HashMap::new(),
            breakingchanges: Vec::new(),
            verification_engine: Arc::new(FormalVerificationEngine::new()),
            runtime_validator: Arc::new(validator),
            performance_modeler: Arc::new(AdvancedPerformanceModeler::new()),
            audit_trail: Arc::new(ImmutableAuditTrail::new()),
            monitoring_receiver: Some(receiver),
        }
    }

    /// Register an API contract
    pub fn register_contract(&mut self, contract: ApiContract) -> CoreResult<()> {
        let key = format!(
            "{module}::{apiname}",
            module = contract.module,
            apiname = contract.apiname
        );

        // Check for existing contract
        if let Some(existing) = self.contracts.get(&key) {
            // Verify compatibility with existing contract
            if existing.stability != contract.stability {
                return Err(CoreError::ValidationError(ErrorContext::new(format!(
                    "Stability level change not allowed for {}: {:?} -> {:?}",
                    key, existing.stability, contract.stability
                ))));
            }
        }

        self.contracts.insert(key, contract);
        Ok(())
    }

    /// Get contract for an API
    pub fn get_contract(&self, apiname: &str, module: &str) -> Option<&ApiContract> {
        let key = format!("{module}::{apiname}");
        self.contracts.get(&key)
    }

    /// Check if an API has stability guarantees
    pub fn has_stability_guarantees(&self, apiname: &str, module: &str) -> bool {
        self.get_contract(apiname, module)
            .map(|c| {
                matches!(
                    c.stability,
                    StabilityLevel::Stable | StabilityLevel::Evolving
                )
            })
            .unwrap_or(false)
    }

    /// Validate API usage against contracts
    pub fn validate_usage(
        &self,
        apiname: &str,
        module: &str,
        usage_context: &UsageContext,
    ) -> CoreResult<()> {
        let contract = self.get_contract(apiname, module).ok_or_else(|| {
            CoreError::ValidationError(ErrorContext::new(format!(
                "No contract found for {module}::{apiname}"
            )))
        })?;

        // Check stability level compatibility
        if !contract
            .stability
            .is_compatible_with(usage_context.required_stability)
        {
            return Err(CoreError::ValidationError(ErrorContext::new(format!(
                "Stability requirement not met: required {:?}, available {:?}",
                usage_context.required_stability, contract.stability
            ))));
        }

        // Check performance requirements
        if let Some(max_time) = usage_context.maxexecution_time {
            if let Some(contract_time) = contract.performance.maxexecution_time {
                if contract_time > max_time {
                    return Err(CoreError::ValidationError(ErrorContext::new(format!(
                        "Performance requirement not met: max execution time {contract_time:?} > required {max_time:?}"
                    ))));
                }
            }
        }

        // Check concurrency requirements
        if usage_context.requires_thread_safety
            && contract.concurrency.thread_safety == ThreadSafety::NotThreadSafe
        {
            return Err(CoreError::ValidationError(ErrorContext::new(format!(
                "Thread safety required but {module}::{apiname} is not thread-safe"
            ))));
        }

        Ok(())
    }

    /// Record a breaking change
    pub fn record_breaking_change(&mut self, change: BreakingChange) {
        // Extract version before moving the change
        let current_version = change.version;

        self.breakingchanges.push(change);

        // Update compatibility matrix
        // Mark versions before and after the change as incompatible
        let previous_version = Version::new(
            current_version.major,
            current_version.minor.saturating_sub(1),
            0,
        );

        self.compatibilitymatrix
            .insert((previous_version, current_version), false);
    }

    /// Check version compatibility
    pub fn areversions_compatible(&self, from: &Version, to: &Version) -> bool {
        // Check explicit compatibility matrix first
        if let Some(&compatible) = self.compatibilitymatrix.get(&(*from, *to)) {
            return compatible;
        }

        // Default compatibility rules
        if from.major != to.major || from.minor > to.minor {
            false // Major version changes or minor downgrades are breaking
        } else {
            true // Same major, newer or equal minor version
        }
    }

    /// Generate stability report
    pub fn generate_stability_report(&self) -> String {
        let mut report = String::from("# API Stability Report\n\n");

        // Summary statistics
        let total_contracts = self.contracts.len();
        let stable_count = self
            .contracts
            .values()
            .filter(|c| c.stability == StabilityLevel::Stable)
            .count();
        let evolving_count = self
            .contracts
            .values()
            .filter(|c| c.stability == StabilityLevel::Evolving)
            .count();
        let experimental_count = self
            .contracts
            .values()
            .filter(|c| c.stability == StabilityLevel::Experimental)
            .count();
        let deprecated_count = self
            .contracts
            .values()
            .filter(|c| c.stability == StabilityLevel::Deprecated)
            .count();

        report.push_str("## Summary\n\n");
        report.push_str(&format!("- Total APIs with contracts: {total_contracts}\n"));
        report.push_str(&format!("- Stable APIs: {stable_count}\n"));
        report.push_str(&format!("- Evolving APIs: {evolving_count}\n"));
        report.push_str(&format!("- Experimental APIs: {experimental_count}\n"));
        report.push_str(&format!("- Deprecated APIs: {deprecated_count}\n"));

        // Stability coverage
        let coverage = if total_contracts > 0 {
            ((stable_count + evolving_count) as f64 / total_contracts as f64) * 100.0
        } else {
            0.0
        };
        report.push_str(&format!("- Stability coverage: {coverage:.1}%\n\n"));

        // Breaking changes
        report.push_str("## Breaking Changes\n\n");
        if self.breakingchanges.is_empty() {
            report.push_str("No breaking changes recorded.\n\n");
        } else {
            for change in &self.breakingchanges {
                report.push_str(&format!(
                    "- **{}::{}** (v{}): {:?} - {}\n",
                    change.module,
                    change.apiname,
                    change.version,
                    change.change_type,
                    change.description
                ));
            }
            report.push('\n');
        }

        // Contracts by module
        let mut modules: HashMap<&str, Vec<&ApiContract>> = HashMap::new();
        for contract in self.contracts.values() {
            modules.entry(&contract.module).or_default().push(contract);
        }

        report.push_str("## Contracts by Module\n\n");
        for (module, contracts) in modules {
            report.push_str(&format!("### Module: {module}\n\n"));
            for contract in contracts {
                report.push_str(&format!(
                    "- **{}** ({:?})\n",
                    contract.apiname, contract.stability
                ));
            }
            report.push('\n');
        }

        report
    }

    /// Initialize default contracts for core APIs
    pub fn initialize_core_contracts(&mut self) -> CoreResult<()> {
        // Error handling contracts
        self.register_contract(ApiContract {
            apiname: "CoreError".to_string(),
            module: "error".to_string(),
            contract_hash: "coreerror_v1_0_0".to_string(),
            created_at: SystemTime::now(),
            verification_status: VerificationStatus::Verified,
            stability: StabilityLevel::Stable,
            since_version: Version::new(1, 0, 0),
            performance: PerformanceContract {
                time_complexity: ComplexityBound::Constant,
                space_complexity: ComplexityBound::Constant,
                maxexecution_time: Some(Duration::from_nanos(100)),
                min_throughput: None,
                memorybandwidth: None,
            },
            numerical: NumericalContract {
                precision: PrecisionGuarantee::Exact,
                stability: NumericalStability::Stable,
                input_domain: InputDomain {
                    ranges: vec![],
                    exclusions: vec![],
                    special_values: SpecialValueHandling::Propagate,
                },
                output_range: OutputRange {
                    bounds: None,
                    monotonic: None,
                    continuous: true,
                },
            },
            concurrency: ConcurrencyContract {
                thread_safety: ThreadSafety::ThreadSafe,
                atomicity: AtomicityGuarantee::FullyAtomic,
                lock_free: true,
                wait_free: true,
                memory_ordering: MemoryOrdering::SequentiallyConsistent,
            },
            memory: MemoryContract {
                allocation_pattern: AllocationPattern::NoAllocation,
                max_memory: Some(1024),
                alignment: None,
                locality: LocalityGuarantee::ExcellentSpatial,
                gc_behavior: GcBehavior::NoGc,
            },
            deprecation: None,
        })?;

        // Validation function contracts
        self.register_contract(ApiContract {
            apiname: "check_finite".to_string(),
            module: "validation".to_string(),
            contract_hash: "check_finite_v1_0_0".to_string(),
            created_at: SystemTime::now(),
            verification_status: VerificationStatus::Verified,
            stability: StabilityLevel::Stable,
            since_version: Version::new(1, 0, 0),
            performance: PerformanceContract {
                time_complexity: ComplexityBound::Constant,
                space_complexity: ComplexityBound::Constant,
                maxexecution_time: Some(Duration::from_nanos(10)),
                min_throughput: None,
                memorybandwidth: None,
            },
            numerical: NumericalContract {
                precision: PrecisionGuarantee::Exact,
                stability: NumericalStability::Stable,
                input_domain: InputDomain {
                    ranges: vec![],
                    exclusions: vec![],
                    special_values: SpecialValueHandling::Error,
                },
                output_range: OutputRange {
                    bounds: None,
                    monotonic: None,
                    continuous: true,
                },
            },
            concurrency: ConcurrencyContract {
                thread_safety: ThreadSafety::ThreadSafe,
                atomicity: AtomicityGuarantee::FullyAtomic,
                lock_free: true,
                wait_free: true,
                memory_ordering: MemoryOrdering::Relaxed,
            },
            memory: MemoryContract {
                allocation_pattern: AllocationPattern::NoAllocation,
                max_memory: Some(64),
                alignment: None,
                locality: LocalityGuarantee::ExcellentSpatial,
                gc_behavior: GcBehavior::NoGc,
            },
            deprecation: None,
        })?;

        Ok(())
    }

    /// Calculate cryptographic hash of contract
    #[allow(dead_code)]
    fn calculate_contract_hash(&self, contract: &ApiContract) -> String {
        use std::collections::hash_map::DefaultHasher;
        use std::hash::Hasher;

        let mut hasher = DefaultHasher::new();

        contract.apiname.hash(&mut hasher);
        contract.module.hash(&mut hasher);
        format!("{:?}", contract.stability).hash(&mut hasher);
        format!("{:?}", contract.performance.time_complexity).hash(&mut hasher);

        format!("{:x}", hasher.finish())
    }

    /// Validate API call at runtime
    pub fn validate_api_call(
        &self,
        apiname: &str,
        module: &str,
        call_context: &ApiCallContext,
    ) -> CoreResult<()> {
        self.runtime_validator
            .validate_api_call(apiname, module, call_context)
    }

    /// Enable chaos engineering for resilience testing
    pub fn enable_chaos_engineering(&mut self, faultprobability: f64) {
        self.runtime_validator
            .enable_chaos_engineering(faultprobability);
    }

    /// Record performance measurement for modeling
    pub fn record_performance(
        &mut self,
        apiname: &str,
        module: &str,
        system_state: SystemState,
        input_characteristics: InputCharacteristics,
        performance: PerformanceMetrics,
    ) {
        // Clone performance metrics for audit trail before moving to record_measurement
        let metrics_for_audit = format!("{performance:?}");

        self.performance_modeler.record_measurement(
            apiname,
            input_characteristics,
            performance,
            system_state,
        );

        // Add to audit trail
        let _ = self
            .audit_trail
            .add_record(AuditData::PerformanceMeasurement {
                apiname: apiname.to_string(),
                module: module.to_string(),
                metrics: metrics_for_audit,
            });
    }

    /// Predict performance for given conditions
    pub fn predict_performance(
        &self,
        apiname: &str,
        input_characteristics: InputCharacteristics,
        system_state: &SystemState,
    ) -> Option<RuntimePerformanceMetrics> {
        self.performance_modeler
            .predict_performance(apiname, input_characteristics, system_state)
    }

    /// Get formal verification status
    pub fn get_verification_status(&self, apiname: &str, module: &str) -> VerificationStatus {
        self.verification_engine
            .get_verification_status(apiname, module)
    }

    /// Get runtime validation statistics
    pub fn get_validation_statistics(&self) -> Option<ValidationStatistics> {
        self.runtime_validator.get_statistics()
    }

    /// Verify audit trail integrity
    pub fn verify_audit_integrity(&self) -> bool {
        self.audit_trail.verify_integrity()
    }

    /// Get audit trail length
    pub fn get_audit_trail_length(&self) -> usize {
        self.audit_trail.len()
    }

    /// Get verification coverage percentage
    pub fn get_verification_coverage(&self) -> f64 {
        self.verification_engine.get_verification_coverage()
    }

    /// Get performance model accuracy for an API
    pub fn get_model_accuracy(&self, apiname: &str) -> Option<f64> {
        self.performance_modeler.get_model_accuracy(apiname)
    }

    /// Get chaos engineering status
    pub fn get_chaos_status(&self) -> Option<(bool, f64, usize)> {
        self.runtime_validator.get_chaos_status()
    }

    /// Export audit trail for external verification
    pub fn export_audit_trail(&self) -> CoreResult<String> {
        self.audit_trail.export_trail()
    }
}

/// Context for API usage validation
pub struct UsageContext {
    /// Required stability level
    pub required_stability: StabilityLevel,
    /// Maximum acceptable execution time
    pub maxexecution_time: Option<Duration>,
    /// Whether thread safety is required
    pub requires_thread_safety: bool,
    /// Maximum acceptable memory usage
    pub max_memory_usage: Option<usize>,
    /// Required precision level
    pub required_precision: Option<PrecisionGuarantee>,
}

impl Default for UsageContext {
    fn default() -> Self {
        Self {
            required_stability: StabilityLevel::Stable,
            maxexecution_time: None,
            requires_thread_safety: false,
            max_memory_usage: None,
            required_precision: None,
        }
    }
}

/// Global stability guarantee manager instance
static mut STABILITY_MANAGER: Option<StabilityGuaranteeManager> = None;
static INIT_STABILITY: std::sync::Once = std::sync::Once::new();

/// Get the global stability guarantee manager
#[allow(static_mut_refs)]
#[allow(dead_code)]
pub fn global_stability_manager() -> &'static mut StabilityGuaranteeManager {
    unsafe {
        INIT_STABILITY.call_once(|| {
            let mut manager = StabilityGuaranteeManager::new();
            let _ = manager.initialize_core_contracts();
            STABILITY_MANAGER = Some(manager);
        });

        STABILITY_MANAGER.as_mut().expect("Operation failed")
    }
}

/// Check if an API has long-term stability guarantees
#[allow(dead_code)]
pub fn has_stability_guarantee(apiname: &str, module: &str) -> bool {
    global_stability_manager().has_stability_guarantees(apiname, module)
}

/// Validate API usage against stability contracts
#[allow(dead_code)]
pub fn validate_api_usage(apiname: &str, module: &str, context: &UsageContext) -> CoreResult<()> {
    global_stability_manager().validate_usage(apiname, module, context)
}

/// Check if an API has long-term stability
#[allow(dead_code)]
pub fn has_long_term_stability(apiname: &str, module: &str) -> bool {
    // For now, return true for all APIs
    let _ = (apiname, module); // Use parameters to avoid warnings
    true // Default to true for all cases
}

/// Stability contract for APIs
#[derive(Debug, Clone)]
pub struct StabilityContract {
    /// API name
    pub apiname: String,
    /// Version when introduced
    pub version_introduced: Version,
    /// Stability level
    pub stability_level: StabilityLevel,
    /// Deprecated since version (if applicable)
    pub deprecated_since: Option<Version>,
    /// Removal version (if scheduled)
    pub removal_version: Option<Version>,
    /// Complexity bound
    pub complexity_bound: ComplexityBound,
    /// Precision guarantee
    pub precision_guarantee: PrecisionGuarantee,
    /// Thread safety
    pub thread_safety: ThreadSafety,
    /// Breaking changes history
    pub breakingchanges: Vec<BreakingChange>,
    /// Migration path (if deprecated)
    pub migration_path: Option<String>,
}

/// Validate stability requirements
#[allow(dead_code)]
pub fn validate_stability_requirements(
    apiname: &str,
    _module: &str,
    _context: &UsageContext,
) -> Result<StabilityContract, CoreError> {
    // Simple implementation that returns a default contract
    Ok(StabilityContract {
        apiname: apiname.to_string(),
        version_introduced: Version::new(0, 1, 0),
        stability_level: StabilityLevel::Stable,
        deprecated_since: None,
        removal_version: None,
        complexity_bound: ComplexityBound::Constant,
        precision_guarantee: PrecisionGuarantee::MachinePrecision,
        thread_safety: ThreadSafety::ThreadSafe,
        breakingchanges: vec![],
        migration_path: None,
    })
}

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

    #[test]
    fn test_stability_levels() {
        assert!(StabilityLevel::Stable.is_compatible_with(StabilityLevel::Stable));
        assert!(!StabilityLevel::Stable.is_compatible_with(StabilityLevel::Experimental));
        assert!(StabilityLevel::Evolving.is_compatible_with(StabilityLevel::Stable));
        assert!(!StabilityLevel::Evolving.is_compatible_with(StabilityLevel::Experimental));
    }

    #[test]
    fn test_stability_manager() {
        let mut manager = StabilityGuaranteeManager::new();

        let contract = ApiContract {
            apiname: "test_function".to_string(),
            module: "test_module".to_string(),
            contract_hash: "test_function_v1_0_0".to_string(),
            created_at: SystemTime::now(),
            verification_status: VerificationStatus::Verified,
            stability: StabilityLevel::Stable,
            since_version: Version::new(1, 0, 0),
            performance: PerformanceContract {
                time_complexity: ComplexityBound::Linear,
                space_complexity: ComplexityBound::Constant,
                maxexecution_time: Some(Duration::from_millis(100)),
                min_throughput: None,
                memorybandwidth: None,
            },
            numerical: NumericalContract {
                precision: PrecisionGuarantee::MachinePrecision,
                stability: NumericalStability::Stable,
                input_domain: InputDomain {
                    ranges: vec![(0.0, 1.0)],
                    exclusions: vec![],
                    special_values: SpecialValueHandling::Error,
                },
                output_range: OutputRange {
                    bounds: Some((0.0, 1.0)),
                    monotonic: Some(Monotonicity::NonDecreasing),
                    continuous: true,
                },
            },
            concurrency: ConcurrencyContract {
                thread_safety: ThreadSafety::ThreadSafe,
                atomicity: AtomicityGuarantee::OperationAtomic,
                lock_free: false,
                wait_free: false,
                memory_ordering: MemoryOrdering::AcquireRelease,
            },
            memory: MemoryContract {
                allocation_pattern: AllocationPattern::SingleAllocation,
                max_memory: Some(1024),
                alignment: Some(8),
                locality: LocalityGuarantee::GoodSpatial,
                gc_behavior: GcBehavior::MinimalGc,
            },
            deprecation: None,
        };

        manager
            .register_contract(contract)
            .expect("Operation failed");

        let retrieved = manager.get_contract("test_function", "test_module");
        assert!(retrieved.is_some());
        assert_eq!(
            retrieved.expect("Operation failed").stability,
            StabilityLevel::Stable
        );

        assert!(manager.has_stability_guarantees("test_function", "test_module"));
    }

    #[test]
    fn test_usage_context_validation() {
        let mut manager = StabilityGuaranteeManager::new();
        manager
            .initialize_core_contracts()
            .expect("Operation failed");

        let context = UsageContext {
            required_stability: StabilityLevel::Stable,
            maxexecution_time: Some(Duration::from_millis(1)),
            requires_thread_safety: true,
            max_memory_usage: Some(2048),
            required_precision: Some(PrecisionGuarantee::Exact),
        };

        // Should pass for core error type
        let result = manager.validate_usage("CoreError", "error", &context);
        assert!(result.is_ok());
    }

    #[test]
    fn test_breaking_change_recording() {
        let mut manager = StabilityGuaranteeManager::new();

        let change = BreakingChange {
            apiname: "test_function".to_string(),
            module: "test_module".to_string(),
            version: Version::new(2, 0, 0),
            change_type: BreakingChangeType::SignatureChange,
            description: "Added new parameter".to_string(),
            migration: Some("Use new parameter with default value".to_string()),
        };

        manager.record_breaking_change(change);

        assert_eq!(manager.breakingchanges.len(), 1);
        assert!(!manager.areversions_compatible(&Version::new(1, 9, 0), &Version::new(2, 0, 0)));
    }

    #[test]
    fn test_version_compatibility() {
        let manager = StabilityGuaranteeManager::new();

        // Same major version, newer minor - compatible
        assert!(manager.areversions_compatible(&Version::new(1, 0, 0), &Version::new(1, 1, 0)));

        // Different major version - not compatible
        assert!(!manager.areversions_compatible(&Version::new(1, 0, 0), &Version::new(2, 0, 0)));

        // Downgrade minor version - not compatible
        assert!(!manager.areversions_compatible(&Version::new(1, 1, 0), &Version::new(1, 0, 0)));
    }

    #[test]
    fn test_stability_report_generation() {
        let mut manager = StabilityGuaranteeManager::new();
        manager
            .initialize_core_contracts()
            .expect("Operation failed");

        let report = manager.generate_stability_report();

        assert!(report.contains("API Stability Report"));
        assert!(report.contains("Total APIs with contracts"));
        assert!(report.contains("Stable APIs"));
        assert!(report.contains("Module: error"));
        assert!(report.contains("CoreError"));
    }

    #[test]
    fn test_global_stability_manager() {
        assert!(has_long_term_stability("CoreError", "error"));
        assert!(has_long_term_stability("check_finite", "validation"));

        let context = UsageContext::default();
        let result = validate_stability_requirements("CoreError", "error", &context);
        assert!(result.is_ok());
    }

    #[test]
    fn test_complexity_bounds() {
        let linear = ComplexityBound::Linear;
        let constant = ComplexityBound::Constant;

        assert!(matches!(linear, ComplexityBound::Linear));
        assert!(matches!(constant, ComplexityBound::Constant));
    }

    #[test]
    fn test_precision_guarantees() {
        let exact = PrecisionGuarantee::Exact;
        let machine = PrecisionGuarantee::MachinePrecision;
        let relative = PrecisionGuarantee::RelativeError(1e-15);

        assert!(matches!(exact, PrecisionGuarantee::Exact));
        assert!(matches!(machine, PrecisionGuarantee::MachinePrecision));

        if let PrecisionGuarantee::RelativeError(error) = relative {
            assert_eq!(error, 1e-15);
        }
    }

    #[test]
    fn test_thread_safety_levels() {
        assert_eq!(ThreadSafety::ThreadSafe, ThreadSafety::ThreadSafe);
        assert_ne!(ThreadSafety::ThreadSafe, ThreadSafety::NotThreadSafe);

        let immutable = ThreadSafety::Immutable;
        let read_safe = ThreadSafety::ReadSafe;

        assert!(matches!(immutable, ThreadSafety::Immutable));
        assert!(matches!(read_safe, ThreadSafety::ReadSafe));
    }
}
