asupersync 0.3.4

//! Database Metamorphic Testing: Connection Pooling, Authentication, and Transaction Isolation
//!
//! This module implements comprehensive metamorphic relations for database components,
//! focusing on PostgreSQL SCRAM authentication determinism, query parsing round-trips,
//! connection pool reservation/return symmetry, and transaction isolation properties.
//! These tests address the oracle problem for complex database state management
//! where the expected outcomes depend on intricate protocol details.
//!
//! ## Metamorphic Relations Implemented
//!
//! ### PostgreSQL SCRAM Authentication (3 MRs)
//! - MR-SCRAMTranscriptDeterminism: SCRAM-SHA-256 transcripts are deterministic
//! - MR-AuthenticationIdempotency: successful auth can be repeated with same credentials
//! - MR-SCRAMNonceMonotonicity: client nonces must be unique across sessions
//!
//! ### Query Parsing Round-trips (3 MRs)
//! - MR-QueryParseSerialize: parse(sql) → serialize() preserves semantics
//! - MR-ParameterBindingConsistency: parameterized queries bind consistently
//! - MR-QueryNormalizationStability: normalized queries are stable under re-normalization
//!
//! ### Connection Pool Management (4 MRs)
//! - MR-PoolReservationSymmetry: acquire() → release() maintains pool invariants
//! - MR-ConnectionValidationConsistency: is_valid() is deterministic for same connection state
//! - MR-HealthCheckStability: health checks are idempotent when connection state unchanged
//! - MR-PoolSizeBounds: pool never exceeds configured limits under concurrent access
//!
//! ### Transaction Isolation Properties (3 MRs)
//! - MR-TransactionACIDCommutivity: independent transactions can be reordered
//! - MR-SavepointNesting: nested savepoints follow stack discipline
//! - MR-IsolationLevelMonotonicity: higher isolation levels preserve lower-level guarantees

#![allow(dead_code)]

#[cfg(test)]
mod tests {
    #[cfg(test)]
    use proptest::prelude::*;
    use std::collections::{HashMap, HashSet, VecDeque};
    use std::sync::{Arc, Mutex};
    use std::time::{Duration, SystemTime};

    // ═══════════════════════════════════════════════════════════════════════════
    // Deterministic implementations for database metamorphic testing
    // ═══════════════════════════════════════════════════════════════════════════

    #[derive(Debug, Clone, PartialEq)]
    pub struct MockSCRAMTranscript {
        pub client_first_message: String,
        pub server_first_message: String,
        pub client_final_message: String,
        pub server_final_message: String,
        pub channel_binding: Option<Vec<u8>>,
        pub salt: Vec<u8>,
        pub iterations: u32,
    }

    impl MockSCRAMTranscript {
        pub fn new(username: &str, password: &str, salt: Vec<u8>, iterations: u32) -> Self {
            let client_nonce = format!("r={}", Self::generate_client_nonce());
            let client_first_message = format!("n,,n={},r={}", username, client_nonce);

            let server_nonce = format!("{}DEADBEEF", client_nonce);
            let server_first_message = format!(
                "r={},s={},i={}",
                server_nonce,
                base64::encode(&salt),
                iterations
            );

            let client_final_message =
                format!("c=biws,r={},p=dHVyZiBhbmQgdHVyZiBhZ2Fpbg==", server_nonce);
            let server_final_message = "v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=".to_string();

            Self {
                client_first_message,
                server_first_message,
                client_final_message,
                server_final_message,
                channel_binding: None,
                salt,
                iterations,
            }
        }

        fn generate_client_nonce() -> String {
            use std::collections::hash_map::DefaultHasher;
            use std::hash::{Hash, Hasher};

            let mut hasher = DefaultHasher::new();
            SystemTime::now().hash(&mut hasher);
            format!("{:x}", hasher.finish())
        }

        pub fn is_valid_transcript(&self) -> bool {
            !self.client_first_message.is_empty()
                && !self.server_first_message.is_empty()
                && self.client_final_message.contains("r=")
                && self.server_final_message.contains("v=")
        }
    }

    #[derive(Debug, Clone, PartialEq)]
    pub struct MockQuery {
        pub sql: String,
        pub parameters: Vec<MockValue>,
        pub normalized_form: String,
        pub parameter_types: Vec<String>,
    }

    #[derive(Debug, Clone, PartialEq)]
    pub enum MockValue {
        Integer(i64),
        Text(String),
        Boolean(bool),
        Null,
    }

    impl MockQuery {
        pub fn new(sql: &str) -> Self {
            Self {
                sql: sql.to_string(),
                parameters: Vec::new(),
                normalized_form: Self::normalize_sql(sql),
                parameter_types: Vec::new(),
            }
        }

        pub fn with_parameters(mut self, params: Vec<MockValue>) -> Self {
            self.parameter_types = params.iter().map(|v| v.type_name()).collect();
            self.parameters = params;
            self
        }

        fn normalize_sql(sql: &str) -> String {
            sql.trim()
                .replace('\n', " ")
                .replace('\t', " ")
                .split_whitespace()
                .collect::<Vec<_>>()
                .join(" ")
                .to_uppercase()
        }

        pub fn parse_and_serialize(&self) -> String {
            // Deterministic implementation: parse SQL and serialize back.
            let parsed = Self::normalize_sql(&self.sql);
            parsed
                .replace(" WHERE ", " WHERE ")
                .replace(" AND ", " AND ")
        }

        pub fn bind_parameters(&self, params: &[MockValue]) -> Result<String, String> {
            let mut result = self.sql.clone();
            let mut param_index = 0;

            while let Some(pos) = result.find('$') {
                if param_index >= params.len() {
                    return Err("Not enough parameters".to_string());
                }

                let end_pos = result[pos + 1..]
                    .find(|c: char| !c.is_ascii_digit())
                    .unwrap_or(result.len() - pos - 1)
                    + pos
                    + 1;
                let _param_marker = &result[pos..end_pos];
                let param_value = match &params[param_index] {
                    MockValue::Integer(i) => i.to_string(),
                    MockValue::Text(s) => format!("'{}'", s.replace('\'', "''")),
                    MockValue::Boolean(b) => b.to_string(),
                    MockValue::Null => "NULL".to_string(),
                };

                result.replace_range(pos..end_pos, &param_value);
                param_index += 1;
            }

            Ok(result)
        }
    }

    impl MockValue {
        fn type_name(&self) -> String {
            match self {
                MockValue::Integer(_) => "INTEGER".to_string(),
                MockValue::Text(_) => "TEXT".to_string(),
                MockValue::Boolean(_) => "BOOLEAN".to_string(),
                MockValue::Null => "NULL".to_string(),
            }
        }
    }

    #[derive(Debug, Clone)]
    pub struct MockConnection {
        pub id: u64,
        pub is_valid: bool,
        pub in_transaction: bool,
        pub last_activity: SystemTime,
        pub query_count: u64,
    }

    impl MockConnection {
        pub fn new(id: u64) -> Self {
            Self {
                id,
                is_valid: true,
                in_transaction: false,
                last_activity: SystemTime::now(),
                query_count: 0,
            }
        }

        pub fn is_healthy(&self) -> bool {
            self.is_valid
                && !self.in_transaction
                && self.last_activity.elapsed().unwrap_or(Duration::MAX) < Duration::from_secs(300)
        }

        pub fn execute_query(&mut self) {
            self.query_count += 1;
            self.last_activity = SystemTime::now();
        }

        pub fn begin_transaction(&mut self) {
            self.in_transaction = true;
        }

        pub fn commit_transaction(&mut self) {
            self.in_transaction = false;
        }

        pub fn rollback_transaction(&mut self) {
            self.in_transaction = false;
        }
    }

    #[derive(Debug)]
    pub struct MockConnectionPool {
        pub max_size: usize,
        pub idle_connections: Arc<Mutex<VecDeque<MockConnection>>>,
        pub active_connections: Arc<Mutex<HashMap<u64, MockConnection>>>,
        pub next_connection_id: Arc<Mutex<u64>>,
        pub stats: Arc<Mutex<PoolStats>>,
    }

    #[derive(Debug, Default)]
    pub struct PoolStats {
        pub total_acquired: u64,
        pub total_returned: u64,
        pub current_active: usize,
        pub current_idle: usize,
    }

    impl MockConnectionPool {
        pub fn new(max_size: usize) -> Self {
            Self {
                max_size,
                idle_connections: Arc::new(Mutex::new(VecDeque::new())),
                active_connections: Arc::new(Mutex::new(HashMap::new())),
                next_connection_id: Arc::new(Mutex::new(1)),
                stats: Arc::new(Mutex::new(PoolStats::default())),
            }
        }

        pub fn acquire(&self) -> Option<MockConnection> {
            let mut idle = self.idle_connections.lock().unwrap();
            let mut active = self.active_connections.lock().unwrap();
            let mut stats = self.stats.lock().unwrap();

            if let Some(mut conn) = idle.pop_front() {
                if conn.is_healthy() {
                    conn.last_activity = SystemTime::now();
                    let conn_id = conn.id;
                    active.insert(conn_id, conn.clone());
                    stats.total_acquired += 1;
                    stats.current_active = active.len();
                    stats.current_idle = idle.len();
                    return Some(conn);
                }
            }

            if active.len() < self.max_size {
                let mut next_id = self.next_connection_id.lock().unwrap();
                let conn = MockConnection::new(*next_id);
                *next_id += 1;
                let conn_id = conn.id;
                active.insert(conn_id, conn.clone());
                stats.total_acquired += 1;
                stats.current_active = active.len();
                stats.current_idle = idle.len();
                Some(conn)
            } else {
                None
            }
        }

        pub fn return_connection(&self, mut conn: MockConnection) {
            let mut idle = self.idle_connections.lock().unwrap();
            let mut active = self.active_connections.lock().unwrap();
            let mut stats = self.stats.lock().unwrap();

            active.remove(&conn.id);

            if conn.is_healthy() {
                conn.last_activity = SystemTime::now();
                idle.push_back(conn);
            }

            stats.total_returned += 1;
            stats.current_active = active.len();
            stats.current_idle = idle.len();
        }

        pub fn get_stats(&self) -> PoolStats {
            let stats = self.stats.lock().unwrap();
            PoolStats {
                total_acquired: stats.total_acquired,
                total_returned: stats.total_returned,
                current_active: stats.current_active,
                current_idle: stats.current_idle,
            }
        }
    }

    #[derive(Debug, Clone)]
    pub struct MockTransaction {
        pub id: String,
        pub isolation_level: IsolationLevel,
        pub read_only: bool,
        pub savepoints: Vec<String>,
        pub operations: Vec<String>,
        pub committed: bool,
        pub rolled_back: bool,
    }

    #[derive(Debug, Clone, PartialEq)]
    pub enum IsolationLevel {
        ReadUncommitted,
        ReadCommitted,
        RepeatableRead,
        Serializable,
    }

    impl MockTransaction {
        pub fn new(id: String, isolation_level: IsolationLevel, read_only: bool) -> Self {
            Self {
                id,
                isolation_level,
                read_only,
                savepoints: Vec::new(),
                operations: Vec::new(),
                committed: false,
                rolled_back: false,
            }
        }

        pub fn create_savepoint(&mut self, name: String) {
            self.savepoints.push(name);
        }

        pub fn rollback_to_savepoint(&mut self, name: &str) -> bool {
            if let Some(pos) = self.savepoints.iter().rposition(|sp| sp == name) {
                self.savepoints.truncate(pos + 1);
                true
            } else {
                false
            }
        }

        pub fn execute_operation(&mut self, operation: String) {
            if !self.committed && !self.rolled_back {
                self.operations.push(operation);
            }
        }

        pub fn commit(&mut self) -> bool {
            if !self.rolled_back {
                self.committed = true;
                true
            } else {
                false
            }
        }

        pub fn rollback(&mut self) -> bool {
            if !self.committed {
                self.rolled_back = true;
                true
            } else {
                false
            }
        }

        pub fn can_read_uncommitted(&self, other: &MockTransaction) -> bool {
            matches!(self.isolation_level, IsolationLevel::ReadUncommitted) || other.committed
        }

        pub fn can_see_changes(
            &self,
            other: &MockTransaction,
            operation_timestamp: SystemTime,
        ) -> bool {
            match self.isolation_level {
                IsolationLevel::ReadUncommitted => true,
                IsolationLevel::ReadCommitted => other.committed,
                IsolationLevel::RepeatableRead => {
                    other.committed && operation_timestamp < SystemTime::now()
                }
                IsolationLevel::Serializable => other.committed && self.id < other.id,
            }
        }
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Metamorphic Relations: PostgreSQL SCRAM Authentication
    // ═══════════════════════════════════════════════════════════════════════════

    proptest! {
        /// **MR-SCRAMTranscriptDeterminism**: SCRAM-SHA-256 authentication transcripts
        /// are deterministic for the same username, password, salt, and iteration count.
        ///
        /// **Property**: For fixed auth inputs, multiple SCRAM handshakes should produce
        /// identical client/server message exchanges.
        ///
        /// **Catches**: Non-deterministic nonce generation, salt reuse, iteration count drift
        #[test]
        fn mr_scram_transcript_determinism(
            username in "[a-zA-Z][a-zA-Z0-9_]{2,15}",
            password in "[a-zA-Z0-9!@#$%]{8,20}",
            salt in prop::collection::vec(0u8..255u8, 16..32),
            iterations in 4096u32..8192u32
        ) {
            let transcript1 = MockSCRAMTranscript::new(&username, &password, salt.clone(), iterations);
            let transcript2 = MockSCRAMTranscript::new(&username, &password, salt.clone(), iterations);

            // Core determinism: same inputs → same client messages (modulo nonce generation)
            prop_assert!(transcript1.is_valid_transcript());
            prop_assert!(transcript2.is_valid_transcript());

            // Salt and iteration count must be identical
            prop_assert_eq!(transcript1.salt, transcript2.salt);
            prop_assert_eq!(transcript1.iterations, transcript2.iterations);

            // Server responses should be deterministic given client messages
            let iteration_marker = format!("i={iterations}");
            prop_assert!(transcript1.server_first_message.contains(&iteration_marker));
            prop_assert!(transcript2.server_first_message.contains(&iteration_marker));
        }
    }

    proptest! {
        /// **MR-AuthenticationIdempotency**: Successful authentication can be repeated
        /// with the same credentials without changing system state.
        ///
        /// **Property**: auth(credentials) → Success ⇒ auth(credentials) → Success
        ///
        /// **Catches**: State corruption after successful auth, session exhaustion
        #[test]
        fn mr_authentication_idempotency(
            username in "[a-zA-Z][a-zA-Z0-9_]{2,15}",
            password in "[a-zA-Z0-9!@#$%]{8,20}",
            salt in prop::collection::vec(0u8..255u8, 16..32),
            iterations in 4096u32..8192u32
        ) {
            let transcript1 = MockSCRAMTranscript::new(&username, &password, salt.clone(), iterations);
            let transcript2 = MockSCRAMTranscript::new(&username, &password, salt.clone(), iterations);

            let auth1_valid = transcript1.is_valid_transcript();
            let auth2_valid = transcript2.is_valid_transcript();

            // Idempotency: if first auth succeeds, second auth with same credentials must succeed
            if auth1_valid {
                prop_assert!(auth2_valid,
                    "Authentication idempotency failed: first auth succeeded but second failed");
            }

            // Credential consistency across attempts
            prop_assert_eq!(transcript1.salt, transcript2.salt);
            prop_assert_eq!(transcript1.iterations, transcript2.iterations);
        }
    }

    proptest! {
        /// **MR-SCRAMNonceMonotonicity**: Client nonces must be unique across concurrent
        /// authentication sessions to prevent replay attacks.
        ///
        /// **Property**: For simultaneous auth attempts, all client nonces are distinct
        ///
        /// **Catches**: Nonce reuse vulnerabilities, insufficient entropy
        #[test]
        fn mr_scram_nonce_monotonicity(
            usernames in prop::collection::vec("[a-zA-Z][a-zA-Z0-9_]{2,15}", 2..8),
            password in "[a-zA-Z0-9!@#$%]{8,20}",
            salt in prop::collection::vec(0u8..255u8, 16..32),
            iterations in 4096u32..8192u32
        ) {
            let mut client_nonces = HashSet::new();
            let mut transcripts = Vec::new();

            for username in &usernames {
                let transcript = MockSCRAMTranscript::new(username, &password, salt.clone(), iterations);

                // Extract client nonce from client_first_message
                if let Some(nonce_start) = transcript.client_first_message.find("r=") {
                    let nonce_part = &transcript.client_first_message[nonce_start+2..];
                    if let Some(nonce_end) = nonce_part.find(',') {
                        let nonce = &nonce_part[..nonce_end];
                        prop_assert!(client_nonces.insert(nonce.to_string()),
                            "Client nonce reuse detected: {}", nonce);
                    }
                }

                transcripts.push(transcript);
            }

            // Nonce uniqueness: all client nonces must be distinct
            prop_assert_eq!(client_nonces.len(), usernames.len(),
                "Expected {} unique nonces, got {}", usernames.len(), client_nonces.len());
        }
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Metamorphic Relations: Query Parsing Round-trips
    // ═══════════════════════════════════════════════════════════════════════════

    proptest! {
        /// **MR-QueryParseSerialize**: Parsing SQL and serializing back preserves semantics.
        ///
        /// **Property**: normalize(parse(serialize(query))) = normalize(parse(query))
        ///
        /// **Catches**: Parser/serializer mismatches, semantic drift, formatting bugs
        #[test]
        fn mr_query_parse_serialize(
            table_name in "[a-zA-Z][a-zA-Z0-9_]{2,15}",
            column_name in "[a-zA-Z][a-zA-Z0-9_]{2,15}",
            where_value in 1i64..1000000i64
        ) {
            let sql = format!("SELECT {} FROM {} WHERE id = {}", column_name, table_name, where_value);
            let query = MockQuery::new(&sql);

            let serialized = query.parse_and_serialize();
            let reparsed = MockQuery::new(&serialized);

            // Semantic preservation: normalized forms should be equivalent
            prop_assert_eq!(&query.normalized_form, &reparsed.normalized_form,
                "Parse-serialize round-trip changed semantics: '{}' vs '{}'",
                query.normalized_form, reparsed.normalized_form);

            // Structure preservation: both should contain the same components
            prop_assert!(serialized.contains(&table_name.to_uppercase()));
            prop_assert!(serialized.contains(&column_name.to_uppercase()));
            prop_assert!(serialized.contains(&where_value.to_string()));
        }
    }

    proptest! {
        /// **MR-ParameterBindingConsistency**: Parameterized queries bind consistently
        /// regardless of parameter binding order.
        ///
        /// **Property**: bind(query, [p1, p2]) semantically equivalent across parameter orders
        ///
        /// **Catches**: Parameter index corruption, type coercion bugs
        #[test]
        fn mr_parameter_binding_consistency(
            table_name in "[a-zA-Z][a-zA-Z0-9_]{2,15}",
            int_param in 1i64..1000i64,
            text_param in "[a-zA-Z]{3,20}"
        ) {
            let sql = format!("SELECT * FROM {} WHERE id = $1 AND name = $2", table_name);
            let query = MockQuery::new(&sql);

            let params1 = vec![MockValue::Integer(int_param), MockValue::Text(text_param.clone())];
            let params2 = vec![MockValue::Integer(int_param), MockValue::Text(text_param.clone())];

            let bound1 = query.bind_parameters(&params1).expect("Failed to bind parameters");
            let bound2 = query.bind_parameters(&params2).expect("Failed to bind parameters");

            // Consistency: same parameters should produce identical bound queries
            prop_assert_eq!(&bound1, &bound2,
                "Parameter binding inconsistency: '{}' vs '{}'", bound1, bound2);

            // Correctness: bound query should contain parameter values
            prop_assert!(bound1.contains(&int_param.to_string()));
            let text_literal = format!("'{text_param}'");
            prop_assert!(bound1.contains(&text_literal));
        }
    }

    proptest! {
        /// **MR-QueryNormalizationStability**: Query normalization is stable under
        /// repeated application.
        ///
        /// **Property**: normalize(normalize(query)) = normalize(query)
        ///
        /// **Catches**: Normalization convergence bugs, whitespace handling errors
        #[test]
        fn mr_query_normalization_stability(
            sql in "(?i)select [a-zA-Z_][a-zA-Z0-9_]* from [a-zA-Z_][a-zA-Z0-9_]*( where [a-zA-Z_][a-zA-Z0-9_]* = [0-9]+)?"
        ) {
            let query = MockQuery::new(&sql);
            let normalized_once = query.normalized_form.clone();

            let query_normalized = MockQuery::new(&normalized_once);
            let normalized_twice = query_normalized.normalized_form;

            // Stability: repeated normalization converges to fixed point
            prop_assert_eq!(&normalized_once, &normalized_twice,
                "Query normalization not stable: '{}' vs '{}'", normalized_once, normalized_twice);

            // Consistency: normalized form should be uppercase and whitespace-normalized
            let uppercase_once = normalized_once.to_uppercase();
            prop_assert_eq!(&normalized_once, &uppercase_once);
            prop_assert!(!normalized_once.contains("  "), "Normalized query contains double spaces");
        }
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Metamorphic Relations: Connection Pool Management
    // ═══════════════════════════════════════════════════════════════════════════

    proptest! {
        /// **MR-PoolReservationSymmetry**: Acquiring a connection from the pool and
        /// returning it maintains pool invariants.
        ///
        /// **Property**: acquire() → return() preserves total connection count
        ///
        /// **Catches**: Connection leaks, pool size corruption, state tracking bugs
        #[test]
        fn mr_pool_reservation_symmetry(
            max_size in 1usize..20usize,
            operations in prop::collection::vec(0u8..2u8, 1..50)
        ) {
            let pool = MockConnectionPool::new(max_size);
            let mut acquired_connections = Vec::new();

            let initial_stats = pool.get_stats();
            prop_assert_eq!(initial_stats.current_active + initial_stats.current_idle, 0);

            for &op in &operations {
                match op {
                    0 => {
                        // Acquire connection
                        if let Some(conn) = pool.acquire() {
                            acquired_connections.push(conn);
                        }
                    }
                    1 => {
                        // Return connection
                        if let Some(conn) = acquired_connections.pop() {
                            pool.return_connection(conn);
                        }
                    }
                    _ => unreachable!()
                }
            }

            // Return all remaining connections
            while let Some(conn) = acquired_connections.pop() {
                pool.return_connection(conn);
            }

            let final_stats = pool.get_stats();

            // Symmetry: total acquired should equal total returned
            prop_assert_eq!(final_stats.total_acquired, final_stats.total_returned,
                "Pool reservation asymmetry: {} acquired, {} returned",
                final_stats.total_acquired, final_stats.total_returned);

            // Invariants: no active connections, all returned to idle
            prop_assert_eq!(final_stats.current_active, 0);
            prop_assert!(final_stats.current_idle <= max_size);
        }
    }

    proptest! {
        /// **MR-ConnectionValidationConsistency**: Connection health checks are
        /// deterministic for the same connection state.
        ///
        /// **Property**: is_valid(conn) returns same result when connection state unchanged
        ///
        /// **Catches**: Non-deterministic validation, state corruption during checks
        #[test]
        fn mr_connection_validation_consistency(
            connection_id in 1u64..1000u64,
            is_valid in any::<bool>(),
            in_transaction in any::<bool>()
        ) {
            let mut conn = MockConnection::new(connection_id);
            conn.is_valid = is_valid;
            conn.in_transaction = in_transaction;

            // Record initial state
            let initial_health = conn.is_healthy();
            let initial_valid = conn.is_valid;
            let initial_transaction = conn.in_transaction;

            // Repeated validation should be consistent
            let health1 = conn.is_healthy();
            let health2 = conn.is_healthy();
            let health3 = conn.is_healthy();

            // Consistency: health check results must be identical
            prop_assert_eq!(health1, health2);
            prop_assert_eq!(health2, health3);
            prop_assert_eq!(health1, initial_health);

            // State preservation: validation shouldn't mutate connection state
            prop_assert_eq!(conn.is_valid, initial_valid);
            prop_assert_eq!(conn.in_transaction, initial_transaction);
        }
    }

    proptest! {
        /// **MR-HealthCheckStability**: Health checks are idempotent when connection
        /// state remains unchanged.
        ///
        /// **Property**: health_check(conn) repeated gives same result if state unchanged
        ///
        /// **Catches**: Health check side effects, state pollution
        #[test]
        fn mr_health_check_stability(
            connection_id in 1u64..1000u64,
            query_count in 0u64..100u64
        ) {
            let mut conn = MockConnection::new(connection_id);
            conn.query_count = query_count;

            let health_before = conn.is_healthy();
            let valid_before = conn.is_valid;
            let transaction_before = conn.in_transaction;
            let query_count_before = conn.query_count;

            // Perform multiple health checks
            let health1 = conn.is_healthy();
            let health2 = conn.is_healthy();
            let health3 = conn.is_healthy();

            // Stability: health check results must be stable
            prop_assert_eq!(health1, health2);
            prop_assert_eq!(health2, health3);
            prop_assert_eq!(health1, health_before);

            // Idempotency: health checks must not modify connection state
            prop_assert_eq!(conn.is_valid, valid_before);
            prop_assert_eq!(conn.in_transaction, transaction_before);
            prop_assert_eq!(conn.query_count, query_count_before);
        }
    }

    proptest! {
        /// **MR-PoolSizeBounds**: Connection pool never exceeds configured limits
        /// under concurrent acquisition attempts.
        ///
        /// **Property**: active_connections + idle_connections ≤ max_pool_size
        ///
        /// **Catches**: Race conditions in pool size enforcement, limit violations
        #[test]
        fn mr_pool_size_bounds(
            max_size in 1usize..20usize,
            acquire_attempts in 1usize..100usize
        ) {
            let pool = MockConnectionPool::new(max_size);
            let mut acquired_connections = Vec::new();

            // Attempt to acquire more connections than pool limit
            for _ in 0..acquire_attempts {
                if let Some(conn) = pool.acquire() {
                    acquired_connections.push(conn);
                }

                let stats = pool.get_stats();
                // Bounds check: never exceed max pool size
                prop_assert!(stats.current_active <= max_size,
                    "Pool size exceeded: {} active connections, max {}",
                    stats.current_active, max_size);
                prop_assert!(stats.current_active + stats.current_idle <= max_size,
                    "Total connections exceeded: {} total, max {}",
                    stats.current_active + stats.current_idle, max_size);
            }

            // Verify we acquired at most max_size connections
            prop_assert!(acquired_connections.len() <= max_size,
                "Acquired {} connections, max pool size {}",
                acquired_connections.len(), max_size);

            // Return connections and verify bounds still hold
            while let Some(conn) = acquired_connections.pop() {
                pool.return_connection(conn);
                let stats = pool.get_stats();
                prop_assert!(stats.current_active + stats.current_idle <= max_size);
            }
        }
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Metamorphic Relations: Transaction Isolation Properties
    // ═══════════════════════════════════════════════════════════════════════════

    proptest! {
        /// **MR-TransactionACIDCommutivity**: Independent transactions can be reordered
        /// without affecting final database state.
        ///
        /// **Property**: execute(T1); execute(T2) ≡ execute(T2); execute(T1) for independent T1, T2
        ///
        /// **Catches**: Phantom dependencies, isolation level violations
        #[test]
        fn mr_transaction_acid_commutivity(
            isolation_level in prop::sample::select(vec![
                IsolationLevel::ReadCommitted,
                IsolationLevel::RepeatableRead,
                IsolationLevel::Serializable
            ]),
            tx1_ops in prop::collection::vec("(INSERT|UPDATE|DELETE) [A-Z]+", 1..5),
            tx2_ops in prop::collection::vec("(INSERT|UPDATE|DELETE) [A-Z]+", 1..5)
        ) {
            let mut tx1 = MockTransaction::new("tx1".to_string(), isolation_level.clone(), false);
            let mut tx2 = MockTransaction::new("tx2".to_string(), isolation_level, false);

            // Execute T1 then T2
            for op in &tx1_ops {
                tx1.execute_operation(op.clone());
            }
            tx1.commit();

            for op in &tx2_ops {
                tx2.execute_operation(op.clone());
            }
            tx2.commit();

            let state1_tx1_ops = tx1.operations.len();
            let state1_tx2_ops = tx2.operations.len();

            // Reset and execute T2 then T1
            let mut tx1_alt = MockTransaction::new("tx1".to_string(), tx1.isolation_level.clone(), false);
            let mut tx2_alt = MockTransaction::new("tx2".to_string(), tx2.isolation_level.clone(), false);

            for op in &tx2_ops {
                tx2_alt.execute_operation(op.clone());
            }
            tx2_alt.commit();

            for op in &tx1_ops {
                tx1_alt.execute_operation(op.clone());
            }
            tx1_alt.commit();

            let state2_tx1_ops = tx1_alt.operations.len();
            let state2_tx2_ops = tx2_alt.operations.len();

            // Commutativity: operation counts should be preserved regardless of order
            prop_assert_eq!(state1_tx1_ops, state2_tx1_ops);
            prop_assert_eq!(state1_tx2_ops, state2_tx2_ops);

            // Both transactions should commit successfully in both orders
            prop_assert!(tx1.committed && tx2.committed);
            prop_assert!(tx1_alt.committed && tx2_alt.committed);
        }
    }

    proptest! {
        /// **MR-SavepointNesting**: Nested savepoints follow strict stack discipline
        /// with LIFO rollback semantics.
        ///
        /// **Property**: rollback_to(inner) removes outer savepoints; rollback_to(outer) preserves inner
        ///
        /// **Catches**: Savepoint stack corruption, incorrect nesting behavior
        #[test]
        fn mr_savepoint_nesting(
            savepoint_names in prop::collection::vec("[a-zA-Z][a-zA-Z0-9_]{1,10}", 2..8)
        ) {
            let mut tx = MockTransaction::new("nested_tx".to_string(), IsolationLevel::ReadCommitted, false);

            // Create nested savepoints
            for name in &savepoint_names {
                tx.create_savepoint(name.clone());
            }

            let initial_depth = tx.savepoints.len();
            prop_assert_eq!(initial_depth, savepoint_names.len());

            // Test LIFO rollback: rolling back to an inner savepoint should remove outer ones
            if savepoint_names.len() >= 2 {
                let middle_savepoint = &savepoint_names[savepoint_names.len() / 2];
                let rollback_success = tx.rollback_to_savepoint(middle_savepoint);

                prop_assert!(rollback_success, "Failed to rollback to savepoint '{}'", middle_savepoint);

                // Stack discipline: savepoints after the rollback target should be removed
                let expected_depth = savepoint_names.iter().position(|sp| sp == middle_savepoint).unwrap() + 1;
                prop_assert_eq!(tx.savepoints.len(), expected_depth,
                    "Savepoint stack depth wrong after rollback: expected {}, got {}",
                    expected_depth, tx.savepoints.len());

                // Verify stack integrity: remaining savepoints should be in correct order
                for (i, expected_sp) in savepoint_names.iter().take(expected_depth).enumerate() {
                    prop_assert_eq!(&tx.savepoints[i], expected_sp);
                }
            }
        }
    }

    proptest! {
        /// **MR-IsolationLevelMonotonicity**: Higher isolation levels preserve all
        /// guarantees provided by lower isolation levels.
        ///
        /// **Property**: guarantees(ReadCommitted) ⊆ guarantees(RepeatableRead) ⊆ guarantees(Serializable)
        ///
        /// **Catches**: Isolation level regression, insufficient isolation guarantees
        #[test]
        fn mr_isolation_level_monotonicity(
            tx1_level in prop::sample::select(vec![
                IsolationLevel::ReadCommitted,
                IsolationLevel::RepeatableRead,
                IsolationLevel::Serializable
            ]),
            tx2_level in prop::sample::select(vec![
                IsolationLevel::ReadCommitted,
                IsolationLevel::RepeatableRead,
                IsolationLevel::Serializable
            ])
        ) {
            let tx1 = MockTransaction::new("tx1".to_string(), tx1_level.clone(), false);
            let tx2_committed = MockTransaction::new("tx2_committed".to_string(), tx2_level, false);
            let mut tx2_committed = tx2_committed;
            tx2_committed.commit();

            let operation_time = SystemTime::now();

            // Test visibility guarantees at different isolation levels
            let can_read_uncommitted = tx1.can_read_uncommitted(&tx2_committed);
            let can_see_changes = tx1.can_see_changes(&tx2_committed, operation_time);

            // Monotonicity: higher isolation levels should be at least as restrictive
            match tx1_level {
                IsolationLevel::ReadUncommitted => {
                    // Most permissive: should see committed and uncommitted
                    prop_assert!(can_read_uncommitted || can_see_changes);
                }
                IsolationLevel::ReadCommitted => {
                    // Should only see committed transactions
                    if can_see_changes {
                        prop_assert!(tx2_committed.committed);
                    }
                }
                IsolationLevel::RepeatableRead => {
                    // Should provide consistent snapshots
                    if can_see_changes {
                        prop_assert!(tx2_committed.committed);
                    }
                }
                IsolationLevel::Serializable => {
                    // Most restrictive: additional serialization constraints
                    if can_see_changes {
                        prop_assert!(tx2_committed.committed);
                        // Additional constraint: transaction ordering
                        prop_assert!(tx1.id < tx2_committed.id || tx1.id > tx2_committed.id);
                    }
                }
            }
        }
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Validation Tests
    // ═══════════════════════════════════════════════════════════════════════════

    #[test]
    fn test_scram_transcript_mock_validity() {
        let transcript = MockSCRAMTranscript::new("testuser", "testpass", vec![1, 2, 3, 4], 4096);
        assert!(transcript.is_valid_transcript());
        assert_eq!(transcript.iterations, 4096);
        assert_eq!(transcript.salt, vec![1, 2, 3, 4]);
    }

    #[test]
    fn test_query_parse_serialize_mock() {
        let query = MockQuery::new("SELECT id FROM users WHERE active = true");
        let serialized = query.parse_and_serialize();
        assert!(serialized.contains("SELECT"));
        assert!(serialized.contains("USERS"));
        assert!(serialized.contains("WHERE"));
    }

    #[test]
    fn test_connection_pool_basic_operations() {
        let pool = MockConnectionPool::new(2);

        let conn1 = pool.acquire().expect("Should acquire first connection");
        assert_eq!(conn1.id, 1);

        let conn2 = pool.acquire().expect("Should acquire second connection");
        assert_eq!(conn2.id, 2);

        // Pool exhausted
        assert!(pool.acquire().is_none());

        // Return connection
        pool.return_connection(conn1);

        // Should be able to acquire again
        assert!(pool.acquire().is_some());
    }

    #[test]
    fn test_transaction_savepoint_stack() {
        let mut tx =
            MockTransaction::new("test_tx".to_string(), IsolationLevel::ReadCommitted, false);

        tx.create_savepoint("sp1".to_string());
        tx.create_savepoint("sp2".to_string());
        tx.create_savepoint("sp3".to_string());

        assert_eq!(tx.savepoints.len(), 3);

        // Rollback to middle savepoint
        assert!(tx.rollback_to_savepoint("sp2"));
        assert_eq!(tx.savepoints.len(), 2);
        assert_eq!(tx.savepoints[1], "sp2");
    }
}