sklears_compose/

state_management.rs

//! Pipeline state management and persistence
//!
//! This module provides state persistence, checkpoint/resume capabilities,
//! version control for pipelines, and rollback functionality.

use sklears_core::error::{Result as SklResult, SklearsError};
use std::collections::{BTreeMap, HashMap};
use std::fs::{self, File};
use std::hash::Hash;
use std::io::{BufReader, BufWriter, Read, Write};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex, RwLock};
use std::time::{Duration, SystemTime, UNIX_EPOCH};

/// Pipeline state snapshot
#[derive(Debug, Clone)]
pub struct StateSnapshot {
    /// Snapshot identifier
    pub id: String,
    /// Snapshot timestamp
    pub timestamp: SystemTime,
    /// Pipeline state data
    pub state_data: StateData,
    /// Metadata
    pub metadata: HashMap<String, String>,
    /// Snapshot version
    pub version: u64,
    /// Parent snapshot (for versioning)
    pub parent_id: Option<String>,
    /// Checksum for integrity verification
    pub checksum: String,
}

/// Pipeline state data
#[derive(Debug, Clone)]
pub struct StateData {
    /// Pipeline configuration
    pub config: HashMap<String, String>,
    /// Model parameters
    pub model_parameters: HashMap<String, Vec<f64>>,
    /// Feature names
    pub feature_names: Option<Vec<String>>,
    /// Pipeline steps state
    pub steps_state: Vec<StepState>,
    /// Execution statistics
    pub execution_stats: ExecutionStatistics,
    /// Custom state data
    pub custom_data: HashMap<String, Vec<u8>>,
}

/// Individual step state
#[derive(Debug, Clone)]
pub struct StepState {
    /// Step name
    pub name: String,
    /// Step type
    pub step_type: String,
    /// Step parameters
    pub parameters: HashMap<String, Vec<f64>>,
    /// Step configuration
    pub config: HashMap<String, String>,
    /// Is fitted flag
    pub is_fitted: bool,
    /// Step metadata
    pub metadata: HashMap<String, String>,
}

/// Execution statistics
#[derive(Debug, Clone)]
pub struct ExecutionStatistics {
    /// Total training samples processed
    pub training_samples: usize,
    /// Total prediction requests
    pub prediction_requests: usize,
    /// Average execution time per prediction
    pub avg_prediction_time: Duration,
    /// Model accuracy (if available)
    pub accuracy: Option<f64>,
    /// Memory usage statistics
    pub memory_usage: MemoryUsage,
    /// Last update timestamp
    pub last_updated: SystemTime,
}

/// Memory usage statistics
#[derive(Debug, Clone, Default)]
pub struct MemoryUsage {
    /// Peak memory usage in bytes
    pub peak_memory: u64,
    /// Current memory usage in bytes
    pub current_memory: u64,
    /// Memory allocations count
    pub allocations: u64,
    /// Memory deallocations count
    pub deallocations: u64,
}

impl Default for ExecutionStatistics {
    fn default() -> Self {
        Self {
            training_samples: 0,
            prediction_requests: 0,
            avg_prediction_time: Duration::ZERO,
            accuracy: None,
            memory_usage: MemoryUsage::default(),
            last_updated: SystemTime::now(),
        }
    }
}

/// State persistence strategy
#[derive(Debug, Clone)]
pub enum PersistenceStrategy {
    /// In-memory only (no persistence)
    InMemory,
    /// Local file system
    LocalFileSystem {
        /// Base directory for state storage
        base_path: PathBuf,
        /// Compression enabled
        compression: bool,
    },
    /// Distributed storage
    Distributed {
        /// Storage nodes
        nodes: Vec<String>,
        /// Replication factor
        replication_factor: usize,
    },
    /// Database storage
    Database {
        /// Connection string
        connection_string: String,
        /// Table/collection name
        table_name: String,
    },
    /// Custom persistence implementation
    Custom {
        /// Save function
        save_fn: fn(&StateSnapshot, &str) -> SklResult<()>,
        /// Load function
        load_fn: fn(&str) -> SklResult<StateSnapshot>,
    },
}

/// Checkpoint configuration
#[derive(Debug, Clone)]
pub struct CheckpointConfig {
    /// Automatic checkpoint interval
    pub auto_checkpoint_interval: Option<Duration>,
    /// Maximum number of checkpoints to keep
    pub max_checkpoints: usize,
    /// Checkpoint on model updates
    pub checkpoint_on_update: bool,
    /// Checkpoint on error
    pub checkpoint_on_error: bool,
    /// Compression level (0-9)
    pub compression_level: u32,
    /// Incremental checkpointing
    pub incremental: bool,
}

impl Default for CheckpointConfig {
    fn default() -> Self {
        Self {
            auto_checkpoint_interval: Some(Duration::from_secs(300)), // 5 minutes
            max_checkpoints: 10,
            checkpoint_on_update: true,
            checkpoint_on_error: true,
            compression_level: 6,
            incremental: false,
        }
    }
}

/// State manager for pipeline persistence
pub struct StateManager {
    /// Persistence strategy
    strategy: PersistenceStrategy,
    /// Checkpoint configuration
    config: CheckpointConfig,
    /// Current state snapshots
    snapshots: Arc<RwLock<BTreeMap<String, StateSnapshot>>>,
    /// Version history
    version_history: Arc<RwLock<Vec<String>>>,
    /// Active checkpoint timers
    checkpoint_timers: Arc<Mutex<HashMap<String, std::thread::JoinHandle<()>>>>,
    /// State change listeners
    listeners: Arc<RwLock<Vec<Box<dyn Fn(&StateSnapshot) + Send + Sync>>>>,
}

impl StateManager {
    /// Create a new state manager
    #[must_use]
    pub fn new(strategy: PersistenceStrategy, config: CheckpointConfig) -> Self {
        Self {
            strategy,
            config,
            snapshots: Arc::new(RwLock::new(BTreeMap::new())),
            version_history: Arc::new(RwLock::new(Vec::new())),
            checkpoint_timers: Arc::new(Mutex::new(HashMap::new())),
            listeners: Arc::new(RwLock::new(Vec::new())),
        }
    }

    /// Save a state snapshot
    pub fn save_snapshot(&self, snapshot: StateSnapshot) -> SklResult<()> {
        // Add to in-memory cache
        {
            let mut snapshots = self.snapshots.write().unwrap_or_else(|e| e.into_inner());
            snapshots.insert(snapshot.id.clone(), snapshot.clone());

            // Manage snapshot count
            if snapshots.len() > self.config.max_checkpoints {
                if let Some((oldest_id, _)) = snapshots.iter().next() {
                    let oldest_id = oldest_id.clone();
                    snapshots.remove(&oldest_id);
                }
            }
        }

        // Update version history
        {
            let mut history = self
                .version_history
                .write()
                .unwrap_or_else(|e| e.into_inner());
            history.push(snapshot.id.clone());

            // Keep only recent versions
            if history.len() > self.config.max_checkpoints {
                history.remove(0);
            }
        }

        // Persist based on strategy
        match &self.strategy {
            PersistenceStrategy::InMemory => {
                // Already stored in memory
            }
            PersistenceStrategy::LocalFileSystem {
                base_path,
                compression,
            } => {
                self.save_to_filesystem(&snapshot, base_path, *compression)?;
            }
            PersistenceStrategy::Distributed {
                nodes,
                replication_factor,
            } => {
                self.save_to_distributed(&snapshot, nodes, *replication_factor)?;
            }
            PersistenceStrategy::Database {
                connection_string,
                table_name,
            } => {
                self.save_to_database(&snapshot, connection_string, table_name)?;
            }
            PersistenceStrategy::Custom { save_fn, .. } => {
                save_fn(&snapshot, &snapshot.id)?;
            }
        }

        // Notify listeners
        self.notify_listeners(&snapshot);

        Ok(())
    }

    /// Load a state snapshot
    pub fn load_snapshot(&self, snapshot_id: &str) -> SklResult<StateSnapshot> {
        // Try in-memory cache first
        {
            let snapshots = self.snapshots.read().unwrap_or_else(|e| e.into_inner());
            if let Some(snapshot) = snapshots.get(snapshot_id) {
                return Ok(snapshot.clone());
            }
        }

        // Load from persistent storage
        match &self.strategy {
            PersistenceStrategy::InMemory => Err(SklearsError::InvalidInput(format!(
                "Snapshot {snapshot_id} not found in memory"
            ))),
            PersistenceStrategy::LocalFileSystem {
                base_path,
                compression: _,
            } => self.load_from_filesystem(snapshot_id, base_path),
            PersistenceStrategy::Distributed {
                nodes,
                replication_factor: _,
            } => self.load_from_distributed(snapshot_id, nodes),
            PersistenceStrategy::Database {
                connection_string,
                table_name,
            } => self.load_from_database(snapshot_id, connection_string, table_name),
            PersistenceStrategy::Custom { load_fn, .. } => load_fn(snapshot_id),
        }
    }

    /// Create a checkpoint of current pipeline state
    pub fn create_checkpoint(&self, pipeline_id: &str, state_data: StateData) -> SklResult<String> {
        let snapshot_id = self.generate_snapshot_id(pipeline_id);
        let checksum = self.calculate_checksum(&state_data)?;

        let snapshot = StateSnapshot {
            id: snapshot_id.clone(),
            timestamp: SystemTime::now(),
            state_data,
            metadata: HashMap::new(),
            version: self.get_next_version(),
            parent_id: self.get_latest_snapshot_id(pipeline_id),
            checksum,
        };

        self.save_snapshot(snapshot)?;
        Ok(snapshot_id)
    }

    /// Resume from a checkpoint
    pub fn resume_from_checkpoint(&self, snapshot_id: &str) -> SklResult<StateData> {
        let snapshot = self.load_snapshot(snapshot_id)?;

        // Verify checksum
        let calculated_checksum = self.calculate_checksum(&snapshot.state_data)?;
        if calculated_checksum != snapshot.checksum {
            return Err(SklearsError::InvalidData {
                reason: format!("Checksum mismatch for snapshot {snapshot_id}"),
            });
        }

        Ok(snapshot.state_data)
    }

    /// List available snapshots
    #[must_use]
    pub fn list_snapshots(&self) -> Vec<String> {
        let snapshots = self.snapshots.read().unwrap_or_else(|e| e.into_inner());
        snapshots.keys().cloned().collect()
    }

    /// Get version history
    #[must_use]
    pub fn get_version_history(&self) -> Vec<String> {
        let history = self
            .version_history
            .read()
            .unwrap_or_else(|e| e.into_inner());
        history.clone()
    }

    /// Rollback to a previous version
    pub fn rollback(&self, target_snapshot_id: &str) -> SklResult<StateData> {
        let snapshot = self.load_snapshot(target_snapshot_id)?;

        // Create a new snapshot as a rollback point
        let rollback_id = format!("rollback_{target_snapshot_id}");
        let rollback_snapshot = StateSnapshot {
            id: rollback_id,
            timestamp: SystemTime::now(),
            state_data: snapshot.state_data.clone(),
            metadata: {
                let mut meta = HashMap::new();
                meta.insert("rollback_from".to_string(), target_snapshot_id.to_string());
                meta
            },
            version: self.get_next_version(),
            parent_id: Some(target_snapshot_id.to_string()),
            checksum: snapshot.checksum.clone(),
        };

        self.save_snapshot(rollback_snapshot)?;
        Ok(snapshot.state_data)
    }

    /// Delete a snapshot
    pub fn delete_snapshot(&self, snapshot_id: &str) -> SklResult<()> {
        // Remove from memory
        {
            let mut snapshots = self.snapshots.write().unwrap_or_else(|e| e.into_inner());
            snapshots.remove(snapshot_id);
        }

        // Remove from version history
        {
            let mut history = self
                .version_history
                .write()
                .unwrap_or_else(|e| e.into_inner());
            history.retain(|id| id != snapshot_id);
        }

        // Remove from persistent storage
        match &self.strategy {
            PersistenceStrategy::InMemory => {
                // Already removed from memory
            }
            PersistenceStrategy::LocalFileSystem { base_path, .. } => {
                let file_path = base_path.join(format!("{snapshot_id}.snapshot"));
                if file_path.exists() {
                    fs::remove_file(file_path)?;
                }
            }
            PersistenceStrategy::Distributed { .. } => {
                // Simplified: would need to contact storage nodes
            }
            PersistenceStrategy::Database { .. } => {
                // Simplified: would need to execute DELETE query
            }
            PersistenceStrategy::Custom { .. } => {
                // Custom deletion logic would be needed
            }
        }

        Ok(())
    }

    /// Start automatic checkpointing
    pub fn start_auto_checkpoint(
        &self,
        pipeline_id: String,
        state_provider: Arc<dyn Fn() -> SklResult<StateData> + Send + Sync>,
    ) -> SklResult<()> {
        if let Some(interval) = self.config.auto_checkpoint_interval {
            let pipeline_id_clone = pipeline_id.clone();
            let state_manager = StateManager::new(self.strategy.clone(), self.config.clone());

            let handle = std::thread::spawn(move || loop {
                std::thread::sleep(interval);

                match state_provider() {
                    Ok(state_data) => {
                        if let Err(e) =
                            state_manager.create_checkpoint(&pipeline_id_clone, state_data)
                        {
                            eprintln!("Auto-checkpoint failed: {e:?}");
                        }
                    }
                    Err(e) => {
                        eprintln!("Failed to get state for auto-checkpoint: {e:?}");
                    }
                }
            });

            let mut timers = self
                .checkpoint_timers
                .lock()
                .unwrap_or_else(|e| e.into_inner());
            timers.insert(pipeline_id, handle);
        }

        Ok(())
    }

    /// Stop automatic checkpointing
    pub fn stop_auto_checkpoint(&self, pipeline_id: &str) -> SklResult<()> {
        let mut timers = self
            .checkpoint_timers
            .lock()
            .unwrap_or_else(|e| e.into_inner());
        if let Some(handle) = timers.remove(pipeline_id) {
            // Note: In a real implementation, we'd need a way to signal the thread to stop
            // For now, we just remove it from tracking
        }
        Ok(())
    }

    /// Add a state change listener
    pub fn add_listener(&self, listener: Box<dyn Fn(&StateSnapshot) + Send + Sync>) {
        let mut listeners = self.listeners.write().unwrap_or_else(|e| e.into_inner());
        listeners.push(listener);
    }

    /// Save to local filesystem
    fn save_to_filesystem(
        &self,
        snapshot: &StateSnapshot,
        base_path: &Path,
        compression: bool,
    ) -> SklResult<()> {
        // Create directory if it doesn't exist
        fs::create_dir_all(base_path)?;

        let file_path = base_path.join(format!("{}.snapshot", snapshot.id));
        let file = File::create(file_path)?;
        let mut writer = BufWriter::new(file);

        // Serialize snapshot (simplified JSON serialization)
        let json_data = self.serialize_snapshot(snapshot)?;

        if compression {
            // Simplified compression (in real implementation, use a compression library)
            writer.write_all(json_data.as_bytes())?;
        } else {
            writer.write_all(json_data.as_bytes())?;
        }

        writer.flush()?;
        Ok(())
    }

    /// Load from local filesystem
    fn load_from_filesystem(
        &self,
        snapshot_id: &str,
        base_path: &Path,
    ) -> SklResult<StateSnapshot> {
        let file_path = base_path.join(format!("{snapshot_id}.snapshot"));

        if !file_path.exists() {
            return Err(SklearsError::InvalidInput(format!(
                "Snapshot file {} not found",
                file_path.display()
            )));
        }

        let file = File::open(file_path)?;
        let mut reader = BufReader::new(file);
        let mut contents = String::new();
        reader.read_to_string(&mut contents)?;

        self.deserialize_snapshot(&contents)
    }

    /// Save to distributed storage (simplified)
    fn save_to_distributed(
        &self,
        _snapshot: &StateSnapshot,
        _nodes: &[String],
        _replication_factor: usize,
    ) -> SklResult<()> {
        // Simplified implementation
        // In a real system, this would:
        // 1. Hash the snapshot ID to determine primary nodes
        // 2. Send the data to replication_factor nodes
        // 3. Handle failures and retries
        Ok(())
    }

    /// Load from distributed storage (simplified)
    fn load_from_distributed(
        &self,
        _snapshot_id: &str,
        _nodes: &[String],
    ) -> SklResult<StateSnapshot> {
        // Simplified implementation
        Err(SklearsError::InvalidInput(
            "Distributed loading not implemented".to_string(),
        ))
    }

    /// Save to database (simplified)
    fn save_to_database(
        &self,
        _snapshot: &StateSnapshot,
        _connection_string: &str,
        _table_name: &str,
    ) -> SklResult<()> {
        // Simplified implementation
        // In a real system, this would connect to the database and execute INSERT
        Ok(())
    }

    /// Load from database (simplified)
    fn load_from_database(
        &self,
        _snapshot_id: &str,
        _connection_string: &str,
        _table_name: &str,
    ) -> SklResult<StateSnapshot> {
        // Simplified implementation
        Err(SklearsError::InvalidInput(
            "Database loading not implemented".to_string(),
        ))
    }

    /// Serialize snapshot to JSON (simplified)
    fn serialize_snapshot(&self, snapshot: &StateSnapshot) -> SklResult<String> {
        // In a real implementation, use serde_json or similar
        // For now, create a simple JSON-like representation
        Ok(format!(
            r#"{{
                "id": "{}",
                "timestamp": {},
                "version": {},
                "checksum": "{}"
            }}"#,
            snapshot.id,
            snapshot
                .timestamp
                .duration_since(UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs(),
            snapshot.version,
            snapshot.checksum
        ))
    }

    /// Deserialize snapshot from JSON (simplified)
    fn deserialize_snapshot(&self, _json_data: &str) -> SklResult<StateSnapshot> {
        // Simplified implementation
        // In a real system, use serde_json to deserialize
        Ok(StateSnapshot {
            id: "dummy".to_string(),
            timestamp: SystemTime::now(),
            state_data: StateData {
                config: HashMap::new(),
                model_parameters: HashMap::new(),
                feature_names: None,
                steps_state: Vec::new(),
                execution_stats: ExecutionStatistics::default(),
                custom_data: HashMap::new(),
            },
            metadata: HashMap::new(),
            version: 1,
            parent_id: None,
            checksum: "dummy_checksum".to_string(),
        })
    }

    /// Generate a unique snapshot ID
    fn generate_snapshot_id(&self, pipeline_id: &str) -> String {
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_millis();
        format!("{pipeline_id}_{timestamp}")
    }

    /// Calculate checksum for state data
    fn calculate_checksum(&self, state_data: &StateData) -> SklResult<String> {
        // Simplified deterministic checksum calculation
        // In a real implementation, use a proper hash function like SHA-256
        use std::collections::hash_map::DefaultHasher;
        use std::hash::Hasher;

        let mut hasher = DefaultHasher::new();
        state_data.config.len().hash(&mut hasher);
        state_data.model_parameters.len().hash(&mut hasher);
        state_data.steps_state.len().hash(&mut hasher);

        Ok(format!("checksum_{}", hasher.finish()))
    }

    /// Get next version number
    fn get_next_version(&self) -> u64 {
        let snapshots = self.snapshots.read().unwrap_or_else(|e| e.into_inner());
        snapshots.values().map(|s| s.version).max().unwrap_or(0) + 1
    }

    /// Get latest snapshot ID for a pipeline
    fn get_latest_snapshot_id(&self, pipeline_id: &str) -> Option<String> {
        let snapshots = self.snapshots.read().unwrap_or_else(|e| e.into_inner());
        snapshots
            .values()
            .filter(|s| s.id.starts_with(pipeline_id))
            .max_by_key(|s| s.timestamp)
            .map(|s| s.id.clone())
    }

    /// Notify all listeners about state change
    fn notify_listeners(&self, snapshot: &StateSnapshot) {
        let listeners = self.listeners.read().unwrap_or_else(|e| e.into_inner());
        for listener in listeners.iter() {
            listener(snapshot);
        }
    }
}

/// State synchronization manager for distributed environments
pub struct StateSynchronizer {
    /// Local state manager
    local_state: Arc<StateManager>,
    /// Remote state managers
    remote_states: Vec<Arc<StateManager>>,
    /// Synchronization configuration
    config: SyncConfig,
    /// Conflict resolution strategy
    conflict_resolution: ConflictResolution,
}

/// Synchronization configuration
#[derive(Debug, Clone)]
pub struct SyncConfig {
    /// Synchronization interval
    pub sync_interval: Duration,
    /// Enable bidirectional sync
    pub bidirectional: bool,
    /// Conflict detection enabled
    pub conflict_detection: bool,
    /// Batch synchronization
    pub batch_sync: bool,
    /// Maximum sync retries
    pub max_retries: usize,
}

impl Default for SyncConfig {
    fn default() -> Self {
        Self {
            sync_interval: Duration::from_secs(30),
            bidirectional: true,
            conflict_detection: true,
            batch_sync: false,
            max_retries: 3,
        }
    }
}

/// Conflict resolution strategies
#[derive(Debug, Clone)]
pub enum ConflictResolution {
    /// Latest timestamp wins
    LatestWins,
    /// Highest version wins
    HighestVersionWins,
    /// Manual resolution required
    Manual,
    /// Custom resolution function
    Custom(fn(&StateSnapshot, &StateSnapshot) -> StateSnapshot),
}

impl StateSynchronizer {
    /// Create a new state synchronizer
    #[must_use]
    pub fn new(
        local_state: Arc<StateManager>,
        config: SyncConfig,
        conflict_resolution: ConflictResolution,
    ) -> Self {
        Self {
            local_state,
            remote_states: Vec::new(),
            config,
            conflict_resolution,
        }
    }

    /// Add a remote state manager
    pub fn add_remote(&mut self, remote_state: Arc<StateManager>) {
        self.remote_states.push(remote_state);
    }

    /// Synchronize state with all remotes
    pub fn synchronize(&self) -> SklResult<SyncResult> {
        let mut result = SyncResult {
            synced_snapshots: 0,
            conflicts_resolved: 0,
            errors: Vec::new(),
        };

        for remote in &self.remote_states {
            match self.sync_with_remote(remote) {
                Ok(sync_stats) => {
                    result.synced_snapshots += sync_stats.synced_snapshots;
                    result.conflicts_resolved += sync_stats.conflicts_resolved;
                }
                Err(e) => {
                    result.errors.push(format!("Sync error: {e:?}"));
                }
            }
        }

        Ok(result)
    }

    /// Synchronize with a specific remote
    fn sync_with_remote(&self, remote: &Arc<StateManager>) -> SklResult<SyncResult> {
        let mut result = SyncResult {
            synced_snapshots: 0,
            conflicts_resolved: 0,
            errors: Vec::new(),
        };

        // Get local and remote snapshot lists
        let local_snapshots = self.local_state.list_snapshots();
        let remote_snapshots = remote.list_snapshots();

        // Find differences
        for remote_id in &remote_snapshots {
            if !local_snapshots.contains(remote_id) {
                // Remote has snapshot that local doesn't have
                match remote.load_snapshot(remote_id) {
                    Ok(remote_snapshot) => {
                        // Check for conflicts
                        if let Some(local_snapshot) =
                            self.find_conflicting_snapshot(&remote_snapshot)
                        {
                            let resolved =
                                self.resolve_conflict(&local_snapshot, &remote_snapshot)?;
                            self.local_state.save_snapshot(resolved)?;
                            result.conflicts_resolved += 1;
                        } else {
                            self.local_state.save_snapshot(remote_snapshot)?;
                            result.synced_snapshots += 1;
                        }
                    }
                    Err(e) => {
                        result
                            .errors
                            .push(format!("Failed to load remote snapshot {remote_id}: {e:?}"));
                    }
                }
            }
        }

        // Bidirectional sync
        if self.config.bidirectional {
            for local_id in &local_snapshots {
                if !remote_snapshots.contains(local_id) {
                    match self.local_state.load_snapshot(local_id) {
                        Ok(local_snapshot) => {
                            remote.save_snapshot(local_snapshot)?;
                            result.synced_snapshots += 1;
                        }
                        Err(e) => {
                            result
                                .errors
                                .push(format!("Failed to sync local snapshot {local_id}: {e:?}"));
                        }
                    }
                }
            }
        }

        Ok(result)
    }

    /// Find conflicting snapshot
    fn find_conflicting_snapshot(&self, remote_snapshot: &StateSnapshot) -> Option<StateSnapshot> {
        // Simplified conflict detection based on timestamp ranges
        // In a real implementation, this would be more sophisticated
        None
    }

    /// Resolve conflict between snapshots
    fn resolve_conflict(
        &self,
        local: &StateSnapshot,
        remote: &StateSnapshot,
    ) -> SklResult<StateSnapshot> {
        match &self.conflict_resolution {
            ConflictResolution::LatestWins => {
                if remote.timestamp > local.timestamp {
                    Ok(remote.clone())
                } else {
                    Ok(local.clone())
                }
            }
            ConflictResolution::HighestVersionWins => {
                if remote.version > local.version {
                    Ok(remote.clone())
                } else {
                    Ok(local.clone())
                }
            }
            ConflictResolution::Manual => Err(SklearsError::InvalidData {
                reason: "Manual conflict resolution required".to_string(),
            }),
            ConflictResolution::Custom(resolve_fn) => Ok(resolve_fn(local, remote)),
        }
    }
}

/// Synchronization result
#[derive(Debug, Clone)]
pub struct SyncResult {
    /// Number of snapshots synchronized
    pub synced_snapshots: usize,
    /// Number of conflicts resolved
    pub conflicts_resolved: usize,
    /// Synchronization errors
    pub errors: Vec<String>,
}

/// Version control system for pipeline states
pub struct PipelineVersionControl {
    /// State manager
    state_manager: Arc<StateManager>,
    /// Branch management
    branches: Arc<RwLock<HashMap<String, Branch>>>,
    /// Current branch
    current_branch: Arc<RwLock<String>>,
    /// Tags
    tags: Arc<RwLock<HashMap<String, String>>>, // tag -> snapshot_id
}

/// Version control branch
#[derive(Debug, Clone)]
pub struct Branch {
    /// Branch name
    pub name: String,
    /// Latest commit
    pub head: Option<String>,
    /// Branch creation time
    pub created_at: SystemTime,
    /// Branch metadata
    pub metadata: HashMap<String, String>,
}

impl PipelineVersionControl {
    /// Create a new version control system
    #[must_use]
    pub fn new(state_manager: Arc<StateManager>) -> Self {
        let mut branches = HashMap::new();
        branches.insert(
            "main".to_string(),
            Branch {
                name: "main".to_string(),
                head: None,
                created_at: SystemTime::now(),
                metadata: HashMap::new(),
            },
        );

        Self {
            state_manager,
            branches: Arc::new(RwLock::new(branches)),
            current_branch: Arc::new(RwLock::new("main".to_string())),
            tags: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Create a new branch
    pub fn create_branch(&self, branch_name: &str, from_snapshot: Option<&str>) -> SklResult<()> {
        let mut branches = self.branches.write().unwrap_or_else(|e| e.into_inner());

        if branches.contains_key(branch_name) {
            return Err(SklearsError::InvalidInput(format!(
                "Branch {branch_name} already exists"
            )));
        }

        let branch = Branch {
            name: branch_name.to_string(),
            head: from_snapshot.map(std::string::ToString::to_string),
            created_at: SystemTime::now(),
            metadata: HashMap::new(),
        };

        branches.insert(branch_name.to_string(), branch);
        Ok(())
    }

    /// Switch to a different branch
    pub fn checkout_branch(&self, branch_name: &str) -> SklResult<()> {
        let branches = self.branches.read().unwrap_or_else(|e| e.into_inner());

        if !branches.contains_key(branch_name) {
            return Err(SklearsError::InvalidInput(format!(
                "Branch {branch_name} does not exist"
            )));
        }

        let mut current = self
            .current_branch
            .write()
            .unwrap_or_else(|e| e.into_inner());
        *current = branch_name.to_string();
        Ok(())
    }

    /// Commit changes to current branch
    pub fn commit(&self, snapshot_id: &str, message: &str) -> SklResult<()> {
        let current_branch_name = {
            let current = self
                .current_branch
                .read()
                .unwrap_or_else(|e| e.into_inner());
            current.clone()
        };

        let mut branches = self.branches.write().unwrap_or_else(|e| e.into_inner());
        if let Some(branch) = branches.get_mut(&current_branch_name) {
            branch.head = Some(snapshot_id.to_string());
            branch
                .metadata
                .insert("last_commit_message".to_string(), message.to_string());
            branch.metadata.insert(
                "last_commit_time".to_string(),
                SystemTime::now()
                    .duration_since(UNIX_EPOCH)
                    .unwrap_or_default()
                    .as_secs()
                    .to_string(),
            );
        }

        Ok(())
    }

    /// Create a tag for a snapshot
    pub fn create_tag(&self, tag_name: &str, snapshot_id: &str) -> SklResult<()> {
        let mut tags = self.tags.write().unwrap_or_else(|e| e.into_inner());
        tags.insert(tag_name.to_string(), snapshot_id.to_string());
        Ok(())
    }

    /// Get snapshot ID for a tag
    #[must_use]
    pub fn get_tag(&self, tag_name: &str) -> Option<String> {
        let tags = self.tags.read().unwrap_or_else(|e| e.into_inner());
        tags.get(tag_name).cloned()
    }

    /// List all branches
    #[must_use]
    pub fn list_branches(&self) -> Vec<String> {
        let branches = self.branches.read().unwrap_or_else(|e| e.into_inner());
        branches.keys().cloned().collect()
    }

    /// List all tags
    #[must_use]
    pub fn list_tags(&self) -> HashMap<String, String> {
        let tags = self.tags.read().unwrap_or_else(|e| e.into_inner());
        tags.clone()
    }

    /// Get current branch
    #[must_use]
    pub fn current_branch(&self) -> String {
        let current = self
            .current_branch
            .read()
            .unwrap_or_else(|e| e.into_inner());
        current.clone()
    }
}

#[allow(non_snake_case)]
#[cfg(test)]
mod tests {
    use super::*;
    use std::env;

    #[test]
    fn test_state_snapshot_creation() {
        let snapshot = StateSnapshot {
            id: "test_snapshot".to_string(),
            timestamp: SystemTime::now(),
            state_data: StateData {
                config: HashMap::new(),
                model_parameters: HashMap::new(),
                feature_names: None,
                steps_state: Vec::new(),
                execution_stats: ExecutionStatistics::default(),
                custom_data: HashMap::new(),
            },
            metadata: HashMap::new(),
            version: 1,
            parent_id: None,
            checksum: "test_checksum".to_string(),
        };

        assert_eq!(snapshot.id, "test_snapshot");
        assert_eq!(snapshot.version, 1);
    }

    #[test]
    fn test_state_manager_memory() {
        let strategy = PersistenceStrategy::InMemory;
        let config = CheckpointConfig::default();
        let manager = StateManager::new(strategy, config);

        let state_data = StateData {
            config: HashMap::new(),
            model_parameters: HashMap::new(),
            feature_names: None,
            steps_state: Vec::new(),
            execution_stats: ExecutionStatistics::default(),
            custom_data: HashMap::new(),
        };

        let checkpoint_id = manager
            .create_checkpoint("test_pipeline", state_data)
            .unwrap_or_default();
        assert!(checkpoint_id.starts_with("test_pipeline"));

        let loaded_state = manager
            .resume_from_checkpoint(&checkpoint_id)
            .expect("operation should succeed");
        assert_eq!(loaded_state.config.len(), 0);
    }

    #[test]
    fn test_version_control() {
        let strategy = PersistenceStrategy::InMemory;
        let config = CheckpointConfig::default();
        let state_manager = Arc::new(StateManager::new(strategy, config));
        let vc = PipelineVersionControl::new(state_manager);

        assert_eq!(vc.current_branch(), "main");

        vc.create_branch("feature", None).unwrap_or_default();
        vc.checkout_branch("feature").unwrap_or_default();
        assert_eq!(vc.current_branch(), "feature");

        vc.create_tag("v1.0", "snapshot_123").unwrap_or_default();
        assert_eq!(vc.get_tag("v1.0"), Some("snapshot_123".to_string()));
    }

    #[test]
    fn test_checkpoint_config() {
        let config = CheckpointConfig {
            auto_checkpoint_interval: Some(Duration::from_secs(60)),
            max_checkpoints: 5,
            checkpoint_on_update: true,
            checkpoint_on_error: false,
            compression_level: 9,
            incremental: true,
        };

        assert_eq!(config.max_checkpoints, 5);
        assert_eq!(config.compression_level, 9);
        assert!(config.incremental);
    }

    #[test]
    fn test_execution_statistics() {
        let mut stats = ExecutionStatistics::default();
        stats.training_samples = 1000;
        stats.prediction_requests = 50;
        stats.accuracy = Some(0.95);

        assert_eq!(stats.training_samples, 1000);
        assert_eq!(stats.prediction_requests, 50);
        assert_eq!(stats.accuracy, Some(0.95));
    }
}