grafeo_engine/

database.rs

//! The main database struct and operations.
//!
//! Start here with [`GrafeoDB`] - it's your handle to everything.

use std::path::Path;
use std::sync::Arc;

use parking_lot::RwLock;

#[cfg(feature = "wal")]
use grafeo_adapters::storage::wal::{
    DurabilityMode as WalDurabilityMode, WalConfig, WalManager, WalRecord, WalRecovery,
};
use grafeo_common::memory::buffer::{BufferManager, BufferManagerConfig};
use grafeo_common::types::{EdgeId, NodeId, Value};
use grafeo_common::utils::error::{Error, Result};
use grafeo_core::graph::lpg::LpgStore;
#[cfg(feature = "rdf")]
use grafeo_core::graph::rdf::RdfStore;

use crate::config::Config;
use crate::query::cache::QueryCache;
use crate::session::Session;
use crate::transaction::TransactionManager;

/// Your handle to a Grafeo database.
///
/// Start here. Create one with [`new_in_memory()`](Self::new_in_memory) for
/// quick experiments, or [`open()`](Self::open) for persistent storage.
/// Then grab a [`session()`](Self::session) to start querying.
///
/// # Examples
///
/// ```
/// use grafeo_engine::GrafeoDB;
///
/// // Quick in-memory database
/// let db = GrafeoDB::new_in_memory();
///
/// // Add some data
/// db.create_node(&["Person"]);
///
/// // Query it
/// let session = db.session();
/// let result = session.execute("MATCH (p:Person) RETURN p")?;
/// # Ok::<(), grafeo_common::utils::error::Error>(())
/// ```
pub struct GrafeoDB {
    /// Database configuration.
    config: Config,
    /// The underlying graph store.
    store: Arc<LpgStore>,
    /// RDF triple store (if RDF feature is enabled).
    #[cfg(feature = "rdf")]
    rdf_store: Arc<RdfStore>,
    /// Transaction manager.
    tx_manager: Arc<TransactionManager>,
    /// Unified buffer manager.
    buffer_manager: Arc<BufferManager>,
    /// Write-ahead log manager (if durability is enabled).
    #[cfg(feature = "wal")]
    wal: Option<Arc<WalManager>>,
    /// Query cache for parsed and optimized plans.
    query_cache: Arc<QueryCache>,
    /// Whether the database is open.
    is_open: RwLock<bool>,
}

impl GrafeoDB {
    /// Creates an in-memory database - fast to create, gone when dropped.
    ///
    /// Use this for tests, experiments, or when you don't need persistence.
    /// For data that survives restarts, use [`open()`](Self::open) instead.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let session = db.session();
    /// session.execute("INSERT (:Person {name: 'Alice'})")?;
    /// # Ok::<(), grafeo_common::utils::error::Error>(())
    /// ```
    #[must_use]
    pub fn new_in_memory() -> Self {
        Self::with_config(Config::in_memory()).expect("In-memory database creation should not fail")
    }

    /// Opens a database at the given path, creating it if it doesn't exist.
    ///
    /// If you've used this path before, Grafeo recovers your data from the
    /// write-ahead log automatically. First open on a new path creates an
    /// empty database.
    ///
    /// # Errors
    ///
    /// Returns an error if the path isn't writable or recovery fails.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::open("./my_social_network")?;
    /// # Ok::<(), grafeo_common::utils::error::Error>(())
    /// ```
    #[cfg(feature = "wal")]
    pub fn open(path: impl AsRef<Path>) -> Result<Self> {
        Self::with_config(Config::persistent(path.as_ref()))
    }

    /// Creates a database with custom configuration.
    ///
    /// Use this when you need fine-grained control over memory limits,
    /// thread counts, or persistence settings. For most cases,
    /// [`new_in_memory()`](Self::new_in_memory) or [`open()`](Self::open)
    /// are simpler.
    ///
    /// # Errors
    ///
    /// Returns an error if the database can't be created or recovery fails.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::{GrafeoDB, Config};
    ///
    /// // In-memory with a 512MB limit
    /// let config = Config::in_memory()
    ///     .with_memory_limit(512 * 1024 * 1024);
    ///
    /// let db = GrafeoDB::with_config(config)?;
    /// # Ok::<(), grafeo_common::utils::error::Error>(())
    /// ```
    pub fn with_config(config: Config) -> Result<Self> {
        // Validate configuration before proceeding
        config
            .validate()
            .map_err(|e| grafeo_common::utils::error::Error::Internal(e.to_string()))?;

        let store = Arc::new(LpgStore::new());
        #[cfg(feature = "rdf")]
        let rdf_store = Arc::new(RdfStore::new());
        let tx_manager = Arc::new(TransactionManager::new());

        // Create buffer manager with configured limits
        let buffer_config = BufferManagerConfig {
            budget: config.memory_limit.unwrap_or_else(|| {
                (BufferManagerConfig::detect_system_memory() as f64 * 0.75) as usize
            }),
            spill_path: config
                .spill_path
                .clone()
                .or_else(|| config.path.as_ref().map(|p| p.join("spill"))),
            ..BufferManagerConfig::default()
        };
        let buffer_manager = BufferManager::new(buffer_config);

        // Initialize WAL if persistence is enabled
        #[cfg(feature = "wal")]
        let wal = if config.wal_enabled {
            if let Some(ref db_path) = config.path {
                // Create database directory if it doesn't exist
                std::fs::create_dir_all(db_path)?;

                let wal_path = db_path.join("wal");

                // Check if WAL exists and recover if needed
                if wal_path.exists() {
                    let recovery = WalRecovery::new(&wal_path);
                    let records = recovery.recover()?;
                    Self::apply_wal_records(&store, &records)?;
                }

                // Open/create WAL manager with configured durability
                let wal_durability = match config.wal_durability {
                    crate::config::DurabilityMode::Sync => WalDurabilityMode::Sync,
                    crate::config::DurabilityMode::Batch {
                        max_delay_ms,
                        max_records,
                    } => WalDurabilityMode::Batch {
                        max_delay_ms,
                        max_records,
                    },
                    crate::config::DurabilityMode::Adaptive { target_interval_ms } => {
                        WalDurabilityMode::Adaptive { target_interval_ms }
                    }
                    crate::config::DurabilityMode::NoSync => WalDurabilityMode::NoSync,
                };
                let wal_config = WalConfig {
                    durability: wal_durability,
                    ..WalConfig::default()
                };
                let wal_manager = WalManager::with_config(&wal_path, wal_config)?;
                Some(Arc::new(wal_manager))
            } else {
                None
            }
        } else {
            None
        };

        // Create query cache with default capacity (1000 queries)
        let query_cache = Arc::new(QueryCache::default());

        Ok(Self {
            config,
            store,
            #[cfg(feature = "rdf")]
            rdf_store,
            tx_manager,
            buffer_manager,
            #[cfg(feature = "wal")]
            wal,
            query_cache,
            is_open: RwLock::new(true),
        })
    }

    /// Applies WAL records to restore the database state.
    #[cfg(feature = "wal")]
    fn apply_wal_records(store: &LpgStore, records: &[WalRecord]) -> Result<()> {
        for record in records {
            match record {
                WalRecord::CreateNode { id, labels } => {
                    let label_refs: Vec<&str> = labels.iter().map(|s| s.as_str()).collect();
                    store.create_node_with_id(*id, &label_refs);
                }
                WalRecord::DeleteNode { id } => {
                    store.delete_node(*id);
                }
                WalRecord::CreateEdge {
                    id,
                    src,
                    dst,
                    edge_type,
                } => {
                    store.create_edge_with_id(*id, *src, *dst, edge_type);
                }
                WalRecord::DeleteEdge { id } => {
                    store.delete_edge(*id);
                }
                WalRecord::SetNodeProperty { id, key, value } => {
                    store.set_node_property(*id, key, value.clone());
                }
                WalRecord::SetEdgeProperty { id, key, value } => {
                    store.set_edge_property(*id, key, value.clone());
                }
                WalRecord::AddNodeLabel { id, label } => {
                    store.add_label(*id, label);
                }
                WalRecord::RemoveNodeLabel { id, label } => {
                    store.remove_label(*id, label);
                }
                WalRecord::TxCommit { .. }
                | WalRecord::TxAbort { .. }
                | WalRecord::Checkpoint { .. } => {
                    // Transaction control records don't need replay action
                    // (recovery already filtered to only committed transactions)
                }
            }
        }
        Ok(())
    }

    /// Opens a new session for running queries.
    ///
    /// Sessions are cheap to create - spin up as many as you need. Each
    /// gets its own transaction context, so concurrent sessions won't
    /// block each other on reads.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let session = db.session();
    ///
    /// // Run queries through the session
    /// let result = session.execute("MATCH (n) RETURN count(n)")?;
    /// # Ok::<(), grafeo_common::utils::error::Error>(())
    /// ```
    #[must_use]
    pub fn session(&self) -> Session {
        #[cfg(feature = "rdf")]
        {
            Session::with_rdf_store_and_adaptive(
                Arc::clone(&self.store),
                Arc::clone(&self.rdf_store),
                Arc::clone(&self.tx_manager),
                Arc::clone(&self.query_cache),
                self.config.adaptive.clone(),
                self.config.factorized_execution,
                self.config.graph_model,
            )
        }
        #[cfg(not(feature = "rdf"))]
        {
            Session::with_adaptive(
                Arc::clone(&self.store),
                Arc::clone(&self.tx_manager),
                Arc::clone(&self.query_cache),
                self.config.adaptive.clone(),
                self.config.factorized_execution,
                self.config.graph_model,
            )
        }
    }

    /// Returns the adaptive execution configuration.
    #[must_use]
    pub fn adaptive_config(&self) -> &crate::config::AdaptiveConfig {
        &self.config.adaptive
    }

    /// Runs a query directly on the database.
    ///
    /// A convenience method that creates a temporary session behind the
    /// scenes. If you're running multiple queries, grab a
    /// [`session()`](Self::session) instead to avoid the overhead.
    ///
    /// # Errors
    ///
    /// Returns an error if parsing or execution fails.
    pub fn execute(&self, query: &str) -> Result<QueryResult> {
        let session = self.session();
        session.execute(query)
    }

    /// Executes a query with parameters and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    pub fn execute_with_params(
        &self,
        query: &str,
        params: std::collections::HashMap<String, grafeo_common::types::Value>,
    ) -> Result<QueryResult> {
        let session = self.session();
        session.execute_with_params(query, params)
    }

    /// Executes a Cypher query and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "cypher")]
    pub fn execute_cypher(&self, query: &str) -> Result<QueryResult> {
        let session = self.session();
        session.execute_cypher(query)
    }

    /// Executes a Cypher query with parameters and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "cypher")]
    pub fn execute_cypher_with_params(
        &self,
        query: &str,
        params: std::collections::HashMap<String, grafeo_common::types::Value>,
    ) -> Result<QueryResult> {
        use crate::query::processor::{QueryLanguage, QueryProcessor};

        // Create processor
        let processor = QueryProcessor::for_lpg(Arc::clone(&self.store));
        processor.process(query, QueryLanguage::Cypher, Some(&params))
    }

    /// Executes a Gremlin query and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "gremlin")]
    pub fn execute_gremlin(&self, query: &str) -> Result<QueryResult> {
        let session = self.session();
        session.execute_gremlin(query)
    }

    /// Executes a Gremlin query with parameters and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "gremlin")]
    pub fn execute_gremlin_with_params(
        &self,
        query: &str,
        params: std::collections::HashMap<String, grafeo_common::types::Value>,
    ) -> Result<QueryResult> {
        let session = self.session();
        session.execute_gremlin_with_params(query, params)
    }

    /// Executes a GraphQL query and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "graphql")]
    pub fn execute_graphql(&self, query: &str) -> Result<QueryResult> {
        let session = self.session();
        session.execute_graphql(query)
    }

    /// Executes a GraphQL query with parameters and returns the result.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    #[cfg(feature = "graphql")]
    pub fn execute_graphql_with_params(
        &self,
        query: &str,
        params: std::collections::HashMap<String, grafeo_common::types::Value>,
    ) -> Result<QueryResult> {
        let session = self.session();
        session.execute_graphql_with_params(query, params)
    }

    /// Executes a SPARQL query and returns the result.
    ///
    /// SPARQL queries operate on the RDF triple store.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails.
    ///
    /// # Examples
    ///
    /// ```ignore
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let result = db.execute_sparql("SELECT ?s ?p ?o WHERE { ?s ?p ?o }")?;
    /// ```
    #[cfg(all(feature = "sparql", feature = "rdf"))]
    pub fn execute_sparql(&self, query: &str) -> Result<QueryResult> {
        use crate::query::{
            Executor, optimizer::Optimizer, planner_rdf::RdfPlanner, sparql_translator,
        };

        // Parse and translate the SPARQL query to a logical plan
        let logical_plan = sparql_translator::translate(query)?;

        // Optimize the plan
        let optimizer = Optimizer::from_store(&self.store);
        let optimized_plan = optimizer.optimize(logical_plan)?;

        // Convert to physical plan using RDF planner
        let planner = RdfPlanner::new(Arc::clone(&self.rdf_store));
        let mut physical_plan = planner.plan(&optimized_plan)?;

        // Execute the plan
        let executor = Executor::with_columns(physical_plan.columns.clone());
        executor.execute(physical_plan.operator.as_mut())
    }

    /// Returns the RDF store.
    ///
    /// This provides direct access to the RDF store for triple operations.
    #[cfg(feature = "rdf")]
    #[must_use]
    pub fn rdf_store(&self) -> &Arc<RdfStore> {
        &self.rdf_store
    }

    /// Executes a query and returns a single scalar value.
    ///
    /// # Errors
    ///
    /// Returns an error if the query fails or doesn't return exactly one row.
    pub fn query_scalar<T: FromValue>(&self, query: &str) -> Result<T> {
        let result = self.execute(query)?;
        result.scalar()
    }

    /// Returns the configuration.
    #[must_use]
    pub fn config(&self) -> &Config {
        &self.config
    }

    /// Returns the graph data model of this database.
    #[must_use]
    pub fn graph_model(&self) -> crate::config::GraphModel {
        self.config.graph_model
    }

    /// Returns the configured memory limit in bytes, if any.
    #[must_use]
    pub fn memory_limit(&self) -> Option<usize> {
        self.config.memory_limit
    }

    /// Returns the underlying store.
    ///
    /// This provides direct access to the LPG store for algorithm implementations.
    #[must_use]
    pub fn store(&self) -> &Arc<LpgStore> {
        &self.store
    }

    /// Returns the buffer manager for memory-aware operations.
    #[must_use]
    pub fn buffer_manager(&self) -> &Arc<BufferManager> {
        &self.buffer_manager
    }

    /// Closes the database, flushing all pending writes.
    ///
    /// For persistent databases, this ensures everything is safely on disk.
    /// Called automatically when the database is dropped, but you can call
    /// it explicitly if you need to guarantee durability at a specific point.
    ///
    /// # Errors
    ///
    /// Returns an error if the WAL can't be flushed (check disk space/permissions).
    pub fn close(&self) -> Result<()> {
        let mut is_open = self.is_open.write();
        if !*is_open {
            return Ok(());
        }

        // Commit and checkpoint WAL
        #[cfg(feature = "wal")]
        if let Some(ref wal) = self.wal {
            let epoch = self.store.current_epoch();

            // Use the last assigned transaction ID, or create a checkpoint-only tx
            let checkpoint_tx = self.tx_manager.last_assigned_tx_id().unwrap_or_else(|| {
                // No transactions have been started; begin one for checkpoint
                self.tx_manager.begin()
            });

            // Log a TxCommit to mark all pending records as committed
            wal.log(&WalRecord::TxCommit {
                tx_id: checkpoint_tx,
            })?;

            // Then checkpoint
            wal.checkpoint(checkpoint_tx, epoch)?;
            wal.sync()?;
        }

        *is_open = false;
        Ok(())
    }

    /// Returns the WAL manager if available.
    #[cfg(feature = "wal")]
    #[must_use]
    pub fn wal(&self) -> Option<&Arc<WalManager>> {
        self.wal.as_ref()
    }

    /// Logs a WAL record if WAL is enabled.
    #[cfg(feature = "wal")]
    fn log_wal(&self, record: &WalRecord) -> Result<()> {
        if let Some(ref wal) = self.wal {
            wal.log(record)?;
        }
        Ok(())
    }

    /// Returns the number of nodes in the database.
    #[must_use]
    pub fn node_count(&self) -> usize {
        self.store.node_count()
    }

    /// Returns the number of edges in the database.
    #[must_use]
    pub fn edge_count(&self) -> usize {
        self.store.edge_count()
    }

    /// Returns the number of distinct labels in the database.
    #[must_use]
    pub fn label_count(&self) -> usize {
        self.store.label_count()
    }

    /// Returns the number of distinct property keys in the database.
    #[must_use]
    pub fn property_key_count(&self) -> usize {
        self.store.property_key_count()
    }

    /// Returns the number of distinct edge types in the database.
    #[must_use]
    pub fn edge_type_count(&self) -> usize {
        self.store.edge_type_count()
    }

    // === Node Operations ===

    /// Creates a node with the given labels and returns its ID.
    ///
    /// Labels categorize nodes - think of them like tags. A node can have
    /// multiple labels (e.g., `["Person", "Employee"]`).
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let alice = db.create_node(&["Person"]);
    /// let company = db.create_node(&["Company", "Startup"]);
    /// ```
    pub fn create_node(&self, labels: &[&str]) -> grafeo_common::types::NodeId {
        let id = self.store.create_node(labels);

        // Log to WAL if enabled
        #[cfg(feature = "wal")]
        if let Err(e) = self.log_wal(&WalRecord::CreateNode {
            id,
            labels: labels.iter().map(|s| (*s).to_string()).collect(),
        }) {
            tracing::warn!("Failed to log CreateNode to WAL: {}", e);
        }

        id
    }

    /// Creates a new node with labels and properties.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn create_node_with_props(
        &self,
        labels: &[&str],
        properties: impl IntoIterator<
            Item = (
                impl Into<grafeo_common::types::PropertyKey>,
                impl Into<grafeo_common::types::Value>,
            ),
        >,
    ) -> grafeo_common::types::NodeId {
        // Collect properties first so we can log them to WAL
        let props: Vec<(
            grafeo_common::types::PropertyKey,
            grafeo_common::types::Value,
        )> = properties
            .into_iter()
            .map(|(k, v)| (k.into(), v.into()))
            .collect();

        let id = self
            .store
            .create_node_with_props(labels, props.iter().map(|(k, v)| (k.clone(), v.clone())));

        // Log node creation to WAL
        #[cfg(feature = "wal")]
        {
            if let Err(e) = self.log_wal(&WalRecord::CreateNode {
                id,
                labels: labels.iter().map(|s| (*s).to_string()).collect(),
            }) {
                tracing::warn!("Failed to log CreateNode to WAL: {}", e);
            }

            // Log each property to WAL for full durability
            for (key, value) in props {
                if let Err(e) = self.log_wal(&WalRecord::SetNodeProperty {
                    id,
                    key: key.to_string(),
                    value,
                }) {
                    tracing::warn!("Failed to log SetNodeProperty to WAL: {}", e);
                }
            }
        }

        id
    }

    /// Gets a node by ID.
    #[must_use]
    pub fn get_node(
        &self,
        id: grafeo_common::types::NodeId,
    ) -> Option<grafeo_core::graph::lpg::Node> {
        self.store.get_node(id)
    }

    /// Deletes a node and all its edges.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn delete_node(&self, id: grafeo_common::types::NodeId) -> bool {
        let result = self.store.delete_node(id);

        #[cfg(feature = "wal")]
        if result && let Err(e) = self.log_wal(&WalRecord::DeleteNode { id }) {
            tracing::warn!("Failed to log DeleteNode to WAL: {}", e);
        }

        result
    }

    /// Sets a property on a node.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn set_node_property(
        &self,
        id: grafeo_common::types::NodeId,
        key: &str,
        value: grafeo_common::types::Value,
    ) {
        // Log to WAL first
        #[cfg(feature = "wal")]
        if let Err(e) = self.log_wal(&WalRecord::SetNodeProperty {
            id,
            key: key.to_string(),
            value: value.clone(),
        }) {
            tracing::warn!("Failed to log SetNodeProperty to WAL: {}", e);
        }

        self.store.set_node_property(id, key, value);
    }

    /// Adds a label to an existing node.
    ///
    /// Returns `true` if the label was added, `false` if the node doesn't exist
    /// or already has the label.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let alice = db.create_node(&["Person"]);
    ///
    /// // Promote Alice to Employee
    /// let added = db.add_node_label(alice, "Employee");
    /// assert!(added);
    /// ```
    pub fn add_node_label(&self, id: grafeo_common::types::NodeId, label: &str) -> bool {
        let result = self.store.add_label(id, label);

        #[cfg(feature = "wal")]
        if result {
            // Log to WAL if enabled
            if let Err(e) = self.log_wal(&WalRecord::AddNodeLabel {
                id,
                label: label.to_string(),
            }) {
                tracing::warn!("Failed to log AddNodeLabel to WAL: {}", e);
            }
        }

        result
    }

    /// Removes a label from a node.
    ///
    /// Returns `true` if the label was removed, `false` if the node doesn't exist
    /// or doesn't have the label.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let alice = db.create_node(&["Person", "Employee"]);
    ///
    /// // Remove Employee status
    /// let removed = db.remove_node_label(alice, "Employee");
    /// assert!(removed);
    /// ```
    pub fn remove_node_label(&self, id: grafeo_common::types::NodeId, label: &str) -> bool {
        let result = self.store.remove_label(id, label);

        #[cfg(feature = "wal")]
        if result {
            // Log to WAL if enabled
            if let Err(e) = self.log_wal(&WalRecord::RemoveNodeLabel {
                id,
                label: label.to_string(),
            }) {
                tracing::warn!("Failed to log RemoveNodeLabel to WAL: {}", e);
            }
        }

        result
    }

    /// Gets all labels for a node.
    ///
    /// Returns `None` if the node doesn't exist.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let alice = db.create_node(&["Person", "Employee"]);
    ///
    /// let labels = db.get_node_labels(alice).unwrap();
    /// assert!(labels.contains(&"Person".to_string()));
    /// assert!(labels.contains(&"Employee".to_string()));
    /// ```
    #[must_use]
    pub fn get_node_labels(&self, id: grafeo_common::types::NodeId) -> Option<Vec<String>> {
        self.store
            .get_node(id)
            .map(|node| node.labels.iter().map(|s| s.to_string()).collect())
    }

    // === Edge Operations ===

    /// Creates an edge (relationship) between two nodes.
    ///
    /// Edges connect nodes and have a type that describes the relationship.
    /// They're directed - the order of `src` and `dst` matters.
    ///
    /// # Examples
    ///
    /// ```
    /// use grafeo_engine::GrafeoDB;
    ///
    /// let db = GrafeoDB::new_in_memory();
    /// let alice = db.create_node(&["Person"]);
    /// let bob = db.create_node(&["Person"]);
    ///
    /// // Alice knows Bob (directed: Alice -> Bob)
    /// let edge = db.create_edge(alice, bob, "KNOWS");
    /// ```
    pub fn create_edge(
        &self,
        src: grafeo_common::types::NodeId,
        dst: grafeo_common::types::NodeId,
        edge_type: &str,
    ) -> grafeo_common::types::EdgeId {
        let id = self.store.create_edge(src, dst, edge_type);

        // Log to WAL if enabled
        #[cfg(feature = "wal")]
        if let Err(e) = self.log_wal(&WalRecord::CreateEdge {
            id,
            src,
            dst,
            edge_type: edge_type.to_string(),
        }) {
            tracing::warn!("Failed to log CreateEdge to WAL: {}", e);
        }

        id
    }

    /// Creates a new edge with properties.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn create_edge_with_props(
        &self,
        src: grafeo_common::types::NodeId,
        dst: grafeo_common::types::NodeId,
        edge_type: &str,
        properties: impl IntoIterator<
            Item = (
                impl Into<grafeo_common::types::PropertyKey>,
                impl Into<grafeo_common::types::Value>,
            ),
        >,
    ) -> grafeo_common::types::EdgeId {
        // Collect properties first so we can log them to WAL
        let props: Vec<(
            grafeo_common::types::PropertyKey,
            grafeo_common::types::Value,
        )> = properties
            .into_iter()
            .map(|(k, v)| (k.into(), v.into()))
            .collect();

        let id = self.store.create_edge_with_props(
            src,
            dst,
            edge_type,
            props.iter().map(|(k, v)| (k.clone(), v.clone())),
        );

        // Log edge creation to WAL
        #[cfg(feature = "wal")]
        {
            if let Err(e) = self.log_wal(&WalRecord::CreateEdge {
                id,
                src,
                dst,
                edge_type: edge_type.to_string(),
            }) {
                tracing::warn!("Failed to log CreateEdge to WAL: {}", e);
            }

            // Log each property to WAL for full durability
            for (key, value) in props {
                if let Err(e) = self.log_wal(&WalRecord::SetEdgeProperty {
                    id,
                    key: key.to_string(),
                    value,
                }) {
                    tracing::warn!("Failed to log SetEdgeProperty to WAL: {}", e);
                }
            }
        }

        id
    }

    /// Gets an edge by ID.
    #[must_use]
    pub fn get_edge(
        &self,
        id: grafeo_common::types::EdgeId,
    ) -> Option<grafeo_core::graph::lpg::Edge> {
        self.store.get_edge(id)
    }

    /// Deletes an edge.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn delete_edge(&self, id: grafeo_common::types::EdgeId) -> bool {
        let result = self.store.delete_edge(id);

        #[cfg(feature = "wal")]
        if result && let Err(e) = self.log_wal(&WalRecord::DeleteEdge { id }) {
            tracing::warn!("Failed to log DeleteEdge to WAL: {}", e);
        }

        result
    }

    /// Sets a property on an edge.
    ///
    /// If WAL is enabled, the operation is logged for durability.
    pub fn set_edge_property(
        &self,
        id: grafeo_common::types::EdgeId,
        key: &str,
        value: grafeo_common::types::Value,
    ) {
        // Log to WAL first
        #[cfg(feature = "wal")]
        if let Err(e) = self.log_wal(&WalRecord::SetEdgeProperty {
            id,
            key: key.to_string(),
            value: value.clone(),
        }) {
            tracing::warn!("Failed to log SetEdgeProperty to WAL: {}", e);
        }
        self.store.set_edge_property(id, key, value);
    }

    /// Removes a property from a node.
    ///
    /// Returns true if the property existed and was removed, false otherwise.
    pub fn remove_node_property(&self, id: grafeo_common::types::NodeId, key: &str) -> bool {
        // Note: RemoveProperty WAL records not yet implemented, but operation works in memory
        self.store.remove_node_property(id, key).is_some()
    }

    /// Removes a property from an edge.
    ///
    /// Returns true if the property existed and was removed, false otherwise.
    pub fn remove_edge_property(&self, id: grafeo_common::types::EdgeId, key: &str) -> bool {
        // Note: RemoveProperty WAL records not yet implemented, but operation works in memory
        self.store.remove_edge_property(id, key).is_some()
    }

    // =========================================================================
    // PROPERTY INDEX API
    // =========================================================================

    /// Creates an index on a node property for O(1) lookups by value.
    ///
    /// After creating an index, calls to [`Self::find_nodes_by_property`] will be
    /// O(1) instead of O(n) for this property. The index is automatically
    /// maintained when properties are set or removed.
    ///
    /// # Example
    ///
    /// ```ignore
    /// // Create an index on the 'email' property
    /// db.create_property_index("email");
    ///
    /// // Now lookups by email are O(1)
    /// let nodes = db.find_nodes_by_property("email", &Value::from("alice@example.com"));
    /// ```
    pub fn create_property_index(&self, property: &str) {
        self.store.create_property_index(property);
    }

    /// Creates a vector similarity index on a node property.
    ///
    /// This enables efficient approximate nearest-neighbor search on vector
    /// properties. Currently validates the index parameters and scans existing
    /// nodes to verify the property contains vectors of the expected dimensions.
    ///
    /// # Arguments
    ///
    /// * `label` - Node label to index (e.g., `"Doc"`)
    /// * `property` - Property containing vector embeddings (e.g., `"embedding"`)
    /// * `dimensions` - Expected vector dimensions (inferred from data if `None`)
    /// * `metric` - Distance metric: `"cosine"` (default), `"euclidean"`, `"dot_product"`, `"manhattan"`
    /// * `m` - HNSW links per node (default: 16). Higher = better recall, more memory.
    /// * `ef_construction` - Construction beam width (default: 128). Higher = better index quality, slower build.
    ///
    /// # Errors
    ///
    /// Returns an error if the metric is invalid, no vectors are found, or
    /// dimensions don't match.
    pub fn create_vector_index(
        &self,
        label: &str,
        property: &str,
        dimensions: Option<usize>,
        metric: Option<&str>,
        m: Option<usize>,
        ef_construction: Option<usize>,
    ) -> Result<()> {
        use grafeo_common::types::{PropertyKey, Value};
        use grafeo_core::index::vector::DistanceMetric;

        let metric = match metric {
            Some(m) => DistanceMetric::from_str(m).ok_or_else(|| {
                grafeo_common::utils::error::Error::Internal(format!(
                    "Unknown distance metric '{}'. Use: cosine, euclidean, dot_product, manhattan",
                    m
                ))
            })?,
            None => DistanceMetric::Cosine,
        };

        // Scan nodes to validate vectors exist and check dimensions
        let prop_key = PropertyKey::new(property);
        let mut found_dims: Option<usize> = dimensions;
        let mut vector_count = 0usize;

        #[cfg(feature = "vector-index")]
        let mut vectors: Vec<(grafeo_common::types::NodeId, Vec<f32>)> = Vec::new();

        for node in self.store.nodes_with_label(label) {
            if let Some(Value::Vector(v)) = node.properties.get(&prop_key) {
                if let Some(expected) = found_dims {
                    if v.len() != expected {
                        return Err(grafeo_common::utils::error::Error::Internal(format!(
                            "Vector dimension mismatch: expected {}, found {} on node {}",
                            expected,
                            v.len(),
                            node.id.0
                        )));
                    }
                } else {
                    found_dims = Some(v.len());
                }
                vector_count += 1;
                #[cfg(feature = "vector-index")]
                vectors.push((node.id, v.to_vec()));
            }
        }

        if vector_count == 0 {
            return Err(grafeo_common::utils::error::Error::Internal(format!(
                "No vector properties found on :{label}({property})"
            )));
        }

        let dims = found_dims.unwrap_or(0);

        // Build and populate the HNSW index
        #[cfg(feature = "vector-index")]
        {
            use grafeo_core::index::vector::{HnswConfig, HnswIndex};

            let mut config = HnswConfig::new(dims, metric);
            if let Some(m_val) = m {
                config = config.with_m(m_val);
            }
            if let Some(ef_c) = ef_construction {
                config = config.with_ef_construction(ef_c);
            }

            let index = HnswIndex::with_capacity(config, vectors.len());
            for (node_id, vec) in &vectors {
                index.insert(*node_id, vec);
            }

            self.store
                .add_vector_index(label, property, Arc::new(index));
        }

        // Suppress unused variable warnings when vector-index is off
        let _ = (m, ef_construction);

        tracing::info!(
            "Vector index created: :{label}({property}) - {vector_count} vectors, {dims} dimensions, metric={metric_name}",
            metric_name = metric.name()
        );

        Ok(())
    }

    /// Searches for the k nearest neighbors of a query vector.
    ///
    /// Uses the HNSW index created by [`create_vector_index`](Self::create_vector_index).
    ///
    /// # Arguments
    ///
    /// * `label` - Node label that was indexed
    /// * `property` - Property that was indexed
    /// * `query` - Query vector (slice of floats)
    /// * `k` - Number of nearest neighbors to return
    /// * `ef` - Search beam width (higher = better recall, slower). Uses index default if `None`.
    ///
    /// # Returns
    ///
    /// Vector of `(NodeId, distance)` pairs sorted by distance ascending.
    #[cfg(feature = "vector-index")]
    pub fn vector_search(
        &self,
        label: &str,
        property: &str,
        query: &[f32],
        k: usize,
        ef: Option<usize>,
    ) -> Result<Vec<(grafeo_common::types::NodeId, f32)>> {
        let index = self.store.get_vector_index(label, property).ok_or_else(|| {
            grafeo_common::utils::error::Error::Internal(format!(
                "No vector index found for :{label}({property}). Call create_vector_index() first."
            ))
        })?;

        let results = match ef {
            Some(ef_val) => index.search_with_ef(query, k, ef_val),
            None => index.search(query, k),
        };

        Ok(results)
    }

    /// Creates multiple nodes in bulk, each with a single vector property.
    ///
    /// Much faster than individual `create_node_with_props` calls because it
    /// acquires internal locks once and loops in Rust rather than crossing
    /// the FFI boundary per vector.
    ///
    /// # Arguments
    ///
    /// * `label` - Label applied to all created nodes
    /// * `property` - Property name for the vector data
    /// * `vectors` - Vector data for each node
    ///
    /// # Returns
    ///
    /// Vector of created `NodeId`s in the same order as the input vectors.
    pub fn batch_create_nodes(
        &self,
        label: &str,
        property: &str,
        vectors: Vec<Vec<f32>>,
    ) -> Vec<grafeo_common::types::NodeId> {
        use grafeo_common::types::{PropertyKey, Value};

        let prop_key = PropertyKey::new(property);
        let labels: &[&str] = &[label];

        vectors
            .into_iter()
            .map(|vec| {
                let value = Value::Vector(vec.into());
                let id = self.store.create_node_with_props(
                    labels,
                    std::iter::once((prop_key.clone(), value.clone())),
                );

                // Log to WAL
                #[cfg(feature = "wal")]
                {
                    if let Err(e) = self.log_wal(&WalRecord::CreateNode {
                        id,
                        labels: labels.iter().map(|s| (*s).to_string()).collect(),
                    }) {
                        tracing::warn!("Failed to log CreateNode to WAL: {}", e);
                    }
                    if let Err(e) = self.log_wal(&WalRecord::SetNodeProperty {
                        id,
                        key: property.to_string(),
                        value,
                    }) {
                        tracing::warn!("Failed to log SetNodeProperty to WAL: {}", e);
                    }
                }

                id
            })
            .collect()
    }

    /// Searches for nearest neighbors for multiple query vectors in parallel.
    ///
    /// Uses rayon parallel iteration under the hood for multi-core throughput.
    ///
    /// # Arguments
    ///
    /// * `label` - Node label that was indexed
    /// * `property` - Property that was indexed
    /// * `queries` - Batch of query vectors
    /// * `k` - Number of nearest neighbors per query
    /// * `ef` - Search beam width (uses index default if `None`)
    #[cfg(feature = "vector-index")]
    pub fn batch_vector_search(
        &self,
        label: &str,
        property: &str,
        queries: &[Vec<f32>],
        k: usize,
        ef: Option<usize>,
    ) -> Result<Vec<Vec<(grafeo_common::types::NodeId, f32)>>> {
        let index = self.store.get_vector_index(label, property).ok_or_else(|| {
            grafeo_common::utils::error::Error::Internal(format!(
                "No vector index found for :{label}({property}). Call create_vector_index() first."
            ))
        })?;

        let results = match ef {
            Some(ef_val) => index.batch_search_with_ef(queries, k, ef_val),
            None => index.batch_search(queries, k),
        };

        Ok(results)
    }

    /// Drops an index on a node property.
    ///
    /// Returns `true` if the index existed and was removed.
    pub fn drop_property_index(&self, property: &str) -> bool {
        self.store.drop_property_index(property)
    }

    /// Returns `true` if the property has an index.
    #[must_use]
    pub fn has_property_index(&self, property: &str) -> bool {
        self.store.has_property_index(property)
    }

    /// Finds all nodes that have a specific property value.
    ///
    /// If the property is indexed, this is O(1). Otherwise, it scans all nodes
    /// which is O(n). Use [`Self::create_property_index`] for frequently queried properties.
    ///
    /// # Example
    ///
    /// ```ignore
    /// // Create index for fast lookups (optional but recommended)
    /// db.create_property_index("city");
    ///
    /// // Find all nodes where city = "NYC"
    /// let nyc_nodes = db.find_nodes_by_property("city", &Value::from("NYC"));
    /// ```
    #[must_use]
    pub fn find_nodes_by_property(
        &self,
        property: &str,
        value: &grafeo_common::types::Value,
    ) -> Vec<grafeo_common::types::NodeId> {
        self.store.find_nodes_by_property(property, value)
    }

    // =========================================================================
    // ADMIN API: Introspection
    // =========================================================================

    /// Returns true if this database is backed by a file (persistent).
    ///
    /// In-memory databases return false.
    #[must_use]
    pub fn is_persistent(&self) -> bool {
        self.config.path.is_some()
    }

    /// Returns the database file path, if persistent.
    ///
    /// In-memory databases return None.
    #[must_use]
    pub fn path(&self) -> Option<&Path> {
        self.config.path.as_deref()
    }

    /// Returns high-level database information.
    ///
    /// Includes node/edge counts, persistence status, and mode (LPG/RDF).
    #[must_use]
    pub fn info(&self) -> crate::admin::DatabaseInfo {
        crate::admin::DatabaseInfo {
            mode: crate::admin::DatabaseMode::Lpg,
            node_count: self.store.node_count(),
            edge_count: self.store.edge_count(),
            is_persistent: self.is_persistent(),
            path: self.config.path.clone(),
            wal_enabled: self.config.wal_enabled,
            version: env!("CARGO_PKG_VERSION").to_string(),
        }
    }

    /// Returns detailed database statistics.
    ///
    /// Includes counts, memory usage, and index information.
    #[must_use]
    pub fn detailed_stats(&self) -> crate::admin::DatabaseStats {
        #[cfg(feature = "wal")]
        let disk_bytes = self.config.path.as_ref().and_then(|p| {
            if p.exists() {
                Self::calculate_disk_usage(p).ok()
            } else {
                None
            }
        });
        #[cfg(not(feature = "wal"))]
        let disk_bytes: Option<usize> = None;

        crate::admin::DatabaseStats {
            node_count: self.store.node_count(),
            edge_count: self.store.edge_count(),
            label_count: self.store.label_count(),
            edge_type_count: self.store.edge_type_count(),
            property_key_count: self.store.property_key_count(),
            index_count: 0, // TODO: implement index tracking
            memory_bytes: self.buffer_manager.allocated(),
            disk_bytes,
        }
    }

    /// Calculates total disk usage for the database directory.
    #[cfg(feature = "wal")]
    fn calculate_disk_usage(path: &Path) -> Result<usize> {
        let mut total = 0usize;
        if path.is_dir() {
            for entry in std::fs::read_dir(path)? {
                let entry = entry?;
                let metadata = entry.metadata()?;
                if metadata.is_file() {
                    total += metadata.len() as usize;
                } else if metadata.is_dir() {
                    total += Self::calculate_disk_usage(&entry.path())?;
                }
            }
        }
        Ok(total)
    }

    /// Returns schema information (labels, edge types, property keys).
    ///
    /// For LPG mode, returns label and edge type information.
    /// For RDF mode, returns predicate and named graph information.
    #[must_use]
    pub fn schema(&self) -> crate::admin::SchemaInfo {
        let labels = self
            .store
            .all_labels()
            .into_iter()
            .map(|name| crate::admin::LabelInfo {
                name: name.clone(),
                count: self.store.nodes_with_label(&name).count(),
            })
            .collect();

        let edge_types = self
            .store
            .all_edge_types()
            .into_iter()
            .map(|name| crate::admin::EdgeTypeInfo {
                name: name.clone(),
                count: self.store.edges_with_type(&name).count(),
            })
            .collect();

        let property_keys = self.store.all_property_keys();

        crate::admin::SchemaInfo::Lpg(crate::admin::LpgSchemaInfo {
            labels,
            edge_types,
            property_keys,
        })
    }

    /// Returns RDF schema information.
    ///
    /// Only available when the RDF feature is enabled.
    #[cfg(feature = "rdf")]
    #[must_use]
    pub fn rdf_schema(&self) -> crate::admin::SchemaInfo {
        let stats = self.rdf_store.stats();

        let predicates = self
            .rdf_store
            .predicates()
            .into_iter()
            .map(|predicate| {
                let count = self.rdf_store.triples_with_predicate(&predicate).len();
                crate::admin::PredicateInfo {
                    iri: predicate.to_string(),
                    count,
                }
            })
            .collect();

        crate::admin::SchemaInfo::Rdf(crate::admin::RdfSchemaInfo {
            predicates,
            named_graphs: Vec::new(), // Named graphs not yet implemented in RdfStore
            subject_count: stats.subject_count,
            object_count: stats.object_count,
        })
    }

    /// Validates database integrity.
    ///
    /// Checks for:
    /// - Dangling edge references (edges pointing to non-existent nodes)
    /// - Internal index consistency
    ///
    /// Returns a list of errors and warnings. Empty errors = valid.
    #[must_use]
    pub fn validate(&self) -> crate::admin::ValidationResult {
        let mut result = crate::admin::ValidationResult::default();

        // Check for dangling edge references
        for edge in self.store.all_edges() {
            if self.store.get_node(edge.src).is_none() {
                result.errors.push(crate::admin::ValidationError {
                    code: "DANGLING_SRC".to_string(),
                    message: format!(
                        "Edge {} references non-existent source node {}",
                        edge.id.0, edge.src.0
                    ),
                    context: Some(format!("edge:{}", edge.id.0)),
                });
            }
            if self.store.get_node(edge.dst).is_none() {
                result.errors.push(crate::admin::ValidationError {
                    code: "DANGLING_DST".to_string(),
                    message: format!(
                        "Edge {} references non-existent destination node {}",
                        edge.id.0, edge.dst.0
                    ),
                    context: Some(format!("edge:{}", edge.id.0)),
                });
            }
        }

        // Add warnings for potential issues
        if self.store.node_count() > 0 && self.store.edge_count() == 0 {
            result.warnings.push(crate::admin::ValidationWarning {
                code: "NO_EDGES".to_string(),
                message: "Database has nodes but no edges".to_string(),
                context: None,
            });
        }

        result
    }

    /// Returns WAL (Write-Ahead Log) status.
    ///
    /// Returns None if WAL is not enabled.
    #[must_use]
    pub fn wal_status(&self) -> crate::admin::WalStatus {
        #[cfg(feature = "wal")]
        if let Some(ref wal) = self.wal {
            return crate::admin::WalStatus {
                enabled: true,
                path: self.config.path.as_ref().map(|p| p.join("wal")),
                size_bytes: wal.size_bytes(),
                record_count: wal.record_count() as usize,
                last_checkpoint: wal.last_checkpoint_timestamp(),
                current_epoch: self.store.current_epoch().as_u64(),
            };
        }

        crate::admin::WalStatus {
            enabled: false,
            path: None,
            size_bytes: 0,
            record_count: 0,
            last_checkpoint: None,
            current_epoch: self.store.current_epoch().as_u64(),
        }
    }

    /// Forces a WAL checkpoint.
    ///
    /// Flushes all pending WAL records to the main storage.
    ///
    /// # Errors
    ///
    /// Returns an error if the checkpoint fails.
    pub fn wal_checkpoint(&self) -> Result<()> {
        #[cfg(feature = "wal")]
        if let Some(ref wal) = self.wal {
            let epoch = self.store.current_epoch();
            let tx_id = self
                .tx_manager
                .last_assigned_tx_id()
                .unwrap_or_else(|| self.tx_manager.begin());
            wal.checkpoint(tx_id, epoch)?;
            wal.sync()?;
        }
        Ok(())
    }

    // =========================================================================
    // ADMIN API: Persistence Control
    // =========================================================================

    /// Saves the database to a file path.
    ///
    /// - If in-memory: creates a new persistent database at path
    /// - If file-backed: creates a copy at the new path
    ///
    /// The original database remains unchanged.
    ///
    /// # Errors
    ///
    /// Returns an error if the save operation fails.
    ///
    /// Requires the `wal` feature for persistence support.
    #[cfg(feature = "wal")]
    pub fn save(&self, path: impl AsRef<Path>) -> Result<()> {
        let path = path.as_ref();

        // Create target database with WAL enabled
        let target_config = Config::persistent(path);
        let target = Self::with_config(target_config)?;

        // Copy all nodes using WAL-enabled methods
        for node in self.store.all_nodes() {
            let label_refs: Vec<&str> = node.labels.iter().map(|s| &**s).collect();
            target.store.create_node_with_id(node.id, &label_refs);

            // Log to WAL
            target.log_wal(&WalRecord::CreateNode {
                id: node.id,
                labels: node.labels.iter().map(|s| s.to_string()).collect(),
            })?;

            // Copy properties
            for (key, value) in node.properties {
                target
                    .store
                    .set_node_property(node.id, key.as_str(), value.clone());
                target.log_wal(&WalRecord::SetNodeProperty {
                    id: node.id,
                    key: key.to_string(),
                    value,
                })?;
            }
        }

        // Copy all edges using WAL-enabled methods
        for edge in self.store.all_edges() {
            target
                .store
                .create_edge_with_id(edge.id, edge.src, edge.dst, &edge.edge_type);

            // Log to WAL
            target.log_wal(&WalRecord::CreateEdge {
                id: edge.id,
                src: edge.src,
                dst: edge.dst,
                edge_type: edge.edge_type.to_string(),
            })?;

            // Copy properties
            for (key, value) in edge.properties {
                target
                    .store
                    .set_edge_property(edge.id, key.as_str(), value.clone());
                target.log_wal(&WalRecord::SetEdgeProperty {
                    id: edge.id,
                    key: key.to_string(),
                    value,
                })?;
            }
        }

        // Checkpoint and close the target database
        target.close()?;

        Ok(())
    }

    /// Creates an in-memory copy of this database.
    ///
    /// Returns a new database that is completely independent.
    /// Useful for:
    /// - Testing modifications without affecting the original
    /// - Faster operations when persistence isn't needed
    ///
    /// # Errors
    ///
    /// Returns an error if the copy operation fails.
    pub fn to_memory(&self) -> Result<Self> {
        let config = Config::in_memory();
        let target = Self::with_config(config)?;

        // Copy all nodes
        for node in self.store.all_nodes() {
            let label_refs: Vec<&str> = node.labels.iter().map(|s| &**s).collect();
            target.store.create_node_with_id(node.id, &label_refs);

            // Copy properties
            for (key, value) in node.properties {
                target.store.set_node_property(node.id, key.as_str(), value);
            }
        }

        // Copy all edges
        for edge in self.store.all_edges() {
            target
                .store
                .create_edge_with_id(edge.id, edge.src, edge.dst, &edge.edge_type);

            // Copy properties
            for (key, value) in edge.properties {
                target.store.set_edge_property(edge.id, key.as_str(), value);
            }
        }

        Ok(target)
    }

    /// Opens a database file and loads it entirely into memory.
    ///
    /// The returned database has no connection to the original file.
    /// Changes will NOT be written back to the file.
    ///
    /// # Errors
    ///
    /// Returns an error if the file can't be opened or loaded.
    #[cfg(feature = "wal")]
    pub fn open_in_memory(path: impl AsRef<Path>) -> Result<Self> {
        // Open the source database (triggers WAL recovery)
        let source = Self::open(path)?;

        // Create in-memory copy
        let target = source.to_memory()?;

        // Close the source (releases file handles)
        source.close()?;

        Ok(target)
    }

    // =========================================================================
    // ADMIN API: Snapshot Export/Import
    // =========================================================================

    /// Exports the entire database to a binary snapshot.
    ///
    /// The returned bytes can be stored (e.g. in IndexedDB) and later
    /// restored with [`import_snapshot()`](Self::import_snapshot).
    ///
    /// # Errors
    ///
    /// Returns an error if serialization fails.
    pub fn export_snapshot(&self) -> Result<Vec<u8>> {
        let nodes: Vec<SnapshotNode> = self
            .store
            .all_nodes()
            .map(|n| SnapshotNode {
                id: n.id,
                labels: n.labels.iter().map(|l| l.to_string()).collect(),
                properties: n
                    .properties
                    .into_iter()
                    .map(|(k, v)| (k.to_string(), v))
                    .collect(),
            })
            .collect();

        let edges: Vec<SnapshotEdge> = self
            .store
            .all_edges()
            .map(|e| SnapshotEdge {
                id: e.id,
                src: e.src,
                dst: e.dst,
                edge_type: e.edge_type.to_string(),
                properties: e
                    .properties
                    .into_iter()
                    .map(|(k, v)| (k.to_string(), v))
                    .collect(),
            })
            .collect();

        let snapshot = Snapshot {
            version: 1,
            nodes,
            edges,
        };

        let config = bincode::config::standard();
        bincode::serde::encode_to_vec(&snapshot, config)
            .map_err(|e| Error::Internal(format!("snapshot export failed: {e}")))
    }

    /// Creates a new in-memory database from a binary snapshot.
    ///
    /// The `data` must have been produced by [`export_snapshot()`](Self::export_snapshot).
    ///
    /// # Errors
    ///
    /// Returns an error if the snapshot is invalid or deserialization fails.
    pub fn import_snapshot(data: &[u8]) -> Result<Self> {
        let config = bincode::config::standard();
        let (snapshot, _): (Snapshot, _) = bincode::serde::decode_from_slice(data, config)
            .map_err(|e| Error::Internal(format!("snapshot import failed: {e}")))?;

        if snapshot.version != 1 {
            return Err(Error::Internal(format!(
                "unsupported snapshot version: {}",
                snapshot.version
            )));
        }

        let db = Self::new_in_memory();

        for node in snapshot.nodes {
            let label_refs: Vec<&str> = node.labels.iter().map(|s| s.as_str()).collect();
            db.store.create_node_with_id(node.id, &label_refs);
            for (key, value) in node.properties {
                db.store.set_node_property(node.id, &key, value);
            }
        }

        for edge in snapshot.edges {
            db.store
                .create_edge_with_id(edge.id, edge.src, edge.dst, &edge.edge_type);
            for (key, value) in edge.properties {
                db.store.set_edge_property(edge.id, &key, value);
            }
        }

        Ok(db)
    }

    // =========================================================================
    // ADMIN API: Iteration
    // =========================================================================

    /// Returns an iterator over all nodes in the database.
    ///
    /// Useful for dump/export operations.
    pub fn iter_nodes(&self) -> impl Iterator<Item = grafeo_core::graph::lpg::Node> + '_ {
        self.store.all_nodes()
    }

    /// Returns an iterator over all edges in the database.
    ///
    /// Useful for dump/export operations.
    pub fn iter_edges(&self) -> impl Iterator<Item = grafeo_core::graph::lpg::Edge> + '_ {
        self.store.all_edges()
    }
}

/// Binary snapshot format for database export/import.
#[derive(serde::Serialize, serde::Deserialize)]
struct Snapshot {
    version: u8,
    nodes: Vec<SnapshotNode>,
    edges: Vec<SnapshotEdge>,
}

#[derive(serde::Serialize, serde::Deserialize)]
struct SnapshotNode {
    id: NodeId,
    labels: Vec<String>,
    properties: Vec<(String, Value)>,
}

#[derive(serde::Serialize, serde::Deserialize)]
struct SnapshotEdge {
    id: EdgeId,
    src: NodeId,
    dst: NodeId,
    edge_type: String,
    properties: Vec<(String, Value)>,
}

impl Drop for GrafeoDB {
    fn drop(&mut self) {
        if let Err(e) = self.close() {
            tracing::error!("Error closing database: {}", e);
        }
    }
}

/// The result of running a query.
///
/// Contains rows and columns, like a table. Use [`iter()`](Self::iter) to
/// loop through rows, or [`scalar()`](Self::scalar) if you expect a single value.
///
/// # Examples
///
/// ```
/// use grafeo_engine::GrafeoDB;
///
/// let db = GrafeoDB::new_in_memory();
/// db.create_node(&["Person"]);
///
/// let result = db.execute("MATCH (p:Person) RETURN count(p) AS total")?;
///
/// // Check what we got
/// println!("Columns: {:?}", result.columns);
/// println!("Rows: {}", result.row_count());
///
/// // Iterate through results
/// for row in result.iter() {
///     println!("{:?}", row);
/// }
/// # Ok::<(), grafeo_common::utils::error::Error>(())
/// ```
#[derive(Debug)]
pub struct QueryResult {
    /// Column names from the RETURN clause.
    pub columns: Vec<String>,
    /// Column types - useful for distinguishing NodeId/EdgeId from plain integers.
    pub column_types: Vec<grafeo_common::types::LogicalType>,
    /// The actual result rows.
    pub rows: Vec<Vec<grafeo_common::types::Value>>,
    /// Query execution time in milliseconds (if timing was enabled).
    pub execution_time_ms: Option<f64>,
    /// Number of rows scanned during query execution (estimate).
    pub rows_scanned: Option<u64>,
}

impl QueryResult {
    /// Creates a new empty query result.
    #[must_use]
    pub fn new(columns: Vec<String>) -> Self {
        let len = columns.len();
        Self {
            columns,
            column_types: vec![grafeo_common::types::LogicalType::Any; len],
            rows: Vec::new(),
            execution_time_ms: None,
            rows_scanned: None,
        }
    }

    /// Creates a new empty query result with column types.
    #[must_use]
    pub fn with_types(
        columns: Vec<String>,
        column_types: Vec<grafeo_common::types::LogicalType>,
    ) -> Self {
        Self {
            columns,
            column_types,
            rows: Vec::new(),
            execution_time_ms: None,
            rows_scanned: None,
        }
    }

    /// Sets the execution metrics on this result.
    pub fn with_metrics(mut self, execution_time_ms: f64, rows_scanned: u64) -> Self {
        self.execution_time_ms = Some(execution_time_ms);
        self.rows_scanned = Some(rows_scanned);
        self
    }

    /// Returns the execution time in milliseconds, if available.
    #[must_use]
    pub fn execution_time_ms(&self) -> Option<f64> {
        self.execution_time_ms
    }

    /// Returns the number of rows scanned, if available.
    #[must_use]
    pub fn rows_scanned(&self) -> Option<u64> {
        self.rows_scanned
    }

    /// Returns the number of rows.
    #[must_use]
    pub fn row_count(&self) -> usize {
        self.rows.len()
    }

    /// Returns the number of columns.
    #[must_use]
    pub fn column_count(&self) -> usize {
        self.columns.len()
    }

    /// Returns true if the result is empty.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.rows.is_empty()
    }

    /// Extracts a single value from the result.
    ///
    /// Use this when your query returns exactly one row with one column,
    /// like `RETURN count(n)` or `RETURN sum(p.amount)`.
    ///
    /// # Errors
    ///
    /// Returns an error if the result has multiple rows or columns.
    pub fn scalar<T: FromValue>(&self) -> Result<T> {
        if self.rows.len() != 1 || self.columns.len() != 1 {
            return Err(grafeo_common::utils::error::Error::InvalidValue(
                "Expected single value".to_string(),
            ));
        }
        T::from_value(&self.rows[0][0])
    }

    /// Returns an iterator over the rows.
    pub fn iter(&self) -> impl Iterator<Item = &Vec<grafeo_common::types::Value>> {
        self.rows.iter()
    }
}

/// Converts a [`Value`] to a concrete Rust type.
///
/// Implemented for common types like `i64`, `f64`, `String`, and `bool`.
/// Used by [`QueryResult::scalar()`] to extract typed values.
pub trait FromValue: Sized {
    /// Attempts the conversion, returning an error on type mismatch.
    fn from_value(value: &grafeo_common::types::Value) -> Result<Self>;
}

impl FromValue for i64 {
    fn from_value(value: &grafeo_common::types::Value) -> Result<Self> {
        value
            .as_int64()
            .ok_or_else(|| grafeo_common::utils::error::Error::TypeMismatch {
                expected: "INT64".to_string(),
                found: value.type_name().to_string(),
            })
    }
}

impl FromValue for f64 {
    fn from_value(value: &grafeo_common::types::Value) -> Result<Self> {
        value
            .as_float64()
            .ok_or_else(|| grafeo_common::utils::error::Error::TypeMismatch {
                expected: "FLOAT64".to_string(),
                found: value.type_name().to_string(),
            })
    }
}

impl FromValue for String {
    fn from_value(value: &grafeo_common::types::Value) -> Result<Self> {
        value.as_str().map(String::from).ok_or_else(|| {
            grafeo_common::utils::error::Error::TypeMismatch {
                expected: "STRING".to_string(),
                found: value.type_name().to_string(),
            }
        })
    }
}

impl FromValue for bool {
    fn from_value(value: &grafeo_common::types::Value) -> Result<Self> {
        value
            .as_bool()
            .ok_or_else(|| grafeo_common::utils::error::Error::TypeMismatch {
                expected: "BOOL".to_string(),
                found: value.type_name().to_string(),
            })
    }
}

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

    #[test]
    fn test_create_in_memory_database() {
        let db = GrafeoDB::new_in_memory();
        assert_eq!(db.node_count(), 0);
        assert_eq!(db.edge_count(), 0);
    }

    #[test]
    fn test_database_config() {
        let config = Config::in_memory().with_threads(4).with_query_logging();

        let db = GrafeoDB::with_config(config).unwrap();
        assert_eq!(db.config().threads, 4);
        assert!(db.config().query_logging);
    }

    #[test]
    fn test_database_session() {
        let db = GrafeoDB::new_in_memory();
        let _session = db.session();
        // Session should be created successfully
    }

    #[cfg(feature = "wal")]
    #[test]
    fn test_persistent_database_recovery() {
        use grafeo_common::types::Value;
        use tempfile::tempdir;

        let dir = tempdir().unwrap();
        let db_path = dir.path().join("test_db");

        // Create database and add some data
        {
            let db = GrafeoDB::open(&db_path).unwrap();

            let alice = db.create_node(&["Person"]);
            db.set_node_property(alice, "name", Value::from("Alice"));

            let bob = db.create_node(&["Person"]);
            db.set_node_property(bob, "name", Value::from("Bob"));

            let _edge = db.create_edge(alice, bob, "KNOWS");

            // Explicitly close to flush WAL
            db.close().unwrap();
        }

        // Reopen and verify data was recovered
        {
            let db = GrafeoDB::open(&db_path).unwrap();

            assert_eq!(db.node_count(), 2);
            assert_eq!(db.edge_count(), 1);

            // Verify nodes exist
            let node0 = db.get_node(grafeo_common::types::NodeId::new(0));
            assert!(node0.is_some());

            let node1 = db.get_node(grafeo_common::types::NodeId::new(1));
            assert!(node1.is_some());
        }
    }

    #[cfg(feature = "wal")]
    #[test]
    fn test_wal_logging() {
        use tempfile::tempdir;

        let dir = tempdir().unwrap();
        let db_path = dir.path().join("wal_test_db");

        let db = GrafeoDB::open(&db_path).unwrap();

        // Create some data
        let node = db.create_node(&["Test"]);
        db.delete_node(node);

        // WAL should have records
        if let Some(wal) = db.wal() {
            assert!(wal.record_count() > 0);
        }

        db.close().unwrap();
    }

    #[cfg(feature = "wal")]
    #[test]
    fn test_wal_recovery_multiple_sessions() {
        // Tests that WAL recovery works correctly across multiple open/close cycles
        use grafeo_common::types::Value;
        use tempfile::tempdir;

        let dir = tempdir().unwrap();
        let db_path = dir.path().join("multi_session_db");

        // Session 1: Create initial data
        {
            let db = GrafeoDB::open(&db_path).unwrap();
            let alice = db.create_node(&["Person"]);
            db.set_node_property(alice, "name", Value::from("Alice"));
            db.close().unwrap();
        }

        // Session 2: Add more data
        {
            let db = GrafeoDB::open(&db_path).unwrap();
            assert_eq!(db.node_count(), 1); // Previous data recovered
            let bob = db.create_node(&["Person"]);
            db.set_node_property(bob, "name", Value::from("Bob"));
            db.close().unwrap();
        }

        // Session 3: Verify all data
        {
            let db = GrafeoDB::open(&db_path).unwrap();
            assert_eq!(db.node_count(), 2);

            // Verify properties were recovered correctly
            let node0 = db.get_node(grafeo_common::types::NodeId::new(0)).unwrap();
            assert!(node0.labels.iter().any(|l| l.as_str() == "Person"));

            let node1 = db.get_node(grafeo_common::types::NodeId::new(1)).unwrap();
            assert!(node1.labels.iter().any(|l| l.as_str() == "Person"));
        }
    }

    #[cfg(feature = "wal")]
    #[test]
    fn test_database_consistency_after_mutations() {
        // Tests that database remains consistent after a series of create/delete operations
        use grafeo_common::types::Value;
        use tempfile::tempdir;

        let dir = tempdir().unwrap();
        let db_path = dir.path().join("consistency_db");

        {
            let db = GrafeoDB::open(&db_path).unwrap();

            // Create nodes
            let a = db.create_node(&["Node"]);
            let b = db.create_node(&["Node"]);
            let c = db.create_node(&["Node"]);

            // Create edges
            let e1 = db.create_edge(a, b, "LINKS");
            let _e2 = db.create_edge(b, c, "LINKS");

            // Delete middle node and its edge
            db.delete_edge(e1);
            db.delete_node(b);

            // Set properties on remaining nodes
            db.set_node_property(a, "value", Value::Int64(1));
            db.set_node_property(c, "value", Value::Int64(3));

            db.close().unwrap();
        }

        // Reopen and verify consistency
        {
            let db = GrafeoDB::open(&db_path).unwrap();

            // Should have 2 nodes (a and c), b was deleted
            // Note: node_count includes deleted nodes in some implementations
            // What matters is that the non-deleted nodes are accessible
            let node_a = db.get_node(grafeo_common::types::NodeId::new(0));
            assert!(node_a.is_some());

            let node_c = db.get_node(grafeo_common::types::NodeId::new(2));
            assert!(node_c.is_some());

            // Middle node should be deleted
            let node_b = db.get_node(grafeo_common::types::NodeId::new(1));
            assert!(node_b.is_none());
        }
    }

    #[cfg(feature = "wal")]
    #[test]
    fn test_close_is_idempotent() {
        // Calling close() multiple times should not cause errors
        use tempfile::tempdir;

        let dir = tempdir().unwrap();
        let db_path = dir.path().join("close_test_db");

        let db = GrafeoDB::open(&db_path).unwrap();
        db.create_node(&["Test"]);

        // First close should succeed
        assert!(db.close().is_ok());

        // Second close should also succeed (idempotent)
        assert!(db.close().is_ok());
    }

    #[test]
    fn test_query_result_has_metrics() {
        // Verifies that query results include execution metrics
        let db = GrafeoDB::new_in_memory();
        db.create_node(&["Person"]);
        db.create_node(&["Person"]);

        #[cfg(feature = "gql")]
        {
            let result = db.execute("MATCH (n:Person) RETURN n").unwrap();

            // Metrics should be populated
            assert!(result.execution_time_ms.is_some());
            assert!(result.rows_scanned.is_some());
            assert!(result.execution_time_ms.unwrap() >= 0.0);
            assert_eq!(result.rows_scanned.unwrap(), 2);
        }
    }

    #[test]
    fn test_empty_query_result_metrics() {
        // Verifies metrics are correct for queries returning no results
        let db = GrafeoDB::new_in_memory();
        db.create_node(&["Person"]);

        #[cfg(feature = "gql")]
        {
            // Query that matches nothing
            let result = db.execute("MATCH (n:NonExistent) RETURN n").unwrap();

            assert!(result.execution_time_ms.is_some());
            assert!(result.rows_scanned.is_some());
            assert_eq!(result.rows_scanned.unwrap(), 0);
        }
    }
}