velesdb-core 1.6.0

//! Graph edge types and storage for knowledge graph relationships.
//!
//! This module provides:
//! - `GraphEdge`: A typed relationship between nodes with properties
//! - `EdgeStore`: Bidirectional index for efficient edge traversal
//!
//! # Edge Removal Semantics
//!
//! During edge removal, the internal indexes may be temporarily inconsistent
//! while the operation is in progress. The final state is always consistent.
//! For concurrent access, use `ConcurrentEdgeStore` instead.

use crate::error::{Error, Result};
use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::collections::HashMap;

/// A directed edge (relationship) in the knowledge graph.
///
/// Edges connect nodes and can have a label (type) and properties.
///
/// # Example
///
/// ```rust,ignore
/// use velesdb_core::collection::graph::GraphEdge;
/// use serde_json::json;
/// use std::collections::HashMap;
///
/// let mut props = HashMap::new();
/// props.insert("since".to_string(), json!("2020-01-01"));
///
/// let edge = GraphEdge::new(1, 100, 200, "KNOWS")
///     .with_properties(props);
/// ```
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct GraphEdge {
    id: u64,
    source: u64,
    target: u64,
    label: String,
    properties: HashMap<String, Value>,
}

impl GraphEdge {
    /// Creates a new edge with the given ID, endpoints, and label.
    ///
    /// # Errors
    ///
    /// Returns `Error::InvalidEdgeLabel` if the label is empty or whitespace-only.
    pub fn new(id: u64, source: u64, target: u64, label: &str) -> Result<Self> {
        let trimmed = label.trim();
        if trimmed.is_empty() {
            return Err(Error::InvalidEdgeLabel(
                "Edge label cannot be empty or whitespace-only".to_string(),
            ));
        }
        Ok(Self {
            id,
            source,
            target,
            label: trimmed.to_string(),
            properties: HashMap::new(),
        })
    }

    /// Adds properties to this edge (builder pattern).
    #[must_use]
    pub fn with_properties(mut self, properties: HashMap<String, Value>) -> Self {
        self.properties = properties;
        self
    }

    /// Returns the edge ID.
    #[must_use]
    pub fn id(&self) -> u64 {
        self.id
    }

    /// Returns the source node ID.
    #[must_use]
    pub fn source(&self) -> u64 {
        self.source
    }

    /// Returns the target node ID.
    #[must_use]
    pub fn target(&self) -> u64 {
        self.target
    }

    /// Returns the edge label (relationship type).
    #[must_use]
    pub fn label(&self) -> &str {
        &self.label
    }

    /// Returns all properties of this edge.
    #[must_use]
    pub fn properties(&self) -> &HashMap<String, Value> {
        &self.properties
    }

    /// Returns a specific property value, if it exists.
    #[must_use]
    pub fn property(&self, name: &str) -> Option<&Value> {
        self.properties.get(name)
    }
}

/// Storage for graph edges with bidirectional indexing.
///
/// Provides O(1) access to edges by ID and O(degree) access to
/// outgoing/incoming edges for any node.
///
/// # Index Structure (EPIC-019 US-003)
///
/// - `by_label`: Secondary index for O(k) label-based queries
/// - `outgoing_by_label`: Composite index (source, label) for O(k) filtered traversal
#[derive(Debug, Default, Serialize, Deserialize)]
pub struct EdgeStore {
    /// All edges indexed by ID
    edges: HashMap<u64, GraphEdge>,
    /// Outgoing edges: source_id -> Vec<edge_id>
    outgoing: HashMap<u64, Vec<u64>>,
    /// Incoming edges: target_id -> Vec<edge_id>
    incoming: HashMap<u64, Vec<u64>>,
    /// Secondary index: label -> Vec<edge_id> for fast label queries
    by_label: HashMap<String, Vec<u64>>,
    /// Composite index: (source_id, label) -> Vec<edge_id> for fast filtered traversal
    outgoing_by_label: HashMap<(u64, String), Vec<u64>>,
}

impl EdgeStore {
    /// Creates a new empty edge store.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Creates an edge store with pre-allocated capacity for better performance.
    ///
    /// Pre-allocating reduces memory reallocation overhead when inserting many edges.
    /// With 10M edges, this can reduce peak memory usage by ~2x and improve insert throughput.
    ///
    /// # Arguments
    ///
    /// * `expected_edges` - Expected number of edges to store
    /// * `expected_nodes` - Expected number of unique nodes (sources + targets)
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// // For a graph with ~1M edges and ~100K nodes
    /// let store = EdgeStore::with_capacity(1_000_000, 100_000);
    /// ```
    #[must_use]
    pub fn with_capacity(expected_edges: usize, expected_nodes: usize) -> Self {
        // Estimate ~10 unique labels typical for knowledge graphs
        let expected_labels = 10usize;
        // Use saturating_mul to prevent overflow for extreme inputs
        let outgoing_by_label_cap = expected_nodes
            .saturating_mul(expected_labels)
            .saturating_div(10);
        Self {
            edges: HashMap::with_capacity(expected_edges),
            outgoing: HashMap::with_capacity(expected_nodes),
            incoming: HashMap::with_capacity(expected_nodes),
            by_label: HashMap::with_capacity(expected_labels),
            outgoing_by_label: HashMap::with_capacity(outgoing_by_label_cap),
        }
    }

    /// Adds an edge to the store.
    ///
    /// Creates bidirectional index entries for efficient traversal.
    /// Also maintains label-based secondary indices (EPIC-019 US-003).
    ///
    /// # Errors
    ///
    /// Returns `Error::EdgeExists` if an edge with the same ID already exists.
    pub fn add_edge(&mut self, edge: GraphEdge) -> Result<()> {
        let id = edge.id();
        let source = edge.source();
        let target = edge.target();
        let label = edge.label().to_string();

        // Check for duplicate ID
        if self.edges.contains_key(&id) {
            return Err(Error::EdgeExists(id));
        }

        // Add to outgoing index
        self.outgoing.entry(source).or_default().push(id);

        // Add to incoming index
        self.incoming.entry(target).or_default().push(id);

        // Add to label index (US-003)
        self.by_label.entry(label.clone()).or_default().push(id);

        // Add to composite (source, label) index (US-003)
        self.outgoing_by_label
            .entry((source, label))
            .or_default()
            .push(id);

        // Store the edge
        self.edges.insert(id, edge);
        Ok(())
    }

    /// Adds an edge with only the outgoing index (for cross-shard storage).
    ///
    /// Used by `ConcurrentEdgeStore` when source and target are in different shards.
    /// The edge is stored and indexed by source node only.
    ///
    /// # Errors
    ///
    /// Returns `Error::EdgeExists` if an edge with the same ID already exists.
    pub fn add_edge_outgoing_only(&mut self, edge: GraphEdge) -> Result<()> {
        let id = edge.id();
        let source = edge.source();
        let label = edge.label().to_string();

        // Check for duplicate ID
        if self.edges.contains_key(&id) {
            return Err(Error::EdgeExists(id));
        }

        // Add to outgoing index only
        self.outgoing.entry(source).or_default().push(id);

        // Add to label index (US-003)
        self.by_label.entry(label.clone()).or_default().push(id);

        // Add to composite (source, label) index (US-003)
        self.outgoing_by_label
            .entry((source, label))
            .or_default()
            .push(id);

        // Store the edge
        self.edges.insert(id, edge);
        Ok(())
    }

    /// Adds an edge with only the incoming index (for cross-shard storage).
    ///
    /// Used by `ConcurrentEdgeStore` when source and target are in different shards.
    /// The edge is stored and indexed by target node only.
    /// Note: Label indices are maintained by the source shard in ConcurrentEdgeStore.
    ///
    /// # Errors
    ///
    /// Returns `Error::EdgeExists` if an edge with the same ID already exists.
    pub fn add_edge_incoming_only(&mut self, edge: GraphEdge) -> Result<()> {
        let id = edge.id();
        let target = edge.target();

        // Check for duplicate ID
        if self.edges.contains_key(&id) {
            return Err(Error::EdgeExists(id));
        }

        // Add to incoming index only
        self.incoming.entry(target).or_default().push(id);

        // Note: by_label and outgoing_by_label are maintained by source shard
        // Store the edge
        self.edges.insert(id, edge);
        Ok(())
    }

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

    /// Returns the count of edges where this shard is the source (for accurate cross-shard counting).
    #[must_use]
    pub fn outgoing_edge_count(&self) -> usize {
        self.outgoing.values().map(Vec::len).sum()
    }

    /// Gets an edge by its ID.
    #[must_use]
    pub fn get_edge(&self, id: u64) -> Option<&GraphEdge> {
        self.edges.get(&id)
    }

    /// Gets all outgoing edges from a node.
    #[must_use]
    pub fn get_outgoing(&self, node_id: u64) -> Vec<&GraphEdge> {
        self.outgoing
            .get(&node_id)
            .map(|ids| ids.iter().filter_map(|id| self.edges.get(id)).collect())
            .unwrap_or_default()
    }

    /// Gets all incoming edges to a node.
    #[must_use]
    pub fn get_incoming(&self, node_id: u64) -> Vec<&GraphEdge> {
        self.incoming
            .get(&node_id)
            .map(|ids| ids.iter().filter_map(|id| self.edges.get(id)).collect())
            .unwrap_or_default()
    }

    /// Gets outgoing edges filtered by label using composite index - O(k) where k = result count.
    ///
    /// Uses the `outgoing_by_label` composite index for fast lookup instead of
    /// iterating through all outgoing edges (EPIC-019 US-003).
    #[must_use]
    pub fn get_outgoing_by_label(&self, node_id: u64, label: &str) -> Vec<&GraphEdge> {
        self.outgoing_by_label
            .get(&(node_id, label.to_string()))
            .map(|ids| ids.iter().filter_map(|id| self.edges.get(id)).collect())
            .unwrap_or_default()
    }

    /// Gets all edges with a specific label - O(k) where k = result count.
    ///
    /// Uses the `by_label` secondary index for fast lookup (EPIC-019 US-003).
    #[must_use]
    pub fn get_edges_by_label(&self, label: &str) -> Vec<&GraphEdge> {
        self.by_label
            .get(label)
            .map(|ids| ids.iter().filter_map(|id| self.edges.get(id)).collect())
            .unwrap_or_default()
    }

    /// Gets incoming edges filtered by label.
    #[must_use]
    pub fn get_incoming_by_label(&self, node_id: u64, label: &str) -> Vec<&GraphEdge> {
        self.get_incoming(node_id)
            .into_iter()
            .filter(|e| e.label() == label)
            .collect()
    }

    /// Checks if an edge with the given ID exists.
    #[must_use]
    pub fn contains_edge(&self, edge_id: u64) -> bool {
        self.edges.contains_key(&edge_id)
    }

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

    /// Returns true if the store contains no edges.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.edges.is_empty()
    }

    /// Returns all edges in the store.
    #[must_use]
    pub fn all_edges(&self) -> Vec<&GraphEdge> {
        self.edges.values().collect()
    }

    /// Removes an edge by ID.
    ///
    /// Cleans up all indices: outgoing, incoming, by_label, and outgoing_by_label.
    pub fn remove_edge(&mut self, edge_id: u64) {
        if let Some(edge) = self.edges.remove(&edge_id) {
            let source = edge.source();
            let label = edge.label().to_string();

            // Remove from outgoing index
            if let Some(ids) = self.outgoing.get_mut(&source) {
                ids.retain(|&id| id != edge_id);
            }
            // Remove from incoming index
            if let Some(ids) = self.incoming.get_mut(&edge.target()) {
                ids.retain(|&id| id != edge_id);
            }
            // Remove from label index (US-003)
            if let Some(ids) = self.by_label.get_mut(&label) {
                ids.retain(|&id| id != edge_id);
            }
            // Remove from composite index (US-003)
            if let Some(ids) = self.outgoing_by_label.get_mut(&(source, label)) {
                ids.retain(|&id| id != edge_id);
            }
        }
    }

    /// Removes an edge by ID, only cleaning the outgoing index.
    ///
    /// Used by `ConcurrentEdgeStore` for cross-shard cleanup.
    /// Also cleans up label indices since they are maintained by source shard.
    pub fn remove_edge_outgoing_only(&mut self, edge_id: u64) {
        if let Some(edge) = self.edges.remove(&edge_id) {
            let source = edge.source();
            let label = edge.label().to_string();

            if let Some(ids) = self.outgoing.get_mut(&source) {
                ids.retain(|&id| id != edge_id);
            }
            // Clean label indices (US-003)
            if let Some(ids) = self.by_label.get_mut(&label) {
                ids.retain(|&id| id != edge_id);
            }
            if let Some(ids) = self.outgoing_by_label.get_mut(&(source, label)) {
                ids.retain(|&id| id != edge_id);
            }
        }
    }

    /// Removes an edge by ID, only cleaning the incoming index.
    ///
    /// Used by `ConcurrentEdgeStore` for cross-shard cleanup.
    pub fn remove_edge_incoming_only(&mut self, edge_id: u64) {
        if let Some(edge) = self.edges.remove(&edge_id) {
            if let Some(ids) = self.incoming.get_mut(&edge.target()) {
                ids.retain(|&id| id != edge_id);
            }
        }
    }

    // =========================================================================
    // Persistence
    // =========================================================================

    /// Serializes the edge store to bytes using `postcard`.
    ///
    /// # Errors
    /// Returns an error if serialization fails.
    pub fn to_bytes(&self) -> std::result::Result<Vec<u8>, postcard::Error> {
        postcard::to_allocvec(self)
    }

    /// Deserializes an edge store from bytes.
    ///
    /// # Errors
    /// Returns an error if deserialization fails (e.g., corrupted data).
    pub fn from_bytes(bytes: &[u8]) -> std::result::Result<Self, postcard::Error> {
        postcard::from_bytes(bytes)
    }

    /// Saves the edge store to a file.
    ///
    /// # Errors
    /// Returns an error if serialization or file I/O fails.
    pub fn save_to_file(&self, path: &std::path::Path) -> std::io::Result<()> {
        let bytes = self
            .to_bytes()
            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e.to_string()))?;
        std::fs::write(path, bytes)
    }

    /// Loads an edge store from a file.
    ///
    /// # Errors
    /// Returns an error if file I/O or deserialization fails.
    pub fn load_from_file(path: &std::path::Path) -> std::io::Result<Self> {
        let bytes = std::fs::read(path)?;
        Self::from_bytes(&bytes)
            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e.to_string()))
    }

    /// Removes all edges connected to a node (cascade delete).
    ///
    /// Removes both outgoing and incoming edges, cleaning up all indices
    /// including label indices (EPIC-019 US-003).
    pub fn remove_node_edges(&mut self, node_id: u64) {
        // Collect edge IDs to remove (outgoing)
        let outgoing_ids: Vec<u64> = self.outgoing.remove(&node_id).unwrap_or_default();

        // Collect edge IDs to remove (incoming)
        let incoming_ids: Vec<u64> = self.incoming.remove(&node_id).unwrap_or_default();

        // Remove outgoing edges: clean incoming + label indices for each
        for edge_id in outgoing_ids {
            if let Some(edge) = self.edges.remove(&edge_id) {
                self.purge_incoming_index(edge_id, edge.target());
                self.purge_label_indices(edge_id, node_id, edge.label());
            }
        }

        // Remove incoming edges: clean outgoing + label indices for each
        for edge_id in incoming_ids {
            if let Some(edge) = self.edges.remove(&edge_id) {
                let source = edge.source();
                self.purge_outgoing_index(edge_id, source);
                self.purge_label_indices(edge_id, source, edge.label());
            }
        }
    }

    /// Removes `edge_id` from the incoming index of `target_node`.
    #[inline]
    fn purge_incoming_index(&mut self, edge_id: u64, target_node: u64) {
        if let Some(ids) = self.incoming.get_mut(&target_node) {
            ids.retain(|&id| id != edge_id);
        }
    }

    /// Removes `edge_id` from the outgoing index of `source_node`.
    #[inline]
    fn purge_outgoing_index(&mut self, edge_id: u64, source_node: u64) {
        if let Some(ids) = self.outgoing.get_mut(&source_node) {
            ids.retain(|&id| id != edge_id);
        }
    }

    /// Removes `edge_id` from the `by_label` and `outgoing_by_label` indices (US-003).
    #[inline]
    fn purge_label_indices(&mut self, edge_id: u64, source_node: u64, label: &str) {
        if let Some(ids) = self.by_label.get_mut(label) {
            ids.retain(|&id| id != edge_id);
        }
        if let Some(ids) = self
            .outgoing_by_label
            .get_mut(&(source_node, label.to_string()))
        {
            ids.retain(|&id| id != edge_id);
        }
    }
}