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//! Hypergraph is data structure library to generate directed [hypergraphs](https://en.wikipedia.org/wiki/Hypergraph).
//!
//! > A hypergraph is a generalization of a graph in which a hyperedge can join any number of vertices.
//!
//! ## Features
//!
//! This library enables you to:
//!
//! - represent **non-simple** hypergraphs with two or more hyperedges containing the exact same set of vertices
//! - represent **self-loops** — i.e., hyperedges containing vertices directed to themselves one or more times
//! - represent **unaries** — i.e., hyperedges containing a unique vertex
//!
//! Additional features:
//!
//! - Safe Rust implementation
//! - Proper error handling
//! - Stable indexes for each hyperedge and each vertex — identity is the index, not the weight; duplicate weights are permitted on both sides
//! - Graph traversal: BFS, DFS, topological sort, reachability check, all simple paths
//! - Shortest paths: Dijkstra point-to-point and single-source
//! - Structural analysis: strongly connected components, weakly connected components, subgraph extraction, cycle detection
//! - Filtered views: `retain_vertices`, `retain_hyperedges`
//! - Generic query interface: [`HypergraphQuery`] trait — implement 9 primitives to get all
//! graph algorithms for free; write generic code that works with either backend
//! - Optional **`serde`** feature for serialization/deserialization support
//! (enable with `features = ["serde"]` in `Cargo.toml`)
//! - Optional **`persistence`** feature for disk-backed graphs larger than RAM
//! (enable with `features = ["persistence"]` in `Cargo.toml`)
//!
//! ## Persistent disk-backed graphs
//!
//! Enable the `persistence` feature to unlock [`PersistentHypergraph`], a variant
//! backed by an [LSM-tree](https://en.wikipedia.org/wiki/Log-structured_merge-tree)
//! (via [fjall](https://github.com/fjall-rs/fjall)) with an in-memory hot-data
//! cache. It supports graphs that exceed available RAM and survives process
//! restarts without any manual serialization step.
//!
//! ```toml
//! # Cargo.toml
//! [dependencies]
//! hypergraph = { version = "*", features = ["persistence"] }
//! ```
//!
//! ### Vertex and hyperedge types
//!
//! In addition to the usual [`VertexTrait`] / [`HyperedgeTrait`] bounds, both
//! types must implement `serde::Serialize + serde::DeserializeOwned` so they
//! can be encoded to disk.
//!
//! ### Opening a graph
//!
//! [`PersistentHypergraph::open`] creates the database directory if it does not
//! exist, or recovers all data if it does.
//!
//! ```ignore
//! use std::sync::Arc;
//! use hypergraph::PersistentHypergraph;
//!
//! // Open (or create) a persistent graph.
//! let g = Arc::new(PersistentHypergraph::<MyVertex, MyEdge>::open("/var/data/my-graph")?);
//!
//! // All write methods take &self, so the Arc can be shared across threads.
//! let g2 = Arc::clone(&g);
//! std::thread::spawn(move || -> anyhow::Result<()> {
//! g2.add_vertex(my_vertex)?;
//! Ok(())
//! });
//! ```
//!
//! ### Thread safety
//!
//! [`PersistentHypergraph`] is `Send + Sync`. All write methods take `&self` and use
//! atomic counters internally, so the same instance can be shared across threads
//! via an `Arc` without an external `Mutex`.
//!
//! > **Note**: individual multi-step operations such as `add_hyperedge` are not
//! > serializable with respect to concurrent writers. If full operation-level
//! > isolation is required, wrap the `Arc<PersistentHypergraph>` in a `Mutex`.
//!
//! ### Persistence
//!
//! Writes are appended to the WAL immediately and are durable on process crash.
//! Call [`PersistentHypergraph::persist`] to additionally fsync to the physical
//! medium when you need a hard durability guarantee.
//!
//! ### Cache capacity
//!
//! By default the hot-data cache holds up to 10 000 entries per layer (vertices
//! and hyperedges). Use [`PersistentHypergraph::open_with_capacity`] to tune this for
//! your workload.
//!
//! ## Example
//!
//! Please notice that the hyperedges and the vertices must implement the
//! [`HyperedgeTrait`] and the [`VertexTrait`] respectively.
//!
//! ```
//! use hypergraph::{HyperedgeIndex, Hypergraph, VertexIndex};
//! use std::fmt::{Display, Formatter, Result};
//!
//! // Create a new struct to represent a person.
//! #[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
//! pub struct Person<'a> {
//! name: &'a str,
//! }
//!
//! impl<'a> Person<'a> {
//! pub fn new(name: &'a str) -> Self {
//! Self { name }
//! }
//! }
//!
//! impl<'a> Display for Person<'a> {
//! fn fmt(&self, f: &mut Formatter<'_>) -> Result {
//! write!(f, "{}", self.name)
//! }
//! }
//!
//! // Create a new struct to represent a relation.
//! #[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
//! pub struct Relation<'a> {
//! cost: usize,
//! name: &'a str,
//! }
//!
//! impl<'a> Relation<'a> {
//! pub fn new(name: &'a str, cost: usize) -> Self {
//! Self { cost, name }
//! }
//! }
//!
//! impl<'a> Display for Relation<'a> {
//! fn fmt(&self, f: &mut Formatter<'_>) -> Result {
//! write!(f, "{}", self.name)
//! }
//! }
//!
//! impl<'a> From<Relation<'a>> for usize {
//! fn from(relation: Relation<'a>) -> usize {
//! relation.cost
//! }
//! }
//!
//! fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
//! let mut graph = Hypergraph::<Person, Relation>::new();
//!
//! // Create some folks.
//! let ava_person = Person::new("Ava");
//! let bianca_person = Person::new("Bianca");
//! let charles_person = Person::new("Charles");
//! let daena_person = Person::new("Daena");
//! let ewan_person = Person::new("Ewan");
//! let faarooq_person = Person::new("Faarooq");
//! let ghanda_person = Person::new("Ghanda");
//!
//! // Add those to the graph as vertices.
//! let ava = graph.add_vertex(ava_person)?;
//! let bianca = graph.add_vertex(bianca_person)?;
//! let charles = graph.add_vertex(charles_person)?;
//! let daena = graph.add_vertex(daena_person)?;
//! let ewan = graph.add_vertex(ewan_person)?;
//! let faarooq = graph.add_vertex(faarooq_person)?;
//! let ghanda = graph.add_vertex(ghanda_person)?;
//!
//! // Each vertex gets a unique index by insertion order.
//! assert_eq!(ava, VertexIndex(0));
//! assert_eq!(ghanda, VertexIndex(6));
//!
//! // Get the weight of a vertex.
//! assert_eq!(graph.get_vertex_weight(VertexIndex(0)), Ok(&ava_person));
//!
//! // The hypergraph has seven vertices.
//! assert_eq!(graph.count_vertices(), 7);
//!
//! // Create some relations.
//! let cat_video = Relation::new("share a viral video with a cat", 1);
//! let dog_video = Relation::new("share a viral video with a dog", 1);
//! let beaver_video = Relation::new("share a viral video with a beaver", 1);
//! let playing_online = Relation::new("play online", 1);
//! let passing_ball = Relation::new("pass the ball", 1);
//!
//! // Add those to the graph as hyperedges.
//! let first_relation = graph.add_hyperedge(vec![faarooq, ava, ghanda], cat_video)?;
//! let second_relation = graph.add_hyperedge(vec![faarooq, ava, ghanda], dog_video)?;
//! let third_relation = graph.add_hyperedge(vec![ewan, ava, bianca], beaver_video)?;
//! let fourth_relation = graph.add_hyperedge(vec![daena], playing_online)?;
//! let fifth_relation = graph.add_hyperedge(vec![ewan, charles, bianca, bianca, ewan], passing_ball)?;
//!
//! // Each hyperedge gets a unique index by insertion order.
//! assert_eq!(first_relation, HyperedgeIndex(0));
//! assert_eq!(fifth_relation, HyperedgeIndex(4));
//!
//! // Get the weight of a hyperedge.
//! assert_eq!(graph.get_hyperedge_weight(HyperedgeIndex(0)), Ok(&cat_video));
//!
//! // Get the vertices of a hyperedge.
//! assert_eq!(graph.get_hyperedge_vertices(HyperedgeIndex(0)), Ok(vec![faarooq, ava, ghanda]));
//!
//! // The hypergraph has 5 hyperedges.
//! assert_eq!(graph.count_hyperedges(), 5);
//!
//! // Get the hyperedges of a vertex.
//! assert_eq!(graph.get_vertex_hyperedges(VertexIndex(0)), Ok(vec![first_relation, second_relation, third_relation]));
//! assert_eq!(graph.get_full_vertex_hyperedges(VertexIndex(0)), Ok(vec![vec![faarooq, ava, ghanda], vec![faarooq, ava, ghanda], vec![ewan, ava, bianca]]));
//!
//! // Get the intersection of some hyperedges.
//! assert_eq!(graph.get_hyperedges_intersections(&[second_relation, third_relation]), Ok(vec![ava]));
//!
//! // Find a hyperedge containing a connection between two vertices.
//! assert_eq!(graph.get_hyperedges_connecting(bianca, bianca), Ok(vec![fifth_relation]));
//!
//! // Get the adjacent vertices from a vertex.
//! assert_eq!(graph.get_adjacent_vertices_from(VertexIndex(0)), Ok(vec![bianca, ghanda]));
//!
//! // Get the adjacent vertices to a vertex.
//! assert_eq!(graph.get_adjacent_vertices_to(VertexIndex(0)), Ok(vec![ewan, faarooq]));
//!
//! // Find the shortest paths between some vertices.
//! assert_eq!(graph.get_dijkstra_connections(faarooq, bianca), Ok(vec![(faarooq, None), (ava, Some(first_relation)), (bianca, Some(third_relation))]));
//!
//! // Update the weight of a vertex.
//! graph.update_vertex_weight(ava, Person::new("Avā"))?;
//!
//! // Update the weight of a hyperedge.
//! graph.update_hyperedge_weight(third_relation, Relation::new("share a viral video with a capybara", 1))?;
//!
//! // Update the vertices of a hyperedge.
//! graph.update_hyperedge_vertices(third_relation, vec![ewan, ava, daena])?;
//!
//! // Remove a hyperedge.
//! graph.remove_hyperedge(first_relation)?;
//!
//! // Remove a vertex.
//! graph.remove_vertex(ewan)?;
//!
//! // Reverse a hyperedge.
//! graph.reverse_hyperedge(fifth_relation)?;
//!
//! // Get the in-degree of a vertex.
//! assert_eq!(graph.get_vertex_degree_in(ava), Ok(1));
//!
//! // Get the out-degree of a vertex.
//! assert_eq!(graph.get_vertex_degree_out(ghanda), Ok(0));
//!
//! // Contract a hyperedge's vertices.
//! graph.contract_hyperedge_vertices(fifth_relation, vec![bianca, charles], bianca)?;
//!
//! // Join some hyperedges.
//! graph.join_hyperedges(&[fifth_relation, third_relation]);
//!
//! // Clear the hyperedges.
//! graph.clear_hyperedges()?;
//!
//! // Clear the whole hypergraph.
//! graph.clear();
//!
//! Ok(())
//! }
//! ```
// Reexport of the public API.
pub use crate*;