// Copyright 2019 Parity Technologies (UK) Ltd.
//
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// The basis of this file has been taken from the rust-libp2p codebase:
// https://github.com/libp2p/rust-libp2p

//! Peer selection strategies for queries in the form of iterator-like state machines.
//!
//! Using a peer iterator in a query involves performing the following steps
//! repeatedly and in an alternating fashion:
//!
//!   1. Calling `next` to observe the next state of the iterator and determine
//!      what to do, which is to either issue new requests to peers or continue
//!      waiting for responses.
//!
//!   2. When responses are received or requests fail, providing input to the
//!      iterator via the `on_success` and `on_failure` callbacks,
//!      respectively, followed by repeating step (1).
//!
//! When a call to `next` returns [`Finished`], no more peers can be obtained
//! from the iterator and the results can be obtained from `into_result`.
//!
//! A peer iterator can be finished prematurely at any time through `finish`.
//!
//! [`Finished`]: QueryState::Finished

pub mod closest;
pub mod predicate;

/// The state of the query reported by [`closest::FindNodeQuery::next`] or
/// [`predicate::PredicateQuery::next`].
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum QueryState<TNodeId> {
    /// The query is waiting for results.
    ///
    /// `Some(peer)` indicates that the query is now waiting for a result
    /// from `peer`, in addition to any other peers for which the query is already
    /// waiting for results.
    ///
    /// `None` indicates that the query is waiting for results and there is no
    /// new peer to contact, despite the query not being at capacity w.r.t.
    /// the permitted parallelism.
    Waiting(Option<TNodeId>),

    /// The query is waiting for results and is at capacity w.r.t. the
    /// permitted parallelism.
    WaitingAtCapacity,

    /// The query finished.
    Finished,
}