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//! 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`]: PeersIterState::Finished

pub mod closest;
pub mod fixed;

use libp2p_core::PeerId;
use std::borrow::Cow;

/// The state of a peer iterator.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum PeersIterState<'a> {
    /// The iterator is waiting for results.
    ///
    /// `Some(peer)` indicates that the iterator is now waiting for a result
    /// from `peer`, in addition to any other peers for which it is already
    /// waiting for results.
    ///
    /// `None` indicates that the iterator is waiting for results and there is no
    /// new peer to contact, despite the iterator not being at capacity w.r.t.
    /// the permitted parallelism.
    Waiting(Option<Cow<'a, PeerId>>),

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

    /// The iterator finished.
    Finished
}
