//! RFC 010 — clustering (smarm⇄smarm, explicit remote boundary).
//!
//! c1: feature flag + optional deps. c2: the owned envelope. c3: the
//! transport trait (control connection), framed codec, and the TCP +
//! loopback impls. c5: the handshake state machine. c6: the connection
//! [`manager`] (registry) and per-peer connection actors ([`conn`]), started
//! as an explicit supervision subtree, plus the handshake on the
//! accept/connect path ([`connect`]). Everything above them lands in later
//! chunks.

pub mod conn;
pub mod connect;
pub mod connector;
pub mod discovery;
pub mod envelope;
pub mod expose;
pub mod handshake;
pub mod manager;
pub mod membership;
pub mod transport;

use std::io;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

use crate::gen_server::{self, GenServerBuilder};
use crate::monitor::monitor;
use crate::pg::Incarnation;
use crate::scheduler::{sleep, spawn, JoinHandle};
use crate::supervisor::{ChildSpec, OneForOne, Restart};

use envelope::NodeMeta;
use handshake::Local;
use transport::tcp::TcpTransport;
use transport::Transport;

pub use conn::{spawn_established, ConnHandle};
pub use connect::{dial, spawn_acceptor, AcceptorHandle};
pub use connector::{spawn_connector, ConnectorHandle};
pub use discovery::{Discovery, StaticSeeds, Strategy};
pub use expose::{expose, expose_type, type_hash, DeliverError};
pub use manager::{Manager, MANAGER};
pub use membership::{subscribe, view, MembershipEvents, NodeEvent, NodeInfo};

/// c6d — the derived build hash for [`handshake::LocalNode::build_hash`]:
/// two builds may mesh only when this matches, and it is a pure function of
/// the compile-time inputs that define wire compatibility today — the exact
/// toolchain (`rustc -V`), the declared feature set, and
/// [`envelope::PROTO_VERSION`]. FNV-1a 64 over the build-script string, then
/// the proto version folded byte-wise, so a proto bump moves the hash even
/// on an identical toolchain. The domain is deliberately lean and
/// tightenable later without a wire change — it is just a `u64`.
pub const BUILD_HASH: u64 = fold_u32(
    fnv1a64(env!("SMARM_BUILD_HASH_INPUTS").as_bytes()),
    envelope::PROTO_VERSION,
);

/// FNV-1a 64 (const so [`BUILD_HASH`] is a compile-time fact).
const fn fnv1a64(bytes: &[u8]) -> u64 {
    let mut h: u64 = 0xcbf2_9ce4_8422_2325;
    let mut i = 0;
    while i < bytes.len() {
        h ^= bytes[i] as u64;
        h = h.wrapping_mul(0x0000_0100_0000_01b3);
        i += 1;
    }
    h
}

/// Continue an FNV-1a state over a `u32`'s little-endian bytes.
const fn fold_u32(mut h: u64, v: u32) -> u64 {
    let b = v.to_le_bytes();
    let mut i = 0;
    while i < b.len() {
        h ^= b[i] as u64;
        h = h.wrapping_mul(0x0000_0100_0000_01b3);
        i += 1;
    }
    h
}

/// How to run this node: its identity and how it finds peers.
pub struct Config {
    /// This node's claimed name — the mesh-wide identity peers dial by and
    /// the tie-break input. Must be unique across the mesh.
    pub node_name: String,
    /// Metadata offered in this node's `Hello`.
    pub meta: NodeMeta,
    /// The control-connection listen address (e.g. `"127.0.0.1:0"`; the
    /// concrete bound address is [`Cluster::local_addr`]).
    pub listen_addr: String,
    /// The peer-discovery strategy — [`StaticSeeds`] until richer ones land.
    pub strategy: Box<dyn Strategy>,
}

/// A running cluster node: the supervised [`Manager`], the acceptor over the
/// bound listener, and the connector driving its [`Strategy`]. Roles will
/// eventually mount this; until the role mechanism lands it is started by
/// hand (RFC 010 §7).
///
/// Dropping the handle stops the acceptor and connector loops (no new
/// connections in either direction) but detaches the manager subtree, which
/// — with every established connection — keeps running for the life of the
/// runtime, the same split as [`AcceptorHandle`] alone.
pub struct Cluster {
    _sup: JoinHandle,
    acceptor: AcceptorHandle,
    connector: ConnectorHandle,
    local: Local,
}

impl Cluster {
    /// The concrete bound listen address, dialable as-is.
    pub fn local_addr(&self) -> &str {
        self.acceptor.local_addr()
    }

    /// This node's handshake identity (name, incarnation, build hash, meta).
    pub fn local(&self) -> &Local {
        &self.local
    }

    /// Stop accepting and dialing. Established connections stay up (they
    /// belong to the manager); tear those down via the manager.
    pub fn shutdown(&self) {
        self.acceptor.shutdown();
        self.connector.shutdown();
    }
}

/// Start a cluster node: the supervised manager (blocking until it is
/// registered and ready to answer), the acceptor bound per
/// [`Config::listen_addr`], and the connector running [`Config::strategy`].
/// The node's identity is completed here: `incarnation` is
/// [`self_incarnation`] and `build_hash` is [`BUILD_HASH`] — c7 is its first
/// consumer. Errs only if the listener cannot bind.
///
/// The manager is a supervised child (restarted on crash); per-peer
/// connection actors are dynamic and monitored by the manager rather than
/// statically supervised — a lost connection is re-established by the
/// connector's dial loop, never resurrected onto a stale socket.
pub fn start(config: Config) -> io::Result<Cluster> {
    let sup = spawn(|| {
        OneForOne::new()
            .child(ChildSpec::new(Restart::Permanent, manager_child))
            .run()
    });
    while gen_server::whereis_server(MANAGER).is_none() {
        sleep(Duration::from_millis(1));
    }
    let local = Local {
        node_name: config.node_name,
        incarnation: self_incarnation(),
        build_hash: BUILD_HASH,
        meta: config.meta,
    };
    let listener = TcpTransport.listen(&config.listen_addr)?;
    let acceptor = spawn_acceptor(listener, local.clone());
    let connector = spawn_connector(Box::new(TcpTransport), local.clone(), config.strategy);
    Ok(Cluster {
        _sup: sup,
        acceptor,
        connector,
        local,
    })
}

/// This process's incarnation epoch: milliseconds since the Unix epoch,
/// truncated to `u32`. Not a clock — its one job is separating a node from
/// its own restart (two starts of the same name land on the same value only
/// if they happen within the same millisecond modulo ~49.7 days). Seconds
/// would be too coarse: a crash-and-restart inside one second is routine
/// under supervision.
pub fn self_incarnation() -> Incarnation {
    let ms = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_millis())
        .unwrap_or(0);
    Incarnation::new(ms as u32)
}

/// The supervised manager child body. It *is* the child actor: it starts the
/// named manager, then parks on the manager's own termination so this actor's
/// lifetime tracks the manager's — the supervisor's restart accounting keys off
/// this actor exiting.
fn manager_child() {
    let m = match GenServerBuilder::new(Manager::new()).named(MANAGER).start() {
        Ok(m) => m,
        // Name still held by a not-yet-reaped prior instance: return and let
        // the supervisor retry under its restart policy.
        Err(_) => return,
    };
    let _ = monitor(m.pid()).rx.recv();
}

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

    /// The hash core against the published FNV-1a 64 test vectors — the
    /// contract is "this is FNV-1a", not "whatever the fn does".
    #[test]
    fn fnv1a64_known_vectors() {
        assert_eq!(fnv1a64(b""), 0xcbf2_9ce4_8422_2325);
        assert_eq!(fnv1a64(b"a"), 0xaf63_dc4c_8601_ec8c);
        assert_eq!(fnv1a64(b"foobar"), 0x85944171f73967e8);
    }

    /// Folding the proto version continues the same FNV state: identical
    /// inputs with a different version must land on a different hash.
    #[test]
    fn proto_version_moves_the_hash() {
        let base = fnv1a64(b"same-toolchain;features=CLUSTER");
        assert_ne!(fold_u32(base, 1), fold_u32(base, 2));
        // And it equals hashing the bytes in one pass — the fold is a
        // continuation, not a second construction.
        let mut all = b"same-toolchain;features=CLUSTER".to_vec();
        all.extend_from_slice(&1u32.to_le_bytes());
        assert_eq!(fold_u32(base, 1), fnv1a64(&all));
    }

    /// The derived constant exists, is compile-time, and is not degenerate.
    #[test]
    fn build_hash_is_nonzero() {
        const H: u64 = BUILD_HASH;
        assert_ne!(H, 0);
    }
}