//! Cluster discovery: etcd-driven ractor_cluster node discovery.
//!
//! Architecture:
//!   1. Start a `ractor_cluster::NodeServer` (TCP listener for actor remoting)
//!   2. Connect to etcd and register this node
//!   3. Discover existing peers → `client_connect()` to each
//!   4. Watch etcd for future peer join/leave → connect/disconnect dynamically
//!
//! Once ractor_cluster TCP connections are established, the existing
//! `pg::get_members()` / `ractor::call_t!()` APIs automatically work
//! cross-network — no changes needed in actor/handler.rs or server/mod.rs.

pub mod discovery;
pub mod types;

pub use discovery::EtcdRegistry;
pub use types::PeerInfo;

use std::sync::Arc;

use ractor::ActorRef;
use ractor_cluster::node::NodeConnectionMode;
use ractor_cluster::{NodeServer, NodeServerMessage, client_connect};

use crate::error::{GitError, GitResult};

/// Configuration for the cluster subsystem.
#[derive(Debug, Clone)]
pub struct ClusterConfig {
    /// etcd endpoints (e.g. ["http://etcd1:2379", "http://etcd2:2379"])
    pub etcd_endpoints: Vec<String>,
    /// Logical name for this storage node
    pub storage_name: String,
    /// gRPC address advertised to clients
    pub grpc_addr: String,
    /// TCP port for ractor_cluster NodeServer
    pub cluster_port: u16,
    /// Shared authentication cookie for ractor_cluster
    pub cookie: String,
    /// etcd lease TTL in seconds
    pub lease_ttl_secs: i64,
    /// etcd connection timeout in milliseconds
    pub connect_timeout_ms: u64,
    /// Hostname used in the ractor_cluster node name (`name@hostname`).
    /// Also used by remote nodes to connect back via `{cluster_hostname}:{cluster_port}`.
    /// In K8s/Docker, this should be a resolvable address (Pod IP, service DNS, etc.)
    pub cluster_hostname: String,
}

/// The running cluster manager. Holds references to the NodeServer and etcd registry.
/// Dropping this will stop the background tasks.
pub struct ClusterManager {
    /// The ractor_cluster NodeServer actor
    pub node_server: ActorRef<NodeServerMessage>,
    /// The etcd registry (for health checks, etc.)
    pub registry: Arc<EtcdRegistry>,
    /// Handles for background tasks (keepalive + watch)
    _keepalive_handle: tokio::task::JoinHandle<()>,
    _watch_handle: tokio::task::JoinHandle<()>,
}

impl ClusterManager {
    /// Start the full cluster subsystem:
    ///   1. Spawn NodeServer (TCP listener)
    ///   2. Connect to etcd + register
    ///   3. Discover peers → client_connect
    ///   4. Start keepalive + watch loops
    ///
    /// Returns `Err` if etcd is unreachable (caller should fall back to standalone).
    pub async fn start(config: ClusterConfig) -> GitResult<Self> {
        // ── Step 1: Start NodeServer ──
        let node_server = spawn_node_server(&config).await?;
        tracing::info!(
            port = config.cluster_port,
            hostname = %config.cluster_hostname,
            "NodeServer started"
        );

        // ── Step 2: Connect to etcd and register ──
        let cluster_addr = format!("{}:{}", config.cluster_hostname, config.cluster_port);
        let peer_info = PeerInfo {
            storage_name: config.storage_name.clone(),
            cluster_addr: cluster_addr.clone(),
            grpc_addr: config.grpc_addr.clone(),
            version: env!("CARGO_PKG_VERSION").to_string(),
        };

        let registry = Arc::new(
            EtcdRegistry::register(
                config.etcd_endpoints.clone(),
                &peer_info,
                config.lease_ttl_secs,
                config.connect_timeout_ms,
            )
            .await
            .map_err(|e| GitError::Internal(format!("etcd registration failed: {e}")))?,
        );

        // ── Step 3: Discover existing peers and connect ──
        let peers = registry
            .discover_peers()
            .await
            .map_err(|e| GitError::Internal(format!("peer discovery failed: {e}")))?;

        for peer in &peers {
            connect_to_peer(&node_server, peer, &config.storage_name).await;
        }

        // ── Step 4: Start background tasks ──
        let keepalive_handle = registry.start_keepalive();

        let ns_for_watch = node_server.clone();
        let my_name_for_watch = config.storage_name.clone();
        let watch_handle = registry.start_watch(
            move |peer| {
                let ns = ns_for_watch.clone();
                let my_name = my_name_for_watch.clone();
                tokio::spawn(async move {
                    connect_to_peer(&ns, &peer, &my_name).await;
                });
            },
            move |name| {
                tracing::info!(
                    peer = %name,
                    "peer left etcd registry (ractor_cluster will cleanup TCP session)"
                );
                // ractor_cluster automatically:
                //   1. Detects TCP disconnection
                //   2. Stops the NodeSession actor
                //   3. Stops all RemoteActors for that session
                //   4. Removes them from Process Groups
                // No manual cleanup needed.
            },
        );

        tracing::info!(
            storage_name = %config.storage_name,
            peers_found = peers.len(),
            "cluster manager started"
        );

        Ok(Self {
            node_server,
            registry,
            _keepalive_handle: keepalive_handle,
            _watch_handle: watch_handle,
        })
    }
}

/// Spawn the ractor_cluster NodeServer actor (TCP listener for inter-node communication).
async fn spawn_node_server(config: &ClusterConfig) -> GitResult<ActorRef<NodeServerMessage>> {
    let server = NodeServer::new(
        config.cluster_port,
        config.cookie.clone(),
        config.storage_name.clone(),
        config.cluster_hostname.clone(),
        None, // no encryption (internal network)
        Some(NodeConnectionMode::Transitive),
    );

    let (actor_ref, _handle) = ractor::Actor::spawn(
        Some(format!("node_server_{}", config.storage_name)),
        server,
        (),
    )
    .await
    .map_err(|e| GitError::Internal(format!("failed to spawn NodeServer: {e}")))?;

    Ok(actor_ref)
}

/// Establish a ractor_cluster TCP connection to a remote peer.
///
/// Uses ordering optimization: only the node with the lexicographically
/// smaller `storage_name` initiates the connection. The other side will
/// accept the incoming connection. This prevents duplicate connections.
async fn connect_to_peer(
    node_server: &ActorRef<NodeServerMessage>,
    peer: &PeerInfo,
    my_name: &str,
) {
    // Ordering optimization: only smaller-named node connects
    if my_name >= peer.storage_name.as_str() {
        tracing::debug!(
            peer = %peer.storage_name,
            "skipping connect (peer has lower/equal name, they connect to us)"
        );
        return;
    }

    tracing::info!(
        peer = %peer.storage_name,
        cluster_addr = %peer.cluster_addr,
        "connecting to peer via ractor_cluster"
    );

    match client_connect(node_server, peer.cluster_addr.as_str()).await {
        Ok(()) => {
            tracing::info!(
                peer = %peer.storage_name,
                "ractor_cluster connection initiated"
            );
        }
        Err(e) => {
            tracing::warn!(
                peer = %peer.storage_name,
                cluster_addr = %peer.cluster_addr,
                error = %e,
                "failed to connect to peer (will retry on next watch event)"
            );
        }
    }
}