nodedb-cluster 0.0.0-beta.1

//! Cluster topology — tracks which nodes exist and their state.

use std::collections::HashMap;
use std::net::SocketAddr;

/// Node lifecycle states.
#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub enum NodeState {
    /// Node is connecting, receiving initial topology.
    Joining,
    /// Node is catching up as a non-voting learner.
    /// Receives Raft log entries but doesn't vote in elections.
    /// Promoted to Active (voting member) after state catch-up
    /// and checksum validation.
    Learner,
    /// Node is fully operational, hosting Raft groups as voting member.
    Active,
    /// Node is being decommissioned, migrating data off.
    Draining,
    /// Node has been removed from the cluster.
    Decommissioned,
}

impl NodeState {
    pub fn as_u8(self) -> u8 {
        match self {
            Self::Joining => 0,
            Self::Active => 1,
            Self::Draining => 2,
            Self::Decommissioned => 3,
            Self::Learner => 4,
        }
    }

    pub fn from_u8(v: u8) -> Option<Self> {
        match v {
            0 => Some(Self::Joining),
            1 => Some(Self::Active),
            2 => Some(Self::Draining),
            3 => Some(Self::Decommissioned),
            4 => Some(Self::Learner),
            _ => None,
        }
    }

    /// Whether this node can vote in Raft elections.
    pub fn is_voter(self) -> bool {
        matches!(self, Self::Active)
    }

    /// Whether this node receives Raft log entries (learner + active).
    pub fn receives_log(self) -> bool {
        matches!(self, Self::Learner | Self::Active)
    }
}

/// Information about a single node in the cluster.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct NodeInfo {
    pub node_id: u64,
    /// Listen address for Raft RPCs (as string for serialization portability).
    pub addr: String,
    pub state: NodeState,
    /// Raft groups hosted on this node.
    pub raft_groups: Vec<u64>,
}

impl NodeInfo {
    pub fn new(node_id: u64, addr: SocketAddr, state: NodeState) -> Self {
        Self {
            node_id,
            addr: addr.to_string(),
            state,
            raft_groups: Vec::new(),
        }
    }

    pub fn socket_addr(&self) -> Option<SocketAddr> {
        self.addr.parse().ok()
    }
}

/// Cluster topology — authoritative registry of all nodes.
///
/// Updated atomically via Raft (metadata group) in production.
/// Persisted to the cluster catalog (redb).
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct ClusterTopology {
    nodes: HashMap<u64, NodeInfo>,
    /// Monotonically increasing version for stale detection.
    version: u64,
}

impl ClusterTopology {
    pub fn new() -> Self {
        Self {
            nodes: HashMap::new(),
            version: 0,
        }
    }

    /// Add or update a node. Bumps the version.
    pub fn add_node(&mut self, info: NodeInfo) {
        self.nodes.insert(info.node_id, info);
        self.version += 1;
    }

    /// Remove a node. Bumps the version.
    pub fn remove_node(&mut self, node_id: u64) -> Option<NodeInfo> {
        let removed = self.nodes.remove(&node_id);
        if removed.is_some() {
            self.version += 1;
        }
        removed
    }

    pub fn get_node(&self, node_id: u64) -> Option<&NodeInfo> {
        self.nodes.get(&node_id)
    }

    pub fn get_node_mut(&mut self, node_id: u64) -> Option<&mut NodeInfo> {
        self.nodes.get_mut(&node_id)
    }

    /// Update a node's state. Bumps the version.
    pub fn set_state(&mut self, node_id: u64, state: NodeState) -> bool {
        if let Some(info) = self.nodes.get_mut(&node_id) {
            info.state = state;
            self.version += 1;
            true
        } else {
            false
        }
    }

    /// All nodes with Active state.
    pub fn active_nodes(&self) -> Vec<&NodeInfo> {
        self.nodes
            .values()
            .filter(|n| n.state == NodeState::Active)
            .collect()
    }

    /// All nodes (any state).
    pub fn all_nodes(&self) -> impl Iterator<Item = &NodeInfo> {
        self.nodes.values()
    }

    pub fn node_count(&self) -> usize {
        self.nodes.len()
    }

    pub fn version(&self) -> u64 {
        self.version
    }

    pub fn contains(&self, node_id: u64) -> bool {
        self.nodes.contains_key(&node_id)
    }

    /// Add a new node as a non-voting learner.
    ///
    /// The node receives Raft log entries and catches up with the cluster
    /// state, but doesn't participate in elections. Once caught up and
    /// validated, call `promote_to_voter()`.
    pub fn join_as_learner(&mut self, info: NodeInfo) -> bool {
        if self.nodes.contains_key(&info.node_id) {
            return false; // Already exists.
        }
        let mut learner = info;
        learner.state = NodeState::Learner;
        self.nodes.insert(learner.node_id, learner);
        self.version += 1;
        true
    }

    /// Promote a learner node to a full voting member.
    ///
    /// Only valid for nodes in `Learner` state. After promotion, the node
    /// participates in Raft elections and counts toward quorum.
    pub fn promote_to_voter(&mut self, node_id: u64) -> bool {
        if let Some(info) = self.nodes.get_mut(&node_id)
            && info.state == NodeState::Learner
        {
            info.state = NodeState::Active;
            self.version += 1;
            return true;
        }
        false
    }

    /// All learner nodes (catching up, not yet voting).
    pub fn learner_nodes(&self) -> Vec<&NodeInfo> {
        self.nodes
            .values()
            .filter(|n| n.state == NodeState::Learner)
            .collect()
    }
}

impl Default for ClusterTopology {
    fn default() -> Self {
        Self::new()
    }
}

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

    #[test]
    fn add_and_lookup() {
        let mut topo = ClusterTopology::new();
        topo.add_node(NodeInfo::new(
            1,
            "127.0.0.1:9400".parse().unwrap(),
            NodeState::Active,
        ));
        topo.add_node(NodeInfo::new(
            2,
            "127.0.0.1:9401".parse().unwrap(),
            NodeState::Joining,
        ));

        assert_eq!(topo.node_count(), 2);
        assert_eq!(topo.version(), 2);
        assert_eq!(topo.active_nodes().len(), 1);
        assert!(topo.contains(1));
        assert!(topo.contains(2));
    }

    #[test]
    fn remove_node() {
        let mut topo = ClusterTopology::new();
        topo.add_node(NodeInfo::new(
            1,
            "127.0.0.1:9400".parse().unwrap(),
            NodeState::Active,
        ));
        let removed = topo.remove_node(1);
        assert!(removed.is_some());
        assert_eq!(topo.node_count(), 0);
        assert_eq!(topo.version(), 2); // add + remove
    }

    #[test]
    fn set_state() {
        let mut topo = ClusterTopology::new();
        topo.add_node(NodeInfo::new(
            1,
            "127.0.0.1:9400".parse().unwrap(),
            NodeState::Joining,
        ));
        assert!(topo.set_state(1, NodeState::Active));
        assert_eq!(topo.get_node(1).unwrap().state, NodeState::Active);
    }

    #[test]
    fn node_state_roundtrip() {
        for state in [
            NodeState::Joining,
            NodeState::Active,
            NodeState::Draining,
            NodeState::Decommissioned,
        ] {
            assert_eq!(NodeState::from_u8(state.as_u8()), Some(state));
        }
        assert_eq!(NodeState::from_u8(255), None);
    }

    #[test]
    fn serde_roundtrip() {
        let mut topo = ClusterTopology::new();
        topo.add_node(NodeInfo::new(
            1,
            "127.0.0.1:9400".parse().unwrap(),
            NodeState::Active,
        ));
        topo.add_node(NodeInfo::new(
            2,
            "127.0.0.1:9401".parse().unwrap(),
            NodeState::Active,
        ));

        let bytes = rmp_serde::to_vec(&topo).unwrap();
        let decoded: ClusterTopology = rmp_serde::from_slice(&bytes).unwrap();
        assert_eq!(decoded.node_count(), 2);
        assert_eq!(decoded.version(), 2);
    }
}