//! The [`TopologyGraph`] data model: role-slot nodes and typed edges.

use std::collections::{BTreeMap, HashSet};

use serde::{Deserialize, Serialize};

use crate::kind::TopologyKind;
use crate::TopologyError;

/// A role slot in the topology. At run time a node is bound to a concrete
/// claw (`AgentId`); here it is purely structural.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Node {
    /// Stable identifier, unique within the graph.
    pub id: String,
    /// The role this slot plays (e.g. "orchestrator", "researcher").
    pub role: String,
    /// Optional depth hint (0 = top) for layered topologies.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub level: Option<u32>,
    /// Free-form attributes (model, budget, persona…).
    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
    pub attrs: BTreeMap<String, String>,
}

impl Node {
    /// Convenience constructor for a bare role slot.
    pub fn new(id: impl Into<String>, role: impl Into<String>) -> Self {
        Node {
            id: id.into(),
            role: role.into(),
            level: None,
            attrs: BTreeMap::new(),
        }
    }
}

/// The semantic of an edge — how the `from` node relates to `to`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum EdgeKind {
    /// `from` delegates work down to `to`.
    DelegatesTo,
    /// `from` reports results up to `to`.
    ReportsTo,
    /// `from` pipes its output into `to` (pipeline stage).
    PipesTo,
    /// `from` and `to` are collaborating peers.
    PeersWith,
    /// `from` routes/dispatches to `to` (hub/router).
    RoutesTo,
    /// `from` bids work out to `to` (market).
    BidsTo,
    /// `from` and `to` share a workspace (blackboard).
    ReadsWrites,
}

/// A directed relationship between two nodes.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Edge {
    /// Source node id.
    pub from: String,
    /// Target node id.
    pub to: String,
    /// Relationship semantic.
    pub kind: EdgeKind,
}

/// A full topology: a declared [`TopologyKind`] plus its node/edge graph.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct TopologyGraph {
    /// The declared topology kind (the classifier can also infer one).
    pub kind: TopologyKind,
    /// Role-slot nodes.
    pub nodes: Vec<Node>,
    /// Directed, typed edges.
    pub edges: Vec<Edge>,
}

impl TopologyGraph {
    /// Build a graph and validate it in one step.
    pub fn new(
        kind: TopologyKind,
        nodes: Vec<Node>,
        edges: Vec<Edge>,
    ) -> Result<Self, TopologyError> {
        let g = TopologyGraph { kind, nodes, edges };
        g.validate()?;
        Ok(g)
    }

    /// Ensure the graph is well-formed: non-empty, unique ids, edges resolve.
    pub fn validate(&self) -> Result<(), TopologyError> {
        if self.nodes.is_empty() {
            return Err(TopologyError::Empty);
        }
        let mut ids = HashSet::with_capacity(self.nodes.len());
        for n in &self.nodes {
            if !ids.insert(n.id.as_str()) {
                return Err(TopologyError::DuplicateNode(n.id.clone()));
            }
        }
        for e in &self.edges {
            if !ids.contains(e.from.as_str()) {
                return Err(TopologyError::UnknownNode(e.from.clone()));
            }
            if !ids.contains(e.to.as_str()) {
                return Err(TopologyError::UnknownNode(e.to.clone()));
            }
        }
        Ok(())
    }

    /// Node count.
    pub fn order(&self) -> usize {
        self.nodes.len()
    }

    /// Edge count.
    pub fn size(&self) -> usize {
        self.edges.len()
    }

    /// Undirected adjacency as index sets (used by metrics). Self-loops and
    /// duplicate edges are collapsed. Returns `(index_of, neighbors)`.
    pub(crate) fn undirected_adjacency(&self) -> (BTreeMap<&str, usize>, Vec<HashSet<usize>>) {
        let index_of: BTreeMap<&str, usize> = self
            .nodes
            .iter()
            .enumerate()
            .map(|(i, n)| (n.id.as_str(), i))
            .collect();
        let mut adj = vec![HashSet::new(); self.nodes.len()];
        for e in &self.edges {
            if let (Some(&a), Some(&b)) =
                (index_of.get(e.from.as_str()), index_of.get(e.to.as_str()))
            {
                if a != b {
                    adj[a].insert(b);
                    adj[b].insert(a);
                }
            }
        }
        (index_of, adj)
    }

    /// Directed in-degree per node index (used for hierarchy detection).
    pub(crate) fn in_degrees(&self) -> Vec<usize> {
        let index_of: BTreeMap<&str, usize> = self
            .nodes
            .iter()
            .enumerate()
            .map(|(i, n)| (n.id.as_str(), i))
            .collect();
        let mut indeg = vec![0usize; self.nodes.len()];
        for e in &self.edges {
            if let Some(&b) = index_of.get(e.to.as_str()) {
                if index_of.get(e.from.as_str()).copied() != Some(b) {
                    indeg[b] += 1;
                }
            }
        }
        indeg
    }
}

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

    #[test]
    fn validate_rejects_empty() {
        let g = TopologyGraph {
            kind: TopologyKind::Flat,
            nodes: vec![],
            edges: vec![],
        };
        assert_eq!(g.validate(), Err(TopologyError::Empty));
    }

    #[test]
    fn validate_rejects_unknown_edge() {
        let err = TopologyGraph::new(
            TopologyKind::Pipeline,
            vec![Node::new("a", "x")],
            vec![Edge {
                from: "a".into(),
                to: "ghost".into(),
                kind: EdgeKind::PipesTo,
            }],
        )
        .unwrap_err();
        assert_eq!(err, TopologyError::UnknownNode("ghost".into()));
    }

    #[test]
    fn validate_rejects_duplicate_node() {
        let err = TopologyGraph::new(
            TopologyKind::Flat,
            vec![Node::new("a", "x"), Node::new("a", "y")],
            vec![],
        )
        .unwrap_err();
        assert_eq!(err, TopologyError::DuplicateNode("a".into()));
    }
}