//! EngramClient trait — thin abstraction over the Engram graph engine.
//!
//! el-identity does not depend on the Engram crate directly. Instead, it
//! defines this trait and accepts any implementor. In production, the host
//! application wires in a real Engram client. In tests, `MockEngramClient`
//! provides an in-memory HashMap-backed implementation.

use crate::error::IdentityError;
use std::collections::HashMap;
use std::sync::{Arc, RwLock};

/// Minimal graph operations required by el-identity.
pub trait EngramClient: Send + Sync {
    /// Fetch a node by its ID. Returns `None` if the node does not exist.
    fn get_node(&self, id: &str) -> Result<Option<serde_json::Value>, IdentityError>;

    /// Create a new node of the given type with the given data.
    /// Returns the new node's ID.
    fn create_node(
        &self,
        node_type: &str,
        data: serde_json::Value,
    ) -> Result<String, IdentityError>;

    /// Create a directed edge between two nodes.
    fn create_edge(
        &self,
        from: &str,
        to: &str,
        edge_type: &str,
    ) -> Result<(), IdentityError>;

    /// Find nodes of the given type matching the query (field equality).
    fn find_nodes(
        &self,
        node_type: &str,
        query: serde_json::Value,
    ) -> Result<Vec<serde_json::Value>, IdentityError>;

    /// Delete a node by ID. Edges referencing it are also removed.
    fn delete_node(&self, id: &str) -> Result<(), IdentityError>;

    /// Find all nodes reachable from `from_id` via `edge_type`.
    fn find_connected(
        &self,
        from_id: &str,
        edge_type: &str,
    ) -> Result<Vec<serde_json::Value>, IdentityError>;
}

// ── MockEngramClient ──────────────────────────────────────────────────────────

#[derive(Debug)]
struct NodeEntry {
    node_type: String,
    data: serde_json::Value,
}

#[derive(Debug, Clone)]
struct Edge {
    from: String,
    to: String,
    edge_type: String,
}

/// In-memory Engram client for unit tests.
///
/// Stores nodes in a `HashMap<id, NodeEntry>` and edges in a `Vec<Edge>`.
/// Thread-safe via `RwLock`.
#[derive(Debug, Default)]
pub struct MockEngramClient {
    nodes: RwLock<HashMap<String, NodeEntry>>,
    edges: RwLock<Vec<Edge>>,
}

impl MockEngramClient {
    pub fn new() -> Self {
        Self::default()
    }

    /// Count nodes of a specific type (useful in tests).
    pub fn count_nodes(&self, node_type: &str) -> usize {
        self.nodes
            .read()
            .expect("nodes lock poisoned")
            .values()
            .filter(|n| n.node_type == node_type)
            .count()
    }

    /// Count edges of a specific type.
    pub fn count_edges(&self, edge_type: &str) -> usize {
        self.edges
            .read()
            .expect("edges lock poisoned")
            .iter()
            .filter(|e| e.edge_type == edge_type)
            .count()
    }
}

impl EngramClient for MockEngramClient {
    fn get_node(&self, id: &str) -> Result<Option<serde_json::Value>, IdentityError> {
        let nodes = self.nodes.read().expect("nodes lock poisoned");
        Ok(nodes.get(id).map(|n| n.data.clone()))
    }

    fn create_node(
        &self,
        node_type: &str,
        data: serde_json::Value,
    ) -> Result<String, IdentityError> {
        // Extract the node's own "id" field if present, otherwise generate one.
        let id = data
            .get("id")
            .and_then(|v| v.as_str())
            .map(|s| s.to_string())
            .unwrap_or_else(|| uuid::Uuid::new_v4().to_string());

        self.nodes
            .write()
            .expect("nodes lock poisoned")
            .insert(
                id.clone(),
                NodeEntry {
                    node_type: node_type.to_string(),
                    data,
                },
            );
        Ok(id)
    }

    fn create_edge(
        &self,
        from: &str,
        to: &str,
        edge_type: &str,
    ) -> Result<(), IdentityError> {
        self.edges.write().expect("edges lock poisoned").push(Edge {
            from: from.to_string(),
            to: to.to_string(),
            edge_type: edge_type.to_string(),
        });
        Ok(())
    }

    fn find_nodes(
        &self,
        node_type: &str,
        query: serde_json::Value,
    ) -> Result<Vec<serde_json::Value>, IdentityError> {
        let nodes = self.nodes.read().expect("nodes lock poisoned");
        let results = nodes
            .values()
            .filter(|n| n.node_type == node_type)
            .filter(|n| matches_query(&n.data, &query))
            .map(|n| n.data.clone())
            .collect();
        Ok(results)
    }

    fn delete_node(&self, id: &str) -> Result<(), IdentityError> {
        self.nodes
            .write()
            .expect("nodes lock poisoned")
            .remove(id);
        // Remove any edges referencing this node.
        self.edges
            .write()
            .expect("edges lock poisoned")
            .retain(|e| e.from != id && e.to != id);
        Ok(())
    }

    fn find_connected(
        &self,
        from_id: &str,
        edge_type: &str,
    ) -> Result<Vec<serde_json::Value>, IdentityError> {
        let edges = self.edges.read().expect("edges lock poisoned");
        let to_ids: Vec<String> = edges
            .iter()
            .filter(|e| e.from == from_id && e.edge_type == edge_type)
            .map(|e| e.to.clone())
            .collect();
        drop(edges);

        let nodes = self.nodes.read().expect("nodes lock poisoned");
        let results = to_ids
            .iter()
            .filter_map(|id| nodes.get(id).map(|n| n.data.clone()))
            .collect();
        Ok(results)
    }
}

/// Check whether a node's data matches all key-value pairs in the query.
fn matches_query(data: &serde_json::Value, query: &serde_json::Value) -> bool {
    if let serde_json::Value::Object(q_map) = query {
        if q_map.is_empty() {
            return true;
        }
        if let serde_json::Value::Object(data_map) = data {
            return q_map.iter().all(|(k, v)| data_map.get(k) == Some(v));
        }
        return false;
    }
    true // empty or non-object query matches everything
}

/// Convenience: wrap a MockEngramClient in Arc for trait object use.
pub fn mock_client() -> Arc<dyn EngramClient> {
    Arc::new(MockEngramClient::new())
}