//! Proxy relay for symmetric NAT nodes.
//!
//! When a node is
//! behind a symmetric NAT (where hole-punching fails),
//! it registers with a global node that acts as a relay:
//!
//! - **Store**: the NAT'd node sends store requests to
//!   its proxy, which forwards them to the DHT.
//! - **Get**: the NAT'd node sends get requests to its
//!   proxy, which performs the lookup and returns results.
//! - **Dgram**: datagrams to/from NAT'd nodes are
//!   forwarded through the proxy.
//! - **RDP**: reliable transport is also tunnelled
//!   through the proxy (type_proxy_rdp).

use std::collections::HashMap;
use std::net::SocketAddr;
use std::time::{Duration, Instant};

use crate::id::NodeId;
use crate::peers::PeerInfo;

// ── Constants ────────────────────────────────────────

/// Registration timeout.
pub const PROXY_REGISTER_TIMEOUT: Duration = Duration::from_secs(2);

/// Registration TTL.
pub const PROXY_REGISTER_TTL: Duration = Duration::from_secs(300);

/// Get request timeout.
pub const PROXY_GET_TIMEOUT: Duration = Duration::from_secs(10);

/// Maintenance timer interval.
pub const PROXY_TIMER_INTERVAL: Duration = Duration::from_secs(30);

/// RDP timeout for proxy connections.
pub const PROXY_RDP_TIMEOUT: Duration = Duration::from_secs(30);

/// RDP port for proxy store.
pub const PROXY_STORE_PORT: u16 = 200;

/// RDP port for proxy get.
pub const PROXY_GET_PORT: u16 = 201;

/// RDP port for proxy get reply.
pub const PROXY_GET_REPLY_PORT: u16 = 202;

// ── Client state ────────────────────────────────────

/// A node registered as a client of this proxy.
#[derive(Debug, Clone)]
pub struct ProxyClient {
    /// Client's address (behind NAT).
    pub addr: SocketAddr,

    /// DTUN session for validation.
    pub session: u32,

    /// When the client last registered/refreshed.
    pub registered_at: Instant,
}

impl ProxyClient {
    pub fn is_expired(&self) -> bool {
        self.registered_at.elapsed() >= PROXY_REGISTER_TTL
    }
}

// ── Pending get state ───────────────────────────────

/// State for a pending proxy get request.
#[derive(Debug)]
pub struct PendingGet {
    /// Key being looked up.
    pub key: Vec<u8>,

    /// Nonce for correlation.
    pub nonce: u32,

    /// When the request was sent.
    pub sent_at: Instant,

    /// Whether we've received a result.
    pub completed: bool,

    /// Collected values.
    pub values: Vec<Vec<u8>>,
}

// ── Proxy ───────────────────────────────────────────

/// Proxy relay for symmetric NAT traversal.
///
/// Acts in two roles:
/// - **Client**: when we're behind symmetric NAT, we
///   register with a proxy server and route operations
///   through it.
/// - **Server**: when we have a public IP, we accept
///   registrations from NAT'd nodes and relay their
///   traffic.
pub struct Proxy {
    /// Our proxy server (when we're a client).
    server: Option<PeerInfo>,

    /// Whether we've successfully registered with our
    /// proxy server.
    is_registered: bool,

    /// Whether registration is in progress.
    is_registering: bool,

    /// Nonce for registration correlation.
    register_nonce: u32,

    /// Clients registered with us. Capped at 500.
    clients: HashMap<NodeId, ProxyClient>,

    /// Pending get requests. Capped at 100.
    pending_gets: HashMap<u32, PendingGet>,
}

impl Proxy {
    pub fn new(_id: NodeId) -> Self {
        Self {
            server: None,
            is_registered: false,
            is_registering: false,
            register_nonce: 0,
            clients: HashMap::new(),
            pending_gets: HashMap::new(),
        }
    }

    // ── Client role ─────────────────────────────────

    /// Set the proxy server to use.
    pub fn set_server(&mut self, server: PeerInfo) {
        self.server = Some(server);
        self.is_registered = false;
    }

    /// Get the current proxy server.
    pub fn server(&self) -> Option<&PeerInfo> {
        self.server.as_ref()
    }

    /// Whether we're registered with a proxy server.
    pub fn is_registered(&self) -> bool {
        self.is_registered
    }

    /// Start proxy registration. Returns the nonce to
    /// include in the register message.
    pub fn start_register(&mut self, nonce: u32) -> Option<u32> {
        self.server.as_ref()?;
        self.is_registering = true;
        self.register_nonce = nonce;
        Some(nonce)
    }

    /// Handle registration reply.
    pub fn recv_register_reply(&mut self, nonce: u32) -> bool {
        if nonce != self.register_nonce {
            return false;
        }
        self.is_registering = false;
        self.is_registered = true;
        log::info!("Registered with proxy server");
        true
    }

    // ── Server role ─────────────────────────────────

    /// Register a client node (we act as their proxy).
    pub fn register_client(
        &mut self,
        id: NodeId,
        addr: SocketAddr,
        session: u32,
    ) -> bool {
        const MAX_CLIENTS: usize = 500;
        if self.clients.len() >= MAX_CLIENTS && !self.clients.contains_key(&id)
        {
            return false;
        }
        if let Some(existing) = self.clients.get(&id) {
            if existing.session != session && !existing.is_expired() {
                return false;
            }
        }
        self.clients.insert(
            id,
            ProxyClient {
                addr,
                session,
                registered_at: Instant::now(),
            },
        );
        log::debug!("Proxy: registered client {id:?}");
        true
    }

    /// Check if a node is registered as our client.
    pub fn is_client_registered(&self, id: &NodeId) -> bool {
        self.clients
            .get(id)
            .map(|c| !c.is_expired())
            .unwrap_or(false)
    }

    /// Get a registered client's info.
    pub fn get_client(&self, id: &NodeId) -> Option<&ProxyClient> {
        self.clients.get(id).filter(|c| !c.is_expired())
    }

    /// Number of active proxy clients.
    pub fn client_count(&self) -> usize {
        self.clients.values().filter(|c| !c.is_expired()).count()
    }

    // ── Pending get management ──────────────────────

    /// Start a proxied get request.
    pub fn start_get(&mut self, nonce: u32, key: Vec<u8>) {
        const MAX_GETS: usize = 100;
        if self.pending_gets.len() >= MAX_GETS {
            log::debug!("Proxy: too many pending gets");
            return;
        }
        self.pending_gets.insert(
            nonce,
            PendingGet {
                key,
                nonce,
                sent_at: Instant::now(),
                completed: false,
                values: Vec::new(),
            },
        );
    }

    /// Add a value to a pending get.
    pub fn add_get_value(&mut self, nonce: u32, value: Vec<u8>) -> bool {
        if let Some(pg) = self.pending_gets.get_mut(&nonce) {
            pg.values.push(value);
            true
        } else {
            false
        }
    }

    /// Complete a pending get request. Returns the
    /// collected values.
    pub fn complete_get(&mut self, nonce: u32) -> Option<Vec<Vec<u8>>> {
        self.pending_gets.remove(&nonce).map(|pg| pg.values)
    }

    // ── Maintenance ─────────────────────────────────

    /// Remove expired clients and timed-out gets.
    pub fn refresh(&mut self) {
        self.clients.retain(|_, c| !c.is_expired());

        self.pending_gets
            .retain(|_, pg| pg.sent_at.elapsed() < PROXY_GET_TIMEOUT);
    }
}

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

    fn addr(port: u16) -> SocketAddr {
        SocketAddr::from(([127, 0, 0, 1], port))
    }

    fn peer(byte: u8, port: u16) -> PeerInfo {
        PeerInfo::new(NodeId::from_bytes([byte; 32]), addr(port))
    }

    // ── Client tests ────────────────────────────────

    #[test]
    fn client_register_flow() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));

        assert!(!proxy.is_registered());

        proxy.set_server(peer(0x02, 5000));
        let nonce = proxy.start_register(42).unwrap();
        assert_eq!(nonce, 42);

        // Wrong nonce
        assert!(!proxy.recv_register_reply(99));
        assert!(!proxy.is_registered());

        // Correct nonce
        assert!(proxy.recv_register_reply(42));
        assert!(proxy.is_registered());
    }

    #[test]
    fn client_no_server() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));
        assert!(proxy.start_register(1).is_none());
    }

    // ── Server tests ────────────────────────────────

    #[test]
    fn server_register_client() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));
        let client_id = NodeId::from_bytes([0x02; 32]);

        assert!(proxy.register_client(client_id, addr(3000), 1));
        assert!(proxy.is_client_registered(&client_id));
        assert_eq!(proxy.client_count(), 1);
    }

    #[test]
    fn server_rejects_different_session() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));
        let client_id = NodeId::from_bytes([0x02; 32]);

        proxy.register_client(client_id, addr(3000), 1);
        assert!(!proxy.register_client(client_id, addr(3001), 2));
    }

    #[test]
    fn server_expire_clients() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));
        let client_id = NodeId::from_bytes([0x02; 32]);

        proxy.clients.insert(
            client_id,
            ProxyClient {
                addr: addr(3000),
                session: 1,
                registered_at: Instant::now() - Duration::from_secs(600),
            },
        );

        proxy.refresh();
        assert_eq!(proxy.client_count(), 0);
    }

    // ── Pending get tests ───────────────────────────

    #[test]
    fn pending_get_flow() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));

        proxy.start_get(42, b"mykey".to_vec());
        assert!(proxy.add_get_value(42, b"val1".to_vec()));
        assert!(proxy.add_get_value(42, b"val2".to_vec()));

        let vals = proxy.complete_get(42).unwrap();
        assert_eq!(vals.len(), 2);
        assert_eq!(vals[0], b"val1");
        assert_eq!(vals[1], b"val2");
    }

    #[test]
    fn pending_get_unknown_nonce() {
        let mut proxy = Proxy::new(NodeId::from_bytes([0x01; 32]));
        assert!(!proxy.add_get_value(999, b"v".to_vec()));
        assert!(proxy.complete_get(999).is_none());
    }
}