//! Rendezvous client: connect to a remote peer, authenticate, and exchange CRDT ops.

use bft_json_crdt::json_crdt::SignedOp;
use futures::{SinkExt, StreamExt};

use crate::crdt_state;
use crate::crdt_wire;
use crate::slog;
use crate::slog_error;
use crate::slog_warn;

use super::auth;
use super::dispatch::{handle_incoming_binary, handle_incoming_text};
use super::rpc::try_handle_rpc_text;
use super::wire::{AuthMessage, ChallengeMessage, HelloMessage, ServerAuthMessage, SyncMessage};
use super::{AUTH_TIMEOUT_SECS, PING_INTERVAL_SECS, PONG_TIMEOUT_SECS};

#[allow(unused_imports)]
use auth::{add_join_token, init_token_auth}; // needed by tests

// ── Rendezvous client ───────────────────────────────────────────────

/// Number of consecutive connection failures before escalating from WARN to ERROR.
pub const RENDEZVOUS_ERROR_THRESHOLD: u32 = 10;

/// Spawn a background task that connects to the configured rendezvous
/// peer and exchanges CRDT ops bidirectionally.
///
/// The client reconnects with exponential backoff if the connection drops.
/// Individual failures are logged at WARN; after [`RENDEZVOUS_ERROR_THRESHOLD`]
/// consecutive failures the log level escalates to ERROR.
///
/// When `token` is provided it is appended to the upgrade URL as
/// `?token=<token>` so the server's bearer-token check is satisfied.  This
/// reuses the existing `--join-token` / `HUSKIES_JOIN_TOKEN` plumbing on the
/// agent side.
pub fn spawn_rendezvous_client(url: String, token: Option<String>) {
    tokio::spawn(async move {
        let mut backoff_secs = 1u64;
        let mut consecutive_failures: u32 = 0;
        loop {
            slog!("[crdt-sync] Connecting to rendezvous peer: {url}");
            match connect_and_sync(&url, token.as_deref()).await {
                Ok(()) => {
                    slog!("[crdt-sync] Rendezvous connection closed cleanly");
                    backoff_secs = 1;
                    consecutive_failures = 0;
                }
                Err(e) => {
                    consecutive_failures += 1;
                    if consecutive_failures >= RENDEZVOUS_ERROR_THRESHOLD {
                        slog_error!(
                            "[crdt-sync] Rendezvous peer unreachable ({consecutive_failures} consecutive failures): {e}"
                        );
                    } else {
                        slog_warn!(
                            "[crdt-sync] Rendezvous connection error (attempt {consecutive_failures}): {e}"
                        );
                    }
                }
            }
            slog!("[crdt-sync] Reconnecting in {backoff_secs}s...");
            tokio::time::sleep(std::time::Duration::from_secs(backoff_secs)).await;
            backoff_secs = (backoff_secs * 2).min(30);
        }
    });
}

/// Connect to a remote sync endpoint and exchange ops until disconnect.
///
/// When `token` is supplied it is appended as `?token=<token>` to the
/// connection URL so the server's bearer-token check passes.
pub(crate) async fn connect_and_sync(url: &str, token: Option<&str>) -> Result<(), String> {
    let connect_url = match token {
        Some(t) => {
            if url.contains('?') {
                format!("{url}&token={t}")
            } else {
                format!("{url}?token={t}")
            }
        }
        None => url.to_string(),
    };
    let (ws_stream, _) = tokio_tungstenite::connect_async(connect_url.as_str())
        .await
        .map_err(|e| format!("WebSocket connect failed: {e}"))?;

    let (mut sink, mut stream) = ws_stream.split();

    slog!("[crdt-sync] Connected to rendezvous peer, starting mutual-auth handshake");

    use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;

    // ── Step 1: Send hello with a fresh client nonce ──────────────
    let client_nonce = crate::node_identity::generate_challenge();
    let hello = HelloMessage {
        r#type: "hello".to_string(),
        nonce: client_nonce.clone(),
    };
    let hello_json = serde_json::to_string(&hello).map_err(|e| format!("Serialize hello: {e}"))?;
    sink.send(TungsteniteMsg::Text(hello_json.into()))
        .await
        .map_err(|e| format!("Send hello failed: {e}"))?;

    slog!("[crdt-sync] Hello sent, awaiting server_auth");

    // ── Step 2: Receive server_auth from the responding node ──────
    let server_auth_frame = tokio::time::timeout(
        std::time::Duration::from_secs(AUTH_TIMEOUT_SECS),
        stream.next(),
    )
    .await
    .map_err(|_| "Auth timeout waiting for server_auth".to_string())?
    .ok_or_else(|| "Connection closed before server_auth".to_string())?
    .map_err(|e| format!("WebSocket read error: {e}"))?;

    let server_auth_text = match server_auth_frame {
        TungsteniteMsg::Text(t) => t.to_string(),
        _ => return Err("Expected text frame for server_auth".to_string()),
    };

    let server_auth: ServerAuthMessage = serde_json::from_str(&server_auth_text)
        .map_err(|e| format!("Invalid server_auth message: {e}"))?;

    if server_auth.r#type != "server_auth" {
        return Err(format!(
            "Expected server_auth message, got type={}",
            server_auth.r#type
        ));
    }

    // ── Step 3: Verify server's signature and check trusted-key list ─
    let versioned_challenge = format!("huskies-v1:{client_nonce}");
    let server_sig_valid = crate::node_identity::verify_message_strict(
        &server_auth.pubkey_hex,
        versioned_challenge.as_bytes(),
        &server_auth.signature_hex,
    );
    let server_key_trusted = auth::trusted_keys()
        .iter()
        .any(|k| k == &server_auth.pubkey_hex);

    if !server_sig_valid || !server_key_trusted {
        slog!(
            "[crdt-sync] Server auth failed \
             (sig_valid={server_sig_valid}, key_trusted={server_key_trusted}, \
             server_pubkey={})",
            server_auth.pubkey_hex
        );
        return Err(format!(
            "Server auth rejected: sig_valid={server_sig_valid}, \
             key_trusted={server_key_trusted}, server_pubkey={}",
            server_auth.pubkey_hex
        ));
    }

    slog!(
        "[crdt-sync] Server authenticated: {:.12}…",
        &server_auth.pubkey_hex
    );

    // ── Step 4: Receive challenge from the responding node ────────
    let challenge_frame = tokio::time::timeout(
        std::time::Duration::from_secs(AUTH_TIMEOUT_SECS),
        stream.next(),
    )
    .await
    .map_err(|_| "Auth timeout waiting for challenge".to_string())?
    .ok_or_else(|| "Connection closed before challenge".to_string())?
    .map_err(|e| format!("WebSocket read error: {e}"))?;

    let challenge_text = match challenge_frame {
        TungsteniteMsg::Text(t) => t.to_string(),
        _ => return Err("Expected text frame for challenge".to_string()),
    };

    let challenge_msg: ChallengeMessage = serde_json::from_str(&challenge_text)
        .map_err(|e| format!("Invalid challenge message: {e}"))?;

    if challenge_msg.r#type != "challenge" {
        return Err(format!(
            "Expected challenge message, got type={}",
            challenge_msg.r#type
        ));
    }

    // ── Step 5: Sign challenge and send auth reply ────────────────
    let (pubkey_hex, signature_hex) = crdt_state::sign_challenge(&challenge_msg.nonce)
        .ok_or_else(|| "CRDT not initialised — cannot sign challenge".to_string())?;

    let auth_msg = AuthMessage {
        r#type: "auth".to_string(),
        pubkey_hex,
        signature_hex,
    };
    let auth_json = serde_json::to_string(&auth_msg).map_err(|e| format!("Serialize auth: {e}"))?;
    sink.send(TungsteniteMsg::Text(auth_json.into()))
        .await
        .map_err(|e| format!("Send auth failed: {e}"))?;

    slog!("[crdt-sync] Auth reply sent, waiting for sync data");

    // v2 protocol: send our vector clock.
    let our_clock = crdt_state::our_vector_clock().unwrap_or_default();
    let clock_msg = SyncMessage::Clock { clock: our_clock };
    if let Ok(json) = serde_json::to_string(&clock_msg) {
        sink.send(TungsteniteMsg::Text(json.into()))
            .await
            .map_err(|e| format!("Send clock failed: {e}"))?;
    }

    // Wait for the server's first sync message.
    let first_msg = tokio::time::timeout(
        std::time::Duration::from_secs(AUTH_TIMEOUT_SECS),
        wait_for_rendezvous_sync_text(&mut stream),
    )
    .await
    .map_err(|_| "Timeout waiting for server sync message".to_string())?;

    match first_msg {
        Some(SyncMessage::Clock { clock: peer_clock }) => {
            // v2 server — send only the ops the server is missing.
            let delta = crdt_state::ops_since(&peer_clock).unwrap_or_default();
            slog!(
                "[crdt-sync] v2 delta sync: sending {} ops to server (server missing)",
                delta.len()
            );
            let msg = SyncMessage::Bulk { ops: delta };
            if let Ok(json) = serde_json::to_string(&msg) {
                sink.send(TungsteniteMsg::Text(json.into()))
                    .await
                    .map_err(|e| format!("Send delta failed: {e}"))?;
            }
        }
        Some(SyncMessage::Bulk { ops }) => {
            // v1 server — apply their bulk and send our full bulk.
            let mut applied = 0u64;
            for op_json in &ops {
                if let Ok(signed_op) = serde_json::from_str::<SignedOp>(op_json)
                    && crdt_state::apply_remote_op(signed_op)
                {
                    applied += 1;
                }
            }
            slog!(
                "[crdt-sync] v1 bulk sync: received {} ops from server, applied {applied}",
                ops.len()
            );
            if let Some(all) = crdt_state::all_ops_json() {
                let msg = SyncMessage::Bulk { ops: all };
                if let Ok(json) = serde_json::to_string(&msg) {
                    sink.send(TungsteniteMsg::Text(json.into()))
                        .await
                        .map_err(|e| format!("Send bulk failed: {e}"))?;
                }
            }
        }
        _ => {
            // Fallback — send full bulk.
            slog!("[crdt-sync] No sync message from server; sending full bulk as fallback");
            if let Some(all) = crdt_state::all_ops_json() {
                let msg = SyncMessage::Bulk { ops: all };
                if let Ok(json) = serde_json::to_string(&msg) {
                    sink.send(TungsteniteMsg::Text(json.into()))
                        .await
                        .map_err(|e| format!("Send bulk failed: {e}"))?;
                }
            }
        }
    }

    // Bulk-delta phase complete — signal the server that we are ready for
    // real-time op streaming.
    if let Ok(json) = serde_json::to_string(&SyncMessage::Ready) {
        sink.send(TungsteniteMsg::Text(json.into()))
            .await
            .map_err(|e| format!("Send ready failed: {e}"))?;
    }

    // Subscribe to new local ops.
    let Some(mut op_rx) = crdt_state::subscribe_ops() else {
        return Err("CRDT not initialised".to_string());
    };

    // Buffer for locally-generated ops produced before the server's `ready`
    // arrives.  Flushed in-order once the server signals catch-up.
    let mut peer_ready = false;
    let mut op_buffer: Vec<bft_json_crdt::json_crdt::SignedOp> = Vec::new();

    // ── Keepalive state ───────────────────────────────────────────────
    let mut pong_deadline =
        tokio::time::Instant::now() + std::time::Duration::from_secs(PONG_TIMEOUT_SECS);
    let mut ping_ticker = tokio::time::interval_at(
        tokio::time::Instant::now() + std::time::Duration::from_secs(PING_INTERVAL_SECS),
        std::time::Duration::from_secs(PING_INTERVAL_SECS),
    );

    loop {
        tokio::select! {
            // Send periodic Ping and enforce Pong timeout.
            _ = ping_ticker.tick() => {
                if tokio::time::Instant::now() >= pong_deadline {
                    slog_warn!(
                        "[crdt-sync] No pong from rendezvous peer {} in {}s; disconnecting",
                        url,
                        PONG_TIMEOUT_SECS
                    );
                    return Err(format!(
                        "Keepalive timeout: no pong from {url} in {PONG_TIMEOUT_SECS}s"
                    ));
                }
                use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;
                if sink.send(TungsteniteMsg::Ping(bytes::Bytes::new())).await.is_err() {
                    break;
                }
            }
            result = op_rx.recv() => {
                match result {
                    Ok(signed_op) => {
                        if peer_ready {
                            // Encode via wire codec and send as binary frame.
                            let bytes = crdt_wire::encode(&signed_op);
                            use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;
                            if sink.send(TungsteniteMsg::Binary(bytes.into())).await.is_err() {
                                break;
                            }
                        } else {
                            // Buffer until the server signals ready.
                            op_buffer.push(signed_op);
                        }
                    }
                    Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
                        slog!("[crdt-sync] Slow rendezvous link lagged {n} ops; disconnecting");
                        break;
                    }
                    Err(_) => break,
                }
            }
            frame = stream.next() => {
                match frame {
                    Some(Ok(tokio_tungstenite::tungstenite::Message::Pong(_))) => {
                        // Reset the pong deadline on every Pong received.
                        pong_deadline = tokio::time::Instant::now()
                            + std::time::Duration::from_secs(PONG_TIMEOUT_SECS);
                    }
                    Some(Ok(tokio_tungstenite::tungstenite::Message::Ping(_))) => {
                        // tungstenite auto-responds to Ping with Pong at the
                        // protocol level; no manual response needed here.
                    }
                    Some(Ok(tokio_tungstenite::tungstenite::Message::Text(text))) => {
                        // Check for the ready signal before other text frames.
                        if let Ok(SyncMessage::Ready) = serde_json::from_str(text.as_ref()) {
                            peer_ready = true;
                            slog!("[crdt-sync] Server ready; flushing {} buffered ops", op_buffer.len());
                            let mut flush_ok = true;
                            for op in op_buffer.drain(..) {
                                let bytes = crdt_wire::encode(&op);
                                use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;
                                if sink.send(TungsteniteMsg::Binary(bytes.into())).await.is_err() {
                                    flush_ok = false;
                                    break;
                                }
                            }
                            if !flush_ok {
                                break;
                            }
                        } else if let Some(rpc_resp) = try_handle_rpc_text(text.as_ref()).await {
                            // RPC request from the peer — dispatch and reply.
                            use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;
                            if let Ok(json) = serde_json::to_string(&rpc_resp)
                                && sink.send(TungsteniteMsg::Text(json.into())).await.is_err()
                            {
                                break;
                            }
                        } else {
                            handle_incoming_text(text.as_ref());
                        }
                    }
                    Some(Ok(tokio_tungstenite::tungstenite::Message::Binary(bytes))) => {
                        // Real-time op — applied immediately regardless of ready state.
                        handle_incoming_binary(&bytes);
                    }
                    Some(Ok(tokio_tungstenite::tungstenite::Message::Close(_))) | None => break,
                    Some(Err(e)) => {
                        slog!("[crdt-sync] Rendezvous read error: {e}");
                        break;
                    }
                    _ => {}
                }
            }
        }
    }

    Ok(())
}

/// Wait for the next text-frame sync message from a tungstenite stream,
/// handling Ping/Pong transparently.
///
/// Returns `None` on connection close or read error.
async fn wait_for_rendezvous_sync_text(
    stream: &mut futures::stream::SplitStream<
        tokio_tungstenite::WebSocketStream<
            tokio_tungstenite::MaybeTlsStream<tokio::net::TcpStream>,
        >,
    >,
) -> Option<SyncMessage> {
    use tokio_tungstenite::tungstenite::Message as TungsteniteMsg;
    loop {
        match stream.next().await {
            Some(Ok(TungsteniteMsg::Text(text))) => {
                return serde_json::from_str(text.as_ref()).ok();
            }
            Some(Ok(TungsteniteMsg::Ping(_) | TungsteniteMsg::Pong(_))) => continue,
            _ => return None,
        }
    }
}

// ── Tests ────────────────────────────────────────────────────────────

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

    #[test]
    fn config_rendezvous_parsed_from_toml() {
        let toml_str = r#"
rendezvous = "ws://remote:3001/crdt-sync"

[[agent]]
name = "test"
"#;
        let config: crate::config::ProjectConfig = toml::from_str(toml_str).unwrap();
        assert_eq!(
            config.rendezvous.as_deref(),
            Some("ws://remote:3001/crdt-sync")
        );
    }

    #[test]
    fn config_rendezvous_defaults_to_none() {
        let config = crate::config::ProjectConfig::default();
        assert!(config.rendezvous.is_none());
    }

    #[test]
    fn failure_counter_warn_below_threshold() {
        let threshold = RENDEZVOUS_ERROR_THRESHOLD;
        let mut consecutive_failures: u32 = 0;

        // First threshold-1 failures are below the ERROR threshold.
        for _ in 0..(threshold - 1) {
            consecutive_failures += 1;
            assert!(
                consecutive_failures < threshold,
                "failure {consecutive_failures} must be below ERROR threshold {threshold}"
            );
        }
    }

    #[test]
    fn failure_counter_error_at_threshold() {
        let threshold = RENDEZVOUS_ERROR_THRESHOLD;
        let consecutive_failures: u32 = threshold;
        assert!(
            consecutive_failures >= threshold,
            "failure {consecutive_failures} must reach or exceed ERROR threshold {threshold}"
        );
    }

    #[test]
    fn failure_counter_resets_on_success() {
        let threshold = RENDEZVOUS_ERROR_THRESHOLD;
        // Simulate sustained failure.
        let mut consecutive_failures: u32 = threshold + 5;
        assert!(consecutive_failures >= threshold);

        // Simulate a clean reconnect.
        consecutive_failures = 0;
        assert_eq!(
            consecutive_failures, 0,
            "counter must reset to 0 on success"
        );

        // Next error is attempt 1 — well below the ERROR threshold.
        consecutive_failures += 1;
        assert!(
            consecutive_failures < threshold,
            "first failure after reset must be below ERROR threshold"
        );
    }

    #[test]
    fn error_threshold_is_ten() {
        assert_eq!(
            RENDEZVOUS_ERROR_THRESHOLD, 10,
            "ERROR escalation threshold must be 10 consecutive failures"
        );
    }

    #[test]
    fn rendezvous_url_with_token_appended() {
        let base = "ws://host:3001/crdt-sync";
        let token = "my-secret-token";
        let url_with_token = if base.contains('?') {
            format!("{base}&token={token}")
        } else {
            format!("{base}?token={token}")
        };
        assert_eq!(
            url_with_token,
            "ws://host:3001/crdt-sync?token=my-secret-token"
        );

        // With existing query params.
        let base_with_query = "ws://host:3001/crdt-sync?foo=bar";
        let url_appended = if base_with_query.contains('?') {
            format!("{base_with_query}&token={token}")
        } else {
            format!("{base_with_query}?token={token}")
        };
        assert_eq!(
            url_appended,
            "ws://host:3001/crdt-sync?foo=bar&token=my-secret-token"
        );
    }

    #[test]
    fn rendezvous_url_without_token_unchanged() {
        let base = "ws://host:3001/crdt-sync";
        let token: Option<&str> = None;
        let connect_url = match token {
            Some(t) => format!("{base}?token={t}"),
            None => base.to_string(),
        };
        assert_eq!(connect_url, base);
    }
}