//! noiseml-server — Delivery Service + Authentication Service binary.
//!
//! # M3 scope
//!
//! The server exposes two Noise_XX-protected Cap'n Proto RPC endpoints:
//!
//! * **AS** (`--listen`, default `0.0.0.0:7000`) — `AuthenticationService`:
//!   upload and fetch single-use MLS KeyPackages.
//! * **DS** (`--ds-listen`, default `0.0.0.0:7001`) — `DeliveryService`:
//!   enqueue and fetch opaque payloads (Welcome messages, Commits, Application
//!   messages) keyed by recipient Ed25519 public key.
//!
//! # Architecture
//!
//! ```text
//! TcpListener (AS, 7000)    TcpListener (DS, 7001)
//!   └─ Noise_XX handshake     └─ Noise_XX handshake
//!        └─ capnp-rpc VatNetwork (LocalSet, !Send)
//!             ├─ AuthServiceImpl  (shares KeyPackageStore via Arc)
//!             └─ DeliveryServiceImpl (shares DeliveryStore via Arc)
//! ```
//!
//! Because `capnp-rpc` uses `Rc<RefCell<>>` internally it is `!Send`.
//! The entire RPC stack lives on a `tokio::task::LocalSet` spawned per
//! connection.
//!
//! # Configuration
//!
//! | Env var             | CLI flag       | Default         |
//! |---------------------|----------------|-----------------|
//! | `NOISEML_LISTEN`    | `--listen`     | `0.0.0.0:7000`  |
//! | `NOISEML_DS_LISTEN` | `--ds-listen`  | `0.0.0.0:7001`  |
//! | `RUST_LOG`          | —              | `info`          |

use std::{collections::VecDeque, sync::Arc};

use anyhow::Context;
use capnp::capability::Promise;
use capnp_rpc::{RpcSystem, rpc_twoparty_capnp::Side, twoparty};
use clap::Parser;
use dashmap::DashMap;
use noiseml_core::{NoiseKeypair, handshake_responder};
use noiseml_proto::{
    auth_capnp::authentication_service,
    delivery_capnp::delivery_service,
};
use sha2::{Digest, Sha256};
use tokio::net::{TcpListener, TcpStream};
use tokio_util::compat::{TokioAsyncReadCompatExt, TokioAsyncWriteCompatExt};
use tracing::Instrument;

// ── CLI ───────────────────────────────────────────────────────────────────────

#[derive(Debug, Parser)]
#[command(
    name = "noiseml-server",
    about = "noiseml Delivery Service + Authentication Service",
    version
)]
struct Args {
    /// TCP address for the Authentication Service.
    #[arg(long, default_value = "0.0.0.0:7000", env = "NOISEML_LISTEN")]
    listen: String,

    /// TCP address for the Delivery Service.
    #[arg(long, default_value = "0.0.0.0:7001", env = "NOISEML_DS_LISTEN")]
    ds_listen: String,
}

// ── Shared store types ────────────────────────────────────────────────────────

/// Thread-safe map from Ed25519 identity public key bytes (32 B) to a queue
/// of serialised MLS KeyPackage blobs.
///
/// Each KeyPackage is single-use per RFC 9420: `fetch_key_package` removes
/// and returns exactly one entry.
type KeyPackageStore = Arc<DashMap<Vec<u8>, VecDeque<Vec<u8>>>>;

/// Thread-safe message queue for the Delivery Service.
///
/// Maps recipient Ed25519 public key (32 bytes) to a FIFO queue of opaque
/// payload bytes (TLS-encoded MLS messages or other framed data).
type DeliveryStore = Arc<DashMap<Vec<u8>, VecDeque<Vec<u8>>>>;

// ── Authentication Service implementation ─────────────────────────────────────

/// Cap'n Proto RPC server implementation for `AuthenticationService`.
struct AuthServiceImpl {
    store: KeyPackageStore,
}

impl authentication_service::Server for AuthServiceImpl {
    /// Upload a single-use KeyPackage and return its SHA-256 fingerprint.
    fn upload_key_package(
        &mut self,
        params: authentication_service::UploadKeyPackageParams,
        mut results: authentication_service::UploadKeyPackageResults,
    ) -> Promise<(), capnp::Error> {
        let params = params.get().map_err(|e| {
            capnp::Error::failed(format!("upload_key_package: bad params: {e}"))
        });

        let (identity_key, package) = match params {
            Ok(p) => {
                let ik = match p.get_identity_key() {
                    Ok(v) => v.to_vec(),
                    Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
                };
                let pkg = match p.get_package() {
                    Ok(v) => v.to_vec(),
                    Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
                };
                (ik, pkg)
            }
            Err(e) => return Promise::err(e),
        };

        if identity_key.len() != 32 {
            return Promise::err(capnp::Error::failed(format!(
                "identityKey must be exactly 32 bytes, got {}",
                identity_key.len()
            )));
        }
        if package.is_empty() {
            return Promise::err(capnp::Error::failed(
                "package must not be empty".to_string(),
            ));
        }

        let fingerprint: Vec<u8> = Sha256::digest(&package).to_vec();

        self.store
            .entry(identity_key)
            .or_default()
            .push_back(package);

        results
            .get()
            .set_fingerprint(&fingerprint);

        tracing::debug!(
            fingerprint = %fmt_hex(&fingerprint[..4]),
            "KeyPackage uploaded"
        );

        Promise::ok(())
    }

    /// Atomically remove and return one KeyPackage for the given identity key.
    fn fetch_key_package(
        &mut self,
        params: authentication_service::FetchKeyPackageParams,
        mut results: authentication_service::FetchKeyPackageResults,
    ) -> Promise<(), capnp::Error> {
        let identity_key = match params.get() {
            Ok(p) => match p.get_identity_key() {
                Ok(v) => v.to_vec(),
                Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
            },
            Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
        };

        if identity_key.len() != 32 {
            return Promise::err(capnp::Error::failed(format!(
                "identityKey must be exactly 32 bytes, got {}",
                identity_key.len()
            )));
        }

        // Atomically pop one package from the front of the queue.
        let package = self
            .store
            .get_mut(&identity_key)
            .and_then(|mut q| q.pop_front());

        match package {
            Some(pkg) => {
                tracing::debug!(
                    identity = %fmt_hex(&identity_key[..4]),
                    "KeyPackage fetched"
                );
                results.get().set_package(&pkg);
            }
            None => {
                tracing::debug!(
                    identity = %fmt_hex(&identity_key[..4]),
                    "no KeyPackage available for identity"
                );
                // Return empty Data — schema specifies this as the "no package" sentinel.
                results.get().set_package(&[]);
            }
        }

        Promise::ok(())
    }
}

// ── Delivery Service implementation ───────────────────────────────────────────

/// Cap'n Proto RPC server implementation for `DeliveryService`.
///
/// Provides a simple store-and-forward relay for MLS messages:
/// * `enqueue` appends an opaque payload to the recipient's FIFO queue.
/// * `fetch` atomically drains and returns the entire queue.
struct DeliveryServiceImpl {
    store: DeliveryStore,
}

impl delivery_service::Server for DeliveryServiceImpl {
    /// Append `payload` to the queue for `recipient_key`.
    fn enqueue(
        &mut self,
        params: delivery_service::EnqueueParams,
        _results: delivery_service::EnqueueResults,
    ) -> Promise<(), capnp::Error> {
        let p = match params.get() {
            Ok(p) => p,
            Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
        };
        let recipient_key = match p.get_recipient_key() {
            Ok(v) => v.to_vec(),
            Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
        };
        let payload = match p.get_payload() {
            Ok(v) => v.to_vec(),
            Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
        };

        if recipient_key.len() != 32 {
            return Promise::err(capnp::Error::failed(format!(
                "recipientKey must be exactly 32 bytes, got {}",
                recipient_key.len()
            )));
        }
        if payload.is_empty() {
            return Promise::err(capnp::Error::failed(
                "payload must not be empty".to_string(),
            ));
        }

        self.store
            .entry(recipient_key.clone())
            .or_default()
            .push_back(payload);

        tracing::debug!(
            recipient = %fmt_hex(&recipient_key[..4]),
            "message enqueued"
        );

        Promise::ok(())
    }

    /// Atomically drain and return all queued payloads for `recipient_key`.
    fn fetch(
        &mut self,
        params: delivery_service::FetchParams,
        mut results: delivery_service::FetchResults,
    ) -> Promise<(), capnp::Error> {
        let recipient_key = match params.get() {
            Ok(p) => match p.get_recipient_key() {
                Ok(v) => v.to_vec(),
                Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
            },
            Err(e) => return Promise::err(capnp::Error::failed(format!("{e}"))),
        };

        if recipient_key.len() != 32 {
            return Promise::err(capnp::Error::failed(format!(
                "recipientKey must be exactly 32 bytes, got {}",
                recipient_key.len()
            )));
        }

        // Atomically drain the entire queue.
        let messages: Vec<Vec<u8>> = self
            .store
            .get_mut(&recipient_key)
            .map(|mut q| q.drain(..).collect())
            .unwrap_or_default();

        tracing::debug!(
            recipient = %fmt_hex(&recipient_key[..4]),
            count = messages.len(),
            "messages fetched"
        );

        let mut list = results.get().init_payloads(messages.len() as u32);
        for (i, msg) in messages.iter().enumerate() {
            list.set(i as u32, msg);
        }

        Promise::ok(())
    }
}

// ── Entry point ───────────────────────────────────────────────────────────────

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
        )
        .init();

    let args = Args::parse();

    // Generate a fresh static Noise keypair for this server instance.
    // M6 replaces this with persistent key loading from SQLite.
    let keypair = Arc::new(NoiseKeypair::generate());

    {
        let pub_bytes = keypair.public_bytes();
        tracing::info!(
            listen    = %args.listen,
            ds_listen = %args.ds_listen,
            public_key = %fmt_hex(&pub_bytes[..4]),
            "noiseml-server starting (M3) — keypair is ephemeral"
        );
    }

    // Shared stores — all connections share the same in-memory maps.
    let kp_store: KeyPackageStore = Arc::new(DashMap::new());
    let ds_store: DeliveryStore = Arc::new(DashMap::new());

    let as_listener = TcpListener::bind(&args.listen)
        .await
        .with_context(|| format!("failed to bind AS to {}", args.listen))?;

    let ds_listener = TcpListener::bind(&args.ds_listen)
        .await
        .with_context(|| format!("failed to bind DS to {}", args.ds_listen))?;

    tracing::info!(
        as_addr = %args.listen,
        ds_addr = %args.ds_listen,
        "accepting connections"
    );

    // capnp-rpc is !Send (Rc internals), so all RPC tasks must stay on a
    // LocalSet. Both accept loops share one LocalSet.
    let local = tokio::task::LocalSet::new();
    local
        .run_until(async move {
            loop {
                tokio::select! {
                    result = as_listener.accept() => {
                        let (stream, peer_addr) = result.context("AS accept failed")?;
                        let keypair = Arc::clone(&keypair);
                        let store   = Arc::clone(&kp_store);
                        tokio::task::spawn_local(
                            async move {
                                match handle_as_connection(stream, keypair, store).await {
                                    Ok(()) => tracing::debug!("AS connection closed"),
                                    Err(e) => tracing::warn!(error = %e, "AS connection error"),
                                }
                            }
                            .instrument(tracing::info_span!("as_conn", peer = %peer_addr)),
                        );
                    }
                    result = ds_listener.accept() => {
                        let (stream, peer_addr) = result.context("DS accept failed")?;
                        let keypair = Arc::clone(&keypair);
                        let store   = Arc::clone(&ds_store);
                        tokio::task::spawn_local(
                            async move {
                                match handle_ds_connection(stream, keypair, store).await {
                                    Ok(()) => tracing::debug!("DS connection closed"),
                                    Err(e) => tracing::warn!(error = %e, "DS connection error"),
                                }
                            }
                            .instrument(tracing::info_span!("ds_conn", peer = %peer_addr)),
                        );
                    }
                }
            }
            #[allow(unreachable_code)]
            Ok::<(), anyhow::Error>(())
        })
        .await
}

// ── Per-connection handlers ───────────────────────────────────────────────────

/// Handle one Authentication Service connection.
async fn handle_as_connection(
    stream: TcpStream,
    keypair: Arc<NoiseKeypair>,
    store: KeyPackageStore,
) -> Result<(), anyhow::Error> {
    let transport = noise_handshake(stream, &keypair, "AS").await?;
    let (reader, writer) = transport.into_capnp_io();

    let network = twoparty::VatNetwork::new(
        reader.compat(),
        writer.compat_write(),
        Side::Server,
        Default::default(),
    );

    let service: authentication_service::Client =
        capnp_rpc::new_client(AuthServiceImpl { store });

    RpcSystem::new(Box::new(network), Some(service.client))
        .await
        .map_err(|e| anyhow::anyhow!("AS RPC error: {e}"))
}

/// Handle one Delivery Service connection.
async fn handle_ds_connection(
    stream: TcpStream,
    keypair: Arc<NoiseKeypair>,
    store: DeliveryStore,
) -> Result<(), anyhow::Error> {
    let transport = noise_handshake(stream, &keypair, "DS").await?;
    let (reader, writer) = transport.into_capnp_io();

    let network = twoparty::VatNetwork::new(
        reader.compat(),
        writer.compat_write(),
        Side::Server,
        Default::default(),
    );

    let service: delivery_service::Client =
        capnp_rpc::new_client(DeliveryServiceImpl { store });

    RpcSystem::new(Box::new(network), Some(service.client))
        .await
        .map_err(|e| anyhow::anyhow!("DS RPC error: {e}"))
}

/// Perform the Noise_XX handshake and log the remote key.
async fn noise_handshake(
    stream: TcpStream,
    keypair: &NoiseKeypair,
    label: &str,
) -> anyhow::Result<noiseml_core::NoiseTransport> {
    let transport = handshake_responder(stream, keypair)
        .await
        .map_err(|e| anyhow::anyhow!("{label} Noise handshake failed: {e}"))?;

    let remote = transport
        .remote_static_public_key()
        .map(|k| fmt_hex(&k[..4]))
        .unwrap_or_else(|| "unknown".into());
    tracing::info!(remote_key = %remote, "{label} Noise_XX handshake complete");

    Ok(transport)
}

// ── Helpers ───────────────────────────────────────────────────────────────────

/// Format the first `n` bytes of a slice as lowercase hex with a trailing `…`.
fn fmt_hex(bytes: &[u8]) -> String {
    let hex: String = bytes.iter().map(|b| format!("{b:02x}")).collect();
    format!("{hex}…")
}