//! Protocol handshakes and library synchronization between peers.

use std::{net::SocketAddr, sync::Arc};

use lanspread_proto::{Hello, HelloAck, LibraryDelta, LibrarySnapshot, PROTOCOL_VERSION};
use tokio::sync::{RwLock, mpsc::UnboundedSender};

use crate::{
    PeerEvent,
    context::PeerCtx,
    events,
    identity::default_features,
    library::{LocalLibraryState, build_library_snapshot, build_library_summary},
    network::{exchange_hello, send_library_delta, send_library_snapshot, send_library_summary},
    peer_db::{PeerGameDB, PeerId, PeerUpsert},
};

enum LibraryUpdate {
    Delta(LibraryDelta),
    Snapshot(LibrarySnapshot),
}

pub(super) async fn build_hello_ack(ctx: &PeerCtx) -> HelloAck {
    let library_guard = ctx.local_library.read().await;
    HelloAck {
        peer_id: ctx.peer_id.as_ref().clone(),
        proto_ver: PROTOCOL_VERSION,
        library_rev: library_guard.revision,
        library_digest: library_guard.digest,
        features: default_features(),
    }
}

async fn build_hello_from_state(
    peer_id: &str,
    local_library: &Arc<RwLock<LocalLibraryState>>,
) -> Hello {
    let library_guard = local_library.read().await;
    Hello {
        peer_id: peer_id.to_string(),
        proto_ver: PROTOCOL_VERSION,
        library_rev: library_guard.revision,
        library_digest: library_guard.digest,
        features: default_features(),
    }
}

pub(crate) async fn perform_handshake_with_peer(
    peer_id: Arc<String>,
    local_library: Arc<RwLock<LocalLibraryState>>,
    peer_game_db: Arc<RwLock<PeerGameDB>>,
    tx_notify_ui: UnboundedSender<PeerEvent>,
    peer_addr: SocketAddr,
    peer_id_hint: Option<PeerId>,
) -> eyre::Result<()> {
    let hello = build_hello_from_state(peer_id.as_ref(), &local_library).await;
    let ack = exchange_hello(peer_addr, hello).await?;

    if ack.proto_ver != PROTOCOL_VERSION {
        log::warn!(
            "Peer {peer_addr} uses incompatible protocol {} (expected {PROTOCOL_VERSION})",
            ack.proto_ver
        );
        return Ok(());
    }

    if ack.peer_id == *peer_id {
        log::trace!("Ignoring handshake with self for {peer_addr}");
        return Ok(());
    }

    if let Some(expected) = peer_id_hint.as_ref()
        && expected != &ack.peer_id
    {
        log::warn!(
            "Peer {peer_addr} id mismatch: mDNS advertised {expected}, hello ack returned {}",
            ack.peer_id
        );
        let _ = peer_game_db.write().await.remove_peer(expected);
    }

    let upsert = record_remote_library(
        &peer_game_db,
        ack.peer_id.clone(),
        peer_addr,
        ack.library_rev,
        ack.library_digest,
        ack.features.clone(),
    )
    .await;

    after_peer_library_recorded(
        upsert,
        peer_addr,
        ack.library_rev,
        ack.library_digest,
        &local_library,
        &peer_game_db,
        &tx_notify_ui,
    )
    .await;

    Ok(())
}

pub(super) async fn accept_inbound_hello(
    ctx: &PeerCtx,
    remote_addr: Option<SocketAddr>,
    hello: Hello,
) -> HelloAck {
    if hello.peer_id == *ctx.peer_id {
        log::trace!("Ignoring hello from self");
        return build_hello_ack(ctx).await;
    }

    if hello.proto_ver != PROTOCOL_VERSION {
        log::warn!(
            "Incompatible protocol from {remote_addr:?}: {}",
            hello.proto_ver
        );
        return build_hello_ack(ctx).await;
    }

    if let Some(addr) = peer_record_addr(&ctx.peer_game_db, &hello.peer_id, remote_addr).await {
        let upsert = record_remote_library(
            &ctx.peer_game_db,
            hello.peer_id.clone(),
            addr,
            hello.library_rev,
            hello.library_digest,
            hello.features.clone(),
        )
        .await;

        after_peer_library_recorded(
            upsert,
            addr,
            hello.library_rev,
            hello.library_digest,
            &ctx.local_library,
            &ctx.peer_game_db,
            &ctx.tx_notify_ui,
        )
        .await;
    }

    build_hello_ack(ctx).await
}

async fn peer_record_addr(
    peer_game_db: &Arc<RwLock<PeerGameDB>>,
    peer_id: &PeerId,
    remote_addr: Option<SocketAddr>,
) -> Option<SocketAddr> {
    let remote_addr = remote_addr?;
    let db = peer_game_db.read().await;
    Some(db.peer_addr(peer_id).unwrap_or(remote_addr))
}

pub(super) fn spawn_library_resync(
    peer_id: Arc<String>,
    local_library: Arc<RwLock<LocalLibraryState>>,
    peer_game_db: Arc<RwLock<PeerGameDB>>,
    tx_notify_ui: UnboundedSender<PeerEvent>,
    peer_addr: SocketAddr,
    peer_id_hint: PeerId,
    reason: &'static str,
) {
    tokio::spawn(async move {
        if let Err(err) = perform_handshake_with_peer(
            peer_id,
            local_library,
            peer_game_db,
            tx_notify_ui,
            peer_addr,
            Some(peer_id_hint),
        )
        .await
        {
            log::warn!("Failed to {reason} library from {peer_addr}: {err}");
        }
    });
}

async fn record_remote_library(
    peer_game_db: &Arc<RwLock<PeerGameDB>>,
    peer_id: PeerId,
    peer_addr: SocketAddr,
    library_rev: u64,
    library_digest: u64,
    features: Vec<String>,
) -> PeerUpsert {
    let mut db = peer_game_db.write().await;
    let upsert = db.upsert_peer(peer_id.clone(), peer_addr);
    db.update_peer_library(&peer_id, library_rev, library_digest, features);
    upsert
}

async fn after_peer_library_recorded(
    upsert: PeerUpsert,
    peer_addr: SocketAddr,
    remote_library_rev: u64,
    remote_library_digest: u64,
    local_library: &Arc<RwLock<LocalLibraryState>>,
    peer_game_db: &Arc<RwLock<PeerGameDB>>,
    tx_notify_ui: &UnboundedSender<PeerEvent>,
) {
    if upsert.is_new {
        events::emit_peer_discovered(peer_game_db, tx_notify_ui, peer_addr).await;
        send_local_library_summary(peer_addr, local_library).await;
    }

    send_local_library_update_if_needed(
        peer_addr,
        local_library,
        remote_library_rev,
        remote_library_digest,
    )
    .await;
}

async fn send_local_library_summary(
    peer_addr: SocketAddr,
    local_library: &Arc<RwLock<LocalLibraryState>>,
) {
    let summary = {
        let library_guard = local_library.read().await;
        build_library_summary(&library_guard)
    };

    tokio::spawn(async move {
        if let Err(err) = send_library_summary(peer_addr, summary).await {
            log::warn!("Failed to send library summary to {peer_addr}: {err}");
        }
    });
}

async fn send_local_library_update_if_needed(
    peer_addr: SocketAddr,
    local_library: &Arc<RwLock<LocalLibraryState>>,
    remote_rev: u64,
    remote_digest: u64,
) {
    if let Some(update) = select_library_update(local_library, remote_rev, remote_digest).await {
        tokio::spawn(async move {
            let result = match update {
                LibraryUpdate::Delta(delta) => send_library_delta(peer_addr, delta).await,
                LibraryUpdate::Snapshot(snapshot) => {
                    send_library_snapshot(peer_addr, snapshot).await
                }
            };

            if let Err(err) = result {
                log::warn!("Failed to send library update to {peer_addr}: {err}");
            }
        });
    }
}

async fn select_library_update(
    local_library: &Arc<RwLock<LocalLibraryState>>,
    remote_rev: u64,
    remote_digest: u64,
) -> Option<LibraryUpdate> {
    let library_guard = local_library.read().await;
    if library_guard.digest == remote_digest || remote_rev > library_guard.revision {
        return None;
    }

    if let Some(delta) = library_guard.delta_since(remote_rev) {
        return Some(LibraryUpdate::Delta(delta));
    }

    Some(LibraryUpdate::Snapshot(build_library_snapshot(
        &library_guard,
    )))
}

#[cfg(test)]
mod tests {
    use std::{net::SocketAddr, sync::Arc};

    use tokio::sync::RwLock;

    use super::peer_record_addr;
    use crate::peer_db::PeerGameDB;

    fn addr(ip: [u8; 4], port: u16) -> SocketAddr {
        SocketAddr::from((ip, port))
    }

    #[tokio::test]
    async fn inbound_hello_keeps_existing_listening_addr() {
        let peer_game_db = Arc::new(RwLock::new(PeerGameDB::new()));
        let advertised = addr([10, 66, 0, 2], 40000);
        let transport_source = addr([10, 66, 0, 2], 52000);
        peer_game_db
            .write()
            .await
            .upsert_peer("peer".to_string(), advertised);

        let record_addr =
            peer_record_addr(&peer_game_db, &"peer".to_string(), Some(transport_source)).await;

        assert_eq!(record_addr, Some(advertised));
    }
}