//! Request dispatch for a single bidirectional QUIC stream.

use std::net::SocketAddr;

use futures::{SinkExt, StreamExt};
use lanspread_db::db::{Game, GameFileDescription};
use lanspread_proto::{LibraryDelta, Message, Request, Response};
use s2n_quic::stream::{BidirectionalStream, SendStream};
use tokio_util::codec::{FramedRead, FramedWrite, LengthDelimitedCodec};

use crate::{
    context::PeerCtx,
    error::PeerError,
    events,
    local_games::{get_game_file_descriptions, is_local_dir_name, local_download_matches_catalog},
    peer::{send_game_file_chunk, send_game_file_data},
    services::handshake::{HandshakeCtx, accept_inbound_hello, spawn_library_resync},
};

type ResponseWriter = FramedWrite<SendStream, LengthDelimitedCodec>;

/// Handles a bidirectional stream from a peer.
pub(super) async fn handle_peer_stream(
    stream: BidirectionalStream,
    ctx: PeerCtx,
    remote_addr: Option<SocketAddr>,
) -> eyre::Result<()> {
    let (rx, tx) = stream.split();
    let mut framed_rx = FramedRead::new(rx, LengthDelimitedCodec::new());
    let mut framed_tx = FramedWrite::new(tx, LengthDelimitedCodec::new());

    log::trace!("{remote_addr:?} peer stream opened");

    loop {
        let next_message = tokio::select! {
            () = ctx.shutdown.cancelled() => break,
            next_message = framed_rx.next() => next_message,
        };

        match next_message {
            Some(Ok(data)) => {
                log::trace!(
                    "{:?} msg: (raw): {}",
                    remote_addr,
                    String::from_utf8_lossy(&data)
                );

                let request = Request::decode(data.freeze());
                log::debug!("{remote_addr:?} msg: {request:?}");
                note_peer_activity(&ctx, remote_addr).await;
                framed_tx = dispatch_request(&ctx, remote_addr, request, framed_tx).await;
            }
            Some(Err(err)) => {
                log::error!("{remote_addr:?} peer stream error: {err}");
                break;
            }
            None => {
                log::trace!("{remote_addr:?} peer stream closed");
                break;
            }
        }
    }

    Ok(())
}

async fn dispatch_request(
    ctx: &PeerCtx,
    remote_addr: Option<SocketAddr>,
    request: Request,
    framed_tx: ResponseWriter,
) -> ResponseWriter {
    match request {
        Request::Ping => send_response(framed_tx, Response::Pong, "pong").await,
        Request::Hello(hello) => match accept_inbound_hello(ctx, remote_addr, hello).await {
            Ok(ack) => send_response(framed_tx, Response::HelloAck(ack), "HelloAck").await,
            Err(err) => {
                log::error!("Failed to accept inbound hello: {err}");
                send_response(
                    framed_tx,
                    Response::InternalPeerError(err.to_string()),
                    "HelloAck",
                )
                .await
            }
        },
        Request::ListGames => handle_list_games(ctx, framed_tx).await,
        Request::LibraryDelta { peer_id, delta } => {
            handle_library_delta(ctx, peer_id, delta).await;
            framed_tx
        }
        Request::GetGame { id } => handle_get_game(ctx, id, framed_tx).await,
        Request::GetGameFileData(desc) => handle_file_data_request(ctx, desc, framed_tx).await,
        Request::GetGameFileChunk {
            game_id,
            relative_path,
            offset,
            length,
        } => {
            handle_file_chunk_request(ctx, game_id, relative_path, offset, length, framed_tx).await
        }
        Request::Goodbye { peer_id } => {
            handle_goodbye(ctx, remote_addr, peer_id).await;
            framed_tx
        }
        Request::Invalid(_, _) => {
            log::error!("Received invalid request from peer");
            framed_tx
        }
    }
}

async fn note_peer_activity(ctx: &PeerCtx, remote_addr: Option<SocketAddr>) {
    if let Some(addr) = remote_addr {
        ctx.peer_game_db
            .write()
            .await
            .update_last_seen_by_addr(&addr);
    }
}

async fn send_response(
    mut framed_tx: ResponseWriter,
    response: Response,
    label: &str,
) -> ResponseWriter {
    if let Err(err) = framed_tx.send(response.encode()).await {
        log::error!("Failed to send {label} response: {err}");
    }
    framed_tx
}

async fn handle_list_games(ctx: &PeerCtx, framed_tx: ResponseWriter) -> ResponseWriter {
    log::info!("Received ListGames request from peer");
    let snapshot = {
        let db_guard = ctx.local_game_db.read().await;
        if let Some(db) = db_guard.as_ref() {
            db.all_games().into_iter().cloned().collect::<Vec<Game>>()
        } else {
            log::info!("Local game database not yet loaded, responding with empty game list");
            Vec::new()
        }
    };

    let games = if snapshot.is_empty() {
        snapshot
    } else {
        let active_operations = ctx.active_operations.read().await;
        snapshot
            .into_iter()
            .filter(|game| !active_operations.contains_key(&game.id))
            .collect()
    };

    send_response(framed_tx, Response::ListGames(games), "ListGames").await
}

async fn handle_library_delta(ctx: &PeerCtx, peer_id: String, delta: LibraryDelta) {
    let applied = {
        let mut db = ctx.peer_game_db.write().await;
        db.apply_library_delta(&peer_id, delta)
    };

    if applied {
        events::emit_peer_game_list(&ctx.peer_game_db, &ctx.catalog, &ctx.tx_notify_ui).await;
    } else {
        let addr = {
            let db = ctx.peer_game_db.read().await;
            db.peer_addr(&peer_id)
        };
        let Some(addr) = addr else {
            log::debug!("Ignoring library delta from unknown peer {peer_id}");
            return;
        };

        spawn_library_resync(HandshakeCtx::from_peer_ctx(ctx), addr, peer_id, "resync");
    }
}

async fn handle_get_game(ctx: &PeerCtx, id: String, framed_tx: ResponseWriter) -> ResponseWriter {
    log::info!("Received GetGame request for {id} from peer");
    let response = get_game_response(ctx, id).await;
    send_response(framed_tx, response, "GetGame").await
}

async fn get_game_response(ctx: &PeerCtx, id: String) -> Response {
    let game_dir = ctx.game_dir.read().await.clone();
    if !can_serve_game(ctx, &game_dir, &id).await {
        return Response::GameNotFound(id);
    }

    match get_game_file_descriptions(&id, &game_dir).await {
        Ok(file_descriptions) => Response::GetGame {
            id,
            file_descriptions,
        },
        Err(PeerError::FileSizeDetermination { path, source }) => {
            let error_msg = format!("Failed to determine file size for {path}: {source}");
            log::error!("File size determination error for game {id}: {error_msg}");
            Response::InternalPeerError(error_msg)
        }
        Err(err) => {
            log::error!("Failed to get game file descriptions for {id}: {err}");
            Response::GameNotFound(id)
        }
    }
}

async fn can_serve_game(ctx: &PeerCtx, game_dir: &std::path::Path, game_id: &str) -> bool {
    let active_operations = ctx.active_operations.read().await;
    let catalog = ctx.catalog.read().await;
    local_download_matches_catalog(game_dir, game_id, &active_operations, &catalog).await
}

async fn can_dispatch_file_transfer(
    ctx: &PeerCtx,
    game_dir: &std::path::Path,
    game_id: &str,
    relative_path: &str,
) -> bool {
    !path_points_inside_local(game_id, relative_path)
        && can_serve_game(ctx, game_dir, game_id).await
}

fn path_points_inside_local(game_id: &str, relative_path: &str) -> bool {
    let normalised = relative_path.replace('\\', "/");
    let mut parts = normalised.split('/').filter(|part| !part.is_empty());
    match (parts.next(), parts.next()) {
        (Some(first), _) if is_local_dir_name(first) => true,
        (Some(first), Some(second)) if first == game_id && is_local_dir_name(second) => true,
        _ => false,
    }
}

use std::sync::atomic::{AtomicU64, Ordering};

static NEXT_TRANSFER_ID: AtomicU64 = AtomicU64::new(1);

struct TransferGuard {
    game_id: String,
    id: u64,
    active_outbound_transfers: crate::context::OutboundTransfers,
    tx_notify_ui: tokio::sync::mpsc::UnboundedSender<crate::PeerEvent>,
}

impl TransferGuard {
    async fn new(
        game_id: String,
        active_outbound_transfers: crate::context::OutboundTransfers,
        tx_notify_ui: tokio::sync::mpsc::UnboundedSender<crate::PeerEvent>,
        shutdown: &tokio_util::sync::CancellationToken,
    ) -> (Self, tokio_util::sync::CancellationToken) {
        let id = NEXT_TRANSFER_ID.fetch_add(1, Ordering::SeqCst);
        let token = shutdown.child_token();
        {
            let mut active = active_outbound_transfers.write().await;
            active
                .entry(game_id.clone())
                .or_default()
                .push((id, token.clone()));
        }
        let _ = tx_notify_ui.send(crate::PeerEvent::OutboundTransferCountChanged);
        (
            Self {
                game_id,
                id,
                active_outbound_transfers,
                tx_notify_ui,
            },
            token,
        )
    }
}

impl Drop for TransferGuard {
    fn drop(&mut self) {
        let game_id = self.game_id.clone();
        let id = self.id;
        let active_outbound_transfers = self.active_outbound_transfers.clone();
        let tx_notify_ui = self.tx_notify_ui.clone();
        tokio::spawn(async move {
            {
                let mut active = active_outbound_transfers.write().await;
                if let Some(tokens) = active.get_mut(&game_id) {
                    tokens.retain(|(tid, _)| *tid != id);
                    if tokens.is_empty() {
                        active.remove(&game_id);
                    }
                }
            }
            let _ = tx_notify_ui.send(crate::PeerEvent::OutboundTransferCountChanged);
        });
    }
}

async fn handle_file_data_request(
    ctx: &PeerCtx,
    desc: GameFileDescription,
    framed_tx: ResponseWriter,
) -> ResponseWriter {
    log::info!(
        "Received GetGameFileData request for {} from peer",
        desc.relative_path
    );

    let (guard, cancel_token) = TransferGuard::new(
        desc.game_id.clone(),
        ctx.active_outbound_transfers.clone(),
        ctx.tx_notify_ui.clone(),
        &ctx.shutdown,
    )
    .await;

    let mut tx = framed_tx.into_inner();
    let game_dir = ctx.game_dir.read().await.clone();
    if !can_dispatch_file_transfer(ctx, &game_dir, &desc.game_id, &desc.relative_path).await {
        log::info!(
            "Declining GetGameFileData for {} because the game is not currently transferable",
            desc.relative_path
        );
        drop(guard);
        let _ = tx.close().await;
        return FramedWrite::new(tx, LengthDelimitedCodec::new());
    }

    send_game_file_data(&desc, &mut tx, &game_dir, cancel_token).await;
    drop(guard);
    FramedWrite::new(tx, LengthDelimitedCodec::new())
}

async fn handle_file_chunk_request(
    ctx: &PeerCtx,
    game_id: String,
    relative_path: String,
    offset: u64,
    length: u64,
    framed_tx: ResponseWriter,
) -> ResponseWriter {
    log::info!(
        "Received GetGameFileChunk request for {relative_path} (offset {offset}, length {length})"
    );

    let (guard, cancel_token) = TransferGuard::new(
        game_id.clone(),
        ctx.active_outbound_transfers.clone(),
        ctx.tx_notify_ui.clone(),
        &ctx.shutdown,
    )
    .await;

    let mut tx = framed_tx.into_inner();
    let game_dir = ctx.game_dir.read().await.clone();
    if !can_dispatch_file_transfer(ctx, &game_dir, &game_id, &relative_path).await {
        log::info!(
            "Declining GetGameFileChunk for {relative_path} because the game is not currently transferable"
        );
        drop(guard);
        let _ = tx.close().await;
        return FramedWrite::new(tx, LengthDelimitedCodec::new());
    }

    send_game_file_chunk(
        &game_id,
        &relative_path,
        offset,
        length,
        &mut tx,
        &game_dir,
        cancel_token,
    )
    .await;
    drop(guard);
    FramedWrite::new(tx, LengthDelimitedCodec::new())
}

async fn handle_goodbye(ctx: &PeerCtx, _remote_addr: Option<SocketAddr>, peer_id: String) {
    log::info!("Received Goodbye from peer {peer_id}");
    let removed = { ctx.peer_game_db.write().await.remove_peer(&peer_id) };
    let Some(peer) = removed else { return };

    events::emit_peer_lost(&ctx.peer_game_db, &ctx.tx_notify_ui, peer.addr).await;
    events::emit_peer_game_list(&ctx.peer_game_db, &ctx.catalog, &ctx.tx_notify_ui).await;
}

#[cfg(test)]
mod tests {
    use std::{
        path::{Path, PathBuf},
        sync::Arc,
    };

    use lanspread_db::db::GameCatalog;
    use tokio::sync::{RwLock, mpsc};
    use tokio_util::{sync::CancellationToken, task::TaskTracker};

    use super::*;
    use crate::{
        UnpackFuture,
        Unpacker,
        context::{Ctx, OperationKind},
        peer_db::PeerGameDB,
        test_support::TempDir,
    };

    struct NoopUnpacker;

    impl Unpacker for NoopUnpacker {
        fn unpack<'a>(&'a self, _archive: &'a Path, _dest: &'a Path) -> UnpackFuture<'a> {
            Box::pin(async { Ok(()) })
        }
    }

    fn write_file(path: &Path, bytes: &[u8]) {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent).expect("parent dir should be created");
        }
        std::fs::write(path, bytes).expect("file should be written");
    }

    fn test_ctx(game_dir: PathBuf, catalog: GameCatalog) -> PeerCtx {
        let (tx_notify_ui, _rx) = mpsc::unbounded_channel();
        Ctx::new(
            Arc::new(RwLock::new(PeerGameDB::new())),
            "peer".to_string(),
            game_dir.clone(),
            game_dir.join(".test-state"),
            Arc::new(NoopUnpacker),
            CancellationToken::new(),
            TaskTracker::new(),
            Arc::new(RwLock::new(catalog)),
            Arc::new(RwLock::new(std::collections::HashMap::new())),
        )
        .to_peer_ctx(tx_notify_ui)
    }

    #[test]
    fn local_relative_paths_are_never_transferable() {
        assert!(path_points_inside_local("game", "game/local/save.dat"));
        assert!(path_points_inside_local("game", "local/save.dat"));
        assert!(path_points_inside_local("game", "game\\local\\save.dat"));
        assert!(!path_points_inside_local("game", "game/version.ini"));
        assert!(!path_points_inside_local("game", "game/archive.eti"));
    }

    #[tokio::test]
    async fn get_game_response_respects_serve_gates() {
        let temp = TempDir::new("lanspread-stream");
        write_file(&temp.path().join("ready").join("version.ini"), b"20250101");
        write_file(
            &temp.path().join("non-catalog").join("version.ini"),
            b"20250101",
        );
        write_file(&temp.path().join("active").join("version.ini"), b"20250101");
        write_file(
            &temp.path().join("wrong-version").join("version.ini"),
            b"20260101",
        );
        std::fs::create_dir_all(temp.path().join("missing-sentinel"))
            .expect("missing sentinel root should be created");

        let mut catalog = GameCatalog::empty();
        catalog.insert("ready".to_string(), Some("20250101".to_string()));
        catalog.insert("active".to_string(), Some("20250101".to_string()));
        catalog.insert("missing-sentinel".to_string(), Some("20250101".to_string()));
        catalog.insert("wrong-version".to_string(), Some("20250101".to_string()));
        let ctx = test_ctx(temp.path().to_path_buf(), catalog);
        ctx.active_operations
            .write()
            .await
            .insert("active".to_string(), OperationKind::Downloading);

        assert!(matches!(
            get_game_response(&ctx, "ready".to_string()).await,
            Response::GetGame { id, .. } if id == "ready"
        ));
        assert!(matches!(
            get_game_response(&ctx, "non-catalog".to_string()).await,
            Response::GameNotFound(id) if id == "non-catalog"
        ));
        assert!(matches!(
            get_game_response(&ctx, "active".to_string()).await,
            Response::GameNotFound(id) if id == "active"
        ));
        assert!(matches!(
            get_game_response(&ctx, "wrong-version".to_string()).await,
            Response::GameNotFound(id) if id == "wrong-version"
        ));
        assert!(matches!(
            get_game_response(&ctx, "missing-sentinel".to_string()).await,
            Response::GameNotFound(id) if id == "missing-sentinel"
        ));
    }

    #[tokio::test]
    async fn file_transfer_dispatch_respects_serve_gates() {
        let temp = TempDir::new("lanspread-stream");
        write_file(&temp.path().join("ready").join("version.ini"), b"20250101");
        write_file(
            &temp.path().join("non-catalog").join("version.ini"),
            b"20250101",
        );
        write_file(&temp.path().join("active").join("version.ini"), b"20250101");
        write_file(
            &temp.path().join("wrong-version").join("version.ini"),
            b"20260101",
        );
        std::fs::create_dir_all(temp.path().join("missing-sentinel"))
            .expect("missing sentinel root should be created");

        let mut catalog = GameCatalog::empty();
        catalog.insert("ready".to_string(), Some("20250101".to_string()));
        catalog.insert("active".to_string(), Some("20250101".to_string()));
        catalog.insert("missing-sentinel".to_string(), Some("20250101".to_string()));
        catalog.insert("wrong-version".to_string(), Some("20250101".to_string()));
        let ctx = test_ctx(temp.path().to_path_buf(), catalog);
        ctx.active_operations
            .write()
            .await
            .insert("active".to_string(), OperationKind::Downloading);

        assert!(can_dispatch_file_transfer(&ctx, temp.path(), "ready", "ready/version.ini").await);
        assert!(
            !can_dispatch_file_transfer(
                &ctx,
                temp.path(),
                "non-catalog",
                "non-catalog/version.ini",
            )
            .await
        );
        assert!(
            !can_dispatch_file_transfer(&ctx, temp.path(), "active", "active/version.ini").await
        );
        assert!(
            !can_dispatch_file_transfer(
                &ctx,
                temp.path(),
                "wrong-version",
                "wrong-version/version.ini",
            )
            .await
        );
        assert!(
            !can_dispatch_file_transfer(
                &ctx,
                temp.path(),
                "missing-sentinel",
                "missing-sentinel/archive.eti",
            )
            .await
        );
        assert!(
            !can_dispatch_file_transfer(&ctx, temp.path(), "ready", "ready/local/save.dat").await
        );
    }
}