//! 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, LibrarySnapshot, LibrarySummary, Message, Request, Response};
use s2n_quic::stream::{BidirectionalStream, SendStream};
use tokio_util::codec::{FramedRead, FramedWrite, LengthDelimitedCodec};

use crate::{
    PeerEvent,
    context::PeerCtx,
    error::PeerError,
    events,
    local_games::{get_game_file_descriptions, is_local_dir_name, local_download_available},
    peer::{send_game_file_chunk, send_game_file_data},
    remote_peer::{ensure_peer_id_for_addr, update_peer_from_game_list},
    services::handshake::{
        accept_inbound_hello,
        perform_handshake_with_peer,
        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) => {
            let ack = accept_inbound_hello(ctx, remote_addr, hello).await;
            send_response(framed_tx, Response::HelloAck(ack), "HelloAck").await
        }
        Request::ListGames => handle_list_games(ctx, framed_tx).await,
        Request::LibrarySummary(summary) => {
            handle_library_summary(ctx, remote_addr, summary).await;
            framed_tx
        }
        Request::LibrarySnapshot(snapshot) => {
            handle_library_snapshot(ctx, remote_addr, snapshot).await;
            framed_tx
        }
        Request::LibraryDelta(delta) => {
            handle_library_delta(ctx, remote_addr, 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
        }
        Request::AnnounceGames(games) => {
            handle_announce_games(ctx, remote_addr, games).await;
            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_summary(
    ctx: &PeerCtx,
    remote_addr: Option<SocketAddr>,
    summary: LibrarySummary,
) {
    let Some(addr) = remote_addr else {
        return;
    };

    let peer_id = ensure_peer_id_for_addr(&ctx.peer_game_db, addr).await;
    let (previous_digest, previous_count, features) = {
        let db = ctx.peer_game_db.read().await;
        let (_, digest) = db.peer_library_state(&peer_id).unwrap_or((0, 0));
        (
            digest,
            db.peer_game_count(&peer_id),
            db.peer_features(&peer_id),
        )
    };

    {
        let mut db = ctx.peer_game_db.write().await;
        db.update_peer_library(
            &peer_id,
            summary.library_rev,
            summary.library_digest,
            features,
        );
    }

    if summary.library_digest != previous_digest || previous_count == 0 {
        ctx.task_tracker.spawn({
            let peer_id_arc = ctx.peer_id.clone();
            let local_library = ctx.local_library.clone();
            let peer_game_db = ctx.peer_game_db.clone();
            let tx_notify_ui = ctx.tx_notify_ui.clone();
            async move {
                if let Err(err) = perform_handshake_with_peer(
                    peer_id_arc,
                    local_library,
                    peer_game_db,
                    tx_notify_ui,
                    addr,
                    Some(peer_id),
                )
                .await
                {
                    log::warn!("Failed to refresh library from {addr}: {err}");
                }
            }
        });
    }
}

async fn handle_library_snapshot(
    ctx: &PeerCtx,
    remote_addr: Option<SocketAddr>,
    snapshot: LibrarySnapshot,
) {
    if let Some(addr) = remote_addr {
        let peer_id = ensure_peer_id_for_addr(&ctx.peer_game_db, addr).await;
        {
            let mut db = ctx.peer_game_db.write().await;
            db.apply_library_snapshot(&peer_id, snapshot);
        }

        events::emit_peer_game_list(&ctx.peer_game_db, &ctx.tx_notify_ui).await;
    }
}

async fn handle_library_delta(ctx: &PeerCtx, remote_addr: Option<SocketAddr>, delta: LibraryDelta) {
    let Some(addr) = remote_addr else {
        return;
    };

    let peer_id = ensure_peer_id_for_addr(&ctx.peer_game_db, addr).await;
    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.tx_notify_ui).await;
    } else {
        spawn_library_resync(
            ctx.peer_id.clone(),
            ctx.local_library.clone(),
            ctx.peer_game_db.clone(),
            ctx.tx_notify_ui.clone(),
            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_available(game_dir, game_id, &active_operations, &catalog).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,
    }
}

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

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

    send_game_file_chunk(&game_id, &relative_path, offset, length, &mut tx, &game_dir).await;
    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) };
    if removed.is_none() {
        return;
    }

    if let Some(addr) = remote_addr {
        events::emit_peer_lost(&ctx.peer_game_db, &ctx.tx_notify_ui, addr).await;
    }

    events::emit_peer_game_list(&ctx.peer_game_db, &ctx.tx_notify_ui).await;
}

async fn handle_announce_games(ctx: &PeerCtx, remote_addr: Option<SocketAddr>, games: Vec<Game>) {
    log::info!(
        "Received {} announced games from peer {remote_addr:?}",
        games.len()
    );

    if let Some(addr) = remote_addr {
        let aggregated_games = update_peer_from_game_list(&ctx.peer_game_db, addr, &games).await;
        events::send(&ctx.tx_notify_ui, PeerEvent::ListGames(aggregated_games));
    }
}

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

    #[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"));
    }
}