//! `server` — the authoritative match server (Phase B of `plan2.md`), built on
//! `std::net` with no external crates.
//!
//! Responsibilities the server owns: match state, the turn timer, collecting
//! submitted actions, driving resolution through [`game_runtime`], visibility
//! filtering, replay recording, and disconnect handling. The browser is served
//! the embedded client and then speaks the `protocol` over a WebSocket.
//!
//! Authority guarantees enforced here and covered by tests:
//! * **No panic on bad input** — every client packet is decoded with the total
//!   `protocol` decoder; a failure becomes a `ValidationReport`, never a crash.
//! * **Late input rejected deterministically** — a `SubmitTurn` for any turn
//!   other than the live one, or after the deadline, is rejected with a stable
//!   reason.
//! * **Disconnect cannot corrupt a match** — a dropped connection simply stops
//!   submitting; that player's turns default to `Wait` and the match continues.
//! * **Client cannot mutate hidden state** — only intent is accepted, and the
//!   hidden ground truth is never serialized to a client.

pub mod http;
pub mod ws;

use std::collections::BTreeMap;
use std::io::{BufReader, Write};
use std::net::{SocketAddr, TcpListener, TcpStream};
use std::sync::mpsc::{self, Sender};
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::{Duration, Instant};

use game_runtime::{duel_roster, solo_roster, Match};
use protocol::{
    Action, ClientMessage, MatchId, PlayerId, ReplayTurn, RuneDiagnostics, ServerMessage,
};

/// How long the timer thread sleeps between ticks.
const TICK: Duration = Duration::from_millis(40);
/// Replay turns per `ReplayChunk`.
const REPLAY_CHUNK: usize = 16;

/// An outbound item for a single connection's writer thread. Routing every
/// write through one thread keeps frames from interleaving.
enum Out {
    Text(String),
    Pong(Vec<u8>),
    Close,
}

/// One live match plus its scheduling and connection state.
struct Session {
    m: Match,
    turn_len: Duration,
    deadline: Instant,
    pending: BTreeMap<u32, Action>,
    conns: BTreeMap<u32, Sender<Out>>,
    /// Entity ids that are human-controlled (vs. a dummy).
    human_slots: Vec<u32>,
}

impl Session {
    fn deadline_ms(&self, now: Instant) -> u64 {
        self.deadline.saturating_duration_since(now).as_millis() as u64
    }

    fn snapshot_msg(&self, player: u32) -> ServerMessage {
        ServerMessage::MatchState {
            match_id: self.m.id,
            player_id: PlayerId(player),
            turn: self.m.turn,
            snapshot: self.m.visible_for(player),
        }
    }
}

/// The shared manager: all matches, behind one mutex.
pub struct Manager {
    sessions: BTreeMap<u64, Session>,
    next_auto_id: u64,
    turn_ms: u64,
}

/// Result of a successful join.
struct JoinOk {
    match_id: MatchId,
    player_id: u32,
    initial: ServerMessage,
    turn_started: ServerMessage,
}

impl Manager {
    fn new(turn_ms: u64) -> Manager {
        Manager { sessions: BTreeMap::new(), next_auto_id: 1, turn_ms }
    }

    fn turn_len(&self) -> Duration {
        Duration::from_millis(self.turn_ms)
    }

    /// Join (or create) a match. `requested = None` creates a fresh solo match
    /// (player + dummy). `requested = Some(id)` joins an existing duel by id, or
    /// creates that duel and takes the first human slot.
    fn join(
        &mut self,
        name: &str,
        requested: Option<MatchId>,
        tx: Sender<Out>,
    ) -> Result<JoinOk, String> {
        let now = Instant::now();
        let turn_len = self.turn_len();
        let key = match requested {
            Some(m) => m.0,
            None => {
                let id = self.next_auto_id;
                self.next_auto_id += 1;
                id
            }
        };

        // Create the session if absent.
        if !self.sessions.contains_key(&key) {
            let (roster, human_slots) = if requested.is_some() {
                (duel_roster(name, "opponent"), vec![1u32, 2])
            } else {
                (solo_roster(name), vec![1u32])
            };
            let m = Match::new(MatchId(key), key, roster);
            self.sessions.insert(
                key,
                Session {
                    m,
                    turn_len,
                    deadline: now + turn_len,
                    pending: BTreeMap::new(),
                    conns: BTreeMap::new(),
                    human_slots,
                },
            );
        }

        let session = self.sessions.get_mut(&key).unwrap();
        // Find the first human slot without a live connection.
        let slot = session
            .human_slots
            .iter()
            .copied()
            .find(|s| !session.conns.contains_key(s))
            .ok_or_else(|| "match is full".to_string())?;

        // Adopt the player's chosen name on their entity.
        if let Some(e) = session.m.entity_mut(slot) {
            e.name = name.to_string();
        }
        session.conns.insert(slot, tx);

        Ok(JoinOk {
            match_id: MatchId(key),
            player_id: slot,
            initial: session.snapshot_msg(slot),
            turn_started: ServerMessage::TurnStarted {
                turn: session.m.turn,
                deadline_ms: session.deadline_ms(now),
            },
        })
    }

    /// Queue a turn submission. Rejects late / wrong-turn submissions
    /// deterministically.
    fn submit(
        &mut self,
        match_key: u64,
        player: u32,
        turn: u64,
        action: Action,
    ) -> Result<(), String> {
        let now = Instant::now();
        let session = self
            .sessions
            .get_mut(&match_key)
            .ok_or_else(|| "no such match".to_string())?;
        if session.m.finished {
            return Err("match has ended".to_string());
        }
        if turn != session.m.turn {
            return Err(format!(
                "wrong turn: submitted {}, live turn is {}",
                turn, session.m.turn
            ));
        }
        if now > session.deadline {
            return Err("late: turn deadline has passed".to_string());
        }
        session.pending.insert(player, action);
        Ok(())
    }

    fn set_program(
        &mut self,
        match_key: u64,
        player: u32,
        tokens: Vec<protocol::RuneTokenWire>,
    ) -> Result<RuneDiagnostics, String> {
        let session = self
            .sessions
            .get_mut(&match_key)
            .ok_or_else(|| "no such match".to_string())?;
        session.m.set_program(player, tokens);
        Ok(session.m.diagnostics_for_player(player))
    }

    fn inspect(&self, match_key: u64, target: u32) -> Result<ServerMessage, String> {
        let session = self
            .sessions
            .get(&match_key)
            .ok_or_else(|| "no such match".to_string())?;
        let diagnostics = session.m.diagnostics_for_player(target);
        Ok(ServerMessage::ObservationResult { target, diagnostics })
    }

    fn replay_chunks(&self, match_key: u64) -> Result<Vec<ServerMessage>, String> {
        let session = self
            .sessions
            .get(&match_key)
            .ok_or_else(|| "no such match".to_string())?;
        let m = &session.m;
        let turns: Vec<ReplayTurn> = m
            .replay
            .turns
            .iter()
            .map(|rt| ReplayTurn {
                turn: rt.turn,
                inputs: rt
                    .inputs
                    .iter()
                    .map(|i| (i.player, i.action.clone()))
                    .collect(),
                runtime_hash: format!("{}", rt.turn_hash),
            })
            .collect();
        let final_hash = m.final_hash_hex();
        let chunks: Vec<&[ReplayTurn]> = if turns.is_empty() {
            vec![&[]]
        } else {
            turns.chunks(REPLAY_CHUNK).collect()
        };
        let total = chunks.len() as u32;
        Ok(chunks
            .into_iter()
            .enumerate()
            .map(|(i, c)| ServerMessage::ReplayChunk {
                match_id: m.id,
                seed: m.seed,
                index: i as u32,
                total,
                turns: c.to_vec(),
                final_hash: final_hash.clone(),
            })
            .collect())
    }

    /// Advance any match whose deadline has elapsed. Runs under the lock; sends
    /// are non-blocking on unbounded channels.
    fn tick(&mut self, now: Instant) {
        let mut empty: Vec<u64> = Vec::new();
        for (key, session) in self.sessions.iter_mut() {
            if session.conns.is_empty() {
                empty.push(*key);
                continue;
            }
            if session.m.finished || now < session.deadline {
                continue;
            }
            // Resolve the turn from queued submissions.
            let subs: Vec<(u32, Action)> =
                session.pending.iter().map(|(p, a)| (*p, a.clone())).collect();
            let events = session.m.resolve_turn(&subs);
            session.pending.clear();
            let runtime_hash = session.m.last_turn_hash_hex();
            let turn = session.m.turn;
            // Broadcast the resolved state, filtered per player.
            for (pid, tx) in session.conns.iter() {
                let msg = ServerMessage::TurnResolved {
                    turn,
                    snapshot: session.m.visible_for(*pid),
                    runtime_hash: runtime_hash.clone(),
                    events: events.clone(),
                };
                let _ = tx.send(Out::Text(msg.encode()));
            }
            // Open the next turn unless the match just ended.
            if !session.m.finished {
                session.deadline = now + session.turn_len;
                let ts = ServerMessage::TurnStarted {
                    turn,
                    deadline_ms: session.turn_len.as_millis() as u64,
                };
                for tx in session.conns.values() {
                    let _ = tx.send(Out::Text(ts.encode()));
                }
            }
        }
        // Drop sessions nobody is connected to (replay no longer reachable).
        for key in empty {
            self.sessions.remove(&key);
        }
    }

    fn disconnect(&mut self, match_key: u64, player: u32) {
        if let Some(session) = self.sessions.get_mut(&match_key) {
            session.conns.remove(&player);
            if session.conns.is_empty() {
                self.sessions.remove(&match_key);
            }
        }
    }
}

/// Configuration.
pub struct Config {
    pub turn_ms: u64,
}

impl Config {
    pub fn from_env() -> Config {
        let turn_ms = std::env::var("MAGICKA_TURN_MS")
            .ok()
            .and_then(|v| v.parse().ok())
            .unwrap_or(5000);
        Config { turn_ms }
    }
}

/// Start the server on `addr`. Returns the bound address (useful when binding
/// to port 0 in tests). Spawns the accept loop and the turn-timer thread as
/// detached background threads.
pub fn serve(addr: &str, cfg: Config) -> std::io::Result<SocketAddr> {
    let listener = TcpListener::bind(addr)?;
    let local = listener.local_addr()?;
    let manager = Arc::new(Mutex::new(Manager::new(cfg.turn_ms)));

    // Turn timer.
    {
        let mgr = Arc::clone(&manager);
        thread::spawn(move || loop {
            thread::sleep(TICK);
            let now = Instant::now();
            lock(&mgr).tick(now);
        });
    }

    // Accept loop.
    {
        let mgr = Arc::clone(&manager);
        thread::spawn(move || {
            for stream in listener.incoming() {
                if let Ok(stream) = stream {
                    let mgr = Arc::clone(&mgr);
                    thread::spawn(move || {
                        let _ = handle_conn(stream, mgr);
                    });
                }
            }
        });
    }

    Ok(local)
}

/// Blocking entry point for the binary.
pub fn run(addr: &str) -> std::io::Result<()> {
    let local = serve(addr, Config::from_env())?;
    eprintln!("magicka-server listening on http://{local}  (open it in a browser)");
    loop {
        thread::sleep(Duration::from_secs(3600));
    }
}

fn handle_conn(stream: TcpStream, mgr: Arc<Mutex<Manager>>) -> std::io::Result<()> {
    stream.set_nodelay(true).ok();
    let mut head_reader = BufReader::new(stream.try_clone()?);
    let req = match http::read_request(&mut head_reader)? {
        Some(r) => r,
        None => return Ok(()),
    };

    if !req.is_websocket_upgrade() {
        // Static asset.
        let mut s = stream;
        let resp = web_client::http_response(&req.path).unwrap_or_else(web_client::not_found);
        s.write_all(&resp)?;
        return Ok(());
    }

    // Complete the WebSocket handshake.
    let key = match req.websocket_key() {
        Some(k) => k,
        None => return Ok(()),
    };
    let accept = ws::accept_key(key);
    {
        let mut s = stream.try_clone()?;
        s.write_all(http::handshake_response(&accept).as_bytes())?;
        s.flush()?;
    }

    // Writer thread: the only thing that ever writes to this socket.
    let (tx, rx) = mpsc::channel::<Out>();
    let mut write_stream = stream.try_clone()?;
    let writer = thread::spawn(move || {
        for out in rx {
            let r = match out {
                Out::Text(s) => ws::write_text(&mut write_stream, &s),
                Out::Pong(p) => ws::write_pong(&mut write_stream, &p),
                Out::Close => {
                    let _ = ws::write_close(&mut write_stream);
                    break;
                }
            };
            if r.is_err() {
                break;
            }
        }
    });

    // Reader loop.
    let mut read_stream = stream;
    let mut match_key: Option<u64> = None;
    let mut player_id: Option<u32> = None;

    loop {
        match ws::read_message(&mut read_stream) {
            Ok(Some(ws::Message::Text(raw))) => {
                dispatch(&mgr, &tx, &raw, &mut match_key, &mut player_id);
            }
            Ok(Some(ws::Message::Ping(p))) => {
                let _ = tx.send(Out::Pong(p));
            }
            Ok(Some(ws::Message::Pong)) => {}
            Ok(Some(ws::Message::Close)) | Ok(None) => break,
            Err(_) => break,
        }
    }

    // Disconnect: deregister so the match continues without corruption.
    if let (Some(k), Some(p)) = (match_key, player_id) {
        lock(&mgr).disconnect(k, p);
    }
    let _ = tx.send(Out::Close);
    drop(tx);
    let _ = writer.join();
    Ok(())
}

/// Dispatch one decoded client message. Never panics: a decode failure or any
/// rejected operation becomes a `ValidationReport`/`ErrorEvent`.
fn dispatch(
    mgr: &Arc<Mutex<Manager>>,
    tx: &Sender<Out>,
    raw: &str,
    match_key: &mut Option<u64>,
    player_id: &mut Option<u32>,
) {
    let msg = match ClientMessage::decode(raw) {
        Ok(m) => m,
        Err(e) => {
            send(tx, ServerMessage::ValidationReport {
                accepted: false,
                detail: format!("malformed packet: {e}"),
                diagnostics: RuneDiagnostics::default(),
            });
            return;
        }
    };

    match msg {
        ClientMessage::JoinMatch { name, match_id } => {
            if player_id.is_some() {
                send(tx, err_event("already_joined", "this connection already joined a match"));
                return;
            }
            let mut m = lock(mgr);
            match m.join(&name, match_id, tx.clone()) {
                Ok(ok) => {
                    *match_key = Some(ok.match_id.0);
                    *player_id = Some(ok.player_id);
                    send(tx, ok.initial);
                    send(tx, ok.turn_started);
                }
                Err(detail) => send(tx, err_event("join_failed", &detail)),
            }
        }
        ClientMessage::SubmitTurn { turn, action } => {
            let (Some(k), Some(p)) = (*match_key, *player_id) else {
                send(tx, err_event("not_joined", "join a match first"));
                return;
            };
            let res = lock(mgr).submit(k, p, turn, action);
            match res {
                Ok(()) => send(tx, ServerMessage::ValidationReport {
                    accepted: true,
                    detail: format!("action queued for turn {turn}"),
                    diagnostics: RuneDiagnostics::default(),
                }),
                Err(detail) => send(tx, ServerMessage::ValidationReport {
                    accepted: false,
                    detail,
                    diagnostics: RuneDiagnostics::default(),
                }),
            }
        }
        ClientMessage::EditRuneProgram { tokens } => {
            let (Some(k), Some(p)) = (*match_key, *player_id) else {
                send(tx, err_event("not_joined", "join a match first"));
                return;
            };
            match lock(mgr).set_program(k, p, tokens) {
                Ok(diagnostics) => send(tx, ServerMessage::ValidationReport {
                    accepted: true,
                    detail: "program updated".to_string(),
                    diagnostics,
                }),
                Err(detail) => send(tx, err_event("edit_failed", &detail)),
            }
        }
        ClientMessage::InspectTarget { target } => {
            let Some(k) = *match_key else {
                send(tx, err_event("not_joined", "join a match first"));
                return;
            };
            match lock(mgr).inspect(k, target) {
                Ok(m) => send(tx, m),
                Err(detail) => send(tx, err_event("inspect_failed", &detail)),
            }
        }
        ClientMessage::RequestReplay { match_id } => {
            match lock(mgr).replay_chunks(match_id.0) {
                Ok(chunks) => {
                    for c in chunks {
                        send(tx, c);
                    }
                }
                Err(detail) => send(tx, err_event("replay_failed", &detail)),
            }
        }
        ClientMessage::Ping { .. } => {
            // Liveness only; the WebSocket layer already handles control pings.
        }
    }
}

fn send(tx: &Sender<Out>, msg: ServerMessage) {
    let _ = tx.send(Out::Text(msg.encode()));
}

/// Acquire the manager lock, recovering a poisoned guard. A panic in any single
/// connection or tick must not permanently brick the server for everyone else.
fn lock(mgr: &Arc<Mutex<Manager>>) -> std::sync::MutexGuard<'_, Manager> {
    mgr.lock().unwrap_or_else(|p| p.into_inner())
}

fn err_event(code: &str, detail: &str) -> ServerMessage {
    ServerMessage::ErrorEvent { code: code.to_string(), detail: detail.to_string() }
}

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

    #[test]
    fn manager_join_and_resolve_is_authoritative() {
        let mut m = Manager::new(10);
        let (tx, _rx) = mpsc::channel();
        let ok = m.join("dev", None, tx).unwrap();
        assert_eq!(ok.player_id, 1);
        let key = ok.match_id.0;
        // Submit a cast for the live turn.
        assert!(m.submit(key, 1, 0, Action::Cast).is_ok());
        // Wrong turn is rejected deterministically.
        let e = m.submit(key, 1, 99, Action::Cast).unwrap_err();
        assert!(e.contains("wrong turn"), "{e}");
    }

    #[test]
    fn disconnect_drops_session_when_last_leaves() {
        let mut m = Manager::new(10);
        let (tx, _rx) = mpsc::channel();
        let ok = m.join("dev", None, tx).unwrap();
        let key = ok.match_id.0;
        assert!(m.sessions.contains_key(&key));
        m.disconnect(key, 1);
        assert!(!m.sessions.contains_key(&key));
    }

    #[test]
    fn duel_assigns_two_human_slots() {
        let mut m = Manager::new(10);
        let (tx1, _r1) = mpsc::channel();
        let (tx2, _r2) = mpsc::channel();
        let a = m.join("a", Some(MatchId(42)), tx1).unwrap();
        let b = m.join("b", Some(MatchId(42)), tx2).unwrap();
        assert_eq!(a.player_id, 1);
        assert_eq!(b.player_id, 2);
        // Third join to a full duel is rejected.
        let (tx3, _r3) = mpsc::channel();
        assert!(m.join("c", Some(MatchId(42)), tx3).is_err());
    }
}