import crypto from 'node:crypto';
import type { ServerMessage, Snapshot, PartialCharacterDiff, PrivateHandout } from '@/lib/sync/messages';
import type { Character } from '@/lib/schemas/character';

export interface Sender {
  send: (msg: ServerMessage) => void;
}

interface Seat {
  sender: Sender;
  characterId: string;
  name: string;
  /** the granted sheet, re-sent on reconnect so the player regains control seamlessly */
  character: Character;
  /** set when the holder's socket drops; the seat survives a short grace window */
  disconnectedAt?: number;
}

/** How long a seat survives after its player disconnects, so a reconnect can reclaim it. */
const SEAT_GRACE_MS = 5 * 60 * 1000;

interface SeatRequest {
  playerId: string;
  characterId: string;
  offlineSnapshot?: Character;
}

interface Room {
  roomId: string;
  joinCode: string;
  gmSecretHash: string;
  passwordHash: string | null;
  gm: Sender | null;
  players: Set<Sender>;
  snapshot: Snapshot | null;
  images: Map<string, string>;
  /** running total of bytes in `images`, kept so the cap is O(1) to check */
  imageBytes: number;
  /** granted seats keyed by playerId */
  seats: Map<string, Seat>;
  /** seat requests awaiting GM approval (re-sent when the GM reconnects) */
  pendingSeatRequests: SeatRequest[];
  lastActivity: number;
}

const JOIN_ALPHABET = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789'; // no ambiguous chars
const ROOM_TTL_MS = 6 * 60 * 60 * 1000; // 6h idle
// Memory guardrails so an anonymous GM can't balloon the (in-RAM) hub on a small box.
export interface RoomLimits { maxRooms: number; maxImagesPerRoom: number; maxRoomImageBytes: number }
const DEFAULT_LIMITS: RoomLimits = {
  maxRooms: Number(process.env.MAX_ROOMS) || 200,
  maxImagesPerRoom: 40,
  maxRoomImageBytes: 40 * 1024 * 1024, // 40 MB of map images per room
};

function sha256(s: string): string {
  return crypto.createHash('sha256').update(s).digest('hex');
}
function timingEqual(a: string, b: string): boolean {
  const ab = Buffer.from(a), bb = Buffer.from(b);
  return ab.length === bb.length && crypto.timingSafeEqual(ab, bb);
}

/**
 * In-memory, GM-authoritative room registry. No persistence. The GM is the only
 * writer of shared state; players are read-only EXCEPT for their own seat (HP,
 * slots, conditions, rolls), which the hub forwards to the GM to persist.
 * `now` is injectable for tests.
 */
export class RoomHub {
  private rooms = new Map<string, Room>();
  private byCode = new Map<string, string>();
  private conns = new Map<Sender, { roomId: string; role: 'gm' | 'player'; playerId: string; name?: string }>();
  private limits: RoomLimits;
  constructor(private now: () => number = () => Date.now(), limits: Partial<RoomLimits> = {}) {
    this.limits = { ...DEFAULT_LIMITS, ...limits };
  }

  private mintJoinCode(): string {
    for (let attempt = 0; attempt < 50; attempt++) {
      let code = '';
      const bytes = crypto.randomBytes(6);
      for (let i = 0; i < 6; i++) code += JOIN_ALPHABET[bytes[i]! % JOIN_ALPHABET.length];
      if (!this.byCode.has(code)) return code;
    }
    return crypto.randomBytes(8).toString('hex').toUpperCase().slice(0, 6);
  }

  host(socket: Sender, password?: string, resume?: string): void {
    // Resume an existing room if the GM presents its secret (seamless reconnect).
    if (resume) {
      const hash = sha256(resume);
      for (const room of this.rooms.values()) {
        if (timingEqual(room.gmSecretHash, hash)) {
          room.gm = socket;
          room.lastActivity = this.now();
          this.conns.set(socket, { roomId: room.roomId, role: 'gm', playerId: 'gm' });
          socket.send({ t: 'hosted', roomId: room.roomId, joinCode: room.joinCode, gmSecret: resume });
          for (const req of room.pendingSeatRequests) socket.send({ t: 'seatRequest', ...req });
          this.sendRoster(room);
          return;
        }
      }
    }
    // Cap concurrent rooms so socket-spam can't exhaust memory. Idle rooms TTL out;
    // a sweep runs first to reclaim any that just expired before we refuse.
    if (this.rooms.size >= this.limits.maxRooms) {
      this.sweep();
      if (this.rooms.size >= this.limits.maxRooms) { socket.send({ t: 'error', code: 'busy', message: 'The server is at capacity — please try again shortly.' }); return; }
    }
    const roomId = crypto.randomUUID();
    const joinCode = this.mintJoinCode();
    const gmSecret = crypto.randomBytes(32).toString('base64url');
    const room: Room = {
      roomId, joinCode, gmSecretHash: sha256(gmSecret),
      passwordHash: password ? sha256(password) : null,
      gm: socket, players: new Set(), snapshot: null, images: new Map(), imageBytes: 0,
      seats: new Map(), pendingSeatRequests: [], lastActivity: this.now(),
    };
    this.rooms.set(roomId, room);
    this.byCode.set(joinCode, roomId);
    this.conns.set(socket, { roomId, role: 'gm', playerId: 'gm' });
    socket.send({ t: 'hosted', roomId, joinCode, gmSecret });
  }

  join(socket: Sender, joinCode: string, password?: string, clientPlayerId?: string): void {
    const roomId = this.byCode.get(joinCode.trim().toUpperCase());
    const room = roomId ? this.rooms.get(roomId) : undefined;
    if (!room) { socket.send({ t: 'error', code: 'no-room', message: 'No session with that code.' }); return; }
    if (room.passwordHash && (!password || !timingEqual(room.passwordHash, sha256(password)))) {
      socket.send({ t: 'error', code: 'bad-password', message: 'Wrong session password.' });
      return;
    }
    room.players.add(socket);
    room.lastActivity = this.now();
    // Reuse the client's stable id (so a transient drop keeps the seat) ONLY when it
    // isn't already live on another connection — preventing a second tab/peer from
    // seizing an active seat. The id is a client-generated UUID kept in localStorage.
    let playerId: string = crypto.randomUUID();
    if (clientPlayerId && clientPlayerId !== 'gm' && clientPlayerId.length <= 64) {
      const liveElsewhere = [...this.conns.values()].some((c) => c.roomId === room.roomId && c.playerId === clientPlayerId);
      if (!liveElsewhere) playerId = clientPlayerId;
    }
    this.conns.set(socket, { roomId: room.roomId, role: 'player', playerId });
    socket.send({ t: 'joined', roomId: room.roomId });
    if (room.snapshot) socket.send({ t: 'snapshot', snapshot: room.snapshot });
    // Reconnect: if this player still owns a seat, re-bind it to the new socket and
    // re-grant the sheet so their HP/condition/roll messages are accepted again.
    const seat = room.seats.get(playerId);
    if (seat) {
      seat.sender = socket;
      delete seat.disconnectedAt;
      socket.send({ t: 'seatGranted', character: seat.character });
    }
    this.sendRoster(room);
  }

  state(socket: Sender, gmSecret: string, snapshot: Snapshot): void {
    const room = this.gmRoom(socket, gmSecret);
    if (!room) { socket.send({ t: 'error', code: 'forbidden', message: 'Not the GM of this room.' }); return; }
    room.snapshot = snapshot;
    room.lastActivity = this.now();
    for (const p of room.players) p.send({ t: 'snapshot', snapshot });
  }

  image(socket: Sender, gmSecret: string, id: string, dataUrl: string): void {
    const room = this.gmRoom(socket, gmSecret);
    if (!room) { socket.send({ t: 'error', code: 'forbidden', message: 'Not the GM of this room.' }); return; }
    // Bound per-room image memory: cap the count of distinct images and the total bytes.
    const size = Buffer.byteLength(dataUrl);
    const prev = room.images.get(id);
    const prevSize = prev ? Buffer.byteLength(prev) : 0;
    const isNew = prev === undefined;
    if ((isNew && room.images.size >= this.limits.maxImagesPerRoom) || room.imageBytes - prevSize + size > this.limits.maxRoomImageBytes) {
      socket.send({ t: 'error', code: 'image-limit', message: 'This session has reached its map-image limit.' });
      return;
    }
    room.images.set(id, dataUrl);
    room.imageBytes += size - prevSize;
    room.lastActivity = this.now();
    for (const p of room.players) p.send({ t: 'mapImage', id, dataUrl });
  }

  requestImage(socket: Sender, id: string): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    const dataUrl = room?.images.get(id);
    if (dataUrl) socket.send({ t: 'mapImage', id, dataUrl });
  }

  /** Player asks to control a character; the request is forwarded to the GM. */
  claimSeat(socket: Sender, characterId: string, offlineSnapshot?: Character): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    if (!conn || conn.role !== 'player' || !room) return;
    room.lastActivity = this.now();
    const req: SeatRequest = { playerId: conn.playerId, characterId, ...(offlineSnapshot ? { offlineSnapshot } : {}) };
    room.pendingSeatRequests = room.pendingSeatRequests.filter((r) => r.playerId !== conn.playerId);
    room.pendingSeatRequests.push(req);
    room.gm?.send({ t: 'seatRequest', ...req });
  }

  /** GM approves a seat request and hands the player their authoritative sheet. */
  seatGrant(socket: Sender, gmSecret: string, targetPlayerId: string, character: Character): void {
    const room = this.gmRoom(socket, gmSecret);
    if (!room) { socket.send({ t: 'error', code: 'forbidden', message: 'Not the GM of this room.' }); return; }
    room.lastActivity = this.now();
    room.pendingSeatRequests = room.pendingSeatRequests.filter((r) => r.playerId !== targetPlayerId);
    let target: Sender | undefined;
    for (const [s, c] of this.conns) { if (c.roomId === room.roomId && c.playerId === targetPlayerId) { target = s; break; } }
    if (!target) return;
    room.seats.set(targetPlayerId, { sender: target, characterId: character.id, name: character.name, character });
    target.send({ t: 'seatGranted', character });
    this.sendRoster(room);
  }

  /** GM sends a private handout/note/image to one player; non-recipients never receive it. */
  privateState(socket: Sender, gmSecret: string, targetPlayerId: string, handout: PrivateHandout | null): void {
    const room = this.gmRoom(socket, gmSecret);
    if (!room) { socket.send({ t: 'error', code: 'forbidden', message: 'Not the GM of this room.' }); return; }
    room.lastActivity = this.now();
    for (const [s, c] of this.conns) {
      if (c.roomId === room.roomId && c.playerId === targetPlayerId) s.send({ t: 'privateHandout', handout });
    }
  }

  /** Tell everyone (GM + players) the current roster: the GM (if present) + players. */
  private sendRoster(room: Room): void {
    const players: { playerId: string; name: string; character?: string }[] = [];
    if (room.gm) players.push({ playerId: 'gm', name: 'GM' });
    const seen = new Set<string>();
    for (const s of room.players) {
      const conn = this.conns.get(s);
      if (!conn || seen.has(conn.playerId)) continue;
      seen.add(conn.playerId);
      const seatName = room.seats.get(conn.playerId)?.name;
      const name = conn.name ?? seatName ?? `Player ${conn.playerId.slice(0, 4)}`;
      players.push({ playerId: conn.playerId, name, ...(conn.name && seatName ? { character: seatName } : {}) });
    }
    const msg = { t: 'roster', players } as const;
    room.gm?.send(msg);
    for (const p of room.players) p.send(msg);
  }

  /** A player sets their display name (roster + chat). */
  setName(socket: Sender, name: string): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    if (!conn || conn.role !== 'player' || !room) return;
    const trimmed = name.trim().slice(0, 40);
    if (trimmed) conn.name = trimmed; else delete conn.name;
    room.lastActivity = this.now();
    this.sendRoster(room);
  }

  /** A seated player edits their own sheet; the diff is forwarded to the GM only. */
  playerPatch(socket: Sender, characterId: string, diff: PartialCharacterDiff): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    if (!conn || conn.role !== 'player' || !room) return;
    const seat = room.seats.get(conn.playerId);
    if (!seat || seat.characterId !== characterId) return; // must hold the seat for this character
    room.lastActivity = this.now();
    room.gm?.send({ t: 'playerPatched', characterId, diff });
  }

  /** A seated player rolls dice; broadcast to the GM and the rest of the table. */
  playerRoll(socket: Sender, _characterId: string, label: string, expression: string, total: number, breakdown: string): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    if (!conn || conn.role !== 'player' || !room) return;
    const seat = room.seats.get(conn.playerId);
    if (!seat) return; // only seated players broadcast rolls
    room.lastActivity = this.now();
    const msg = { t: 'rollBroadcast', playerName: seat.name, label, expression, total, breakdown } as const;
    room.gm?.send(msg);
    for (const p of room.players) if (p !== socket) p.send(msg);
  }

  /** The GM broadcasts one of their own (public) rolls to the players. */
  gmRoll(socket: Sender, gmSecret: string, label: string, expression: string, total: number, breakdown: string): void {
    const room = this.gmRoom(socket, gmSecret);
    if (!room) return;
    room.lastActivity = this.now();
    const msg = { t: 'rollBroadcast', playerName: 'GM', label, expression, total, breakdown } as const;
    for (const p of room.players) p.send(msg); // players only; the GM already sees it locally
  }

  /** Table chat (to all) or a whisper. GM `to` = target player; player `to` set = whisper to GM. */
  chat(socket: Sender, body: string, to?: string): void {
    const conn = this.conns.get(socket);
    const room = conn ? this.rooms.get(conn.roomId) : undefined;
    if (!conn || !room) return;
    room.lastActivity = this.now();
    if (conn.role === 'gm') {
      if (to) {
        const msg = { t: 'chat', from: 'GM', body, scope: 'whisper' } as const;
        for (const [s, c] of this.conns) if (c.roomId === room.roomId && c.playerId === to) s.send(msg);
      } else {
        const msg = { t: 'chat', from: 'GM', body, scope: 'table' } as const;
        for (const p of room.players) p.send(msg);
      }
    } else {
      const from = conn.name ?? room.seats.get(conn.playerId)?.name ?? `Player ${conn.playerId.slice(0, 4)}`;
      if (to) {
        room.gm?.send({ t: 'chat', from, body, scope: 'whisper' });
      } else {
        const msg = { t: 'chat', from, body, scope: 'table' } as const;
        room.gm?.send(msg);
        for (const p of room.players) if (p !== socket) p.send(msg);
      }
    }
  }

  disconnect(socket: Sender): void {
    const conn = this.conns.get(socket);
    if (!conn) return;
    const room = this.rooms.get(conn.roomId);
    if (room) {
      if (conn.role === 'gm' && room.gm === socket) room.gm = null;
      room.players.delete(socket);
      // Don't drop the seat on disconnect — start its grace timer so a reconnect (same
      // stable playerId) can reclaim it. sweep() evicts seats that stay gone too long.
      for (const [, seat] of room.seats) if (seat.sender === socket) seat.disconnectedAt = this.now();
      // Refresh the roster for whoever remains (GM left → players see it; player left → GM sees it).
      this.sendRoster(room);
    }
    this.conns.delete(socket);
  }

  /** Evict rooms idle past the TTL, and seats whose holder has been gone past the grace window. */
  sweep(): void {
    const now = this.now();
    const cutoff = now - ROOM_TTL_MS;
    for (const [id, room] of this.rooms) {
      if (room.lastActivity < cutoff) { this.byCode.delete(room.joinCode); this.rooms.delete(id); continue; }
      let dropped = false;
      for (const [pid, seat] of room.seats) {
        if (seat.disconnectedAt !== undefined && now - seat.disconnectedAt > SEAT_GRACE_MS) {
          room.seats.delete(pid);
          dropped = true;
        }
      }
      if (dropped) this.sendRoster(room);
    }
  }

  roomCount(): number { return this.rooms.size; }

  /** Admin overview of live rooms. Deliberately excludes join codes and secrets —
   *  the admin can see load, not enter private games. */
  stats(): Array<{ players: number; seats: number; images: number; imageBytes: number; idleMs: number; hasGm: boolean }> {
    const now = this.now();
    return [...this.rooms.values()].map((r) => ({
      players: r.players.size,
      seats: r.seats.size,
      images: r.images.size,
      imageBytes: r.imageBytes,
      idleMs: Math.max(0, now - r.lastActivity),
      hasGm: r.gm !== null,
    }));
  }

  private gmRoom(socket: Sender, gmSecret: string): Room | null {
    const conn = this.conns.get(socket);
    if (!conn || conn.role !== 'gm') return null;
    const room = this.rooms.get(conn.roomId);
    if (!room || room.gm !== socket || !timingEqual(room.gmSecretHash, sha256(gmSecret))) return null;
    return room;
  }
}