/**
 * WebSocket client with auto-reconnect, seq ordering, ping/clock sync (docs/03 §4–§8).
 * Room/game state lives in the zustand store below; components only read it.
 */
import { create } from 'zustand';
import { PROTOCOL, type GameResultView, type PublicUser, type RoomView, type ServerMessage } from '@bg/shared/lite';
import { toast } from '../store/toast';

export type ConnStatus = 'idle' | 'connecting' | 'open' | 'reconnecting' | 'replaced' | 'offline';

export interface ChatLine {
  id: number;
  from: PublicUser | null;
  text: string;
  at: number;
}

export interface GameState {
  seq: number;
  view: unknown;
  active: string[];
  deadline: number | null;
  events: unknown[];
}

interface RoomStore {
  status: ConnStatus;
  me: PublicUser | null;
  code: string | null;
  room: RoomView | null;
  roomSeq: number;
  game: GameState | null;
  result: GameResultView | null;
  chat: ChatLine[];
  emotes: { id: number; from: string; emote: string }[];
  pending: number | null;
  slow: boolean;
  rttMs: number | null;
  clockOffset: number;
  joinError: string | null;
  kicked: boolean;
  needsRefresh: boolean;
}

export const useRoom = create<RoomStore>(() => ({
  status: 'idle',
  me: null,
  code: null,
  room: null,
  roomSeq: -1,
  game: null,
  result: null,
  chat: [],
  emotes: [],
  pending: null,
  slow: false,
  rttMs: null,
  clockOffset: 0,
  joinError: null,
  kicked: false,
  needsRefresh: false,
}));

const BACKOFF = [500, 1000, 2000, 4000, 8000];
const MAX_BACKOFF = 10_000;
const PING_EVERY = 10_000;
const PONG_TIMEOUT = 5_000;

class GameSocket {
  private ws: WebSocket | null = null;
  private attempt = 0;
  private retryTimer: ReturnType<typeof setTimeout> | null = null;
  private pingTimer: ReturnType<typeof setInterval> | null = null;
  private pongTimer: ReturnType<typeof setTimeout> | null = null;
  private pendingTimer: ReturnType<typeof setTimeout> | null = null;
  private offsets: number[] = [];
  private wanted = false;
  private cs = Date.now();
  private chatId = 1;
  private onMessageHooks = new Set<(m: ServerMessage) => void>();

  constructor() {
    if (typeof window !== 'undefined') {
      document.addEventListener('visibilitychange', () => {
        if (document.visibilityState === 'visible') this.kick();
      });
      window.addEventListener('online', () => this.kick());
      window.addEventListener('offline', () => useRoom.setState({ status: 'offline' }));
    }
  }

  /** Start (or keep) a connection. Safe to call repeatedly. */
  start(): void {
    this.wanted = true;
    if (this.ws && (this.ws.readyState === WebSocket.OPEN || this.ws.readyState === WebSocket.CONNECTING)) return;
    this.open();
  }

  stop(): void {
    this.wanted = false;
    this.clearTimers();
    this.ws?.close();
    this.ws = null;
    useRoom.setState({ status: 'idle' });
  }

  /** Reconnect immediately if we should be connected but are not. */
  private kick(): void {
    if (!this.wanted) return;
    if (!this.ws || this.ws.readyState === WebSocket.CLOSED || this.ws.readyState === WebSocket.CLOSING) {
      if (this.retryTimer) clearTimeout(this.retryTimer);
      this.retryTimer = null;
      this.open();
    } else if (this.ws.readyState === WebSocket.OPEN) {
      this.ping();
    }
  }

  private open(): void {
    const proto = location.protocol === 'https:' ? 'wss:' : 'ws:';
    const ws = new WebSocket(`${proto}//${location.host}/ws`);
    this.ws = ws;
    useRoom.setState({ status: this.attempt === 0 ? 'connecting' : 'reconnecting' });
    ws.onopen = () => {
      this.attempt = 0;
      this.pingTimer = setInterval(() => this.ping(), PING_EVERY);
    };
    ws.onmessage = (e) => {
      let m: ServerMessage;
      try {
        m = JSON.parse(String(e.data));
      } catch {
        return;
      }
      this.handle(m);
      for (const h of this.onMessageHooks) h(m);
    };
    ws.onclose = (e) => {
      if (this.ws !== ws) return;
      this.clearTimers();
      this.ws = null;
      const st = useRoom.getState().status;
      if (!this.wanted || st === 'replaced' || useRoom.getState().kicked) return;
      if (e.code === 4401 || e.code === 1008) {
        // Not logged in (session expired): stop and let the page ask for a nickname.
        useRoom.setState({ status: 'idle' });
        this.wanted = false;
        window.dispatchEvent(new Event('bg:unauthorized'));
        return;
      }
      if (this.attempt >= 1) {
        // Repeated failures may mean the session is gone (the upgrade got a 401).
        fetch('/api/me', { credentials: 'same-origin' })
          .then((r) => r.json())
          .then((d: { me: unknown }) => {
            if (d.me === null) {
              this.wanted = false;
              useRoom.setState({ status: 'idle' });
              window.dispatchEvent(new Event('bg:unauthorized'));
            }
          })
          .catch(() => {});
      }
      this.scheduleReconnect();
    };
  }

  private scheduleReconnect(extraDelay = 0): void {
    const base = BACKOFF[this.attempt] ?? MAX_BACKOFF;
    const jitter = base * (0.7 + Math.random() * 0.6);
    this.attempt++;
    useRoom.setState({ status: navigator.onLine === false ? 'offline' : 'reconnecting' });
    this.retryTimer = setTimeout(() => {
      this.retryTimer = null;
      if (this.wanted) this.open();
    }, jitter + extraDelay);
  }

  private clearTimers(): void {
    if (this.pingTimer) clearInterval(this.pingTimer);
    if (this.pongTimer) clearTimeout(this.pongTimer);
    this.pingTimer = null;
    this.pongTimer = null;
  }

  private ping(): void {
    if (this.ws?.readyState !== WebSocket.OPEN || this.pongTimer) return;
    this.send({ t: 'ping', ts: Date.now() });
    this.pongTimer = setTimeout(() => {
      this.pongTimer = null;
      // Dead connection: force a reconnect.
      this.ws?.close();
    }, PONG_TIMEOUT);
  }

  send(m: unknown): boolean {
    if (this.ws?.readyState !== WebSocket.OPEN) return false;
    this.ws.send(JSON.stringify(m));
    return true;
  }

  subscribe(fn: (m: ServerMessage) => void): () => void {
    this.onMessageHooks.add(fn);
    return () => this.onMessageHooks.delete(fn);
  }

  // ------------------------------------------------------------- room commands

  join(code: string, as: 'player' | 'spectator' = 'player'): void {
    const cur = useRoom.getState();
    if (cur.code !== code) {
      useRoom.setState({ code, room: null, roomSeq: -1, game: null, result: null, chat: [], joinError: null, kicked: false, pending: null });
    }
    this.start();
    this.send({ t: 'join', code, as });
  }

  leave(): void {
    this.send({ t: 'leave' });
    useRoom.setState({ code: null, room: null, roomSeq: -1, game: null, result: null, chat: [], pending: null });
  }

  /** Sends a game action; returns false when not connected. */
  act(a: unknown): boolean {
    const cs = ++this.cs;
    if (!this.send({ t: 'act', cs, a })) {
      toast('연결이 끊겨 있어요. 다시 연결되면 해 주세요.', 'error');
      return false;
    }
    useRoom.setState({ pending: cs, slow: false });
    if (this.pendingTimer) clearTimeout(this.pendingTimer);
    this.pendingTimer = setTimeout(() => {
      if (useRoom.getState().pending === cs) {
        useRoom.setState({ slow: true });
        this.ping();
      }
    }, 2000);
    return true;
  }

  /** Server time estimate. */
  now(): number {
    return Date.now() + useRoom.getState().clockOffset;
  }

  // ------------------------------------------------------------- inbound

  private handle(m: ServerMessage): void {
    const st = useRoom.getState();
    switch (m.t) {
      case 'welcome': {
        if (m.protocol !== PROTOCOL) useRoom.setState({ needsRefresh: true });
        useRoom.setState({ status: 'open', me: m.me });
        this.offsets = [m.serverTime - Date.now()];
        useRoom.setState({ clockOffset: this.offsets[0]! });
        // Re-join the room we were in (reconnect path).
        if (st.code && !st.kicked) this.send({ t: 'join', code: st.code, as: 'player' });
        break;
      }
      case 'room':
        if (m.seq >= st.roomSeq || m.room.code !== st.room?.code) {
          useRoom.setState({ room: m.room, roomSeq: m.seq, joinError: null });
          if (m.room.status === 'playing' && st.result) useRoom.setState({ result: null });
        }
        break;
      case 'state': {
        if (st.game && m.seq < st.game.seq) break; // stale
        const patch: Partial<RoomStore> = {
          game: { seq: m.seq, view: m.view, active: m.active, deadline: m.deadline, events: m.events },
        };
        if (m.cs !== undefined && m.cs === st.pending) {
          patch.pending = null;
          patch.slow = false;
        }
        useRoom.setState(patch);
        break;
      }
      case 'reject':
        if (m.cs === st.pending) useRoom.setState({ pending: null, slow: false });
        toast(m.reason, 'error');
        break;
      case 'result':
        useRoom.setState({ result: m.result });
        break;
      case 'chat':
        useRoom.setState({ chat: [...st.chat, { id: this.chatId++, from: m.from, text: m.text, at: m.at }].slice(-100) });
        break;
      case 'emote': {
        const id = this.chatId++;
        useRoom.setState({ emotes: [...st.emotes, { id, from: m.from, emote: m.id }].slice(-10) });
        setTimeout(() => useRoom.setState((s) => ({ emotes: s.emotes.filter((e) => e.id !== id) })), 2500);
        break;
      }
      case 'notice':
        toast(m.message);
        break;
      case 'error':
        if (m.code === 'room-not-found' || m.code === 'join-failed') useRoom.setState({ joinError: m.message });
        else toast(m.message, 'error');
        break;
      case 'pong': {
        if (this.pongTimer) clearTimeout(this.pongTimer);
        this.pongTimer = null;
        const now = Date.now();
        const rtt = now - m.ts;
        const offset = m.serverTime + rtt / 2 - now;
        this.offsets = [...this.offsets, offset].slice(-5);
        const sorted = [...this.offsets].sort((a, b) => a - b);
        useRoom.setState({ rttMs: rtt, clockOffset: sorted[Math.floor(sorted.length / 2)]! });
        if (st.slow && st.pending) {
          // Connection is alive but our action got no answer: resync instead of resending.
          this.send({ t: 'sync' });
          useRoom.setState({ pending: null, slow: false });
        }
        break;
      }
      case 'bye':
        if (m.reason === 'restart') {
          toast('서버를 업데이트하고 있어요. 잠시 후 자동으로 다시 연결돼요.');
          this.attempt = 0;
          this.ws?.close();
          // onclose schedules a reconnect; add 1–3s so clients don't all return at once.
          this.ws = null;
          this.clearTimers();
          this.scheduleReconnect(1000 + Math.random() * 2000);
        } else if (m.reason === 'replaced') {
          useRoom.setState({ status: 'replaced' });
        } else if (m.reason === 'kicked') {
          useRoom.setState({ kicked: true, joinError: '방장이 방에서 내보냈어요.' });
        }
        break;
    }
  }

  /** "Use here" after another tab took over. */
  reclaim(): void {
    useRoom.setState({ status: 'connecting' });
    this.wanted = true;
    this.attempt = 0;
    this.open();
  }
}

export const socket = new GameSocket();