// Undercooked — the screen state machine (phase 07 task 02; the
// composition root — URL params, the snapshot buffer, the render
// loop, the wire routing — is `main.js`, phase 07 task 03).
//
// `createApp()` owns the one client-side state machine: an explicit
// screen enum (`LANDING, CONNECTING, LOBBY, COUNTDOWN, PLAYING,
// ROUND_END, ERROR`), `show(screen, data)`, and the message reducer
// that maps the wire contract (docs/PROTOCOL.md) onto screens —
// `welcome`/`lobby` by the room's state, `countdown` → COUNTDOWN,
// `snap` → PLAYING, `round` → ROUND_END, fatal `err` codes → ERROR.
// Every screen is a module exporting `{ mount, unmount }` (plus an
// optional same-screen `update`); no global DOM lives outside them.
//
// `identity.js` keeps the per-tab identity (PLAN A16): the anonymous
// session token and the last room code, both in `sessionStorage`.
// The app instance is exposed as `window.__undercooked` — the documented test seam the
// e2e suites drive (and the task-05 keyboard module will feed).
//
// It is a plain ES module served from /static/ — no bundler, no
// framework, no remote import (PLAN A10/A12).

import { createConnection, FATAL_ERR_CODES } from "./net/connection.js";
import { getToken, lastCode, rememberCode, randomToken } from "./identity.js";
import * as landingScreen from "./screens/landing.js";
import * as connectingScreen from "./screens/connecting.js";
import * as lobbyScreen from "./screens/lobby.js";
import * as countdownScreen from "./screens/countdown.js";
import * as playScreen from "./screens/play.js";
import * as roundEndScreen from "./screens/round_end.js";
import * as errorScreen from "./screens/error.js";

export { randomToken, getToken, lastCode, rememberCode };

/** The screen enum (the task's list, frozen). */
export const SCREENS = Object.freeze({
  LANDING: "landing",
  CONNECTING: "connecting",
  LOBBY: "lobby",
  COUNTDOWN: "countdown",
  PLAYING: "playing",
  ROUND_END: "round_end",
  ERROR: "error",
});

const SCREEN_MODULES = {
  landing: landingScreen,
  connecting: connectingScreen,
  lobby: lobbyScreen,
  countdown: countdownScreen,
  playing: playScreen,
  round_end: roundEndScreen,
  error: errorScreen,
};

/** The room-state value → screen (the `welcome`/`lobby` mapping half). */
const SCREEN_BY_ROOM_STATE = {
  lobby: SCREENS.LOBBY,
  countdown: SCREENS.COUNTDOWN,
  playing: SCREENS.PLAYING,
  round_end: SCREENS.ROUND_END,
  closed: SCREENS.ERROR,
};

const LOG_CAP = 2000;

export function createApp(root = document, options = {}) {
  const { onWireMessage = null } = options;
  const screenRoot = root.getElementById("screen-root");
  const app = {
    token: getToken(),
    lastCode: lastCode(),
    screen: null, // set by the first show()
    data: {},
    roomCode: "",
    welcome: null,
    you: null, // the viewer's seat (YouWire)
    spectator: false, // joined mid-round (or the token holds no seat)
    lobby: null, // the latest `lobby` frame
    round: null, // the latest `round` frame
    lastSnapshot: null, // the latest `snap` raw body (the render path is task 03's buffer; this view is the DOM path the screens and the choreography read)
    session: null, // the `/api/session` projection
    levels: null, // the `/api/levels` cards (null = not fetched yet)
    view: makeView(), // the merged snapshot view (full frames reset, deltas patch)
    error: null, // the fatal `err` frame, when one caused ERROR
    banner: null, // non-fatal `err` text for the mounted screen
    messageLog: [], // bounded wire-census for the e2e suites
    leaving: false, // we closed the socket on purpose
  };
  const connection = createConnection();
  const warnedUnknown = new Set();
  let mounted = null;

  /**
   * The merged snapshot view — the task-02 seed of task 03's buffer: a
   * full frame resets the entity maps, a delta patches them (an upsert on
   * the identity key, a `gone` tombstone drops). The stream's full cadence
   * (every 20 encoded frames) plus the fresh-connection full keeps this
   * resyncable; a client-side drift is what task 03's decoder handles.
   */
  function makeView() {
    return { players: {}, stations: {}, orders: {} };
  }

  function stationKey(entry) {
    return `${entry.k}@${entry.x},${entry.y}`;
  }

  function applySnapshot(raw) {
    app.lastSnapshot = raw;
    const view = app.view;
    if (raw.full) {
      view.players = {};
      view.stations = {};
      view.orders = {};
      for (const entry of raw.p ?? []) view.players[entry.i] = entry;
      for (const entry of raw.st ?? []) view.stations[stationKey(entry)] = entry;
      for (const entry of raw.o ?? []) view.orders[entry.id] = entry;
      return;
    }
    const delta = raw.d ?? {};
    for (const entry of delta.p ?? []) {
      if (entry.gone) delete view.players[entry.i];
      else view.players[entry.i] = entry;
    }
    for (const entry of delta.st ?? []) {
      const key = stationKey(entry);
      if (entry.gone) delete view.stations[key];
      else view.stations[key] = entry;
    }
    for (const entry of delta.o ?? []) {
      if (entry.gone) delete view.orders[entry.id];
      else view.orders[entry.id] = entry;
    }
  }

  function pushLog(frame) {
    app.messageLog.push(frame);
    if (app.messageLog.length > LOG_CAP) app.messageLog.shift();
  }

  /**
   * Show one screen. An unknown screen name (a bug) logs once and
   * becomes ERROR; the same screen re-shown in place calls the
   * module's `update` (a re-mount would drop focus off live controls).
   */
  function show(screen, data = {}) {
    if (!(screen in SCREEN_MODULES)) {
      if (!warnedUnknown.has(screen)) {
        console.warn(
          `undercooked: unknown screen "${String(screen)}" — going to the error screen`,
        );
        warnedUnknown.add(screen);
      }
      screen = SCREENS.ERROR;
    }
    app.data = data;
    if (app.screen === screen && mounted !== null) {
      if (typeof mounted.update === "function") mounted.update(data, app);
      return screen;
    }
    if (mounted !== null && typeof mounted.unmount === "function") mounted.unmount();
    mounted = null;
    app.screen = screen;
    mounted = SCREEN_MODULES[screen];
    // The previous screen's DOM is the previous screen's problem no
    // more: a screen module appends, it does not replace, so the
    // machine clears the root before mounting (a re-mount would stack
    // a second copy of the screen on top of the first).
    screenRoot.replaceChildren();
    if (typeof mounted.mount === "function") mounted.mount(screenRoot, data, app);
    return screen;
  }

  function failToLanding(banner) {
    app.banner = banner;
    show(SCREENS.LANDING, {});
  }

  // ------------------------------------------------------------- verbs

  async function createLobby({ name = null } = {}) {
    app.leaving = false;
    show(SCREENS.CONNECTING, { what: "creating" });
    let response;
    try {
      response = await fetch("/api/rooms", {
        method: "POST",
        headers: { "content-type": "application/json" },
        body: JSON.stringify({
          token: app.token,
          ...(name !== null && name !== "" ? { name } : {}),
        }),
      });
    } catch {
      failToLanding("Cannot reach the server — check the address and try again.");
      return;
    }
    if (response.status === 503) {
      failToLanding("The server is at capacity — try again in a moment.");
      return;
    }
    if (response.status !== 201) {
      failToLanding("The server refused the room. Try again.");
      return;
    }
    const body = await response.json().catch(() => null);
    if (body === null || typeof body.room_code !== "string") {
      failToLanding("The server answered something unrecognisable. Try again.");
      return;
    }
    app.roomCode = body.room_code;
    rememberCode(body.room_code);
    connection.connect(body.room_code, { token: app.token });
  }

  function join(code) {
    app.leaving = false;
    app.roomCode = code;
    rememberCode(code);
    show(SCREENS.CONNECTING, { what: "joining", code });
    connection.connect(code, { token: app.token });
  }

  function leave() {
    app.leaving = true;
    connection.close();
    show(SCREENS.LANDING, {});
  }

  function backToLanding() {
    app.leaving = true;
    connection.close();
    app.banner = null;
    show(SCREENS.LANDING, {});
  }

  function retryJoin() {
    if (app.roomCode === "") return;
    app.leaving = false;
    show(SCREENS.CONNECTING, { what: "joining", code: app.roomCode });
    connection.connect(app.roomCode, { token: app.token });
  }

  function ready() {
    connection.send({ type: "ready" });
  }

  function start() {
    connection.send({ type: "start" });
  }

  function setLevel(level) {
    connection.send({ type: "set_level", level });
  }

  function emote(id) {
    connection.send({ type: "emote", id });
  }

  function toLobby() {
    connection.send({ type: "to_lobby" });
  }

  function nextLevel() {
    connection.send({ type: "next_level" });
  }

  function sendInput(move, act) {
    connection.sendInput(move, act);
  }

  async function fetchSession() {
    try {
      const response = await fetch("/api/session", {
        headers: { "X-Undercooked-Token": app.token },
      });
      if (response.ok) {
        app.session = await response.json();
        if (mounted !== null && typeof mounted.renderBest === "function") {
          mounted.renderBest(app);
        }
      }
    } catch {
      /* offline: the previous session stays */
    }
    return app.session;
  }

  async function fetchLevels() {
    if (app.levels !== null) return app.levels;
    try {
      const response = await fetch("/api/levels");
      app.levels = response.ok ? await response.json() : [];
    } catch {
      app.levels = [];
    }
    return app.levels;
  }

  /** The merged view's own half (a `snap` landed, delta or full). */
  function orderOpen() {
    return Object.keys(app.view.orders).length > 0;
  }

  function showReconnecting(visible) {
    if (mounted !== null && typeof mounted.showReconnecting === "function") {
      mounted.showReconnecting(visible);
    }
  }

  // ------------------------------------------------------------- reducer

  connection.onMessage = (frame) => {
    // The composition root's half (phase 07 task 03): the `snap` frames
    // also feed the render buffer before the reducer's DOM view.
    if (onWireMessage !== null) onWireMessage(frame);
    pushLog(frame);
    switch (frame.type) {
      case "welcome": {
        app.welcome = frame;
        app.roomCode = frame.room;
        app.you = frame.you;
        // A fresh token in a non-lobby room is a spectator (a rejoin
        // reclaims its seat, so `rejoined` is the discriminator).
        app.spectator = frame.state !== "lobby" && frame.rejoined !== true;
        show(SCREEN_BY_ROOM_STATE[frame.state] ?? SCREENS.ERROR, { code: frame.room });
        break;
      }
      case "lobby": {
        app.lobby = frame;
        app.roomCode = frame.code;
        show(
          frame.state === "lobby" ? SCREENS.LOBBY : SCREEN_BY_ROOM_STATE[frame.state] ?? SCREENS.ERROR,
          {},
        );
        break;
      }
      case "countdown":
        show(SCREENS.COUNTDOWN, { n: frame.n });
        break;
      case "snap":
        if (frame.raw !== undefined) applySnapshot(frame.raw);
        show(SCREENS.PLAYING, {});
        break;
      case "round":
        app.round = frame;
        show(SCREENS.ROUND_END, {});
        break;
      case "err": {
        connection.noteError(frame);
        if (FATAL_ERR_CODES.includes(frame.code)) {
          app.error = frame;
          show(SCREENS.ERROR, { code: frame.code, msg: frame.msg });
        } else if (mounted !== null && typeof mounted.setBanner === "function") {
          app.banner = frame.msg;
          mounted.setBanner(frame.msg);
        }
        break;
      }
      case "pong":
        break; // the keep-alive's answer: nothing to render
      case "ev":
        break; // FX/log (task 04's renderer consumes these)
      default:
        break; // unknown server types are ignored (patch-compatible)
    }
  };

  connection.onStatus = (status) => {
    if (status === "mismatch") {
      show(SCREENS.ERROR, { code: "protocol_mismatch" });
      return;
    }
    if (status !== "closed") return;
    if (app.leaving) return; // an intentional close: no error screen
    const code = connection.lastCloseCode;
    if (code === 1000 && app.screen === SCREENS.PLAYING) {
      // A drop mid-round: the seat is kept for the grace; phase 08
      // reconnects. This task's half is the overlay.
      showReconnecting(true);
      return;
    }
    show(SCREENS.ERROR, { code: code === 1006 ? "unreachable" : "closed" });
  };

  // The public verbs — assigned onto `app` itself so the screens (which
  // hold `app`) and the e2e seam (`window.__undercooked`) see one and
  // the same live object: a `show()` later is visible through the seam.
  Object.assign(app, {
    connection,
    show,
    createLobby,
    join,
    leave,
    backToLanding,
    retryJoin,
    ready,
    start,
    setLevel,
    emote,
    toLobby,
    nextLevel,
    sendInput,
    fetchSession,
    fetchLevels,
    orderOpen,
    showReconnecting,
  });

  show(SCREENS.LANDING, {});

  return app;
}

// Auto-mount when loaded directly as the page's module; stay
// importable (and therefore testable) without one. The instance is
// the e2e test seam. `main.js` (the composition root) sets
// `globalThis.__uc_main` before importing this module — when it is
// set, main.js boots the app and this auto-boot stays out of the way.
if (
  typeof document !== "undefined" &&
  document.getElementById("screen-root") &&
  !globalThis.__uc_main
) {
  const boot = () => {
    globalThis.__undercooked = createApp();
  };
  if (document.readyState === "loading") {
    document.addEventListener("DOMContentLoaded", boot, { once: true });
  } else {
    boot();
  }
}