/**
 * The boundary between the page and the game.
 *
 * The page draws a `Frame` and offers a `Menu`, and submits intents. It does not care whether the
 * rules are being applied a function call away or across a network — which is the whole point:
 *
 *   - `LocalSession` runs the engine in this browser. Solitaire, exactly as it has always worked,
 *     with no server involved at any point.
 *   - `RemoteSession` (not built yet — see `docs/architecture/multiplayer.md` Phase 2) will hold no
 *     authoritative state at all. It cannot: it has neither the deck order nor the other players'
 *     hands, and if it did the game would be cheatable.
 *
 * So this interface is deliberately the SMALLER of the two — everything a remote client could
 * possibly offer, and nothing that only a local one can do. What a local session can do beyond it is
 * declared in `capabilities`, and the page hides those controls rather than calling them and failing.
 */

import type { Intent } from '../engine/intents.ts';
import type { Frame } from '../sim/view.ts';
import type { PlayerIndex } from '../engine/state.ts';
import { applyDelta } from '../sim/frame-delta.ts';
import type { FrameDelta } from '../sim/frame-delta.ts';
import type { Game, Menu, NewGameOptions, Save } from './game.ts';
import {
  actionMenu,
  configWith,
  currentActor,
  fromSave,
  handPlayable,
  newGame,
  overHandLimit,
  submit,
  toSave,
  undo,
  view,
} from './game.ts';

/**
 * What this session can do beyond the common interface.
 *
 * None of these survive a server. Undo would have to un-see what other players have already seen;
 * a local save is meaningless when the server is the store; and dealing a new game is the lobby's
 * job. The page reads these rather than assuming, so the same code drives both.
 */
export type Capabilities = {
  undo: boolean;
  saveLocal: boolean;
  newGame: boolean;
};

export type Session = {
  /** The board as this seat sees it. */
  view(): Frame;
  /** What this seat may do right now. */
  menu(): Menu;
  /** Which seat this client is playing. */
  seat(): PlayerIndex;
  /** Whose turn it is, or null when the game is over or waiting on nothing. */
  actor(): PlayerIndex | null;
  /** True when the hand is over §6.2's limit and the turn cannot be ended. */
  overHandLimit(): boolean;
  /** Which cards in hand are playable right now, in hand order. */
  handPlayable(): boolean[];
  /**
   * Propose an action. Resolves false if the rules refused it.
   *
   * Async because a remote session must be, even though the local one answers immediately — a page
   * written against a synchronous `submit` would have to be rewritten for the server.
   */
  submit(intent: Intent): Promise<boolean>;
  /** Called whenever something changed and the page should redraw. Returns an unsubscribe. */
  subscribe(fn: () => void): () => void;
  capabilities: Capabilities;

  /**
   * WHAT JUST HAPPENED — three transient signals the page uses to draw a moment rather than a state.
   *
   * They are separate from `view()` because two of them are CONSUMED: a Stage flash and a sound play
   * once and are then gone, whereas the Frame can be rebuilt any number of times per render. Putting
   * them on the Frame would mean re-flashing on every redraw.
   *
   * A remote session fills these from the server's pushes rather than from a local event log; the
   * page cannot tell the difference. Whether they eventually ride on the Frame as animation hints is
   * a Phase 2 question (`docs/architecture/multiplayer.md` D3).
   */
  /** The narrated history, newest last. */
  lines(): { text: string; tone: string }[];
  /** Sounds earned since the last call. Draining. */
  takeCues(): string[];
  /** The timetable slot the last 1D12 filled, once. Draining. */
  takeScheduled(): number | null;
  /** A one-line announcement to flash, once. Draining. */
  takeAnnouncement(): string | null;
  /** The card most recently drawn into this seat's hand. Persists until another draw replaces it. */
  justDrawn(): string | null;
  /**
   * Which OTHER seats are currently connected, as last reported by the server — always empty for a
   * `LocalSession` (there is nobody else to track). `lobby-and-sessions.md` §5: a disconnect keeps
   * the seat and waits; this is what lets the page say why, instead of going quiet with no
   * explanation. Reflects the last presence push for each seat the server has ever mentioned, not
   * only the ones currently disconnected — a seat that reconnects updates its own entry rather than
   * disappearing, so the page can tell "never heard from" apart from "was here, then left."
   */
  presence(): { seat: PlayerIndex; connected: boolean }[];
};

/**
 * Everything a LOCAL session can additionally do. Kept off `Session` so that reaching for one of
 * these in shared page code is a type error rather than a runtime surprise against a server.
 */
export type LocalSession = Session & {
  readonly game: Game;
  seed(): number;
  save(): Save;
  /** How many intents have been submitted — what the Undo button counts down. */
  steps(): number;
  /** Steps back one intent by replaying the history without it. Returns false at the start. */
  undo(): boolean;
  restore(save: Save): void;
};

/**
 * A session that owns the engine in this process.
 *
 * `Game` is mutated in place by `submit`, so the wrapper keeps a mutable reference rather than
 * copying — `undo` and `restore` replace the whole game, which is why `game` is a getter.
 *
 * It takes `NewGameOptions` rather than a whole `GameConfig` because DEALING is the only thing on the
 * far side of this that the page is allowed to decide. A config carries the mode and the optional
 * rules — table settings a lobby owns — and handing main.ts a `GameConfig` to build meant importing
 * the engine's own defaults into the page, which is the boundary `session.test.ts` guards. The seed,
 * the house rules and the victory-condition dials are what a player picks when they press New game.
 */
export function createLocalSession(seed: number, options?: NewGameOptions): LocalSession {
  let game: Game = options ? newGame(seed, configWith(options)) : newGame(seed);
  const listeners = new Set<() => void>();
  const changed = (): void => {
    for (const fn of [...listeners]) fn();
  };

  return {
    get game() {
      return game;
    },
    view: () => view(game),
    menu: () => actionMenu(game),
    seat: () => 0,
    actor: () => currentActor(game),
    overHandLimit: () => overHandLimit(game),
    handPlayable: () => handPlayable(game),
    submit: async (intent: Intent) => {
      const ok = submit(game, intent);
      if (ok) changed();
      return ok;
    },
    subscribe(fn: () => void) {
      listeners.add(fn);
      return () => listeners.delete(fn);
    },
    capabilities: { undo: true, saveLocal: true, newGame: true },

    lines: () => game.log,
    takeCues: () => game.cues.splice(0, game.cues.length),
    takeScheduled: () => {
      const slot = game.scheduled;
      game.scheduled = null;
      return slot;
    },
    takeAnnouncement: () => {
      const text = game.announced;
      game.announced = null;
      return text;
    },
    justDrawn: () => game.justDrawn,
    presence: () => [],

    seed: () => game.seed,
    save: () => toSave(game),
    steps: () => game.history.length,
    undo() {
      const back = undo(game);
      if (!back) return false;
      game = back;
      // The rebuilt game replays its own history, so every cue and draw in it is old news.
      back.cues.length = 0;
      back.scheduled = null;
      back.justDrawn = null;
      back.announced = null;
      changed();
      return true;
    },
    restore(save: Save) {
      game = fromSave(save);
      // Restoring replays the whole history and re-records every draw; none of it is news.
      game.justDrawn = null;
      game.announced = null;
      changed();
    },
  };
}

/** The push envelope `src/server/session.ts` sends over SSE — mirrored here rather than imported,
 * so this file never depends on anything under `src/server/` even at the type level. */
type Push = {
  frame?: FrameDelta;
  menu: Menu | null;
  lines: { text: string; tone: string }[];
  presence?: { seat: PlayerIndex; connected: boolean };
};

/**
 * A session backed by a server (Phase 2, extended Phase 4). Holds no authoritative state — no deck
 * order, no other seat's hand — only the last `Frame`/`Menu` a push actually told it. `capabilities`
 * are all `false`: undo would have to un-see what other players already saw, a local save is
 * meaningless when the server is the store, and dealing a new game is the lobby's job.
 *
 * `token` is `lobby-and-sessions.md` §1's session token, issued at `Lobby.Create`/`Lobby.Join` and
 * stored by the caller (`main.ts`, in `localStorage`) — it alone proves identity to `/api/stream`
 * and `/api/intent`, so this function no longer takes a join secret at all; that gate belongs to
 * the lobby endpoints only. `seat` still has to be passed in rather than learned from a push,
 * because the very FIRST thing this session needs — `seat()` — has to answer before any push has
 * necessarily arrived; the caller already knows it from the join/create/start response.
 *
 * Construction is synchronous (the `Session` interface has no async surface), but the first real
 * `Frame` only exists once the SSE connection's first push arrives — `main.ts` accounts for this by
 * not rendering until `subscribe`'s callback fires at least once for a session whose `capabilities`
 * are all `false` (a `LocalSession` always has data the instant it is constructed; this does not).
 */
export function createRemoteSession(
  token: string,
  seat: PlayerIndex,
  /**
   * Called once when this session's game is established to be gone for good, so the page can stop
   * waiting for it. Without this the only symptom is a blank screen: `EventSource` retries a 404
   * forever and reports nothing, and `frame` never becomes non-null.
   */
  onGone?: () => void,
): Session {
  let frame: Frame | null = null;
  let menu: Menu | null = null;
  let lines: { text: string; tone: string }[] = [];
  const presence = new Map<PlayerIndex, boolean>();
  let nextSeq = 1;
  const listeners = new Set<() => void>();
  const changed = (): void => {
    for (const fn of [...listeners]) fn();
  };

  const qs = `token=${encodeURIComponent(token)}`;
  const source = new EventSource(`/api/stream?${qs}`);

  /**
   * A DROPPED CONNECTION AND A DEAD GAME LOOK IDENTICAL HERE, so ask before giving up.
   *
   * `EventSource` fires `error` for both a transient blip — which it recovers from by itself, and
   * which is the expected shape of a game that sits idle for minutes (multiplayer.md §9) — and a
   * 404 it will nonetheless retry forever. It exposes no status code either way. `/api/session` is
   * the cheap question that separates them: only a definite 404 closes the stream and reports the
   * game gone, so a flaky network still self-heals.
   */
  let reportedGone = false;
  source.onerror = () => {
    if (reportedGone) return;
    void fetch(`/api/session?${qs}`)
      .then((r) => {
        if (r.status !== 404 || reportedGone) return;
        reportedGone = true;
        source.close();
        onGone?.();
      })
      .catch(() => {
        // The probe itself failed, so this says nothing about the game — leave the retry running.
      });
  };
  source.onmessage = (ev: MessageEvent<string>) => {
    const push = JSON.parse(ev.data) as Push;
    // A presence-only push (no `frame`) carries `menu: null` too, but that is not news about this
    // seat's turn — only a push that actually came from the game (always carries a real `frame`,
    // per `session.ts`'s `Push`) updates the board or the menu.
    if (push.frame) {
      frame = applyDelta(frame, push.frame);
      menu = push.menu;
    }
    lines = [...lines, ...push.lines];
    if (push.presence) presence.set(push.presence.seat, push.presence.connected);
    changed();
  };

  const need = (): Frame => {
    if (frame === null) throw new Error('RemoteSession.view() called before the first Frame arrived');
    return frame;
  };

  return {
    view: need,
    menu: () => menu ?? { options: [], direct: [], placeable: [], hand: [], makeUp: null },
    seat: () => seat,
    actor: () => need().actor,
    overHandLimit: () => need().overHandLimit,
    handPlayable: () => (menu?.hand ?? []).map((h) => h.playNow !== null),
    async submit(intent: Intent): Promise<boolean> {
      const seq = nextSeq++;
      const res = await fetch(`/api/intent?${qs}`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ seq, intent }),
      });
      const result = (await res.json()) as { ok: boolean; code?: string };
      // The visible update arrives via the SSE push (broadcast to every seat, including this one),
      // not from this response — this only reports whether the rules accepted it.
      return result.ok;
    },
    subscribe(fn: () => void) {
      listeners.add(fn);
      return () => listeners.delete(fn);
    },
    capabilities: { undo: false, saveLocal: false, newGame: false },

    lines: () => lines,
    takeCues: () => [],
    takeScheduled: () => null,
    takeAnnouncement: () => null,
    justDrawn: () => null,
    presence: () => [...presence].map(([s, connected]) => ({ seat: s, connected })),
  };
}