// In-memory per-game cache. A game the player has opened once — or one warmed ahead of time
// by the lobby preload (see lib/preload) — is kept here so opening it renders instantly from
// the cache while a fresh fetch updates it in the background, removing the blank "loading"
// flash and the full redraw on every lobby <-> game navigation. It is intentionally
// process-memory only (no persistence): stale entries are corrected by the background
// refresh, and the cache is cleared on logout.

import type { MoveRecord, StateView } from './model';

export interface CachedGame {
  view: StateView;
  moves: MoveRecord[];
  /**
   * The player's saved draft (composition) as the opaque JSON the server stores, so a warm
   * open paints the pending tiles already on the board with no rack→board jump. An empty
   * string means no draft; undefined means it has not been fetched for this entry yet.
   */
  draft?: string;
}

const cache = new Map<string, CachedGame>();

/** getCachedGame returns the last-seen state+history for a game, or undefined. */
export function getCachedGame(id: string): CachedGame | undefined {
  return cache.get(id);
}

/**
 * setCachedGame stores the latest state+history for a game. Omitting draft preserves the
 * cached composition: the live-event delta path advances view+moves without refetching the
 * draft and must not drop it, while passing an empty string clears it (a committed move does,
 * mirroring the server).
 */
export function setCachedGame(id: string, view: StateView, moves: MoveRecord[], draft?: string): void {
  const prev = cache.get(id);
  cache.set(id, { view, moves, draft: draft ?? prev?.draft });
}

/** setCachedDraft updates only the saved draft of an already-cached game (a no-op otherwise),
 *  keeping the cache coherent with the draft persisted while composing. */
export function setCachedDraft(id: string, draft: string): void {
  const prev = cache.get(id);
  if (prev) cache.set(id, { ...prev, draft });
}

/** clearGameCache drops every cached game (called on logout). */
export function clearGameCache(): void {
  cache.clear();
}