Made of little things.

/**
 * The page's line into the running game: its Lua API, through the two
 * functions patches/the-powder-toy-napplet-bridge.patch exports. Usable once
 * the game has marked itself presentable (before that its Lua state and game
 * view do not exist yet).
 */

/** Lua reported an error (a syntax error, or one raised while running). */
export class LuaError extends Error {
  name = 'LuaError';
}

/** Long enough for any scene; the argument is copied onto the wasm stack (64 KiB). */
const MAX_CODE = 24_000;

export function connectGame(module) {
  const run = module.cwrap('Napplet_Lua', 'string', ['string']);
  const onTop = module.cwrap('Napplet_GameViewActive', 'number', []);
  return {
    /** Runs Lua as the game's console does; returns what it prints, throws what it reports. */
    lua(code) {
      if (code.length > MAX_CODE) throw new LuaError(`Lua code of ${code.length} characters is longer than ${MAX_CODE}`);
      const reply = run(code);
      if (reply.startsWith('ok:')) return reply.slice(3);
      throw new LuaError(reply.replace(/^error:/, '') || 'Lua failed');
    },
    /** Whether the game's own view is on top: no dialog, save browser or console over it. */
    gameViewActive: () => onTop() === 1,
  };
}