Crystal/tests/game-corner.test.ts

import { describe, expect, it } from "vitest";
import { existsSync, readFileSync } from "node:fs";
import { RomReader } from "../src/game/rom/reader";
import { PokemonData } from "../src/game/rom/pokemon";
import { emptyScriptState, type ScriptEffect } from "../src/game/scripts/interpreter";
import { defaultTextContext, readText } from "../src/game/scripts/text";
import { C } from "../src/game/battle/constants";
import {
  slotMachine,
  initBias,
  SLOTS_NO_BIAS,
  SLOTS_SEVEN,
  makeReel,
  spinAllReels,
  ReelAction,
  type SlotsSession,
} from "../src/game/scripts/slot-machine";
import {
  cardFlip,
  shuffleDeck,
  cardFlipPayout,
  moveCardFlipCursor,
} from "../src/game/scripts/card-flip";
import type { SpecialContext } from "../src/game/scripts/special-context";
import { CrystalAssets } from "../src/game/rom/assets";
import { GameWorld } from "../src/game/world/world";
import { settle } from "./world-driver";
import { JOHTO } from "../src/game/rom/profile";
import { SCREEN_WIDTH } from "../src/game/scripts/screen";

const romPath =
  process.env.CRYSTAL_ROM_PATH ?? "Pokemon - Crystal Version (UE) (V1.1) [C][!].gbc";

/** A simple deterministic byte stream, like the other seeded-RNG tests. */
function seededRandom(seed: number) {
  let s = seed >>> 0;
  return () => {
    s = (s * 1103515245 + 12345) >>> 0;
    return (s >>> 16) & 0xff;
  };
}

/** A minimal SpecialContext over the real ROM: enough state for the Game
 * Corner's coin checks and text, built the same way interpreter.ts's own
 * `specialContext` is. */
function makeContext(
  reader: RomReader,
  data: PokemonData,
  random: () => number,
  coins: number,
): SpecialContext {
  const state = emptyScriptState();
  state.coins = coins;
  state.bag.keyItems.push(C.COIN_CASE);
  const pages: string[] = [];
  const strings: Record<number, string> = {},
    numbers: Record<number, number> = {};
  // Merge the mutable string/number buffers into the text context, as
  // interpreter.ts's own `text()` does with `this.strings`/`this.numbers`.
  const text = () => ({ ...defaultTextContext("CHRIS"), strings, numbers });
  return {
    reader,
    data,
    state,
    strings,
    numbers,
    text,
    random,
    player: () => ({ id: 1, name: "CHRIS" }),
    today: () => 0,
    weekday: () => 0,
    write: (address: number) => {
      const content = readText(reader, address, text());
      if (content) pages.push(...content.split("\n\n"));
    },
    take: () => pages.splice(0, pages.length),
    flush: function* () {
      if (pages.length) yield { kind: "text", pages: pages.splice(0, pages.length) } as ScriptEffect;
    },
    selectMon: function* () {
      return -1;
    },
  };
}

type Answer = number | string | undefined;
/** Drive a Game Corner generator to completion: `screens` answers "screen"
 * effects in order (defaulting to A once exhausted, which both confirms a
 * choice and passes every non-interactive realtime frame); `plays` answers
 * "yesno" effects in order (defaulting to YES); the bet menu always picks
 * `bet` coins. */
function play<T>(
  generator: Generator<ScriptEffect, T, Answer>,
  options: { bet?: number; screens?: string[]; plays?: boolean[] } = {},
): T {
  const screens = [...(options.screens ?? [])];
  const plays = [...(options.plays ?? [])];
  let result = generator.next();
  let steps = 0;
  while (!result.done) {
    if (++steps > 300_000) throw new Error("The Game Corner session did not finish.");
    const effect = result.value;
    let answer: Answer;
    if (effect.kind === "menu") answer = options.bet !== undefined ? 3 - options.bet : 1;
    else if (effect.kind === "yesno") answer = (plays.length ? plays.shift() : true) ? 1 : 0;
    else if (effect.kind === "screen") answer = screens.length ? screens.shift() : "a";
    result = generator.next(answer);
  }
  return result.value;
}
/** ChooseCard_HandleJoypad's board (CollapseCursorPosition: Y*6+X), moved
 * one cell per press as this port's `moveCardFlipCursor` does. */
function moveButtons(fromX: number, fromY: number, toX: number, toY: number): string[] {
  const buttons: string[] = [];
  for (let i = 0; i < Math.abs(toY - fromY); i++) buttons.push(toY > fromY ? "down" : "up");
  for (let i = 0; i < Math.abs(toX - fromX); i++) buttons.push(toX > fromX ? "right" : "left");
  return buttons;
}

describe("CardFlip_CheckWinCondition's paytable", () => {
  it("pays the species pair, exact species, level pair, exact level and exact card cells", () => {
    // Card 0: species 0 (Pikachu), level 0 ("1").
    expect(cardFlipPayout(0, 0)).toBe(0); // row 0's outer cells always lose
    expect(cardFlipPayout(1, 0)).toBe(0);
    expect(cardFlipPayout(2, 0)).toBe(6); // Pikachu/Jigglypuff pair
    expect(cardFlipPayout(4, 0)).toBe(0); // Poliwag/Oddish pair does not match
    expect(cardFlipPayout(8, 0)).toBe(12); // row 1, exact species (Pikachu)
    expect(cardFlipPayout(12, 0)).toBe(9); // row 2, level pair ("1"-"2")
    expect(cardFlipPayout(13, 0)).toBe(18); // row 2, exact level ("1")
    expect(cardFlipPayout(14, 0)).toBe(72); // row 2, exact card (Pikachu "1")
    expect(cardFlipPayout(14, 1)).toBe(0); // the same cell loses for a different card
    // Card 23: species 3 (Oddish), level 5 ("6").
    expect(cardFlipPayout(5, 23)).toBe(6); // Poliwag/Oddish pair
    expect(cardFlipPayout(11, 23)).toBe(12); // row 1, exact species (Oddish)
    expect(cardFlipPayout(42, 23)).toBe(9); // row 6/7's shared level pair ("5"-"6")
    expect(cardFlipPayout(43, 23)).toBe(18); // row 7, exact level ("6")
    expect(cardFlipPayout(47, 23)).toBe(72); // row 7, exact card (Oddish "6")
  });
});

describe("ChooseCard_HandleJoypad's exact navigation", () => {
  const at = (cursorX: number, cursorY: number) => ({ cursorX, cursorY });
  it("snaps left/right to the nearest even cell in the Pokémon-pair row (Y=0)", () => {
    const session = at(5, 0);
    moveCardFlipCursor(session, "left");
    // 5 & 0xe = 4, which is not below 3, so it becomes 4 - 2.
    expect(session).toEqual({ cursorX: 2, cursorY: 0 });
    const session2 = at(3, 0);
    moveCardFlipCursor(session2, "left");
    // 3 & 0xe = 2, which is below 3, so the cursor jumps to the mon-group
    // junction cell instead of stopping on the pair row.
    expect(session2).toEqual({ cursorX: 1, cursorY: 2 });
    const session3 = at(4, 0);
    moveCardFlipCursor(session3, "right");
    // 4 & 0xe = 4, which is not below 4, so right is refused (but the
    // mask is still applied, a kept quirk of the original).
    expect(session3).toEqual({ cursorX: 4, cursorY: 0 });
  });
  it("snaps to the mon-group junction from the Pokémon-group row (Y=1) too, without masking", () => {
    const session = at(2, 1);
    moveCardFlipCursor(session, "left");
    expect(session).toEqual({ cursorX: 1, cursorY: 2 });
    const session2 = at(4, 1);
    moveCardFlipCursor(session2, "left");
    expect(session2).toEqual({ cursorX: 3, cursorY: 1 });
  });
  it("snaps up/down to the nearest even cell in the number-pair column (X=0), or to the number-group junction", () => {
    const session = at(0, 5);
    moveCardFlipCursor(session, "up");
    expect(session).toEqual({ cursorX: 0, cursorY: 2 });
    const session2 = at(0, 3);
    moveCardFlipCursor(session2, "up");
    expect(session2).toEqual({ cursorX: 2, cursorY: 1 });
    const session3 = at(0, 4);
    moveCardFlipCursor(session3, "down");
    expect(session3).toEqual({ cursorX: 0, cursorY: 6 });
    const session4 = at(0, 6);
    moveCardFlipCursor(session4, "down");
    expect(session4).toEqual({ cursorX: 0, cursorY: 6 });
  });
  it("moves one cell at a time everywhere else, refusing past either edge", () => {
    const session = at(3, 5);
    moveCardFlipCursor(session, "left");
    expect(session).toEqual({ cursorX: 2, cursorY: 5 });
    moveCardFlipCursor(session, "right");
    moveCardFlipCursor(session, "right");
    expect(session).toEqual({ cursorX: 4, cursorY: 5 });
    moveCardFlipCursor(session, "right");
    expect(session).toEqual({ cursorX: 5, cursorY: 5 }); // the last column
    moveCardFlipCursor(session, "right");
    expect(session).toEqual({ cursorX: 5, cursorY: 5 }); // refused past it
    const bottom = at(2, 7);
    moveCardFlipCursor(bottom, "down");
    expect(bottom).toEqual({ cursorX: 2, cursorY: 7 }); // the last row, refused
  });
});

describe.skipIf(!existsSync(romPath))("the slot machine with the local ROM", () => {
  const bytes = existsSync(romPath) ? new Uint8Array(readFileSync(romPath)) : new Uint8Array();
  const reader = new RomReader(bytes);
  const data = new PokemonData(reader);

  describe("Slots_InitBias", () => {
    it("re-rolls a fresh bias every round, except when it is already SLOTS_SEVEN", () => {
      // Slots_InitBias's own "and a; ret z" guard: a seven bias is never
      // re-rolled, keeping last round's streak untouched.
      expect(initBias({ reader, random: () => 0 }, SLOTS_SEVEN, false)).toBe(SLOTS_SEVEN);
      // 255 falls past every real entry, into the table's own 100% "no
      // bias" slice for both tables.
      expect(initBias({ reader, random: () => 255 }, SLOTS_NO_BIAS, false)).toBe(SLOTS_NO_BIAS);
      expect(initBias({ reader, random: () => 255 }, SLOTS_NO_BIAS, true)).toBe(SLOTS_NO_BIAS);
    });
    it("the lucky machine (wScriptVar true) widens the cherry slice well past the normal table's", () => {
      // Normal's cumulative cherry threshold is 19 percent (48 of 255);
      // Lucky's is 31 percent + 1 (80 of 255). A byte of 60 falls past
      // Normal's cherry slice (into "no bias") but still inside Lucky's.
      const byte = 60;
      const normal = initBias({ reader, random: () => byte }, SLOTS_NO_BIAS, false);
      const lucky = initBias({ reader, random: () => byte }, SLOTS_NO_BIAS, true);
      expect(normal).toBe(SLOTS_NO_BIAS);
      expect(lucky).not.toBe(SLOTS_NO_BIAS);
    });
  });

  describe("the Golem and Chansey/egg replay (reel 3's real frame-by-frame hops)", () => {
    const sevenEverywhere = Array<number>(18).fill(SLOTS_SEVEN);
    // Positions 0 and 15 (the wraparound repeat of 0) are the seven; every
    // other position (including the reel's own starting position, 14) is
    // not, so InitGolem's own first check does not already count as a win.
    const oneSevenReel3 = [0, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0, 4, 4];
    // Every position but the reel's own starting one (14) is the seven, so
    // InitChansey's own first check does not already count as a win, but
    // wherever DropReel's 16-rate spin leaves it afterward still does.
    const allButStartingSeven = Array<number>(18).fill(SLOTS_SEVEN).map((value, i) => (i === 14 ? 4 : value));
    function newSession(reel3Tilemap: readonly number[], bias: number): SlotsSession {
      return {
        reels: [makeReel(sevenEverywhere), makeReel(sevenEverywhere), makeReel(reel3Tilemap)],
        bias,
        bet: 1, // only the middle line, so reel1/reel2's own middle entry decides the match
        matched: -1,
        firstTwoReelsMatching: true,
        firstTwoReelsMatchingSevens: true,
        buildingMatch: 0,
        payout: 0,
        delay: 0,
        phase: 0,
        joypadSumA: false,
        flashFrame: 0,
        resultLines: [],
      };
    }
    function runUntilStopped(session: SlotsSession) {
      const host = { reader, random: () => 0 };
      for (let tick = 0; tick < 5000 && session.reels[2].action !== ReelAction.DoNothing; tick++)
        spinAllReels(session, host);
      if (session.reels[2].action !== ReelAction.DoNothing)
        throw new Error("Reel 3 never stopped.");
    }

    it("Golem's replay advances reel 3 by exactly the probe's real hop count, not the probe's own discarded position", () => {
      const session = newSession(oneSevenReel3, SLOTS_SEVEN);
      const reel3 = session.reels[2];
      reel3.action = ReelAction.InitGolem;
      const startPosition = reel3.position;
      runUntilStopped(session);
      // Slots_GetNumberOfGolems' seven-bias probe (reel.position starts at
      // 14): the very first incremented position (raw 15, the tilemap's
      // own wraparound repeat of index 0) already matches, so the probe
      // reports one hop, and reel 3's real position should have advanced
      // by exactly that one hop for real.
      expect(reel3.position).toBe((startPosition + 1) % 15);
      expect(session.matched).toBe(SLOTS_SEVEN);
      // Removed (wSlotsDelay 2); a removed struct is still drawn that tick.
      expect(session.golem?.removed ?? true).toBe(true);
    });

    it("Chansey's replay walks in, lays the egg and lets DropReel stop reel 3 on seven", () => {
      const session = newSession(allButStartingSeven, SLOTS_NO_BIAS); // Chansey always targets seven, regardless of bias
      const reel3 = session.reels[2];
      reel3.action = ReelAction.InitChansey;
      runUntilStopped(session);
      expect(session.matched).toBe(SLOTS_SEVEN);
      // The egg always finishes its bounce (and clears itself) before
      // DropReel's own match check runs, whether that check succeeds or
      // (EggAgain) loops back through Chansey for another egg.
      expect(session.egg?.removed ?? true).toBe(true);
    });
  });

  it("spins through a seeded random source, over several rounds, to a payout", () => {
    const context = makeContext(reader, data, seededRandom(7), 150);
    const rounds = 30;
    const plays = Array<boolean>(rounds - 1).fill(true).concat([false]);
    play(slotMachine(context, true), { bet: 3, plays });
    // 30 rounds at 3 coins each (90 total) must have paid out at least
    // once for the balance to end this high; a run that only ever lost
    // could not exceed 150 - 90.
    expect(context.state.coins).toBeGreaterThan(150 - rounds * 3);
  });

  it("the lucky machine plays a full round without refusing", () => {
    const context = makeContext(reader, data, seededRandom(21), 50);
    play(slotMachine(context, true), { bet: 1, plays: [false] });
    expect(context.state.coins).toBeGreaterThanOrEqual(0);
    expect(context.state.coins).toBeLessThanOrEqual(C.MAX_COINS);
  });

  it("refuses to start with no coins, and takes nothing", () => {
    const context = makeContext(reader, data, seededRandom(1), 0);
    play(slotMachine(context, false), {});
    expect(context.state.coins).toBe(0);
  });

  it("refuses to start without a Coin Case, even with coins", () => {
    const context = makeContext(reader, data, seededRandom(1), 50);
    context.state.bag.keyItems = [];
    play(slotMachine(context, false), {});
    expect(context.state.coins).toBe(50);
  });

  it("the coin case never exceeds 9999 while paying out", () => {
    const context = makeContext(reader, data, seededRandom(13), 9990);
    const rounds = 40;
    const plays = Array<boolean>(rounds - 1).fill(true).concat([false]);
    play(slotMachine(context, true), { bet: 3, plays });
    expect(context.state.coins).toBeLessThanOrEqual(C.MAX_COINS);
  });

  it("quitting the bet menu (B) ends the game without spending coins", () => {
    const context = makeContext(reader, data, seededRandom(9), 20);
    const generator = slotMachine(context, false);
    const first = generator.next();
    expect(first.done).toBe(false);
    const second = generator.next(-1); // B cancels Slots_AskBet's menu
    expect(second.done).toBe(true);
    expect(context.state.coins).toBe(20);
  });
});

describe.skipIf(!existsSync(romPath))("Card Flip with the local ROM", () => {
  const bytes = existsSync(romPath) ? new Uint8Array(readFileSync(romPath)) : new Uint8Array();
  const reader = new RomReader(bytes);
  const data = new PokemonData(reader);

  it("a round the player bets on the dealt card's exact species wins", () => {
    const deck = shuffleDeck({ random: seededRandom(5) });
    const species = deck[0] & 3;
    const context = makeContext(reader, data, seededRandom(5), 50);
    const buttons = ["a", ...moveButtons(2, 2, 2 + species, 1), "a"];
    play(cardFlip(context), { screens: buttons, plays: [true, false] });
    expect(context.state.coins).toBe(50 - 3 + 12);
  });

  it("a round the player bets on the wrong exact species and loses", () => {
    // ChooseCard_HandleJoypad's own snapping keeps the cursor off the
    // board's four truly "impossible" cells (row 0-1, col 0-1) from any
    // reachable approach, so this port's exact translation of it cannot
    // reach one either; betting the wrong exact species is an equally
    // sure loss that stays reachable.
    const deck = shuffleDeck({ random: seededRandom(6) });
    const wrongSpecies = ((deck[0] & 3) + 1) % 4;
    const context = makeContext(reader, data, seededRandom(6), 50);
    const buttons = ["a", ...moveButtons(2, 2, 2 + wrongSpecies, 1), "a"];
    play(cardFlip(context), { screens: buttons, plays: [true, false] });
    expect(context.state.coins).toBe(50 - 3);
  });

  it("refuses to start with no coins, and takes nothing", () => {
    const context = makeContext(reader, data, seededRandom(1), 0);
    play(cardFlip(context), {});
    expect(context.state.coins).toBe(0);
  });

  it("refuses to start without a Coin Case, even with coins", () => {
    const context = makeContext(reader, data, seededRandom(1), 50);
    context.state.bag.keyItems = [];
    play(cardFlip(context), {});
    expect(context.state.coins).toBe(50);
  });

  it("the coin case never exceeds 9999, even betting the dealt card's exact match (72 coins)", () => {
    const deck = shuffleDeck({ random: seededRandom(5) });
    const card = deck[0];
    const level = card >> 2,
      species = card & 3;
    const pairIndex = Math.floor(level / 2),
      isPairRow = level % 2 === 0;
    const row = 2 + pairIndex * 2 + (isPairRow ? 0 : 1);
    const col = 2 + species;
    const context = makeContext(reader, data, seededRandom(5), 9995);
    const buttons = ["a", ...moveButtons(2, 2, col, row), "a"];
    play(cardFlip(context), { screens: buttons, plays: [true, false] });
    expect(context.state.coins).toBe(C.MAX_COINS);
  });

  it("declining to play with three coins ends the game without spending any", () => {
    const context = makeContext(reader, data, seededRandom(2), 30);
    play(cardFlip(context), { plays: [false] });
    expect(context.state.coins).toBe(30);
  });
});

describe.skipIf(!existsSync(romPath))(
  "the Game Corner's realtime screen through the world, with the local ROM",
  () => {
    const bytes = existsSync(romPath) ? new Uint8Array(readFileSync(romPath)) : new Uint8Array();
    const GAME_CORNER = "11:19";

    function enterGameCorner(coins: number) {
      let seed = 17;
      const game = new GameWorld(
        new CrystalAssets(bytes),
        () => new Date("2026-09-22T12:00:00"),
        () => {
          seed = (seed * 1103515245 + 12345) >>> 0;
          return (seed >>> 16) & 0xff;
        },
      );
      game.state.coins = coins;
      game.state.bag.keyItems.push(C.COIN_CASE);
      return game;
    }
    /** Stand beside the object at (x, y), face it and press A, as
     * tests/goldenrod.test.ts's own `talk` helper does. No settle() runs
     * after `interact()`: the special's first effect may be a realtime
     * screen, which the generic turn-based driver cannot answer. */
    function talk(game: GameWorld, map: string, x: number, y: number) {
      const STEP = {
        up: [0, -1],
        down: [0, 1],
        left: [-1, 0],
        right: [1, 0],
      } as const;
      for (const [face, [dx, dy]] of Object.entries(STEP) as [
        keyof typeof STEP,
        readonly [number, number],
      ][]) {
        try {
          game.warpTo(map, x - dx, y - dy);
        } catch {
          continue;
        }
        settle(game);
        game.move(face);
        settle(game);
        game.interact();
        return;
      }
      throw new Error(`No place to talk to ${x},${y} on ${map}`);
    }
    /** Turn-based effects (Slots_AskBet's menu, a refusal's text) up to
     * the first realtime screen, picking the first menu item and YES. */
    function driveToScreen(game: GameWorld) {
      for (let tick = 0; tick < 2000; tick++) {
        const dialogue = game.dialogue;
        if (dialogue?.choice?.kind === "screen") return;
        if (dialogue) {
          const last = dialogue.index === dialogue.pages.length - 1;
          if (last && dialogue.choice) game.choose(dialogue.choice.kind === "yesno" ? 1 : 0);
          else if (last && dialogue.holdTicks !== undefined) game.tick();
          else game.advanceDialogue();
        } else if (game.busy) game.tick();
        else return;
      }
      throw new Error("Did not reach a screen choice.");
    }
    /** The realtime screen itself, holding A every fourth tick (as a
     * player holding the button would, since setButton only reports
     * presses) until Slots_AskPlayAgain's yes/no replaces it. */
    function driveRealtimeToPlayAgain(game: GameWorld) {
      for (let tick = 0; tick < 20_000; tick++) {
        const choice = game.dialogue?.choice;
        if (choice?.kind === "yesno") return;
        if (choice?.kind === "screen" && (choice as { realtime?: boolean }).realtime) {
          if (tick % 4 === 0) game.bufferScreenButton("a");
          game.tick();
          continue;
        }
        if (game.dialogue) {
          const dialogue = game.dialogue;
          const last = dialogue.index === dialogue.pages.length - 1;
          if (last && dialogue.choice) game.choose(dialogue.choice.kind === "menu" ? 0 : 1);
          else if (last && dialogue.holdTicks !== undefined) game.tick();
          else game.advanceDialogue();
        } else game.tick();
      }
      throw new Error("Did not reach the play-again question.");
    }

    it("opens the lucky slot machine as a realtime screen, driven through world.tick", () => {
      const game = enterGameCorner(50);
      // GoldenrodGameCornerLuckySlotsMachineScript's fixed tile.
      talk(game, GAME_CORNER, 7, 7);
      driveToScreen(game);
      const choice = game.dialogue?.choice;
      expect(choice?.kind).toBe("screen");
      expect((choice as { realtime?: boolean }).realtime).toBe(true);
      driveRealtimeToPlayAgain(game);
      expect(game.dialogue?.choice?.kind).toBe("yesno");
      // A bet was taken (3 coins) before any payout; a win would only add
      // to the balance, never make it exceed the starting amount after
      // the bet.
      expect(game.state.coins).toBeLessThanOrEqual(50);
      expect(game.state.coins).toBeLessThanOrEqual(50 - 3 + 300);
      game.choose(0); // Slots_AskPlayAgain: No.
      settle(game);
      expect(game.busy).toBe(false);
      expect(game.dialogue).toBeUndefined();
    });

    it("opens Card Flip as a realtime screen, driven through world.tick", () => {
      const game = enterGameCorner(50);
      talk(game, GAME_CORNER, 13, 7); // GoldenrodGameCornerCardFlipMachineScript
      // CardFlip.AskPlayWithThree is a plain yes/no before any screen.
      driveToScreen(game);
      expect(game.dialogue?.choice?.kind).toBe("screen");
      driveRealtimeToPlayAgain(game);
      expect(game.dialogue?.choice?.kind).toBe("yesno");
      expect(game.state.coins).toBeLessThanOrEqual(50 - 3 + 72);
      game.choose(0); // CardFlip.PlayAgain: No.
      settle(game);
      expect(game.busy).toBe(false);
    });
  },
);

describe.skipIf(!existsSync(romPath))(
  "the port's own static tilemaps match the ROM's data, copied the asm's way",
  () => {
    const bytes = existsSync(romPath) ? new Uint8Array(readFileSync(romPath)) : new Uint8Array();
    const reader = new RomReader(bytes);
    const data = new PokemonData(reader);

    /** Drive a Game Corner generator to its first "screen" effect that
     * carries sprites (PlaceYourBet for Card Flip, any spinning frame for
     * the slot machine; ChooseACard's own screen has none), answering
     * every other effect the same way `play()` does. A regression here
     * would mean the board/frame these screens draw moved or changed
     * shape without anyone noticing a pixel. */
    function firstScreenWithSprites<T>(generator: Generator<ScriptEffect, T, Answer>) {
      let result = generator.next();
      let steps = 0;
      while (!result.done) {
        if (++steps > 2000) throw new Error("Did not reach a screen with sprites.");
        const effect = result.value;
        let answer: Answer;
        if (effect.kind === "menu") answer = 1; // bet 2
        else if (effect.kind === "yesno") answer = 1; // yes
        else if (effect.kind === "screen") {
          if (effect.screen.sprites && effect.screen.sprites.length > 0) return effect.screen;
          answer = "a";
        }
        result = generator.next(answer);
      }
      throw new Error("The generator finished before a screen with sprites appeared.");
    }

    it("the slot machine's static frame matches SlotsTilemap's own flat 20x12 copy (InitGFX's CopyBytes)", () => {
      const context = makeContext(reader, data, seededRandom(11), 50);
      const screen = firstScreenWithSprites(slotMachine(context, false));
      const ground = Array.from(reader.slice(JOHTO.SlotsTilemap, SCREEN_WIDTH * 12));
      const port = Array.from(screen.map.slice(0, SCREEN_WIDTH * 12));
      // Mask out the two cells PrintNum/illuminateBetLights redraw every
      // tick (the CREDIT/PAYOUT digits at row 1, and the bet-light column
      // at x=3/16 rows 2-7): everywhere else must still match the ROM's
      // own static SlotsTilemap bytes exactly.
      for (let col = 5; col < 9; col++) port[1 * SCREEN_WIDTH + col] = ground[1 * SCREEN_WIDTH + col];
      for (let col = 11; col < 15; col++) port[1 * SCREEN_WIDTH + col] = ground[1 * SCREEN_WIDTH + col];
      for (let row = 2; row < 8; row++)
        for (const col of [3, 16]) port[row * SCREEN_WIDTH + col] = ground[row * SCREEN_WIDTH + col];
      expect(port).toEqual(ground);
    });

    it("Card Flip's paytable board matches CardFlipTilemap's own 12-row by 11-column copy (CardFlip_InitTilemap's `lb bc, 12, 11`)", () => {
      const context = makeContext(reader, data, seededRandom(11), 50);
      const screen = firstScreenWithSprites(cardFlip(context));
      const ground = reader.slice(JOHTO.CardFlipTilemap, 12 * 11);
      const board: number[] = [];
      for (let row = 0; row < 12; row++)
        for (let col = 0; col < 11; col++) board.push(screen.map[row * SCREEN_WIDTH + 9 + col]);
      expect(board).toEqual(Array.from(ground));
      // Columns 0-1 (left of the dealt-card box, which PlaceYourBet's own
      // `cards: "chosen"` view draws at x=2..6) stay untouched background,
      // never leaked-into by a row/column dimension mismatch.
      for (let row = 0; row < 12; row++)
        for (let col = 0; col < 2; col++) expect(screen.map[row * SCREEN_WIDTH + col]).toBe(0x29);
    });
  },
);