Crystal/tests/npc-movement.test.ts

import { describe, expect, it } from "vitest";
import { existsSync, readFileSync } from "node:fs";
import { CrystalAssets } from "../src/game/rom/assets";
import { GameWorld } from "../src/game/world/world";
import type { Direction } from "../src/game/world/types";
import { walkTo } from "./world-driver";

const romPath =
  process.env.CRYSTAL_ROM_PATH ??
  "Pokemon - Crystal Version (UE) (V1.1) [C][!].gbc";
const ROUTE_29 = "24:3";
// object_event ids are their index + 2 (maps/Route29.asm).
const YOUNGSTER = 3; // 27,16 SPRITEMOVEDATA_WALK_UP_DOWN, radius 0, 1
const TEACHER = 4; // 15,11 SPRITEMOVEDATA_WALK_LEFT_RIGHT, radius 1, 0
const DUDE = 2; // 50,12 SPRITEMOVEDATA_SPINRANDOM_SLOW

describe.skipIf(!existsSync(romPath))("NPC movement with the local ROM", () => {
  const assets = new CrystalAssets(new Uint8Array(readFileSync(romPath)));
  /** A seeded Random so every run takes the same steps. */
  const at = (x: number, y: number, direction: Direction = "down") => {
    let seed = 7;
    const world = new GameWorld(
      assets,
      () => new Date("2026-09-22T12:00:00"),
      () => {
        seed = (seed * 1103515245 + 12345) >>> 0;
        return (seed >>> 16) & 255;
      },
    );
    world.restore({ ...world.save(), map: ROUTE_29, x, y, direction });
    return world;
  };
  const object = (world: GameWorld, id: number) =>
    world.objects().find((candidate) => candidate.id === id)!;
  const track = (world: GameWorld, id: number, ticks: number) => {
    const seen = new Set<string>(),
      facings = new Set<Direction>();
    for (let tick = 0; tick < ticks; tick++) {
      world.tick();
      const { x, y, direction } = object(world, id);
      seen.add(`${x},${y}`);
      facings.add(direction);
    }
    return { seen, facings };
  };

  it("walks up and down within the object's radius", () => {
    const world = at(29, 16);
    const { seen, facings } = track(world, YOUNGSTER, 3000);
    // Radius 1: home and one tile either way, never off the column.
    expect(seen.size).toBeGreaterThan(1);
    for (const tile of seen) {
      const [x, y] = tile.split(",").map(Number);
      expect(x).toBe(27);
      expect(Math.abs(y - 16)).toBeLessThanOrEqual(1);
    }
    expect([...facings].every((facing) => facing === "up" || facing === "down")).toBe(true);
    expect(world.notice, world.diagnostic).toBe("");
  });

  it("walks left and right for WALK_LEFT_RIGHT", () => {
    const world = at(13, 12);
    const { seen } = track(world, TEACHER, 3000);
    expect(seen.size).toBeGreaterThan(1);
    for (const tile of seen) {
      const [x, y] = tile.split(",").map(Number);
      expect(y).toBe(11);
      expect(Math.abs(x - 15)).toBeLessThanOrEqual(1);
    }
  });

  it("spins in place for SPINRANDOM_SLOW", () => {
    const world = at(52, 12);
    const { seen, facings } = track(world, DUDE, 3000);
    expect([...seen]).toEqual(["50,12"]);
    expect(facings.size).toBeGreaterThan(2);
  });

  it("never steps onto the player, and freezes while text is open", () => {
    // Standing on the youngster's lower tile blocks that step.
    const world = at(27, 17, "up");
    const { seen } = track(world, YOUNGSTER, 3000);
    expect(seen.has("27,17")).toBe(false);
    // Talk to the youngster once he stands next to the player.
    for (let tick = 0; tick < 5000; tick++) {
      const youngster = object(world, YOUNGSTER);
      if (youngster.x === 27 && youngster.y === 16 && !world.busy) break;
      world.tick();
    }
    world.interact();
    expect(world.dialogue).toBeDefined();
    const frozen = world.objects().map(({ id, x, y, direction }) => [id, x, y, direction]);
    for (let tick = 0; tick < 500; tick++) world.tick();
    expect(world.objects().map(({ id, x, y, direction }) => [id, x, y, direction])).toEqual(frozen);
  });

  it("stays put while off screen and returns home once far away", () => {
    // Nine tiles east: the youngster's steps would leave the screen.
    const far = at(36, 16);
    const { seen } = track(far, YOUNGSTER, 2000);
    expect([...seen]).toEqual(["27,16"]);
    // Let him wander, then walk away until home and tile leave the window.
    const world = at(29, 16);
    for (let tick = 0; tick < 5000 && object(world, YOUNGSTER).y === 16; tick++)
      world.tick();
    expect(object(world, YOUNGSTER).y).not.toBe(16);
    const wandered = [object(world, YOUNGSTER).x, object(world, YOUNGSTER).y];
    // Walking east leaves both his tile and home beyond the object window.
    walkTo(world, 40, 16);
    world.tick();
    expect(wandered).not.toEqual([27, 16]);
    expect([object(world, YOUNGSTER).x, object(world, YOUNGSTER).y]).toEqual([27, 16]);
  });

  it("does not save wandering positions", () => {
    const world = at(29, 16);
    for (let tick = 0; tick < 5000 && object(world, YOUNGSTER).y === 16; tick++)
      world.tick();
    const saved = world.save();
    expect(saved.objects).toEqual([]);
    world.restore(saved);
    expect([object(world, YOUNGSTER).x, object(world, YOUNGSTER).y]).toEqual([27, 16]);
  });
});