isaacscript-common/src/classes/features/other/StartAmbush.ts

Helper functions and features for IsaacScript mods.

import { SackSubType } from "isaac-typescript-definitions";
import { Exported } from "../../../decorators";
import { ISCFeature } from "../../../enums/ISCFeature";
import { removeEntities } from "../../../functions/entities";
import {
  getCoins,
  spawnSackWithSeed,
} from "../../../functions/pickupsSpecific";
import { Feature } from "../../private/Feature";
import type { RunInNFrames } from "./RunInNFrames";

/** Hard-coding this makes it easier to clean up the pickups afterwards. */
const SACK_SEED_THAT_SPAWNS_TWO_COINS = 6 as Seed;

export class StartAmbush extends Feature {
  private readonly runInNFrames: RunInNFrames;

  /** @internal */
  constructor(runInNFrames: RunInNFrames) {
    super();

    this.featuresUsed = [ISCFeature.RUN_IN_N_FRAMES];

    this.runInNFrames = runInNFrames;
  }

  /**
   * Helper function to start a Challenge Room or the Boss Rush.
   *
   * Specifically, this is performed by spawning a sack on top of the player, waiting a game frame,
   * and then removing the sack and the pickups that the sack dropped.
   *
   * In order to use this function, you must upgrade your mod with `ISCFeature.START_AMBUSH`.
   *
   * @public
   */
  @Exported
  public startAmbush(): void {
    const player = Isaac.GetPlayer();
    const sack = spawnSackWithSeed(
      SackSubType.NULL,
      player.Position,
      SACK_SEED_THAT_SPAWNS_TWO_COINS,
    );

    // The sack will play the "Appear" animation and the player will not be able to interact with it
    // while this is occurring. By stopping the animation, it will transition to the "Idle"
    // animation and be interactable on the next game frame.
    const sprite = sack.GetSprite();
    sprite.Stop();
    const sackPtr = EntityPtr(sack);
    this.runInNFrames.runNextGameFrame(() => {
      const futureSack = sackPtr.Ref;
      if (futureSack === undefined) {
        return;
      }

      futureSack.Remove();
      const sackPtrHash = GetPtrHash(futureSack);
      const coins = getCoins();
      const coinsFromSack = coins.filter(
        (pickup) =>
          pickup.SpawnerEntity !== undefined
          && GetPtrHash(pickup.SpawnerEntity) === sackPtrHash,
      );
      removeEntities(coinsFromSack);
    });
  }
}