/**
 * The minimal external-store base every controller in this package extends —
 * the same shape as fnf-web's `SyncExternalStorage` (the InputMediaController
 * pattern): the controller itself is the stable object React holds, and the
 * snapshot is a version counter that bumps on every `commit()`. Reads go
 * through the controller's getters, so renders never chase object identity.
 *
 * Framework-agnostic on purpose: controllers are fully usable (and testable)
 * without React; `useStore` is the one-line binding.
 */
export class ExternalStore {
  private version = 0
  private readonly listeners = new Set<() => void>()

  readonly snapshot = (): number => this.version

  readonly subscribe = (listener: () => void): (() => void) => {
    this.listeners.add(listener)
    return () => this.listeners.delete(listener)
  }

  protected commit(): void {
    this.version++
    for (const listener of this.listeners) listener()
  }
}