export interface IEvent<T> {
  do(handler: { (data?: T): void }): void
  off(handler: { (data?: T): void }): void
}

export class Event<T> implements IEvent<T> {
  private handlers: { (data?: T): void }[] = []

  public do(handler: { (data?: T): void }) {
    this.handlers.push(handler)
  }

  public off(handler: { (data?: T): void }) {
    this.handlers = this.handlers.filter((h) => h !== handler)
  }

  public emit(data?: T) {
    this.handlers.slice(0).forEach((h) => h(data))
  }
}