// 轻量事件总线（mitt 风格，零依赖），供跨组件通信使用
// 使用方式：emitter.on('event', handler) / emitter.emit('event', payload) / emitter.off('event', handler)
const eventMap = new Map()

export const emitter = {
  on(type, handler) {
    const handlers = eventMap.get(type)
    if (handlers) {
      handlers.push(handler)
    } else {
      eventMap.set(type, [handler])
    }
    return this
  },
  off(type, handler) {
    const handlers = eventMap.get(type)
    if (!handlers) return this
    if (handler) {
      const index = handlers.indexOf(handler)
      if (index > -1) handlers.splice(index, 1)
      if (!handlers.length) eventMap.delete(type)
    } else {
      eventMap.delete(type)
    }
    return this
  },
  emit(type, evt) {
    const handlers = eventMap.get(type)
    if (handlers) {
      ;[...handlers].forEach((fn) => fn(evt))
    }
    return this
  },
  clear() {
    eventMap.clear()
    return this
  },
}

export default emitter