/**
 * 简易事件总线（与全局 uni.$emit 隔离，避免命名冲突）
 */
export default class EventEmitter {
  constructor() {
    this._listeners = {}
  }

  on(event, handler) {
    if (typeof handler !== 'function') return () => {}
    if (!this._listeners[event]) this._listeners[event] = []
    this._listeners[event].push(handler)
    return () => this.off(event, handler)
  }

  once(event, handler) {
    const wrapper = (...args) => {
      this.off(event, wrapper)
      handler(...args)
    }
    return this.on(event, wrapper)
  }

  off(event, handler) {
    if (!this._listeners[event]) return
    if (!handler) {
      delete this._listeners[event]
      return
    }
    this._listeners[event] = this._listeners[event].filter(fn => fn !== handler)
  }

  emit(event, ...args) {
    const list = this._listeners[event]
    if (!list || !list.length) return
    // 复制一份，避免回调中修改监听器
    list.slice().forEach(fn => {
      try { fn(...args) } catch (e) { console.error(`[EventEmitter] ${event}`, e) }
    })
  }

  clear() { this._listeners = {} }
}