import { deepCopy } from './utils'

// 历史记录管理
export default class History {
  constructor(app) {
    this.app = app
    this.historyStack = []
    this.length = 0
    this.index = -1
  }

  // 添加
  add(data) {
    let prev = this.length > 0 ? this.historyStack[this.length - 1] : null
    let copyData = deepCopy(data)
    if (copyData === prev) {
      return
    }
    this.historyStack.push(copyData)
    this.length++
    this.index = this.length - 1
    this.emitChange()
  }

  // 后退
  undo() {
    if (this.index <= 0) {
      return
    }
    this.index--
    this.shuttle()
  }

  // 前进
  redo() {
    if (this.index >= this.length - 1) {
      return
    }
    this.index++
    this.shuttle()
  }

  // 前进后退
  async shuttle() {
    let data = this.historyStack[this.index]
    await this.app.setData(data, true)
    this.emitChange()
    this.app.emit('change', data)
  }

  // 清空数据
  clear() {
    this.index = -1
    this.length = 0
    this.historyStack = []
    this.emitChange()
  }

  // 触发事件
  emitChange() {
    this.app.emit('shuttle', this.index, this.length)
  }
}