export class UndoManager {
  constructor () {
    this._stack = []
    this._limit = Infinity
    // index 表示下一个可以 redo 的项目
    this._index = 0
  }

  get hasRedo () {
    return this._stack.length > 0 && this._index < this._stack.length
  }

  get hasUndo () {
    return this._stack.length > 0 && this._index > 0
  }

  get size () {
    return this._stack.length
  }

  get limit () {
    return this._limit
  }

  set limit (limit) {
    this.setLimit(limit)
  }

  get index () {
    return this._index
  }

  get isEmpty () {
    return this._stack.length === 0
  }

  get isFull () {
    return this._stack.length === this._limit
  }

  getSize () {
    return this.size
  }

  getIndex () {
    return this.index
  }

  setLimit (limit) {
    this._limit = limit >= 0 ? parseInt(limit) : 0
    this._clipStack()
  }

  _clipStack () {
    if (this._limit >= this._stack.length) return
    if (this._limit < this._stack.length) {
      const step = this._stack.length - this._limit
      while (this._index < step) {
        this.redo()
      }
      this._index = this._index - step || 0
    }

    this._stack = this._stack.slice(-this._limit)
  }

  clear () {
    this._stack = []
    this._index = 0
  }

  record ({ redo, undo }) {
    if (!redo || !undo) {
      throw (new TypeError('"redo" & "undo" are both expected to be type of "Function".'))
    }
    this._stack.push({ redo, undo })
    this._clipStack()
  }

  execute ({ redo, undo }) {
    if (!redo || !undo) {
      throw (new TypeError('"redo" & "undo" are both expected to be type of "Function".'))
    }
    if (!this.hasRedo) {
      this._stack.push({ redo, undo })
      this.redo()
      this._clipStack()
    } else {
      throw (new Error('UndoManager has redo, can not execute.'))
    }
  }

  redo () {
    if (this.hasRedo) {
      this._stack[this._index].redo()
      this._index = this._index + 1
    }
  }

  undo () {
    if (this.hasUndo) {
      this._stack[this._index - 1].undo()
      this._index = this._index - 1
    }
  }

  bindHotKeys () {
    // TODO: bindHotKeys
  }
}