// https://github.com/rsms/js-lru
let Cache = new function() {
  // jshint ignore:line
  function LRU(maxLength) {
    this.size = 0
    this.limit = maxLength
    this.head = this.tail = void 0
    this._keymap = {}
  }

  let p = LRU.prototype

  p.put = function(key, value) {
    let entry = {
      key: key,
      value: value
    }
    this._keymap[key] = entry
    if (this.tail) {
      this.tail.newer = entry
      entry.older = this.tail
    } else {
      this.head = entry
    }
    this.tail = entry
    if (this.size === this.limit) {
      this.shift()
    } else {
      this.size++
    }
    return value
  }

  p.shift = function() {
    let entry = this.head
    if (entry) {
      this.head = this.head.newer
      this.head.older = entry.newer = entry.older = this._keymap[
        entry.key
      ] = void 0
      delete this._keymap[entry.key] //#1029
    }
  }
  p.get = function(key) {
    let entry = this._keymap[key]
    if (entry === void 0) return
    if (entry === this.tail) {
      return entry.value
    }
    // HEAD--------------TAIL
    //   <.older   .newer>
    //  <--- add direction --
    //   A  B  C  <D>  E
    if (entry.newer) {
      if (entry === this.head) {
        this.head = entry.newer
      }
      entry.newer.older = entry.older // C <-- E.
    }
    if (entry.older) {
      entry.older.newer = entry.newer // C. --> E
    }
    entry.newer = void 0 // D --x
    entry.older = this.tail // D. --> E
    if (this.tail) {
      this.tail.newer = entry // E. <-- D
    }
    this.tail = entry
    return entry.value
  }
  return LRU
}() // jshint ignore:line