lru-cache.js

;(function () { // closure for web browsers

if (typeof module === 'object' && module.exports) {
  module.exports = LRUCache
} else {
  // just set the global for non-node platforms.
  this.LRUCache = LRUCache
}

function hOP (obj, key) {
  return Object.prototype.hasOwnProperty.call(obj, key)
}

function naiveLength () { return 1 }

function LRUCache (options) {
  if (!(this instanceof LRUCache))
    return new LRUCache(options)

  if (typeof options === 'number')
    options = { max: options }

  if (!options)
    options = {}

  this._max = options.max
  // Kind of weird to have a default max of Infinity, but oh well.
  if (!this._max || !(typeof this._max === "number") || this._max <= 0 )
    this._max = Infinity

  this._lengthCalculator = options.length || naiveLength
  if (typeof this._lengthCalculator !== "function")
    this._lengthCalculator = naiveLength

  this._allowStale = options.stale || false
  this._maxAge = options.maxAge || null
  this._dispose = options.dispose
  this.reset()
}

// resize the cache when the max changes.
Object.defineProperty(LRUCache.prototype, "max",
  { set : function (mL) {
      if (!mL || !(typeof mL === "number") || mL <= 0 ) mL = Infinity
      this._max = mL
      if (this._length > this._max) trim(this)
    }
  , get : function () { return this._max }
  , enumerable : true
  })

// resize the cache when the lengthCalculator changes.
Object.defineProperty(LRUCache.prototype, "lengthCalculator",
  { set : function (lC) {
      if (typeof lC !== "function") {
        this._lengthCalculator = naiveLength
        this._length = this._itemCount
        for (var key in this._cache) {
          this._cache[key].length = 1
        }
      } else {
        this._lengthCalculator = lC
        this._length = 0
        for (var key in this._cache) {
          this._cache[key].length = this._lengthCalculator(this._cache[key].value)
          this._length += this._cache[key].length
        }
      }

      if (this._length > this._max) trim(this)
    }
  , get : function () { return this._lengthCalculator }
  , enumerable : true
  })

Object.defineProperty(LRUCache.prototype, "length",
  { get : function () { return this._length }
  , enumerable : true
  })


Object.defineProperty(LRUCache.prototype, "itemCount",
  { get : function () { return this._itemCount }
  , enumerable : true
  })

LRUCache.prototype.forEach = function (fn, thisp) {
  thisp = thisp || this
  var i = 0
  var itemCount = this._itemCount

  for (var k = this._mru - 1; k >= 0 && i < itemCount; k--) if (this._lruList[k]) {
    i++
    var hit = this._lruList[k]
    if (isStale(this, hit)) {
      del(this, hit)
      if (!this._allowStale) hit = undefined
    }
    if (hit) {
      fn.call(thisp, hit.value, hit.key, this)
    }
  }
}

LRUCache.prototype.keys = function () {
  var keys = new Array(this._itemCount)
  var i = 0
  for (var k = this._mru - 1; k >= 0 && i < this._itemCount; k--) if (this._lruList[k]) {
    var hit = this._lruList[k]
    keys[i++] = hit.key
  }
  return keys
}

LRUCache.prototype.values = function () {
  var values = new Array(this._itemCount)
  var i = 0
  for (var k = this._mru - 1; k >= 0 && i < this._itemCount; k--) if (this._lruList[k]) {
    var hit = this._lruList[k]
    values[i++] = hit.value
  }
  return values
}

LRUCache.prototype.reset = function () {
  if (this._dispose && this._cache) {
    for (var k in this._cache) {
      this._dispose(k, this._cache[k].value)
    }
  }

  this._cache = Object.create(null) // hash of items by key
  this._lruList = Object.create(null) // list of items in order of use recency
  this._mru = 0 // most recently used
  this._lru = 0 // least recently used
  this._length = 0 // number of items in the list
  this._itemCount = 0
}

// Provided for debugging/dev purposes only. No promises whatsoever that
// this API stays stable.
LRUCache.prototype.dump = function () {
  return this._cache
}

LRUCache.prototype.dumpLru = function () {
  return this._lruList
}

LRUCache.prototype.set = function (key, value, maxAge) {
  maxAge = maxAge || this._maxAge
  var now = maxAge ? Date.now() : 0

  if (hOP(this._cache, key)) {
    // dispose of the old one before overwriting
    if (this._dispose)
      this._dispose(key, this._cache[key].value)

    this._cache[key].now = now
    this._cache[key].maxAge = maxAge
    this._cache[key].value = value
    this.get(key)
    return true
  }

  var len = this._lengthCalculator(value)
  var hit = new Entry(key, value, this._mru++, len, now, maxAge)

  // oversized objects fall out of cache automatically.
  if (hit.length > this._max) {
    if (this._dispose) this._dispose(key, value)
    return false
  }

  this._length += hit.length
  this._lruList[hit.lu] = this._cache[key] = hit
  this._itemCount ++

  if (this._length > this._max)
    trim(this)

  return true
}

LRUCache.prototype.has = function (key) {
  if (!hOP(this._cache, key)) return false
  var hit = this._cache[key]
  if (isStale(this, hit)) {
    return false
  }
  return true
}

LRUCache.prototype.get = function (key) {
  return get(this, key, true)
}

LRUCache.prototype.peek = function (key) {
  return get(this, key, false)
}

LRUCache.prototype.pop = function () {
  var hit = this._lruList[this._lru]
  del(this, hit)
  return hit || null
}

LRUCache.prototype.del = function (key) {
  del(this, this._cache[key])
}

function get (self, key, doUse) {
  var hit = self._cache[key]
  if (hit) {
    if (isStale(self, hit)) {
      del(self, hit)
      if (!self._allowStale) hit = undefined
    } else {
      if (doUse) use(self, hit)
    }
    if (hit) hit = hit.value
  }
  return hit
}

function isStale(self, hit) {
  if (!hit || (!hit.maxAge && !self._maxAge)) return false
  var stale = false;
  var diff = Date.now() - hit.now
  if (hit.maxAge) {
    stale = diff > hit.maxAge
  } else {
    stale = self._maxAge && (diff > self._maxAge)
  }
  return stale;
}

function use (self, hit) {
  shiftLU(self, hit)
  hit.lu = self._mru ++
  self._lruList[hit.lu] = hit
}

function trim (self) {
  while (self._lru < self._mru && self._length > self._max)
    del(self, self._lruList[self._lru])
}

function shiftLU (self, hit) {
  delete self._lruList[ hit.lu ]
  while (self._lru < self._mru && !self._lruList[self._lru]) self._lru ++
}

function del (self, hit) {
  if (hit) {
    if (self._dispose) self._dispose(hit.key, hit.value)
    self._length -= hit.length
    self._itemCount --
    delete self._cache[ hit.key ]
    shiftLU(self, hit)
  }
}

// classy, since V8 prefers predictable objects.
function Entry (key, value, lu, length, now, maxAge) {
  this.key = key
  this.value = value
  this.lu = lu
  this.length = length
  this.now = now
  if (maxAge) this.maxAge = maxAge
}

})()