'use strict'
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// A linked list to keep track of recently-used-ness
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const Yallist = require('yallist')
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const MAX = Symbol('max')
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const LENGTH = Symbol('length')
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const LENGTH_CALCULATOR = Symbol('lengthCalculator')
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const ALLOW_STALE = Symbol('allowStale')
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const MAX_AGE = Symbol('maxAge')
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const DISPOSE = Symbol('dispose')
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const NO_DISPOSE_ON_SET = Symbol('noDisposeOnSet')
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const LRU_LIST = Symbol('lruList')
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const CACHE = Symbol('cache')
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const UPDATE_AGE_ON_GET = Symbol('updateAgeOnGet')
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const naiveLength = () => 1
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// lruList is a yallist where the head is the youngest
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// item, and the tail is the oldest. the list contains the Hit
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// objects as the entries.
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// Each Hit object has a reference to its Yallist.Node. This
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// never changes.
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//
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// cache is a Map (or PseudoMap) that matches the keys to
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// the Yallist.Node object.
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class LRUCache {
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constructor (options) {
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if (typeof options === 'number')
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options = { max: options }
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if (!options)
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options = {}
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if (options.max && (typeof options.max !== 'number' || options.max < 0))
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throw new TypeError('max must be a non-negative number')
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// Kind of weird to have a default max of Infinity, but oh well.
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const max = this[MAX] = options.max || Infinity
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const lc = options.length || naiveLength
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this[LENGTH_CALCULATOR] = (typeof lc !== 'function') ? naiveLength : lc
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this[ALLOW_STALE] = options.stale || false
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if (options.maxAge && typeof options.maxAge !== 'number')
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throw new TypeError('maxAge must be a number')
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this[MAX_AGE] = options.maxAge || 0
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this[DISPOSE] = options.dispose
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this[NO_DISPOSE_ON_SET] = options.noDisposeOnSet || false
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this[UPDATE_AGE_ON_GET] = options.updateAgeOnGet || false
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this.reset()
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}
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// resize the cache when the max changes.
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set max (mL) {
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if (typeof mL !== 'number' || mL < 0)
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throw new TypeError('max must be a non-negative number')
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this[MAX] = mL || Infinity
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trim(this)
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}
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get max () {
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return this[MAX]
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}
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set allowStale (allowStale) {
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this[ALLOW_STALE] = !!allowStale
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}
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get allowStale () {
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return this[ALLOW_STALE]
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}
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set maxAge (mA) {
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if (typeof mA !== 'number')
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throw new TypeError('maxAge must be a non-negative number')
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this[MAX_AGE] = mA
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trim(this)
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}
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get maxAge () {
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return this[MAX_AGE]
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}
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// resize the cache when the lengthCalculator changes.
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set lengthCalculator (lC) {
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if (typeof lC !== 'function')
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lC = naiveLength
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if (lC !== this[LENGTH_CALCULATOR]) {
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this[LENGTH_CALCULATOR] = lC
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this[LENGTH] = 0
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this[LRU_LIST].forEach(hit => {
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hit.length = this[LENGTH_CALCULATOR](hit.value, hit.key)
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this[LENGTH] += hit.length
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})
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}
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trim(this)
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}
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get lengthCalculator () { return this[LENGTH_CALCULATOR] }
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get length () { return this[LENGTH] }
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get itemCount () { return this[LRU_LIST].length }
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rforEach (fn, thisp) {
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thisp = thisp || this
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for (let walker = this[LRU_LIST].tail; walker !== null;) {
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const prev = walker.prev
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forEachStep(this, fn, walker, thisp)
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walker = prev
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}
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}
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forEach (fn, thisp) {
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thisp = thisp || this
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for (let walker = this[LRU_LIST].head; walker !== null;) {
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const next = walker.next
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forEachStep(this, fn, walker, thisp)
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walker = next
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}
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}
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keys () {
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return this[LRU_LIST].toArray().map(k => k.key)
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}
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values () {
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return this[LRU_LIST].toArray().map(k => k.value)
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}
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reset () {
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if (this[DISPOSE] &&
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this[LRU_LIST] &&
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this[LRU_LIST].length) {
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this[LRU_LIST].forEach(hit => this[DISPOSE](hit.key, hit.value))
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}
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this[CACHE] = new Map() // hash of items by key
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this[LRU_LIST] = new Yallist() // list of items in order of use recency
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this[LENGTH] = 0 // length of items in the list
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}
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dump () {
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return this[LRU_LIST].map(hit =>
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isStale(this, hit) ? false : {
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k: hit.key,
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v: hit.value,
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e: hit.now + (hit.maxAge || 0)
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}).toArray().filter(h => h)
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}
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dumpLru () {
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return this[LRU_LIST]
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}
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set (key, value, maxAge) {
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maxAge = maxAge || this[MAX_AGE]
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if (maxAge && typeof maxAge !== 'number')
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throw new TypeError('maxAge must be a number')
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const now = maxAge ? Date.now() : 0
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const len = this[LENGTH_CALCULATOR](value, key)
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if (this[CACHE].has(key)) {
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if (len > this[MAX]) {
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del(this, this[CACHE].get(key))
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return false
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}
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const node = this[CACHE].get(key)
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const item = node.value
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// dispose of the old one before overwriting
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// split out into 2 ifs for better coverage tracking
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if (this[DISPOSE]) {
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if (!this[NO_DISPOSE_ON_SET])
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this[DISPOSE](key, item.value)
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}
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item.now = now
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item.maxAge = maxAge
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item.value = value
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this[LENGTH] += len - item.length
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item.length = len
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this.get(key)
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trim(this)
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return true
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}
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const hit = new Entry(key, value, len, now, maxAge)
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// oversized objects fall out of cache automatically.
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if (hit.length > this[MAX]) {
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if (this[DISPOSE])
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this[DISPOSE](key, value)
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return false
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}
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this[LENGTH] += hit.length
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this[LRU_LIST].unshift(hit)
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this[CACHE].set(key, this[LRU_LIST].head)
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trim(this)
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return true
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}
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has (key) {
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if (!this[CACHE].has(key)) return false
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const hit = this[CACHE].get(key).value
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return !isStale(this, hit)
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}
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get (key) {
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return get(this, key, true)
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}
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peek (key) {
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return get(this, key, false)
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}
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pop () {
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const node = this[LRU_LIST].tail
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if (!node)
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return null
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del(this, node)
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return node.value
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}
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del (key) {
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del(this, this[CACHE].get(key))
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}
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load (arr) {
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// reset the cache
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this.reset()
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const now = Date.now()
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// A previous serialized cache has the most recent items first
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for (let l = arr.length - 1; l >= 0; l--) {
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const hit = arr[l]
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const expiresAt = hit.e || 0
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if (expiresAt === 0)
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// the item was created without expiration in a non aged cache
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this.set(hit.k, hit.v)
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else {
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const maxAge = expiresAt - now
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// dont add already expired items
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if (maxAge > 0) {
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this.set(hit.k, hit.v, maxAge)
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}
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}
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}
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}
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prune () {
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this[CACHE].forEach((value, key) => get(this, key, false))
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}
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}
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const get = (self, key, doUse) => {
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const node = self[CACHE].get(key)
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if (node) {
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const hit = node.value
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if (isStale(self, hit)) {
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del(self, node)
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if (!self[ALLOW_STALE])
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return undefined
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} else {
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if (doUse) {
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if (self[UPDATE_AGE_ON_GET])
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node.value.now = Date.now()
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self[LRU_LIST].unshiftNode(node)
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}
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}
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return hit.value
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}
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}
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const isStale = (self, hit) => {
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if (!hit || (!hit.maxAge && !self[MAX_AGE]))
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return false
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const diff = Date.now() - hit.now
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return hit.maxAge ? diff > hit.maxAge
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: self[MAX_AGE] && (diff > self[MAX_AGE])
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}
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const trim = self => {
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if (self[LENGTH] > self[MAX]) {
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for (let walker = self[LRU_LIST].tail;
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self[LENGTH] > self[MAX] && walker !== null;) {
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// We know that we're about to delete this one, and also
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// what the next least recently used key will be, so just
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// go ahead and set it now.
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const prev = walker.prev
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del(self, walker)
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walker = prev
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}
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}
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}
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const del = (self, node) => {
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if (node) {
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const hit = node.value
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if (self[DISPOSE])
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self[DISPOSE](hit.key, hit.value)
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self[LENGTH] -= hit.length
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self[CACHE].delete(hit.key)
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self[LRU_LIST].removeNode(node)
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}
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}
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class Entry {
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constructor (key, value, length, now, maxAge) {
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this.key = key
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this.value = value
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this.length = length
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this.now = now
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this.maxAge = maxAge || 0
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}
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}
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const forEachStep = (self, fn, node, thisp) => {
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let hit = node.value
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if (isStale(self, hit)) {
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del(self, node)
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if (!self[ALLOW_STALE])
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hit = undefined
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}
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if (hit)
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fn.call(thisp, hit.value, hit.key, self)
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}
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module.exports = LRUCache
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