// (c) 2018, Mariusz Nowak

// SPDX-License-Identifier: ISC

// Derived from https://github.com/medikoo/lru-queue

export function lruQueue (limit) {

let size = 0

let base = 1

let queue = Object.create(null)

let map = Object.create(null)

let index = 0

const del = function (id) {

const oldIndex = map[id]

if (!oldIndex) return

delete queue[oldIndex]

delete map[id]

--size

if (base !== oldIndex) return

if (!size) {

index = 0

base = 1

return

}

while (!hasOwnProperty.call(queue, ++base)) continue

}

limit = Math.abs(limit)

return {

hit: function (id) {

const oldIndex = map[id]; const nuIndex = ++index

queue[nuIndex] = id

map[id] = nuIndex

if (!oldIndex) {

++size

if (size <= limit) return undefined

id = queue[base]

del(id)

return id

}

delete queue[oldIndex]

if (base !== oldIndex) return undefined

while (!hasOwnProperty.call(queue, ++base)) continue

return undefined

},

delete: del,

clear: function () {

size = index = 0

base = 1

queue = Object.create(null)

map = Object.create(null)

}

}

};