Queue.js

demo.js

const Queue = require('Queue')

const q = new Queue(10)
q.push([1, 2, 3, 4, 5, 6])
q.pop(3) // [1, 2, 3]
q.push([1, 2, 3, 4, 5, 6])
q.pop(5) // [4, 5, 6, 1, 2]

Queue.js

export default class Queue {
  constructor(size = 2000) {
    this.size = size
    this.buffer = new Uint8Array(this.size)
    this.first = 0
    this.end = 0
    this.empty = true
  }

  /**
   * Push buffer to the queue
   * @param e {Buffer}
   */
  push(e) {
    this.empty = false
    if (e.length + this.first < this.size) {
      if (this.end >= this.first && this.first + e.length >= this.end && (!this.empty)) {
        // overflowed
        this.end = this.first + e.length
      }
      this.buffer.set(e, this.first)
      this.first += e.length
    } else {
      // overflowed
      this.buffer.set(e.slice(0, this.size - this.first), this.first)
      this.buffer.set(e.slice(this.size - this.first), 0)
      this.first = e.length + this.first - this.size
      if (this.end <= this.first) {
        this.end = this.first
      }
    }
  }

  /**
   * Pop back
   * @param length
   * @return {null|Uint8Array}
   */
  pop(length) {
    if (this.empty) {
      return null
    }
    if (this.first > this.end) {
      if (this.end + length <= this.first) {
        this.end += length
        this.empty = this.end === this.first
        return this.buffer.slice(this.end - length, this.end)
      }
      return null
    }
    // end >= first
    if (this.end + length - this.size <= this.first) {
      const end = this.end
      if (this.end + length < this.size) {
        this.end += length
        return this.buffer.slice(end, this.end)
      }
      this.end = (this.end + length) % this.size
      this.empty = this.end === this.first
      return Uint8Array.concat([this.buffer.slice(end), this.buffer.slice(0, this.end)])
    }
    return null
  }
}