queueCreator = () => {
  const queue = []
  return {
    add(x) {
      queue.unshift(x)
    },
    remove() {
      if (queue.length === 0) {
        return undefined
      }
      return queue.pop()
    },
    next() {
      if (queue.length === 0) {
        return undefined
      }
      return queue[queue.length - 1]
    },
    get length() {
      return queue.length
    },
    empty() {
      return queue.length === 0
    }
  }
}

nodeCreator = (id) => {
  const neighbors = []
  return {
    id,
    neighbors,
    addNeighbors(node) {
      neighbors.push(node)
    }
  }
}

graphCreator = (uni = false) {
  const nodes = []
  const edges = []
  return {
    uni,
    nodes,
    edges,
    addNode(id) {
      nodes.push(nodeCreator(id))  
    },
    searchNode(id) {
      return nodes.find(n => n.id === id)
    },
    addEdge(idOne, idTwo) {
      const a = this.searchNode(idOne)
      const b = this.searchNode(idTwo)

      a.addNeighbors(b)
      if (!uni) {
        b.addNeighbors(a)
      }
      edges.push(`${idOne}${idTwo}`)
    },
    display() {
      return nodes.map(({neighbors, id}) => {
        let output = `${id}`
        if (neighbors.length) {
          output += ` => ${neighbors.map(node => node.id).join(' ')}`
        }
        return output
      }).joing('\n')
    },
  }
}