'use strict'

/**
 * A Doubly Linked List, because there aren't enough in the world...
 * this is pretty much a direct JS port of the one wikipedia
 * https://en.wikipedia.org/wiki/Doubly_linked_list
 *
 * For most usage 'insertBeginning' and 'insertEnd' should be enough
 *
 * nodes are expected to something like a POJSO like
 * {
 *   prev: null,
 *   next: null,
 *   something: 'whatever you like'
 * }
 */
class DoublyLinkedList {
  constructor () {
    this.head = null
    this.tail = null
    this.length = 0
  }

  insertBeginning (node) {
    if (this.head === null) {
      this.head = node
      this.tail = node
      node.prev = null
      node.next = null
      this.length++
    } else {
      this.insertBefore(this.head, node)
    }
  }

  insertEnd (node) {
    if (this.tail === null) {
      this.insertBeginning(node)
    } else {
      this.insertAfter(this.tail, node)
    }
  }

  insertAfter (node, newNode) {
    newNode.prev = node
    newNode.next = node.next
    if (node.next === null) {
      this.tail = newNode
    } else {
      node.next.prev = newNode
    }
    node.next = newNode
    this.length++
  }

  insertBefore (node, newNode) {
    newNode.prev = node.prev
    newNode.next = node
    if (node.prev === null) {
      this.head = newNode
    } else {
      node.prev.next = newNode
    }
    node.prev = newNode
    this.length++
  }

  remove (node) {
    if (node.prev === null) {
      this.head = node.next
    } else {
      node.prev.next = node.next
    }
    if (node.next === null) {
      this.tail = node.prev
    } else {
      node.next.prev = node.prev
    }
    node.prev = null
    node.next = null
    this.length--
  }

  // FIXME: this should not live here and has become a dumping ground...
  static createNode (data) {
    return {
      prev: null,
      next: null,
      data: data
    }
  }
}

module.exports = DoublyLinkedList