/*
 * Simple doubly linked list implementation derived from Cormen, et al.,
 * "Introduction to Algorithms".
 */

export class List {
  _sentinel: any;
  constructor() {
    const sentinel = {} as any;
    sentinel._next = sentinel._prev = sentinel;
    this._sentinel = sentinel;
  }
  dequeue() { }
  // @ts-ignore
  enqueue(entry: any) { }
}

List.prototype.dequeue = function() {
  const sentinel = this._sentinel;
  const entry = sentinel._prev;
  if (entry !== sentinel) {
    unlink(entry);
    return entry;
  }
};

List.prototype.enqueue = function(entry: any) {
  const sentinel = this._sentinel;
  if (entry._prev && entry._next) {
    unlink(entry);
  }
  entry._next = sentinel._next;
  sentinel._next._prev = entry;
  sentinel._next = entry;
  entry._prev = sentinel;
};

List.prototype.toString = function() {
  const strs = [];
  const sentinel = this._sentinel;
  let curr = sentinel._prev;
  while (curr !== sentinel) {
    strs.push(JSON.stringify(curr, filterOutLinks));
    curr = curr._prev;
  }
  return '[' + strs.join(', ') + ']';
};

function unlink(entry: any) {
  entry._prev._next = entry._next;
  entry._next._prev = entry._prev;
  delete entry._next;
  delete entry._prev;
}

function filterOutLinks(k: any, v: any) {
  if (k !== '_next' && k !== '_prev') {
    return v;
  }
}

export default List;