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Filename : index.js
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'use strict';

/**
 * Custom implementation of a double ended queue.
 */
function Denque(array, options) {
  var options = options || {};
  this._capacity = options.capacity;

  this._head = 0;
  this._tail = 0;

  if (Array.isArray(array)) {
    this._fromArray(array);
  } else {
    this._capacityMask = 0x3;
    this._list = new Array(4);
  }
}

/**
 * --------------
 *  PUBLIC API
 * -------------
 */

/**
 * Returns the item at the specified index from the list.
 * 0 is the first element, 1 is the second, and so on...
 * Elements at negative values are that many from the end: -1 is one before the end
 * (the last element), -2 is two before the end (one before last), etc.
 * @param index
 * @returns {*}
 */
Denque.prototype.peekAt = function peekAt(index) {
  var i = index;
  // expect a number or return undefined
  if ((i !== (i | 0))) {
    return void 0;
  }
  var len = this.size();
  if (i >= len || i < -len) return undefined;
  if (i < 0) i += len;
  i = (this._head + i) & this._capacityMask;
  return this._list[i];
};

/**
 * Alias for peekAt()
 * @param i
 * @returns {*}
 */
Denque.prototype.get = function get(i) {
  return this.peekAt(i);
};

/**
 * Returns the first item in the list without removing it.
 * @returns {*}
 */
Denque.prototype.peek = function peek() {
  if (this._head === this._tail) return undefined;
  return this._list[this._head];
};

/**
 * Alias for peek()
 * @returns {*}
 */
Denque.prototype.peekFront = function peekFront() {
  return this.peek();
};

/**
 * Returns the item that is at the back of the queue without removing it.
 * Uses peekAt(-1)
 */
Denque.prototype.peekBack = function peekBack() {
  return this.peekAt(-1);
};

/**
 * Returns the current length of the queue
 * @return {Number}
 */
Object.defineProperty(Denque.prototype, 'length', {
  get: function length() {
    return this.size();
  }
});

/**
 * Return the number of items on the list, or 0 if empty.
 * @returns {number}
 */
Denque.prototype.size = function size() {
  if (this._head === this._tail) return 0;
  if (this._head < this._tail) return this._tail - this._head;
  else return this._capacityMask + 1 - (this._head - this._tail);
};

/**
 * Add an item at the beginning of the list.
 * @param item
 */
Denque.prototype.unshift = function unshift(item) {
  if (arguments.length === 0) return this.size();
  var len = this._list.length;
  this._head = (this._head - 1 + len) & this._capacityMask;
  this._list[this._head] = item;
  if (this._tail === this._head) this._growArray();
  if (this._capacity && this.size() > this._capacity) this.pop();
  if (this._head < this._tail) return this._tail - this._head;
  else return this._capacityMask + 1 - (this._head - this._tail);
};

/**
 * Remove and return the first item on the list,
 * Returns undefined if the list is empty.
 * @returns {*}
 */
Denque.prototype.shift = function shift() {
  var head = this._head;
  if (head === this._tail) return undefined;
  var item = this._list[head];
  this._list[head] = undefined;
  this._head = (head + 1) & this._capacityMask;
  if (head < 2 && this._tail > 10000 && this._tail <= this._list.length >>> 2) this._shrinkArray();
  return item;
};

/**
 * Add an item to the bottom of the list.
 * @param item
 */
Denque.prototype.push = function push(item) {
  if (arguments.length === 0) return this.size();
  var tail = this._tail;
  this._list[tail] = item;
  this._tail = (tail + 1) & this._capacityMask;
  if (this._tail === this._head) {
    this._growArray();
  }
  if (this._capacity && this.size() > this._capacity) {
    this.shift();
  }
  if (this._head < this._tail) return this._tail - this._head;
  else return this._capacityMask + 1 - (this._head - this._tail);
};

/**
 * Remove and return the last item on the list.
 * Returns undefined if the list is empty.
 * @returns {*}
 */
Denque.prototype.pop = function pop() {
  var tail = this._tail;
  if (tail === this._head) return undefined;
  var len = this._list.length;
  this._tail = (tail - 1 + len) & this._capacityMask;
  var item = this._list[this._tail];
  this._list[this._tail] = undefined;
  if (this._head < 2 && tail > 10000 && tail <= len >>> 2) this._shrinkArray();
  return item;
};

/**
 * Remove and return the item at the specified index from the list.
 * Returns undefined if the list is empty.
 * @param index
 * @returns {*}
 */
Denque.prototype.removeOne = function removeOne(index) {
  var i = index;
  // expect a number or return undefined
  if ((i !== (i | 0))) {
    return void 0;
  }
  if (this._head === this._tail) return void 0;
  var size = this.size();
  var len = this._list.length;
  if (i >= size || i < -size) return void 0;
  if (i < 0) i += size;
  i = (this._head + i) & this._capacityMask;
  var item = this._list[i];
  var k;
  if (index < size / 2) {
    for (k = index; k > 0; k--) {
      this._list[i] = this._list[i = (i - 1 + len) & this._capacityMask];
    }
    this._list[i] = void 0;
    this._head = (this._head + 1 + len) & this._capacityMask;
  } else {
    for (k = size - 1 - index; k > 0; k--) {
      this._list[i] = this._list[i = (i + 1 + len) & this._capacityMask];
    }
    this._list[i] = void 0;
    this._tail = (this._tail - 1 + len) & this._capacityMask;
  }
  return item;
};

/**
 * Remove number of items from the specified index from the list.
 * Returns array of removed items.
 * Returns undefined if the list is empty.
 * @param index
 * @param count
 * @returns {array}
 */
Denque.prototype.remove = function remove(index, count) {
  var i = index;
  var removed;
  var del_count = count;
  // expect a number or return undefined
  if ((i !== (i | 0))) {
    return void 0;
  }
  if (this._head === this._tail) return void 0;
  var size = this.size();
  var len = this._list.length;
  if (i >= size || i < -size || count < 1) return void 0;
  if (i < 0) i += size;
  if (count === 1 || !count) {
    removed = new Array(1);
    removed[0] = this.removeOne(i);
    return removed;
  }
  if (i === 0 && i + count >= size) {
    removed = this.toArray();
    this.clear();
    return removed;
  }
  if (i + count > size) count = size - i;
  var k;
  removed = new Array(count);
  for (k = 0; k < count; k++) {
    removed[k] = this._list[(this._head + i + k) & this._capacityMask];
  }
  i = (this._head + i) & this._capacityMask;
  if (index + count === size) {
    this._tail = (this._tail - count + len) & this._capacityMask;
    for (k = count; k > 0; k--) {
      this._list[i = (i + 1 + len) & this._capacityMask] = void 0;
    }
    return removed;
  }
  if (index === 0) {
    this._head = (this._head + count + len) & this._capacityMask;
    for (k = count - 1; k > 0; k--) {
      this._list[i = (i + 1 + len) & this._capacityMask] = void 0;
    }
    return removed;
  }
  if (i < size / 2) {
    this._head = (this._head + index + count + len) & this._capacityMask;
    for (k = index; k > 0; k--) {
      this.unshift(this._list[i = (i - 1 + len) & this._capacityMask]);
    }
    i = (this._head - 1 + len) & this._capacityMask;
    while (del_count > 0) {
      this._list[i = (i - 1 + len) & this._capacityMask] = void 0;
      del_count--;
    }
    if (index < 0) this._tail = i;
  } else {
    this._tail = i;
    i = (i + count + len) & this._capacityMask;
    for (k = size - (count + index); k > 0; k--) {
      this.push(this._list[i++]);
    }
    i = this._tail;
    while (del_count > 0) {
      this._list[i = (i + 1 + len) & this._capacityMask] = void 0;
      del_count--;
    }
  }
  if (this._head < 2 && this._tail > 10000 && this._tail <= len >>> 2) this._shrinkArray();
  return removed;
};

/**
 * Native splice implementation.
 * Remove number of items from the specified index from the list and/or add new elements.
 * Returns array of removed items or empty array if count == 0.
 * Returns undefined if the list is empty.
 *
 * @param index
 * @param count
 * @param {...*} [elements]
 * @returns {array}
 */
Denque.prototype.splice = function splice(index, count) {
  var i = index;
  // expect a number or return undefined
  if ((i !== (i | 0))) {
    return void 0;
  }
  var size = this.size();
  if (i < 0) i += size;
  if (i > size) return void 0;
  if (arguments.length > 2) {
    var k;
    var temp;
    var removed;
    var arg_len = arguments.length;
    var len = this._list.length;
    var arguments_index = 2;
    if (!size || i < size / 2) {
      temp = new Array(i);
      for (k = 0; k < i; k++) {
        temp[k] = this._list[(this._head + k) & this._capacityMask];
      }
      if (count === 0) {
        removed = [];
        if (i > 0) {
          this._head = (this._head + i + len) & this._capacityMask;
        }
      } else {
        removed = this.remove(i, count);
        this._head = (this._head + i + len) & this._capacityMask;
      }
      while (arg_len > arguments_index) {
        this.unshift(arguments[--arg_len]);
      }
      for (k = i; k > 0; k--) {
        this.unshift(temp[k - 1]);
      }
    } else {
      temp = new Array(size - (i + count));
      var leng = temp.length;
      for (k = 0; k < leng; k++) {
        temp[k] = this._list[(this._head + i + count + k) & this._capacityMask];
      }
      if (count === 0) {
        removed = [];
        if (i != size) {
          this._tail = (this._head + i + len) & this._capacityMask;
        }
      } else {
        removed = this.remove(i, count);
        this._tail = (this._tail - leng + len) & this._capacityMask;
      }
      while (arguments_index < arg_len) {
        this.push(arguments[arguments_index++]);
      }
      for (k = 0; k < leng; k++) {
        this.push(temp[k]);
      }
    }
    return removed;
  } else {
    return this.remove(i, count);
  }
};

/**
 * Soft clear - does not reset capacity.
 */
Denque.prototype.clear = function clear() {
  this._list = new Array(this._list.length);
  this._head = 0;
  this._tail = 0;
};

/**
 * Returns true or false whether the list is empty.
 * @returns {boolean}
 */
Denque.prototype.isEmpty = function isEmpty() {
  return this._head === this._tail;
};

/**
 * Returns an array of all queue items.
 * @returns {Array}
 */
Denque.prototype.toArray = function toArray() {
  return this._copyArray(false);
};

/**
 * -------------
 *   INTERNALS
 * -------------
 */

/**
 * Fills the queue with items from an array
 * For use in the constructor
 * @param array
 * @private
 */
Denque.prototype._fromArray = function _fromArray(array) {
  var length = array.length;
  var capacity = this._nextPowerOf2(length);

  this._list = new Array(capacity);
  this._capacityMask = capacity - 1;
  this._tail = length;

  for (var i = 0; i < length; i++) this._list[i] = array[i];
};

/**
 *
 * @param fullCopy
 * @param size Initialize the array with a specific size. Will default to the current list size
 * @returns {Array}
 * @private
 */
Denque.prototype._copyArray = function _copyArray(fullCopy, size) {
  var src = this._list;
  var capacity = src.length;
  var length = this.length;
  size = size | length;

  // No prealloc requested and the buffer is contiguous
  if (size == length && this._head < this._tail) {
    // Simply do a fast slice copy
    return this._list.slice(this._head, this._tail);
  }

  var dest = new Array(size);

  var k = 0;
  var i;
  if (fullCopy || this._head > this._tail) {
    for (i = this._head; i < capacity; i++) dest[k++] = src[i];
    for (i = 0; i < this._tail; i++) dest[k++] = src[i];
  } else {
    for (i = this._head; i < this._tail; i++) dest[k++] = src[i];
  }

  return dest;
}

/**
 * Grows the internal list array.
 * @private
 */
Denque.prototype._growArray = function _growArray() {
  if (this._head != 0) {
    // double array size and copy existing data, head to end, then beginning to tail.
    var newList = this._copyArray(true, this._list.length << 1);

    this._tail = this._list.length;
    this._head = 0;

    this._list = newList;
  } else {
    this._tail = this._list.length;
    this._list.length <<= 1;
  }

  this._capacityMask = (this._capacityMask << 1) | 1;
};

/**
 * Shrinks the internal list array.
 * @private
 */
Denque.prototype._shrinkArray = function _shrinkArray() {
  this._list.length >>>= 1;
  this._capacityMask >>>= 1;
};

/**
 * Find the next power of 2, at least 4
 * @private
 * @param {number} num 
 * @returns {number}
 */
Denque.prototype._nextPowerOf2 = function _nextPowerOf2(num) {
  var log2 = Math.log(num) / Math.log(2);
  var nextPow2 = 1 << (log2 + 1);

  return Math.max(nextPow2, 4);
}

module.exports = Denque;