// Copyright 2009 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


/**
 * Constructs a ConsArray object. It is used mainly for tree traversal.
 * In this use case we have lots of arrays that we need to iterate
 * sequentally. The internal Array implementation is horribly slow
 * when concatenating on large (10K items) arrays due to memory copying.
 * That's why we avoid copying memory and insead build a linked list
 * of arrays to iterate through.
 *
 * @constructor
 */
export function ConsArray() {
  this.tail_ = new ConsArray.Cell(null, null);
  this.currCell_ = this.tail_;
  this.currCellPos_ = 0;
};


/**
 * Concatenates another array for iterating. Empty arrays are ignored.
 * This operation can be safely performed during ongoing ConsArray
 * iteration.
 *
 * @param {Array} arr Array to concatenate.
 */
ConsArray.prototype.concat = function(arr) {
  if (arr.length > 0) {
    this.tail_.data = arr;
    this.tail_ = this.tail_.next = new ConsArray.Cell(null, null);
  }
};


/**
 * Whether the end of iteration is reached.
 */
ConsArray.prototype.atEnd = function() {
  return this.currCell_ === null ||
      this.currCell_.data === null ||
      this.currCellPos_ >= this.currCell_.data.length;
};


/**
 * Returns the current item, moves to the next one.
 */
ConsArray.prototype.next = function() {
  const result = this.currCell_.data[this.currCellPos_++];
  if (this.currCellPos_ >= this.currCell_.data.length) {
    this.currCell_ = this.currCell_.next;
    this.currCellPos_ = 0;
  }
  return result;
};


/**
 * A cell object used for constructing a list in ConsArray.
 *
 * @constructor
 */
ConsArray.Cell = function(data, next) {
  this.data = data;
  this.next = next;
};
