/*!
 * lunr.Vector
 * Copyright (C) @YEAR Oliver Nightingale
 */

/**
 * lunr.Vectors implement vector related operations for
 * a series of elements.
 *
 * @constructor
 */
lunr.Vector = function () {
  this._magnitude = null
  this.list = undefined
  this.length = 0
}

/**
 * lunr.Vector.Node is a simple struct for each node
 * in a lunr.Vector.
 *
 * @private
 * @param {Number} The index of the node in the vector.
 * @param {Object} The data at this node in the vector.
 * @param {lunr.Vector.Node} The node directly after this node in the vector.
 * @constructor
 * @memberOf Vector
 */
lunr.Vector.Node = function (idx, val, next) {
  this.idx = idx
  this.val = val
  this.next = next
}

/**
 * Inserts a new value at a position in a vector.
 *
 * @param {Number} The index at which to insert a value.
 * @param {Object} The object to insert in the vector.
 * @memberOf Vector.
 */
lunr.Vector.prototype.insert = function (idx, val) {
  this._magnitude = undefined;
  var list = this.list

  if (!list) {
    this.list = new lunr.Vector.Node (idx, val, list)
    return this.length++
  }

  if (idx < list.idx) {
    this.list = new lunr.Vector.Node (idx, val, list)
    return this.length++
  }

  var prev = list,
      next = list.next

  while (next != undefined) {
    if (idx < next.idx) {
      prev.next = new lunr.Vector.Node (idx, val, next)
      return this.length++
    }

    prev = next, next = next.next
  }

  prev.next = new lunr.Vector.Node (idx, val, next)
  return this.length++
}

/**
 * Calculates the magnitude of this vector.
 *
 * @returns {Number}
 * @memberOf Vector
 */
lunr.Vector.prototype.magnitude = function () {
  if (this._magnitude) return this._magnitude
  var node = this.list,
      sumOfSquares = 0,
      val

  while (node) {
    val = node.val
    sumOfSquares += val * val
    node = node.next
  }

  return this._magnitude = Math.sqrt(sumOfSquares)
}

/**
 * Calculates the dot product of this vector and another vector.
 *
 * @param {lunr.Vector} otherVector The vector to compute the dot product with.
 * @returns {Number}
 * @memberOf Vector
 */
lunr.Vector.prototype.dot = function (otherVector) {
  var node = this.list,
      otherNode = otherVector.list,
      dotProduct = 0

  while (node && otherNode) {
    if (node.idx < otherNode.idx) {
      node = node.next
    } else if (node.idx > otherNode.idx) {
      otherNode = otherNode.next
    } else {
      dotProduct += node.val * otherNode.val
      node = node.next
      otherNode = otherNode.next
    }
  }

  return dotProduct
}

/**
 * Calculates the cosine similarity between this vector and another
 * vector.
 *
 * @param {lunr.Vector} otherVector The other vector to calculate the
 * similarity with.
 * @returns {Number}
 * @memberOf Vector
 */
lunr.Vector.prototype.similarity = function (otherVector) {
  return this.dot(otherVector) / (this.magnitude() * otherVector.magnitude())
}