/**
 * @requires ./PriorityQueue.js
 */

if (typeof module !== 'undefined' && module.exports) {
      var PriorityQueue = require('./PriorityQueue.js');
}

/**
 * OPTICS - Ordering points to identify the clustering structure
 *
 * @author Lukasz Krawczyk <contact@lukaszkrawczyk.eu>
 * @copyright MIT
 */

/**
 * OPTICS class constructor
 * @constructor
 *
 * @param {Array} dataset
 * @param {number} epsilon
 * @param {number} minPts
 * @param {function} distanceFunction
 * @returns {OPTICS}
 */
function OPTICS(dataset, epsilon, minPts, distanceFunction) {
  /** @type {number} */
  this.epsilon = 1;
  /** @type {number} */
  this.minPts = 1;
  /** @type {function} */
  this.distance = this._euclideanDistance;

  // temporary variables used during computation

  /** @type {Array} */
  this._reachability = [];
  /** @type {Array} */
  this._processed = [];
  /** @type {number} */
  this._coreDistance = 0;
  /** @type {Array} */
  this._orderedList = [];

  this._init(dataset, epsilon, minPts, distanceFunction);
}

/******************************************************************************/
// pulic functions

/**
 * Start clustering
 *
 * @param {Array} dataset
 * @returns {undefined}
 * @access public
 */
OPTICS.prototype.run = function(dataset, epsilon, minPts, distanceFunction) {
  this._init(dataset, epsilon, minPts, distanceFunction);

  for (var pointId = 0, l = this.dataset.length; pointId < l; pointId++) {
    if (this._processed[pointId] !== 1) {
      this._processed[pointId] = 1;
      this.clusters.push([pointId]);
      var clusterId = this.clusters.length - 1;

      this._orderedList.push(pointId);
      var priorityQueue = new PriorityQueue(null, null, 'asc');
      var neighbors = this._regionQuery(pointId);

      // using priority queue assign elements to new cluster
      if (this._distanceToCore(pointId) !== undefined) {
        this._updateQueue(pointId, neighbors, priorityQueue);
        this._expandCluster(clusterId, priorityQueue);
      }
    }
  }

  return this.clusters;
};

/**
 * Generate reachability plot for all points
 *
 * @returns {array}
 * @access public
 */
OPTICS.prototype.getReachabilityPlot = function() {
  var reachabilityPlot = [];

  for (var i = 0, l = this._orderedList.length; i < l; i++) {
    var pointId = this._orderedList[i];
    var distance = this._reachability[pointId];

    reachabilityPlot.push([pointId, distance]);
  }

  return reachabilityPlot;
};

/******************************************************************************/
// protected functions

/**
 * Set object properties
 *
 * @param {Array} dataset
 * @param {number} epsilon
 * @param {number} minPts
 * @param {function} distance
 * @returns {undefined}
 * @access protected
 */
OPTICS.prototype._init = function(dataset, epsilon, minPts, distance) {

  if (dataset) {

    if (!(dataset instanceof Array)) {
      throw Error('Dataset must be of type array, ' +
        typeof dataset + ' given');
    }

    this.dataset = dataset;
    this.clusters = [];
    this._reachability = new Array(this.dataset.length);
    this._processed = new Array(this.dataset.length);
    this._coreDistance = 0;
    this._orderedList = [];
  }

  if (epsilon) {
    this.epsilon = epsilon;
  }

  if (minPts) {
    this.minPts = minPts;
  }

  if (distance) {
    this.distance = distance;
  }
};

/**
 * Update information in queue
 *
 * @param {number} pointId
 * @param {Array} neighbors
 * @param {PriorityQueue} queue
 * @returns {undefined}
 * @access protected
 */
OPTICS.prototype._updateQueue = function(pointId, neighbors, queue) {
  var self = this;

  this._coreDistance = this._distanceToCore(pointId);
  neighbors.forEach(function(pointId2) {
    if (self._processed[pointId2] === undefined) {
      var dist = self.distance(self.dataset[pointId], self.dataset[pointId2]);
      var newReachableDistance = Math.max(self._coreDistance, dist);

      if (self._reachability[pointId2] === undefined) {
        self._reachability[pointId2] = newReachableDistance;
        queue.insert(pointId2, newReachableDistance);
      } else {
        if (newReachableDistance < self._reachability[pointId2]) {
          self._reachability[pointId2] = newReachableDistance;
          queue.remove(pointId2);
          queue.insert(pointId2, newReachableDistance);
        }
      }
    }
  });
};

/**
 * Expand cluster
 *
 * @param {number} clusterId
 * @param {PriorityQueue} queue
 * @returns {undefined}
 * @access protected
 */
OPTICS.prototype._expandCluster = function(clusterId, queue) {
  var queueElements = queue.getElements();

  for (var p = 0, l = queueElements.length; p < l; p++) {
    var pointId = queueElements[p];
    if (this._processed[pointId] === undefined) {
      var neighbors = this._regionQuery(pointId);
      this._processed[pointId] = 1;

      this.clusters[clusterId].push(pointId);
      this._orderedList.push(pointId);

      if (this._distanceToCore(pointId) !== undefined) {
        this._updateQueue(pointId, neighbors, queue);
        this._expandCluster(clusterId, queue);
      }
    }
  }
};

/**
 * Calculating distance to cluster core
 *
 * @param {number} pointId
 * @returns {number}
 * @access protected
 */
OPTICS.prototype._distanceToCore = function(pointId) {
  var l = this.epsilon;
  for (var coreDistCand = 0; coreDistCand < l; coreDistCand++) {
    var neighbors = this._regionQuery(pointId, coreDistCand);
    if (neighbors.length >= this.minPts) {
      return coreDistCand;
    }
  }

  return;
};

/**
 * Find all neighbors around given point
 *
 * @param {number} pointId
 * @param {number} epsilon
 * @returns {Array}
 * @access protected
 */
OPTICS.prototype._regionQuery = function(pointId, epsilon) {
  epsilon = epsilon || this.epsilon;
  var neighbors = [];

  for (var id = 0, l = this.dataset.length; id < l; id++) {
    if (this.distance(this.dataset[pointId], this.dataset[id]) < epsilon) {
      neighbors.push(id);
    }
  }

  return neighbors;
};

/******************************************************************************/
// helpers

/**
 * Calculate euclidean distance in multidimensional space
 *
 * @param {Array} p
 * @param {Array} q
 * @returns {number}
 * @access protected
 */
OPTICS.prototype._euclideanDistance = function(p, q) {
  var sum = 0;
  var i = Math.min(p.length, q.length);

  while (i--) {
    sum += (p[i] - q[i]) * (p[i] - q[i]);
  }

  return Math.sqrt(sum);
};

if (typeof module !== 'undefined' && module.exports) {
  module.exports = OPTICS;
}