'use strict';

var defaultcomparator = function (a, b) {
  return a < b;
};

// the provided comparator function should take a, b and return *true* when a < b
function FastPriorityQueue(comparator) {
  if (!(this instanceof FastPriorityQueue)) return new FastPriorityQueue(comparator);
  this.array = [];
  this.size = 0;
  this.compare = comparator || defaultcomparator;
}

// copy the priority queue into another, and return it. Queue items are shallow-copied.
// Runs in `O(n)` time.
FastPriorityQueue.prototype.clone = function() {
  var fpq = new FastPriorityQueue(this.compare);
  fpq.size = this.size;
  fpq.array = this.array.slice(0, this.size);
  return fpq;
};

// Add an element into the queue
// runs in O(log n) time
FastPriorityQueue.prototype.add = function(value, obj) {
  var i = this.size;
  this.array[this.size] = { value, obj };
  this.size += 1;

  var p;
  var ap;

  while (i > 0) {
    p = (i - 1) >> 1;
    ap = this.array[p];
    if (!this.compare(value, ap.value)) break;

    this.array[i] = ap;
    i = p;
  };

  this.array[i] = { value, obj };
};

// replace the content of the heap by provided array and "heapify it"
FastPriorityQueue.prototype.heapify = function(arr) {
  this.array = arr;
  this.size = arr.length;
  var i;
  for (i = this.size >> 1; i >= 0; i--) {
    this._percolateDown(i);
  }
};

// for internal use
FastPriorityQueue.prototype._percolateUp = function(i, force) {
  var myval = this.array[i];
  var p;
  var ap;
  while (i > 0) {
    p = (i - 1) >> 1;
    ap = this.array[p];
    // force will skip the compare
    if (!force && !this.compare(myval.value, ap.value)) {
      break;
    }
    this.array[i] = ap;
    i = p;
  }
  this.array[i] = myval;
};

// for internal use
FastPriorityQueue.prototype._percolateDown = function(i) {
  var size = this.size;
  var hsize = this.size >>> 1;
  var ai = this.array[i];
  var l;
  var r;
  var bestc;
  while (i < hsize) {
    l = (i << 1) + 1;
    r = l + 1;
    bestc = this.array[l];
    if (r < size) {
      if (this.compare(this.array[r].value, bestc.value)) {
        l = r;
        bestc = this.array[r];
      }
    }
    if (!this.compare(bestc.value, ai.value)) {
      break;
    }
    this.array[i] = bestc;
    i = l;
  }
  this.array[i] = ai;
};

// internal
// _removeAt(index) will remove the item at the given index from the queue,
// retaining balance. returns the removed item, or undefined if nothing is removed.
FastPriorityQueue.prototype._removeAt = function(index) {
  if (index > this.size - 1 || index < 0) return undefined;

  // impl1:
  //this.array.splice(index, 1);
  //this.heapify(this.array);
  // impl2:
  this._percolateUp(index, true);
  return this.poll();
};

// remove(myval) will remove an item matching the provided value from the
// queue, checked for equality by using the queue's comparator.
// return true if removed, false otherwise.
FastPriorityQueue.prototype.remove = function(myval) {
  for (var i = 0; i < this.size; i++) {
    if (!this.compare(this.array[i], myval) && !this.compare(myval, this.array[i])) {
      // items match, comparator returns false both ways, remove item
      this._removeAt(i);
      return true;
    }
  }
  return false;
};

// removeOne(callback) will execute the callback function for each item of the queue
// and will remove the first item for which the callback will return true.
// return the removed item, or undefined if nothing is removed.
FastPriorityQueue.prototype.removeOne = function(callback) {
  if (typeof callback !== "function") {
    return undefined;
  }
  for (var i = 0; i < this.size; i++) {
    if (callback(this.array[i])) {
      return this._removeAt(i);
    }
  }
};

// remove(callback[, limit]) will execute the callback function for each item of
// the queue and will remove each item for which the callback returns true, up to
// a max limit of removed items if specified or no limit if unspecified.
// return an array containing the removed items.
// The callback function should be a pure function.
FastPriorityQueue.prototype.removeMany = function(callback, limit) {
  // Skip unnecessary processing for edge cases
  if (typeof callback !== "function" || this.size < 1) {
    return [];
  }
  limit = limit ? Math.min(limit, this.size) : this.size;

  // Prepare the results container to hold up to the results limit
  var resultSize = 0;
  var result = new Array(limit);

  // Prepare a temporary array to hold items we'll traverse through and need to keep
  var tmpSize = 0;
  var tmp = new Array(this.size);

  while (resultSize < limit && !this.isEmpty()) {
    // Dequeue items into either the results or our temporary array
    var item = this.poll();
    if (callback(item)) {
      result[resultSize++] = item;
    } else {
      tmp[tmpSize++] = item;
    }
  }
  // Update the result array with the exact number of results
  result.length = resultSize;

  // Re-add all the items we can keep
  var i = 0;
  while (i < tmpSize) {
      const elem = tmp[i++];
      this.add(elem.value, elem.obj);
  }

  return result;
};

// Look at the top of the queue (one of the smallest elements) without removing it
// executes in constant time
//
// Calling peek on an empty priority queue returns
// the "undefined" value.
// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined
//
FastPriorityQueue.prototype.peek = function() {
  if (this.size == 0) return undefined;
  return this.array[0];
};

// remove the element on top of the heap (one of the smallest elements)
// runs in logarithmic time
//
// If the priority queue is empty, the function returns the
// "undefined" value.
// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined
//
// For long-running and large priority queues, or priority queues
// storing large objects, you may  want to call the trim function
// at strategic times to recover allocated memory.
FastPriorityQueue.prototype.poll = function() {
  if (this.size == 0) return undefined;
  var ans = this.array[0];

  if (this.size > 1) {
    this.array[0] = this.array[--this.size];
    this._percolateDown(0);
  } else {
    this.size -= 1;
  }
  return ans;
};

// This function adds the provided value to the heap, while removing
// and returning one of the smallest elements (like poll). The size of the queue
// thus remains unchanged.
FastPriorityQueue.prototype.replaceTop = function(myval) {
  if (this.size == 0) return undefined;
  var ans = this.array[0];
  this.array[0] = myval;
  this._percolateDown(0);
  return ans;
};

// recover unused memory (for long-running priority queues)
FastPriorityQueue.prototype.trim = function() {
  this.array = this.array.slice(0, this.size);
};

// Check whether the heap is empty
FastPriorityQueue.prototype.isEmpty = function() {
  return this.size === 0;
};

FastPriorityQueue.prototype.forEach = function(callback) {
  if (this.isEmpty() || typeof callback != 'function') return;
  var i = 0;
  var fpq = this.clone();
  let isRunning = true;

  while (!fpq.isEmpty() && isRunning) {
    isRunning = callback(fpq.poll(), i++);
  }
};

// return the k 'smallest' elements of the queue as an array,
// runs in O(k log k) time, the elements are not removed
// from the priority queue.
FastPriorityQueue.prototype.kSmallest = function(k) {
  if ((this.size == 0) || (k<=0)) return [];
  k = Math.min(this.size, k);
  const newSize = Math.min(this.size, (2 ** (k - 1)) + 1);
  if (newSize < 2) { return [this.peek()] }

  const fpq = new FastPriorityQueue(this.compare);
  fpq.size = newSize;
  fpq.array = this.array.slice(0, newSize);

  const smallest = new Array(k);
  for (let i = 0; i < k; i++) {
    smallest[i] = fpq.poll();
  }
  return smallest;
}

module.exports = FastPriorityQueue;