;
(function () {
    function defaultComparator(a, b) {
        return a < b;
    }

    BI.Heap = function (items, comparator) {
        this._items = items || [];
        this._size = this._items.length;
        this._comparator = comparator || defaultComparator;
        this._heapify();
    };

    BI.Heap.prototype = {
        constructor: BI.Heap,
        empty: function () {
            return this._size === 0;
        },

        pop: function () {
            if (this._size === 0) {
                return;
            }

            var elt = this._items[0];

            var lastElt = this._items.pop();
            this._size--;

            if (this._size > 0) {
                this._items[0] = lastElt;
                this._sinkDown(0);
            }

            return elt;
        },

        push: function (item) {
            this._items[this._size++] = item;
            this._bubbleUp(this._size - 1);
        },

        size: function () {
            return this._size;
        },

        peek: function () {
            if (this._size === 0) {
                return;
            }

            return this._items[0];
        },

        _heapify: function () {
            for (var index = Math.floor((this._size + 1) / 2); index >= 0; index--) {
                this._sinkDown(index);
            }
        },

        _bubbleUp: function (index) {
            var elt = this._items[index];
            while (index > 0) {
                var parentIndex = Math.floor((index + 1) / 2) - 1;
                var parentElt = this._items[parentIndex];

                // if parentElt < elt, stop
                if (this._comparator(parentElt, elt)) {
                    return;
                }

                // swap
                this._items[parentIndex] = elt;
                this._items[index] = parentElt;
                index = parentIndex;
            }
        },

        _sinkDown: function (index) {
            var elt = this._items[index];

            while (true) {
                var leftChildIndex = 2 * (index + 1) - 1;
                var rightChildIndex = 2 * (index + 1);
                var swapIndex = -1;

                if (leftChildIndex < this._size) {
                    var leftChild = this._items[leftChildIndex];
                    if (this._comparator(leftChild, elt)) {
                        swapIndex = leftChildIndex;
                    }
                }

                if (rightChildIndex < this._size) {
                    var rightChild = this._items[rightChildIndex];
                    if (this._comparator(rightChild, elt)) {
                        if (swapIndex === -1 ||
                            this._comparator(rightChild, this._items[swapIndex])) {
                            swapIndex = rightChildIndex;
                        }
                    }
                }

                // if we don't have a swap, stop
                if (swapIndex === -1) {
                    return;
                }

                this._items[index] = this._items[swapIndex];
                this._items[swapIndex] = elt;
                index = swapIndex;
            }
        }
    }
})();