class Heap {
    constructor(sort) {
        this._array = [];
        if (!(sort instanceof Function))
            sort = (a, b) => b - a;
        this._sort = sort;
        Object.defineProperty(this, 'length', {
            enumerable: true,
            get: function() { return this._array.length },
        });
    }

    push(node) {
        node = node || {};
        this._array.push(node);
        this._bubble();
    }
    pop() {
        if (this.isEmpty()) return null;
        let top = this.peek();
        let last = this._array.pop();
        if (this.length > 0) {
            this._array[0] = last;
            this._sink();
        }
        return top;
    }
    peek() {
        return this._array[0];
    }
    isEmpty() {
        return this.length === 0;
    }

    _compare(i, j) {
        return this._sort(this._array[i], this._array[j]) > 0;
    }
    _bubble() {
        let i = this.length - 1;
        let j = this._parent(i);
        while (j !== null && this._compare(i, j)) {
            this._swap(i, j);
            i = j;
            j = this._parent(i);
        }
    }
    _sink() {
        let i = 0;
        let lc = this._left(i);
        let rc = this._right(i);
        let next;

        while (lc !== null) {
            next = lc;
            if (rc !== null && this._compare(rc, lc))
                next = rc;
            if (this._compare(next, i)) {
                this._swap(i, next);
                i = next;
                lc = this._left(i);
                rc = this._right(i);
            }
            else return;
        }
    }
    print() {
      var s = '';
      var nodes = 1;
      var values = 0;
      for (var i = 0; i < this.length; i++) {
        s += ' ' + this._array[i].toString();
        values++;
        if (values === nodes) {
          nodes = nodes << 1;
          values = 0;
          s += '\n';
        }
      }
      console.log('\n' + s + '\n');
    };
    _parent(i) {
        let pi = (i - 1)/2 >> 0;
        return pi >= 0 ? pi : null;
    }
    _left(i) {
        let li = i*2 + 1;
        return li < this.length ? li : null;
    }
    _right(i) {
        let ri = i*2 + 2;
        return ri < this.length ? ri : null;
    }
    _swap(i, j) {
        var a = this._array;
        var v = a[i];
        a[i] = a[j];
        a[j] = v;
    }
}