shipshapecode/tether

import { isFunction, isString } from './utils/type-check';

export default {
  position({ top, left }) {
    if (!this.options.shift) {
      return;
    }

    let { shift } = this.options;
    if (isFunction(shift)) {
      shift = shift.call(this, { top, left });
    }

    let shiftTop, shiftLeft;
    if (isString(shift)) {
      shift = shift.split(' ');
      shift[1] = shift[1] || shift[0];

      ([shiftTop, shiftLeft] = shift);

      shiftTop = parseFloat(shiftTop, 10);
      shiftLeft = parseFloat(shiftLeft, 10);
    } else {
      ([shiftTop, shiftLeft] = [shift.top, shift.left]);
    }

    top += shiftTop;
    left += shiftLeft;

    return { top, left };
  }
};