/**
 * Most Visible v1.5.0
 *
 * @author Andy Palmer <andy@andypalmer.me>
 * @license MIT
 */
(function (root, factory) {
  // Universal Module Definition

  /* jshint strict:false */

  /* global define: false, module: false */
  if (typeof define === 'function' && define.amd) {
    define([], function () {
      return factory(root);
    });
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory(root);
  } else {
    root.mostVisible = factory(root);
  }
})(typeof self !== 'undefined' ? self : this, function (window) {
  /* jshint unused: vars */
  'use strict';
  /**
   * MostVisible constructor
   *
   * @param {NodeList|string} elements
   * @param {{}} options
   * @constructor
   */

  function MostVisible(elements, options) {
    if (!(this instanceof MostVisible)) {
      return new MostVisible(elements, options).getMostVisible();
    }

    if (typeof elements === 'string') {
      elements = document.querySelectorAll(elements);
    }

    this.elements = elements;
    this.options = extend({}, MostVisible.defaults, options);
  }
  /**
   * MostVisible default options
   *
   * @namespace
   * @property {{}}      defaults             Default options hash.
   * @property {boolean} defaults.percentage  Whether to calculate visibility as a percentage of height.
   * @property {number}  defaults.offset      An offset to take into account when calculating visibility.
   */

  MostVisible.defaults = {
    percentage: false,
    offset: 0,
  };
  MostVisible.prototype = {
    /**
     * Returns the most visible element from the instance's NodeList.
     *
     * @returns {HTMLElement} Most visible element.
     */
    getMostVisible: function () {
      var _this = this;

      var viewportHeight = document.documentElement.clientHeight;
      return Array.prototype.reduce.call(
        this.elements,
        function (carry, element) {
          var value = _this.getVisibleHeight(element, viewportHeight);

          return value > carry[0] ? [value, element] : carry;
        },
        [0, null]
      )[1];
    },

    /**
     * Returns the visible height of an element.
     *
     * @param {HTMLElement} element Element to check the visibility of.
     * @param {number}      viewportHeight
     * @returns {number}    Visible height of the element in pixels or a percentage of the element's total height.
     */
    getVisibleHeight: function (element, viewportHeight) {
      var rect = element.getBoundingClientRect(),
        rectTopOffset = rect.top - this.options.offset,
        rectBottomOffset = rect.bottom - this.options.offset,
        height = rect.bottom - rect.top,
        visible = {
          top: rectTopOffset >= 0 && rectTopOffset < viewportHeight,
          bottom: rectBottomOffset > 0 && rectBottomOffset < viewportHeight,
        };
      var visiblePx = 0;

      if (visible.top && visible.bottom) {
        // Whole element is visible
        visiblePx = height;
      } else if (visible.top) {
        visiblePx = viewportHeight - rect.top;
      } else if (visible.bottom) {
        visiblePx = rectBottomOffset;
      } else if (height > viewportHeight && rectTopOffset < 0) {
        var absTop = Math.abs(rectTopOffset);

        if (absTop < height) {
          // Part of the element is visible
          visiblePx = height - absTop;
        }
      }

      if (this.options.percentage) {
        return (visiblePx / height) * 100;
      }

      return visiblePx;
    },
  };

  MostVisible.makeJQueryPlugin = function ($) {
    if (!$) {
      return;
    }

    $.fn.mostVisible = function (options) {
      var instance = new MostVisible(this.get(), options);
      return this.filter(instance.getMostVisible());
    };
  }; // Try adding the jQuery plugin to window.jQuery

  MostVisible.makeJQueryPlugin(window.jQuery);
  /**
   * Extends obj by adding the properties of all other objects passed to the function.
   *
   * @param {...{}} obj
   * @returns {{}} The extended object.
   */

  function extend(obj) {
    for (var i = 1; i < arguments.length; i++) {
      for (var key in arguments[i]) {
        obj[key] = arguments[i][key];
      }
    }

    return obj;
  }

  return MostVisible;
});