element-ui/src/utils/popper.js

/**
 * @fileOverview Kickass library to create and place poppers near their reference elements.
 * @version {{version}}
 * @license
 * Copyright (c) 2016 Federico Zivolo and contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

//
// Cross module loader
// Supported: Node, AMD, Browser globals
//
;(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as an anonymous module.
        define(factory);
    } else if (typeof module === 'object' && module.exports) {
        // Node. Does not work with strict CommonJS, but
        // only CommonJS-like environments that support module.exports,
        // like Node.
        module.exports = factory();
    } else {
        // Browser globals (root is window)
        root.Popper = factory();
    }
}(this, function () {

    'use strict';

    var root = window;

    // default options
    var DEFAULTS = {
        // placement of the popper
        placement: 'bottom',

        gpuAcceleration: true,

        // shift popper from its origin by the given amount of pixels (can be negative)
        offset: 0,

        // the element which will act as boundary of the popper
        boundariesElement: 'viewport',

        // amount of pixel used to define a minimum distance between the boundaries and the popper
        boundariesPadding: 5,

        // popper will try to prevent overflow following this order,
        // by default, then, it could overflow on the left and on top of the boundariesElement
        preventOverflowOrder: ['left', 'right', 'top', 'bottom'],

        // the behavior used by flip to change the placement of the popper
        flipBehavior: 'flip',

        arrowElement: '[x-arrow]',

        // list of functions used to modify the offsets before they are applied to the popper
        modifiers: [ 'shift', 'offset', 'preventOverflow', 'keepTogether', 'arrow', 'flip', 'applyStyle'],

        modifiersIgnored: [],

        forceAbsolute: false
    };

    /**
     * Create a new Popper.js instance
     * @constructor Popper
     * @param {HTMLElement} reference - The reference element used to position the popper
     * @param {HTMLElement|Object} popper
     *      The HTML element used as popper, or a configuration used to generate the popper.
     * @param {String} [popper.tagName='div'] The tag name of the generated popper.
     * @param {Array} [popper.classNames=['popper']] Array of classes to apply to the generated popper.
     * @param {Array} [popper.attributes] Array of attributes to apply, specify `attr:value` to assign a value to it.
     * @param {HTMLElement|String} [popper.parent=window.document.body] The parent element, given as HTMLElement or as query string.
     * @param {String} [popper.content=''] The content of the popper, it can be text, html, or node; if it is not text, set `contentType` to `html` or `node`.
     * @param {String} [popper.contentType='text'] If `html`, the `content` will be parsed as HTML. If `node`, it will be appended as-is.
     * @param {String} [popper.arrowTagName='div'] Same as `popper.tagName` but for the arrow element.
     * @param {Array} [popper.arrowClassNames='popper__arrow'] Same as `popper.classNames` but for the arrow element.
     * @param {String} [popper.arrowAttributes=['x-arrow']] Same as `popper.attributes` but for the arrow element.
     * @param {Object} options
     * @param {String} [options.placement=bottom]
     *      Placement of the popper accepted values: `top(-start, -end), right(-start, -end), bottom(-start, -right),
     *      left(-start, -end)`
     *
     * @param {HTMLElement|String} [options.arrowElement='[x-arrow]']
     *      The DOM Node used as arrow for the popper, or a CSS selector used to get the DOM node. It must be child of
     *      its parent Popper. Popper.js will apply to the given element the style required to align the arrow with its
     *      reference element.
     *      By default, it will look for a child node of the popper with the `x-arrow` attribute.
     *
     * @param {Boolean} [options.gpuAcceleration=true]
     *      When this property is set to true, the popper position will be applied using CSS3 translate3d, allowing the
     *      browser to use the GPU to accelerate the rendering.
     *      If set to false, the popper will be placed using `top` and `left` properties, not using the GPU.
     *
     * @param {Number} [options.offset=0]
     *      Amount of pixels the popper will be shifted (can be negative).
     *
     * @param {String|Element} [options.boundariesElement='viewport']
     *      The element which will define the boundaries of the popper position, the popper will never be placed outside
     *      of the defined boundaries (except if `keepTogether` is enabled)
     *
     * @param {Number} [options.boundariesPadding=5]
     *      Additional padding for the boundaries
     *
     * @param {Array} [options.preventOverflowOrder=['left', 'right', 'top', 'bottom']]
     *      Order used when Popper.js tries to avoid overflows from the boundaries, they will be checked in order,
     *      this means that the last ones will never overflow
     *
     * @param {String|Array} [options.flipBehavior='flip']
     *      The behavior used by the `flip` modifier to change the placement of the popper when the latter is trying to
     *      overlap its reference element. Defining `flip` as value, the placement will be flipped on
     *      its axis (`right - left`, `top - bottom`).
     *      You can even pass an array of placements (eg: `['right', 'left', 'top']` ) to manually specify
     *      how alter the placement when a flip is needed. (eg. in the above example, it would first flip from right to left,
     *      then, if even in its new placement, the popper is overlapping its reference element, it will be moved to top)
     *
     * @param {Array} [options.modifiers=[ 'shift', 'offset', 'preventOverflow', 'keepTogether', 'arrow', 'flip', 'applyStyle']]
     *      List of functions used to modify the data before they are applied to the popper, add your custom functions
     *      to this array to edit the offsets and placement.
     *      The function should reflect the @params and @returns of preventOverflow
     *
     * @param {Array} [options.modifiersIgnored=[]]
     *      Put here any built-in modifier name you want to exclude from the modifiers list
     *      The function should reflect the @params and @returns of preventOverflow
     *
     * @param {Boolean} [options.removeOnDestroy=false]
     *      Set to true if you want to automatically remove the popper when you call the `destroy` method.
     */
    function Popper(reference, popper, options) {
        this._reference = reference.jquery ? reference[0] : reference;
        this.state = {};

        // if the popper variable is a configuration object, parse it to generate an HTMLElement
        // generate a default popper if is not defined
        var isNotDefined = typeof popper === 'undefined' || popper === null;
        var isConfig = popper && Object.prototype.toString.call(popper) === '[object Object]';
        if (isNotDefined || isConfig) {
            this._popper = this.parse(isConfig ? popper : {});
        }
        // otherwise, use the given HTMLElement as popper
        else {
            this._popper = popper.jquery ? popper[0] : popper;
        }

        // with {} we create a new object with the options inside it
        this._options = Object.assign({}, DEFAULTS, options);

        // refactoring modifiers' list
        this._options.modifiers = this._options.modifiers.map(function(modifier){
            // remove ignored modifiers
            if (this._options.modifiersIgnored.indexOf(modifier) !== -1) return;

            // set the x-placement attribute before everything else because it could be used to add margins to the popper
            // margins needs to be calculated to get the correct popper offsets
            if (modifier === 'applyStyle') {
                this._popper.setAttribute('x-placement', this._options.placement);
            }

            // return predefined modifier identified by string or keep the custom one
            return this.modifiers[modifier] || modifier;
        }.bind(this));

        // make sure to apply the popper position before any computation
        this.state.position = this._getPosition(this._popper, this._reference);
        setStyle(this._popper, { position: this.state.position});

        // fire the first update to position the popper in the right place
        this.update();

        // setup event listeners, they will take care of update the position in specific situations
        this._setupEventListeners();
        return this;
    }


    //
    // Methods
    //
    /**
     * Destroy the popper
     * @method
     * @memberof Popper
     */
    Popper.prototype.destroy = function() {
        this._popper.removeAttribute('x-placement');
        this._popper.style.left = '';
        this._popper.style.position = '';
        this._popper.style.top = '';
        this._popper.style[getSupportedPropertyName('transform')] = '';
        this._removeEventListeners();

        // remove the popper if user explicity asked for the deletion on destroy
        if (this._options.removeOnDestroy) {
            this._popper.remove();
        }
        return this;
    };

    /**
     * Updates the position of the popper, computing the new offsets and applying the new style
     * @method
     * @memberof Popper
     */
    Popper.prototype.update = function() {
        var data = { instance: this, styles: {} };

        // store placement inside the data object, modifiers will be able to edit `placement` if needed
        // and refer to _originalPlacement to know the original value
        data.placement = this._options.placement;
        data._originalPlacement = this._options.placement;

        // compute the popper and reference offsets and put them inside data.offsets
        data.offsets = this._getOffsets(this._popper, this._reference, data.placement);

        // get boundaries
        data.boundaries = this._getBoundaries(data, this._options.boundariesPadding, this._options.boundariesElement);

        data = this.runModifiers(data, this._options.modifiers);

        if (typeof this.state.updateCallback === 'function') {
            this.state.updateCallback(data);
        }

    };

    /**
     * If a function is passed, it will be executed after the initialization of popper with as first argument the Popper instance.
     * @method
     * @memberof Popper
     * @param {Function} callback
     */
    Popper.prototype.onCreate = function(callback) {
        // the createCallbacks return as first argument the popper instance
        callback(this);
        return this;
    };

    /**
     * If a function is passed, it will be executed after each update of popper with as first argument the set of coordinates and informations
     * used to style popper and its arrow.
     * NOTE: it doesn't get fired on the first call of the `Popper.update()` method inside the `Popper` constructor!
     * @method
     * @memberof Popper
     * @param {Function} callback
     */
    Popper.prototype.onUpdate = function(callback) {
        this.state.updateCallback = callback;
        return this;
    };

    /**
     * Helper used to generate poppers from a configuration file
     * @method
     * @memberof Popper
     * @param config {Object} configuration
     * @returns {HTMLElement} popper
     */
    Popper.prototype.parse = function(config) {
        var defaultConfig = {
            tagName: 'div',
            classNames: [ 'popper' ],
            attributes: [],
            parent: root.document.body,
            content: '',
            contentType: 'text',
            arrowTagName: 'div',
            arrowClassNames: [ 'popper__arrow' ],
            arrowAttributes: [ 'x-arrow']
        };
        config = Object.assign({}, defaultConfig, config);

        var d = root.document;

        var popper = d.createElement(config.tagName);
        addClassNames(popper, config.classNames);
        addAttributes(popper, config.attributes);
        if (config.contentType === 'node') {
            popper.appendChild(config.content.jquery ? config.content[0] : config.content);
        }else if (config.contentType === 'html') {
            popper.innerHTML = config.content;
        } else {
            popper.textContent = config.content;
        }

        if (config.arrowTagName) {
            var arrow = d.createElement(config.arrowTagName);
            addClassNames(arrow, config.arrowClassNames);
            addAttributes(arrow, config.arrowAttributes);
            popper.appendChild(arrow);
        }

        var parent = config.parent.jquery ? config.parent[0] : config.parent;

        // if the given parent is a string, use it to match an element
        // if more than one element is matched, the first one will be used as parent
        // if no elements are matched, the script will throw an error
        if (typeof parent === 'string') {
            parent = d.querySelectorAll(config.parent);
            if (parent.length > 1) {
                console.warn('WARNING: the given `parent` query(' + config.parent + ') matched more than one element, the first one will be used');
            }
            if (parent.length === 0) {
                throw 'ERROR: the given `parent` doesn\'t exists!';
            }
            parent = parent[0];
        }
        // if the given parent is a DOM nodes list or an array of nodes with more than one element,
        // the first one will be used as parent
        if (parent.length > 1 && parent instanceof Element === false) {
            console.warn('WARNING: you have passed as parent a list of elements, the first one will be used');
            parent = parent[0];
        }

        // append the generated popper to its parent
        parent.appendChild(popper);

        return popper;

        /**
         * Adds class names to the given element
         * @function
         * @ignore
         * @param {HTMLElement} target
         * @param {Array} classes
         */
        function addClassNames(element, classNames) {
            classNames.forEach(function(className) {
                element.classList.add(className);
            });
        }

        /**
         * Adds attributes to the given element
         * @function
         * @ignore
         * @param {HTMLElement} target
         * @param {Array} attributes
         * @example
         * addAttributes(element, [ 'data-info:foobar' ]);
         */
        function addAttributes(element, attributes) {
            attributes.forEach(function(attribute) {
                element.setAttribute(attribute.split(':')[0], attribute.split(':')[1] || '');
            });
        }

    };

    /**
     * Helper used to get the position which will be applied to the popper
     * @method
     * @memberof Popper
     * @param config {HTMLElement} popper element
     * @param reference {HTMLElement} reference element
     * @returns {String} position
     */
    Popper.prototype._getPosition = function(popper, reference) {
        var container = getOffsetParent(reference);

        if (this._options.forceAbsolute) {
            return 'absolute';
        }

        // Decide if the popper will be fixed
        // If the reference element is inside a fixed context, the popper will be fixed as well to allow them to scroll together
        var isParentFixed = isFixed(reference, container);
        return isParentFixed ? 'fixed' : 'absolute';
    };

    /**
     * Get offsets to the popper
     * @method
     * @memberof Popper
     * @access private
     * @param {Element} popper - the popper element
     * @param {Element} reference - the reference element (the popper will be relative to this)
     * @returns {Object} An object containing the offsets which will be applied to the popper
     */
    Popper.prototype._getOffsets = function(popper, reference, placement) {
        placement = placement.split('-')[0];
        var popperOffsets = {};

        popperOffsets.position = this.state.position;
        var isParentFixed = popperOffsets.position === 'fixed';

        //
        // Get reference element position
        //
        var referenceOffsets = getOffsetRectRelativeToCustomParent(reference, getOffsetParent(popper), isParentFixed);

        //
        // Get popper sizes
        //
        var popperRect = getOuterSizes(popper);

        //
        // Compute offsets of popper
        //

        // depending by the popper placement we have to compute its offsets slightly differently
        if (['right', 'left'].indexOf(placement) !== -1) {
            popperOffsets.top = referenceOffsets.top + referenceOffsets.height / 2 - popperRect.height / 2;
            if (placement === 'left') {
                popperOffsets.left = referenceOffsets.left - popperRect.width;
            } else {
                popperOffsets.left = referenceOffsets.right;
            }
        } else {
            popperOffsets.left = referenceOffsets.left + referenceOffsets.width / 2 - popperRect.width / 2;
            if (placement === 'top') {
                popperOffsets.top = referenceOffsets.top - popperRect.height;
            } else {
                popperOffsets.top = referenceOffsets.bottom;
            }
        }

        // Add width and height to our offsets object
        popperOffsets.width   = popperRect.width;
        popperOffsets.height  = popperRect.height;


        return {
            popper: popperOffsets,
            reference: referenceOffsets
        };
    };


    /**
     * Setup needed event listeners used to update the popper position
     * @method
     * @memberof Popper
     * @access private
     */
    Popper.prototype._setupEventListeners = function() {
        // NOTE: 1 DOM access here
        this.state.updateBound = this.update.bind(this);
        root.addEventListener('resize', this.state.updateBound);
        // if the boundariesElement is window we don't need to listen for the scroll event
        if (this._options.boundariesElement !== 'window') {
            var target = getScrollParent(this._reference);
            // here it could be both `body` or `documentElement` thanks to Firefox, we then check both
            if (target === root.document.body || target === root.document.documentElement) {
                target = root;
            }
            target.addEventListener('scroll', this.state.updateBound);
        }
    };

    /**
     * Remove event listeners used to update the popper position
     * @method
     * @memberof Popper
     * @access private
     */
    Popper.prototype._removeEventListeners = function() {
        // NOTE: 1 DOM access here
        root.removeEventListener('resize', this.state.updateBound);
        if (this._options.boundariesElement !== 'window') {
            var target = getScrollParent(this._reference);
            // here it could be both `body` or `documentElement` thanks to Firefox, we then check both
            if (target === root.document.body || target === root.document.documentElement) {
                target = root;
            }
            target.removeEventListener('scroll', this.state.updateBound);
        }
        this.state.updateBound = null;
    };

    /**
     * Computed the boundaries limits and return them
     * @method
     * @memberof Popper
     * @access private
     * @param {Object} data - Object containing the property "offsets" generated by `_getOffsets`
     * @param {Number} padding - Boundaries padding
     * @param {Element} boundariesElement - Element used to define the boundaries
     * @returns {Object} Coordinates of the boundaries
     */
    Popper.prototype._getBoundaries = function(data, padding, boundariesElement) {
        // NOTE: 1 DOM access here
        var boundaries = {};
        var width, height;
        if (boundariesElement === 'window') {
            var body = root.document.body,
                html = root.document.documentElement;

            height = Math.max( body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight );
            width = Math.max( body.scrollWidth, body.offsetWidth, html.clientWidth, html.scrollWidth, html.offsetWidth );

            boundaries = {
                top: 0,
                right: width,
                bottom: height,
                left: 0
            };
        } else if (boundariesElement === 'viewport') {
            var offsetParent = getOffsetParent(this._popper);
            var scrollParent = getScrollParent(this._popper);
            var offsetParentRect = getOffsetRect(offsetParent);

            // if the popper is fixed we don't have to substract scrolling from the boundaries
            var scrollTop = data.offsets.popper.position === 'fixed' ? 0 : scrollParent.scrollTop;
            var scrollLeft = data.offsets.popper.position === 'fixed' ? 0 : scrollParent.scrollLeft;

            boundaries = {
                top: 0 - (offsetParentRect.top - scrollTop),
                right: root.document.documentElement.clientWidth - (offsetParentRect.left - scrollLeft),
                bottom: root.document.documentElement.clientHeight - (offsetParentRect.top - scrollTop),
                left: 0 - (offsetParentRect.left - scrollLeft)
            };
        } else {
            if (getOffsetParent(this._popper) === boundariesElement) {
                boundaries = {
                    top: 0,
                    left: 0,
                    right: boundariesElement.clientWidth,
                    bottom: boundariesElement.clientHeight
                };
            } else {
                boundaries = getOffsetRect(boundariesElement);
            }
        }
        boundaries.left += padding;
        boundaries.right -= padding;
        boundaries.top = boundaries.top + padding;
        boundaries.bottom = boundaries.bottom - padding;
        return boundaries;
    };


    /**
     * Loop trough the list of modifiers and run them in order, each of them will then edit the data object
     * @method
     * @memberof Popper
     * @access public
     * @param {Object} data
     * @param {Array} modifiers
     * @param {Function} ends
     */
    Popper.prototype.runModifiers = function(data, modifiers, ends) {
        var modifiersToRun = modifiers.slice();
        if (ends !== undefined) {
            modifiersToRun = this._options.modifiers.slice(0, getArrayKeyIndex(this._options.modifiers, ends));
        }

        modifiersToRun.forEach(function(modifier) {
            if (isFunction(modifier)) {
                data = modifier.call(this, data);
            }
        }.bind(this));

        return data;
    };

    /**
     * Helper used to know if the given modifier depends from another one.
     * @method
     * @memberof Popper
     * @param {String} requesting - name of requesting modifier
     * @param {String} requested - name of requested modifier
     * @returns {Boolean}
     */
    Popper.prototype.isModifierRequired = function(requesting, requested) {
        var index = getArrayKeyIndex(this._options.modifiers, requesting);
        return !!this._options.modifiers.slice(0, index).filter(function(modifier) {
            return modifier === requested;
        }).length;
    };

    //
    // Modifiers
    //

    /**
     * Modifiers list
     * @namespace Popper.modifiers
     * @memberof Popper
     * @type {Object}
     */
    Popper.prototype.modifiers = {};

    /**
     * Apply the computed styles to the popper element
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by `update` method
     * @returns {Object} The same data object
     */
    Popper.prototype.modifiers.applyStyle = function(data) {
        // apply the final offsets to the popper
        // NOTE: 1 DOM access here
        var styles = {
            position: data.offsets.popper.position
        };

        // round top and left to avoid blurry text
        var left = Math.round(data.offsets.popper.left);
        var top = Math.round(data.offsets.popper.top);

        // if gpuAcceleration is set to true and transform is supported, we use `translate3d` to apply the position to the popper
        // we automatically use the supported prefixed version if needed
        var prefixedProperty;
        if (this._options.gpuAcceleration && (prefixedProperty = getSupportedPropertyName('transform'))) {
            styles[prefixedProperty] = 'translate3d(' + left + 'px, ' + top + 'px, 0)';
            styles.top = 0;
            styles.left = 0;
        }
        // othwerise, we use the standard `left` and `top` properties
        else {
            styles.left =left;
            styles.top = top;
        }

        // any property present in `data.styles` will be applied to the popper,
        // in this way we can make the 3rd party modifiers add custom styles to it
        // Be aware, modifiers could override the properties defined in the previous
        // lines of this modifier!
        Object.assign(styles, data.styles);

        setStyle(this._popper, styles);

        // set an attribute which will be useful to style the tooltip (use it to properly position its arrow)
        // NOTE: 1 DOM access here
        this._popper.setAttribute('x-placement', data.placement);

        // if the arrow modifier is required and the arrow style has been computed, apply the arrow style
        if (this.isModifierRequired(this.modifiers.applyStyle, this.modifiers.arrow) && data.offsets.arrow) {
            setStyle(data.arrowElement, data.offsets.arrow);
        }

        return data;
    };

    /**
     * Modifier used to shift the popper on the start or end of its reference element side
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by `update` method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.shift = function(data) {
        var placement = data.placement;
        var basePlacement = placement.split('-')[0];
        var shiftVariation = placement.split('-')[1];

        // if shift shiftVariation is specified, run the modifier
        if (shiftVariation) {
            var reference = data.offsets.reference;
            var popper = getPopperClientRect(data.offsets.popper);

            var shiftOffsets = {
                y: {
                    start:  { top: reference.top },
                    end:    { top: reference.top + reference.height - popper.height }
                },
                x: {
                    start:  { left: reference.left },
                    end:    { left: reference.left + reference.width - popper.width }
                }
            };

            var axis = ['bottom', 'top'].indexOf(basePlacement) !== -1 ? 'x' : 'y';

            data.offsets.popper = Object.assign(popper, shiftOffsets[axis][shiftVariation]);
        }

        return data;
    };


    /**
     * Modifier used to make sure the popper does not overflows from it's boundaries
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by `update` method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.preventOverflow = function(data) {
        var order = this._options.preventOverflowOrder;
        var popper = getPopperClientRect(data.offsets.popper);

        var check = {
            left: function() {
                var left = popper.left;
                if (popper.left < data.boundaries.left) {
                    left = Math.max(popper.left, data.boundaries.left);
                }
                return { left: left };
            },
            right: function() {
                var left = popper.left;
                if (popper.right > data.boundaries.right) {
                    left = Math.min(popper.left, data.boundaries.right - popper.width);
                }
                return { left: left };
            },
            top: function() {
                var top = popper.top;
                if (popper.top < data.boundaries.top) {
                    top = Math.max(popper.top, data.boundaries.top);
                }
                return { top: top };
            },
            bottom: function() {
                var top = popper.top;
                if (popper.bottom > data.boundaries.bottom) {
                    top = Math.min(popper.top, data.boundaries.bottom - popper.height);
                }
                return { top: top };
            }
        };

        order.forEach(function(direction) {
            data.offsets.popper = Object.assign(popper, check[direction]());
        });

        return data;
    };

    /**
     * Modifier used to make sure the popper is always near its reference
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by _update method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.keepTogether = function(data) {
        var popper  = getPopperClientRect(data.offsets.popper);
        var reference = data.offsets.reference;
        var f = Math.floor;

        if (popper.right < f(reference.left)) {
            data.offsets.popper.left = f(reference.left) - popper.width;
        }
        if (popper.left > f(reference.right)) {
            data.offsets.popper.left = f(reference.right);
        }
        if (popper.bottom < f(reference.top)) {
            data.offsets.popper.top = f(reference.top) - popper.height;
        }
        if (popper.top > f(reference.bottom)) {
            data.offsets.popper.top = f(reference.bottom);
        }

        return data;
    };

    /**
     * Modifier used to flip the placement of the popper when the latter is starting overlapping its reference element.
     * Requires the `preventOverflow` modifier before it in order to work.
     * **NOTE:** This modifier will run all its previous modifiers everytime it tries to flip the popper!
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by _update method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.flip = function(data) {
        // check if preventOverflow is in the list of modifiers before the flip modifier.
        // otherwise flip would not work as expected.
        if (!this.isModifierRequired(this.modifiers.flip, this.modifiers.preventOverflow)) {
            console.warn('WARNING: preventOverflow modifier is required by flip modifier in order to work, be sure to include it before flip!');
            return data;
        }

        if (data.flipped && data.placement === data._originalPlacement) {
            // seems like flip is trying to loop, probably there's not enough space on any of the flippable sides
            return data;
        }

        var placement = data.placement.split('-')[0];
        var placementOpposite = getOppositePlacement(placement);
        var variation = data.placement.split('-')[1] || '';

        var flipOrder = [];
        if(this._options.flipBehavior === 'flip') {
            flipOrder = [
                placement,
                placementOpposite
            ];
        } else {
            flipOrder = this._options.flipBehavior;
        }

        flipOrder.forEach(function(step, index) {
            if (placement !== step || flipOrder.length === index + 1) {
                return;
            }

            placement = data.placement.split('-')[0];
            placementOpposite = getOppositePlacement(placement);

            var popperOffsets = getPopperClientRect(data.offsets.popper);

            // this boolean is used to distinguish right and bottom from top and left
            // they need different computations to get flipped
            var a = ['right', 'bottom'].indexOf(placement) !== -1;

            // using Math.floor because the reference offsets may contain decimals we are not going to consider here
            if (
                a && Math.floor(data.offsets.reference[placement]) > Math.floor(popperOffsets[placementOpposite]) ||
                !a && Math.floor(data.offsets.reference[placement]) < Math.floor(popperOffsets[placementOpposite])
            ) {
                // we'll use this boolean to detect any flip loop
                data.flipped = true;
                data.placement = flipOrder[index + 1];
                if (variation) {
                    data.placement += '-' + variation;
                }
                data.offsets.popper = this._getOffsets(this._popper, this._reference, data.placement).popper;

                data = this.runModifiers(data, this._options.modifiers, this._flip);
            }
        }.bind(this));
        return data;
    };

    /**
     * Modifier used to add an offset to the popper, useful if you more granularity positioning your popper.
     * The offsets will shift the popper on the side of its reference element.
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by _update method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.offset = function(data) {
        var offset = this._options.offset;
        var popper  = data.offsets.popper;

        if (data.placement.indexOf('left') !== -1) {
            popper.top -= offset;
        }
        else if (data.placement.indexOf('right') !== -1) {
            popper.top += offset;
        }
        else if (data.placement.indexOf('top') !== -1) {
            popper.left -= offset;
        }
        else if (data.placement.indexOf('bottom') !== -1) {
            popper.left += offset;
        }
        return data;
    };

    /**
     * Modifier used to move the arrows on the edge of the popper to make sure them are always between the popper and the reference element
     * It will use the CSS outer size of the arrow element to know how many pixels of conjuction are needed
     * @method
     * @memberof Popper.modifiers
     * @argument {Object} data - The data object generated by _update method
     * @returns {Object} The data object, properly modified
     */
    Popper.prototype.modifiers.arrow = function(data) {
        var arrow  = this._options.arrowElement;

        // if the arrowElement is a string, suppose it's a CSS selector
        if (typeof arrow === 'string') {
            arrow = this._popper.querySelector(arrow);
        }

        // if arrow element is not found, don't run the modifier
        if (!arrow) {
            return data;
        }

        // the arrow element must be child of its popper
        if (!this._popper.contains(arrow)) {
            console.warn('WARNING: `arrowElement` must be child of its popper element!');
            return data;
        }

        // arrow depends on keepTogether in order to work
        if (!this.isModifierRequired(this.modifiers.arrow, this.modifiers.keepTogether)) {
            console.warn('WARNING: keepTogether modifier is required by arrow modifier in order to work, be sure to include it before arrow!');
            return data;
        }

        var arrowStyle  = {};
        var placement   = data.placement.split('-')[0];
        var popper      = getPopperClientRect(data.offsets.popper);
        var reference   = data.offsets.reference;
        var isVertical  = ['left', 'right'].indexOf(placement) !== -1;

        var len         = isVertical ? 'height' : 'width';
        var side        = isVertical ? 'top' : 'left';
        var altSide     = isVertical ? 'left' : 'top';
        var opSide      = isVertical ? 'bottom' : 'right';
        var arrowSize   = getOuterSizes(arrow)[len];

        //
        // extends keepTogether behavior making sure the popper and its reference have enough pixels in conjuction
        //

        // top/left side
        if (reference[opSide] - arrowSize < popper[side]) {
            data.offsets.popper[side] -= popper[side] - (reference[opSide] - arrowSize);
        }
        // bottom/right side
        if (reference[side] + arrowSize > popper[opSide]) {
            data.offsets.popper[side] += (reference[side] + arrowSize) - popper[opSide];
        }

        // compute center of the popper
        var center = reference[side] + (reference[len] / 2) - (arrowSize / 2);

        var sideValue = center - popper[side];

        // prevent arrow from being placed not contiguously to its popper
        sideValue = Math.max(Math.min(popper[len] - arrowSize, sideValue), 0);
        arrowStyle[side] = sideValue;
        arrowStyle[altSide] = ''; // make sure to remove any old style from the arrow

        data.offsets.arrow = arrowStyle;
        data.arrowElement = arrow;

        return data;
    };


    //
    // Helpers
    //

    /**
     * Get the outer sizes of the given element (offset size + margins)
     * @function
     * @ignore
     * @argument {Element} element
     * @returns {Object} object containing width and height properties
     */
    function getOuterSizes(element) {
        // NOTE: 1 DOM access here
        var _display = element.style.display, _visibility = element.style.visibility;
        element.style.display = 'block'; element.style.visibility = 'hidden';
        var calcWidthToForceRepaint = element.offsetWidth;

        // original method
        var styles = root.getComputedStyle(element);
        var x = parseFloat(styles.marginTop) + parseFloat(styles.marginBottom);
        var y = parseFloat(styles.marginLeft) + parseFloat(styles.marginRight);
        var result = { width: element.offsetWidth + y, height: element.offsetHeight + x };

        // reset element styles
        element.style.display = _display; element.style.visibility = _visibility;
        return result;
    }

    /**
     * Get the opposite placement of the given one/
     * @function
     * @ignore
     * @argument {String} placement
     * @returns {String} flipped placement
     */
    function getOppositePlacement(placement) {
        var hash = {left: 'right', right: 'left', bottom: 'top', top: 'bottom' };
        return placement.replace(/left|right|bottom|top/g, function(matched){
            return hash[matched];
        });
    }

    /**
     * Given the popper offsets, generate an output similar to getBoundingClientRect
     * @function
     * @ignore
     * @argument {Object} popperOffsets
     * @returns {Object} ClientRect like output
     */
    function getPopperClientRect(popperOffsets) {
        var offsets = Object.assign({}, popperOffsets);
        offsets.right = offsets.left + offsets.width;
        offsets.bottom = offsets.top + offsets.height;
        return offsets;
    }

    /**
     * Given an array and the key to find, returns its index
     * @function
     * @ignore
     * @argument {Array} arr
     * @argument keyToFind
     * @returns index or null
     */
    function getArrayKeyIndex(arr, keyToFind) {
        var i = 0, key;
        for (key in arr) {
            if (arr[key] === keyToFind) {
                return i;
            }
            i++;
        }
        return null;
    }

    /**
     * Get CSS computed property of the given element
     * @function
     * @ignore
     * @argument {Eement} element
     * @argument {String} property
     */
    function getStyleComputedProperty(element, property) {
        // NOTE: 1 DOM access here
        var css = root.getComputedStyle(element, null);
        return css[property];
    }

    /**
     * Returns the offset parent of the given element
     * @function
     * @ignore
     * @argument {Element} element
     * @returns {Element} offset parent
     */
    function getOffsetParent(element) {
        // NOTE: 1 DOM access here
        var offsetParent = element.offsetParent;
        return offsetParent === root.document.body || !offsetParent ? root.document.documentElement : offsetParent;
    }

    /**
     * Returns the scrolling parent of the given element
     * @function
     * @ignore
     * @argument {Element} element
     * @returns {Element} offset parent
     */
    function getScrollParent(element) {
        var parent = element.parentNode;

        if (!parent) {
            return element;
        }

        if (parent === root.document) {
            // Firefox puts the scrollTOp value on `documentElement` instead of `body`, we then check which of them is
            // greater than 0 and return the proper element
            if (root.document.body.scrollTop) {
                return root.document.body;
            } else {
                return root.document.documentElement;
            }
        }

        // Firefox want us to check `-x` and `-y` variations as well
        if (
            ['scroll', 'auto'].indexOf(getStyleComputedProperty(parent, 'overflow')) !== -1 ||
            ['scroll', 'auto'].indexOf(getStyleComputedProperty(parent, 'overflow-x')) !== -1 ||
            ['scroll', 'auto'].indexOf(getStyleComputedProperty(parent, 'overflow-y')) !== -1
        ) {
            // If the detected scrollParent is body, we perform an additional check on its parentNode
            // in this way we'll get body if the browser is Chrome-ish, or documentElement otherwise
            // fixes issue #65
            return parent;
        }
        return getScrollParent(element.parentNode);
    }

    /**
     * Check if the given element is fixed or is inside a fixed parent
     * @function
     * @ignore
     * @argument {Element} element
     * @argument {Element} customContainer
     * @returns {Boolean} answer to "isFixed?"
     */
    function isFixed(element) {
        if (element === root.document.body) {
            return false;
        }
        if (getStyleComputedProperty(element, 'position') === 'fixed') {
            return true;
        }
        return element.parentNode ? isFixed(element.parentNode) : element;
    }

    /**
     * Set the style to the given popper
     * @function
     * @ignore
     * @argument {Element} element - Element to apply the style to
     * @argument {Object} styles - Object with a list of properties and values which will be applied to the element
     */
    function setStyle(element, styles) {
        function is_numeric(n) {
            return (n !== '' && !isNaN(parseFloat(n)) && isFinite(n));
        }
        Object.keys(styles).forEach(function(prop) {
            var unit = '';
            // add unit if the value is numeric and is one of the following
            if (['width', 'height', 'top', 'right', 'bottom', 'left'].indexOf(prop) !== -1 && is_numeric(styles[prop])) {
                unit = 'px';
            }
            element.style[prop] = styles[prop] + unit;
        });
    }

    /**
     * Check if the given variable is a function
     * @function
     * @ignore
     * @argument {*} functionToCheck - variable to check
     * @returns {Boolean} answer to: is a function?
     */
    function isFunction(functionToCheck) {
        var getType = {};
        return functionToCheck && getType.toString.call(functionToCheck) === '[object Function]';
    }

    /**
     * Get the position of the given element, relative to its offset parent
     * @function
     * @ignore
     * @param {Element} element
     * @return {Object} position - Coordinates of the element and its `scrollTop`
     */
    function getOffsetRect(element) {
        var elementRect = {
            width: element.offsetWidth,
            height: element.offsetHeight,
            left: element.offsetLeft,
            top: element.offsetTop
        };

        elementRect.right = elementRect.left + elementRect.width;
        elementRect.bottom = elementRect.top + elementRect.height;

        // position
        return elementRect;
    }

    /**
     * Get bounding client rect of given element
     * @function
     * @ignore
     * @param {HTMLElement} element
     * @return {Object} client rect
     */
    function getBoundingClientRect(element) {
        var rect = element.getBoundingClientRect();

        // whether the IE version is lower than 11
        var isIE = navigator.userAgent.indexOf("MSIE") != -1;

        // fix ie document bounding top always 0 bug
        var rectTop = isIE && element.tagName === 'HTML'
            ? -element.scrollTop
            : rect.top;

        return {
            left: rect.left,
            top: rectTop,
            right: rect.right,
            bottom: rect.bottom,
            width: rect.right - rect.left,
            height: rect.bottom - rectTop
        };
    }

    /**
     * Given an element and one of its parents, return the offset
     * @function
     * @ignore
     * @param {HTMLElement} element
     * @param {HTMLElement} parent
     * @return {Object} rect
     */
    function getOffsetRectRelativeToCustomParent(element, parent, fixed) {
        var elementRect = getBoundingClientRect(element);
        var parentRect = getBoundingClientRect(parent);

        if (fixed) {
            var scrollParent = getScrollParent(parent);
            parentRect.top += scrollParent.scrollTop;
            parentRect.bottom += scrollParent.scrollTop;
            parentRect.left += scrollParent.scrollLeft;
            parentRect.right += scrollParent.scrollLeft;
        }

        var rect = {
            top: elementRect.top - parentRect.top ,
            left: elementRect.left - parentRect.left ,
            bottom: (elementRect.top - parentRect.top) + elementRect.height,
            right: (elementRect.left - parentRect.left) + elementRect.width,
            width: elementRect.width,
            height: elementRect.height
        };
        return rect;
    }

    /**
     * Get the prefixed supported property name
     * @function
     * @ignore
     * @argument {String} property (camelCase)
     * @returns {String} prefixed property (camelCase)
     */
    function getSupportedPropertyName(property) {
        var prefixes = ['', 'ms', 'webkit', 'moz', 'o'];

        for (var i = 0; i < prefixes.length; i++) {
            var toCheck = prefixes[i] ? prefixes[i] + property.charAt(0).toUpperCase() + property.slice(1) : property;
            if (typeof root.document.body.style[toCheck] !== 'undefined') {
                return toCheck;
            }
        }
        return null;
    }

    /**
     * The Object.assign() method is used to copy the values of all enumerable own properties from one or more source
     * objects to a target object. It will return the target object.
     * This polyfill doesn't support symbol properties, since ES5 doesn't have symbols anyway
     * Source: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
     * @function
     * @ignore
     */
    if (!Object.assign) {
        Object.defineProperty(Object, 'assign', {
            enumerable: false,
            configurable: true,
            writable: true,
            value: function(target) {
                if (target === undefined || target === null) {
                    throw new TypeError('Cannot convert first argument to object');
                }

                var to = Object(target);
                for (var i = 1; i < arguments.length; i++) {
                    var nextSource = arguments[i];
                    if (nextSource === undefined || nextSource === null) {
                        continue;
                    }
                    nextSource = Object(nextSource);

                    var keysArray = Object.keys(nextSource);
                    for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
                        var nextKey = keysArray[nextIndex];
                        var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
                        if (desc !== undefined && desc.enumerable) {
                            to[nextKey] = nextSource[nextKey];
                        }
                    }
                }
                return to;
            }
        });
    }

    return Popper;
}));