/** @module stance/utils */

define('stance/utils',[
    'exports',

    'core/utils/lang/isElement',
    'core/utils/uniqueId',
], function (
    exports,

    isElement,
    uniqueId
) {
    'use strict';

    /**
     * Extracts element from container if applicable.
     *
     * @param {Element-like} obj
     * @returns {?HTMLElement}
     */
    exports.getElement = function (obj) {
        if (isElement(obj))
            return obj;

        return obj && obj.el;
    };

    exports.EL_ID_ATTR = 'data-visibility-id';
    exports.OBJ_ID_PROP = '_visibility_id';

    /**
     * Get or create an id for the element or element container, or return null.
     *
     * @param {Element-like} obj
     * @returns {?number} Id of the associated element / view
     */
    exports.getId = function (obj) {
        // Gets the id (possibly creating it)
        var id = null;

        // TODO: Refactor
        if (isElement(obj)) {
            // Store the id as an element attribute
            id = obj.getAttribute(exports.EL_ID_ATTR) || null;

            if (!id) {
                id = uniqueId();
                obj.setAttribute(exports.EL_ID_ATTR, id);
            }
        } else if (obj) {
            // Store it as a property
            id = obj[exports.OBJ_ID_PROP] || null;

            if (!id)
                id = obj[exports.OBJ_ID_PROP] = uniqueId();
        }
        return id;
    };

    /**
     * Calculate the the percentage of an element visible in
     * the viewport given the scroll position and the element's offset.
     *
     * @param {ViewportPos} pos - Scroll information.
     * @param {FullOffset} offset - Element's full offset information.
     * @returns {Integer} Percent between 0 and 100
     */
    exports.visiblePercent = function (pos, offset) {
        var percent = 0;

        if (!offset)
            return percent;

        var screenTop = pos.top;
        var screenBottom = screenTop + pos.height;

        var bleedsTop = offset.visibleTop < screenTop;
        var bleedsBottom = offset.visibleBottom > screenBottom;

        // If the view bleeds over the top and bottom of the viewport then it
        // is filling the entire viewport, so report 100%. Otherwise, if it
        // bleeds over neither, then it is completely in view, so also report 100%.
        if ((!bleedsTop && !bleedsBottom) || (bleedsTop && bleedsBottom))
            percent = 1;
        // If the view is bleeding off the top, the calculate how much of the bottom of the view is visible.
        else if (bleedsTop)
            percent = (offset.height - (screenTop - offset.visibleTop)) / offset.height;
        // Otherwise, if bleeding off the bottom, then calculate how much of the top of the view is visible.
        else if (bleedsBottom)
            percent = (screenBottom - offset.visibleTop) / offset.height;

        return Math.round(percent * 100);
    };

});

  // https://c.disquscdn.com/next/next-core/core/stance/utils.js