edx-platform/xmodule/js/src/video/00_iterator.js

(function(define) {
    define(
        'video/00_iterator.js',
        [],
        function() {
            'use strict';

            /**
     * Provides convenient way to work with iterable data.
     * @exports video/00_iterator.js
     * @constructor
     * @param {array} list Array to be iterated.
     */
            var Iterator = function(list) {
                this.list = list;
                this.index = 0;
                this.size = this.list.length;
                this.lastIndex = this.list.length - 1;
            };

            Iterator.prototype = {

                /**
         * Checks validity of provided index for the iterator.
         * @access protected
         * @param {numebr} index
         * @return {boolean}
         */
                _isValid: function(index) {
                    return _.isNumber(index) && index < this.size && index >= 0;
                },

                /**
         * Returns next element.
         * @param {number} [index] Updates current position.
         * @return {any}
         */
                next: function(index) {
                    if (!(this._isValid(index))) {
                        index = this.index;
                    }

                    this.index = (index >= this.lastIndex) ? 0 : index + 1;

                    return this.list[this.index];
                },

                /**
         * Returns previous element.
         * @param {number} [index] Updates current position.
         * @return {any}
         */
                prev: function(index) {
                    if (!(this._isValid(index))) {
                        index = this.index;
                    }

                    this.index = (index < 1) ? this.lastIndex : index - 1;

                    return this.list[this.index];
                },

                /**
         * Returns last element in the list.
         * @return {any}
         */
                last: function() {
                    return this.list[this.lastIndex];
                },

                /**
         * Returns first element in the list.
         * @return {any}
         */
                first: function() {
                    return this.list[0];
                },

                /**
         * Returns `true` if current position is last for the iterator.
         * @return {boolean}
         */
                isEnd: function() {
                    return this.index === this.lastIndex;
                }
            };

            return Iterator;
        });
}(RequireJS.define));