/**
 * @version 1
 * @requires jQuery
 */
(function ($) {
    "use strict";

    /**
     * @param {Number} [required=1] Required size e.g. 1, '!= 1', '>= 5', '< 10'
     * @param {String|Function} [message] Error message
     * @return {jQuery}
     */
    $.fn.required = function (required, message) {
        required = required || 1;
        var size = this.size(), match, expr = '==';
        if ('string' === $.type(required)) {
            match = required.match(/([><!=]*)\s*(\d+)/);
            expr = match[1];
            required = match[2];
        }
        switch (expr) {
            case '==':
                match = (size == required);
                break;
            case '!=':
                match = (size != required);
                break;
            case '>':
                match = (size > required);
                break;
            case '>=':
                match = (size >= required);
                break;
            case '<':
                match = (size < required);
                break;
            case '<=':
                match = (size <= required);
                break;
            default:
                throw new SyntaxError('$.fn.required: Unknown expressions "' + expr + '"');
        }
        if (!match) {
            if ('function' === $.type(message)) {
                message(this);
            } else {
                if (null == message) {
                    message = 'Required node not found' + (this.selector ? ' "' + this.selector + '"' : '');
                }
                throw new Error(message);
            }
        }
        return this;
    };

})(jQuery);