$.fn.validate = function(els){
    if(this.is('form')){
        return this.submit(function(){return $.vdForm.validate(els)});
    }
}
$.vdForm = {
    validate:function(els){
        for(i=0; i<els.length; i++){
            var el = document.getElementsByName(els[i][0])[0];
            if(!el){
                alert('[程序错误] 名为"' + els[i][0] + '"的元素不存在');
                return;
            }
            var rs = [];
            if(typeof els[i][1][0] == 'object'){
                rs = els[i][1];
            }else {
                rs.push(els[i][1]);
            }
            for(var j=0; j < rs.length; ++j){
                var error = $.vdForm.check(el, rs[j]);
                //var msgbox = document.getElementById(el.nodeName + '_msg');
                if(error){
                    alert(error);
                    return false;
                    /*
                    msgbox.innerHTML = els[i].rules[j].emsg;
                    msgbox.style.display = 'block';
                    result = false;
                    break;
                    */
                }else{
                    //msgbox.style.display = 'none';
                }
            }
        }
    },
    check: function(el, rule){
        var p = rule[0].split(':');
        var r = p[0];
        p = p.slice(1);
        if(rules[r]($(el).val(), el, p, $.vdForm.utility)){
            return rule[1]
        }
    }
}
$.vdForm.utility = {
    countChecked: function(el) {
        var num = 0;
        var els = document.getElementsByName(el.name);
        for(var i=0, el; el = els[i]; i++) {
            if(el.checked) {
                num++;
            }
        }
        return num;
    },
    
    getLength: function(value, element) {
        var length;
        switch( element.nodeName.toLowerCase() ) {
        case 'select':
            length = this.getSelectedOptions(element).length;
            break;
        case 'input':
            switch( element.type.toLowerCase() ) {
                case 'checkbox':
                    length = this.countChecked(element);
                    break;
                default: 
                    length = value.length;
            }
            break;
        default: 
            length = value.length;
        }
        return length;
    },

    /**
     * Returns an array of all selected options of a
     * select element. Very useful to validate a select
     * with multiple="multiple".
     */
    getSelectedOptions: function(select) {
        return $("option:selected", select).get();
    },
    
    isRadioButtonSelected: function(radio) {
        var elements = document.getElementsByName(radio.name);
        for(var i=0, element; element = elements[i]; i++) {
            if(element.checked) {
                return true;
            }
        }
        return false;
    }
}
rules = {
    /**
     * Return true if the element is empty.
     * Works with all kind of text inputs, select and checkbox.
     * To force a user to select an option from a select box, provide
     * an empty options like <option value="">Choose...</option>
     */
    required: function(value, element, parameters, utility) {
        switch( element.nodeName.toLowerCase() ) {
        case 'select':
            var options = utility.getSelectedOptions(element);
            return options.length == 0 || options[0].value.length == 0;
        case 'input':
            switch( element.type.toLowerCase() ) {
            case 'checkbox':
                return utility.countChecked(element) == 0;
            case 'radio':
                return utility.countChecked(element) == 0;
            default:
                return value.length == 0;
            }
        default:
            return value.length == 0;
        }
    },
    
    /**
     * Return true, if the element is
     * - some kind of text input and its value is too short or too long
     * - a select and has not enough or too many options selected
     * Works with all kind of text inputs and select.
     */
    length: function(value, element, parameters, utility) {
        var length = utility.getLength(value, element);
        //alert('length:'+length+'  p0:'+ parameters[1]+'  p1:'+parameters[2]);
        return length < parameters[0] || length > parameters[1];
    },
    
    /**
     * Return true, if the value is not a valid email address.
     * Works with all kind of text inputs.
     */
    email: function(value) {
        return !value.match(/^[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i);
    },
    
    /**
     * Return true, if the value is not a valid url.
     * Works with all kind of text inputs.
     * WARNING: Is not fully implemented yet, eg. it does not allow a query string.
     * @see http://www.w3.org/Addressing/rfc1738.txt
     */
    url: function(value) {
        return !value.match(/^(https?|ftp):\/\/[A-Z0-9](\.?[A-Z0-9][A-Z0-9_\-]*)*(\/([A-Z0-9][A-Z0-9_\-\.]*)?)*(\?([A-Z0-9][A-Z0-9_\-\.%\+=&]*)?)?$/i);
    },
    
    /**
     * Return true, if the value is a valid date.
     * Works with all kind of text inputs.
     * WARNING: Limited due to the capability of the JS Date object
     * Use dateDE to check german dates.
     */
    date: function(value) {
        return /Invalid|NaN/.test(new Date(value));
    },
    
    /**
     * Checks a date according to german oldschool standard (not ISO).
     * eg. 25.03.2006 or 1.5.05
     * WARNING: Does not make sanity checks, eg. for 50.13.06 or 30.03.05
     */
    dateDE: function(value) {
        return !value.match(/\d\d?\.\d\d?\.\d\d\d?\d?/);
    },
    
    /**
     * 如果被检查的值不是有效的数字,或值不在指定范围内,则返回 "True"
     */
    number: function(value, element, parameters, utility) {
        value -= 0;
        return value != value || value < parameters[0] || value > parameters[1];
    }
};