function Form(ids)
{
    this.ids = ids;
}

Form.prototype.isAValidForm = function()
{
    this.setupForm();
    var isValid = true;
    
    if (!this.isAValidInput('first_name'))
    {
        isValid = false;
    }
    if (!this.isAValidInput('last_name'))
    {
        isValid = false;
    }
    if (!this.isAValidEmail('email'))
    {
        isValid = false;
    }
    if (!this.isAValidConfirmation('email', 'confirm_email'))
    {
        isValid = false;
    }
    
    this.showErrorMessage(isValid);
    return isValid;
}

Form.prototype.setupForm = function()
{
    this.removeRequiredFieldHints();
    this.removeErrorMessage();
}

Form.prototype.removeRequiredFieldHints = function()
{
    for (var i = 0; i < this.ids.length; i++)
    {
        document.getElementById(this.ids[i]).removeAttribute('style');
    }
}

Form.prototype.removeErrorMessage = function()
{
    var parent = document.getElementById('main_content');
    var nodes = parent.getElementsByTagName('div');
    
    for (var i = 0; i < nodes.length; i++)
    {
        if (nodes[i].id == 'success' || nodes[i].id == 'error')
        {
            parent.removeChild(nodes[i]);
            break;
        }
    }
}

Form.prototype.isAValidEmail = function(id)
{
    if (this.isAValidInput(id))
    {
        var pattern = /^.+@.+\..+$/;
        
        if (pattern.test(document.getElementById(id).value))
        {
            return true;
        }
        else
        {
            this.showRequiredFieldHint(id);
        }
    }
    
    return false;
}

Form.prototype.isAValidInput = function(id)
{
    if (document.getElementById(id).value.length > 0)
    {
        return true;
    }
    else
    {
        this.showRequiredFieldHint(id);
        return false;
    }
}

Form.prototype.isAValidConfirmation = function(input, confirmInput)
{
    if (document.getElementById(input).value == document.getElementById(confirmInput).value)
    {
        return true;
    }
    else
    {
        this.showRequiredFieldHint(confirmInput);
        return false;
    }
}

Form.prototype.showRequiredFieldHint = function(id)
{
    document.getElementById(id).setAttribute('style', 'border-color:red');
}

Form.prototype.showErrorMessage = function(isValid)
{
    if (!isValid)
    {
        var div = document.createElement('div');
        div.setAttribute('id', 'error');
        div.appendChild(document.createTextNode(this.getErrorMessage()));
        var form = document.getElementsByTagName('form').item(0);
        document.getElementById('main_content').insertBefore(div, form);
    }
}

Form.prototype.getErrorMessage = function()
{
    var nodes = this.getLanguageNode().getElementsByTagName('feedback');
    
    for (var i = 0; i < nodes.length; i++)
    {
        var node = nodes[i].getElementsByTagName('source')[0].firstChild;
        
        if (node.nodeValue == 'form_error')
        {
            return nodes[i].getElementsByTagName('text')[0].firstChild.nodeValue;
        }
    }
    
    return null;
}

Form.prototype.getLanguageNode = function()
{
    var xmlDoc = new Document().loadXMLDocument('form_feedback.xml');
    var nodes = xmlDoc.getElementsByTagName('language');
    var language = document.getElementById('language').value;
    
    for (var i = 0; i < nodes.length; i++)
    {
        if (nodes[i].attributes.getNamedItem('id').value == language)
        {
            return nodes[i];
        }
    }
    
    return null;
}