Drupal Form Builder class using ArrayAccess and Builder pattern

gistfile1.php

<?php 

class DrupalFormBuilder implements ArrayAccess 
{
    
    private $data = array();

    public function __construct(array $fieldsets = array('fs1'=>'fs1')) {
        foreach($fieldsets as $key=>$fieldset){
            $this->addFieldset($fieldset); 
        }
    }

    public static function get(){
        $called=get_called_class();
        return new $called();
    }

    public function toArray(){
        
        return $this->data;
    }

    public function offsetSet($offset, $value) {
        if (is_null($offset)) {
            $this->data[] = $value;
        } 
        else {
            $this->data[$offset] = $value;
        }
    }

    public function offsetExists($offset) {
        return isset($this->data[$offset]);
    }

    public function offsetUnset($offset) {
        unset($this->data[$offset]);
    }

    public function offsetGet($offset) {
        return isset($this->data[$offset]) 
            ? $this->data[$offset] 
            : null;
    }
    public function addTextfield($key, $fs = 'fs1'){
         $this->data[$fs][$key] = array(
            '#type' => 'textfield',
            '#title' => $key,
          );
         return $this;
    }
    public function addItem($key, $fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'item',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addSelect($key, $fs = 'fs1', array $opts = array('Option 1'=>'Option 1')){
        $this->data[$fs][$key] = array(
            '#type' => 'select',
             '#options' => $opts,
              '#default_value' => array('Option 1'=>'Option 1'),
              '#empty_option' => '- Select -',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addCheckbox($key,$fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'checkbox',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addCheckboxes($key, $fs = 'fs1', array $opts = array('Option 1'=>'Option 1','Option 2'=>'Option 2','Option 3'=>'Option 3')){
        $this->data[$fs][$key] = array(
            '#type' => 'checkboxes',
            '#options' => $opts,
            '#default_value' => array('Option 1'=>'Option 1'),
             '#empty_option' => '- Select -',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
     public function addRadio($key,  $fs = 'fs1', array $opts = array('Option 1'=>'Option 1')){
        $this->data[$fs][$key] = array(
            '#type' => 'radio',
             '#options' => $opts,
              '#default_value' => array('Option 1'=>'Option 1'),
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    protected function addFieldset($key){
        $this->data[$key] = array(
            '#collapsible' => false,
            '#title' => t($key),
            '#type' => 'fieldset',
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addFile($key , $fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'file',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addTextarea($key){
        $this->data[$fs]['fs1'][$key] = array(
            '#type' => 'textarea',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addPassword($key, $fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'password',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addPasswordConfirm($key, $fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'password_confirm',
            '#title' => $key,
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;
    }
    public function addButton($key, $fs = 'fs1'){
        $this->data[$fs][$key] = array(
            '#type' => 'button',
            '#value' => ucfirst($key),
            '#prefix' => '',
            '#suffix' => ''
        );
        return $this;

    }
    public function addSubmit($key){
        $this->data[$key] = array(
            '#type' => 'submit',
            '#value' => ucfirst($key),
        );
        return $this;
    }
}

Cool!