<?php

class GFRandomFields {

    public static $all_random_field_ids;
    public static $display_count;
    public static $selected_field_ids = array();

    function __construct($form_id, $display_count = 5, $random_field_ids = false) {

        $this->all_random_field_ids = $random_field_ids;
        $this->display_count = $display_count;

        add_filter("gform_pre_render_$form_id", array(&$this, 'pre_render'));
        add_filter("gform_form_tag_$form_id", array(&$this, 'store_selected_field_ids'));
        add_filter("gform_validation_$form_id", array(&$this, 'validate'));

    }

    function pre_render($form) {
        return $this->filter_form_fields($form, $this->get_selected_field_ids());
    }

    function store_selected_field_ids($form_tag) {
        $value = implode(',', $this->get_selected_field_ids());
        $input = sprintf( '<input type="hidden" value="%s" name="gfrf_field_ids">', $value );
        return $form_tag . $input;
    }

    function validate($validation_result) {

        $validation_result['form'] = $this->filter_form_fields($validation_result['form'], $this->get_selected_field_ids());
        $validation_result['is_valid'] = true;

        foreach($validation_result['form']['fields'] as $field) {
            if($field['failed_validation'])
                $validation_result['is_valid'] = false;
        }

        return $validation_result;
    }

    function filter_form_fields($form, $selected_fields) {

        $filtered_fields = array();

        foreach($form['fields'] as $field) {

            if(in_array($field['id'], $this->all_random_field_ids)) {
                if(in_array($field['id'], $selected_fields))
                    $filtered_fields[] = $field;
            } else {
                $filtered_fields[] = $field;
            }

        }

        $form['fields'] = $filtered_fields;

        return $form;
    }

    function get_selected_field_ids() {

        // check if class has already init fields
        if(!empty($this->selected_field_ids))
            return $this->selected_field_ids;

        // check if fields have been submitted
        if(rgpost('gfrf_field_ids'))
            return explode(',', rgpost('gfrf_field_ids'));

        $field_ids = array();
        $keys = array_rand($this->all_random_field_ids, $this->display_count);

        foreach($keys as $key) {
            $field_ids[] = $this->all_random_field_ids[$key];
        }

        $this->selected_field_ids = $field_ids;

        return $field_ids;
    }

}

new GFRandomFields(11, 200, array(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284));