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<?php
/**
* Calculated Shipping
* 
* A simple method for using a calculated product field as a shipping field. This provides the ability to use
* calculations when determining a shipping price.
* 
* @author    David Smith <david@gravitywiz.com>
* @license   GPL-2.0+
* @link      http://gravitywiz.com/...
* @copyright 2013 Gravity Wiz
*/
class GWCalculatedShipping {
    
    function __construct( $args ) {
        
        $this->_args = wp_parse_args( $args, array( 
            'form_id' => false,
            'field_id' => false
        ) );
        
        add_filter( 'gform_pre_submission_filter_' . $this->_args['form_id'], array( $this, 'add_shipping_field' ) );
        
    }
    
    function add_shipping_field( $form ) {
        
        // get our calc shipping field and convert it to default shipping field
        $calc_shipping_field = GFFormsModel::get_field( $form, $this->_args['field_id'] );
        $calc_shipping_field['type'] = 'shipping';
        $calc_shipping_field['inputType'] = 'singleshipping';
        $calc_shipping_field['inputs'] = null;
        
        // map calc value as shipping value
        $_POST['input_' . $calc_shipping_field['id']] = rgpost( "input_{$calc_shipping_field['id']}_2" );
        
        foreach( $form['fields'] as &$field ) {
            if( $field['id'] == $calc_shipping_field['id'] ) {
                $field = $calc_shipping_field;
                break;
            }
        }
        
        return $form;
    }
    
    function field( $args = array() ) {
        return wp_parse_args( $args, array(
            'id' => false,
            'formId' => false,
            'pageNumber' => 1,
            'adminLabel' => '',
            'adminOnly' => '',
            'allowsPrepopulate' => 1,
            'defaultValue' => '',
            'description' => '',
            'content' => '',
            'cssClass' => '',
            'errorMessage' => '',
            'inputName' => '',
            'isRequired' => '',
            'label' => 'Shipping',
            'noDuplicates' => '',
            'size' => 'medium',
            'type' => 'shipping',
            'displayCaption' => '',
            'displayDescription' => '',
            'displayTitle' => '',
            'inputType' => 'singleshipping',
            'inputs' => '',
            'basePrice' => '$0.00'
        ) );
    }
    
    /**
    * Direct port of private method GFFormDisplay::get_max_page_number()
    */
    function get_max_page_number( $form ) {
        $page_number = 0;
        foreach($form["fields"] as $field){
            if($field["type"] == "page"){
               $page_number++;
            }
        }
        return $page_number == 0 ? 0 : $page_number + 1;
    }
    
}

new GWCalculatedShipping( array( 
    'form_id' => 375,
    'field_id' => 4
) );