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<?php
/**
 * Stephen Kam // Gravity Forms // Get Username from Email
 *
 * Capture username portion of an email address and store it into another field.
 *
 * @version   0.1
 * @author    David Smith <david@gravitywiz.com>
 * @license   GPL-2.0+
 * @link      http://gravitywiz.com/...
 *
 * Plugin Name: Gravity Forms Username from Email
 * Plugin URI: http://gravitywiz.com/
 * Description: Capture username portion of an email address and store it into another field.
 * Author: Gravity Wiz
 * Version: 0.1
 * Author URI: http://gravitywiz.com
 */
class SK_Username_From_Email {

    public function __construct( $args = array() ) {

        // set our default arguments, parse against the provided arguments, and store for use throughout the class
        $this->_args = wp_parse_args( $args, array(
            'form_id'         => false,
            'source_field_id' => false,
            'target_field_id' => false
        ) );

        // do version check in the init to make sure if GF is going to be loaded, it is already loaded
        add_action( 'init', array( $this, 'init' ) );

    }

    public function init() {

        // make sure we're running the required minimum version of Gravity Forms
        if( ! property_exists( 'GFCommon', 'version' ) || ! version_compare( GFCommon::$version, '1.8', '>=' ) ) {
            return;
}
        // carry on
        add_action( 'gform_pre_submission', array( $this, 'update_submitted_data' ) );

    }

    public function update_submitted_data( $form ) {

	    if( ! $this->is_applicable_form( $form ) ) {
		    return;
	    }

        $value = (string) rgpost( "input_{$this->_args['source_field_id']}" );
        if( ! $value ) {
            return;
        }

        $bits = explode( '@', $value );

        $_POST[ "input_{$this->_args['target_field_id']}"] = $bits[0];

    }

    public function is_applicable_form( $form ) {

        $form_id = isset( $form['id'] ) ? $form['id'] : $form;

        return $form_id == $this->_args['form_id'];
    }

}

# Configuration

new SK_Username_From_Email( array(
    'form_id' => 1315,
    'source_field_id' => 2,
    'target_field_id' => 1
) );