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<?php
/**
 * WARNING! THIS SNIPPET MAY BE OUTDATED.
 * The latest version of this snippet can be found in the Gravity Wiz Snippet Library:
 * https://github.com/gravitywiz/snippet-library/blob/master/gravity-forms/gw-require-unique-values.php
 */
/**
 * Gravity Wiz // Gravity Forms // Require Unique Values Between Fields
 *
 * Allows you to require two or more fields on the same form to be different from each other. For example, if you are
 * collecting a personal phone number and an emergency contact phone number, this functionality can be used to ensure
 * that the same number is not used for both fields.
 *
 * @version   1.6
 * @author    David Smith <david@gravitywiz.com>
 * @license   GPL-2.0+
 * @link      https://gravitywiz.com/gravity-forms-require-unique-values-for-different-fields/
 */
class GW_Require_Unique_Values {

	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,
			'field_ids'           => false,
			'validation_message'  => __( 'Please enter a unique value.' ),
			'validate_all_fields' => false,
			'mode'                => 'collective' // 'collective' or 'individual' (experimental)
		) );

		$this->_args['master_field_id'] = array_shift( $this->_args['field_ids'] );

		// 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, '1.9', '>=' ) ) {
			return;
		}

		add_filter( sprintf( 'gform_field_validation_%s', $this->_args['form_id'] ), array( $this, 'validate' ), 10, 4 );

	}

	public function validate( $result, $value, $form, $field ) {

		if( ! $this->is_applicable_field( $field ) ) {
			return $result;
		}

		$value = $this->get_filtered_value( $field );
		if( empty( $value ) ) {
			return $result;
		}

		if( $this->_args['mode'] === 'individual' ) {

			$groups = $this->get_group_values( $form, $field->id, false );
			$is_unique = true;

			foreach( $value as $target ) {
				foreach( $groups as $group ) {
					if( in_array( $target, $group ) ) {
						$is_unique = false;
						break 2;
					}
				}
			}

		} else {

			$values = $this->get_group_values( $form, $field->id );
			$is_unique = ! in_array( $this->get_value_hash( $value ), $values );

		}



		if ( $result['is_valid'] && ! $is_unique ) {
			$result['is_valid'] = false;
			$result['message']  = $this->_args['validation_message'];
		}

		return $result;
	}

	public function get_group_values( $form, $exclude_field_id, $do_hash = true ) {

		$field_ids   = $this->_args['field_ids'];
		$field_ids[] = $this->_args['master_field_id'];

		$values = array();

		foreach( $field_ids as $field_id ) {

			if( $field_id == $exclude_field_id ) {
				continue;
			}

			$field = GFFormsModel::get_field( $form, $field_id );
			$value = $this->get_filtered_value( $field );

			if( ! empty( $value ) ) {
				$values[ $field->id ] = $do_hash ? $this->get_value_hash( $value ) : $value;
			}

		}

		return $values;
	}

	/**
	 * @param GF_Field $field
	 *
	 * @return array
	 */
	public function get_filtered_value( $field ) {

		if( $field->get_input_type() == 'fileupload' && ! $field->multipleFiles ) {
			/** @var GF_Field_FileUpload $field */
			$value = basename( rgars( $_FILES, sprintf( 'input_%d/name', $field->id ) ) );
		} else {
			$value = $field->get_value_submission( array() );
		}

		$value = ! is_array( $value ) ? array( $value ) : $value;
		$value = array_filter( $value );

		return $value;
	}

	public function get_value_hash( $value ) {

		// Replace values like "1.1" with "x.1" to make it generic for comparison.
		if( is_array( $value ) ) {
			$old = $value;
			foreach( $old as $key => $_value ) {
				$ids = explode( '.', $key );
				if( count( $ids ) > 1 ) {
					$ids[0] = 'x';
				}
				unset( $value[ $key ] );
				$value[ implode( '.', $ids ) ] = $_value;
			}
		}

		return json_encode( $value );
	}

	public function is_applicable_field( $field ) {

		if( ! $this->_args['field_ids']  ) {
			return false;
		} else if( $this->_args['validate_all_fields'] && $field->id == $this->_args['master_field_id'] ) {
			return true;
		} else if( ! in_array( $field->id, $this->_args['field_ids'] ) ) {
			return false;
		}

		return true;
	}

}

# Configuration

new GW_Require_Unique_Values( array(
	'form_id' => 123,
	'field_ids' => array( 4, 5 )
) );

<?php
/**
 * Gravity Wiz // Gravity Forms // Require Unique Values Between Fields
 * http://gravitywiz.com/gravity-forms-require-unique-values-for-different-fields/
 */
 
# Set Custom Validation Message

new GW_Require_Unique_Values( array(
	'form_id' => 12,
	'field_ids' => array( 14, 15 ),
	'validation_message' => 'My custom validation message!'
) );

# Create Multiple Unique "Groups" on the Same Form

new GW_Require_Unique_Values( array(
	'form_id' => 2,
	'field_ids' => array( 4, 5 )
) );

new GW_Require_Unique_Values( array(
	'form_id' => 2,
	'field_ids' => array( 7, 8 )
) );

# Unique Field Compared to ALL Form Fields

new GW_Require_Unique_Values( array(
	'form_id' => 2,
	'field_ids' => array( 7 )
) );