Calculate Number of Days Between Two Gravity Form Date Fields

<?php
/**
 * --- STOP! ---
 * Get the latest version:
 * https://gravitywiz.com/documentation/gravity-forms-date-time-calculator/
 * -------------
 *
 * Gravity Wiz // Gravity Forms // Calculate Number of Days Between Two Gravity Form Date Fields
 * https://gravitywiz.com/calculate-number-of-days-between-two-dates/
 *
 * Allows you to calculate the number of days between two Gravity Form date fields and populate that number into a
 * field on your Gravity Form.
 */
class GWDayCount {

	private static $script_output;

	function __construct( $args ) {

		// phpcs:ignore WordPress.PHP.DontExtract.extract_extract
		extract( wp_parse_args( $args, array(
			'form_id'          => false,
			'start_field_id'   => false,
			'end_field_id'     => false,
			'count_field_id'   => false,
			'include_end_date' => true,
		) ) );

		$this->form_id        = $form_id;
		$this->start_field_id = $start_field_id;
		$this->end_field_id   = $end_field_id;
		$this->count_field_id = $count_field_id;
		$this->count_adjust   = $include_end_date ? 1 : 0;

		add_filter( "gform_pre_render_{$form_id}", array( &$this, 'load_form_script' ) );
		add_action( "gform_pre_submission_{$form_id}", array( &$this, 'override_submitted_value' ) );

	}

	function load_form_script( $form ) {

		// workaround to make this work for < 1.7
		$this->form = $form;
		add_filter( 'gform_init_scripts_footer', array( &$this, 'add_init_script' ) );

		if ( self::$script_output ) {
			return $form;
		}

		?>

		<script type="text/javascript">

			(function($){

				window.gwdc = function( options ) {

					this.options = options;
					this.startDateInput = $( '#input_' + this.options.formId + '_' + this.options.startFieldId );
					this.endDateInput = $( '#input_' + this.options.formId + '_' + this.options.endFieldId );
					this.countInput = $( '#input_' + this.options.formId + '_' + this.options.countFieldId );

					this.init = function() {

						var gwdc = this;

						// add data for "format" for parsing date
						gwdc.startDateInput.data( 'format', this.options.startDateFormat );
						gwdc.endDateInput.data( 'format', this.options.endDateFormat );

						gwdc.populateDayCount();

						gwdc.startDateInput.change( function() {
							gwdc.populateDayCount();
						} );

						gwdc.endDateInput.change( function() {
							gwdc.populateDayCount();
						} );

						$( '#ui-datepicker-div' ).hide();

					}

					this.getDayCount = function() {

						var startDate = this.parseDate( this.startDateInput.val(), this.startDateInput.data('format') )
						var endDate = this.parseDate( this.endDateInput.val(), this.endDateInput.data('format') );
						var dayCount = 0;

						if( !this.isValidDate( startDate ) || !this.isValidDate( endDate ) )
							return '';

						if( startDate > endDate ) {
							return 0;
						} else {

							var diff = endDate - startDate;
							dayCount = diff / ( 60 * 60 * 24 * 1000 ); // secs * mins * hours * milliseconds
							dayCount = Math.round( dayCount ) + this.options.countAdjust;

							return dayCount;
						}

					}

					this.parseDate = function( value, format ) {

						if( !value )
							return false;

						format = format.split('_');
						var dateFormat = format[0];
						var separators = { slash: '/', dash: '-', dot: '.' };
						var separator = format.length > 1 ? separators[format[1]] : separators.slash;
						var dateArr = value.split(separator);

						switch( dateFormat ) {
							case 'mdy':
								return new Date( dateArr[2], dateArr[0] - 1, dateArr[1] );
							case 'dmy':
								return new Date( dateArr[2], dateArr[1] - 1, dateArr[0] );
							case 'ymd':
								return new Date( dateArr[0], dateArr[1] - 1, dateArr[2] );
						}

						return false;
					}

					this.populateDayCount = function() {
						this.countInput.val( this.getDayCount() ).change();
					}

					this.isValidDate = function( date ) {
						return !isNaN( Date.parse( date ) );
					}

					this.init();

				}

			})(jQuery);

		</script>

		<?php
		self::$script_output = true;
		return $form;
	}

	function add_init_script( $return ) {

		$start_field_format = false;
		$end_field_format   = false;

		foreach ( $this->form['fields'] as &$field ) {

			if ( $field['id'] == $this->start_field_id ) {
				$start_field_format = $field['dateFormat'] ? $field['dateFormat'] : 'mdy';
			}

			if ( $field['id'] == $this->end_field_id ) {
				$end_field_format = $field['dateFormat'] ? $field['dateFormat'] : 'mdy';
			}
		}

		$script = "new gwdc({
                formId:             {$this->form['id']},
                startFieldId:       {$this->start_field_id},
                startDateFormat:    '$start_field_format',
                endFieldId:         {$this->end_field_id},
                endDateFormat:      '$end_field_format',
                countFieldId:       {$this->count_field_id},
                countAdjust:        {$this->count_adjust}
            });";

		$slug = implode( '_', array( 'gw_display_count', $this->start_field_id, $this->end_field_id, $this->count_field_id ) );
		GFFormDisplay::add_init_script( $this->form['id'], $slug, GFFormDisplay::ON_PAGE_RENDER, $script );

		// remove filter so init script is not output on subsequent forms
		remove_filter( 'gform_init_scripts_footer', array( &$this, 'add_init_script' ) );

		return $return;
	}

	function override_submitted_value( $form ) {

		$start_date = false;
		$end_date   = false;

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

			if ( $field['id'] == $this->start_field_id ) {
				$start_date = self::parse_field_date( $field );
			}

			if ( $field['id'] == $this->end_field_id ) {
				$end_date = self::parse_field_date( $field );
			}
		}

		if ( $start_date > $end_date ) {

			$day_count = 0;

		} else {

			$diff      = $end_date - $start_date;
			$day_count = $diff / ( 60 * 60 * 24 ); // secs * mins * hours
			$day_count = round( $day_count ) + $this->count_adjust;

		}

		$_POST[ "input_{$this->count_field_id}" ] = $day_count;

	}

	static function parse_field_date( $field ) {

		$date_value  = rgpost( "input_{$field['id']}" );
		$date_format = empty( $field['dateFormat'] ) ? 'mdy' : esc_attr( $field['dateFormat'] );
		$date_info   = GFCommon::parse_date( $date_value, $date_format );
		if ( empty( $date_info ) ) {
			return false;
		}

		return strtotime( "{$date_info['year']}-{$date_info['month']}-{$date_info['day']}" );
	}

}

# Configuration

new GWDayCount( array(
	'form_id'        => 16,
	'start_field_id' => 1,
	'end_field_id'   => 2,
	'count_field_id' => 4,
) );