Limit How Many Checkboxes Can Be Checked

<?php
/**
 * Gravity Wiz // Gravity Forms // Limit How Many Checkboxes Can Be Checked
 * https://gravitywiz.com/limiting-how-many-checkboxes-can-be-checked/
 *
 * Limit how many checkboxes can be checked (and how many checkboxes *must* be checked) on a checkbox field.
 */

class GFLimitCheckboxes {

	private $form_id;
	private $field_limits;
	private $output_script;

	function __construct( $form_id, $field_limits ) {

		$this->form_id      = $form_id;
		$this->field_limits = $this->set_field_limits( $field_limits );

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

	}

	function pre_render( $form ) {

		$script        = '';
		$output_script = false;

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

			$field_id     = $field['id'];
			$field_limits = $this->get_field_limits( $field['id'] );

			if ( ! $field_limits                                          // if field limits not provided for this field
				|| RGFormsModel::get_input_type( $field ) !== 'checkbox'  // or if this field is not a checkbox
				|| ! isset( $field_limits['max'] )                        // or if 'max' is not set for this field
				) {
				continue;
			}

			$output_script = true;
			$max           = $field_limits['max'];
			$selectors     = array();

			foreach ( $field_limits['field'] as $checkbox_field ) {
				$selectors[] = "#field_{$form['id']}_{$checkbox_field} .gfield_checkbox input:checkbox";
			}

			$script .= "jQuery( '" . implode( ', ', $selectors ) . "' ).checkboxLimit( {$max} );";

		}

		GFFormDisplay::add_init_script( $form['id'], 'limit_checkboxes', GFFormDisplay::ON_PAGE_RENDER, $script );

		if ( $output_script ) :
			?>

			<script type="text/javascript">
			jQuery(document).ready(function($) {
				$.fn.checkboxLimit = function(n) {

					var checkboxes = this;

					this.toggleDisable = function() {

						// if we have reached or exceeded the limit, disable all other checkboxes
						if(this.filter(':checked').length >= n) {
							var unchecked = this.not(':checked');
							unchecked.prop('disabled', true);
						}
						// if we are below the limit, make sure all checkboxes are available
						else {
							this.prop('disabled', false);
						}

					}

					// when form is rendered, toggle disable
					checkboxes.bind('gform_post_render', checkboxes.toggleDisable());

					// when checkbox is clicked, toggle disable
					checkboxes.click(function(event) {

						checkboxes.toggleDisable();

						// if we are equal to or below the limit, the field should be checked
						return checkboxes.filter(':checked').length <= n;
					});

				}
			});
			</script>

			<?php
		endif;

		return $form;
	}

	function validate( $validation_result ) {

		$form            = $validation_result['form'];
		$checkbox_counts = array();

		// loop through and get counts on all checkbox fields (just to keep things simple)
		foreach ( $form['fields'] as $field ) {

			if ( RGFormsModel::get_input_type( $field ) !== 'checkbox' ) {
				continue;
			}

			$field_id = $field['id'];
			$count    = 0;

			foreach ( $_POST as $key => $value ) {
				if ( strpos( $key, "input_{$field['id']}_" ) !== false ) {
					$count++;
				}
			}

			$checkbox_counts[ $field_id ] = $count;

		}

		// loop through again and actually validate
		foreach ( $form['fields'] as &$field ) {

			if ( ! $this->should_field_be_validated( $form, $field ) ) {
				continue;
			}

			$field_id     = $field['id'];
			$field_limits = $this->get_field_limits( $field_id );

			$min = isset( $field_limits['min'] ) ? $field_limits['min'] : false;
			$max = isset( $field_limits['max'] ) ? $field_limits['max'] : false;

			$count = 0;
			foreach ( $field_limits['field'] as $checkbox_field ) {
				$count += rgar( $checkbox_counts, $checkbox_field );
			}

			if ( $count < $min ) {
				$field['failed_validation'] = true;
				// translators: placeholder is minimum number of checkboxes that must be checked
				$field['validation_message']   = sprintf( _n( 'You must select at least %s item.', 'You must select at least %s items.', $min ), $min );
				$validation_result['is_valid'] = false;
			} elseif ( $count > $max ) {
				$field['failed_validation'] = true;
				// translators: placeholder is maximum number of checkboxes that can be checked
				$field['validation_message']   = sprintf( _n( 'You may only select %s item.', 'You may only select %s items.', $max ), $max );
				$validation_result['is_valid'] = false;
			}
		}

		$validation_result['form'] = $form;

		return $validation_result;
	}

	function should_field_be_validated( $form, $field ) {

		if ( $field['pageNumber'] != GFFormDisplay::get_source_page( $form['id'] ) ) {
			return false;
		}

		// if no limits provided for this field
		if ( ! $this->get_field_limits( $field['id'] ) ) {
			return false;
		}

		// or if this field is not a checkbox
		if ( RGFormsModel::get_input_type( $field ) != 'checkbox' ) {
			return false;
		}

		// or if this field is hidden
		if ( RGFormsModel::is_field_hidden( $form, $field, array() ) ) {
			return false;
		}

		return true;
	}

	function get_field_limits( $field_id ) {

		foreach ( $this->field_limits as $key => $options ) {
			if ( in_array( $field_id, $options['field'], true ) ) {
				return $options;
			}
		}

		return false;
	}

	function set_field_limits( $field_limits ) {

		foreach ( $field_limits as $key => &$options ) {

			if ( isset( $options['field'] ) ) {
				$ids = is_array( $options['field'] ) ? $options['field'] : array( $options['field'] );
			} else {
				$ids = array( $key );
			}

			$options['field'] = $ids;

		}

		return $field_limits;
	}

}

new GFLimitCheckboxes(123, array(
	5  => array(
		'min' => 2,
		'max' => 3,
	),
	13 => array(
		'max' => 3,
	),
));