Only display MDS Shipping fields if MDS was selected as the shipping method on Cart Page

custom_override_checkout_fields.php

<?php

function custom_override_checkout_fields( $fields ) {
	
	// Get global WooCommerce Object
	global $woocommerce;
	
	// Get the shipping label
	$shipping_label = $woocommerce->cart->shipping_label;
	
	// If the first 3 letters of the shipping lable == MDS
	// change fields to the fields required for MDS,
	// else, don't change $fields and return input
	if (substr($shipping_label, 0, 3)=="MDS"){
	
		$mds = new WC_MDS_Collivery();
		$field = $mds->get_field_defaults();
		
		$towns = Array('' => 'Select Town') + $field['towns'];
		
		$cptypes = Array('' => 'Select Premesis Type') + $field['cptypes'];
	
		$billing_data = Array (
			'billing_state' => Array (
				'type'			=> 'select',
				'label'			=> 'Town',
				'required'		=> 1,
				'class'			=> Array ('form-row-first', 'update_totals_on_change'),
				'options'		=> $towns,
				'selected'		=> ''
				),
			'billing_city' => Array (
				'type'			=> 'select',
				'label'			=> 'Suburb',
				'required'		=> 1,
				'class'			=> Array ('form-row-last'),
				'options'		=> Array ('Select town first...')
			),
			'billing_cptypes' => Array (
				'type'			=> 'select',
				'label'			=> 'Location Type',
				'required'		=> 1,
				'class'			=> Array ('form-row-first', 'update_totals_on_change'),
				'options'		=> $cptypes
			),
			'billing_company' => Array (
				'label'			=> 'Company Name',
				'placeholder'	=> 'Company (optional)',
				'class'			=> Array ('form-row-last')
			),
			'billing_building_details' => Array (
				'label'			=> 'Building Details',
				'placeholder'	=> 'Building Details',
				'class'			=> Array ('form-row-wide')
			),
			'billing_address_1' => Array (
				'name'			=> 'billing-streetno',
				'label'			=> 'Street No.',
				'placeholder'	=> 'Street No.',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'billing_address_2' => Array (
				'name'			=> 'billing-street',
				'label'			=> 'Street Name',
				'placeholder'	=> 'Street',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
			'billing_first_name' => Array (
				'label'			=> 'First Name',
				'placeholder'	=> 'First Name',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'billing_last_name' => Array (
				'label'			=> 'Last Name',
				'placeholder'	=> 'Last Name',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
			'billing_phone' => Array (
				'validate'		=> array('phone'),
				'label'			=> 'Cell Phone',
				'placeholder'	=> 'Phone number',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'billing_email' => Array (
				'validate'		=> array('email'),
				'label'			=> 'Email Address',
				'placeholder'	=> 'you@yourdomain.co.za',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
		);
		
		$shipping_data = Array (
			'shipping_state' => Array (
				'type'			=> 'select',
				'label'			=> 'Town',
				'required'		=> 1,
				'class'			=> Array ('form-row-first', 'update_totals_on_change'),
				'options'		=> $towns,
				'selected'		=> ''
				),
			'shipping_city' => Array (
				'type'			=> 'select',
				'label'			=> 'Suburb',
				'required'		=> 1,
				'class'			=> Array ('form-row-last'),
				'options'		=> Array ('Select town first...')
			),
			'shipping_cptypes' => Array (
				'type'			=> 'select',
				'label'			=> 'Location Type',
				'required'		=> 1,
				'class'			=> Array ('form-row-first', 'update_totals_on_change'),
				'options'		=> $cptypes
			),
			'shipping_company' => Array (
				'label'			=> 'Company Name',
				'placeholder'	=> 'Company (optional)',
				'class'			=> Array ('form-row-last')
			),
			'shipping_building_details' => Array (
				'label'			=> 'Building Details',
				'placeholder'	=> 'Building Details',
				'class'			=> Array ('form-row-wide')
			),
			'shipping_address_1' => Array (
				'name'			=> 'billing-streetno',
				'label'			=> 'Street No.',
				'placeholder'	=> 'Street No.',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'shipping_address_2' => Array (
				'name'			=> 'billing-street',
				'label'			=> 'Street Name',
				'placeholder'	=> 'Street',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
			'shipping_first_name' => Array (
				'label'			=> 'First Name',
				'placeholder'	=> 'First Name',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'shipping_last_name' => Array (
				'label'			=> 'Last Name',
				'placeholder'	=> 'Last Name',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
			'shipping_phone' => Array (
				'validate'		=> array('phone'),
				'label'			=> 'Cell Phone',
				'placeholder'	=> 'Phone number',
				'required'		=> 1,
				'class'			=> Array ('form-row-first')
			),
			'shipping_email' => Array (
				'validate'		=> array('email'),
				'label'			=> 'Email Address',
				'placeholder'	=> 'you@yourdomain.co.za',
				'required'		=> 1,
				'class'			=> Array ('form-row-last')
			),
		);
		
		$fields['billing'] = $billing_data;
		
		$fields['shipping'] = $shipping_data;
	}
	return $fields;
}