Add variable USPS insurance fee to WooCommerce cart based on the value of the contents of the cart AND shipping with USPS

WooCommerce Add Insurance Fee

/**
 * Add an insurance surcharge to your cart / checkout
 * change the insurance amount based on value of cart
 * Uses the WooCommerce fees API
 *
 */
add_action( 'woocommerce_cart_calculate_fees','woocommerce_custom_surcharge' );
function woocommerce_custom_surcharge() {
  global $woocommerce;

	if ( is_admin() && ! defined( 'DOING_AJAX' ) )
		return;

	$chosen_methods = WC()->session->get( 'chosen_shipping_methods' );
	$chosen_shipping = $chosen_methods[0];

    if ( strpos($chosen_shipping, 'usps') !== false ) {
    	// this compare needed since if the string is found at beg of target, it returns '0', which is a false value

		$insurance_fee = 5;
		if ( $woocommerce->cart->cart_contents_total  <= 50 ) {
			$insurance_fee = 0;
			return;
		} else {
			if ( $woocommerce->cart->cart_contents_total  > 100  ) { 
				$insurance_fee = 10; 
			}
		}

		$woocommerce->cart->add_fee( 'Insurance', $insurance_fee, true, '' );
	}
	return;
}