Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
Complex classes like WC_Stripe_Customer often do a lot of different things. To break such a class down, we need to identify a cohesive component within that class. A common approach to find such a component is to look for fields/methods that share the same prefixes, or suffixes. You can also have a look at the cohesion graph to spot any un-connected, or weakly-connected components.
Once you have determined the fields that belong together, you can apply the Extract Class refactoring. If the component makes sense as a sub-class, Extract Subclass is also a candidate, and is often faster.
While breaking up the class, it is a good idea to analyze how other classes use WC_Stripe_Customer, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
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| 11 | class WC_Stripe_Customer { | 
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| 12 | |||
| 13 | /**  | 
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| 14 | * Stripe customer ID  | 
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| 15 | * @var string  | 
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| 16 | */  | 
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| 17 | private $id = '';  | 
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| 18 | |||
| 19 | /**  | 
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| 20 | * WP User ID  | 
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| 21 | * @var integer  | 
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| 22 | */  | 
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| 23 | private $user_id = 0;  | 
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| 24 | |||
| 25 | /**  | 
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| 26 | * Data from API  | 
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| 27 | * @var array  | 
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| 28 | */  | 
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| 29 | private $customer_data = array();  | 
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| 30 | |||
| 31 | /**  | 
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| 32 | * Constructor  | 
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| 33 | * @param int $user_id The WP user ID  | 
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| 34 | */  | 
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| 35 | 	public function __construct( $user_id = 0 ) { | 
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| 41 | |||
| 42 | /**  | 
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| 43 | * Get Stripe customer ID.  | 
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| 44 | * @return string  | 
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| 45 | */  | 
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| 46 | 	public function get_id() { | 
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| 49 | |||
| 50 | /**  | 
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| 51 | * Set Stripe customer ID.  | 
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| 52 | * @param [type] $id [description]  | 
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| 53 | */  | 
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| 54 | 	public function set_id( $id ) { | 
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| 64 | |||
| 65 | /**  | 
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| 66 | * User ID in WordPress.  | 
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| 67 | * @return int  | 
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| 68 | */  | 
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| 69 | 	public function get_user_id() { | 
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| 72 | |||
| 73 | /**  | 
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| 74 | * Set User ID used by WordPress.  | 
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| 75 | * @param int $user_id  | 
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| 76 | */  | 
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| 77 | 	public function set_user_id( $user_id ) { | 
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| 80 | |||
| 81 | /**  | 
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| 82 | * Get user object.  | 
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| 83 | * @return WP_User  | 
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| 84 | */  | 
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| 85 | 	protected function get_user() { | 
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| 88 | |||
| 89 | /**  | 
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| 90 | * Store data from the Stripe API about this customer  | 
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| 91 | */  | 
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| 92 | 	public function set_customer_data( $data ) { | 
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| 95 | |||
| 96 | /**  | 
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| 97 | * Generates the customer request, used for both creating and updating customers.  | 
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| 98 | *  | 
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| 99 | * @param array $args Additional arguments (optional).  | 
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| 100 | * @return array  | 
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| 101 | */  | 
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| 102 | 	protected function generate_customer_request( $args = array() ) { | 
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| 155 | |||
| 156 | /**  | 
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| 157 | * Create a customer via API.  | 
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| 158 | * @param array $args  | 
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| 159 | * @return WP_Error|int  | 
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| 160 | */  | 
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| 161 | 	public function create_customer( $args = array() ) { | 
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| 181 | |||
| 182 | /**  | 
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| 183 | * Updates the Stripe customer through the API.  | 
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| 184 | *  | 
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| 185 | * @param array $args Additional arguments for the request (optional).  | 
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| 186 | * @param bool $is_retry Whether the current call is a retry (optional, defaults to false). If true, then an exception will be thrown instead of further retries on error.  | 
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| 187 | *  | 
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| 188 | * @return string Customer ID  | 
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| 189 | *  | 
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| 190 | * @throws WC_Stripe_Exception  | 
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| 191 | */  | 
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| 192 | 	public function update_customer( $args = array(), $is_retry = false ) { | 
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| 219 | |||
| 220 | /**  | 
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| 221 | * Checks to see if error is of invalid request  | 
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| 222 | * error and it is no such customer.  | 
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| 223 | *  | 
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| 224 | * @since 4.1.2  | 
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| 225 | * @param array $error  | 
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| 226 | */  | 
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| 227 | 	public function is_no_such_customer_error( $error ) { | 
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| 234 | |||
| 235 | /**  | 
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| 236 | * Add a source for this stripe customer.  | 
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| 237 | * @param string $source_id  | 
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| 238 | * @return WP_Error|int  | 
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| 239 | */  | 
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| 240 | 	public function add_source( $source_id ) { | 
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| 313 | |||
| 314 | /**  | 
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| 315 | * Get a customers saved sources using their Stripe ID.  | 
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| 316 | *  | 
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| 317 | * @param string $customer_id  | 
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| 318 | * @return array  | 
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| 319 | */  | 
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| 320 | 	public function get_sources() { | 
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| 349 | |||
| 350 | /**  | 
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| 351 | * Delete a source from stripe.  | 
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| 352 | * @param string $source_id  | 
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| 353 | */  | 
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| 354 | 	public function delete_source( $source_id ) { | 
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| 371 | |||
| 372 | /**  | 
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| 373 | * Set default source in Stripe  | 
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| 374 | * @param string $source_id  | 
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| 375 | */  | 
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| 376 | 	public function set_default_source( $source_id ) { | 
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| 395 | |||
| 396 | /**  | 
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| 397 | * Deletes caches for this users cards.  | 
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| 398 | */  | 
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| 399 | 	public function clear_cache() { | 
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| 404 | |||
| 405 | /**  | 
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| 406 | * Retrieves the Stripe Customer ID from the user meta.  | 
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| 407 | *  | 
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| 408 | * @param int $user_id The ID of the WordPress user.  | 
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| 409 | * @return string|bool Either the Stripe ID or false.  | 
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| 410 | */  | 
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| 411 | 	public function get_id_from_meta( $user_id ) { | 
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| 414 | |||
| 415 | /**  | 
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| 416 | * Updates the current user with the right Stripe ID in the meta table.  | 
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| 417 | *  | 
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| 418 | * @param string $id The Stripe customer ID.  | 
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| 419 | */  | 
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| 420 | 	public function update_id_in_meta( $id ) { | 
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| 423 | |||
| 424 | /**  | 
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| 425 | * Deletes the user ID from the meta table with the right key.  | 
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| 426 | */  | 
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| 427 | 	public function delete_id_from_meta() { | 
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| 430 | |||
| 431 | /**  | 
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| 432 | * Recreates the customer for this user.  | 
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| 433 | *  | 
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| 434 | * @return string ID of the new Customer object.  | 
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| 435 | */  | 
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| 436 | 	private function recreate_customer() { | 
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| 440 | }  | 
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| 441 | 
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