abstract class LLMS_Abstract_API_Handler {

	/**
	 * Determines if an empty response body should be interpreted as an error
	 *
	 * @var bool
	 */
	protected $allow_empty_response = false;

	/**
	 * Default request method
	 *
	 * @var  string
	 */
	protected $default_request_method = 'POST';

	/**
	 * Determine if the request should be made as JSON
	 *
	 * @var bool
	 */
	protected $is_json = true;

	/**
	 * Request timeout in seconds
	 *
	 * @var integer
	 */
	protected $request_timeout = 60;

	private $result        = null;
	private $error_message = null;
	private $error_object  = null;
	private $error_type    = null;

	/**
	 * Construct an API call, parameters are passed to private `call()` function
	 *
	 * @param    stirng $resource  url endpoint or resource to make a request to
	 * @param    array  $data      array of data to pass in the body of the request
	 * @param    string $method    method of request (POST, GET, DELETE, PUT, etc...)
	 * @return   void
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function __construct( $resource, $data, $method = null ) {

		$this->call( $resource, $data, $method );

	}

	/**
	 * Execute an API request.
	 *
	 * @since 3.11.2
	 * @since 3.30.1 self::set_request_body() may respond with `null` in order to send a request with no `body`
	 * @since 4.21.3 Use `wp_json_encode()` in favor of `json_encode()`.
	 *                Updated the API connection error message.
	 *
	 * @param    string $resource  url endpoint or resource to make a request to.
	 * @param    array  $data      array of data to pass in the body of the request.
	 * @param    string $method    method of request (POST, GET, DELETE, PUT, etc...).
	 * @return   null
	 */
	private function call( $resource, $data, $method = null ) {

		$method = is_null( $method ) ? $this->default_request_method : $method;

		// setup headers.
		$content_type = $this->is_json ? 'application/json; charset=utf-8' : 'application/x-www-form-urlencoded';
		$headers      = $this->set_request_headers(
			array(
				'content-type' => $content_type,
			),
			$resource,
			$method
		);

		$args = array(
			'headers'    => $headers,
			'method'     => $method,
			'timeout'    => $this->request_timeout,
			'user-agent' => $this->set_user_agent( 'LifterLMS ' . LLMS_VERSION, $resource, $method ),
		);

		// setup body.
		$body = $this->set_request_body( $data, $method, $resource );

		// if "null" if passed to body, don't send a body at all.
		if ( ! is_null( $body ) ) {
			$args['body'] = $this->is_json && $body ? wp_json_encode( $body ) : $body;
		}

		// Attempt to call the API.
		$response = wp_safe_remote_request(
			$this->set_request_url( $resource, $method ),
			$args
		);

		// Connection error.
		if ( is_wp_error( $response ) ) {
			return $this->set_error( __( 'There was a problem connecting to the external API.', 'lifterlms' ), 'api_connection', $response );
		}

		// Empty body.
		if ( ! $this->allow_empty_response && empty( $response['body'] ) ) {

			return $this->set_error( __( 'Empty Response.', 'lifterlms' ), 'empty_response', $response );

		}

		$this->parse_response( $response );

	}

	/**
	 * Retrieve the private "error_message" variable
	 *
	 * @return   string
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function get_error_message() {

		return $this->error_message;

	}

	/**
	 * Get the private "error_object" variable
	 *
	 * @return   mixed
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function get_error_object() {

		return $this->error_object;

	}

	/**
	 * Retrieve the private "error_type" variable
	 *
	 * @return   string
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function get_error_type() {

		return $this->error_type;

	}

	/**
	 * Retrieve the private "result" variable
	 *
	 * @return   mixed
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function get_result() {

		return $this->result;

	}

	/**
	 * Determine if the response is an error
	 *
	 * @return   boolean
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	public function is_error() {

		return is_wp_error( $this->get_result() );

	}

	/**
	 * Parse the body of the response and set a success/error
	 *
	 * @param    array $response  response data
	 * @return   array
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	abstract protected function parse_response( $response );

	/**
	 * Set an Error
	 * Sets all error variables and sets the result as a WP_Error so the result can always be tested with `is_wp_error()`
	 *
	 * @param    string $message  error message
	 * @param    string $type     error code or type
	 * @param    object $obj      full error object or api response
	 * @return   void
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	protected function set_error( $message, $type, $obj ) {

		$this->result        = new WP_Error( $type, $message, $obj );
		$this->error_type    = $type;
		$this->error_message = $message;
		$this->error_object  = $obj;

	}

	/**
	 * Set the result
	 *
	 * @param    mixed $result  result data
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	protected function set_result( $result ) {
		$this->result = $result;
	}

	/**
	 * Set request body
	 *
	 * @param    array  $data      request body
	 * @param    string $method    request method
	 * @param    string $resource  requested resource
	 * @return   array
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	abstract protected function set_request_body( $data, $method, $resource );

	/**
	 * Set request headers
	 *
	 * @param    array  $headers   default request headers
	 * @param    string $resource  request resource
	 * @param    string $method    request method
	 * @return   array
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	protected function set_request_headers( $headers, $resource, $method ) {
		return $headers;
	}

	/**
	 * Set the request URL
	 *
	 * @param    string $resource  requested resource
	 * @param    string $method    request method
	 * @return   string
	 * @since    3.11.2
	 * @version  3.11.2
	 */
	abstract protected function set_request_url( $resource, $method );

	/**
	 * Set the request User Agent
	 * Can be overridden by extending classes when necessary
	 *
	 * @param    string $user_agent  default user agent (LifterLMS {$version})
	 * @param    string $resource    requested resource
	 * @param    string $method      request method
	 * @return   string
	 * @since    3.22.0
	 * @version  3.22.0
	 */
	protected function set_user_agent( $user_agent, $resource, $method ) {
		return $user_agent;
	}

}