<?php
/**
 * NOTE: this is a temporary class and can be replaced by jetpack-abtest after
 * https://github.com/Automattic/jetpack/issues/19596 has been fixed.
 *
 * A class that interacts with Explat A/B tests.
 *
 * This class is experimental. It is a fork of the jetpack-abtest package and
 * updated for use with ExPlat. These changes are planned to be contributed
 * back to the upstream Jetpack package. If accepted, this class should then
 * be superseded by the Jetpack class using Composer.
 *
 * This class should not be used externally.
 *
 * @package WooCommerce\Admin
 * @link https://packagist.org/packages/automattic/jetpack-abtest
 */

namespace WooCommerce\Admin;

use Automattic\Jetpack\Connection\Manager as Jetpack_Connection_Manager;
use Automattic\Jetpack\Connection\Client as Jetpack_Connection_client;
use Automattic\WooCommerce\Admin\WCAdminHelper;

/**
 * This class provides an interface to the Explat A/B tests.
 *
 * Usage:
 *
 * $anon_id = isset( $_COOKIE['tk_ai'] ) ? sanitize_text_field( wp_unslash( $_COOKIE['tk_ai'] ) ) : '';
 * $allow_tracking = 'yes' === get_option( 'woocommerce_allow_tracking' );
 * $abtest = new \WooCommerce\Admin\Experimental_Abtest(
 *      $anon_id,
 *      'woocommerce',
 *      $allow_tracking
 * );
 *
 * OR use the helper function:
 *
 * WooCommerce\Admin\Experimental_Abtest::in_treatment('experiment_name');
 *
 *
 * $isTreatment = $abtest->get_variation('your-experiment-name') === 'treatment';
 *
 * @internal This class is experimental and should not be used externally due to planned breaking changes.
 */
final class Experimental_Abtest {

	/**
	 * A variable to hold the tests we fetched, and their variations for the current user.
	 *
	 * @var array
	 */
	private $tests = array();

	/**
	 * ExPlat Anonymous ID.
	 *
	 * @var string
	 */
	private $anon_id = null;

	/**
	 * ExPlat Platform name.
	 *
	 * @var string
	 */
	private $platform = 'woocommerce';

	/**
	 * Whether trcking consent is given.
	 *
	 * @var bool
	 */
	private $consent = false;

	/**
	 * Request variation as a auth wpcom user or not.
	 *
	 * @var boolean
	 */
	private $as_auth_wpcom_user = false;

	/**
	 * Constructor.
	 *
	 * @param string $anon_id ExPlat anonymous ID.
	 * @param string $platform ExPlat platform name.
	 * @param bool   $consent Whether tracking consent is given.
	 * @param bool   $as_auth_wpcom_user  Request variation as a auth wp user or not.
	 */
	public function __construct( string $anon_id, string $platform, bool $consent, bool $as_auth_wpcom_user = false ) {
		$this->anon_id            = $anon_id;
		$this->platform           = $platform;
		$this->consent            = $consent;
		$this->as_auth_wpcom_user = $as_auth_wpcom_user;
	}

	/**
	 * Returns true if the current user is in the treatment group of the given experiment.
	 *
	 * @param string $experiment_name Name of the experiment.
	 * @param bool   $as_auth_wpcom_user Request variation as a auth wp user or not.
	 * @return bool
	 */
	public static function in_treatment( string $experiment_name, bool $as_auth_wpcom_user = false ) {
		$anon_id        = isset( $_COOKIE['tk_ai'] ) ? sanitize_text_field( wp_unslash( $_COOKIE['tk_ai'] ) ) : '';
		$allow_tracking = 'yes' === get_option( 'woocommerce_allow_tracking' );
		$abtest         = new self(
			$anon_id,
			'woocommerce',
			$allow_tracking,
			$as_auth_wpcom_user
		);

		return $abtest->get_variation( $experiment_name ) === 'treatment';
	}

	/**
	 * Retrieve the test variation for a provided A/B test.
	 *
	 * @param string $test_name Name of the A/B test.
	 * @return mixed|null A/B test variation, or null on failure.
	 */
	public function get_variation( $test_name ) {
		// Default to the control variation when users haven't consented to tracking.
		if ( ! $this->consent ) {
			return 'control';
		}

		$variation = $this->fetch_variation( $test_name );

		// If there was an error retrieving a variation, conceal the error for the consumer.
		if ( is_wp_error( $variation ) ) {
			return 'control';
		}

		return $variation;
	}


	/**
	 * Perform the request for a experiment assignment of a provided A/B test from WP.com.
	 *
	 * @param array $args Arguments to pass to the request for A/B test.
	 * @return array|\WP_Error A/B test variation error on failure.
	 */
	public function request_assignment( $args ) {
		// Request as authenticated wp user.
		if ( $this->as_auth_wpcom_user && class_exists( Jetpack_Connection_Manager::class ) ) {
			$jetpack_connection_manager = new Jetpack_Connection_Manager();
			if ( $jetpack_connection_manager->is_user_connected() ) {
				$response = Jetpack_Connection_client::wpcom_json_api_request_as_user(
					'/experiments/0.1.0/assignments/' . $this->platform,
					'2',
					$args
				);
			}
		}

		// Request as anonymous user.
		if ( ! isset( $response ) ) {
			if ( ! isset( $args['anon_id'] ) || empty( $args['anon_id'] ) ) {
				return new \WP_Error( 'invalid_anon_id', 'anon_id must be an none empty string.' );
			}

			$url      = add_query_arg(
				$args,
				sprintf(
					'https://public-api.wordpress.com/wpcom/v2/experiments/0.1.0/assignments/%s',
					$this->platform
				)
			);
			$response = wp_remote_get( $url );
		}

		return $response;
	}

	/**
	 * Fetch and cache the test variation for a provided A/B test from WP.com.
	 *
	 * ExPlat returns a null value when the assigned variation is control or
	 * an assignment has not been set. In these instances, this method returns
	 * a value of "control".
	 *
	 * @param string $test_name Name of the A/B test.
	 * @return array|\WP_Error A/B test variation, or error on failure.
	 */
	protected function fetch_variation( $test_name ) {
		// Make sure test name exists.
		if ( ! $test_name ) {
			return new \WP_Error( 'test_name_not_provided', 'A/B test name has not been provided.' );
		}

		// Make sure test name is a valid one.
		if ( ! preg_match( '/^[A-Za-z0-9_]+$/', $test_name ) ) {
			return new \WP_Error( 'invalid_test_name', 'Invalid A/B test name.' );
		}

		// Return internal-cached test variations.
		if ( isset( $this->tests[ $test_name ] ) ) {
			return $this->tests[ $test_name ];
		}

		// Return external-cached test variations.
		if ( ! empty( get_transient( 'abtest_variation_' . $test_name ) ) ) {
			return get_transient( 'abtest_variation_' . $test_name );
		}

		// Make the request to the WP.com API.
		$args = array(
			'experiment_name'               => $test_name,
			'anon_id'                       => rawurlencode( $this->anon_id ),
			'woo_country_code'              => rawurlencode( get_option( 'woocommerce_default_country', 'US:CA' ) ),
			'woo_wcadmin_install_timestamp' => rawurlencode( get_option( WCAdminHelper::WC_ADMIN_TIMESTAMP_OPTION ) ),
		);

		/**
		 * Get additional request args.
		 *
		 * @since 6.5.0
		 */
		$args     = apply_filters( 'woocommerce_explat_request_args', $args );
		$response = $this->request_assignment( $args );

		// Bail if there was an error or malformed response.
		if ( is_wp_error( $response ) || ! is_array( $response ) || ! isset( $response['body'] ) ) {
			return new \WP_Error( 'failed_to_fetch_data', 'Unable to fetch the requested data.' );
		}

		// Decode the results.
		$results = json_decode( $response['body'], true );

		// Bail if there were no resultsreturned.
		if ( ! is_array( $results ) ) {
			return new \WP_Error( 'unexpected_data_format', 'Data was not returned in the expected format.' );
		}

		// Store the variation in our internal cache.
		$this->tests[ $test_name ] = $results['variations'][ $test_name ] ?? null;

		$variation = $results['variations'][ $test_name ] ?? 'control';
		// Store the variation in our external cache.
		if ( ! empty( $results['ttl'] ) ) {
			set_transient( 'abtest_variation_' . $test_name, $variation, $results['ttl'] );
		}

		return $variation;
	}
}