<?php
/**
 * LearnDash integration. The only class that references LearnDash APIs.
 *
 * Verified against LearnDash developer docs (see readme.txt for sources):
 * - action learndash_update_course_access( $user_id, $course_id, $course_access_list, $remove ) [since 2.1.0]
 * - action learndash_user_course_access_expired( $user_id, $course_id ) [since 2.6.2]
 * - ld_course_access_expires_on( $course_id, $user_id ) returns a timestamp
 *
 * @package Enrollment_Verifier_Logger
 */

defined( 'ABSPATH' ) || exit;

/**
 * Passive LearnDash listeners.
 */
class EVLFL_LearnDash {

	const MAX_QUEUE = 200;

	/**
	 * Manager.
	 *
	 * @var EVLFL_Event_Manager
	 */
	private $manager;

	/**
	 * Whether LearnDash hooks are registered.
	 *
	 * @var bool
	 */
	private $registered = false;

	/**
	 * Captured events awaiting flush.
	 *
	 * @var array[]
	 */
	private $queue = array();

	/**
	 * Expired markers: "user:course" => true.
	 *
	 * @var array<string,bool>
	 */
	private $expired = array();

	/**
	 * Last action seen per pair in this request (same-request duplicate guard).
	 *
	 * @var array<string,string>
	 */
	private $last_action = array();

	/**
	 * Constructor.
	 *
	 * @param EVLFL_Event_Manager $manager Manager.
	 */
	public function __construct( $manager ) {
		$this->manager = $manager;
	}

	/**
	 * Whether LearnDash looks available.
	 *
	 * @return bool
	 */
	public static function is_available() {
		return defined( 'LEARNDASH_VERSION' ) || class_exists( 'SFWD_LMS' ) || function_exists( 'ld_update_course_access' );
	}

	/**
	 * LearnDash version string, if known.
	 *
	 * @return string
	 */
	public static function version() {
		return defined( 'LEARNDASH_VERSION' ) ? (string) LEARNDASH_VERSION : '';
	}

	/**
	 * Init: register now if LearnDash is loaded, otherwise retry once LearnDash becomes available.
	 *
	 * @return void
	 */
	public function init() {
		add_action( 'shutdown', array( $this, 'flush' ), 5 );
		if ( ! $this->maybe_register() ) {
			add_action( 'init', array( $this, 'maybe_register' ), 0 );
			add_action( 'wp_loaded', array( $this, 'maybe_register' ), 0 );
		}
	}

	/**
	 * Register LearnDash listeners exactly once, only when LearnDash is present.
	 *
	 * @return bool
	 */
	public function maybe_register() {
		if ( $this->registered ) {
			return true;
		}
		if ( ! self::is_available() ) {
			return false;
		}
		add_action( 'learndash_update_course_access', array( $this, 'on_course_access_updated' ), 10, 4 );
		add_action( 'learndash_user_course_access_expired', array( $this, 'on_course_access_expired' ), 10, 2 );
		$this->registered = true;
		return true;
	}

	/**
	 * Whether hooks are registered.
	 *
	 * @return bool
	 */
	public function is_registered() {
		return $this->registered;
	}

	/**
	 * Enrollment/unenrollment hook. Never lets an error escape.
	 *
	 * @param int         $user_id            User ID.
	 * @param int         $course_id          Course ID.
	 * @param string|null $course_access_list Legacy list (null when not used).
	 * @param bool        $remove             True when access was removed.
	 * @return void
	 */
	public function on_course_access_updated( $user_id = 0, $course_id = 0, $course_access_list = null, $remove = false ) {
		try {
			$user_id   = absint( $user_id );
			$course_id = absint( $course_id );
			$action    = $remove ? EVLFL_Event::ACTION_UNENROLLED : EVLFL_Event::ACTION_ENROLLED;
			$key       = $user_id . ':' . $course_id;

			if ( isset( $this->last_action[ $key ] ) && $this->last_action[ $key ] === $action ) {
				return; // LearnDash fired the same change twice in one request.
			}

			$pending = $this->manager->capture(
				array(
					'user_id'   => $user_id,
					'course_id' => $course_id,
					'action'    => $action,
					'hook'      => 'learndash_update_course_access',
					'state'     => $this->snapshot_state( $user_id, $course_id ),
					'metadata'  => array(
						'legacy_access_list' => null !== $course_access_list,
						'learndash_version'  => self::version(),
					),
				)
			);
			if ( null === $pending ) {
				return;
			}
			$this->last_action[ $key ] = $action;
			$pending['key']            = $key;
			$this->queue[]             = $pending;

			if ( count( $this->queue ) >= self::MAX_QUEUE ) {
				$this->flush();
			}
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
	}

	/**
	 * Expiry hook: remembers that LearnDash reported this pair as expired.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return void
	 */
	public function on_course_access_expired( $user_id = 0, $course_id = 0 ) {
		try {
			$this->expired[ absint( $user_id ) . ':' . absint( $course_id ) ] = true;
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
	}

	/**
	 * Process queued events. Runs at shutdown so the expiry marker is known regardless of hook order.
	 *
	 * @return void
	 */
	public function flush() {
		try {
			$queue       = $this->queue;
			$this->queue = array();
			foreach ( $queue as $i => $pending ) {
				$extra = array( 'expired_hook_fired' => ! empty( $this->expired[ $pending['key'] ] ) );
				foreach ( $queue as $j => $other ) {
					if ( $j === $i || $other['key'] !== $pending['key'] ) {
						continue;
					}
					if ( $j > $i && EVLFL_Event::ACTION_UNENROLLED === $pending['event']['action'] && EVLFL_Event::ACTION_ENROLLED === $other['event']['action'] ) {
						$extra['reenrolled_in_request'] = true; // Access removed, then granted again in this same request.
					}
					if ( $j < $i && EVLFL_Event::ACTION_ENROLLED === $pending['event']['action'] && EVLFL_Event::ACTION_UNENROLLED === $other['event']['action'] ) {
						$extra['unenrolled_earlier_in_request'] = true;
					}
				}
				$this->manager->process( $pending, $extra );
			}
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
	}

	/**
	 * Read-only snapshot of access state, guarded per function.
	 *
	 * @param int $user_id   User.
	 * @param int $course_id Course.
	 * @return array
	 */
	private function snapshot_state( $user_id, $course_id ) {
		$state = array(
			'expires_on' => null,
			'has_access' => null,
		);
		try {
			if ( function_exists( 'ld_course_access_expires_on' ) ) {
				$ts = ld_course_access_expires_on( $course_id, $user_id );
				if ( is_numeric( $ts ) && (int) $ts > 0 ) {
					$state['expires_on'] = (int) $ts;
				}
			}
			// Deliberately NOT calling sfwd_lms_has_access(): it may run LearnDash's expiry
			// processing and thereby change enrollments, which this plugin must never do.
			$state['has_access'] = apply_filters( 'evlfl_snapshot_has_access', null, $user_id, $course_id );
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
		return $state;
	}

	/**
	 * Debug-only logging.
	 *
	 * @param \Throwable $e Error.
	 * @return void
	 */
	private function debug( $e ) {
		if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
			error_log( 'EVL LearnDash error: ' . get_class( $e ) . ': ' . $e->getMessage() ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
		}
	}
}