<?php
namespace AccessNow\SimpleLMS;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

// Enrolments live in the plugin's own {prefix}slms_enrollments table, so direct
// queries are required; results are per-user and change on every action, so they
// are not cached. Every value goes through $wpdb->prepare() or $wpdb->insert/update/delete.
// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching

/**
 * Course enrolments.
 */
class Enrollment {

	/** Columns the admin list may be ordered by. */
	const ORDERBY_COLUMNS = array( 'enrolled_at', 'completed_at', 'status', 'id', 'user_id', 'course_id' );

	public static function init() {
		add_action( 'delete_user', array( __CLASS__, 'cleanup_user_data' ) );
		add_action( 'before_delete_post', array( __CLASS__, 'cleanup_course_data' ) );
		add_action( 'before_delete_post', array( __CLASS__, 'cleanup_lesson_data' ) );
		add_action( 'before_delete_post', array( __CLASS__, 'cleanup_quiz_data' ) );

		// New or moved lessons reopen completed enrolments (after Lesson_Meta/Unit_Meta save the parent).
		add_action( 'save_post_slms_lesson', array( __CLASS__, 'on_structure_save' ), 30, 2 );
		add_action( 'save_post_slms_unit', array( __CLASS__, 'on_structure_save' ), 30, 2 );

		// Catch-all for changes made without a save (import, cloning, direct meta edits).
		add_action( 'template_redirect', array( __CLASS__, 'reopen_on_view' ), 20 );
	}

	/**
	 * Reopen a completed enrolment when its course has gained lessons, or a lesson was invalidated,
	 * so that progress is below 100% again.
	 *
	 * The certificate, points and history are kept. The enrolment is completed again when
	 * progress is back at 100% (Ajax::handle_mark_complete()).
	 *
	 * @param object $enrollment Enrolment row.
	 * @return bool Whether it was reopened.
	 */
	public static function reopen_if_incomplete( $enrollment ) {
		if ( ! $enrollment || 'completed' !== $enrollment->status ) {
			return false;
		}
		if ( Progress::get_course_progress( $enrollment->user_id, $enrollment->course_id, $enrollment->id ) >= 100 ) {
			return false;
		}
		// A re-enrolment already holds the one active run for this course.
		if ( self::get_active_enrollment( $enrollment->user_id, $enrollment->course_id ) ) {
			return false;
		}

		global $wpdb;
		$reopened = (bool) $wpdb->update(
			$wpdb->prefix . 'slms_enrollments',
			array(
				'status'       => 'active',
				'completed_at' => null,
			),
			array(
				'id'     => $enrollment->id,
				'status' => 'completed',
			),
			array( '%s', '%s' ),
			array( '%d', '%s' )
		);
		if ( $reopened ) {
			/**
			 * A completed enrolment went back to active because its course changed.
			 *
			 * @since 1.0.0
			 *
			 * @param int $user_id       User ID.
			 * @param int $course_id     Course ID.
			 * @param int $enrollment_id Enrolment ID.
			 */
			do_action( 'accessnow_slms_enrollment_reopened', (int) $enrollment->user_id, (int) $enrollment->course_id, (int) $enrollment->id );
		}
		return $reopened;
	}

	/**
	 * Reopen every completed enrolment in a course that is no longer at 100%.
	 *
	 * @param int $course_id Course ID.
	 * @return int Number reopened.
	 */
	public static function reopen_course( $course_id ) {
		global $wpdb;
		$course_id = (int) $course_id;
		$total     = Progress::count_course_lessons( $course_id );
		if ( ! $course_id || ! $total ) {
			return 0;
		}

		// Only the completed enrolments with fewer completed lessons than the course has.
		$candidates = $wpdb->get_results(
			$wpdb->prepare(
				"SELECT e.* FROM {$wpdb->prefix}slms_enrollments e
				WHERE e.course_id = %d AND e.status = 'completed'
				AND ( SELECT COUNT(*) FROM {$wpdb->prefix}slms_progress p WHERE p.enrollment_id = e.id AND p.course_id = %d AND p.status = 'complete' ) < %d",
				$course_id,
				$course_id,
				$total
			)
		);

		$reopened = 0;
		foreach ( $candidates as $enrollment ) {
			if ( self::reopen_if_incomplete( $enrollment ) ) {
				++$reopened;
			}
		}
		return $reopened;
	}

	/**
	 * A published lesson or unit was saved: its course may have gained lessons.
	 *
	 * @param int     $post_id Post ID.
	 * @param WP_Post $post    Post.
	 */
	public static function on_structure_save( $post_id, $post ) {
		if ( ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) || wp_is_post_revision( $post_id ) || 'publish' !== $post->post_status ) {
			return;
		}
		$course_id = 'slms_unit' === $post->post_type
			? get_post_meta( $post_id, '_slms_parent_course', true )
			: Access_Control::get_course_id_from_content( $post_id, 'slms_lesson' );
		if ( $course_id ) {
			self::reopen_course( $course_id );
		}
	}

	/**
	 * When a completed student opens the course, a lesson or a quiz, reopen their enrolment
	 * if the course has changed since they finished it.
	 */
	public static function reopen_on_view() {
		if ( is_admin() || ! is_user_logged_in() || ! is_singular( array( 'slms_course', 'slms_lesson', 'slms_quiz' ) ) ) {
			return;
		}
		$course_id = (int) Access_Control::get_course_id_from_content( get_the_ID() );
		if ( $course_id ) {
			self::reopen_if_incomplete( self::get_enrollment( get_current_user_id(), $course_id ) );
		}
	}

	public static function enroll( $user_id, $course_id, $enrolled_by = 0 ) {
		global $wpdb;

		// Atomic check-and-insert: only insert if no active enrollment exists
		$now = current_time( 'mysql', true );
		$wpdb->query(
			$wpdb->prepare(
				"INSERT INTO {$wpdb->prefix}slms_enrollments (user_id, course_id, enrolled_by, status, enrolled_at)
				SELECT %d, %d, %d, 'active', %s
				FROM DUAL
				WHERE NOT EXISTS (
					SELECT 1 FROM {$wpdb->prefix}slms_enrollments WHERE user_id = %d AND course_id = %d AND status = 'active'
				)",
				$user_id,
				$course_id,
				$enrolled_by,
				$now,
				$user_id,
				$course_id
			)
		);

		if ( $wpdb->insert_id ) {
			$enrollment_id = (int) $wpdb->insert_id;
			/**
			 * A student was enrolled in a course (a new enrolment row, not an existing one).
			 *
			 * Self-enrolment passes 0 as $enrolled_by; an administrator's enrolment passes their ID.
			 *
			 * @since 1.0.0
			 *
			 * @param int $user_id       User ID.
			 * @param int $course_id     Course ID.
			 * @param int $enrollment_id New enrolment ID.
			 * @param int $enrolled_by   User ID of whoever enrolled them, or 0 for self-enrolment.
			 */
			do_action( 'accessnow_slms_enrolled', (int) $user_id, (int) $course_id, $enrollment_id, (int) $enrolled_by );
			return $enrollment_id;
		}

		// Already enrolled — return existing enrollment ID
		$active = self::get_active_enrollment( $user_id, $course_id );
		return $active ? $active->id : 0;
	}

	/**
	 * Whether a student may enrol themselves in a course.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return true|\WP_Error
	 */
	public static function can_self_enroll( $user_id, $course_id ) {
		$mode    = get_post_meta( $course_id, '_slms_enrollment_mode', true ) ?: 'both';
		$current = self::get_enrollment( $user_id, $course_id );
		if ( $current && self::is_expired( $current ) ) {
			// Enrolling again would start a run with no end date; extending access is for an administrator.
			$allowed = new \WP_Error(
				'access_ended',
				/* translators: %s: date. */
				sprintf( __( 'Your access to this course ended on %s.', 'accessnow-lms' ), self::access_end_date( $current ) )
			);
		} else {
			$allowed = 'admin' === $mode
				? new \WP_Error( 'admin_only', __( 'Self-enrollment is not available for this course.', 'accessnow-lms' ) )
				: true;
		}

		/**
		 * Whether a student may enrol themselves in a course: the hook for payments,
		 * prerequisites and capacity limits.
		 *
		 * Return false, or a WP_Error whose message is shown to the student. Enrolments made by an
		 * administrator are not filtered.
		 *
		 * @since 1.0.0
		 *
		 * @param true|WP_Error $allowed   True, or a WP_Error when the course is admin-enrolment only or
		 *                                 the student's access to it has ended.
		 * @param int           $user_id   User ID.
		 * @param int           $course_id Course ID.
		 */
		$allowed = apply_filters( 'accessnow_slms_can_enroll', $allowed, (int) $user_id, (int) $course_id );

		if ( false === $allowed ) {
			return new \WP_Error( 'not_allowed', __( 'You cannot enroll in this course.', 'accessnow-lms' ) );
		}
		return is_wp_error( $allowed ) ? $allowed : true;
	}

	/**
	 * Drop a student's active enrolment in a course.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return int Rows changed.
	 */
	public static function unenroll( $user_id, $course_id ) {
		$active = self::get_active_enrollment( $user_id, $course_id );
		return $active ? (int) self::drop( $active->id ) : 0;
	}

	/**
	 * Drop an enrolment (active or completed). Its history is kept.
	 *
	 * @param int $enrollment_id Enrolment ID.
	 * @param int $dropped_by    User ID of whoever dropped it, or 0.
	 * @return bool Whether it changed.
	 */
	public static function drop( $enrollment_id, $dropped_by = 0 ) {
		global $wpdb;
		$enrollment = self::get_enrollment_by_id( $enrollment_id );
		if ( ! $enrollment || 'dropped' === $enrollment->status ) {
			return false;
		}
		$changed = (bool) $wpdb->update(
			$wpdb->prefix . 'slms_enrollments',
			array( 'status' => 'dropped' ),
			array(
				'id'     => $enrollment->id,
				'status' => $enrollment->status,
			),
			array( '%s' ),
			array( '%d', '%s' )
		);
		if ( $changed ) {
			/**
			 * An enrolment was dropped.
			 *
			 * @since 1.0.0
			 *
			 * @param int    $user_id       User ID.
			 * @param int    $course_id     Course ID.
			 * @param int    $enrollment_id Enrolment ID.
			 * @param int    $dropped_by    User ID of whoever dropped it, or 0.
			 * @param string $old_status    'active' or 'completed'.
			 */
			do_action( 'accessnow_slms_unenrolled', (int) $enrollment->user_id, (int) $enrollment->course_id, (int) $enrollment->id, (int) $dropped_by, $enrollment->status );
		}
		return $changed;
	}

	/**
	 * Mark a student's active enrolment completed.
	 *
	 * Only an active enrolment changes, so this returns 1 once per completion. Most code wants
	 * maybe_complete(), which also issues the certificate and fires accessnow_slms_course_completed.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return int|false Rows changed.
	 */
	public static function complete_enrollment( $user_id, $course_id ) {
		global $wpdb;
		return $wpdb->query(
			$wpdb->prepare(
				"UPDATE {$wpdb->prefix}slms_enrollments SET status = 'completed', completed_at = %s WHERE user_id = %d AND course_id = %d AND status = 'active'",
				current_time( 'mysql', true ),
				$user_id,
				$course_id
			)
		);
	}

	/**
	 * Complete the enrolment if every lesson is done: mark it completed, issue the certificate
	 * (or keep the one a reopened enrolment already has) and fire accessnow_slms_course_completed.
	 *
	 * @param int $user_id       User ID.
	 * @param int $course_id     Course ID.
	 * @param int $enrollment_id Enrolment ID.
	 * @return bool Whether the course was completed by this call.
	 */
	public static function maybe_complete( $user_id, $course_id, $enrollment_id ) {
		if ( Progress::get_course_progress( $user_id, $course_id, $enrollment_id ) < 100 || ! self::complete_enrollment( $user_id, $course_id ) ) {
			return false;
		}
		// A reopened enrolment keeps its certificate.
		$first_completion = ! Certificates::get_for_enrollment( $enrollment_id, $course_id );
		$certificate      = Certificates::issue( $user_id, $course_id, $enrollment_id );

		/**
		 * A student completed a course. Fires once per completion, including when an enrolment that
		 * was reopened (because the course changed) is completed again; $first_completion is false then.
		 *
		 * The plugin's own completion email and course points are listeners on this action.
		 *
		 * @since 1.0.0
		 *
		 * @param int         $user_id          User ID.
		 * @param int         $course_id        Course ID.
		 * @param int         $enrollment_id    Enrolment ID.
		 * @param bool        $first_completion False when an enrolment is completed again after reopening.
		 * @param object|null $certificate      Certificate row.
		 */
		do_action( 'accessnow_slms_course_completed', (int) $user_id, (int) $course_id, (int) $enrollment_id, $first_completion, $certificate );
		return true;
	}

	public static function is_enrolled( $user_id, $course_id ) {
		$enrollment = self::get_enrollment( $user_id, $course_id );
		return $enrollment && in_array( $enrollment->status, array( 'active', 'completed' ), true );
	}

	/**
	 * Whether a student may use a course's content now: enrolled (active or completed) and their access
	 * hasn't ended. is_enrolled() still answers "enrolled at all", for history and certificates.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return bool
	 */
	public static function has_access( $user_id, $course_id ) {
		$enrollment = self::get_enrollment( $user_id, $course_id );
		$access     = $enrollment && ! self::is_expired( $enrollment );

		/**
		 * Whether a student may use a course's lessons and quizzes now.
		 *
		 * Every content check goes through this: the lesson and quiz pages, the REST API, marking a
		 * lesson complete, submitting a quiz and saving notes.
		 *
		 * @since 1.1.0
		 *
		 * @param bool        $access     Enrolled (active or completed) and not past the access end date.
		 * @param int         $user_id    User ID.
		 * @param int         $course_id  Course ID.
		 * @param object|null $enrollment The enrolment row, or null.
		 */
		return (bool) apply_filters( 'accessnow_slms_has_course_access', $access, (int) $user_id, (int) $course_id, $enrollment );
	}

	/**
	 * The enrolment, when the student has access to the course now; otherwise null.
	 *
	 * @param int $user_id   User ID.
	 * @param int $course_id Course ID.
	 * @return object|null
	 */
	public static function get_accessible_enrollment( $user_id, $course_id ) {
		$enrollment = self::get_enrollment( $user_id, $course_id );
		return ( $enrollment && self::has_access( $user_id, $course_id ) ) ? $enrollment : null;
	}

	/**
	 * Whether an enrolment's access has ended (expires_at is in the past).
	 *
	 * @param object $enrollment Enrolment row.
	 * @return bool
	 */
	public static function is_expired( $enrollment ) {
		return ! empty( $enrollment->expires_at ) && strtotime( $enrollment->expires_at . ' UTC' ) <= time();
	}

	/**
	 * Set or clear when an enrolment's access ends.
	 *
	 * @param int         $enrollment_id Enrolment ID.
	 * @param string|null $expires_at    UTC 'Y-m-d H:i:s' (the moment access ends), or null for no end.
	 * @return bool False when the enrolment doesn't exist or the date is not valid.
	 */
	public static function set_expiry( $enrollment_id, $expires_at ) {
		global $wpdb;
		$enrollment = self::get_enrollment_by_id( $enrollment_id );
		if ( ! $enrollment ) {
			return false;
		}
		if ( null !== $expires_at ) {
			$parsed = \DateTimeImmutable::createFromFormat( '!Y-m-d H:i:s', (string) $expires_at, new \DateTimeZone( 'UTC' ) );
			if ( ! $parsed || $parsed->format( 'Y-m-d H:i:s' ) !== $expires_at ) {
				return false;
			}
		}
		$old = $enrollment->expires_at ? $enrollment->expires_at : null;
		if ( $old === $expires_at ) {
			return true;
		}
		$wpdb->update( "{$wpdb->prefix}slms_enrollments", array( 'expires_at' => $expires_at ), array( 'id' => (int) $enrollment_id ), array( '%s' ), array( '%d' ) );

		/**
		 * An enrolment's access end date was set, changed or cleared.
		 *
		 * @since 1.1.0
		 *
		 * @param int         $enrollment_id Enrolment ID.
		 * @param string|null $old           Previous UTC end, or null.
		 * @param string|null $new           New UTC end, or null.
		 */
		do_action( 'accessnow_slms_enrollment_expiry_changed', (int) $enrollment_id, $old, $expires_at );
		return true;
	}

	/**
	 * The UTC moment access ends for an "Access until" date: the end of that day in the site's time zone.
	 *
	 * @param string $date 'Y-m-d'.
	 * @return string|null UTC 'Y-m-d H:i:s', or null when the date is not valid.
	 */
	public static function expiry_from_date( $date ) {
		$day = \DateTimeImmutable::createFromFormat( '!Y-m-d', (string) $date, wp_timezone() );
		if ( ! $day || $day->format( 'Y-m-d' ) !== $date ) {
			return null;
		}
		return $day->modify( '+1 day' )->setTimezone( new \DateTimeZone( 'UTC' ) )->format( 'Y-m-d H:i:s' );
	}

	/**
	 * The last day of access, as the site shows dates, or '' when access doesn't end.
	 *
	 * @param object $enrollment Enrolment row.
	 * @param string $format     Date format; the site's by default ('Y-m-d' for form fields).
	 * @return string
	 */
	public static function access_end_date( $enrollment, $format = '' ) {
		if ( empty( $enrollment->expires_at ) ) {
			return '';
		}
		return wp_date( $format ? $format : get_option( 'date_format' ), strtotime( $enrollment->expires_at . ' UTC' ) - 1 );
	}

	public static function get_enrollment( $user_id, $course_id ) {
		global $wpdb;
		return $wpdb->get_row(
			$wpdb->prepare(
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE user_id = %d AND course_id = %d AND status IN ('active','completed') ORDER BY FIELD(status,'active','completed') LIMIT 1",
				$user_id,
				$course_id
			)
		);
	}

	public static function get_active_enrollment( $user_id, $course_id ) {
		global $wpdb;
		return $wpdb->get_row(
			$wpdb->prepare(
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE user_id = %d AND course_id = %d AND status = 'active' LIMIT 1",
				$user_id,
				$course_id
			)
		);
	}

	public static function get_enrollment_by_id( $enrollment_id ) {
		global $wpdb;
		return $wpdb->get_row(
			$wpdb->prepare(
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE id = %d",
				$enrollment_id
			)
		);
	}

	/**
	 * A user's enrolments, newest first.
	 *
	 * @param int          $user_id User ID.
	 * @param string|array $status  One status or a list of statuses.
	 * @return array
	 */
	public static function get_user_enrollments( $user_id, $status = 'active' ) {
		global $wpdb;
		$statuses     = array_values( array_map( 'strval', (array) $status ) );
		$placeholders = implode( ',', array_fill( 0, count( $statuses ), '%s' ) );
		return $wpdb->get_results(
			$wpdb->prepare(
				// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $placeholders is a list of %s placeholders.
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE user_id = %d AND status IN ({$placeholders}) ORDER BY enrolled_at DESC",
				array_merge( array( $user_id ), $statuses )
			)
		);
	}

	public static function get_course_enrollments( $course_id, $status = '' ) {
		global $wpdb;

		if ( $status ) {
			return $wpdb->get_results(
				$wpdb->prepare(
					"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE course_id = %d AND status = %s ORDER BY enrolled_at DESC",
					$course_id,
					$status
				)
			);
		}

		return $wpdb->get_results(
			$wpdb->prepare(
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE course_id = %d ORDER BY enrolled_at DESC",
				$course_id
			)
		);
	}

	public static function get_all_enrollments( $args = array() ) {
		global $wpdb;
		$defaults = array(
			'status'    => '',
			'course_id' => 0,
			'per_page'  => 20,
			'offset'    => 0,
			'orderby'   => 'enrolled_at',
			'order'     => 'DESC',
		);
		$args     = wp_parse_args( $args, $defaults );

		// ORDER BY can't be a placeholder: only whitelisted columns and directions are used.
		$orderby = in_array( $args['orderby'], self::ORDERBY_COLUMNS, true ) ? $args['orderby'] : 'enrolled_at';
		$order   = 'ASC' === strtoupper( (string) $args['order'] ) ? 'ASC' : 'DESC';

		// phpcs:ignore PluginCheck.Security.DirectDB.UnescapedDBParameter -- $orderby/$order are whitelisted above.
		return $wpdb->get_results(
			$wpdb->prepare(
				// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $orderby/$order are whitelisted above.
				"SELECT * FROM {$wpdb->prefix}slms_enrollments WHERE ( %s = '' OR status = %s ) AND ( 0 = %d OR course_id = %d ) ORDER BY {$orderby} {$order} LIMIT %d OFFSET %d",
				(string) $args['status'],
				(string) $args['status'],
				(int) $args['course_id'],
				(int) $args['course_id'],
				(int) $args['per_page'],
				(int) $args['offset']
			)
		);
	}

	public static function count_enrollments( $args = array() ) {
		global $wpdb;
		$status    = ! empty( $args['status'] ) ? (string) $args['status'] : '';
		$course_id = ! empty( $args['course_id'] ) ? (int) $args['course_id'] : 0;

		return (int) $wpdb->get_var(
			$wpdb->prepare(
				"SELECT COUNT(*) FROM {$wpdb->prefix}slms_enrollments WHERE ( %s = '' OR status = %s ) AND ( 0 = %d OR course_id = %d )",
				$status,
				$status,
				$course_id,
				$course_id
			)
		);
	}

	public static function cleanup_user_data( $user_id ) {
		global $wpdb;
		$prefix = $wpdb->prefix;
		$wpdb->delete( $prefix . 'slms_enrollments', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_progress', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_quiz_attempts', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_lesson_notes', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_points', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_badges', array( 'user_id' => $user_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_certificates', array( 'user_id' => $user_id ), array( '%d' ) );
	}

	public static function cleanup_course_data( $post_id ) {
		if ( 'slms_course' !== get_post_type( $post_id ) ) {
			return;
		}
		global $wpdb;
		$prefix = $wpdb->prefix;
		$wpdb->delete( $prefix . 'slms_enrollments', array( 'course_id' => $post_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_progress', array( 'course_id' => $post_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_quiz_attempts', array( 'course_id' => $post_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_certificates', array( 'course_id' => $post_id ), array( '%d' ) );
	}

	public static function cleanup_lesson_data( $post_id ) {
		if ( 'slms_lesson' !== get_post_type( $post_id ) ) {
			return;
		}
		global $wpdb;
		$prefix = $wpdb->prefix;
		$wpdb->delete( $prefix . 'slms_progress', array( 'lesson_id' => $post_id ), array( '%d' ) );
		$wpdb->delete( $prefix . 'slms_lesson_notes', array( 'lesson_id' => $post_id ), array( '%d' ) );
	}

	public static function cleanup_quiz_data( $post_id ) {
		if ( 'slms_quiz' !== get_post_type( $post_id ) ) {
			return;
		}
		global $wpdb;
		$wpdb->delete( $wpdb->prefix . 'slms_quiz_attempts', array( 'quiz_id' => $post_id ), array( '%d' ) );
	}
}