function llms_show_mark_complete_button( $lesson ) {

	$show = true;

	// If a quiz button should be shown, check if user already met quiz requirements.
	if ( llms_show_take_quiz_button( $lesson ) ) {
		$show = false;

		// Check if current user has already met quiz requirements.
		$user_id = get_current_user_id();
		if ( $user_id && $lesson->is_quiz_enabled() ) {
			$student = llms_get_student( $user_id );
			if ( $student ) {
				$quiz_id = $lesson->get( 'quiz' );
				$attempt = $student->quizzes()->get_best_attempt( $quiz_id );

				if ( $attempt ) {
					$passing_required = llms_parse_bool( $lesson->get( 'require_passing_grade' ) );
					// Show button if: passing not required, OR attempt is passing.
					if ( ! $passing_required || $attempt->is_passing() ) {
						$show = true;
					}
				}
			}
		}
	}

	return apply_filters( 'llms_show_mark_complete_button', $show, $lesson );
}