bbp_is_user_subscribed_to_topic( int $user_id, int $topic_id, array $subscribed_ids = array() )

function bbp_is_user_subscribed_to_topic( $user_id = 0, $topic_id = 0, $subscribed_ids = array() ) {

	// Assume user is not subscribed
	$retval = false;

	// Validate user
	$user_id = bbp_get_user_id( $user_id, true, true );
	if ( !empty( $user_id ) ) {

		// Get subscription ID's if none passed
		if ( empty( $subscribed_ids ) ) {
			$subscribed_ids = bbp_get_user_subscribed_topic_ids( $user_id );
		}

		// User has topic subscriptions
		if ( ! empty( $subscribed_ids ) ) {

			// Checking a specific topic id
			if ( ! empty( $topic_id ) ) {
				$topic    = bbp_get_topic( $topic_id );
				$topic_id = ! empty( $topic ) ? $topic->ID : 0;

			// Using the global topic id
			} elseif ( bbp_get_topic_id() ) {
				$topic_id = bbp_get_topic_id();

			// Use the current post id
			} elseif ( !bbp_get_topic_id() ) {
				$topic_id = get_the_ID();
			}

			// Is topic_id in the user's favorites
			if ( ! empty( $topic_id ) ) {
				$retval = in_array( $topic_id, $subscribed_ids );
			}
		}
	}

	return (bool) apply_filters( 'bbp_is_user_subscribed_to_topic', (bool) $retval, $user_id, $topic_id, $subscribed_ids );
}