function bbp_subscriptions_handler( $action = '' ) {

	// Default
	$success = false;

	// Bail if subscriptions not active
	if ( ! bbp_is_subscriptions_active() ) {
		return $success;
	}

	// Bail if no object ID is passed
	if ( empty( $_GET['object_id'] ) ) {
		return $success;
	}

	// Setup possible get actions
	$possible_actions = array(
		'bbp_subscribe',
		'bbp_unsubscribe'
	);

	// Bail if actions aren't meant for this function
	if ( ! in_array( $action, $possible_actions, true ) ) {
		return $success;
	}

	// Get required data
	$user_id     = bbp_get_current_user_id();
	$object_id   = absint( $_GET['object_id'] );
	$object_type = ! empty( $_GET['object_type'] )
		? sanitize_key( $_GET['object_type'] )
		: 'post';

	// Check for empty topic
	if ( empty( $object_id ) ) {
		bbp_add_error( 'bbp_subscription_object_id', __( '<strong>ERROR</strong>: Not found. What are you subscribing/unsubscribing to?', 'bbpress' ) );

	// Check nonce
	} elseif ( ! bbp_verify_nonce_request( 'toggle-subscription_' . $object_id ) ) {
		bbp_add_error( 'bbp_subscription_object_id', __( '<strong>ERROR</strong>: Are you sure you wanted to do that?', 'bbpress' ) );

	// Check current user's ability to edit the user
	} elseif ( ! current_user_can( 'edit_user', $user_id ) ) {
		bbp_add_error( 'bbp_subscription_permission', __( '<strong>ERROR</strong>: You do not have permission to edit subscriptions of that user.', 'bbpress' ) );
	}

	// Bail if we have errors
	if ( bbp_has_errors() ) {
		return $success;
	}

	/** No errors *************************************************************/

	if ( 'bbp_unsubscribe' === $action ) {
		$success = bbp_remove_user_subscription( $user_id, $object_id, $object_type );
	} elseif ( 'bbp_subscribe' === $action ) {
		$success = bbp_add_user_subscription( $user_id, $object_id, $object_type );
	}

	// Do additional subscriptions actions
	do_action( 'bbp_subscriptions_handler', $success, $user_id, $object_id, $action, $object_type );

	// Success!
	if ( true === $success ) {

		// Redirect back from whence we came
		if ( ! empty( $_REQUEST['redirect_to'] ) ) {
			$redirect = $_REQUEST['redirect_to']; // Validated later
		} elseif ( bbp_is_subscriptions() ) {
			$redirect = bbp_get_subscriptions_permalink( $user_id );
		} elseif ( bbp_is_single_user() ) {
			$redirect = bbp_get_user_profile_url();
		} elseif ( is_singular( bbp_get_topic_post_type() ) ) {
			$redirect = bbp_get_topic_permalink( $object_id );
		} elseif ( is_singular( bbp_get_forum_post_type() ) ) {
			$redirect = bbp_get_forum_permalink( $object_id );
		} elseif ( is_single() || is_page() ) {
			$redirect = get_permalink();
		} else {
			$redirect = get_permalink( $object_id );
		}

		bbp_redirect( $redirect );

	// Fail! Handle errors
	} elseif ( 'bbp_unsubscribe' === $action ) {
		bbp_add_error( 'bbp_unsubscribe', __( '<strong>ERROR</strong>: There was a problem unsubscribing.', 'bbpress' ) );
	} elseif ( 'bbp_subscribe' === $action ) {
		bbp_add_error( 'bbp_subscribe',   __( '<strong>ERROR</strong>: There was a problem subscribing.', 'bbpress' ) );
	}

	return (bool) $success;
}