/*
   GoToSocial
   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU Affero General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Affero General Public License for more details.

   You should have received a copy of the GNU Affero General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package distributor

import (
	"github.com/go-fed/activity/pub"
	"github.com/sirupsen/logrus"
)

// Distributor should be passed to api modules (see internal/apimodule/...). It is used for
// passing messages back and forth from the client API and the federating interface, via channels.
// It also contains logic for filtering which messages should end up where.
// It is designed to be used asynchronously: the client API and the federating API should just be able to
// fire messages into the distributor and not wait for a reply before proceeding with other work. This allows
// for clean distribution of messages without slowing down the client API and harming the user experience.
type Distributor interface {
	// ClientAPIIn returns a channel for accepting messages that come from the gts client API.
	ClientAPIIn() chan interface{}
	// ClientAPIOut returns a channel for putting in messages that need to go to the gts client API.
	ClientAPIOut() chan interface{}
	// Start starts the Distributor, reading from its channels and passing messages back and forth.
	Start() error
	// Stop stops the distributor cleanly, finishing handling any remaining messages before closing down.
	Stop() error
}

// distributor just implements the Distributor interface
type distributor struct {
	federator    pub.FederatingActor
	clientAPIIn  chan interface{}
	clientAPIOut chan interface{}
	stop         chan interface{}
	log          *logrus.Logger
}

// New returns a new Distributor that uses the given federator and logger
func New(federator pub.FederatingActor, log *logrus.Logger) Distributor {
	return &distributor{
		federator:    federator,
		clientAPIIn:  make(chan interface{}, 100),
		clientAPIOut: make(chan interface{}, 100),
		stop:         make(chan interface{}),
		log:          log,
	}
}

// ClientAPIIn returns a channel for accepting messages that come from the gts client API.
func (d *distributor) ClientAPIIn() chan interface{} {
	return d.clientAPIIn
}

// ClientAPIOut returns a channel for putting in messages that need to go to the gts client API.
func (d *distributor) ClientAPIOut() chan interface{} {
	return d.clientAPIOut
}

// Start starts the Distributor, reading from its channels and passing messages back and forth.
func (d *distributor) Start() error {
	go func() {
	DistLoop:
		for {
			select {
			case clientMsgIn := <-d.clientAPIIn:
				d.log.Infof("received clientMsgIn: %+v", clientMsgIn)
			case clientMsgOut := <-d.clientAPIOut:
				d.log.Infof("received clientMsgOut: %+v", clientMsgOut)
			case <-d.stop:
				break DistLoop
			}
		}
	}()
	return nil
}

// Stop stops the distributor cleanly, finishing handling any remaining messages before closing down.
// TODO: empty message buffer properly before stopping otherwise we'll lose federating messages.
func (d *distributor) Stop() error {
	close(d.stop)
	return nil
}