/*
Real-time Online/Offline Charging System (OCS) for Telecom & ISP environments
Copyright (C) ITsysCOM GmbH

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU 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 General Public License for more details.

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

package ers

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"time"

	"github.com/cgrates/birpc/context"
	"github.com/cgrates/cgrates/agents"
	"github.com/cgrates/cgrates/config"
	"github.com/cgrates/cgrates/ees"
	"github.com/cgrates/cgrates/engine"
	"github.com/cgrates/cgrates/utils"
	"github.com/nats-io/nats.go"
)

// NewNatsER return a new amqp event reader
func NewNatsER(cfg *config.CGRConfig, cfgIdx int,
	rdrEvents, partialEvents chan *erEvent, rdrErr chan error,
	fltrS *engine.FilterS, rdrExit chan struct{}, connMgr *engine.ConnManager) (_ EventReader, err error) {
	rdr := &NatsER{
		connMgr:       connMgr,
		cgrCfg:        cfg,
		cfgIdx:        cfgIdx,
		fltrS:         fltrS,
		rdrEvents:     rdrEvents,
		partialEvents: partialEvents,
		rdrExit:       rdrExit,
		rdrErr:        rdrErr,
	}
	if concReq := rdr.Config().ConcurrentReqs; concReq != -1 {
		rdr.cap = make(chan struct{}, concReq)
		for i := 0; i < concReq; i++ {
			rdr.cap <- struct{}{}
		}
	}
	if err = rdr.processOpts(); err != nil {
		return
	}
	if err = rdr.createPoster(); err != nil {
		return
	}
	return rdr, nil
}

// NatsER implements EventReader interface for amqp message
type NatsER struct {
	// sync.RWMutex
	cgrCfg  *config.CGRConfig
	cfgIdx  int // index of config instance within ERsCfg.Readers
	fltrS   *engine.FilterS
	connMgr *engine.ConnManager

	rdrEvents     chan *erEvent // channel to dispatch the events created to
	partialEvents chan *erEvent // channel to dispatch the partial events created to
	rdrExit       chan struct{}
	rdrErr        chan error
	cap           chan struct{}

	subject      string
	queueID      string
	jetStream    bool
	consumerName string
	opts         []nats.Option
	jsOpts       []nats.JSOpt

	poster *ees.NatsEE
}

// Config returns the curent configuration
func (rdr *NatsER) Config() *config.EventReaderCfg {
	return rdr.cgrCfg.ERsCfg().Readers[rdr.cfgIdx]
}

// Serve will start the gorutines needed to watch the nats subject
func (rdr *NatsER) Serve() (err error) {
	// Connect to a server
	var nc *nats.Conn
	var js nats.JetStreamContext

	if nc, err = nats.Connect(rdr.Config().SourcePath, rdr.opts...); err != nil {
		return
	}
	ch := make(chan *nats.Msg)
	if !rdr.jetStream {
		if _, err = nc.ChanQueueSubscribe(rdr.subject, rdr.queueID, ch); err != nil {
			return
		}
	} else {
		js, err = nc.JetStream(rdr.jsOpts...)
		if err != nil {
			return
		}
		if _, err = js.QueueSubscribe(rdr.subject, rdr.queueID, func(msg *nats.Msg) {
			ch <- msg
		}, nats.Durable(rdr.consumerName)); err != nil {
			return
		}
	}
	go func() {
		for {
			if rdr.Config().ConcurrentReqs != -1 {
				<-rdr.cap // do not try to read if the limit is reached
			}
			select {
			case <-rdr.rdrExit:
				utils.Logger.Info(
					fmt.Sprintf("<%s> stop monitoring nats path <%s>",
						utils.ERs, rdr.Config().SourcePath))
				nc.Drain()
				if rdr.poster != nil {
					rdr.poster.Close()
				}
				return
			case msg := <-ch:
				go func(msg *nats.Msg) {
					if err := rdr.processMessage(msg.Data); err != nil {
						utils.Logger.Warning(
							fmt.Sprintf("<%s> processing message %s error: %s",
								utils.ERs, string(msg.Data), err.Error()))
					}
					if rdr.poster != nil { // post it
						if err := ees.ExportWithAttempts(context.Background(), rdr.poster, msg.Data, utils.EmptyString,
							rdr.connMgr, rdr.cgrCfg.GeneralCfg().DefaultTenant); err != nil {
							utils.Logger.Warning(
								fmt.Sprintf("<%s> writing message %s error: %s",
									utils.ERs, string(msg.Data), err.Error()))
						}
					}
					if rdr.Config().ConcurrentReqs != -1 {
						rdr.cap <- struct{}{}
					}
				}(msg)
			}
		}
	}()
	return
}

func (rdr *NatsER) processMessage(msg []byte) (err error) {
	var decodedMessage map[string]interface{}
	if err = json.Unmarshal(msg, &decodedMessage); err != nil {
		return
	}
	agReq := agents.NewAgentRequest(
		utils.MapStorage(decodedMessage), nil,
		nil, nil, nil, rdr.Config().Tenant,
		rdr.cgrCfg.GeneralCfg().DefaultTenant,
		utils.FirstNonEmpty(rdr.Config().Timezone,
			rdr.cgrCfg.GeneralCfg().DefaultTimezone),
		rdr.fltrS, nil) // create an AgentRequest
	var pass bool
	if pass, err = rdr.fltrS.Pass(context.TODO(), agReq.Tenant, rdr.Config().Filters,
		agReq); err != nil || !pass {
		return
	}
	if err = agReq.SetFields(rdr.Config().Fields); err != nil {
		return
	}
	cgrEv := utils.NMAsCGREvent(agReq.CGRRequest, agReq.Tenant, utils.NestingSep, agReq.Opts)
	rdrEv := rdr.rdrEvents
	if _, isPartial := cgrEv.APIOpts[utils.PartialOpt]; isPartial {
		rdrEv = rdr.partialEvents
	}
	rdrEv <- &erEvent{
		cgrEvent: cgrEv,
		rdrCfg:   rdr.Config(),
	}
	return
}

func (rdr *NatsER) createPoster() (err error) {
	processedOpt := getProcessOptions(rdr.Config().Opts)
	if processedOpt == nil {
		if len(rdr.Config().ProcessedPath) == 0 {
			return
		}
		processedOpt = new(config.EventExporterOpts)
	}
	rdr.poster, err = ees.NewNatsEE(&config.EventExporterCfg{
		ID: rdr.Config().ID,
		ExportPath: utils.FirstNonEmpty(
			rdr.Config().ProcessedPath, rdr.Config().SourcePath),
		Opts:     processedOpt,
		Attempts: rdr.cgrCfg.EEsCfg().GetDefaultExporter().Attempts,
	}, rdr.cgrCfg.GeneralCfg().NodeID,
		rdr.cgrCfg.GeneralCfg().ConnectTimeout, nil)
	return
}

func (rdr *NatsER) processOpts() (err error) {
	if rdr.Config().Opts.NATSSubject != nil {
		rdr.subject = *rdr.Config().Opts.NATSSubject
	}
	var queueID string
	if rdr.Config().Opts.NATSQueueID != nil {
		queueID = *rdr.Config().Opts.NATSQueueID
	}
	rdr.queueID = utils.FirstNonEmpty(queueID, rdr.cgrCfg.GeneralCfg().NodeID)
	var consumerName string
	if rdr.Config().Opts.NATSConsumerName != nil {
		consumerName = *rdr.Config().Opts.NATSConsumerName
	}
	rdr.consumerName = utils.FirstNonEmpty(consumerName, utils.CGRateSLwr)
	if rdr.Config().Opts.NATSJetStream != nil {
		rdr.jetStream = *rdr.Config().Opts.NATSJetStream
	}
	if rdr.jetStream {
		if rdr.Config().Opts.NATSJetStreamMaxWait != nil {
			rdr.jsOpts = []nats.JSOpt{nats.MaxWait(*rdr.Config().Opts.NATSJetStreamMaxWait)}
		}
	}
	rdr.opts, err = GetNatsOpts(rdr.Config().Opts,
		rdr.cgrCfg.GeneralCfg().NodeID,
		rdr.cgrCfg.GeneralCfg().ConnectTimeout)
	return
}

func GetNatsOpts(opts *config.EventReaderOpts, nodeID string, connTimeout time.Duration) (nop []nats.Option, err error) {
	nop = make([]nats.Option, 0, 7)
	nop = append(nop, nats.Name(utils.CGRateSLwr+nodeID),
		nats.Timeout(connTimeout),
		nats.DrainTimeout(time.Second))
	if opts.NATSJWTFile != nil {
		keys := make([]string, 0, 1)
		if opts.NATSSeedFile != nil {
			keys = append(keys, *opts.NATSSeedFile)
		}
		nop = append(nop, nats.UserCredentials(*opts.NATSJWTFile, keys...))
	}
	if opts.NATSSeedFile != nil {
		opt, err := nats.NkeyOptionFromSeed(*opts.NATSSeedFile)
		if err != nil {
			return nil, err
		}
		nop = append(nop, opt)
	}
	if opts.NATSClientCertificate != nil {
		if opts.NATSClientKey == nil {
			err = fmt.Errorf("has certificate but no key")
			return
		}
		nop = append(nop, nats.ClientCert(*opts.NATSClientCertificate, *opts.NATSClientKey))
	} else if opts.NATSClientKey != nil {
		err = fmt.Errorf("has key but no certificate")
		return
	}
	if opts.NATSCertificateAuthority != nil {
		nop = append(nop,
			func(o *nats.Options) error {
				pool, err := x509.SystemCertPool()
				if err != nil {
					return err
				}
				rootPEM, err := ioutil.ReadFile(*opts.NATSCertificateAuthority)
				if err != nil || rootPEM == nil {
					return fmt.Errorf("nats: error loading or parsing rootCA file: %v", err)
				}
				ok := pool.AppendCertsFromPEM(rootPEM)
				if !ok {
					return fmt.Errorf("nats: failed to parse root certificate from %q",
						*opts.NATSCertificateAuthority)
				}
				if o.TLSConfig == nil {
					o.TLSConfig = &tls.Config{MinVersion: tls.VersionTLS12}
				}
				o.TLSConfig.RootCAs = pool
				o.Secure = true
				return nil
			})
	}
	return
}