// This file originally came from official Nats.io GitHub repository.
// You can reach the original file with the following link:
// https://github.com/nats-io/stan.go/blob/master/examples/stan-sub/main.go

// Copyright 2016-2019 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"flag"
	"fmt"
	"log"
	"os"
	"os/signal"
	"syscall"
	"time"

	nats "github.com/nats-io/nats.go"
	"github.com/nats-io/stan.go"
	"github.com/nats-io/stan.go/pb"
)

var usageStr = `
Usage: stan-sub [options] <subject>

Options:
	-s,  --server   <url>            NATS Streaming server URL(s)
	-c,  --cluster  <cluster name>   NATS Streaming cluster name
	-id, --clientid <client ID>      NATS Streaming client ID
	-cr, --creds    <credentials>    NATS 2.0 Credentials

Subscription Options:
	--qgroup <name>                  Queue group
	--all                            Deliver all available messages
	--last                           Deliver starting with last published message
	--since  <time_ago>              Deliver messages in last interval (e.g. 1s, 1hr)
	--seq    <seqno>                 Start at seqno
	--new_only                       Only deliver new messages
	--durable <name>                 Durable subscriber name
	--unsub                          Unsubscribe the durable on exit
`

// NOTE: Use tls scheme for TLS, e.g. stan-sub -s tls://demo.nats.io:4443 foo
func usage() {
	log.Fatalf(usageStr)
}

func printMsg(m *stan.Msg, i int) {
	log.Printf("[#%d] Received: %s\n", i, m)
}

func main() {
	var (
		clusterID, clientID string
		URL                 string
		userCreds           string
		showTime            bool
		qgroup              string
		unsubscribe         bool
		startSeq            uint64
		startDelta          string
		deliverAll          bool
		newOnly             bool
		deliverLast         bool
		durable             string
	)

	flag.StringVar(&URL, "s", stan.DefaultNatsURL, "The nats server URLs (separated by comma)")
	flag.StringVar(&URL, "server", stan.DefaultNatsURL, "The nats server URLs (separated by comma)")
	flag.StringVar(&clusterID, "c", "test-cluster", "The NATS Streaming cluster ID")
	flag.StringVar(&clusterID, "cluster", "test-cluster", "The NATS Streaming cluster ID")
	flag.StringVar(&clientID, "id", "stan-sub", "The NATS Streaming client ID to connect with")
	flag.StringVar(&clientID, "clientid", "stan-sub", "The NATS Streaming client ID to connect with")
	flag.BoolVar(&showTime, "t", false, "Display timestamps")
	// Subscription options
	flag.Uint64Var(&startSeq, "seq", 0, "Start at sequence no.")
	flag.BoolVar(&deliverAll, "all", true, "Deliver all")
	flag.BoolVar(&newOnly, "new_only", false, "Only new messages")
	flag.BoolVar(&deliverLast, "last", false, "Start with last value")
	flag.StringVar(&startDelta, "since", "", "Deliver messages since specified time offset")
	flag.StringVar(&durable, "durable", "", "Durable subscriber name")
	flag.StringVar(&qgroup, "qgroup", "", "Queue group name")
	flag.BoolVar(&unsubscribe, "unsub", false, "Unsubscribe the durable on exit")
	flag.BoolVar(&unsubscribe, "unsubscribe", false, "Unsubscribe the durable on exit")
	flag.StringVar(&userCreds, "cr", "", "Credentials File")
	flag.StringVar(&userCreds, "creds", "", "Credentials File")

	log.SetFlags(0)
	flag.Usage = usage
	flag.Parse()

	args := flag.Args()

	if len(args) < 1 {
		log.Printf("Error: A subject must be specified.")
		usage()
	}

	// Connect Options.
	opts := []nats.Option{nats.Name("NATS Streaming Example Subscriber")}
	// Use UserCredentials
	if userCreds != "" {
		opts = append(opts, nats.UserCredentials(userCreds))
	}

	// Connect to NATS
	nc, err := nats.Connect(URL, opts...)
	if err != nil {
		log.Fatal(err)
	}
	defer nc.Close()

	sc, err := stan.Connect(clusterID, clientID, stan.NatsConn(nc),
		stan.SetConnectionLostHandler(func(_ stan.Conn, reason error) {
			log.Fatalf("Connection lost, reason: %v", reason)
		}))
	if err != nil {
		log.Fatalf("Can't connect: %v.\nMake sure a NATS Streaming Server is running at: %s", err, URL)
	}
	log.Printf("Connected to %s clusterID: [%s] clientID: [%s]\n", URL, clusterID, clientID)

	// Process Subscriber Options.
	startOpt := stan.StartAt(pb.StartPosition_NewOnly)
	if startSeq != 0 {
		startOpt = stan.StartAtSequence(startSeq)
	} else if deliverLast {
		startOpt = stan.StartWithLastReceived()
	} else if deliverAll && !newOnly {
		startOpt = stan.DeliverAllAvailable()
	} else if startDelta != "" {
		ago, err := time.ParseDuration(startDelta)
		if err != nil {
			sc.Close()
			log.Fatal(err)
		}
		startOpt = stan.StartAtTimeDelta(ago)
	}

	subj, i := args[0], 0
	mcb := func(msg *stan.Msg) {
		i++
		printMsg(msg, i)
	}

	sub, err := sc.QueueSubscribe(subj, qgroup, mcb, startOpt, stan.DurableName(durable))
	if err != nil {
		sc.Close()
		log.Fatal(err)
	}

	log.Printf("Listening on [%s], clientID=[%s], qgroup=[%s] durable=[%s]\n", subj, clientID, qgroup, durable)

	if showTime {
		log.SetFlags(log.LstdFlags)
	}

	// Wait for a SIGINT (perhaps triggered by user with CTRL-C)
	// Run cleanup when signal is received
	signalChan := make(chan os.Signal, 1)
	cleanupDone := make(chan bool)
	signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)
	go func() {
		for sig := range signalChan {
			fmt.Printf("\nReceived signal %s, unsubscribing and closing connection...\n\n", sig.String())
			// Do not unsubscribe a durable on exit, except if asked to.
			if durable == "" || unsubscribe {
				err := sub.Unsubscribe()
				if err != nil {
					log.Fatal(err)
				}
			}
			sc.Close()
			cleanupDone <- true
		}
	}()
	<-cleanupDone
}