// Copyright (C) 2018 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.

package main

import (
	"context"
	"crypto/tls"
	"flag"
	"log"
	"net"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/syncthing/syncthing/lib/build"
	"github.com/syncthing/syncthing/lib/protocol"
	"github.com/syncthing/syncthing/lib/tlsutil"
	"github.com/syndtr/goleveldb/leveldb/opt"
	"github.com/thejerf/suture/v4"
)

const (
	addressExpiryTime          = 2 * time.Hour
	databaseStatisticsInterval = 5 * time.Minute

	// Reannounce-After is set to reannounceAfterSeconds +
	// random(reannounzeFuzzSeconds), similar for Retry-After
	reannounceAfterSeconds = 3300
	reannounzeFuzzSeconds  = 300
	errorRetryAfterSeconds = 1500
	errorRetryFuzzSeconds  = 300

	// Retry for not found is minSeconds + failures * incSeconds +
	// random(fuzz), where failures is the number of consecutive lookups
	// with no answer, up to maxSeconds. The fuzz is applied after capping
	// to maxSeconds.
	notFoundRetryMinSeconds  = 60
	notFoundRetryMaxSeconds  = 3540
	notFoundRetryIncSeconds  = 10
	notFoundRetryFuzzSeconds = 60

	// How often (in requests) we serialize the missed counter to database.
	notFoundMissesWriteInterval = 10

	httpReadTimeout    = 5 * time.Second
	httpWriteTimeout   = 5 * time.Second
	httpMaxHeaderBytes = 1 << 10

	// Size of the replication outbox channel
	replicationOutboxSize = 10000
)

// These options make the database a little more optimized for writes, at
// the expense of some memory usage and risk of losing writes in a (system)
// crash.
var levelDBOptions = &opt.Options{
	NoSync:      true,
	WriteBuffer: 32 << 20, // default 4<<20
}

var (
	debug = false
)

func main() {
	var listen string
	var dir string
	var metricsListen string
	var replicationListen string
	var replicationPeers string
	var certFile string
	var keyFile string
	var useHTTP bool

	log.SetOutput(os.Stdout)
	log.SetFlags(0)

	flag.StringVar(&certFile, "cert", "./cert.pem", "Certificate file")
	flag.StringVar(&dir, "db-dir", "./discovery.db", "Database directory")
	flag.BoolVar(&debug, "debug", false, "Print debug output")
	flag.BoolVar(&useHTTP, "http", false, "Listen on HTTP (behind an HTTPS proxy)")
	flag.StringVar(&listen, "listen", ":8443", "Listen address")
	flag.StringVar(&keyFile, "key", "./key.pem", "Key file")
	flag.StringVar(&metricsListen, "metrics-listen", "", "Metrics listen address")
	flag.StringVar(&replicationPeers, "replicate", "", "Replication peers, id@address, comma separated")
	flag.StringVar(&replicationListen, "replication-listen", ":19200", "Replication listen address")
	showVersion := flag.Bool("version", false, "Show version")
	flag.Parse()

	log.Println(build.LongVersionFor("stdiscosrv"))
	if *showVersion {
		return
	}

	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
	if os.IsNotExist(err) {
		log.Println("Failed to load keypair. Generating one, this might take a while...")
		cert, err = tlsutil.NewCertificate(certFile, keyFile, "stdiscosrv", 20*365)
		if err != nil {
			log.Fatalln("Failed to generate X509 key pair:", err)
		}
	} else if err != nil {
		log.Fatalln("Failed to load keypair:", err)
	}
	devID := protocol.NewDeviceID(cert.Certificate[0])
	log.Println("Server device ID is", devID)

	// Parse the replication specs, if any.
	var allowedReplicationPeers []protocol.DeviceID
	var replicationDestinations []string
	parts := strings.Split(replicationPeers, ",")
	for _, part := range parts {
		fields := strings.Split(part, "@")

		switch len(fields) {
		case 2:
			// This is an id@address specification. Grab the address for the
			// destination list. Try to resolve it once to catch obvious
			// syntax errors here rather than having the sender service fail
			// repeatedly later.
			_, err := net.ResolveTCPAddr("tcp", fields[1])
			if err != nil {
				log.Fatalln("Resolving address:", err)
			}
			replicationDestinations = append(replicationDestinations, fields[1])
			fallthrough // N.B.

		case 1:
			// The first part is always a device ID.
			id, err := protocol.DeviceIDFromString(fields[0])
			if err != nil {
				log.Fatalln("Parsing device ID:", err)
			}
			allowedReplicationPeers = append(allowedReplicationPeers, id)

		default:
			log.Fatalln("Unrecognized replication spec:", part)
		}
	}

	// Root of the service tree.
	main := suture.New("main", suture.Spec{
		PassThroughPanics: true,
	})

	// Start the database.
	db, err := newLevelDBStore(dir)
	if err != nil {
		log.Fatalln("Open database:", err)
	}
	main.Add(db)

	// Start any replication senders.
	var repl replicationMultiplexer
	for _, dst := range replicationDestinations {
		rs := newReplicationSender(dst, cert, allowedReplicationPeers)
		main.Add(rs)
		repl = append(repl, rs)
	}

	// If we have replication configured, start the replication listener.
	if len(allowedReplicationPeers) > 0 {
		rl := newReplicationListener(replicationListen, cert, allowedReplicationPeers, db)
		main.Add(rl)
	}

	// Start the main API server.
	qs := newAPISrv(listen, cert, db, repl, useHTTP)
	main.Add(qs)

	// If we have a metrics port configured, start a metrics handler.
	if metricsListen != "" {
		go func() {
			mux := http.NewServeMux()
			mux.Handle("/metrics", promhttp.Handler())
			log.Fatal(http.ListenAndServe(metricsListen, mux))
		}()
	}

	// Engage!
	main.Serve(context.Background())
}
