// Copyright (C) 2014 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 http://mozilla.org/MPL/2.0/.

package main

import (
	"crypto/tls"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	_ "net/http/pprof"
	"net/url"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"runtime/pprof"
	"strconv"
	"strings"
	"time"

	"github.com/calmh/logger"
	"github.com/juju/ratelimit"
	"github.com/syncthing/protocol"
	"github.com/syncthing/syncthing/lib/config"
	"github.com/syncthing/syncthing/lib/db"
	"github.com/syncthing/syncthing/lib/discover"
	"github.com/syncthing/syncthing/lib/events"
	"github.com/syncthing/syncthing/lib/model"
	"github.com/syncthing/syncthing/lib/osutil"
	"github.com/syncthing/syncthing/lib/symlinks"
	"github.com/syncthing/syncthing/lib/upgrade"
	"github.com/syndtr/goleveldb/leveldb"
	"github.com/syndtr/goleveldb/leveldb/errors"
	"github.com/syndtr/goleveldb/leveldb/opt"
	"github.com/thejerf/suture"
	"golang.org/x/crypto/bcrypt"
)

var (
	Version     = "unknown-dev"
	Codename    = "Aluminium Ant"
	BuildEnv    = "default"
	BuildStamp  = "0"
	BuildDate   time.Time
	BuildHost   = "unknown"
	BuildUser   = "unknown"
	IsRelease   bool
	IsBeta      bool
	LongVersion string
)

const (
	exitSuccess            = 0
	exitError              = 1
	exitNoUpgradeAvailable = 2
	exitRestarting         = 3
	exitUpgrading          = 4
)

const (
	bepProtocolName   = "bep/1.0"
	pingEventInterval = time.Minute
)

var l = logger.DefaultLogger

func init() {
	if Version != "unknown-dev" {
		// If not a generic dev build, version string should come from git describe
		exp := regexp.MustCompile(`^v\d+\.\d+\.\d+(-[a-z0-9]+)*(\+\d+-g[0-9a-f]+)?(-dirty)?$`)
		if !exp.MatchString(Version) {
			l.Fatalf("Invalid version string %q;\n\tdoes not match regexp %v", Version, exp)
		}
	}

	// Check for a clean release build. A release is something like "v0.1.2",
	// with an optional suffix of letters and dot separated numbers like
	// "-beta3.47". If there's more stuff, like a plus sign and a commit hash
	// and so on, then it's not a release. If there's a dash anywhere in
	// there, it's some kind of beta or prerelease version.

	exp := regexp.MustCompile(`^v\d+\.\d+\.\d+(-[a-z]+[\d\.]+)?$`)
	IsRelease = exp.MatchString(Version)
	IsBeta = strings.Contains(Version, "-")

	stamp, _ := strconv.Atoi(BuildStamp)
	BuildDate = time.Unix(int64(stamp), 0)

	date := BuildDate.UTC().Format("2006-01-02 15:04:05 MST")
	LongVersion = fmt.Sprintf(`syncthing %s "%s" (%s %s-%s %s) %s@%s %s`, Version, Codename, runtime.Version(), runtime.GOOS, runtime.GOARCH, BuildEnv, BuildUser, BuildHost, date)

	if os.Getenv("STTRACE") != "" {
		logFlags = log.Ltime | log.Ldate | log.Lmicroseconds | log.Lshortfile
	}
}

var (
	cfg            *config.Wrapper
	myID           protocol.DeviceID
	confDir        string
	logFlags       = log.Ltime
	writeRateLimit *ratelimit.Bucket
	readRateLimit  *ratelimit.Bucket
	stop           = make(chan int)
	discoverer     *discover.Discoverer
	cert           tls.Certificate
	lans           []*net.IPNet
)

const (
	usage      = "syncthing [options]"
	extraUsage = `
The default configuration directory is:

  %s


The -logflags value is a sum of the following:

   1  Date
   2  Time
   4  Microsecond time
   8  Long filename
  16  Short filename

I.e. to prefix each log line with date and time, set -logflags=3 (1 + 2 from
above). The value 0 is used to disable all of the above. The default is to
show time only (2).


Development Settings
--------------------

The following environment variables modify syncthing's behavior in ways that
are mostly useful for developers. Use with care.

 STGUIASSETS     Directory to load GUI assets from. Overrides compiled in assets.

 STTRACE         A comma separated string of facilities to trace. The valid
                 facility strings are:

                 - "beacon"   (the beacon package)
                 - "discover" (the discover package)
                 - "events"   (the events package)
                 - "files"    (the files package)
                 - "http"     (the main package; HTTP requests)
                 - "locks"    (the sync package; trace long held locks)
                 - "net"      (the main package; connections & network messages)
                 - "model"    (the model package)
                 - "scanner"  (the scanner package)
                 - "stats"    (the stats package)
                 - "suture"   (the suture package; service management)
                 - "upnp"     (the upnp package)
                 - "xdr"      (the xdr package)
                 - "all"      (all of the above)

 STPROFILER      Set to a listen address such as "127.0.0.1:9090" to start the
                 profiler with HTTP access.

 STCPUPROFILE    Write a CPU profile to cpu-$pid.pprof on exit.

 STHEAPPROFILE   Write heap profiles to heap-$pid-$timestamp.pprof each time
                 heap usage increases.

 STBLOCKPROFILE  Write block profiles to block-$pid-$timestamp.pprof every 20
                 seconds.

 STPERFSTATS     Write running performance statistics to perf-$pid.csv. Not
                 supported on Windows.

 STNOUPGRADE     Disable automatic upgrades.

 GOMAXPROCS      Set the maximum number of CPU cores to use. Defaults to all
                 available CPU cores.

 GOGC            Percentage of heap growth at which to trigger GC. Default is
                 100. Lower numbers keep peak memory usage down, at the price
                 of CPU usage (ie. performance).`
)

// Command line and environment options
var (
	reset             bool
	showVersion       bool
	doUpgrade         bool
	doUpgradeCheck    bool
	upgradeTo         string
	noBrowser         bool
	noConsole         bool
	generateDir       string
	logFile           string
	auditEnabled      bool
	verbose           bool
	noRestart         = os.Getenv("STNORESTART") != ""
	noUpgrade         = os.Getenv("STNOUPGRADE") != ""
	guiAddress        = os.Getenv("STGUIADDRESS") // legacy
	guiAuthentication = os.Getenv("STGUIAUTH")    // legacy
	guiAPIKey         = os.Getenv("STGUIAPIKEY")  // legacy
	profiler          = os.Getenv("STPROFILER")
	guiAssets         = os.Getenv("STGUIASSETS")
	cpuProfile        = os.Getenv("STCPUPROFILE") != ""
	stRestarting      = os.Getenv("STRESTART") != ""
	innerProcess      = os.Getenv("STNORESTART") != "" || os.Getenv("STMONITORED") != ""
)

func main() {
	if runtime.GOOS == "windows" {
		// On Windows, we use a log file by default. Setting the -logfile flag
		// to "-" disables this behavior.

		flag.StringVar(&logFile, "logfile", "", "Log file name (use \"-\" for stdout)")

		// We also add an option to hide the console window
		flag.BoolVar(&noConsole, "no-console", false, "Hide console window")
	}

	flag.StringVar(&generateDir, "generate", "", "Generate key and config in specified dir, then exit")
	flag.StringVar(&guiAddress, "gui-address", guiAddress, "Override GUI address")
	flag.StringVar(&guiAuthentication, "gui-authentication", guiAuthentication, "Override GUI authentication; username:password")
	flag.StringVar(&guiAPIKey, "gui-apikey", guiAPIKey, "Override GUI API key")
	flag.StringVar(&confDir, "home", "", "Set configuration directory")
	flag.IntVar(&logFlags, "logflags", logFlags, "Select information in log line prefix")
	flag.BoolVar(&noBrowser, "no-browser", false, "Do not start browser")
	flag.BoolVar(&noRestart, "no-restart", noRestart, "Do not restart; just exit")
	flag.BoolVar(&reset, "reset", false, "Reset the database")
	flag.BoolVar(&doUpgrade, "upgrade", false, "Perform upgrade")
	flag.BoolVar(&doUpgradeCheck, "upgrade-check", false, "Check for available upgrade")
	flag.BoolVar(&showVersion, "version", false, "Show version")
	flag.StringVar(&upgradeTo, "upgrade-to", upgradeTo, "Force upgrade directly from specified URL")
	flag.BoolVar(&auditEnabled, "audit", false, "Write events to audit file")
	flag.BoolVar(&verbose, "verbose", false, "Print verbose log output")

	flag.Usage = usageFor(flag.CommandLine, usage, fmt.Sprintf(extraUsage, baseDirs["config"]))
	flag.Parse()

	if noConsole {
		osutil.HideConsole()
	}

	if confDir != "" {
		// Not set as default above because the string can be really long.
		baseDirs["config"] = confDir
	}

	if err := expandLocations(); err != nil {
		l.Fatalln(err)
	}

	if guiAssets == "" {
		guiAssets = locations[locGUIAssets]
	}

	if runtime.GOOS == "windows" {
		if logFile == "" {
			// Use the default log file location
			logFile = locations[locLogFile]
		} else if logFile == "-" {
			// Don't use a logFile
			logFile = ""
		}
	}

	if showVersion {
		fmt.Println(LongVersion)
		return
	}

	l.SetFlags(logFlags)

	if generateDir != "" {
		dir, err := osutil.ExpandTilde(generateDir)
		if err != nil {
			l.Fatalln("generate:", err)
		}

		info, err := os.Stat(dir)
		if err == nil && !info.IsDir() {
			l.Fatalln(dir, "is not a directory")
		}
		if err != nil && os.IsNotExist(err) {
			err = osutil.MkdirAll(dir, 0700)
			if err != nil {
				l.Fatalln("generate:", err)
			}
		}

		certFile, keyFile := filepath.Join(dir, "cert.pem"), filepath.Join(dir, "key.pem")
		cert, err := tls.LoadX509KeyPair(certFile, keyFile)
		if err == nil {
			l.Warnln("Key exists; will not overwrite.")
			l.Infoln("Device ID:", protocol.NewDeviceID(cert.Certificate[0]))
		} else {
			cert, err = newCertificate(certFile, keyFile, tlsDefaultCommonName)
			myID = protocol.NewDeviceID(cert.Certificate[0])
			if err != nil {
				l.Fatalln("load cert:", err)
			}
			if err == nil {
				l.Infoln("Device ID:", protocol.NewDeviceID(cert.Certificate[0]))
			}
		}

		cfgFile := filepath.Join(dir, "config.xml")
		if _, err := os.Stat(cfgFile); err == nil {
			l.Warnln("Config exists; will not overwrite.")
			return
		}
		var myName, _ = os.Hostname()
		var newCfg = defaultConfig(myName)
		var cfg = config.Wrap(cfgFile, newCfg)
		err = cfg.Save()
		if err != nil {
			l.Warnln("Failed to save config", err)
		}

		return
	}

	if info, err := os.Stat(baseDirs["config"]); err == nil && !info.IsDir() {
		l.Fatalln("Config directory", baseDirs["config"], "is not a directory")
	}

	// Ensure that our home directory exists.
	ensureDir(baseDirs["config"], 0700)

	if upgradeTo != "" {
		err := upgrade.ToURL(upgradeTo)
		if err != nil {
			l.Fatalln("Upgrade:", err) // exits 1
		}
		l.Okln("Upgraded from", upgradeTo)
		return
	}

	if doUpgrade || doUpgradeCheck {
		rel, err := upgrade.LatestRelease(Version)
		if err != nil {
			l.Fatalln("Upgrade:", err) // exits 1
		}

		if upgrade.CompareVersions(rel.Tag, Version) <= 0 {
			l.Infof("No upgrade available (current %q >= latest %q).", Version, rel.Tag)
			os.Exit(exitNoUpgradeAvailable)
		}

		l.Infof("Upgrade available (current %q < latest %q)", Version, rel.Tag)

		if doUpgrade {
			// Use leveldb database locks to protect against concurrent upgrades
			_, err = leveldb.OpenFile(locations[locDatabase], &opt.Options{OpenFilesCacheCapacity: 100})
			if err != nil {
				l.Infoln("Attempting upgrade through running Syncthing...")
				err = upgradeViaRest()
				if err != nil {
					l.Fatalln("Upgrade:", err)
				}
				l.Okln("Syncthing upgrading")
				return
			}

			err = upgrade.To(rel)
			if err != nil {
				l.Fatalln("Upgrade:", err) // exits 1
			}
			l.Okf("Upgraded to %q", rel.Tag)
		}

		return
	}

	if reset {
		resetDB()
		return
	}

	if noRestart {
		syncthingMain()
	} else {
		monitorMain()
	}
}

func upgradeViaRest() error {
	cfg, err := config.Load(locations[locConfigFile], protocol.LocalDeviceID)
	if err != nil {
		return err
	}
	target := cfg.GUI().Address
	if cfg.GUI().UseTLS {
		target = "https://" + target
	} else {
		target = "http://" + target
	}
	r, _ := http.NewRequest("POST", target+"/rest/system/upgrade", nil)
	r.Header.Set("X-API-Key", cfg.GUI().APIKey)

	tr := &http.Transport{
		TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
	}
	client := &http.Client{
		Transport: tr,
		Timeout:   60 * time.Second,
	}
	resp, err := client.Do(r)
	if err != nil {
		return err
	}
	if resp.StatusCode != 200 {
		bs, err := ioutil.ReadAll(resp.Body)
		defer resp.Body.Close()
		if err != nil {
			return err
		}
		return errors.New(string(bs))
	}

	return err
}

func syncthingMain() {
	// Create a main service manager. We'll add things to this as we go along.
	// We want any logging it does to go through our log system.
	mainSvc := suture.New("main", suture.Spec{
		Log: func(line string) {
			if debugSuture {
				l.Debugln(line)
			}
		},
	})
	mainSvc.ServeBackground()

	// Set a log prefix similar to the ID we will have later on, or early log
	// lines look ugly.
	l.SetPrefix("[start] ")

	if auditEnabled {
		startAuditing(mainSvc)
	}

	if verbose {
		mainSvc.Add(newVerboseSvc())
	}

	// Event subscription for the API; must start early to catch the early events.
	apiSub := events.NewBufferedSubscription(events.Default.Subscribe(events.AllEvents), 1000)

	if len(os.Getenv("GOMAXPROCS")) == 0 {
		runtime.GOMAXPROCS(runtime.NumCPU())
	}

	// Attempt to increase the limit on number of open files to the maximum
	// allowed, in case we have many peers. We don't really care enough to
	// report the error if there is one.
	osutil.MaximizeOpenFileLimit()

	// Ensure that that we have a certificate and key.
	cert, err := tls.LoadX509KeyPair(locations[locCertFile], locations[locKeyFile])
	if err != nil {
		cert, err = newCertificate(locations[locCertFile], locations[locKeyFile], tlsDefaultCommonName)
		if err != nil {
			l.Fatalln("load cert:", err)
		}
	}

	// We reinitialize the predictable RNG with our device ID, to get a
	// sequence that is always the same but unique to this syncthing instance.
	predictableRandom.Seed(seedFromBytes(cert.Certificate[0]))

	myID = protocol.NewDeviceID(cert.Certificate[0])
	l.SetPrefix(fmt.Sprintf("[%s] ", myID.String()[:5]))

	l.Infoln(LongVersion)
	l.Infoln("My ID:", myID)

	// Emit the Starting event, now that we know who we are.

	events.Default.Log(events.Starting, map[string]string{
		"home": baseDirs["config"],
		"myID": myID.String(),
	})

	// Prepare to be able to save configuration

	cfgFile := locations[locConfigFile]

	var myName string

	// Load the configuration file, if it exists.
	// If it does not, create a template.

	if info, err := os.Stat(cfgFile); err == nil {
		if !info.Mode().IsRegular() {
			l.Fatalln("Config file is not a file?")
		}
		cfg, err = config.Load(cfgFile, myID)
		if err == nil {
			myCfg := cfg.Devices()[myID]
			if myCfg.Name == "" {
				myName, _ = os.Hostname()
			} else {
				myName = myCfg.Name
			}
		} else {
			l.Fatalln("Configuration:", err)
		}
	} else {
		l.Infoln("No config file; starting with empty defaults")
		myName, _ = os.Hostname()
		newCfg := defaultConfig(myName)
		cfg = config.Wrap(cfgFile, newCfg)
		cfg.Save()
		l.Infof("Edit %s to taste or use the GUI\n", cfgFile)
	}

	if cfg.Raw().OriginalVersion != config.CurrentVersion {
		l.Infoln("Archiving a copy of old config file format")
		// Archive a copy
		osutil.Rename(cfgFile, cfgFile+fmt.Sprintf(".v%d", cfg.Raw().OriginalVersion))
		// Save the new version
		cfg.Save()
	}

	if err := checkShortIDs(cfg); err != nil {
		l.Fatalln("Short device IDs are in conflict. Unlucky!\n  Regenerate the device ID of one if the following:\n  ", err)
	}

	if len(profiler) > 0 {
		go func() {
			l.Debugln("Starting profiler on", profiler)
			runtime.SetBlockProfileRate(1)
			err := http.ListenAndServe(profiler, nil)
			if err != nil {
				l.Fatalln(err)
			}
		}()
	}

	// The TLS configuration is used for both the listening socket and outgoing
	// connections.

	tlsCfg := &tls.Config{
		Certificates:           []tls.Certificate{cert},
		NextProtos:             []string{bepProtocolName},
		ClientAuth:             tls.RequestClientCert,
		SessionTicketsDisabled: true,
		InsecureSkipVerify:     true,
		MinVersion:             tls.VersionTLS12,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
		},
	}

	// If the read or write rate should be limited, set up a rate limiter for it.
	// This will be used on connections created in the connect and listen routines.

	opts := cfg.Options()

	if !opts.SymlinksEnabled {
		symlinks.Supported = false
	}

	protocol.PingTimeout = time.Duration(opts.PingTimeoutS) * time.Second
	protocol.PingIdleTime = time.Duration(opts.PingIdleTimeS) * time.Second

	if opts.MaxSendKbps > 0 {
		writeRateLimit = ratelimit.NewBucketWithRate(float64(1000*opts.MaxSendKbps), int64(5*1000*opts.MaxSendKbps))
	}
	if opts.MaxRecvKbps > 0 {
		readRateLimit = ratelimit.NewBucketWithRate(float64(1000*opts.MaxRecvKbps), int64(5*1000*opts.MaxRecvKbps))
	}

	if (opts.MaxRecvKbps > 0 || opts.MaxSendKbps > 0) && !opts.LimitBandwidthInLan {
		lans, _ = osutil.GetLans()
		networks := make([]string, 0, len(lans))
		for _, lan := range lans {
			networks = append(networks, lan.String())
		}
		l.Infoln("Local networks:", strings.Join(networks, ", "))
	}

	dbFile := locations[locDatabase]
	ldb, err := leveldb.OpenFile(dbFile, dbOpts())
	if leveldbIsCorrupted(err) {
		ldb, err = leveldb.RecoverFile(dbFile, dbOpts())
	}
	if leveldbIsCorrupted(err) {
		// The database is corrupted, and we've tried to recover it but it
		// didn't work. At this point there isn't much to do beyond dropping
		// the database and reindexing...
		l.Infoln("Database corruption detected, unable to recover. Reinitializing...")
		if err := resetDB(); err != nil {
			l.Fatalln("Remove database:", err)
		}
		ldb, err = leveldb.OpenFile(dbFile, dbOpts())
	}
	if err != nil {
		l.Fatalln("Cannot open database:", err, "- Is another copy of Syncthing already running?")
	}

	// Remove database entries for folders that no longer exist in the config
	folders := cfg.Folders()
	for _, folder := range db.ListFolders(ldb) {
		if _, ok := folders[folder]; !ok {
			l.Infof("Cleaning data for dropped folder %q", folder)
			db.DropFolder(ldb, folder)
		}
	}

	m := model.NewModel(cfg, myID, myName, "syncthing", Version, ldb)
	cfg.Subscribe(m)

	if t := os.Getenv("STDEADLOCKTIMEOUT"); len(t) > 0 {
		it, err := strconv.Atoi(t)
		if err == nil {
			m.StartDeadlockDetector(time.Duration(it) * time.Second)
		}
	} else if !IsRelease || IsBeta {
		m.StartDeadlockDetector(20 * 60 * time.Second)
	}

	// Clear out old indexes for other devices. Otherwise we'll start up and
	// start needing a bunch of files which are nowhere to be found. This
	// needs to be changed when we correctly do persistent indexes.
	for _, folderCfg := range cfg.Folders() {
		m.AddFolder(folderCfg)
		for _, device := range folderCfg.DeviceIDs() {
			if device == myID {
				continue
			}
			m.Index(device, folderCfg.ID, nil, 0, nil)
		}
		// Routine to pull blocks from other devices to synchronize the local
		// folder. Does not run when we are in read only (publish only) mode.
		if folderCfg.ReadOnly {
			m.StartFolderRO(folderCfg.ID)
		} else {
			m.StartFolderRW(folderCfg.ID)
		}
	}

	mainSvc.Add(m)

	// GUI

	setupGUI(mainSvc, cfg, m, apiSub)

	// The default port we announce, possibly modified by setupUPnP next.

	addr, err := net.ResolveTCPAddr("tcp", opts.ListenAddress[0])
	if err != nil {
		l.Fatalln("Bad listen address:", err)
	}

	// Start discovery

	localPort := addr.Port
	discoverer = discovery(localPort)

	// Start UPnP. The UPnP service will restart global discovery if the
	// external port changes.

	if opts.UPnPEnabled {
		upnpSvc := newUPnPSvc(cfg, localPort)
		mainSvc.Add(upnpSvc)
	}

	connectionSvc := newConnectionSvc(cfg, myID, m, tlsCfg)
	cfg.Subscribe(connectionSvc)
	mainSvc.Add(connectionSvc)

	if cpuProfile {
		f, err := os.Create(fmt.Sprintf("cpu-%d.pprof", os.Getpid()))
		if err != nil {
			log.Fatal(err)
		}
		pprof.StartCPUProfile(f)
	}

	for _, device := range cfg.Devices() {
		if len(device.Name) > 0 {
			l.Infof("Device %s is %q at %v", device.DeviceID, device.Name, device.Addresses)
		}
	}

	if opts.URAccepted > 0 && opts.URAccepted < usageReportVersion {
		l.Infoln("Anonymous usage report has changed; revoking acceptance")
		opts.URAccepted = 0
		opts.URUniqueID = ""
		cfg.SetOptions(opts)
	}
	if opts.URAccepted >= usageReportVersion {
		if opts.URUniqueID == "" {
			// Previously the ID was generated from the node ID. We now need
			// to generate a new one.
			opts.URUniqueID = randomString(8)
			cfg.SetOptions(opts)
			cfg.Save()
		}
	}

	// The usageReportingManager registers itself to listen to configuration
	// changes, and there's nothing more we need to tell it from the outside.
	// Hence we don't keep the returned pointer.
	newUsageReportingManager(m, cfg)

	if opts.RestartOnWakeup {
		go standbyMonitor()
	}

	if opts.AutoUpgradeIntervalH > 0 {
		if noUpgrade {
			l.Infof("No automatic upgrades; STNOUPGRADE environment variable defined.")
		} else if IsRelease {
			go autoUpgrade()
		} else {
			l.Infof("No automatic upgrades; %s is not a release version.", Version)
		}
	}

	events.Default.Log(events.StartupComplete, map[string]string{
		"myID": myID.String(),
	})
	go generatePingEvents()

	cleanConfigDirectory()

	code := <-stop

	mainSvc.Stop()

	l.Okln("Exiting")

	if cpuProfile {
		pprof.StopCPUProfile()
	}

	os.Exit(code)
}

func dbOpts() *opt.Options {
	// Calculate a suitable database block cache capacity.

	// Default is 8 MiB.
	blockCacheCapacity := 8 << 20
	// Increase block cache up to this maximum:
	const maxCapacity = 64 << 20
	// ... which we reach when the box has this much RAM:
	const maxAtRAM = 8 << 30

	if v := cfg.Options().DatabaseBlockCacheMiB; v != 0 {
		// Use the value from the config, if it's set.
		blockCacheCapacity = v << 20
	} else if bytes, err := memorySize(); err == nil {
		// We start at the default of 8 MiB and use larger values for machines
		// with more memory.

		if bytes > maxAtRAM {
			// Cap the cache at maxCapacity when we reach maxAtRam amount of memory
			blockCacheCapacity = maxCapacity
		} else if bytes > maxAtRAM/maxCapacity*int64(blockCacheCapacity) {
			// Grow from the default to maxCapacity at maxAtRam amount of memory
			blockCacheCapacity = int(bytes * maxCapacity / maxAtRAM)
		}
		l.Infoln("Database block cache capacity", blockCacheCapacity/1024, "KiB")
	}

	return &opt.Options{
		OpenFilesCacheCapacity: 100,
		BlockCacheCapacity:     blockCacheCapacity,
		WriteBuffer:            4 << 20,
	}
}

func startAuditing(mainSvc *suture.Supervisor) {
	auditFile := timestampedLoc(locAuditLog)
	fd, err := os.OpenFile(auditFile, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
	if err != nil {
		l.Fatalln("Audit:", err)
	}

	auditSvc := newAuditSvc(fd)
	mainSvc.Add(auditSvc)

	// We wait for the audit service to fully start before we return, to
	// ensure we capture all events from the start.
	auditSvc.WaitForStart()

	l.Infoln("Audit log in", auditFile)
}

func setupGUI(mainSvc *suture.Supervisor, cfg *config.Wrapper, m *model.Model, apiSub *events.BufferedSubscription) {
	opts := cfg.Options()
	guiCfg := overrideGUIConfig(cfg.GUI(), guiAddress, guiAuthentication, guiAPIKey)

	if guiCfg.Enabled && guiCfg.Address != "" {
		addr, err := net.ResolveTCPAddr("tcp", guiCfg.Address)
		if err != nil {
			l.Fatalf("Cannot start GUI on %q: %v", guiCfg.Address, err)
		} else {
			var hostOpen, hostShow string
			switch {
			case addr.IP == nil:
				hostOpen = "localhost"
				hostShow = "0.0.0.0"
			case addr.IP.IsUnspecified():
				hostOpen = "localhost"
				hostShow = addr.IP.String()
			default:
				hostOpen = addr.IP.String()
				hostShow = hostOpen
			}

			var proto = "http"
			if guiCfg.UseTLS {
				proto = "https"
			}

			urlShow := fmt.Sprintf("%s://%s/", proto, net.JoinHostPort(hostShow, strconv.Itoa(addr.Port)))
			l.Infoln("Starting web GUI on", urlShow)
			api, err := newAPISvc(myID, guiCfg, guiAssets, m, apiSub)
			if err != nil {
				l.Fatalln("Cannot start GUI:", err)
			}
			cfg.Subscribe(api)
			mainSvc.Add(api)

			if opts.StartBrowser && !noBrowser && !stRestarting {
				urlOpen := fmt.Sprintf("%s://%s/", proto, net.JoinHostPort(hostOpen, strconv.Itoa(addr.Port)))
				// Can potentially block if the utility we are invoking doesn't
				// fork, and just execs, hence keep it in it's own routine.
				go openURL(urlOpen)
			}
		}
	}
}

func defaultConfig(myName string) config.Configuration {
	newCfg := config.New(myID)
	newCfg.Folders = []config.FolderConfiguration{
		{
			ID:              "default",
			RawPath:         locations[locDefFolder],
			RescanIntervalS: 60,
			MinDiskFreePct:  1,
			Devices:         []config.FolderDeviceConfiguration{{DeviceID: myID}},
		},
	}
	newCfg.Devices = []config.DeviceConfiguration{
		{
			DeviceID:  myID,
			Addresses: []string{"dynamic"},
			Name:      myName,
		},
	}

	port, err := getFreePort("127.0.0.1", 8384)
	if err != nil {
		l.Fatalln("get free port (GUI):", err)
	}
	newCfg.GUI.Address = fmt.Sprintf("127.0.0.1:%d", port)

	port, err = getFreePort("0.0.0.0", 22000)
	if err != nil {
		l.Fatalln("get free port (BEP):", err)
	}
	newCfg.Options.ListenAddress = []string{fmt.Sprintf("0.0.0.0:%d", port)}
	return newCfg
}

func generatePingEvents() {
	for {
		time.Sleep(pingEventInterval)
		events.Default.Log(events.Ping, nil)
	}
}

func resetDB() error {
	return os.RemoveAll(locations[locDatabase])
}

func restart() {
	l.Infoln("Restarting")
	stop <- exitRestarting
}

func shutdown() {
	l.Infoln("Shutting down")
	stop <- exitSuccess
}

func discovery(extPort int) *discover.Discoverer {
	opts := cfg.Options()
	disc := discover.NewDiscoverer(myID, opts.ListenAddress)

	if opts.LocalAnnEnabled {
		l.Infoln("Starting local discovery announcements")
		disc.StartLocal(opts.LocalAnnPort, opts.LocalAnnMCAddr)
	}

	if opts.GlobalAnnEnabled {
		l.Infoln("Starting global discovery announcements")
		disc.StartGlobal(opts.GlobalAnnServers, uint16(extPort))
	}

	return disc
}

func ensureDir(dir string, mode int) {
	fi, err := os.Stat(dir)
	if os.IsNotExist(err) {
		err := osutil.MkdirAll(dir, 0700)
		if err != nil {
			l.Fatalln(err)
		}
	} else if mode >= 0 && err == nil && int(fi.Mode()&0777) != mode {
		err := os.Chmod(dir, os.FileMode(mode))
		// This can fail on crappy filesystems, nothing we can do about it.
		if err != nil {
			l.Warnln(err)
		}
	}
}

// getFreePort returns a free TCP port fort listening on. The ports given are
// tried in succession and the first to succeed is returned. If none succeed,
// a random high port is returned.
func getFreePort(host string, ports ...int) (int, error) {
	for _, port := range ports {
		c, err := net.Listen("tcp", fmt.Sprintf("%s:%d", host, port))
		if err == nil {
			c.Close()
			return port, nil
		}
	}

	c, err := net.Listen("tcp", host+":0")
	if err != nil {
		return 0, err
	}
	addr := c.Addr().(*net.TCPAddr)
	c.Close()
	return addr.Port, nil
}

func overrideGUIConfig(cfg config.GUIConfiguration, address, authentication, apikey string) config.GUIConfiguration {
	if address != "" {
		cfg.Enabled = true

		if !strings.Contains(address, "//") {
			// Assume just an IP was given. Don't touch he TLS setting.
			cfg.Address = address
		} else {
			parsed, err := url.Parse(address)
			if err != nil {
				l.Fatalln(err)
			}
			cfg.Address = parsed.Host
			switch parsed.Scheme {
			case "http":
				cfg.UseTLS = false
			case "https":
				cfg.UseTLS = true
			default:
				l.Fatalln("Unknown scheme:", parsed.Scheme)
			}
		}
	}

	if authentication != "" {
		authenticationParts := strings.SplitN(authentication, ":", 2)

		hash, err := bcrypt.GenerateFromPassword([]byte(authenticationParts[1]), 0)
		if err != nil {
			l.Fatalln("Invalid GUI password:", err)
		}

		cfg.User = authenticationParts[0]
		cfg.Password = string(hash)
	}

	if apikey != "" {
		cfg.APIKey = apikey
	}
	return cfg
}

func standbyMonitor() {
	restartDelay := time.Duration(60 * time.Second)
	now := time.Now()
	for {
		time.Sleep(10 * time.Second)
		if time.Since(now) > 2*time.Minute {
			l.Infof("Paused state detected, possibly woke up from standby. Restarting in %v.", restartDelay)

			// We most likely just woke from standby. If we restart
			// immediately chances are we won't have networking ready. Give
			// things a moment to stabilize.
			time.Sleep(restartDelay)

			restart()
			return
		}
		now = time.Now()
	}
}

func autoUpgrade() {
	timer := time.NewTimer(0)
	sub := events.Default.Subscribe(events.DeviceConnected)
	for {
		select {
		case event := <-sub.C():
			data, ok := event.Data.(map[string]string)
			if !ok || data["clientName"] != "syncthing" || upgrade.CompareVersions(data["clientVersion"], Version) != upgrade.Newer {
				continue
			}
			l.Infof("Connected to device %s with a newer version (current %q < remote %q). Checking for upgrades.", data["id"], Version, data["clientVersion"])
		case <-timer.C:
		}

		rel, err := upgrade.LatestRelease(Version)
		if err == upgrade.ErrUpgradeUnsupported {
			events.Default.Unsubscribe(sub)
			return
		}
		if err != nil {
			// Don't complain too loudly here; we might simply not have
			// internet connectivity, or the upgrade server might be down.
			l.Infoln("Automatic upgrade:", err)
			timer.Reset(time.Duration(cfg.Options().AutoUpgradeIntervalH) * time.Hour)
			continue
		}

		if upgrade.CompareVersions(rel.Tag, Version) != upgrade.Newer {
			// Skip equal, older or majorly newer (incompatible) versions
			timer.Reset(time.Duration(cfg.Options().AutoUpgradeIntervalH) * time.Hour)
			continue
		}

		l.Infof("Automatic upgrade (current %q < latest %q)", Version, rel.Tag)
		err = upgrade.To(rel)
		if err != nil {
			l.Warnln("Automatic upgrade:", err)
			timer.Reset(time.Duration(cfg.Options().AutoUpgradeIntervalH) * time.Hour)
			continue
		}
		events.Default.Unsubscribe(sub)
		l.Warnf("Automatically upgraded to version %q. Restarting in 1 minute.", rel.Tag)
		time.Sleep(time.Minute)
		stop <- exitUpgrading
		return
	}
}

// cleanConfigDirectory removes old, unused configuration and index formats, a
// suitable time after they have gone out of fashion.
func cleanConfigDirectory() {
	patterns := map[string]time.Duration{
		"panic-*.log":    7 * 24 * time.Hour,  // keep panic logs for a week
		"audit-*.log":    7 * 24 * time.Hour,  // keep audit logs for a week
		"index":          14 * 24 * time.Hour, // keep old index format for two weeks
		"config.xml.v*":  30 * 24 * time.Hour, // old config versions for a month
		"*.idx.gz":       30 * 24 * time.Hour, // these should for sure no longer exist
		"backup-of-v0.8": 30 * 24 * time.Hour, // these neither
	}

	for pat, dur := range patterns {
		pat = filepath.Join(baseDirs["config"], pat)
		files, err := osutil.Glob(pat)
		if err != nil {
			l.Infoln("Cleaning:", err)
			continue
		}

		for _, file := range files {
			info, err := osutil.Lstat(file)
			if err != nil {
				l.Infoln("Cleaning:", err)
				continue
			}

			if time.Since(info.ModTime()) > dur {
				if err = os.RemoveAll(file); err != nil {
					l.Infoln("Cleaning:", err)
				} else {
					l.Infoln("Cleaned away old file", filepath.Base(file))
				}
			}
		}
	}
}

// checkShortIDs verifies that the configuration won't result in duplicate
// short ID:s; that is, that the devices in the cluster all have unique
// initial 64 bits.
func checkShortIDs(cfg *config.Wrapper) error {
	exists := make(map[uint64]protocol.DeviceID)
	for deviceID := range cfg.Devices() {
		shortID := deviceID.Short()
		if otherID, ok := exists[shortID]; ok {
			return fmt.Errorf("%v in conflict with %v", deviceID, otherID)
		}
		exists[shortID] = deviceID
	}
	return nil
}

// A "better" version of leveldb's errors.IsCorrupted.
func leveldbIsCorrupted(err error) bool {
	switch {
	case err == nil:
		return false

	case errors.IsCorrupted(err):
		return true

	case strings.Contains(err.Error(), "corrupted"):
		return true
	}

	return false
}
