// 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 https://mozilla.org/MPL/2.0/.

// Package config implements reading and writing of the syncthing configuration file.
package config

import (
	"encoding/json"
	"encoding/xml"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"runtime"
	"sort"
	"strconv"
	"strings"

	"github.com/syncthing/syncthing/lib/fs"
	"github.com/syncthing/syncthing/lib/protocol"
	"github.com/syncthing/syncthing/lib/rand"
	"github.com/syncthing/syncthing/lib/upgrade"
	"github.com/syncthing/syncthing/lib/util"
)

const (
	OldestHandledVersion = 10
	CurrentVersion       = 26
	MaxRescanIntervalS   = 365 * 24 * 60 * 60
)

var (
	// DefaultTCPPort defines default TCP port used if the URI does not specify one, for example tcp://0.0.0.0
	DefaultTCPPort = 22000
	// DefaultKCPPort defines default KCP (UDP) port used if the URI does not specify one, for example kcp://0.0.0.0
	DefaultKCPPort = 22020
	// DefaultListenAddresses should be substituted when the configuration
	// contains <listenAddress>default</listenAddress>. This is done by the
	// "consumer" of the configuration as we don't want these saved to the
	// config.
	DefaultListenAddresses = []string{
		util.Address("tcp", net.JoinHostPort("0.0.0.0", strconv.Itoa(DefaultTCPPort))),
		"dynamic+https://relays.syncthing.net/endpoint",
		util.Address("kcp", net.JoinHostPort("0.0.0.0", strconv.Itoa(DefaultKCPPort))),
	}
	// DefaultDiscoveryServersV4 should be substituted when the configuration
	// contains <globalAnnounceServer>default-v4</globalAnnounceServer>.
	DefaultDiscoveryServersV4 = []string{
		"https://discovery-v4-2.syncthing.net/v2/?id=DVU36WY-H3LVZHW-E6LLFRE-YAFN5EL-HILWRYP-OC2M47J-Z4PE62Y-ADIBDQC", // 45.55.230.38, USA
		"https://discovery-v4-3.syncthing.net/v2/?id=VK6HNJ3-VVMM66S-HRVWSCR-IXEHL2H-U4AQ4MW-UCPQBWX-J2L2UBK-NVZRDQZ", // 128.199.95.124, Singapore
		"https://discovery-v4-4.syncthing.net/v2/?id=LYXKCHX-VI3NYZR-ALCJBHF-WMZYSPK-QG6QJA3-MPFYMSO-U56GTUK-NA2MIAW", // 95.85.19.244, NL
	}
	// DefaultDiscoveryServersV6 should be substituted when the configuration
	// contains <globalAnnounceServer>default-v6</globalAnnounceServer>.
	DefaultDiscoveryServersV6 = []string{
		"https://discovery-v6-2.syncthing.net/v2/?id=DVU36WY-H3LVZHW-E6LLFRE-YAFN5EL-HILWRYP-OC2M47J-Z4PE62Y-ADIBDQC", // 2604:a880:800:10::182:a001, USA
		"https://discovery-v6-3.syncthing.net/v2/?id=VK6HNJ3-VVMM66S-HRVWSCR-IXEHL2H-U4AQ4MW-UCPQBWX-J2L2UBK-NVZRDQZ", // 2400:6180:0:d0::d9:d001, Singapore
		"https://discovery-v6-4.syncthing.net/v2/?id=LYXKCHX-VI3NYZR-ALCJBHF-WMZYSPK-QG6QJA3-MPFYMSO-U56GTUK-NA2MIAW", // 2a03:b0c0:0:1010::4ed:3001, NL
	}
	// DefaultDiscoveryServers should be substituted when the configuration
	// contains <globalAnnounceServer>default</globalAnnounceServer>.
	DefaultDiscoveryServers = append(DefaultDiscoveryServersV4, DefaultDiscoveryServersV6...)
	// DefaultStunServers should be substituted when the configuration
	// contains <stunServer>default</stunServer>.
	DefaultStunServers = []string{
		"stun.callwithus.com:3478",
		"stun.counterpath.com:3478",
		"stun.counterpath.net:3478",
		"stun.ekiga.net:3478",
		"stun.ideasip.com:3478",
		"stun.internetcalls.com:3478",
		"stun.schlund.de:3478",
		"stun.sipgate.net:10000",
		"stun.sipgate.net:3478",
		"stun.voip.aebc.com:3478",
		"stun.voiparound.com:3478",
		"stun.voipbuster.com:3478",
		"stun.voipstunt.com:3478",
		"stun.voxgratia.org:3478",
		"stun.xten.com:3478",
	}
	// DefaultTheme is the default and fallback theme for the web UI.
	DefaultTheme = "default"
)

func New(myID protocol.DeviceID) Configuration {
	var cfg Configuration
	cfg.Version = CurrentVersion
	cfg.OriginalVersion = CurrentVersion

	util.SetDefaults(&cfg)
	util.SetDefaults(&cfg.Options)
	util.SetDefaults(&cfg.GUI)

	// Can't happen.
	if err := cfg.prepare(myID); err != nil {
		panic("bug: error in preparing new folder: " + err.Error())
	}

	return cfg
}

func ReadXML(r io.Reader, myID protocol.DeviceID) (Configuration, error) {
	var cfg Configuration

	util.SetDefaults(&cfg)
	util.SetDefaults(&cfg.Options)
	util.SetDefaults(&cfg.GUI)

	if err := xml.NewDecoder(r).Decode(&cfg); err != nil {
		return Configuration{}, err
	}
	cfg.OriginalVersion = cfg.Version

	if err := cfg.prepare(myID); err != nil {
		return Configuration{}, err
	}
	return cfg, nil
}

func ReadJSON(r io.Reader, myID protocol.DeviceID) (Configuration, error) {
	var cfg Configuration

	util.SetDefaults(&cfg)
	util.SetDefaults(&cfg.Options)
	util.SetDefaults(&cfg.GUI)

	bs, err := ioutil.ReadAll(r)
	if err != nil {
		return Configuration{}, err
	}

	if err := json.Unmarshal(bs, &cfg); err != nil {
		return Configuration{}, err
	}
	cfg.OriginalVersion = cfg.Version

	if err := cfg.prepare(myID); err != nil {
		return Configuration{}, err
	}
	return cfg, nil
}

type Configuration struct {
	Version        int                   `xml:"version,attr" json:"version"`
	Folders        []FolderConfiguration `xml:"folder" json:"folders"`
	Devices        []DeviceConfiguration `xml:"device" json:"devices"`
	GUI            GUIConfiguration      `xml:"gui" json:"gui"`
	Options        OptionsConfiguration  `xml:"options" json:"options"`
	IgnoredDevices []protocol.DeviceID   `xml:"ignoredDevice" json:"ignoredDevices"`
	IgnoredFolders []string              `xml:"ignoredFolder" json:"ignoredFolders"`
	XMLName        xml.Name              `xml:"configuration" json:"-"`

	MyID            protocol.DeviceID `xml:"-" json:"-"` // Provided by the instantiator.
	OriginalVersion int               `xml:"-" json:"-"` // The version we read from disk, before any conversion
}

func (cfg Configuration) Copy() Configuration {
	newCfg := cfg

	// Deep copy FolderConfigurations
	newCfg.Folders = make([]FolderConfiguration, len(cfg.Folders))
	for i := range newCfg.Folders {
		newCfg.Folders[i] = cfg.Folders[i].Copy()
	}

	// Deep copy DeviceConfigurations
	newCfg.Devices = make([]DeviceConfiguration, len(cfg.Devices))
	for i := range newCfg.Devices {
		newCfg.Devices[i] = cfg.Devices[i].Copy()
	}

	newCfg.Options = cfg.Options.Copy()

	// DeviceIDs are values
	newCfg.IgnoredDevices = make([]protocol.DeviceID, len(cfg.IgnoredDevices))
	copy(newCfg.IgnoredDevices, cfg.IgnoredDevices)

	// FolderConfiguraion.ID is type string
	newCfg.IgnoredFolders = make([]string, len(cfg.IgnoredFolders))
	copy(newCfg.IgnoredFolders, cfg.IgnoredFolders)

	return newCfg
}

func (cfg *Configuration) WriteXML(w io.Writer) error {
	e := xml.NewEncoder(w)
	e.Indent("", "    ")
	err := e.Encode(cfg)
	if err != nil {
		return err
	}
	_, err = w.Write([]byte("\n"))
	return err
}

func (cfg *Configuration) prepare(myID protocol.DeviceID) error {
	var myName string

	cfg.MyID = myID

	// Ensure this device is present in the config
	for _, device := range cfg.Devices {
		if device.DeviceID == myID {
			goto found
		}
	}

	myName, _ = os.Hostname()
	cfg.Devices = append(cfg.Devices, DeviceConfiguration{
		DeviceID: myID,
		Name:     myName,
	})

found:

	if err := cfg.clean(); err != nil {
		return err
	}

	// Ensure that we are part of the devices
	for i := range cfg.Folders {
		cfg.Folders[i].Devices = ensureDevicePresent(cfg.Folders[i].Devices, myID)
	}

	return nil
}

func (cfg *Configuration) clean() error {
	util.FillNilSlices(&cfg.Options)

	// Initialize any empty slices
	if cfg.Folders == nil {
		cfg.Folders = []FolderConfiguration{}
	}
	if cfg.IgnoredDevices == nil {
		cfg.IgnoredDevices = []protocol.DeviceID{}
	}
	if cfg.IgnoredFolders == nil {
		cfg.IgnoredFolders = []string{}
	}
	if cfg.Options.AlwaysLocalNets == nil {
		cfg.Options.AlwaysLocalNets = []string{}
	}
	if cfg.Options.UnackedNotificationIDs == nil {
		cfg.Options.UnackedNotificationIDs = []string{}
	}

	// Prepare folders and check for duplicates. Duplicates are bad and
	// dangerous, can't currently be resolved in the GUI, and shouldn't
	// happen when configured by the GUI. We return with an error in that
	// situation.
	seenFolders := make(map[string]struct{})
	for i := range cfg.Folders {
		folder := &cfg.Folders[i]
		folder.prepare()

		if _, ok := seenFolders[folder.ID]; ok {
			return fmt.Errorf("duplicate folder ID %q in configuration", folder.ID)
		}
		seenFolders[folder.ID] = struct{}{}
	}

	// Remove ignored folders that are anyway part of the configuration.
	for i := 0; i < len(cfg.IgnoredFolders); i++ {
		if _, ok := seenFolders[cfg.IgnoredFolders[i]]; ok {
			cfg.IgnoredFolders = append(cfg.IgnoredFolders[:i], cfg.IgnoredFolders[i+1:]...)
			i-- // IgnoredFolders[i] now points to something else, so needs to be rechecked
		}
	}

	cfg.Options.ListenAddresses = util.UniqueStrings(cfg.Options.ListenAddresses)
	cfg.Options.GlobalAnnServers = util.UniqueStrings(cfg.Options.GlobalAnnServers)

	if cfg.Version > 0 && cfg.Version < OldestHandledVersion {
		l.Warnf("Configuration version %d is deprecated. Attempting best effort conversion, but please verify manually.", cfg.Version)
	}

	// Upgrade configuration versions as appropriate
	if cfg.Version <= 10 {
		convertV10V11(cfg)
	}
	if cfg.Version == 11 {
		convertV11V12(cfg)
	}
	if cfg.Version == 12 {
		convertV12V13(cfg)
	}
	if cfg.Version == 13 {
		convertV13V14(cfg)
	}
	if cfg.Version == 14 {
		convertV14V15(cfg)
	}
	if cfg.Version == 15 {
		convertV15V16(cfg)
	}
	if cfg.Version == 16 {
		convertV16V17(cfg)
	}
	if cfg.Version == 17 {
		convertV17V18(cfg)
	}
	if cfg.Version == 18 {
		convertV18V19(cfg)
	}
	if cfg.Version == 19 {
		convertV19V20(cfg)
	}
	if cfg.Version == 20 {
		convertV20V21(cfg)
	}
	if cfg.Version == 21 {
		convertV21V22(cfg)
	}
	if cfg.Version == 22 {
		convertV22V23(cfg)
	}
	if cfg.Version == 23 {
		convertV23V24(cfg)
	}
	if cfg.Version == 24 {
		convertV24V25(cfg)
	}
	if cfg.Version == 25 {
		convertV25V26(cfg)
	}

	// Build a list of available devices
	existingDevices := make(map[protocol.DeviceID]bool)
	for _, device := range cfg.Devices {
		existingDevices[device.DeviceID] = true
	}

	// Ensure that the device list is free from duplicates
	cfg.Devices = ensureNoDuplicateDevices(cfg.Devices)

	sort.Sort(DeviceConfigurationList(cfg.Devices))
	// Ensure that any loose devices are not present in the wrong places
	// Ensure that there are no duplicate devices
	// Ensure that the versioning configuration parameter map is not nil
	for i := range cfg.Folders {
		cfg.Folders[i].Devices = ensureExistingDevices(cfg.Folders[i].Devices, existingDevices)
		cfg.Folders[i].Devices = ensureNoDuplicateFolderDevices(cfg.Folders[i].Devices)
		if cfg.Folders[i].Versioning.Params == nil {
			cfg.Folders[i].Versioning.Params = map[string]string{}
		}
		sort.Sort(FolderDeviceConfigurationList(cfg.Folders[i].Devices))
	}

	for i := range cfg.Devices {
		cfg.Devices[i].prepare()
	}

	// Very short reconnection intervals are annoying
	if cfg.Options.ReconnectIntervalS < 5 {
		cfg.Options.ReconnectIntervalS = 5
	}

	if cfg.GUI.APIKey == "" {
		cfg.GUI.APIKey = rand.String(32)
	}

	// The list of ignored devices should not contain any devices that have
	// been manually added to the config.
	newIgnoredDevices := []protocol.DeviceID{}
	for _, dev := range cfg.IgnoredDevices {
		if !existingDevices[dev] {
			newIgnoredDevices = append(newIgnoredDevices, dev)
		}
	}
	cfg.IgnoredDevices = newIgnoredDevices

	return nil
}

func convertV25V26(cfg *Configuration) {
	// triggers database update
	cfg.Version = 26
}

func convertV24V25(cfg *Configuration) {
	for i := range cfg.Folders {
		cfg.Folders[i].FSWatcherDelayS = 10
	}

	cfg.Version = 25
}

func convertV23V24(cfg *Configuration) {
	cfg.Options.URSeen = 2

	cfg.Version = 24
}

func convertV22V23(cfg *Configuration) {
	permBits := fs.FileMode(0777)
	if runtime.GOOS == "windows" {
		// Windows has no umask so we must chose a safer set of bits to
		// begin with.
		permBits = 0700
	}

	// Upgrade code remains hardcoded for .stfolder despite configurable
	// marker name in later versions.

	for i := range cfg.Folders {
		fs := cfg.Folders[i].Filesystem()
		// Invalid config posted, or tests.
		if fs == nil {
			continue
		}
		if stat, err := fs.Stat(DefaultMarkerName); err == nil && !stat.IsDir() {
			err = fs.Remove(DefaultMarkerName)
			if err == nil {
				err = fs.Mkdir(DefaultMarkerName, permBits)
				fs.Hide(DefaultMarkerName) // ignore error
			}
			if err != nil {
				l.Infoln("Failed to upgrade folder marker:", err)
			}
		}
	}

	cfg.Version = 23
}

func convertV21V22(cfg *Configuration) {
	for i := range cfg.Folders {
		cfg.Folders[i].FilesystemType = fs.FilesystemTypeBasic
		// Migrate to templated external versioner commands
		if cfg.Folders[i].Versioning.Type == "external" {
			cfg.Folders[i].Versioning.Params["command"] += " %FOLDER_PATH% %FILE_PATH%"
		}
	}

	cfg.Version = 22
}

func convertV20V21(cfg *Configuration) {
	for _, folder := range cfg.Folders {
		if folder.FilesystemType != fs.FilesystemTypeBasic {
			continue
		}
		switch folder.Versioning.Type {
		case "simple", "trashcan":
			// Clean out symlinks in the known place
			cleanSymlinks(folder.Filesystem(), ".stversions")
		case "staggered":
			versionDir := folder.Versioning.Params["versionsPath"]
			if versionDir == "" {
				// default place
				cleanSymlinks(folder.Filesystem(), ".stversions")
			} else if filepath.IsAbs(versionDir) {
				// absolute
				cleanSymlinks(fs.NewFilesystem(fs.FilesystemTypeBasic, versionDir), ".")
			} else {
				// relative to folder
				cleanSymlinks(folder.Filesystem(), versionDir)
			}
		}
	}

	cfg.Version = 21
}

func convertV19V20(cfg *Configuration) {
	cfg.Options.MinHomeDiskFree = Size{Value: cfg.Options.DeprecatedMinHomeDiskFreePct, Unit: "%"}
	cfg.Options.DeprecatedMinHomeDiskFreePct = 0

	for i := range cfg.Folders {
		cfg.Folders[i].MinDiskFree = Size{Value: cfg.Folders[i].DeprecatedMinDiskFreePct, Unit: "%"}
		cfg.Folders[i].DeprecatedMinDiskFreePct = 0
	}

	cfg.Version = 20
}

func convertV18V19(cfg *Configuration) {
	// Triggers a database tweak
	cfg.Version = 19
}

func convertV17V18(cfg *Configuration) {
	// Do channel selection for existing users. Those who have auto upgrades
	// and usage reporting on default to the candidate channel. Others get
	// stable.
	if cfg.Options.URAccepted > 0 && cfg.Options.AutoUpgradeIntervalH > 0 {
		cfg.Options.UpgradeToPreReleases = true
	}

	// Show a notification to explain what's going on, except if upgrades
	// are disabled by compilation or environment variable in which case
	// it's not relevant.
	if !upgrade.DisabledByCompilation && os.Getenv("STNOUPGRADE") == "" {
		cfg.Options.UnackedNotificationIDs = append(cfg.Options.UnackedNotificationIDs, "channelNotification")
	}

	cfg.Version = 18
}

func convertV16V17(cfg *Configuration) {
	// Fsync = true removed

	cfg.Version = 17
}

func convertV15V16(cfg *Configuration) {
	// Triggers a database tweak
	cfg.Version = 16
}

func convertV14V15(cfg *Configuration) {
	// Undo v0.13.0 broken migration

	for i, addr := range cfg.Options.GlobalAnnServers {
		switch addr {
		case "default-v4v2/":
			cfg.Options.GlobalAnnServers[i] = "default-v4"
		case "default-v6v2/":
			cfg.Options.GlobalAnnServers[i] = "default-v6"
		}
	}

	cfg.Version = 15
}

func convertV13V14(cfg *Configuration) {
	// Not using the ignore cache is the new default. Disable it on existing
	// configurations.
	cfg.Options.CacheIgnoredFiles = false

	// Migrate UPnP -> NAT options
	cfg.Options.NATEnabled = cfg.Options.DeprecatedUPnPEnabled
	cfg.Options.DeprecatedUPnPEnabled = false
	cfg.Options.NATLeaseM = cfg.Options.DeprecatedUPnPLeaseM
	cfg.Options.DeprecatedUPnPLeaseM = 0
	cfg.Options.NATRenewalM = cfg.Options.DeprecatedUPnPRenewalM
	cfg.Options.DeprecatedUPnPRenewalM = 0
	cfg.Options.NATTimeoutS = cfg.Options.DeprecatedUPnPTimeoutS
	cfg.Options.DeprecatedUPnPTimeoutS = 0

	// Replace the default listen address "tcp://0.0.0.0:22000" with the
	// string "default", but only if we also have the default relay pool
	// among the relay servers as this is implied by the new "default"
	// entry.
	hasDefault := false
	for _, raddr := range cfg.Options.DeprecatedRelayServers {
		if raddr == "dynamic+https://relays.syncthing.net/endpoint" {
			for i, addr := range cfg.Options.ListenAddresses {
				if addr == "tcp://0.0.0.0:22000" {
					cfg.Options.ListenAddresses[i] = "default"
					hasDefault = true
					break
				}
			}
			break
		}
	}

	// Copy relay addresses into listen addresses.
	for _, addr := range cfg.Options.DeprecatedRelayServers {
		if hasDefault && addr == "dynamic+https://relays.syncthing.net/endpoint" {
			// Skip the default relay address if we already have the
			// "default" entry in the list.
			continue
		}
		if addr == "" {
			continue
		}
		cfg.Options.ListenAddresses = append(cfg.Options.ListenAddresses, addr)
	}

	cfg.Options.DeprecatedRelayServers = nil

	// For consistency
	sort.Strings(cfg.Options.ListenAddresses)

	var newAddrs []string
	for _, addr := range cfg.Options.GlobalAnnServers {
		uri, err := url.Parse(addr)
		if err != nil {
			// That's odd. Skip the broken address.
			continue
		}
		if uri.Scheme == "https" {
			uri.Path = path.Join(uri.Path, "v2") + "/"
			addr = uri.String()
		}

		newAddrs = append(newAddrs, addr)
	}
	cfg.Options.GlobalAnnServers = newAddrs

	for i, fcfg := range cfg.Folders {
		if fcfg.DeprecatedReadOnly {
			cfg.Folders[i].Type = FolderTypeSendOnly
		} else {
			cfg.Folders[i].Type = FolderTypeSendReceive
		}
		cfg.Folders[i].DeprecatedReadOnly = false
	}
	// v0.13-beta already had config version 13 but did not get the new URL
	if cfg.Options.ReleasesURL == "https://api.github.com/repos/syncthing/syncthing/releases?per_page=30" {
		cfg.Options.ReleasesURL = "https://upgrades.syncthing.net/meta.json"
	}

	cfg.Version = 14
}

func convertV12V13(cfg *Configuration) {
	if cfg.Options.ReleasesURL == "https://api.github.com/repos/syncthing/syncthing/releases?per_page=30" {
		cfg.Options.ReleasesURL = "https://upgrades.syncthing.net/meta.json"
	}

	cfg.Version = 13
}

func convertV11V12(cfg *Configuration) {
	// Change listen address schema
	for i, addr := range cfg.Options.ListenAddresses {
		if len(addr) > 0 && !strings.HasPrefix(addr, "tcp://") {
			cfg.Options.ListenAddresses[i] = util.Address("tcp", addr)
		}
	}

	for i, device := range cfg.Devices {
		for j, addr := range device.Addresses {
			if addr != "dynamic" && addr != "" {
				cfg.Devices[i].Addresses[j] = util.Address("tcp", addr)
			}
		}
	}

	// Use new discovery server
	var newDiscoServers []string
	var useDefault bool
	for _, addr := range cfg.Options.GlobalAnnServers {
		if addr == "udp4://announce.syncthing.net:22026" {
			useDefault = true
		} else if addr == "udp6://announce-v6.syncthing.net:22026" {
			useDefault = true
		} else {
			newDiscoServers = append(newDiscoServers, addr)
		}
	}
	if useDefault {
		newDiscoServers = append(newDiscoServers, "default")
	}
	cfg.Options.GlobalAnnServers = newDiscoServers

	// Use new multicast group
	if cfg.Options.LocalAnnMCAddr == "[ff32::5222]:21026" {
		cfg.Options.LocalAnnMCAddr = "[ff12::8384]:21027"
	}

	// Use new local discovery port
	if cfg.Options.LocalAnnPort == 21025 {
		cfg.Options.LocalAnnPort = 21027
	}

	// Set MaxConflicts to unlimited
	for i := range cfg.Folders {
		cfg.Folders[i].MaxConflicts = -1
	}

	cfg.Version = 12
}

func convertV10V11(cfg *Configuration) {
	// Set minimum disk free of existing folders to 1%
	for i := range cfg.Folders {
		cfg.Folders[i].DeprecatedMinDiskFreePct = 1
	}
	cfg.Version = 11
}

func ensureDevicePresent(devices []FolderDeviceConfiguration, myID protocol.DeviceID) []FolderDeviceConfiguration {
	for _, device := range devices {
		if device.DeviceID.Equals(myID) {
			return devices
		}
	}

	devices = append(devices, FolderDeviceConfiguration{
		DeviceID: myID,
	})

	return devices
}

func ensureExistingDevices(devices []FolderDeviceConfiguration, existingDevices map[protocol.DeviceID]bool) []FolderDeviceConfiguration {
	count := len(devices)
	i := 0
loop:
	for i < count {
		if _, ok := existingDevices[devices[i].DeviceID]; !ok {
			devices[i] = devices[count-1]
			count--
			continue loop
		}
		i++
	}
	return devices[0:count]
}

func ensureNoDuplicateFolderDevices(devices []FolderDeviceConfiguration) []FolderDeviceConfiguration {
	count := len(devices)
	i := 0
	seenDevices := make(map[protocol.DeviceID]bool)
loop:
	for i < count {
		id := devices[i].DeviceID
		if _, ok := seenDevices[id]; ok {
			devices[i] = devices[count-1]
			count--
			continue loop
		}
		seenDevices[id] = true
		i++
	}
	return devices[0:count]
}

func ensureNoDuplicateDevices(devices []DeviceConfiguration) []DeviceConfiguration {
	count := len(devices)
	i := 0
	seenDevices := make(map[protocol.DeviceID]bool)
loop:
	for i < count {
		id := devices[i].DeviceID
		if _, ok := seenDevices[id]; ok {
			devices[i] = devices[count-1]
			count--
			continue loop
		}
		seenDevices[id] = true
		i++
	}
	return devices[0:count]
}

func cleanSymlinks(filesystem fs.Filesystem, dir string) {
	if runtime.GOOS == "windows" {
		// We don't do symlinks on Windows. Additionally, there may
		// be things that look like symlinks that are not, which we
		// should leave alone. Deduplicated files, for example.
		return
	}
	filesystem.Walk(dir, func(path string, info fs.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsSymlink() {
			l.Infoln("Removing incorrectly versioned symlink", path)
			filesystem.Remove(path)
			return fs.SkipDir
		}
		return nil
	})
}
