package commands

import (
	"cmp"
	"encoding/json"
	"fmt"
	"os"
	"strings"
	"sync"

	"github.com/StackExchange/dnscontrol/v4/models"
	"github.com/StackExchange/dnscontrol/v4/pkg/bindserial"
	"github.com/StackExchange/dnscontrol/v4/pkg/credsfile"
	"github.com/StackExchange/dnscontrol/v4/pkg/nameservers"
	"github.com/StackExchange/dnscontrol/v4/pkg/normalize"
	"github.com/StackExchange/dnscontrol/v4/pkg/notifications"
	"github.com/StackExchange/dnscontrol/v4/pkg/printer"
	"github.com/StackExchange/dnscontrol/v4/pkg/rfc4183"
	"github.com/StackExchange/dnscontrol/v4/pkg/zonerecs"
	"github.com/StackExchange/dnscontrol/v4/providers"
	"github.com/urfave/cli/v2"
	"golang.org/x/exp/slices"
	"golang.org/x/net/idna"
)

type zoneCache struct {
	cache map[string]*[]string
	sync.Mutex
}

var _ = cmd(catMain, func() *cli.Command {
	var args PPreviewArgs
	return &cli.Command{
		Name:  "ppreview",
		Usage: "read live configuration and identify changes to be made, without applying them",
		Action: func(ctx *cli.Context) error {
			return exit(PPreview(args))
		},
		Flags: args.flags(),
	}
}())

// PPreviewArgs contains all data/flags needed to run preview, independently of CLI
type PPreviewArgs struct {
	GetDNSConfigArgs
	GetCredentialsArgs
	FilterArgs
	Notify      bool
	WarnChanges bool
	ConcurMode  string
	NoPopulate  bool
	DePopulate  bool
	Full        bool
}

// ReportItem is a record of corrections for a particular domain/provider/registrar.
//type ReportItem struct {
//	Domain      string `json:"domain"`
//	Corrections int    `json:"corrections"`
//	Provider    string `json:"provider,omitempty"`
//	Registrar   string `json:"registrar,omitempty"`
//}

func (args *PPreviewArgs) flags() []cli.Flag {
	flags := args.GetDNSConfigArgs.flags()
	flags = append(flags, args.GetCredentialsArgs.flags()...)
	flags = append(flags, args.FilterArgs.flags()...)
	flags = append(flags, &cli.BoolFlag{
		Name:        "notify",
		Destination: &args.Notify,
		Usage:       `set to true to send notifications to configured destinations`,
	})
	flags = append(flags, &cli.BoolFlag{
		Name:        "expect-no-changes",
		Destination: &args.WarnChanges,
		Usage:       `set to true for non-zero return code if there are changes`,
	})
	flags = append(flags, &cli.StringFlag{
		Name:        "cmode",
		Destination: &args.ConcurMode,
		Value:       "default",
		Usage:       `Which providers to run concurrently: all, default, none`,
		Action: func(c *cli.Context, s string) error {
			if !slices.Contains([]string{"all", "default", "none"}, s) {
				fmt.Printf("%q is not a valid option for --cmode.  Valie are: all, default, none", s)
			}
			return nil
		},
	})
	flags = append(flags, &cli.BoolFlag{
		Name:        "no-populate",
		Destination: &args.NoPopulate,
		Usage:       `Do not auto-create zones at the provider`,
	})
	flags = append(flags, &cli.BoolFlag{
		Name:        "depopulate",
		Destination: &args.NoPopulate,
		Usage:       `Delete unknown zones at provider (dangerous!)`,
	})
	flags = append(flags, &cli.BoolFlag{
		Name:        "full",
		Destination: &args.Full,
		Usage:       `Add headings, providers names, notifications of no changes, etc`,
	})
	flags = append(flags, &cli.IntFlag{
		Name:   "reportmax",
		Hidden: true,
		Usage:  `Limit the IGNORE/NO_PURGE report to this many lines (Expermental. Will change in the future.)`,
		Action: func(ctx *cli.Context, max int) error {
			printer.MaxReport = max
			return nil
		},
	})
	flags = append(flags, &cli.Int64Flag{
		Name:        "bindserial",
		Destination: &bindserial.ForcedValue,
		Usage:       `Force BIND serial numbers to this value (for reproducibility)`,
	})
	return flags
}

var _ = cmd(catMain, func() *cli.Command {
	var args PPushArgs
	return &cli.Command{
		Name:  "ppush",
		Usage: "identify changes to be made, and perform them",
		Action: func(ctx *cli.Context) error {
			return exit(PPush(args))
		},
		Flags: args.flags(),
	}
}())

// PPushArgs contains all data/flags needed to run push, independently of CLI
type PPushArgs struct {
	PPreviewArgs
	Interactive bool
	Report      string
}

func (args *PPushArgs) flags() []cli.Flag {
	flags := args.PPreviewArgs.flags()
	flags = append(flags, &cli.BoolFlag{
		Name:        "i",
		Destination: &args.Interactive,
		Usage:       "Interactive. Confirm or Exclude each correction before they run",
	})
	flags = append(flags, &cli.StringFlag{
		Name:        "report",
		Destination: &args.Report,
		Usage:       `Generate a machine-parseable report of performed corrections.`,
	})
	return flags
}

// PPreview implements the preview subcommand.
func PPreview(args PPreviewArgs) error {
	return prun(args, false, false, printer.DefaultPrinter, "")
}

// PPush implements the push subcommand.
func PPush(args PPushArgs) error {
	return prun(args.PPreviewArgs, true, args.Interactive, printer.DefaultPrinter, args.Report)
}

var pobsoleteDiff2FlagUsed = false

// run is the main routine common to preview/push
func prun(args PPreviewArgs, push bool, interactive bool, out printer.CLI, report string) error {

	// This is a hack until we have the new printer replacement.
	printer.SkinnyReport = !args.Full
	fullMode := args.Full

	if pobsoleteDiff2FlagUsed {
		printer.Println("WARNING: Please remove obsolete --diff2 flag. This will be an error in v5 or later. See https://github.com/StackExchange/dnscontrol/issues/2262")
	}

	out.PrintfIf(fullMode, "Reading dnsconfig.js or equiv.\n")
	cfg, err := GetDNSConfig(args.GetDNSConfigArgs)
	if err != nil {
		return err
	}

	out.PrintfIf(fullMode, "Reading creds.json or equiv.\n")
	providerConfigs, err := credsfile.LoadProviderConfigs(args.CredsFile)
	if err != nil {
		return err
	}

	out.PrintfIf(fullMode, "Creating an in-memory model of 'desired'...\n")
	notifier, err := PInitializeProviders(cfg, providerConfigs, args.Notify)
	if err != nil {
		return err
	}

	out.PrintfIf(fullMode, "Normalizing and validating 'desired'..\n")
	errs := normalize.ValidateAndNormalizeConfig(cfg)
	if PrintValidationErrors(errs) {
		return fmt.Errorf("exiting due to validation errors")
	}

	zcache := NewZoneCache()

	// Loop over all (or some) zones:
	zonesToProcess := whichZonesToProcess(cfg.Domains, args.Domains)
	zonesSerial, zonesConcurrent := splitConcurrent(zonesToProcess, args.ConcurMode)
	out.PrintfIf(fullMode, "PHASE 1: GATHERING data\n")
	var wg sync.WaitGroup
	wg.Add(len(zonesConcurrent))
	out.Printf("CONCURRENTLY gathering %d zone(s)\n", len(zonesConcurrent))
	for _, zone := range optimizeOrder(zonesConcurrent) {
		out.PrintfIf(fullMode, "Concurrently gathering: %q\n", zone.Name)
		go func(zone *models.DomainConfig, args PPreviewArgs, zcache *zoneCache) {
			defer wg.Done()
			oneZone(zone, args, zcache)
		}(zone, args, zcache)
	}
	out.Printf("SERIALLY gathering %d zone(s)\n", len(zonesSerial))
	for _, zone := range zonesSerial {
		out.Printf("Serially Gathering: %q\n", zone.Name)
		oneZone(zone, args, zcache)
	}
	out.PrintfIf(len(zonesConcurrent) > 0, "Waiting for concurrent gathering(s) to complete...")
	wg.Wait()
	out.PrintfIf(len(zonesConcurrent) > 0, "DONE\n")

	// Now we know what to do, print or do the tasks.
	out.PrintfIf(fullMode, "PHASE 2: CORRECTIONS\n")
	var totalCorrections int
	var reportItems []*ReportItem
	var anyErrors bool
	for _, zone := range zonesToProcess {
		out.StartDomain(zone.GetUniqueName())

		// Process DNS provider changes:
		providersToProcess := whichProvidersToProcess(zone.DNSProviderInstances, args.Providers)
		for _, provider := range zone.DNSProviderInstances {
			skip := skipProvider(provider.Name, providersToProcess)
			out.StartDNSProvider(provider.Name, skip)
			if !skip {
				corrections := zone.GetCorrections(provider.Name)
				numActions := zone.GetChangeCount(provider.Name)
				totalCorrections += numActions
				out.EndProvider2(provider.Name, numActions)
				reportItems = append(reportItems, genReportItem(zone.Name, corrections, provider.Name))
				anyErrors = cmp.Or(anyErrors, pprintOrRunCorrections(zone.Name, provider.Name, corrections, out, push, interactive, notifier, report))
			}
		}

		// Process Registrar changes:
		skip := skipProvider(zone.RegistrarInstance.Name, providersToProcess)
		out.StartRegistrar(zone.RegistrarName, !skip)
		if skip {
			corrections := zone.GetCorrections(zone.RegistrarInstance.Name)
			numActions := zone.GetChangeCount(zone.RegistrarInstance.Name)
			out.EndProvider2(zone.RegistrarName, numActions)
			totalCorrections += numActions
			reportItems = append(reportItems, genReportItem(zone.Name, corrections, zone.RegistrarName))
			anyErrors = cmp.Or(anyErrors, pprintOrRunCorrections(zone.Name, zone.RegistrarInstance.Name, corrections, out, push, interactive, notifier, report))
		}

	}

	if os.Getenv("TEAMCITY_VERSION") != "" {
		fmt.Fprintf(os.Stderr, "##teamcity[buildStatus status='SUCCESS' text='%d corrections']", totalCorrections)
	}
	rfc4183.PrintWarning()
	notifier.Done()
	out.Printf("Done. %d corrections.\n", totalCorrections)
	err = writeReport(report, reportItems)
	if err != nil {
		return fmt.Errorf("could not write report")
	}
	if anyErrors {
		return fmt.Errorf("completed with errors")
	}
	if totalCorrections != 0 && args.WarnChanges {
		return fmt.Errorf("there are pending changes")
	}
	return nil
}

//func countActions(corrections []*models.Correction) int {
//	r := 0
//	for _, c := range corrections {
//		if c.F != nil {
//			r++
//		}
//	}
//	return r
//}

func whichZonesToProcess(domains []*models.DomainConfig, filter string) []*models.DomainConfig {
	if filter == "" || filter == "all" {
		return domains
	}

	permitList := strings.Split(filter, ",")
	var picked []*models.DomainConfig
	for _, domain := range domains {
		if domainInList(domain.Name, permitList) {
			picked = append(picked, domain)
		}
	}
	return picked
}

// splitConcurrent takes a list of DomainConfigs and returns two lists. The
// first list is the items that do NOT support concurrency.  The second is list
// the items that DO support concurrency.
func splitConcurrent(domains []*models.DomainConfig, filter string) (serial []*models.DomainConfig, concurrent []*models.DomainConfig) {
	if filter == "none" {
		return domains, nil
	} else if filter == "all" {
		return nil, domains
	}
	for _, dc := range domains {
		if allConcur(dc) {
			concurrent = append(concurrent, dc)
		} else {
			serial = append(serial, dc)
		}
	}
	return
}

// allConcur returns true if its registrar and all DNS providers support
// concurrency.  Otherwise false is returned.
func allConcur(dc *models.DomainConfig) bool {
	if !providers.ProviderHasCapability(dc.RegistrarInstance.ProviderType, providers.CanConcur) {
		//fmt.Printf("WHY? %q: %+v\n", dc.Name, dc.RegistrarInstance)
		return false
	}
	for _, p := range dc.DNSProviderInstances {
		if !providers.ProviderHasCapability(p.ProviderType, providers.CanConcur) {
			//fmt.Printf("WHY? %q: %+v\n", dc.Name, p)
			return false
		}
	}
	return true
}

// optimizeOrder returns a list of DomainConfigs so that they gather fastest.
//
// The current algorithm is based on the heuistic that larger zones (zones with
// the most records) need the most time to be processed.  Therefore, the largest
// zones are moved to the front of the list.
// This isn't perfect but it is good enough.
func optimizeOrder(zones []*models.DomainConfig) []*models.DomainConfig {
	slices.SortFunc(zones, func(a, b *models.DomainConfig) int {
		return len(b.Records) - len(a.Records) // Biggest to smallest.
	})

	// // For benchmarking. Randomize the list. If you aren't better
	// // than random, you might as well not play.
	// rand.Shuffle(len(zones), func(i, j int) {
	// 	zones[i], zones[j] = zones[j], zones[i]
	// })

	return zones
}

func oneZone(zone *models.DomainConfig, args PPreviewArgs, zc *zoneCache) {
	// Fix the parent zone's delegation: (if able/needed)
	//zone.NameserversMutex.Lock()
	delegationCorrections, dcCount := generateDelegationCorrections(zone, zone.DNSProviderInstances, zone.RegistrarInstance)
	//zone.NameserversMutex.Unlock()

	// Loop over the (selected) providers configured for that zone:
	providersToProcess := whichProvidersToProcess(zone.DNSProviderInstances, args.Providers)
	for _, provider := range providersToProcess {

		// Populate the zones at the provider (if desired/needed/able):
		if !args.NoPopulate {
			populateCorrections := generatePopulateCorrections(provider, zone.Name, zc)
			zone.StoreCorrections(provider.Name, populateCorrections)
		}

		// Update the zone's records at the provider:
		zoneCor, rep, actualChangeCount := generateZoneCorrections(zone, provider)
		zone.StoreCorrections(provider.Name, rep)
		zone.StoreCorrections(provider.Name, zoneCor)
		zone.IncrementChangeCount(provider.Name, actualChangeCount)
	}

	// Do the delegation corrections after the zones are updated.
	zone.StoreCorrections(zone.RegistrarInstance.Name, delegationCorrections)
	zone.IncrementChangeCount(zone.RegistrarInstance.Name, dcCount)
}

func whichProvidersToProcess(providers []*models.DNSProviderInstance, filter string) []*models.DNSProviderInstance {

	if filter == "all" { // all
		return providers
	}

	permitList := strings.Split(filter, ",")
	var picked []*models.DNSProviderInstance

	// Just the default providers:
	if filter == "" {
		for _, provider := range providers {
			if provider.IsDefault {
				picked = append(picked, provider)
			}
		}
		return picked
	}

	// Just the exact matches:
	for _, provider := range providers {
		for _, filterItem := range permitList {
			if provider.Name == filterItem {
				picked = append(picked, provider)
			}
		}
	}
	return picked
}

func skipProvider(name string, providers []*models.DNSProviderInstance) bool {
	return !slices.ContainsFunc(providers, func(p *models.DNSProviderInstance) bool {
		return p.Name == name
	})
}

func genReportItem(zname string, corrections []*models.Correction, pname string) *ReportItem {

	// Only count the actions, not the messages.
	cnt := 0
	for _, cor := range corrections {
		if cor.F != nil {
			cnt++
		}
	}

	r := ReportItem{
		Domain:      zname,
		Corrections: cnt,
		Provider:    pname,
	}
	return &r
}

func pprintOrRunCorrections(zoneName string, providerName string, corrections []*models.Correction, out printer.CLI, push bool, interactive bool, notifier notifications.Notifier, report string) bool {
	if len(corrections) == 0 {
		return false
	}
	var anyErrors bool
	cc := 0
	cn := 0
	for _, correction := range corrections {

		// Print what we're about to do.
		if correction.F == nil {
			out.PrintReport(cn, correction)
			cn++
		} else {
			out.PrintCorrection(cc, correction)
			cc++
		}

		var err error
		if push {

			// If interactive, ask "are you sure?" and skip if not.
			if interactive && !out.PromptToRun() {
				continue
			}

			// If it is an action (not an informational message), notify and execute.
			if correction.F != nil {
				notifier.Notify(zoneName, providerName, correction.Msg, err, false)
				err = correction.F()
				out.EndCorrection(err)
				if err != nil {
					anyErrors = true
				}
			}
		}
	}

	_ = report // File name to write report to. (obsolete)
	return anyErrors
}

func writeReport(report string, reportItems []*ReportItem) error {
	// No filename? No report.
	if report == "" {
		return nil
	}

	f, err := os.OpenFile(report, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return err
	}
	defer f.Close()
	b, err := json.MarshalIndent(reportItems, "", "  ")
	if err != nil {
		return err
	}
	if _, err := f.Write(b); err != nil {
		return err
	}
	return nil
}

func generatePopulateCorrections(provider *models.DNSProviderInstance, zoneName string, zcache *zoneCache) []*models.Correction {

	lister, ok := provider.Driver.(providers.ZoneLister)
	if !ok {
		return nil // We can't generate a list. No corrections are possible.
	}

	z, err := zcache.zoneList(provider.Name, lister)
	if err != nil {
		return []*models.Correction{{Msg: fmt.Sprintf("zoneList failed for %q: %s", provider.Name, err)}}
	}
	zones := *z

	aceZoneName, _ := idna.ToASCII(zoneName)
	if slices.Contains(zones, aceZoneName) {
		return nil // zone exists. Nothing to do.
	}

	creator, ok := provider.Driver.(providers.ZoneCreator)
	if !ok {
		return []*models.Correction{{Msg: fmt.Sprintf("Zone %q does not exist. Can not create because %q does not implement ZoneCreator", aceZoneName, provider.Name)}}
	}

	return []*models.Correction{{
		Msg: fmt.Sprintf("Create zone '%s' in the '%s' profile", aceZoneName, provider.Name),
		F:   func() error { return creator.EnsureZoneExists(aceZoneName) },
	}}
}

func generateZoneCorrections(zone *models.DomainConfig, provider *models.DNSProviderInstance) ([]*models.Correction, []*models.Correction, int) {
	reports, zoneCorrections, actualChangeCount, err := zonerecs.CorrectZoneRecords(provider.Driver, zone)
	if err != nil {
		return []*models.Correction{{Msg: fmt.Sprintf("Domain %q provider %s Error: %s", zone.Name, provider.Name, err)}}, nil, 0
	}
	return zoneCorrections, reports, actualChangeCount
}

func generateDelegationCorrections(zone *models.DomainConfig, providers []*models.DNSProviderInstance, _ *models.RegistrarInstance) ([]*models.Correction, int) {
	//fmt.Printf("DEBUG: generateDelegationCorrections start zone=%q nsList = %v\n", zone.Name, zone.Nameservers)
	nsList, err := nameservers.DetermineNameserversForProviders(zone, providers, true)
	if err != nil {
		return msg(fmt.Sprintf("DetermineNS: zone %q; Error: %s", zone.Name, err)), 0
	}
	zone.Nameservers = nsList
	nameservers.AddNSRecords(zone)

	if len(zone.Nameservers) == 0 && zone.Metadata["no_ns"] != "true" {
		return []*models.Correction{{Msg: fmt.Sprintf("No nameservers declared for domain %q; skipping registrar. Add {no_ns:'true'} to force", zone.Name)}}, 0
	}

	corrections, err := zone.RegistrarInstance.Driver.GetRegistrarCorrections(zone)
	if err != nil {
		return msg(fmt.Sprintf("zone %q; Rprovider %q; Error: %s", zone.Name, zone.RegistrarInstance.Name, err)), 0
	}
	return corrections, len(corrections)
}

func msg(s string) []*models.Correction {
	return []*models.Correction{{Msg: s}}
}

// PInitializeProviders takes (fully processed) configuration and instantiates all providers and returns them.
func PInitializeProviders(cfg *models.DNSConfig, providerConfigs map[string]map[string]string, notifyFlag bool) (notify notifications.Notifier, err error) {
	var notificationCfg map[string]string
	defer func() {
		notify = notifications.Init(notificationCfg)
	}()
	if notifyFlag {
		notificationCfg = providerConfigs["notifications"]
	}
	isNonDefault := map[string]bool{}
	for name, vals := range providerConfigs {
		// add "_exclude_from_defaults":"true" to a provider to exclude it from being run unless
		// -providers=all or -providers=name
		if vals["_exclude_from_defaults"] == "true" {
			isNonDefault[name] = true
		}
	}

	// Populate provider type ids based on values from creds.json:
	msgs, err := ppopulateProviderTypes(cfg, providerConfigs)
	if len(msgs) != 0 {
		fmt.Fprintln(os.Stderr, strings.Join(msgs, "\n"))
	}
	if err != nil {
		return
	}

	registrars := map[string]providers.Registrar{}
	dnsProviders := map[string]providers.DNSServiceProvider{}
	for _, d := range cfg.Domains {
		if registrars[d.RegistrarName] == nil {
			rCfg := cfg.RegistrarsByName[d.RegistrarName]
			r, err := providers.CreateRegistrar(rCfg.Type, providerConfigs[d.RegistrarName])
			if err != nil {
				return nil, err
			}
			registrars[d.RegistrarName] = r
		}
		d.RegistrarInstance.Driver = registrars[d.RegistrarName]
		d.RegistrarInstance.IsDefault = !isNonDefault[d.RegistrarName]
		for _, pInst := range d.DNSProviderInstances {
			if dnsProviders[pInst.Name] == nil {
				dCfg := cfg.DNSProvidersByName[pInst.Name]
				prov, err := providers.CreateDNSProvider(dCfg.Type, providerConfigs[dCfg.Name], dCfg.Metadata)
				if err != nil {
					return nil, err
				}
				dnsProviders[pInst.Name] = prov
			}
			pInst.Driver = dnsProviders[pInst.Name]
			pInst.IsDefault = !isNonDefault[pInst.Name]
		}
	}
	return
}

// pproviderTypeFieldName is the name of the field in creds.json that specifies the provider type id.
const pproviderTypeFieldName = "TYPE"

// ppurl is the documentation URL to list in the warnings related to missing provider type ids.
const purl = "https://docs.dnscontrol.org/commands/creds-json"

// ppopulateProviderTypes scans a DNSConfig for blank provider types and fills them in based on providerConfigs.
// That is, if the provider type is "-" or "", we take that as an flag
// that means this value should be replaced by the type found in creds.json.
func ppopulateProviderTypes(cfg *models.DNSConfig, providerConfigs map[string]map[string]string) ([]string, error) {
	var msgs []string

	for i := range cfg.Registrars {
		pType := cfg.Registrars[i].Type
		pName := cfg.Registrars[i].Name
		nt, warnMsg, err := prefineProviderType(pName, pType, providerConfigs[pName], "NewRegistrar")
		cfg.Registrars[i].Type = nt
		if warnMsg != "" {
			msgs = append(msgs, warnMsg)
		}
		if err != nil {
			return msgs, err
		}
	}

	for i := range cfg.DNSProviders {
		pName := cfg.DNSProviders[i].Name
		pType := cfg.DNSProviders[i].Type
		nt, warnMsg, err := prefineProviderType(pName, pType, providerConfigs[pName], "NewDnsProvider")
		cfg.DNSProviders[i].Type = nt
		if warnMsg != "" {
			msgs = append(msgs, warnMsg)
		}
		if err != nil {
			return msgs, err
		}
	}

	// Update these fields set by
	// commands/commands.go:preloadProviders().
	// This is probably a layering violation.  That said, the
	// fundamental problem here is that we're storing the provider
	// instances by string name, not by a pointer to a struct.  We
	// should clean that up someday.
	for _, domain := range cfg.Domains { // For each domain..
		for _, provider := range domain.DNSProviderInstances { // For each provider...
			pName := provider.ProviderBase.Name
			pType := provider.ProviderBase.ProviderType
			nt, warnMsg, err := prefineProviderType(pName, pType, providerConfigs[pName], "NewDnsProvider")
			provider.ProviderBase.ProviderType = nt
			if warnMsg != "" {
				msgs = append(msgs, warnMsg)
			}
			if err != nil {
				return msgs, err
			}
		}
		p := domain.RegistrarInstance
		pName := p.Name
		pType := p.ProviderType
		nt, warnMsg, err := prefineProviderType(pName, pType, providerConfigs[pName], "NewRegistrar")
		p.ProviderType = nt
		if warnMsg != "" {
			msgs = append(msgs, warnMsg)
		}
		if err != nil {
			return msgs, err
		}
	}

	return puniqueStrings(msgs), nil
}

// puniqueStrings takes an unsorted slice of strings and returns the
// unique strings, in the order they first appeared in the list.
func puniqueStrings(stringSlice []string) []string {
	keys := make(map[string]bool)
	list := []string{}
	for _, entry := range stringSlice {
		if _, ok := keys[entry]; !ok {
			keys[entry] = true
			list = append(list, entry)
		}
	}
	return list
}

func prefineProviderType(credEntryName string, t string, credFields map[string]string, source string) (replacementType string, warnMsg string, err error) {

	// t="" and t="-" are processed the same. Standardize on "-" to reduce the number of cases to check.
	if t == "" {
		t = "-"
	}

	// Use cases:
	//
	// type     credsType
	// ----     ---------
	// - or ""  GANDI        lookup worked. Nothing to say.
	// - or ""  - or ""      ERROR "creds.json has invalid or missing data"
	// GANDI    ""           WARNING "Working but.... Please fix as follows..."
	// GANDI    GANDI        INFO "working but unneeded: clean up as follows..."
	// GANDI    NAMEDOT      ERROR "error mismatched: please fix as follows..."

	// ERROR: Invalid.
	// WARNING: Required change to remain compatible with 4.0
	// INFO: Post-4.0 cleanups or other non-required changes.

	if t != "-" {
		// Old-style, dnsconfig.js specifies the type explicitly.
		// This is supported but we suggest updates for future compatibility.

		// If credFields is nil, that means there was no entry in creds.json:
		if credFields == nil {
			// Warn the user to update creds.json in preparation for 4.0:
			// In 4.0 this should be an error.  We could default to a
			// provider such as "NONE" but I suspect it would be confusing
			// to users to see references to a provider name that they did
			// not specify.
			return t, fmt.Sprintf(`WARNING: For future compatibility, add this entry creds.json: %q: { %q: %q }, (See %s#missing)`,
				credEntryName, pproviderTypeFieldName, t,
				purl,
			), nil
		}

		switch ct := credFields[pproviderTypeFieldName]; ct {
		case "":
			// Warn the user to update creds.json in preparation for 4.0:
			// In 4.0 this should be an error.
			return t, fmt.Sprintf(`WARNING: For future compatibility, update the %q entry in creds.json by adding: %q: %q, (See %s#missing)`,
				credEntryName,
				pproviderTypeFieldName, t,
				purl,
			), nil
		case "-":
			// This should never happen. The user is specifying "-" in a place that it shouldn't be used.
			return "-", "", fmt.Errorf(`ERROR: creds.json entry %q has invalid %q value %q (See %s#hyphen)`,
				credEntryName, pproviderTypeFieldName, ct,
				purl,
			)
		case t:
			// creds.json file is compatible with and dnsconfig.js can be updated.
			return ct, fmt.Sprintf(`INFO: In dnsconfig.js %s(%q, %q) can be simplified to %s(%q) (See %s#cleanup)`,
				source, credEntryName, t,
				source, credEntryName,
				purl,
			), nil
		default:
			// creds.json lists a TYPE but it doesn't match what's in dnsconfig.js!
			return t, "", fmt.Errorf(`ERROR: Mismatch found! creds.json entry %q has %q set to %q but dnsconfig.js specifies %s(%q, %q) (See %s#mismatch)`,
				credEntryName,
				pproviderTypeFieldName, ct,
				source, credEntryName, t,
				purl,
			)
		}
	}

	// t == "-"
	// New-style, dnsconfig.js does not specify the type (t == "") or a
	// command line tool accepted "-" as a positional argument for
	// backwards compatibility.

	// If credFields is nil, that means there was no entry in creds.json:
	if credFields == nil {
		return "", "", fmt.Errorf(`ERROR: creds.json is missing an entry called %q. Suggestion: %q: { %q: %q }, (See %s#missing)`,
			credEntryName,
			credEntryName, pproviderTypeFieldName, "FILL_IN_PROVIDER_TYPE",
			purl,
		)
	}

	// New-style, dnsconfig.js doesn't specifies the type. It will be
	// looked up in creds.json.
	switch ct := credFields[pproviderTypeFieldName]; ct {
	case "":
		return ct, "", fmt.Errorf(`ERROR: creds.json entry %q is missing: %q: %q, (See %s#fixcreds)`,
			credEntryName,
			pproviderTypeFieldName, "FILL_IN_PROVIDER_TYPE",
			purl,
		)
	case "-":
		// This should never happen. The user is confused and specified "-" in the wrong place!
		return "-", "", fmt.Errorf(`ERROR: creds.json entry %q has invalid %q value %q (See %s#hyphen)`,
			credEntryName,
			pproviderTypeFieldName, ct,
			purl,
		)
	default:
		// use the value in creds.json (this should be the normal case)
		return ct, "", nil
	}

}