package bind

/*

bind -
  Generate zonefiles suitable for BIND.

	The zonefiles are read and written to the directory -bind_dir

	If the old zonefiles are readable, we read them to determine
	if an update is actually needed. The old zonefile is also used
	as the basis for generating the new SOA serial number.

*/

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/StackExchange/dnscontrol/v4/models"
	"github.com/StackExchange/dnscontrol/v4/pkg/bindserial"
	"github.com/StackExchange/dnscontrol/v4/pkg/diff2"
	"github.com/StackExchange/dnscontrol/v4/pkg/prettyzone"
	"github.com/StackExchange/dnscontrol/v4/pkg/printer"
	"github.com/StackExchange/dnscontrol/v4/providers"
	"github.com/miekg/dns"
)

var features = providers.DocumentationNotes{
	// The default for unlisted capabilities is 'Cannot'.
	// See providers/capabilities.go for the entire list of capabilities.
	providers.CanAutoDNSSEC:          providers.Can("Just writes out a comment indicating DNSSEC was requested"),
	providers.CanGetZones:            providers.Can(),
	providers.CanConcur:              providers.Can(),
	providers.CanUseCAA:              providers.Can(),
	providers.CanUseDHCID:            providers.Can(),
	providers.CanUseDNAME:            providers.Can(),
	providers.CanUseDS:               providers.Can(),
	providers.CanUseDNSKEY:           providers.Can(),
	providers.CanUseHTTPS:            providers.Can(),
	providers.CanUseLOC:              providers.Can(),
	providers.CanUseNAPTR:            providers.Can(),
	providers.CanUseOPENPGPKEY:       providers.Can(),
	providers.CanUsePTR:              providers.Can(),
	providers.CanUseSOA:              providers.Can(),
	providers.CanUseSRV:              providers.Can(),
	providers.CanUseSSHFP:            providers.Can(),
	providers.CanUseSVCB:             providers.Can(),
	providers.CanUseTLSA:             providers.Can(),
	providers.DocCreateDomains:       providers.Can("Driver just maintains list of zone files. It should automatically add missing ones."),
	providers.DocDualHost:            providers.Can(),
	providers.DocOfficiallySupported: providers.Can(),
}

func initBind(config map[string]string, providermeta json.RawMessage) (providers.DNSServiceProvider, error) {
	// config -- the key/values from creds.json
	// meta -- the json blob from NewReq('name', 'TYPE', meta)
	api := &bindProvider{
		directory:      config["directory"],
		filenameformat: config["filenameformat"],
	}
	if api.directory == "" {
		api.directory = "zones"
	}
	if api.filenameformat == "" {
		api.filenameformat = "%U.zone"
	}
	if len(providermeta) != 0 {
		err := json.Unmarshal(providermeta, api)
		if err != nil {
			return nil, err
		}
	}
	var nss []string
	for i, ns := range api.DefaultNS {
		if ns == "" {
			return nil, fmt.Errorf("empty string in default_ns[%d]", i)
		}
		// If it contains a ".", it must end in a ".".
		if strings.ContainsRune(ns, '.') && ns[len(ns)-1] != '.' {
			return nil, fmt.Errorf("default_ns (%v) must end with a (.) [https://docs.dnscontrol.org/language-reference/why-the-dot]", ns)
		}
		// This is one of the (increasingly rare) cases where we store a
		// name without the trailing dot to indicate a FQDN.
		nss = append(nss, strings.TrimSuffix(ns, "."))
	}
	var err error
	api.nameservers, err = models.ToNameservers(nss)
	return api, err
}

func init() {
	const providerName = "BIND"
	const providerMaintainer = "@tlimoncelli"
	fns := providers.DspFuncs{
		Initializer:   initBind,
		RecordAuditor: AuditRecords,
	}
	providers.RegisterDomainServiceProviderType(providerName, fns, features)
	providers.RegisterMaintainer(providerName, providerMaintainer)
}

// SoaDefaults contains the parts of the default SOA settings.
type SoaDefaults struct {
	Ns      string `json:"master"`
	Mbox    string `json:"mbox"`
	Serial  uint32 `json:"serial"`
	Refresh uint32 `json:"refresh"`
	Retry   uint32 `json:"retry"`
	Expire  uint32 `json:"expire"`
	Minttl  uint32 `json:"minttl"`
	TTL     uint32 `json:"ttl,omitempty"`
}

func (s SoaDefaults) String() string {
	return fmt.Sprintf("%s %s %d %d %d %d %d %d", s.Ns, s.Mbox, s.Serial, s.Refresh, s.Retry, s.Expire, s.Minttl, s.TTL)
}

// bindProvider is the provider handle for the bindProvider driver.
type bindProvider struct {
	DefaultNS      []string    `json:"default_ns"`
	DefaultSoa     SoaDefaults `json:"default_soa"`
	nameservers    []*models.Nameserver
	directory      string
	filenameformat string
}

// GetNameservers returns the nameservers for a domain.
func (c *bindProvider) GetNameservers(string) ([]*models.Nameserver, error) {
	var r []string
	for _, j := range c.nameservers {
		r = append(r, j.Name)
	}
	return models.ToNameservers(r)
}

// ListZones returns all the zones in an account
func (c *bindProvider) ListZones() ([]string, error) {
	if _, err := os.Stat(c.directory); os.IsNotExist(err) {
		return nil, fmt.Errorf("directory %q does not exist", c.directory)
	}

	var files []string
	f, err := os.Open(c.directory)
	if err != nil {
		return files, fmt.Errorf("bind ListZones open dir %q: %w",
			c.directory, err)
	}
	filenames, err := f.Readdirnames(-1)
	if err != nil {
		return files, fmt.Errorf("bind ListZones readdir %q: %w",
			c.directory, err)
	}

	return extractZonesFromFilenames(c.filenameformat, filenames), nil
}

// GetZoneRecords gets the records of a zone and returns them in RecordConfig format.
func (c *bindProvider) GetZoneRecords(domain string, meta map[string]string) (models.Records, error) {
	var zonefile string

	if _, err := os.Stat(c.directory); os.IsNotExist(err) {
		printer.Printf("\nWARNING: BIND directory %q does not exist! (will create)\n", c.directory)
	}
	_, okTag := meta[models.DomainTag]
	_, okUnique := meta[models.DomainUniqueName]
	if !okTag && !okUnique {
		// This layering violation is needed for tests only.
		// Otherwise, this is set already.
		// Note: In this situation there is no "uniquename" or "tag".
		zonefile = filepath.Join(c.directory,
			makeFileName(c.filenameformat, domain, domain, ""))
	} else {
		zonefile = filepath.Join(c.directory,
			makeFileName(c.filenameformat,
				meta[models.DomainUniqueName], domain, meta[models.DomainTag]),
		)
	}
	content, err := os.ReadFile(zonefile)
	if os.IsNotExist(err) {
		// If the file doesn't exist, that's not an error. Just informational.
		fmt.Fprintf(os.Stderr, "File does not yet exist: %q (will create)\n", zonefile)
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("can't open %s: %w", zonefile, err)
	}

	return ParseZoneContents(string(content), domain, zonefile)
}

// ParseZoneContents parses a string as a BIND zone and returns the records.
func ParseZoneContents(content string, zoneName string, zonefileName string) (models.Records, error) {
	zp := dns.NewZoneParser(strings.NewReader(content), zoneName, zonefileName)

	foundRecords := models.Records{}
	for rr, ok := zp.Next(); ok; rr, ok = zp.Next() {
		rec, err := models.RRtoRCTxtBug(rr, zoneName)
		if err != nil {
			return nil, err
		}
		foundRecords = append(foundRecords, &rec)
	}

	if err := zp.Err(); err != nil {
		return nil, fmt.Errorf("error while parsing '%v': %w", zonefileName, err)
	}
	return foundRecords, nil
}

func (c *bindProvider) EnsureZoneExists(_ string) error {
	return nil
}

// GetZoneRecordsCorrections returns a list of corrections that will turn existing records into dc.Records.
func (c *bindProvider) GetZoneRecordsCorrections(dc *models.DomainConfig, foundRecords models.Records) ([]*models.Correction, int, error) {
	var corrections []*models.Correction
	var zonefile string

	changes := false
	var msg string

	// Find the SOA records; use them to make or update the desired SOA.
	var foundSoa *models.RecordConfig
	for _, r := range foundRecords {
		if r.Type == "SOA" && r.Name == "@" {
			foundSoa = r
			break
		}
	}
	var desiredSoa *models.RecordConfig
	for _, r := range dc.Records {
		if r.Type == "SOA" && r.Name == "@" {
			desiredSoa = r
			break
		}
	}
	soaRec, nextSerial := makeSoa(dc.Name, &c.DefaultSoa, foundSoa, desiredSoa)
	if desiredSoa == nil {
		dc.Records = append(dc.Records, soaRec)
		desiredSoa = dc.Records[len(dc.Records)-1]
	} else {
		*desiredSoa = *soaRec
	}

	var msgs []string
	var actualChangeCount int
	result, err := diff2.ByZone(foundRecords, dc, nil)
	if err != nil {
		return nil, 0, err
	}
	msgs, changes, actualChangeCount = result.Msgs, result.HasChanges, result.ActualChangeCount
	if !changes {
		return nil, 0, nil
	}
	msg = strings.Join(msgs, "\n")

	comments := make([]string, 0, 5)
	comments = append(comments,
		"generated with dnscontrol "+time.Now().Format(time.RFC3339),
	)
	if dc.AutoDNSSEC == "on" {
		// This does nothing but reminds the user to add the correct
		// auto-dnssecc zone statement to named.conf.
		// While it is a no-op, it is useful for situations where a zone
		// has multiple providers.
		comments = append(comments, "Automatic DNSSEC signing requested")
	}

	zonefile = filepath.Join(c.directory,
		makeFileName(c.filenameformat,
			dc.Metadata[models.DomainUniqueName], dc.Name, dc.Metadata[models.DomainTag]),
	)

	// We only change the serial number if there is a change.
	desiredSoa.SoaSerial = nextSerial

	// If the --bindserial flag is used, force the serial to that value
	if bindserial.ForcedValue != 0 {
		desiredSoa.SoaSerial = uint32(bindserial.ForcedValue & 0xFFFF)
	}

	corrections = append(corrections,
		&models.Correction{
			Msg: msg,
			F: func() error {
				printer.Printf("WRITING ZONEFILE: %v\n", zonefile)
				fname, err := preprocessFilename(zonefile)
				if err != nil {
					return fmt.Errorf("could not create zonefile: %w", err)
				}
				zf, err := os.Create(fname)
				if err != nil {
					return fmt.Errorf("could not create zonefile: %w", err)
				}
				// Beware that if there are any fake types, then they will
				// be commented out on write, but we don't reverse that when
				// reading, so there will be a diff on every invocation.
				err = prettyzone.WriteZoneFileRC(zf, result.DesiredPlus, dc.Name, 0, comments)
				if err != nil {
					return fmt.Errorf("failed WriteZoneFile: %w", err)
				}
				err = zf.Close()
				if err != nil {
					return fmt.Errorf("closing: %w", err)
				}
				return nil
			},
		})

	return corrections, actualChangeCount, nil
}

// preprocessFilename pre-processes a filename we're about to os.Create()
// * On Windows systems, it translates the separator.
// * It attempts to mkdir the directories leading up to the filename.
// * If running on Linux as root, it does not attempt to create directories.
func preprocessFilename(name string) (string, error) {
	universalName := filepath.FromSlash(name)
	// Running as root? Don't create the parent directories. It is unsafe.
	if os.Getuid() != 0 {
		// Create the parent directories
		dir := filepath.Dir(name)
		universalDir := filepath.FromSlash(dir)
		if err := os.MkdirAll(universalDir, 0o750); err != nil {
			return "", err
		}
	}
	return universalName, nil
}
