package app

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"strings"

	"github.com/owen/vibedns/internal/auditlog"
	"github.com/owen/vibedns/internal/database"
	"github.com/owen/vibedns/internal/models"
	"github.com/owen/vibedns/internal/validate"
	"github.com/owen/vibedns/internal/zonefile"
)

// ZoneInput is the editable surface of a zone.
type ZoneInput struct {
	Name        string  `json:"name"`
	Kind        string  `json:"kind"`
	CIDR        string  `json:"cidr"` // reverse zones may be created from a subnet instead
	Description string  `json:"description"`
	Enabled     *bool   `json:"enabled"`
	DefaultTTL  uint32  `json:"default_ttl"`
	PrimaryNS   string  `json:"primary_ns"`
	AdminEmail  string  `json:"admin_email"`
	Refresh     uint32  `json:"refresh"`
	Retry       uint32  `json:"retry"`
	Expire      uint32  `json:"expire"`
	Minimum     uint32  `json:"minimum"`
	AutoSerial  *bool   `json:"auto_serial"`
	Serial      *uint32 `json:"serial"`
}

// Zones lists zones matching a filter.
func (a *App) Zones(ctx context.Context, f database.ZoneFilter) ([]models.Zone, error) {
	zones, err := a.DB.Zones(ctx, f)
	if err != nil {
		return nil, Internal(err, "The zone list could not be loaded.")
	}
	return zones, nil
}

// Zone loads one zone.
func (a *App) Zone(ctx context.Context, id int64) (models.Zone, error) {
	z, err := a.DB.Zone(ctx, id)
	if errors.Is(err, database.ErrNotFound) {
		return z, NotFound("Zone %d was not found.", id)
	}
	if err != nil {
		return z, Internal(err, "The zone could not be loaded.")
	}
	return z, nil
}

// CreateZone validates and stores a new zone.
//
// A reverse zone may be given either as an explicit apex name or as the subnet
// it covers, which is what the UI sends: administrators should not have to
// reverse octets by hand.
func (a *App) CreateZone(ctx context.Context, actor auditlog.Actor, in ZoneInput) (models.Zone, error) {
	z, note, err := a.normaliseZoneInput(in, models.Zone{})
	if err != nil {
		return models.Zone{}, err
	}

	created, err := a.DB.CreateZone(ctx, z)
	if err != nil {
		return models.Zone{}, translate(err,
			"Zone not found.",
			fmt.Sprintf("A zone named %s already exists.", strings.TrimSuffix(z.Name, ".")))
	}

	a.Audit.RecordID(ctx, actor, "zone.create", auditlog.ObjectZone, created.ID, created.Name,
		auditlog.Changes("kind", string(created.Kind), "ttl", fmt.Sprint(created.DefaultTTL)))
	a.Runtime.RequestReload()

	if note != "" {
		a.Log.Info("reverse zone name derived from subnet", "zone", created.Name, "note", note)
	}
	return created, nil
}

// ReverseZoneName previews the zone apex a subnet maps to, for the UI's live
// hint under the CIDR field.
func (a *App) ReverseZoneName(cidr string) (name, note string, err error) {
	name, note, err = validate.ReverseZone(cidr)
	if err != nil {
		return "", "", Invalid("%s", err.Error())
	}
	return name, note, nil
}

// UpdateZone saves zone metadata.
func (a *App) UpdateZone(ctx context.Context, actor auditlog.Actor, id int64, in ZoneInput) (models.Zone, error) {
	existing, err := a.Zone(ctx, id)
	if err != nil {
		return models.Zone{}, err
	}
	z, _, err := a.normaliseZoneInput(in, existing)
	if err != nil {
		return models.Zone{}, err
	}
	z.ID = id
	z.CreatedAt = existing.CreatedAt

	updated, err := a.DB.UpdateZone(ctx, z)
	if err != nil {
		return models.Zone{}, translate(err,
			fmt.Sprintf("Zone %d was not found.", id),
			fmt.Sprintf("A zone named %s already exists.", strings.TrimSuffix(z.Name, ".")))
	}

	a.Audit.RecordID(ctx, actor, "zone.update", auditlog.ObjectZone, id, updated.Name,
		auditlog.Changes("serial", fmt.Sprint(updated.Serial), "ttl", fmt.Sprint(updated.DefaultTTL)))
	a.Runtime.RequestReload()
	return updated, nil
}

// normaliseZoneInput validates input and merges it over an existing zone.
func (a *App) normaliseZoneInput(in ZoneInput, base models.Zone) (models.Zone, string, error) {
	z := base
	var note string

	name := strings.TrimSpace(in.Name)
	if cidr := strings.TrimSpace(in.CIDR); cidr != "" && name == "" {
		derived, n, err := validate.ReverseZone(cidr)
		if err != nil {
			return z, "", Invalid("%s", err.Error())
		}
		name = derived
		note = n
		kind, err := validate.ReverseZoneKindForCIDR(cidr)
		if err == nil {
			in.Kind = kind
		}
	}
	if name == "" && base.Name == "" {
		return z, "", Invalid("A zone name is required.")
	}
	if name != "" {
		normalised, err := validate.NormaliseZoneName(name)
		if err != nil {
			return z, "", Invalid("%s", err.Error())
		}
		z.Name = normalised
	}

	kind := models.ZoneKind(strings.TrimSpace(in.Kind))
	if kind == "" {
		kind = models.ZoneKind(validate.ZoneKindForName(z.Name))
	}
	if !kind.Valid() {
		return z, "", Invalid("Zone kind %q must be forward, reverse4 or reverse6.", in.Kind)
	}
	z.Kind = kind

	z.Description = strings.TrimSpace(in.Description)
	if in.Enabled != nil {
		z.Enabled = *in.Enabled
	} else if base.ID == 0 {
		z.Enabled = true
	}

	z.DefaultTTL = in.DefaultTTL
	if z.DefaultTTL == 0 {
		z.DefaultTTL = base.DefaultTTL
	}
	if z.DefaultTTL == 0 {
		z.DefaultTTL = a.Settings().DNS.DefaultTTL
	}
	if z.DefaultTTL < 1 || z.DefaultTTL > 604800 {
		return z, "", Invalid("The default TTL must be between 1 and 604800 seconds.")
	}

	z.PrimaryNS = strings.TrimSpace(in.PrimaryNS)
	if z.PrimaryNS == "" {
		z.PrimaryNS = base.PrimaryNS
	}
	if z.PrimaryNS == "" {
		z.PrimaryNS = "ns1." + z.Name
	}
	ns, err := validate.NormaliseFQDN(z.PrimaryNS)
	if err != nil {
		return z, "", Invalid("Primary name server: %s", err.Error())
	}
	z.PrimaryNS = ns

	z.AdminEmail = strings.TrimSpace(in.AdminEmail)
	if z.AdminEmail == "" {
		z.AdminEmail = base.AdminEmail
	}
	if z.AdminEmail == "" {
		z.AdminEmail = "hostmaster@" + strings.TrimSuffix(z.Name, ".")
	}

	z.Refresh = orDefault(in.Refresh, base.Refresh, 7200)
	z.Retry = orDefault(in.Retry, base.Retry, 3600)
	z.Expire = orDefault(in.Expire, base.Expire, 1209600)
	z.Minimum = orDefault(in.Minimum, base.Minimum, 3600)

	if in.AutoSerial != nil {
		z.AutoSerial = *in.AutoSerial
	} else if base.ID == 0 {
		z.AutoSerial = true
	}
	if in.Serial != nil {
		// A manual serial override is allowed, which matters when migrating a
		// zone from another server that is already at a higher serial.
		if *in.Serial == 0 {
			return z, "", Invalid("The serial must be at least 1.")
		}
		z.Serial = *in.Serial
	} else if z.Serial == 0 {
		z.Serial = 1
	}
	return z, note, nil
}

func orDefault(v, fallback, def uint32) uint32 {
	if v != 0 {
		return v
	}
	if fallback != 0 {
		return fallback
	}
	return def
}

// SetZoneEnabled toggles a zone.
func (a *App) SetZoneEnabled(ctx context.Context, actor auditlog.Actor, id int64, enabled bool) error {
	z, err := a.Zone(ctx, id)
	if err != nil {
		return err
	}
	if err := a.DB.SetZoneEnabled(ctx, id, enabled); err != nil {
		return translate(err, fmt.Sprintf("Zone %d was not found.", id), "")
	}
	action := "zone.disable"
	if enabled {
		action = "zone.enable"
	}
	a.Audit.RecordID(ctx, actor, action, auditlog.ObjectZone, id, z.Name, "")
	a.Runtime.RequestReload()
	return nil
}

// DeleteZone removes a zone and all of its records.
func (a *App) DeleteZone(ctx context.Context, actor auditlog.Actor, id int64) error {
	z, err := a.Zone(ctx, id)
	if err != nil {
		return err
	}
	if err := a.DB.DeleteZone(ctx, id); err != nil {
		return translate(err, fmt.Sprintf("Zone %d was not found.", id), "")
	}
	a.Audit.RecordID(ctx, actor, "zone.delete", auditlog.ObjectZone, id, z.Name,
		auditlog.Changes("records", fmt.Sprint(z.RecordCount)))
	a.Runtime.RequestReload()
	return nil
}

// CloneZone copies a zone under a new name.
func (a *App) CloneZone(ctx context.Context, actor auditlog.Actor, id int64, newName, description string) (models.Zone, error) {
	src, err := a.Zone(ctx, id)
	if err != nil {
		return models.Zone{}, err
	}
	name, err := validate.NormaliseZoneName(newName)
	if err != nil {
		return models.Zone{}, Invalid("%s", err.Error())
	}
	if name == src.Name {
		return models.Zone{}, Invalid("The new zone name must differ from the zone being cloned.")
	}

	clone, err := a.DB.CloneZone(ctx, id, name, strings.TrimSpace(description))
	if err != nil {
		return models.Zone{}, translate(err,
			fmt.Sprintf("Zone %d was not found.", id),
			fmt.Sprintf("A zone named %s already exists.", strings.TrimSuffix(name, ".")))
	}
	a.Audit.RecordID(ctx, actor, "zone.clone", auditlog.ObjectZone, clone.ID, clone.Name,
		auditlog.Changes("source", src.Name))
	a.Runtime.RequestReload()
	return clone, nil
}

// --- Zone file import and export ---------------------------------------

// ImportMode selects how an imported zone file is applied.
type ImportMode string

const (
	// ImportReplace discards the zone's existing records.
	ImportReplace ImportMode = "replace"
	// ImportMerge adds the imported records to what is already there.
	ImportMerge ImportMode = "merge"
)

// ImportResult reports the outcome of a zone file import.
type ImportResult struct {
	Zone    models.Zone           `json:"zone"`
	Summary zonefile.ParseSummary `json:"summary"`
	Created bool                  `json:"zone_created"`
}

// ImportZoneFile parses a BIND zone file and stores its records.
//
// The whole file is validated before anything is written, so a syntax error
// halfway through never leaves a zone half-imported.
func (a *App) ImportZoneFile(ctx context.Context, actor auditlog.Actor, zoneID int64,
	r io.Reader, mode ImportMode) (*ImportResult, error) {

	z, err := a.Zone(ctx, zoneID)
	if err != nil {
		return nil, err
	}
	parsed, err := zonefile.Parse(r, z.Name, z.DefaultTTL)
	if err != nil {
		return nil, Invalid("%s", err.Error())
	}
	if problems := zonefile.ValidateRecords(z.Name, parsed.Records, z.DefaultTTL); len(problems) > 0 {
		return nil, Invalid("The zone file contains records this server cannot store:\n%s",
			strings.Join(problems, "\n"))
	}

	switch mode {
	case ImportMerge:
		err = a.DB.AppendZoneRecords(ctx, zoneID, parsed.Records)
	default:
		mode = ImportReplace
		err = a.DB.ReplaceZoneRecords(ctx, zoneID, parsed.Records)
	}
	if err != nil {
		return nil, Internal(err, "The imported records could not be saved.")
	}

	// Adopt the SOA timers from the file, but keep our own serial management
	// unless the file's serial is higher.
	if parsed.SOA != nil {
		updated := z
		zonefile.ZoneMetadataFromSOA(&updated, parsed.SOA)
		if updated.Serial < z.Serial {
			updated.Serial = z.Serial
		}
		if _, err := a.DB.UpdateZone(ctx, updated); err != nil {
			a.Log.Warn("could not apply imported SOA values", "zone", z.Name, "error", err)
		} else {
			z = updated
		}
	}

	a.Audit.RecordID(ctx, actor, "zone.import", auditlog.ObjectZone, zoneID, z.Name,
		auditlog.Changes("mode", string(mode), "records", fmt.Sprint(parsed.Summary.RecordsParsed)))
	a.Runtime.RequestReload()

	return &ImportResult{Zone: z, Summary: parsed.Summary}, nil
}

// ExportZoneFile renders a zone as a BIND zone file.
func (a *App) ExportZoneFile(ctx context.Context, zoneID int64) (models.Zone, []byte, error) {
	z, err := a.Zone(ctx, zoneID)
	if err != nil {
		return z, nil, err
	}
	recs, err := a.DB.ZoneRecordsRaw(ctx, zoneID)
	if err != nil {
		return z, nil, Internal(err, "The zone records could not be loaded.")
	}
	var buf bytes.Buffer
	if err := zonefile.Export(&buf, z, recs); err != nil {
		return z, nil, Internal(err, "The zone file could not be generated.")
	}
	return z, buf.Bytes(), nil
}