package engine

import (
	"context"
	"encoding/json"
	"fmt"
	"net/netip"
	"strings"
	"time"

	"github.com/miekg/dns"

	"jarl/internal/auth"
	"jarl/internal/dnsname"
	"jarl/internal/model"
	"jarl/internal/rr"
	"jarl/internal/validate"
)

// IDAllocator reserves object IDs.
type IDAllocator func(ctx context.Context, n int) ([]int64, error)

type expander struct {
	ctx      context.Context
	st       *model.State // working state: base plus the changeset's ops so far
	alloc    IDAllocator
	p        *auth.Principal
	now      time.Time
	warnings []string
}

func (x *expander) ids(n int) ([]int64, error) {
	ids, err := x.alloc(x.ctx, n)
	if err != nil {
		return nil, fmt.Errorf("allocating IDs: %w", err)
	}
	return ids, nil
}

func mustJSON(v any) json.RawMessage {
	b, err := json.Marshal(v)
	if err != nil {
		panic(err)
	}
	return b
}

func newOp(kind string, id int64, base int, data any, summary string) model.Op {
	op := model.Op{Kind: kind, ID: id, BaseVersion: base, Summary: summary}
	if data != nil {
		op.Data = mustJSON(data)
	}
	return op
}

// resolveZone finds the zone a record request refers to.
func (x *expander) resolveZone(zoneID int64, zone, view string) (*model.Zone, error) {
	if zoneID != 0 {
		z := x.st.Zones[zoneID]
		if z == nil {
			return nil, errf(KindNotFound, "zone %d does not exist", zoneID)
		}
		return z, nil
	}
	if zone == "" {
		return nil, errf(KindBadRequest, "the zone is missing (zone_id or zone)")
	}
	return FindZoneRef(x.st, zone, view)
}

// FindZoneRef finds a zone by name and optional view name.
func FindZoneRef(st *model.State, zone, view string) (*model.Zone, error) {
	name, err := ParseZoneName(zone)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	if view != "" {
		v := st.ViewByName(view)
		if v == nil {
			return nil, errf(KindNotFound, "view %q does not exist", view)
		}
		z := st.FindZone(name, v.ID)
		if z == nil {
			return nil, errf(KindNotFound, "zone %s does not exist in view %s", dnsname.Display(name), v.Name)
		}
		return z, nil
	}
	zs := st.ZonesNamed(name)
	switch len(zs) {
	case 0:
		return nil, errf(KindNotFound, "zone %s does not exist", dnsname.Display(name))
	case 1:
		return zs[0], nil
	}
	var views []string
	for _, z := range zs {
		views = append(views, st.ViewName(z))
	}
	return nil, errf(KindBadRequest, "zone %s exists in several views (%s); say which view", dnsname.Display(name), strings.Join(views, ", "))
}

func zoneDesc(st *model.State, z *model.Zone) string {
	s := dnsname.Display(z.Name)
	if v := st.ViewName(z); v != "" {
		s += " [" + v + "]"
	}
	return s
}

func ttlText(o model.Opt[uint32]) string {
	if o.Set && !o.Null {
		return fmt.Sprintf(" %d", o.Value)
	}
	return ""
}

// InitialSerial returns the first serial for a new zone.
func InitialSerial(policy string, now time.Time) uint32 {
	switch policy {
	case model.SerialIncrement:
		return 1
	case model.SerialUnixtime:
		return uint32(now.Unix())
	}
	return dateSerial(now)
}

func dateSerial(now time.Time) uint32 {
	y, m, d := now.UTC().Date()
	return uint32(y*1000000 + int(m)*10000 + d*100)
}

func (x *expander) expand(req Request) ([]model.Op, error) {
	switch req.Op {
	case OpZoneCreate:
		return x.zoneCreate(req)
	case OpZoneUpdate, OpZoneDelete:
		z := x.st.Zones[req.ID]
		if z == nil {
			return nil, errf(KindNotFound, "zone %d does not exist", req.ID)
		}
		verb := "update"
		if req.Op == OpZoneDelete {
			verb = "delete"
			if n := len(x.st.ZoneRecords(z.ID)); n > 0 {
				verb += fmt.Sprintf(" (with its %d records)", n)
			}
		} else if d := zoneToggle(req, z); d != nil {
			if *d {
				x.warnings = append(x.warnings, disabledZoneEffect(x.st, z))
				return []model.Op{x.versioned(req, z.Version, "disable zone "+zoneDesc(x.st, z))}, nil
			}
			return []model.Op{x.versioned(req, z.Version, "enable zone "+zoneDesc(x.st, z))}, nil
		}
		return []model.Op{x.versioned(req, z.Version, "zone "+verb+" "+zoneDesc(x.st, z))}, nil
	case OpRecordCreate:
		return x.recordCreate(req)
	case OpRecordUpdate:
		return x.recordUpdate(req)
	case OpRecordDelete:
		return x.recordDelete(req)
	case OpRRSetReplace:
		return x.rrsetReplace(req)
	case OpRecordDisable, OpRecordEnable:
		return x.recordSetDisabled(req, req.Op == OpRecordDisable)
	case OpViewCreate:
		return x.viewCreate(req)
	case OpViewUpdate, OpViewDelete:
		v := x.st.Views[req.ID]
		if v == nil {
			return nil, errf(KindNotFound, "view %d does not exist", req.ID)
		}
		return []model.Op{x.versioned(req, v.Version, strings.TrimPrefix(req.Op, "view.")+" view "+v.Name)}, nil
	case OpViewReorder:
		var in ReorderInput
		if err := decode(req.Data, &in); err != nil {
			return nil, err
		}
		var names []string
		for _, id := range in.IDs {
			if v := x.st.Views[id]; v != nil {
				names = append(names, v.Name)
			}
		}
		return []model.Op{newOp(OpViewReorder, 0, 0, in, "reorder views: "+strings.Join(names, ", "))}, nil
	case OpACLCreate:
		return x.simpleCreate(req, OpACLCreate, func(data json.RawMessage) (string, error) {
			var in ACLInput
			if err := decode(data, &in); err != nil {
				return "", err
			}
			if in.Name == nil {
				return "", errf(KindBadRequest, "an ACL needs a name")
			}
			return "create ACL " + *in.Name, nil
		})
	case OpACLUpdate, OpACLDelete:
		a := x.st.ACLs[req.ID]
		if a == nil {
			return nil, errf(KindNotFound, "ACL %d does not exist", req.ID)
		}
		return []model.Op{x.versioned(req, a.Version, strings.TrimPrefix(req.Op, "acl.")+" ACL "+a.Name)}, nil
	case OpTSIGCreate:
		return x.tsigCreate(req)
	case OpTSIGUpdate, OpTSIGDelete:
		k := x.st.Keys[req.ID]
		if k == nil {
			return nil, errf(KindNotFound, "TSIG key %d does not exist", req.ID)
		}
		return []model.Op{x.versioned(req, k.Version, strings.TrimPrefix(req.Op, "tsig.")+" TSIG key "+k.Name)}, nil
	case OpOptionCreate:
		return x.optionCreate(req)
	case OpOptionUpdate, OpOptionDelete:
		o := x.st.Options[req.ID]
		if o == nil {
			return nil, errf(KindNotFound, "option %d does not exist", req.ID)
		}
		summary := strings.TrimPrefix(req.Op, "option.") + " " + optionLabel(x.st, o)
		if req.Op == OpOptionUpdate {
			var in OptionInput
			if err := decode(req.Data, &in); err != nil {
				return nil, err
			}
			if in.Value != nil {
				summary += ": " + o.Value + " → " + *in.Value
			}
		}
		return []model.Op{x.versioned(req, o.Version, summary)}, nil
	case OpSettingsUpdate:
		return []model.Op{newOpRaw(OpSettingsUpdate, 0, 0, req.Data, "update settings")}, nil
	case OpBlocklistCreate:
		return x.blocklistCreate(req)
	case OpBlocklistUpdate, OpBlocklistDelete:
		b := x.st.Blocklists[req.ID]
		if b == nil {
			return nil, errf(KindNotFound, "blocklist %d does not exist", req.ID)
		}
		verb := "change"
		if req.Op == OpBlocklistDelete {
			verb = "delete"
		}
		return []model.Op{x.versioned(req, b.Version, verb+" blocklist "+b.Name)}, nil
	case OpBlockingPause:
		var in BlockingPauseInput
		if err := decode(req.Data, &in); err != nil {
			return nil, err
		}
		summary := "resume blocking"
		if in.Until != nil {
			summary = "pause blocking until " + in.Until.Local().Format("2006-01-02 15:04")
		} else if in.Indefinitely {
			summary = "pause blocking until resumed"
		}
		return []model.Op{newOpRaw(OpBlockingPause, 0, 0, req.Data, summary)}, nil
	case OpBlockRuleCreate:
		return x.blockRuleCreate(req)
	case OpBlockRuleUpdate, OpBlockRuleDelete:
		r := x.st.BlockRules[req.ID]
		if r == nil {
			return nil, errf(KindNotFound, "rule %d does not exist", req.ID)
		}
		verb := "change rule: "
		if req.Op == OpBlockRuleDelete {
			verb = "delete rule: "
		}
		return []model.Op{x.versioned(req, r.Version, verb+ruleLabel(r))}, nil
	case OpBlockStepCreate:
		return x.blockStepCreate(req)
	case OpBlockStepUpdate, OpBlockStepDelete:
		s := x.st.BlockSteps[req.ID]
		if s == nil {
			return nil, errf(KindNotFound, "blocking step %d does not exist", req.ID)
		}
		verb := "change blocking step "
		if req.Op == OpBlockStepDelete {
			verb = "delete blocking step "
		}
		return []model.Op{x.versioned(req, s.Version, verb+s.Name)}, nil
	case OpClientGroupCreate:
		return x.clientGroupCreate(req)
	case OpClientGroupUpdate, OpClientGroupDelete:
		g := x.st.ClientGroups[req.ID]
		if g == nil {
			return nil, errf(KindNotFound, "client group %d does not exist", req.ID)
		}
		verb := "change client group "
		if req.Op == OpClientGroupDelete {
			verb = "delete client group "
		}
		return []model.Op{x.versioned(req, g.Version, verb+g.Name)}, nil
	}
	return nil, errf(KindBadRequest, "unknown operation %q", req.Op)
}

func newOpRaw(kind string, id int64, base int, data json.RawMessage, summary string) model.Op {
	return model.Op{Kind: kind, ID: id, BaseVersion: base, Data: data, Summary: summary}
}

// versioned builds an update/delete operation, recording the object's
// version for conflict detection.
func (x *expander) versioned(req Request, current int, summary string) model.Op {
	base := req.BaseVersion
	if base == 0 {
		base = current
	}
	return newOpRaw(req.Op, req.ID, base, req.Data, summary)
}

func (x *expander) simpleCreate(req Request, kind string, describe func(json.RawMessage) (string, error)) ([]model.Op, error) {
	summary, err := describe(req.Data)
	if err != nil {
		return nil, err
	}
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	return []model.Op{newOpRaw(kind, ids[0], 0, req.Data, summary)}, nil
}

func (x *expander) zoneCreate(req Request) ([]model.Op, error) {
	var in ZoneInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	if in.Name == nil || strings.TrimSpace(*in.Name) == "" {
		return nil, errf(KindBadRequest, "a zone needs a name")
	}
	name, err := ParseZoneName(*in.Name)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	in.Name = &name
	if in.Type == nil {
		in.Type = model.Ptr(model.ZonePrimary)
	}
	zt, err := normalizeZoneType(*in.Type)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	in.Type = &zt
	if in.View != nil {
		if *in.View != "" {
			v := x.st.ViewByName(*in.View)
			if v == nil {
				return nil, errf(KindNotFound, "view %q does not exist", *in.View)
			}
			in.ViewID = &v.ID
		}
		in.View = nil
	}
	nameservers := in.Nameservers
	records := in.Records
	cloneFrom := in.CloneFrom
	zoneOpts := in.Options
	in.Nameservers, in.Records, in.CloneFrom, in.Options = nil, nil, 0, nil

	set := x.st.Settings
	var src *model.Zone
	if cloneFrom != 0 {
		src = x.st.Zones[cloneFrom]
		if src == nil {
			return nil, errf(KindNotFound, "zone %d (clone_from) does not exist", cloneFrom)
		}
		if src.Name != name {
			return nil, errf(KindBadRequest, "clone_from must be a zone with the same name in another view (it is %s)", dnsname.Display(src.Name))
		}
		if !x.p.Can(zoneAction(x.st, src, false)) || !x.p.Can(recordAction(x.st, src, "", "", false)) {
			return nil, errf(KindForbidden, "permission denied: you can't read zone %s", zoneDesc(x.st, src))
		}
	}
	if zt == model.ZonePrimary {
		if len(nameservers) == 0 && src == nil {
			nameservers = set.Nameservers
		}
		if len(nameservers) == 0 && src == nil {
			return nil, errf(KindBadRequest, "a primary zone needs at least one name server: give nameservers, or set default name servers in the settings")
		}
		if in.SOA == nil {
			in.SOA = &SOAInput{}
		}
		s := in.SOA
		if src != nil {
			// Copy the source zone's SOA and TTL unless overridden.
			if s.MName == nil {
				s.MName = model.Ptr(src.SOA.MName)
			}
			if s.RName == nil {
				s.RName = model.Ptr(src.SOA.RName)
			}
			if s.Refresh == nil {
				s.Refresh = model.Ptr(src.SOA.Refresh)
			}
			if s.Retry == nil {
				s.Retry = model.Ptr(src.SOA.Retry)
			}
			if s.Expire == nil {
				s.Expire = model.Ptr(src.SOA.Expire)
			}
			if s.Minimum == nil {
				s.Minimum = model.Ptr(src.SOA.Minimum)
			}
			if in.DefaultTTL == nil {
				in.DefaultTTL = model.Ptr(src.DefaultTTL)
			}
		}
		if s.MName == nil {
			first, err := dnsname.Owner(nameservers[0], name)
			if err != nil {
				return nil, errf(KindBadRequest, "%v", err)
			}
			s.MName = &first
		}
		if s.RName == nil {
			if set.RName != "" {
				s.RName = model.Ptr(set.RName)
			} else {
				s.RName = model.Ptr("hostmaster." + name)
			}
		}
		if s.Refresh == nil {
			s.Refresh = model.Ptr(set.Refresh)
		}
		if s.Retry == nil {
			s.Retry = model.Ptr(set.Retry)
		}
		if s.Expire == nil {
			s.Expire = model.Ptr(set.Expire)
		}
		if s.Minimum == nil {
			s.Minimum = model.Ptr(set.NegativeTTL)
		}
		if in.DefaultTTL == nil {
			in.DefaultTTL = model.Ptr(set.DefaultTTL)
		}
		if s.Serial == nil {
			policy := set.SerialPolicy
			if in.SerialPolicy != nil && *in.SerialPolicy != "" {
				policy = *in.SerialPolicy
			}
			serial := InitialSerial(policy, x.now)
			if src != nil && serialGreater(src.SOA.Serial, serial) {
				serial = src.SOA.Serial
			}
			s.Serial = &serial
		}
	} else if len(nameservers) > 0 || len(records) > 0 || src != nil {
		return nil, errf(KindBadRequest, "nameservers, records and clone_from only apply to primary zones")
	}

	type recSpec struct {
		in      RecordInput
		summary string
	}
	var recs []recSpec
	seen := map[string]bool{}
	addRec := func(ri RecordInput) error {
		tmp := &model.Zone{Name: name, Type: zt}
		owner, p, err := parseRecord(tmp, deref(ri.Name), deref(ri.Type), deref(ri.Data))
		if err != nil {
			return err
		}
		k := owner + "|" + p.Type + "|" + strings.ToLower(p.Data)
		if seen[k] {
			return nil
		}
		seen[k] = true
		ri.Name, ri.Type, ri.Data = &owner, &p.Type, &p.Data
		recs = append(recs, recSpec{ri, fmt.Sprintf("add %s%s IN %s %s", owner, ttlText(ri.TTL), p.Type, p.Data)})
		return nil
	}
	for _, ns := range nameservers {
		target, err := dnsname.Owner(ns, name)
		if err != nil {
			return nil, errf(KindBadRequest, "name server %q: %v", ns, err)
		}
		if err := addRec(RecordInput{Name: model.Ptr("@"), Type: model.Ptr("NS"), Data: model.Ptr(target)}); err != nil {
			return nil, err
		}
	}
	if src != nil {
		for _, r := range x.st.ZoneRecords(src.ID) {
			ri := RecordInput{Name: model.Ptr(r.Name), Type: model.Ptr(r.Type), Data: model.Ptr(r.Data), Comment: model.Ptr(r.Comment)}
			if r.Disabled {
				ri.Disabled = model.Ptr(true)
			}
			if r.TTL != nil {
				ri.TTL = model.Some(*r.TTL)
			} else {
				ri.TTL = model.Opt[uint32]{Set: true, Null: true}
			}
			if err := addRec(ri); err != nil {
				return nil, err
			}
		}
	}
	for _, ri := range records {
		ri.ZoneID, ri.Zone, ri.View = 0, "", ""
		if err := addRec(ri); err != nil {
			return nil, err
		}
	}
	ids, err := x.ids(1 + len(recs) + len(zoneOpts))
	if err != nil {
		return nil, err
	}
	summary := fmt.Sprintf("create %s zone %s", zt, dnsname.Display(name))
	if in.ViewID != nil && *in.ViewID != 0 {
		if v := x.st.Views[*in.ViewID]; v != nil {
			summary += " in view " + v.Name
		}
	}
	if src != nil {
		summary += " (copy of " + zoneDesc(x.st, src) + ")"
	}
	ops := []model.Op{newOp(OpZoneCreate, ids[0], 0, in, summary)}
	for i, zo := range zoneOpts {
		oi := OptionInput{Scope: model.Ptr(model.ScopeZone), ScopeID: model.Ptr(ids[0]), Name: model.Ptr(zo.Name), Value: model.Ptr(zo.Value)}
		if zo.Comment != "" {
			oi.Comment = model.Ptr(zo.Comment)
		}
		ops = append(ops, newOp(OpOptionCreate, ids[1+len(recs)+i], 0, oi, fmt.Sprintf("set zone %s option %s %s", dnsname.Display(name), zo.Name, zo.Value)))
	}
	for i, r := range recs {
		r.in.ZoneID = ids[0]
		ops = append(ops, newOp(OpRecordCreate, ids[1+i], 0, r.in, r.summary))
	}
	return ops, nil
}

func deref(s *string) string {
	if s == nil {
		return ""
	}
	return *s
}

// reverseZoneFor finds the primary reverse zone for addr in a view.
func reverseZoneFor(st *model.State, viewID int64, addr netip.Addr) (*model.Zone, string) {
	name := dnsname.ReverseName(addr)
	var best *model.Zone
	for _, z := range st.ZonesInView(viewID) {
		if z.Type == model.ZonePrimary && dnsname.IsSubdomain(name, z.Name) && (best == nil || len(z.Name) > len(best.Name)) {
			best = z
		}
	}
	return best, name
}

func addrOf(p *rr.Parsed) (netip.Addr, bool) {
	switch v := p.RR.(type) {
	case *dns.A:
		a, ok := netip.AddrFromSlice(v.A.To4())
		return a, ok
	case *dns.AAAA:
		a, ok := netip.AddrFromSlice(v.AAAA)
		return a, ok
	}
	return netip.Addr{}, false
}

// ptrOps returns operations creating the PTR record for an address record.
func (x *expander) ptrCreate(z *model.Zone, owner string, p *rr.Parsed) ([]model.Op, error) {
	addr, ok := addrOf(p)
	if !ok {
		return nil, errf(KindBadRequest, "ptr only applies to A and AAAA records")
	}
	rz, ptrName := reverseZoneFor(x.st, z.ViewID, addr)
	if rz == nil {
		x.warnings = append(x.warnings, fmt.Sprintf("no reverse zone for %s in this view, so no PTR record was added", addr))
		return nil, nil
	}
	for _, r := range x.st.ZoneRecords(rz.ID) {
		if r.Name == ptrName && r.Type == "PTR" {
			if strings.EqualFold(r.Data, owner) {
				if r.Disabled {
					in := RecordInput{Disabled: model.Ptr(false)}
					return []model.Op{newOp(OpRecordUpdate, r.ID, r.Version, in, fmt.Sprintf("enable %s PTR %s", r.Name, r.Data))}, nil
				}
				return nil, nil // already there
			}
			x.warnings = append(x.warnings, fmt.Sprintf("%s already has a PTR record (%s); adding another one", ptrName, r.Data))
		}
	}
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	in := RecordInput{ZoneID: rz.ID, Name: model.Ptr(ptrName), Type: model.Ptr("PTR"), Data: model.Ptr(owner)}
	return []model.Op{newOp(OpRecordCreate, ids[0], 0, in, fmt.Sprintf("add %s IN PTR %s", ptrName, owner))}, nil
}

// ptrSetDisabled returns operations disabling or enabling the PTR record
// of an address record.
func (x *expander) ptrSetDisabled(z *model.Zone, owner string, p *rr.Parsed, disabled bool) []model.Op {
	addr, ok := addrOf(p)
	if !ok {
		return nil
	}
	rz, ptrName := reverseZoneFor(x.st, z.ViewID, addr)
	if rz == nil {
		return nil
	}
	var ops []model.Op
	for _, r := range x.st.ZoneRecords(rz.ID) {
		if r.Name == ptrName && r.Type == "PTR" && strings.EqualFold(r.Data, owner) && r.Disabled != disabled {
			in := RecordInput{Disabled: model.Ptr(disabled)}
			ops = append(ops, newOp(OpRecordUpdate, r.ID, r.Version, in, fmt.Sprintf("%s %s PTR %s", enableWord(disabled), r.Name, r.Data)))
		}
	}
	return ops
}

func enableWord(disabled bool) string {
	if disabled {
		return "disable"
	}
	return "enable"
}

func (x *expander) ptrDelete(z *model.Zone, owner string, p *rr.Parsed) []model.Op {
	addr, ok := addrOf(p)
	if !ok {
		return nil
	}
	rz, ptrName := reverseZoneFor(x.st, z.ViewID, addr)
	if rz == nil {
		return nil
	}
	in := RecordInput{ZoneID: rz.ID, Name: model.Ptr(ptrName), Type: model.Ptr("PTR"), Data: model.Ptr(owner), MissingOK: true}
	return []model.Op{newOp(OpRecordDelete, 0, 0, in, fmt.Sprintf("delete %s IN PTR %s (if present)", ptrName, owner))}
}

// parseWarnings keeps what parsing noticed (e.g. a name read as absolute).
// The stored operation holds the canonical data, so applying it doesn't
// notice again.
func (x *expander) parseWarnings(owner string, p *rr.Parsed) {
	for _, w := range p.Warnings {
		x.warnings = append(x.warnings, fmt.Sprintf("%s %s: %s", dnsname.Display(owner), p.Type, w))
	}
}

func (x *expander) recordCreate(req Request) ([]model.Op, error) {
	var in RecordInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	z, err := x.resolveZone(in.ZoneID, in.Zone, in.View)
	if err != nil {
		return nil, err
	}
	if in.Name == nil || in.Type == nil || in.Data == nil {
		return nil, errf(KindBadRequest, "a record needs a name, a type and data")
	}
	owner, p, err := parseRecord(z, *in.Name, *in.Type, *in.Data)
	if err != nil {
		return nil, err
	}
	x.parseWarnings(owner, p)
	ptr := in.PTR
	in.ZoneID, in.Zone, in.View, in.PTR = z.ID, "", "", false
	in.Name, in.Type, in.Data = &owner, &p.Type, &p.Data
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	ops := []model.Op{newOp(OpRecordCreate, ids[0], 0, in, fmt.Sprintf("add %s%s IN %s %s", owner, ttlText(in.TTL), p.Type, p.Data))}
	if ptr {
		more, err := x.ptrCreate(z, owner, p)
		if err != nil {
			return nil, err
		}
		ops = append(ops, more...)
	}
	return ops, nil
}

func (x *expander) recordUpdate(req Request) ([]model.Op, error) {
	r := x.st.Records[req.ID]
	if r == nil {
		return nil, errf(KindNotFound, "record %d does not exist", req.ID)
	}
	z := x.st.Zones[r.ZoneID]
	var in RecordInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	ptr := in.PTR
	in.PTR = false
	in.Zone, in.View = "", ""
	name, typ, data := r.Name, r.Type, r.Data
	if in.Name != nil {
		name = *in.Name
	}
	if in.Type != nil {
		typ = *in.Type
	}
	if in.Data != nil {
		data = *in.Data
	}
	owner, p, err := parseRecord(z, name, typ, data)
	if err != nil {
		return nil, err
	}
	x.parseWarnings(owner, p)
	if in.Name != nil {
		in.Name = &owner
	}
	if in.Type != nil {
		in.Type = &p.Type
	}
	if in.Data != nil {
		in.Data = &p.Data
	}
	var changes []string
	if owner != r.Name {
		changes = append(changes, "name "+r.Name+" → "+owner)
	}
	if p.Type != r.Type {
		changes = append(changes, "type "+r.Type+" → "+p.Type)
	}
	if p.Data != r.Data {
		changes = append(changes, "data "+r.Data+" → "+p.Data)
	}
	if in.TTL.Set {
		old := "default"
		if r.TTL != nil {
			old = fmt.Sprint(*r.TTL)
		}
		nw := "default"
		if !in.TTL.Null {
			nw = fmt.Sprint(in.TTL.Value)
		}
		if old != nw {
			changes = append(changes, "ttl "+old+" → "+nw)
		}
	}
	if in.Comment != nil && *in.Comment != r.Comment {
		changes = append(changes, "comment")
	}
	toggled := in.Disabled != nil && *in.Disabled != r.Disabled
	summary := fmt.Sprintf("change %s %s %s", r.Name, r.Type, r.Data)
	switch {
	case toggled && len(changes) == 0:
		summary = fmt.Sprintf("%s %s %s %s", enableWord(*in.Disabled), r.Name, r.Type, r.Data)
	case toggled:
		changes = append(changes, enableWord(*in.Disabled)+"d")
		fallthrough
	case len(changes) > 0:
		summary += ": " + strings.Join(changes, ", ")
	}
	base := req.BaseVersion
	if base == 0 {
		base = r.Version
	}
	ops := []model.Op{newOp(OpRecordUpdate, r.ID, base, in, summary)}
	disabled := r.Disabled
	if in.Disabled != nil {
		disabled = *in.Disabled
	}
	moved := p.Data != r.Data || owner != r.Name
	if ptr && moved {
		if old, err := rr.Parse(z.Name, r.Name, r.Type, r.Data); err == nil {
			ops = append(ops, x.ptrDelete(z, r.Name, old)...)
		}
		if !disabled {
			more, err := x.ptrCreate(z, owner, p)
			if err != nil {
				return nil, err
			}
			ops = append(ops, more...)
		}
	}
	if ptr && !moved && toggled {
		if _, ok := addrOf(p); !ok {
			return nil, errf(KindBadRequest, "ptr only applies to A and AAAA records")
		}
		ops = append(ops, x.ptrSetDisabled(z, owner, p, disabled)...)
	}
	return ops, nil
}

func (x *expander) recordDelete(req Request) ([]model.Op, error) {
	var in RecordInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	if req.ID != 0 {
		r := x.st.Records[req.ID]
		if r == nil {
			if in.MissingOK {
				return nil, nil
			}
			return nil, errf(KindNotFound, "record %d does not exist", req.ID)
		}
		base := req.BaseVersion
		if base == 0 {
			base = r.Version
		}
		ops := []model.Op{newOp(OpRecordDelete, r.ID, base, nil, fmt.Sprintf("delete %s %s %s", r.Name, r.Type, r.Data))}
		if in.PTR {
			z := x.st.Zones[r.ZoneID]
			if p, err := rr.Parse(z.Name, r.Name, r.Type, r.Data); err == nil {
				ops = append(ops, x.ptrDelete(z, r.Name, p)...)
			}
		}
		return ops, nil
	}
	z, err := x.resolveZone(in.ZoneID, in.Zone, in.View)
	if err != nil {
		return nil, err
	}
	if in.Name == nil || in.Type == nil {
		return nil, errf(KindBadRequest, "deleting by match needs a name and a type (or give the record id)")
	}
	owner, err := dnsname.Owner(*in.Name, z.Name)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	typ, _, err := rr.NormalizeType(*in.Type)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	what := owner + " " + typ
	var parsed *rr.Parsed
	if in.Data != nil && strings.TrimSpace(*in.Data) != "" {
		_, p, err := parseRecord(z, owner, typ, *in.Data)
		if err != nil {
			return nil, err
		}
		in.Data = &p.Data
		what += " " + p.Data
		parsed = p
	} else {
		in.Data = nil
		what += " (all)"
	}
	if in.MissingOK {
		what += " (if present)"
	}
	ptr := in.PTR
	in.ZoneID, in.Zone, in.View, in.PTR = z.ID, "", "", false
	in.Name, in.Type = &owner, &typ
	ops := []model.Op{newOp(OpRecordDelete, 0, 0, in, "delete "+what)}
	if ptr && parsed != nil {
		ops = append(ops, x.ptrDelete(z, owner, parsed)...)
	}
	return ops, nil
}

// recordSetDisabled expands record.disable and record.enable: the record
// with the request's ID, or the records matching zone, name, type and
// (optionally) data.
func (x *expander) recordSetDisabled(req Request, disabled bool) ([]model.Op, error) {
	var in RecordInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	var recs []*model.Record
	if req.ID != 0 {
		r := x.st.Records[req.ID]
		if r == nil {
			return nil, errf(KindNotFound, "record %d does not exist", req.ID)
		}
		recs = append(recs, r)
	} else {
		z, err := x.resolveZone(in.ZoneID, in.Zone, in.View)
		if err != nil {
			return nil, err
		}
		if in.Name == nil || in.Type == nil {
			return nil, errf(KindBadRequest, "finding records needs a name and a type (or give the record id)")
		}
		owner, err := dnsname.Owner(*in.Name, z.Name)
		if err != nil {
			return nil, errf(KindBadRequest, "%v", err)
		}
		typ, _, err := rr.NormalizeType(*in.Type)
		if err != nil {
			return nil, errf(KindBadRequest, "%v", err)
		}
		data, what := "", owner+" "+typ
		if in.Data != nil && strings.TrimSpace(*in.Data) != "" {
			_, p, err := parseRecord(z, owner, typ, *in.Data)
			if err != nil {
				return nil, err
			}
			data, what = p.Data, what+" "+p.Data
		}
		for _, r := range x.st.ZoneRecords(z.ID) {
			if r.Name == owner && r.Type == typ && (data == "" || strings.EqualFold(r.Data, data)) {
				recs = append(recs, r)
			}
		}
		if len(recs) == 0 {
			if in.MissingOK {
				return nil, nil
			}
			return nil, errf(KindNotFound, "no record %s in zone %s", dnsname.Display(what), dnsname.Display(z.Name))
		}
	}
	var ops []model.Op
	for _, r := range recs {
		if r.Disabled == disabled {
			continue // already so
		}
		base := 0
		if req.ID != 0 {
			base = req.BaseVersion
		}
		more, err := x.recordUpdate(Request{Op: OpRecordUpdate, ID: r.ID, BaseVersion: base, Data: mustJSON(RecordInput{Disabled: model.Ptr(disabled), PTR: in.PTR})})
		if err != nil {
			return nil, err
		}
		ops = append(ops, more...)
	}
	if len(ops) == 0 && !in.MissingOK {
		what := fmt.Sprintf("%s %s %s is", recs[0].Name, recs[0].Type, recs[0].Data)
		if len(recs) > 1 {
			what = fmt.Sprintf("all %d %s %s records are", len(recs), recs[0].Name, recs[0].Type)
		}
		return nil, errf(KindConflict, "%s already %sd", what, enableWord(disabled))
	}
	return ops, nil
}

func (x *expander) rrsetReplace(req Request) ([]model.Op, error) {
	var in RRSetInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	z, err := x.resolveZone(in.ZoneID, in.Zone, in.View)
	if err != nil {
		return nil, err
	}
	owner, err := dnsname.Owner(in.Name, z.Name)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	typ, _, err := rr.NormalizeType(in.Type)
	if err != nil {
		return nil, errf(KindBadRequest, "%v", err)
	}
	var canon []string
	for _, d := range in.Data {
		_, p, err := parseRecord(z, owner, typ, d)
		if err != nil {
			return nil, err
		}
		x.parseWarnings(owner, p)
		canon = append(canon, p.Data)
	}
	in.ZoneID, in.Zone, in.View, in.Name, in.Type, in.Data = z.ID, "", "", owner, typ, canon
	if len(canon) > 0 {
		in.NewIDs, err = x.ids(len(canon))
		if err != nil {
			return nil, err
		}
	}
	summary := fmt.Sprintf("set %s%s IN %s to [%s]", owner, ttlText(in.TTL), typ, strings.Join(canon, ", "))
	if len(canon) == 0 {
		summary = fmt.Sprintf("delete all %s records of %s", typ, owner)
	}
	return []model.Op{newOp(OpRRSetReplace, 0, 0, in, summary)}, nil
}

func (x *expander) viewCreate(req Request) ([]model.Op, error) {
	var in ViewInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	if in.Name == nil || strings.TrimSpace(*in.Name) == "" {
		return nil, errf(KindBadRequest, "a view needs a name")
	}
	adopt := in.AdoptZones
	in.AdoptZones = false
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	ops := []model.Op{newOp(OpViewCreate, ids[0], 0, in, "create view "+*in.Name)}
	if adopt {
		for _, z := range x.st.ZonesInView(0) {
			ops = append(ops, newOp(OpZoneUpdate, z.ID, z.Version, ZoneInput{ViewID: model.Ptr(ids[0])}, "move zone "+dnsname.Display(z.Name)+" into view "+*in.Name))
		}
	}
	return ops, nil
}

func (x *expander) tsigCreate(req Request) ([]model.Op, error) {
	var in TSIGInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	if in.Name == nil {
		return nil, errf(KindBadRequest, "a TSIG key needs a name")
	}
	alg := "hmac-sha256"
	if in.Algorithm != nil {
		alg = strings.ToLower(*in.Algorithm)
	}
	in.Algorithm = &alg
	if in.Secret == nil || *in.Secret == "" {
		n := validate.TSIGAlgorithms[alg]
		if n == 0 {
			return nil, errf(KindBadRequest, "unsupported TSIG algorithm %q", alg)
		}
		in.Secret = model.Ptr(auth.GenerateTSIGSecret(n))
	}
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	return []model.Op{newOp(OpTSIGCreate, ids[0], 0, in, "create TSIG key "+model.NormalizeKeyName(*in.Name)+" ("+alg+")")}, nil
}

func (x *expander) optionCreate(req Request) ([]model.Op, error) {
	var in OptionInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	if in.Scope == nil || in.Name == nil {
		return nil, errf(KindBadRequest, "an option needs a scope and a name")
	}
	scopeID := int64(0)
	if in.ScopeID != nil {
		scopeID = *in.ScopeID
	}
	val := ""
	if in.Value != nil {
		val = *in.Value
	}
	n, v, err := NormalizeOption(x.st, *in.Scope, scopeID, *in.Name, val)
	if err != nil {
		return nil, err
	}
	in.Name, in.Value = &n, &v
	ids, err := x.ids(1)
	if err != nil {
		return nil, err
	}
	o := &model.Option{Scope: *in.Scope, ScopeID: scopeID, Name: n}
	return []model.Op{newOp(OpOptionCreate, ids[0], 0, in, "set "+optionLabel(x.st, o)+" "+v)}, nil
}

// RedactOps hides TSIG secrets in operation data.
func RedactOps(ops []model.Op) []model.Op {
	out := make([]model.Op, len(ops))
	for i, op := range ops {
		out[i] = op
		if op.Kind != OpTSIGCreate && op.Kind != OpTSIGUpdate || len(op.Data) == 0 {
			continue
		}
		var m map[string]any
		if json.Unmarshal(op.Data, &m) == nil {
			if _, ok := m["secret"]; ok {
				m["secret"] = "(hidden)"
				out[i].Data = mustJSON(m)
			}
		}
	}
	return out
}

// zoneToggle returns the new disabled state when a zone update only
// disables or enables the zone (nil otherwise).
func zoneToggle(req Request, z *model.Zone) *bool {
	var in ZoneInput
	if decode(req.Data, &in) != nil || in.Disabled == nil || *in.Disabled == z.Disabled {
		return nil
	}
	only := ZoneInput{Disabled: in.Disabled}
	if string(mustJSON(in)) != string(mustJSON(only)) {
		return nil
	}
	return in.Disabled
}

// disabledZoneEffect says what clients get once named no longer loads a
// zone: in a view that offers recursion, answers from recursion (the
// internet's version of the zone, if it has one); elsewhere, REFUSED.
func disabledZoneEffect(st *model.State, z *model.Zone) string {
	where := "this server"
	if v := st.ViewName(z); v != "" {
		where = "view " + v
	}
	if st.RecursionOn(z.ViewID) {
		return fmt.Sprintf("once zone %s is disabled, clients of %s that may use recursion get its names from recursion: the internet's version of the zone, if there is one", dnsname.Display(z.Name), where)
	}
	return fmt.Sprintf("once zone %s is disabled, %s answers REFUSED for its names", dnsname.Display(z.Name), where)
}