package engine

import (
	"fmt"
	"reflect"
	"sort"

	"jarl/internal/dnsname"
	"jarl/internal/model"
)

// DiffOps returns operations that turn from into to. It is used to record
// how to undo an applied changeset and to turn an imported configuration
// into a changeset. Create operations keep the object IDs of to.
func DiffOps(from, to *model.State) []model.Op {
	var ops []model.Op
	add := func(kind string, id int64, base int, data any, summary string) {
		ops = append(ops, newOp(kind, id, base, data, summary))
	}
	if !reflect.DeepEqual(stripVersion(from.Settings), stripVersion(to.Settings)) {
		s := to.Settings
		add(OpSettingsUpdate, 0, 0, SettingsInput{DefaultTTL: &s.DefaultTTL, Nameservers: model.Ptr(append([]string{}, s.Nameservers...)), RName: &s.RName,
			Refresh: &s.Refresh, Retry: &s.Retry, Expire: &s.Expire, NegativeTTL: &s.NegativeTTL, SerialPolicy: &s.SerialPolicy}, "restore settings")
	}

	for _, k := range sortedKeys(to.Keys) {
		n := to.Keys[k]
		in := TSIGInput{Name: &n.Name, Algorithm: &n.Algorithm, Secret: &n.Secret, Comment: &n.Comment}
		if o, ok := from.Keys[k]; !ok {
			add(OpTSIGCreate, k, 0, in, "create TSIG key "+n.Name)
		} else if !sameObject(o, n) {
			add(OpTSIGUpdate, k, o.Version, in, "restore TSIG key "+n.Name)
		}
	}
	for _, k := range sortedKeys(to.ACLs) {
		n := to.ACLs[k]
		in := ACLInput{Name: &n.Name, Elements: model.Ptr(append([]string{}, n.Elements...)), Comment: &n.Comment}
		if o, ok := from.ACLs[k]; !ok {
			add(OpACLCreate, k, 0, in, "create ACL "+n.Name)
		} else if !sameObject(o, n) {
			add(OpACLUpdate, k, o.Version, in, "restore ACL "+n.Name)
		}
	}
	for _, k := range sortedKeys(to.Views) {
		n := to.Views[k]
		in := ViewInput{Name: &n.Name, MatchClients: model.Ptr(append([]string{}, n.MatchClients...)),
			MatchDestinations: model.Ptr(append([]string{}, n.MatchDestinations...)), Comment: &n.Comment, Position: model.Ptr(n.Position)}
		if n.MatchRecursiveOnly != nil {
			in.MatchRecursiveOnly = model.Some(*n.MatchRecursiveOnly)
		} else {
			in.MatchRecursiveOnly = model.Opt[bool]{Set: true, Null: true}
		}
		if o, ok := from.Views[k]; !ok {
			add(OpViewCreate, k, 0, in, "create view "+n.Name)
		} else if !sameObject(o, n) {
			add(OpViewUpdate, k, o.Version, in, "restore view "+n.Name)
		}
	}
	for _, k := range sortedKeys(to.Zones) {
		n := to.Zones[k]
		s := n.SOA
		in := ZoneInput{Name: &n.Name, ViewID: &n.ViewID, Type: &n.Type, InView: &n.InView, File: &n.File,
			DefaultTTL: &n.DefaultTTL, SerialPolicy: &n.SerialPolicy, DNSSECPolicy: &n.DNSSECPolicy, Comment: &n.Comment}
		if n.Type == model.ZonePrimary {
			in.SOA = &SOAInput{MName: &s.MName, RName: &s.RName, Serial: &s.Serial, Refresh: &s.Refresh, Retry: &s.Retry, Expire: &s.Expire, Minimum: &s.Minimum}
		}
		if o, ok := from.Zones[k]; !ok {
			add(OpZoneCreate, k, 0, in, "create zone "+zoneDesc(to, n))
		} else if !sameObject(o, n) {
			in.Name = nil // zones can't be renamed
			if n.Type == model.ZonePrimary && o.SOA.Serial != s.Serial {
				// Never move a serial backwards: let the normal bump
				// happen instead.
				in.SOA.Serial = nil
			}
			add(OpZoneUpdate, k, o.Version, in, "restore zone "+zoneDesc(to, n))
		}
	}
	for _, k := range sortedKeys(to.Options) {
		n := to.Options[k]
		in := OptionInput{Scope: &n.Scope, ScopeID: &n.ScopeID, Name: &n.Name, Value: &n.Value, Comment: &n.Comment, Position: &n.Position}
		if o, ok := from.Options[k]; !ok {
			add(OpOptionCreate, k, 0, in, "set "+optionLabel(to, n)+" "+n.Value)
		} else if !sameObject(o, n) {
			in.Scope, in.ScopeID = nil, nil
			add(OpOptionUpdate, k, o.Version, in, "restore "+optionLabel(to, n))
		}
	}
	for _, k := range sortedKeys(to.Records) {
		n := to.Records[k]
		in := RecordInput{ZoneID: n.ZoneID, Name: &n.Name, Type: &n.Type, Data: &n.Data, Comment: &n.Comment, Disabled: &n.Disabled}
		if n.TTL != nil {
			in.TTL = model.Some(*n.TTL)
		} else {
			in.TTL = model.Opt[uint32]{Set: true, Null: true}
		}
		if o, ok := from.Records[k]; !ok {
			add(OpRecordCreate, k, 0, in, fmt.Sprintf("add %s %s %s", n.Name, n.Type, n.Data))
		} else if !sameObject(o, n) {
			in.ZoneID = 0
			add(OpRecordUpdate, k, o.Version, in, fmt.Sprintf("restore %s %s %s", n.Name, n.Type, n.Data))
		}
	}
	// Deletions, most dependent objects first.
	for _, k := range sortedKeys(from.Records) {
		if _, ok := to.Records[k]; !ok {
			o := from.Records[k]
			// Records of zones that are deleted go with the zone.
			if _, zoneStays := to.Zones[o.ZoneID]; zoneStays {
				add(OpRecordDelete, k, o.Version, nil, fmt.Sprintf("delete %s %s %s", o.Name, o.Type, o.Data))
			}
		}
	}
	for _, k := range sortedKeys(from.Options) {
		if _, ok := to.Options[k]; !ok {
			o := from.Options[k]
			stays := true
			switch o.Scope {
			case model.ScopeZone:
				_, stays = to.Zones[o.ScopeID]
			case model.ScopeView:
				_, stays = to.Views[o.ScopeID]
			}
			if stays {
				add(OpOptionDelete, k, o.Version, nil, "delete "+optionLabel(from, o))
			}
		}
	}
	for _, k := range sortedKeys(from.Zones) {
		if _, ok := to.Zones[k]; !ok {
			o := from.Zones[k]
			add(OpZoneDelete, k, o.Version, nil, "delete zone "+dnsname.Display(o.Name))
		}
	}
	for _, k := range sortedKeys(from.Views) {
		if _, ok := to.Views[k]; !ok {
			o := from.Views[k]
			add(OpViewDelete, k, o.Version, DeleteInput{Cascade: true}, "delete view "+o.Name)
		}
	}
	for _, k := range sortedKeys(from.ACLs) {
		if _, ok := to.ACLs[k]; !ok {
			add(OpACLDelete, k, from.ACLs[k].Version, nil, "delete ACL "+from.ACLs[k].Name)
		}
	}
	for _, k := range sortedKeys(from.Keys) {
		if _, ok := to.Keys[k]; !ok {
			add(OpTSIGDelete, k, from.Keys[k].Version, nil, "delete TSIG key "+from.Keys[k].Name)
		}
	}
	for i := range ops {
		ops[i].Seq = i + 1
	}
	return ops
}

func stripVersion(s model.Settings) model.Settings {
	s.Version = 0
	return s
}

func sortedKeys[T any](m map[int64]*T) []int64 {
	keys := make([]int64, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Slice(keys, func(i, j int) bool { return keys[i] < keys[j] })
	return keys
}

// sameObject compares two objects ignoring their meta data.
func sameObject[T any](a, b *T) bool {
	ca, cb := *a, *b
	clearMeta(&ca)
	clearMeta(&cb)
	return reflect.DeepEqual(ca, cb)
}

func clearMeta(v any) {
	rv := reflect.ValueOf(v).Elem()
	if f := rv.FieldByName("Meta"); f.IsValid() {
		f.Set(reflect.Zero(f.Type()))
	}
}