package kubeedit

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/client-go/util/retry"

	"git.k8s-git-k6n.net/mats/fancy-dns/internal/kubesource"
	"git.k8s-git-k6n.net/mats/fancy-dns/internal/localzone"
)

// ZoneObject is a stored DNSZone.
type ZoneObject struct {
	Name string
	Apex string // canonical, fully qualified
	Spec kubesource.DNSZoneSpec
}

// Zones lists the DNSZone objects.
func (e *Editor) Zones(ctx context.Context) ([]ZoneObject, error) {
	items, err := e.list(ctx, kubesource.ZoneGVR)
	if err != nil {
		return nil, err
	}
	out := make([]ZoneObject, 0, len(items))
	for i := range items {
		z, ok := zoneOf(&items[i])
		if ok {
			out = append(out, z)
		}
	}
	return out, nil
}

func zoneOf(u *unstructured.Unstructured) (ZoneObject, bool) {
	var s kubesource.DNSZoneSpec
	if err := decodeSpec(u, &s); err != nil {
		return ZoneObject{}, false
	}
	apex, err := localzone.NormalizeOrigin(s.Zone)
	if err != nil {
		return ZoneObject{}, false
	}
	return ZoneObject{Name: u.GetName(), Apex: apex, Spec: s}, true
}

// WriteResult is what a zone edit reports.
type WriteResult struct {
	Zone string
	// Serial is the SOA serial the runtime will serve: the object's
	// generation after this write.
	Serial uint32
}

// editZone applies fn to the zone's spec and writes it back, retrying on a
// conflicting concurrent edit. A zone that does not exist yet is created when
// create is set. The result is rendered with the runtime's own code before it
// is stored, so a spec the runtime would reject is never written.
func (e *Editor) editZone(ctx context.Context, apex string, create bool, actor string, fn func(spec *kubesource.DNSZoneSpec) error) (WriteResult, error) {
	apex, err := localzone.NormalizeOrigin(apex)
	if err != nil {
		return WriteResult{}, err
	}
	var res WriteResult
	err = retry.RetryOnConflict(retry.DefaultRetry, func() error {
		items, err := e.list(ctx, kubesource.ZoneGVR)
		if err != nil {
			return err
		}
		var cur *unstructured.Unstructured
		var zo ZoneObject
		for i := range items {
			if z, ok := zoneOf(&items[i]); ok && z.Apex == apex {
				cur, zo = &items[i], z
				break
			}
		}
		spec := zo.Spec
		if cur == nil {
			if !create {
				return fmt.Errorf("%w: no DNSZone for %s", ErrNotFound, apex)
			}
			spec = kubesource.DNSZoneSpec{Zone: strings.TrimSuffix(apex, ".")}
		}
		spec.Records = append([]kubesource.ZoneRecord(nil), spec.Records...)
		if err := fn(&spec); err != nil {
			return err
		}
		if _, err := kubesource.CheckZone(spec); err != nil {
			return err
		}
		var out *unstructured.Unstructured
		if cur == nil {
			name := strings.TrimSuffix(apex, ".")
			if err := checkName("zone", name); err != nil {
				return err
			}
			obj, err := newObject("DNSZone", name, spec)
			if err != nil {
				return err
			}
			obj.SetNamespace(e.ns)
			stamp(obj, actor)
			out, err = e.res(kubesource.ZoneGVR).Create(ctx, obj, metav1.CreateOptions{})
			if err != nil {
				return err
			}
		} else {
			raw, err := encodeSpec(spec)
			if err != nil {
				return err
			}
			cur.Object["spec"] = raw
			stamp(cur, actor)
			out, err = e.res(kubesource.ZoneGVR).Update(ctx, cur, metav1.UpdateOptions{})
			if err != nil {
				return err
			}
		}
		res = WriteResult{Zone: apex, Serial: uint32(max(out.GetGeneration(), 1))}
		return nil
	})
	return res, err
}

// RecordInput is one record as the console sends it.
type RecordInput struct {
	Name  string
	Type  string
	TTL   uint32
	Value string
}

func canon(apex string, in RecordInput) (localzone.Record, error) {
	name := in.Name
	if name == "@" {
		name = apex
	}
	return localzone.CanonicalRecord(apex, localzone.Record{Name: name, Type: in.Type, TTL: in.TTL, Value: in.Value})
}

// relative stores a name the way an operator would write it.
func relative(apex, name string) string {
	if name == apex {
		return "@"
	}
	return strings.TrimSuffix(name, "."+apex)
}

func stored(apex string, r localzone.Record) kubesource.ZoneRecord {
	return kubesource.ZoneRecord{Name: relative(apex, r.Name), Type: r.Type, TTL: r.TTL, Value: r.Value}
}

// existing canonicalises the spec's records for comparison. A record that does
// not canonicalise is kept as it is, under a key that matches nothing.
func existing(apex string, spec *kubesource.DNSZoneSpec) []localzone.Record {
	out := make([]localzone.Record, len(spec.Records))
	for i, r := range spec.Records {
		c, err := canon(apex, RecordInput{Name: r.Name, Type: r.Type, TTL: r.TTL, Value: r.Value})
		if err != nil {
			c = localzone.Record{Name: "\x00invalid", Type: r.Type, Value: r.Value}
		}
		out[i] = c
	}
	return out
}

// AddRecord adds one record, creating the zone when it does not exist.
func (e *Editor) AddRecord(ctx context.Context, apex string, in RecordInput, actor string) (WriteResult, error) {
	return e.editZone(ctx, apex, true, actor, func(spec *kubesource.DNSZoneSpec) error {
		a, _ := localzone.NormalizeOrigin(apex)
		rec, err := canon(a, in)
		if err != nil {
			return err
		}
		for _, have := range existing(a, spec) {
			if have.Key() == rec.Key() && have.Value == rec.Value {
				return fmt.Errorf("%s %s already exists in %s", rec.Name, rec.Type, a)
			}
		}
		spec.Records = append(spec.Records, stored(a, rec))
		return nil
	})
}

// PutRecord replaces the whole RRset of one name and type.
func (e *Editor) PutRecord(ctx context.Context, apex string, in RecordInput, actor string) (WriteResult, error) {
	return e.editZone(ctx, apex, true, actor, func(spec *kubesource.DNSZoneSpec) error {
		a, _ := localzone.NormalizeOrigin(apex)
		rec, err := canon(a, in)
		if err != nil {
			return err
		}
		spec.Records = dropWhere(a, spec, func(have localzone.Record) bool { return have.Key() == rec.Key() })
		spec.Records = append(spec.Records, stored(a, rec))
		return nil
	})
}

// DeleteRecord removes one record, or the whole RRset when value is empty.
func (e *Editor) DeleteRecord(ctx context.Context, apex, name, rrtype, value, actor string) (WriteResult, error) {
	return e.editZone(ctx, apex, false, actor, func(spec *kubesource.DNSZoneSpec) error {
		a, _ := localzone.NormalizeOrigin(apex)
		var probe localzone.Record
		var want string
		if value != "" {
			full, err := canon(a, RecordInput{Name: name, Type: rrtype, Value: value})
			if err != nil {
				return err
			}
			probe, want = full, full.Value
		} else {
			var err error
			if probe, err = canonProbe(a, name, rrtype); err != nil {
				return err
			}
		}
		before := len(spec.Records)
		spec.Records = dropWhere(a, spec, func(have localzone.Record) bool {
			return have.Key() == probe.Key() && (want == "" || have.Value == want)
		})
		if len(spec.Records) == before {
			return fmt.Errorf("%w: no record matches %s %s in %s", ErrNotFound, name, rrtype, a)
		}
		return nil
	})
}

// canonProbe canonicalises only the owner and type of a record, for matching.
func canonProbe(apex, name, rrtype string) (localzone.Record, error) {
	for _, v := range []string{"10.0.0.1", "ns.example.", "x", "0 0 0 x", "10 ns.example.", "0 issue \"x\""} {
		if r, err := canon(apex, RecordInput{Name: name, Type: rrtype, Value: v}); err == nil {
			return r, nil
		}
	}
	return localzone.Record{}, fmt.Errorf("cannot interpret record %s %s", name, rrtype)
}

func dropWhere(apex string, spec *kubesource.DNSZoneSpec, match func(localzone.Record) bool) []kubesource.ZoneRecord {
	canonical := existing(apex, spec)
	out := make([]kubesource.ZoneRecord, 0, len(spec.Records))
	for i, r := range spec.Records {
		if !match(canonical[i]) {
			out = append(out, r)
		}
	}
	return out
}

// SetDelegation hands a name below the apex to other servers: it replaces the
// NS set at that name. In a zone that does not exist yet the targets also
// become the zone's own NS set, as the file-based writer does.
func (e *Editor) SetDelegation(ctx context.Context, apex, name string, targets []string, ttl uint32, actor string) (WriteResult, error) {
	return e.editZone(ctx, apex, true, actor, func(spec *kubesource.DNSZoneSpec) error {
		a, _ := localzone.NormalizeOrigin(apex)
		if len(targets) == 0 {
			return errors.New("a delegation needs at least one NS target")
		}
		fresh := len(spec.Records) == 0
		cut, err := canon(a, RecordInput{Name: name, Type: "NS", TTL: ttl, Value: targets[0]})
		if err != nil {
			return err
		}
		if cut.Name == a {
			return errors.New("the apex NS set is the zone's own; a delegation is a name below it")
		}
		spec.Records = dropWhere(a, spec, func(have localzone.Record) bool { return have.Key() == cut.Key() })
		for _, t := range targets {
			r, err := canon(a, RecordInput{Name: name, Type: "NS", TTL: ttl, Value: strings.TrimSpace(t)})
			if err != nil {
				return err
			}
			spec.Records = append(spec.Records, stored(a, r))
		}
		if fresh {
			for _, t := range targets {
				r, err := canon(a, RecordInput{Name: "@", Type: "NS", TTL: ttl, Value: strings.TrimSpace(t)})
				if err != nil {
					return err
				}
				spec.Records = append(spec.Records, stored(a, r))
			}
		}
		return nil
	})
}

// RemoveDelegation removes the cut at name.
func (e *Editor) RemoveDelegation(ctx context.Context, apex, name, actor string) (WriteResult, error) {
	return e.editZone(ctx, apex, false, actor, func(spec *kubesource.DNSZoneSpec) error {
		a, _ := localzone.NormalizeOrigin(apex)
		cut, err := canon(a, RecordInput{Name: name, Type: "NS", Value: "ns.example."})
		if err != nil {
			return err
		}
		if cut.Name == a {
			return errors.New("the apex NS set is the zone's own, not a delegation")
		}
		before := len(spec.Records)
		spec.Records = dropWhere(a, spec, func(have localzone.Record) bool { return have.Key() == cut.Key() })
		if len(spec.Records) == before {
			return fmt.Errorf("%w: no delegation for %s in %s", ErrNotFound, name, a)
		}
		return nil
	})
}

// DeleteZone removes the DNSZone object, which hands the names back to
// whatever answered for them before.
func (e *Editor) DeleteZone(ctx context.Context, apex string) error {
	apex, err := localzone.NormalizeOrigin(apex)
	if err != nil {
		return err
	}
	zones, err := e.Zones(ctx)
	if err != nil {
		return err
	}
	for _, z := range zones {
		if z.Apex == apex {
			return e.remove(ctx, kubesource.ZoneGVR, z.Name)
		}
	}
	return fmt.Errorf("%w: no DNSZone for %s", ErrNotFound, apex)
}

// ZoneApexes is the set of apexes held by DNSZone objects.
func (e *Editor) ZoneApexes(ctx context.Context) ([]string, error) {
	zones, err := e.Zones(ctx)
	if err != nil {
		return nil, err
	}
	out := make([]string, len(zones))
	for i, z := range zones {
		out[i] = z.Apex
	}
	sort.Strings(out)
	return out, nil
}