package app

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

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

// The local-zone write path.
//
// Everything the console changes lives in the managed zone directory
// (blocklist.managed_zones), one <apex>.zone per zone. The operator's own master
// files in blocklist.local_zones are read and reported, never rewritten: a
// deployment that never configures a managed directory gets a read-only zone
// browser, and one that does gets a console whose edits land in a file it
// names and owns.
//
// Every change follows the same four steps: write the file, recompile the
// whole store, drop the cached answers, report. A change that does not
// recompile is a change the query path is not serving, so the store is only
// swapped after the new file parsed, and a failure keeps the previous store.

// listZones renders the compiled store for the console.
func (a *App) listZones() (any, error) {
	dir := a.managedZoneDir()
	store := a.local.Get()
	// The slices are never nil: the console reads lengths and maps without
	// a null check, and an empty list is a list.
	res := api.ZonesResponse{
		Zones:      []api.Zone{},
		Files:      []string{},
		ManagedDir: dir,
		Writable:   a.managedZones.Writable(),
		Types:      localzone.EditableTypes(),
	}
	if store != nil {
		res.Files = store.Files()
		res.BuiltAt = store.BuiltAt()
		for _, zone := range store.SnapshotAll(dir) {
			res.Zones = append(res.Zones, *zone)
			res.Records += zone.RecordCount
		}
	}
	res.Error = a.localZoneError()
	return res, nil
}

// addZoneRecord adds one record to a zone.
func (a *App) addZoneRecord(_ context.Context, in api.ZoneRecordInput) (any, error) {
	origin, err := a.zoneOrigin(in.Zone)
	if err != nil {
		return nil, err
	}
	serial, err := a.managedZones.Add(origin, localzone.Record{
		Name:  in.Name,
		Type:  in.Type,
		TTL:   in.TTL,
		Value: in.Value,
	}, a.zoneDefaults(origin))
	if err != nil {
		return nil, err
	}
	a.afterZoneWrite(origin, "add", serial)
	return api.ZoneWriteResponse{OK: true, Zone: origin, Serial: serial}, nil
}

// putZoneRecord replaces the whole RRset of one name and type.
func (a *App) putZoneRecord(_ context.Context, in api.ZoneRecordInput) (any, error) {
	origin, err := a.zoneOrigin(in.Zone)
	if err != nil {
		return nil, err
	}
	serial, err := a.managedZones.Put(origin, localzone.Record{
		Name:  in.Name,
		Type:  in.Type,
		TTL:   in.TTL,
		Value: in.Value,
	}, a.zoneDefaults(origin))
	if err != nil {
		return nil, err
	}
	a.afterZoneWrite(origin, "replace", serial)
	return api.ZoneWriteResponse{OK: true, Zone: origin, Serial: serial}, nil
}

// deleteZoneRecord removes a record, or its whole RRset when value is empty.
func (a *App) deleteZoneRecord(_ context.Context, zone, name, rrtype, value string) error {
	origin, err := a.zoneOrigin(zone)
	if err != nil {
		return err
	}
	serial, removed, err := a.managedZones.Delete(origin, name, rrtype, value)
	if err != nil {
		return err
	}
	a.afterZoneWrite(origin, "delete", serial)
	if !removed {
		return fmt.Errorf("no managed record matches %s %s in %s", name, rrtype, origin)
	}
	return nil
}

// addZoneDelegation hands a name below an apex to other servers.
func (a *App) addZoneDelegation(_ context.Context, in api.ZoneDelegationInput) (any, error) {
	origin, err := a.zoneOrigin(in.Zone)
	if err != nil {
		return nil, err
	}
	targets := make([]string, 0, len(in.Targets))
	for _, t := range in.Targets {
		if t = strings.TrimSpace(t); t != "" {
			targets = append(targets, t)
		}
	}
	if len(targets) == 0 {
		return nil, errors.New("a delegation needs at least one NS target")
	}
	// A brand new zone has no NS set of its own, so the delegation's targets
	// are also the zone's. An existing file ignores this.
	def := a.zoneDefaults(origin)
	def.NS = targets
	if def.TTL == 0 {
		def.TTL = in.TTL
	}
	serial, err := a.managedZones.SetDelegation(origin, in.Name, targets, in.TTL, def)
	if err != nil {
		return nil, err
	}
	a.afterZoneWrite(origin, "delegate", serial)
	return api.ZoneWriteResponse{OK: true, Zone: origin, Serial: serial}, nil
}

// deleteZoneDelegation removes a cut.
func (a *App) deleteZoneDelegation(_ context.Context, zone, name string) error {
	origin, err := a.zoneOrigin(zone)
	if err != nil {
		return err
	}
	serial, removed, err := a.managedZones.RemoveDelegation(origin, name)
	if err != nil {
		return err
	}
	a.afterZoneWrite(origin, "undelegate", serial)
	if !removed {
		return fmt.Errorf("no delegation for %s in %s", name, origin)
	}
	return nil
}

// zoneOrigin canonicalises the apex a write names and refuses to go near the
// disk when the console has no managed directory.
func (a *App) zoneOrigin(zone string) (string, error) {
	origin, err := localzone.NormalizeOrigin(zone)
	if err != nil {
		return "", err
	}
	if err := a.managedZones.Check(); err != nil {
		return "", err
	}
	return origin, nil
}

// deleteZone removes a zone the console created, which is the only way a name
// goes back to upstream once the console has made a zone authoritative for
// it: a zone that exists answers NXDOMAIN for everything it does not hold.
func (a *App) deleteZone(_ context.Context, zone string) error {
	origin, err := a.zoneOrigin(zone)
	if err != nil {
		return err
	}
	// The zone has to be wholly the console's: deleting a managed file that
	// shares its apex with an operator's master file would remove none of
	// the zone, only half of it.
	whole := false
	if store := a.local.Get(); store != nil {
		if view := store.Snapshot(origin, a.managedZoneDir()); view != nil {
			whole = view.Managed
		} else {
			return fmt.Errorf("no zone %s is loaded", origin)
		}
	} else {
		return fmt.Errorf("no zone %s is loaded", origin)
	}
	removed, err := a.managedZones.Remove(origin, whole)
	if err != nil {
		return err
	}
	if !removed {
		return fmt.Errorf("no managed zone file for %s", origin)
	}
	a.afterZoneWrite(origin, "delete-zone", 0)
	return nil
}

// zoneDefaults seeds a managed file for an apex that has none from the zone
// as it is compiled today, so the console never has to restate a zone's
// server list and never invents one.
func (a *App) zoneDefaults(origin string) localzone.ZoneDefaults {
	store := a.local.Get()
	if store == nil {
		return localzone.ZoneDefaults{}
	}
	zone := store.Snapshot(origin, a.managedZoneDir())
	if zone == nil {
		return localzone.ZoneDefaults{}
	}
	def := localzone.ZoneDefaults{TTL: zone.DefaultTTL, Soa: zone.Soa}
	// The apex NS set follows the zone's existing one, from the operator's
	// file if that is where it lives. A managed file that already has its own
	// is not asked for defaults at all, so this only ever happens once.
	for _, rec := range zone.Records {
		if rec.Name == origin && rec.Type == "NS" {
			def.NS = append(def.NS, rec.Value)
		}
	}
	return def
}

// afterZoneWrite is the tail every change shares: recompile, drop the cached
// answers, log. The flush is the blunt half and it is deliberate — a name the
// zone now answers authoritatively may have an upstream answer cached, and
// which names changed is not knowable from here.
func (a *App) afterZoneWrite(origin, action string, serial uint32) {
	a.reloadLocalZones()
	if a.cache != nil {
		a.cache.Flush()
	}
	records := 0
	if store := a.local.Get(); store != nil {
		records = store.Count()
	}
	a.log.Info("local zone changed", "zone", origin, "action", action, "serial", serial, "records", records)
}

// localZoneError is the reason the store is stale, or "" when it is current.
// It comes from the degraded list, so the console and /healthz agree.
func (a *App) localZoneError() string {
	for _, d := range a.Degraded() {
		if rest, ok := strings.CutPrefix(d, "local zones: "); ok {
			return rest
		}
	}
	return ""
}