package dns

import (
	"context"
	"net/netip"
	"sort"
	"time"

	"darvaza.org/core"
	"darvaza.org/slog"
	"github.com/libdns/libdns"
)

// SyncAddrRecord is similar to AddrRecord but include libdns.Record details
// fetched from the Provider
type SyncAddrRecord struct {
	Name  string
	Addrs []SyncAddr
}

// SyncAddr extends netip.Addr with ID and TTL fetched from the Provider
type SyncAddr struct {
	ID   string
	Addr netip.Addr
	TTL  time.Duration
}

// Export assembles a libdns.Record
func (rec *SyncAddr) Export(name string) libdns.Record {
	return libdns.Record{
		ID:    rec.ID,
		Name:  name,
		Type:  core.IIf(rec.Addr.Is6(), "AAAA", "A"),
		TTL:   time.Second,
		Value: rec.Addr.String(),
	}
}

// SortSyncAddrSlice sorts a slice of [SyncAddr] by its address
func SortSyncAddrSlice(s []SyncAddr) []SyncAddr {
	sort.Slice(s, func(i, j int) bool {
		a1 := s[i].Addr
		a2 := s[j].Addr
		return a1.Less(a2)
	})
	return s
}

// GetSyncRecords pulls all the address records on DNS for our domain
func (mgr *Manager) GetSyncRecords(ctx context.Context) ([]SyncAddrRecord, error) {
	recs, err := mgr.GetRecords(ctx)
	if err != nil {
		return nil, err
	}

	return mgr.filteredSyncRecords(recs)
}

// AsSyncAddr converts a A or AAAA [libdns.Record] into a [SyncAddr]
func (*Manager) AsSyncAddr(rr libdns.Record) (SyncAddr, bool, error) {
	var out SyncAddr
	var addr netip.Addr

	// skip non-address types
	if rr.Type != "A" && rr.Type != "AAAA" {
		return out, false, nil
	}

	err := addr.UnmarshalText([]byte(rr.Value))
	if err != nil {
		// invalid address on A or AAAA record
		return out, false, err
	}

	out = SyncAddr{
		ID:   rr.ID,
		TTL:  rr.TTL,
		Addr: addr,
	}

	return out, true, nil
}

func (mgr *Manager) filteredSyncRecords(recs []libdns.Record) ([]SyncAddrRecord, error) {
	// filter and convert
	cache := make(map[string][]SyncAddr)
	for _, rr := range recs {
		addr, ok, err := mgr.AsSyncAddr(rr)
		switch {
		case err != nil:
			// skip invalid addresses
			mgr.l.Error().
				WithField("subsystem", "dns").
				WithField(slog.ErrorFieldName, err).
				WithField("name", rr.Name).
				WithField("type", rr.Type).
				WithField("addr", rr.Value).
				Print()
		case ok:
			// store
			cache[rr.Name] = append(cache[rr.Name], addr)
		}
	}

	// prepare records
	out := make([]SyncAddrRecord, len(cache))
	names := make([]string, 0, len(cache))
	for name := range cache {
		names = append(names, name)
	}
	sort.Strings(names)

	for i, name := range names {
		addrs := cache[name]

		out[i] = SyncAddrRecord{
			Name:  name,
			Addrs: SortSyncAddrSlice(addrs),
		}
	}

	return out, nil
}

// Sync updates all the address records on DNS for our domain
func (mgr *Manager) Sync(ctx context.Context) error {
	current, err := mgr.GetSyncRecords(ctx)
	if err != nil {
		return core.Wrap(err, "GetRecords")
	}

	goal := mgr.genAllAddrRecords()
	for _, p := range makeSyncMap(current, goal) {
		err := mgr.doSync(ctx, p.Name, p.Before, p.After)
		if err != nil {
			return err
		}
	}

	return nil
}

func (mgr *Manager) doSync(ctx context.Context, name string,
	before []SyncAddr, after []netip.Addr) error {
	//
	var err error

	for _, a := range after {
		before, err = mgr.doSyncUpdateOrInsert(ctx, name, a, before)
		if err != nil {
			return err
		}
	}

	for _, b := range before {
		err = mgr.doSyncRemove(ctx, name, b)
		if err != nil {
			return err
		}
	}

	return nil
}

func (mgr *Manager) doSyncUpdateOrInsert(ctx context.Context, name string,
	addr netip.Addr, addrs []SyncAddr) ([]SyncAddr, error) {
	//
	var err error

	i, ok := findSyncAddrSorted(addr, addrs)
	if ok {
		rec := addrs[i]

		addrs = append(addrs[:i], addrs[i+1:]...)
		err = mgr.doSyncUpdate(ctx, name, addr, rec)
	} else {
		err = mgr.doSyncInsert(ctx, name, addr)
	}

	return addrs, err
}

func (mgr *Manager) doSyncUpdate(ctx context.Context, name string,
	addr netip.Addr, rec SyncAddr) error {
	//
	var log slog.Logger
	var msg string
	var err error

	if rec.TTL != time.Second {
		// amend TTL

		// TODO: batch updates
		_, err = mgr.p.SetRecords(ctx, mgr.domain, []libdns.Record{
			rec.Export(name),
		})

		if err == nil {
			log = mgr.l.Info()
			msg = "Updated"
		} else {
			log = mgr.l.Error().
				WithField(slog.ErrorFieldName, err)
			msg = "Failed"
		}
	} else {
		log = mgr.l.Info()
		msg = "OK"
	}

	log.
		WithField("subsystem", "dns").
		WithField("name", name).
		WithField("addr", addr).
		Print(msg)

	return err
}

func (mgr *Manager) doSyncInsert(ctx context.Context, name string,
	addr netip.Addr) error {
	//
	var log slog.Logger
	var msg string

	rec := libdns.Record{
		Name:  name,
		Type:  core.IIf(addr.Is6(), "AAAA", "A"),
		TTL:   time.Second,
		Value: addr.String(),
	}

	_, err := mgr.p.AppendRecords(ctx, mgr.domain, []libdns.Record{
		rec,
	})

	if err != nil {
		log = mgr.l.Error().
			WithField(slog.ErrorFieldName, err)
		msg = "Failed to Add"
	} else {
		log = mgr.l.Info()
		msg = "Added"
	}

	log.
		WithField("subsystem", "dns").
		WithField("name", name).
		WithField("addr", addr).
		Print(msg)
	return err
}

func (mgr *Manager) doSyncRemove(ctx context.Context, name string,
	rec SyncAddr) error {
	//
	var log slog.Logger
	var msg string

	// TODO: batch deletes
	_, err := mgr.p.DeleteRecords(ctx, mgr.domain, []libdns.Record{
		rec.Export(name),
	})

	if err != nil {
		log = mgr.l.Error().
			WithField(slog.ErrorFieldName, err)
		msg = "Failed to Delete"
	} else {
		log = mgr.l.Warn()
		msg = "Deleted"
	}

	log.
		WithField("subsystem", "dns").
		WithField("name", name).
		WithField("addr", rec.Addr).
		Print(msg)
	return err
}

func findSyncAddrSorted(target netip.Addr, addrs []SyncAddr) (int, bool) {
	for i, a := range addrs {
		switch target.Compare(a.Addr) {
		case 0:
			// match
			return i, true
		case -1:
			// miss
			return -1, false
		default:
			// next
		}
	}

	return -1, false
}

type syncMapEntry struct {
	Name   string
	Before []SyncAddr
	After  []netip.Addr
}

func makeSyncMap(current []SyncAddrRecord,
	goal []AddrRecord) map[string]syncMapEntry {
	//
	data := make(map[string]syncMapEntry)

	for _, cur := range current {
		me, ok := data[cur.Name]
		if !ok {
			me = syncMapEntry{
				Name: cur.Name,
			}
		}

		me.Before = append(me.Before, cur.Addrs...)
		data[cur.Name] = me
	}

	for _, rr := range goal {
		me, ok := data[rr.Name]
		if !ok {
			me = syncMapEntry{
				Name: rr.Name,
			}
		}
		me.After = append(me.After, rr.Addr...)
		data[rr.Name] = me
	}

	return data
}