package torrent

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"
	"time"

	"git.kmsign.ru/royalcat/tstor/pkg/rlog"
	"git.kmsign.ru/royalcat/tstor/src/config"
	"git.kmsign.ru/royalcat/tstor/src/vfs"
	"github.com/royalcat/ctxio"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"golang.org/x/exp/maps"

	"github.com/anacrolix/torrent"
	"github.com/anacrolix/torrent/bencode"
	"github.com/anacrolix/torrent/metainfo"
	"github.com/anacrolix/torrent/types/infohash"
	"github.com/go-git/go-billy/v5"
	"github.com/go-git/go-billy/v5/util"
	"github.com/royalcat/kv"
)

var tracer = otel.Tracer("git.kmsign.ru/royalcat/tstor/sources/torrent")

type DirAquire struct {
	Name   string
	Hashes []infohash.T
}

type Service struct {
	client        *torrent.Client
	excludedFiles *filesMappingsStore
	infoBytes     *infoBytesStore
	Storage       *fileStorage
	fis           *fileItemStore
	dirsAquire    kv.Store[string, DirAquire]

	loadMutex     sync.Mutex
	torrentLoaded chan struct{}

	sourceFs billy.Filesystem

	log *rlog.Logger
}

func NewService(sourceFs billy.Filesystem, conf config.TorrentClient) (*Service, error) {
	s := &Service{
		log:           rlog.Component("torrent-service"),
		sourceFs:      sourceFs,
		torrentLoaded: make(chan struct{}),
		loadMutex:     sync.Mutex{},
	}

	err := os.MkdirAll(conf.MetadataFolder, 0744)
	if err != nil {
		return nil, fmt.Errorf("error creating metadata folder: %w", err)
	}

	s.fis, err = newFileItemStore(filepath.Join(conf.MetadataFolder, "items"), 2*time.Hour)
	if err != nil {
		return nil, fmt.Errorf("error starting item store: %w", err)
	}

	s.Storage, _, err = setupStorage(conf)
	if err != nil {
		return nil, err
	}

	s.excludedFiles, err = newFileMappingsStore(conf.MetadataFolder, s.Storage)
	if err != nil {
		return nil, err
	}

	s.infoBytes, err = newInfoBytesStore(conf.MetadataFolder)
	if err != nil {
		return nil, err
	}

	id, err := getOrCreatePeerID(filepath.Join(conf.MetadataFolder, "ID"))
	if err != nil {
		return nil, fmt.Errorf("error creating node ID: %w", err)
	}

	client, err := newClient(s.Storage, s.fis, &conf, id)
	if err != nil {
		return nil, fmt.Errorf("error starting torrent client: %w", err)
	}
	client.AddDhtNodes(conf.DHTNodes)

	s.dirsAquire, err = NewKV[string, DirAquire](conf.MetadataFolder, "dir-acquire")
	if err != nil {
		return nil, err
	}

	go func() {
		ctx := context.Background()
		err := s.loadTorrentFiles(ctx)
		if err != nil {
			s.log.Error(ctx, "initial torrent load failed", rlog.Error(err))
		}
		close(s.torrentLoaded)
	}()

	return s, nil
}

var _ vfs.FsFactory = (*Service)(nil).NewTorrentFs

func (s *Service) Close(ctx context.Context) error {
	return errors.Join(append(
		s.client.Close(),
		s.Storage.Close(),
		s.dirsAquire.Close(ctx),
		s.excludedFiles.Close(ctx),
		s.infoBytes.Close(),
		s.fis.Close(),
	)...)
}

func (s *Service) LoadTorrent(ctx context.Context, f vfs.File) (*Controller, error) {
	ctx, span := tracer.Start(ctx, "LoadTorrent")
	defer span.End()
	log := s.log

	defer f.Close(ctx)

	stat, err := f.Info()
	if err != nil {
		return nil, fmt.Errorf("call stat failed: %w", err)
	}

	span.SetAttributes(attribute.String("filename", stat.Name()))

	mi, err := metainfo.Load(bufio.NewReader(ctxio.IoReader(ctx, f)))
	if err != nil {
		return nil, fmt.Errorf("loading torrent metadata from file %s, error: %w", stat.Name(), err)
	}

	t, ok := s.client.Torrent(mi.HashInfoBytes())
	if !ok {

		span.AddEvent("torrent not found, loading from file")
		log.Info(ctx, "torrent not found, loading from file")

		spec, err := torrent.TorrentSpecFromMetaInfoErr(mi)
		if err != nil {
			return nil, fmt.Errorf("parse spec from metadata: %w", err)
		}
		infoBytes := spec.InfoBytes

		if !isValidInfoHashBytes(infoBytes) {
			log.Warn(ctx, "info loaded from spec not valid")
			infoBytes = nil
		}

		if len(infoBytes) == 0 {
			log.Info(ctx, "no info loaded from file, try to load from cache")
			infoBytes, err = s.infoBytes.GetBytes(spec.InfoHash)
			if err != nil && err != errNotFound {
				return nil, fmt.Errorf("get info bytes from database: %w", err)
			}
		}

		t, _ = s.client.AddTorrentOpt(torrent.AddTorrentOpts{
			InfoHash:  spec.InfoHash,
			Storage:   s.Storage,
			InfoBytes: infoBytes,
			ChunkSize: spec.ChunkSize,
		})
		t.AllowDataDownload()
		t.AllowDataUpload()

		span.AddEvent("torrent added to client")

		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		case <-t.GotInfo():
			err := s.infoBytes.Set(t.InfoHash(), t.Metainfo())
			if err != nil {
				log.Error(ctx, "error setting info bytes for torrent",
					slog.String("torrent-name", t.Name()),
					rlog.Error(err),
				)
			}
		}
		span.AddEvent("got info")

		info := t.Info()
		if info == nil {
			return nil, fmt.Errorf("info is nil")
		}

		compatable, _, err := s.checkTorrentCompatable(ctx, spec.InfoHash, *info)
		if err != nil {
			return nil, err
		}
		if !compatable {
			return nil, fmt.Errorf(
				"torrent with name '%s' not compatable existing infohash: %s, new: %s",
				t.Name(), t.InfoHash().HexString(), spec.InfoHash.HexString(),
			)
		}
	}

	return newController(t, s.excludedFiles), nil
}

func (s *Service) checkTorrentCompatable(ctx context.Context, ih infohash.T, info metainfo.Info) (compatable bool, tryLater bool, err error) {
	log := s.log.With(
		slog.String("new-name", info.BestName()),
		slog.String("new-infohash", ih.String()),
	)

	name := info.BestName()

	aq, found, err := s.dirsAquire.Get(ctx, info.BestName())
	if err != nil {
		return false, false, err
	}
	if !found {
		err = s.dirsAquire.Set(ctx, name, DirAquire{
			Name:   name,
			Hashes: slices.Compact([]infohash.T{ih}),
		})
		if err != nil {
			return false, false, err
		}

		log.Debug(ctx, "acquiring was not found, so created")
		return true, false, nil
	}

	if slices.Contains(aq.Hashes, ih) {
		log.Debug(ctx, "hash already know to be compatable")
		return true, false, nil
	}

	for _, existingTorrent := range s.client.Torrents() {
		if existingTorrent.Name() != name || existingTorrent.InfoHash() == ih {
			continue
		}

		existingInfo := existingTorrent.Info()

		existingFiles := slices.Clone(existingInfo.Files)
		newFiles := slices.Clone(info.Files)

		if !s.checkTorrentFilesCompatable(ctx, aq, existingFiles, newFiles) {
			return false, false, nil
		}

		aq.Hashes = slicesUnique(append(aq.Hashes, ih))
		err = s.dirsAquire.Set(ctx, aq.Name, aq)
		if err != nil {
			log.Warn(ctx, "torrent not compatible")
			return false, false, err
		}

	}

	if slices.Contains(aq.Hashes, ih) {
		log.Debug(ctx, "hash is compatable")
		return true, false, nil
	}

	log.Debug(ctx, "torrent with same name not found, try later")
	return false, true, nil
}

func (s *Service) checkTorrentFilesCompatable(ctx context.Context, aq DirAquire, existingFiles, newFiles []metainfo.FileInfo) bool {
	log := s.log.With(slog.String("name", aq.Name))

	pathCmp := func(a, b metainfo.FileInfo) int {
		return slices.Compare(a.BestPath(), b.BestPath())
	}
	slices.SortStableFunc(existingFiles, pathCmp)
	slices.SortStableFunc(newFiles, pathCmp)

	// torrents basically equals
	if slices.EqualFunc(existingFiles, newFiles, func(fi1, fi2 metainfo.FileInfo) bool {
		return fi1.Length == fi2.Length && slices.Equal(fi1.BestPath(), fi1.BestPath())
	}) {
		return true
	}

	if len(newFiles) > len(existingFiles) {
		type fileInfo struct {
			Path   string
			Length int64
		}
		mapInfo := func(fi metainfo.FileInfo) fileInfo {
			return fileInfo{
				Path:   strings.Join(fi.BestPath(), "/"),
				Length: fi.Length,
			}
		}

		existingFiles := apply(existingFiles, mapInfo)
		newFiles := apply(newFiles, mapInfo)

		for _, n := range newFiles {
			if slices.Contains(existingFiles, n) {
				continue
			}

			for _, e := range existingFiles {
				if e.Path == n.Path && e.Length != n.Length {
					log.Warn(ctx, "torrents not compatible, has files with different length",
						slog.String("path", n.Path),
						slog.Int64("existing-length", e.Length),
						slog.Int64("new-length", e.Length),
					)
					return false
				}
			}
		}
	}

	return true
}

func isValidInfoHashBytes(d []byte) bool {
	var info metainfo.Info
	err := bencode.Unmarshal(d, &info)
	return err == nil
}

func (s *Service) Stats() (*Stats, error) {
	return &Stats{}, nil
}

func (s *Service) GetStats() torrent.ConnStats {
	return s.client.ConnStats()
}

const loadWorkers = 5

func (s *Service) loadTorrentFiles(ctx context.Context) error {
	ctx, span := tracer.Start(ctx, "loadTorrentFiles", trace.WithAttributes(
		attribute.Int("workers", loadWorkers),
	))
	defer span.End()
	log := s.log

	loaderPaths := make(chan string)
	wg := sync.WaitGroup{}

	defer func() {
		close(loaderPaths)
		wg.Wait()
	}()

	loaderWorker := func() {
		wg.Add(1)
		for path := range loaderPaths {
			file, err := vfs.NewLazyOsFile(path)
			if err != nil {
				log.Error(ctx, "error opening torrent file", slog.String("filename", path), rlog.Error(err))
				continue
			}
			defer file.Close(ctx)

			_, err = s.LoadTorrent(ctx, file)
			if err != nil {
				log.Error(ctx, "failed adding torrent", rlog.Error(err))
			}
		}
		wg.Done()
	}

	for range loadWorkers {
		go loaderWorker()
	}

	return util.Walk(s.sourceFs, "/", func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return fmt.Errorf("fs walk error: %w", err)
		}

		if ctx.Err() != nil {
			return ctx.Err()
		}

		if info.IsDir() {
			return nil
		}

		if strings.HasSuffix(path, ".torrent") {
			loaderPaths <- path
		}

		return nil
	})
}

func (s *Service) ListTorrents(ctx context.Context) ([]*Controller, error) {
	<-s.torrentLoaded

	out := []*Controller{}
	for _, v := range s.client.Torrents() {
		out = append(out, newController(v, s.excludedFiles))
	}
	return out, nil
}

func (s *Service) GetTorrent(infohashHex string) (*Controller, error) {
	<-s.torrentLoaded

	t, ok := s.client.Torrent(infohash.FromHexString(infohashHex))
	if !ok {
		return nil, nil
	}

	return newController(t, s.excludedFiles), nil
}

func slicesUnique[S ~[]E, E comparable](in S) S {
	m := map[E]struct{}{}
	for _, v := range in {
		m[v] = struct{}{}
	}

	return maps.Keys(m)
}

func apply[I, O any](in []I, f func(e I) O) []O {
	out := []O{}
	for _, v := range in {
		out = append(out, f(v))
	}
	return out
}