// Package directory implements container which
// checks if hash present in any of torrent file
// placed in some directory.
// Note: Unlike List, this container also stores torrent name as value
package directory

import (
	"context"
	"crypto/sha1"
	"crypto/sha256"
	"fmt"
	"io"
	"iter"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/zeebo/bencode"

	"github.com/sot-tech/mochi/bittorrent"
	"github.com/sot-tech/mochi/middleware/torrentapproval/container"
	"github.com/sot-tech/mochi/middleware/torrentapproval/container/list"
	"github.com/sot-tech/mochi/pkg/conf"
	"github.com/sot-tech/mochi/pkg/log"
	"github.com/sot-tech/mochi/pkg/str2bytes"
	"github.com/sot-tech/mochi/storage"
)

var logger = log.NewLogger("middleware/torrent approval/directory")

const (
	defaultPeriod  = time.Minute
	maxTorrentSize = 10 * 1024 * 1024
)

func init() {
	container.Register("directory", build)
}

// Config - implementation of directory container configuration.
// Extends list.Config because uses the same storage and Approved function.
type Config struct {
	list.Config
	// Path in filesystem where torrent files stored and should be watched
	Path string
	// Period is time between two Path checks
	Period time.Duration
}

func build(conf conf.MapConfig, st storage.DataStorage) (container.Container, error) {
	c := new(Config)
	if err := conf.Unmarshal(c); err != nil {
		return nil, fmt.Errorf("unable to deserialise configuration: %w", err)
	}
	d := NewScanner(list.List{
		Invert:     c.Invert,
		Storage:    st,
		StorageCtx: c.StorageCtx,
	}, path(c.Path), c.Period)
	go d.Run()
	return d, nil
}

type bencodeRawBytes []byte

// UnmarshalBencode just appends raw byte slice to result
func (ba *bencodeRawBytes) UnmarshalBencode(in []byte) error {
	*ba = append([]byte(nil), in...)
	return nil
}

type torrentRawInfoStruct struct {
	Info bencodeRawBytes `bencode:"info"`
}

type torrentNameInfoStruct struct {
	Name string `bencode:"name"`
}

// PathReader - interface for abstract directory-like reader
type PathReader interface {
	// ReadDir returns names of torrent entries.
	// Implementation must return absolute paths of entries
	// to fetch torrent file-like data.
	ReadDir() (it iter.Seq[string], err error)
	// ReadData returns reader for entry data
	ReadData(entry string) (io.ReadCloser, error)
}

type path string

var _ PathReader = path("")

func (p path) ReadDir() (it iter.Seq[string], err error) {
	var entries []os.DirEntry
	dir := string(p)
	if entries, err = os.ReadDir(dir); err == nil {
		it = func(yield func(string) bool) {
			for _, e := range entries {
				if !e.IsDir() && strings.ToLower(filepath.Ext(e.Name())) == ".torrent" {
					if !yield(filepath.Join(dir, e.Name())) {
						return
					}
				}
			}
		}
	}
	return it, err
}

func (p path) ReadData(entry string) (io.ReadCloser, error) {
	return os.Open(entry)
}

// NewScanner creates Scanner instance.
func NewScanner(list list.List, reader PathReader, period time.Duration) *Scanner {
	if len(list.StorageCtx) == 0 {
		logger.Warn().
			Str("name", "StorageCtx").
			Str("provided", list.StorageCtx).
			Str("default", container.DefaultStorageCtxName).
			Msg("falling back to default configuration")
		list.StorageCtx = container.DefaultStorageCtxName
	}
	if period == 0 {
		logger.Warn().
			Str("name", "Period").
			Dur("provided", 0).
			Dur("default", defaultPeriod).
			Msg("falling back to default configuration")
		period = defaultPeriod
	}
	return &Scanner{
		List:   list,
		reader: reader,
		period: period,
		closed: make(chan bool),
	}
}

// Scanner holds list of approved/rejected torrents
type Scanner struct {
	list.List
	reader PathReader
	period time.Duration
	closed chan bool
}

// Run starts periodic directory scanning and blocks until Stop called
func (d *Scanner) Run() {
	if d.reader == nil {
		log.Warn().Msg("reader not provided")
		return
	}
	if d.period == 0 {
		log.Warn().Msg("period not provided")
		return
	}
	t := time.NewTicker(d.period)
	defer t.Stop()
	files := make(map[string][2]bittorrent.InfoHash)
	tmpFiles := make(map[string]bool)
	// nolint:gosec
	s1, s2 := sha1.New(), sha256.New()
	for {
		select {
		case <-d.closed:
			return
		case <-t.C:
			logger.Debug().Msg("starting directory scan")
			if entries, err := d.reader.ReadDir(); err == nil {
				for e := range entries {
					tmpFiles[e] = true
				}
				for p := range tmpFiles {
					if _, exists := files[p]; !exists {
						var f io.ReadCloser
						if f, err = d.reader.ReadData(p); err == nil {
							var info torrentRawInfoStruct
							err = bencode.NewDecoder(io.LimitReader(f, maxTorrentSize)).Decode(&info)
							_ = f.Close()
							if err == nil {
								s1.Write(info.Info)
								h1, _ := bittorrent.NewInfoHash(s1.Sum(nil))
								s1.Reset()

								s2.Write(info.Info)
								h2, _ := bittorrent.NewInfoHash(s2.Sum(nil))
								s2.Reset()

								files[p] = [2]bittorrent.InfoHash{h1, h2}
								var name torrentNameInfoStruct
								if err := bencode.DecodeBytes(info.Info, &name); err != nil {
									logger.Warn().
										Err(err).
										Str("file", p).
										Msg("unable to unmarshal torrent info")
								}
								if len(name.Name) == 0 {
									name.Name = list.DUMMY
								}
								bName := str2bytes.StringToBytes(name.Name)
								logger.Err(d.Storage.Put(context.Background(), d.StorageCtx, storage.Entry{
									Key:   h1.RawString(),
									Value: bName,
								}, storage.Entry{
									Key:   h2.RawString(),
									Value: bName,
								}, storage.Entry{
									Key:   h2.TruncateV1().RawString(),
									Value: bName,
								})).
									Str("file", p).
									Stringer("infoHash", h1).
									Stringer("infoHashV2", h2).
									Msg("added torrent to approval list")
							}
						}
						if err != nil {
							logger.Warn().Err(err).Str("file", p).Msg("unable to read file")
						}
					}
				}
				for p, ih := range files {
					if _, isOk := tmpFiles[p]; !isOk {
						delete(files, p)
						logger.Err(d.Storage.Delete(context.Background(), d.StorageCtx, ih[0].RawString(),
							ih[1].RawString(), ih[1].TruncateV1().RawString())).
							Str("file", p).
							Stringer("infoHash", ih[1]).
							Stringer("infoHashV2", ih[1]).
							Msg("deleted torrent from approval list")
					}
				}
				clear(tmpFiles)
			} else {
				logger.Warn().Err(err).Msg("unable to get directory content")
			}
		}
	}
}

// Close closes watching of torrent directory
func (d *Scanner) Close() error {
	if d.closed != nil {
		close(d.closed)
	}
	return nil
}