/*
   Copyright 2021 Erigon contributors

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package downloader

import (
	"context"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/anacrolix/torrent"
	"github.com/anacrolix/torrent/metainfo"
	"github.com/anacrolix/torrent/storage"
	common2 "github.com/ledgerwatch/erigon-lib/common"
	"github.com/ledgerwatch/erigon-lib/common/dir"
	"github.com/ledgerwatch/erigon-lib/downloader/downloadercfg"
	"github.com/ledgerwatch/erigon-lib/kv"
	"github.com/ledgerwatch/erigon-lib/kv/mdbx"
	"github.com/ledgerwatch/log/v3"
	mdbx2 "github.com/torquem-ch/mdbx-go/mdbx"
	"go.uber.org/atomic"
	"golang.org/x/sync/semaphore"
)

// Downloader - component which downloading historical files. Can use BitTorrent, or other protocols
type Downloader struct {
	db                kv.RwDB
	pieceCompletionDB storage.PieceCompletion
	torrentClient     *torrent.Client
	clientLock        *sync.RWMutex

	cfg *downloadercfg.Cfg

	statsLock *sync.RWMutex
	stats     AggStats

	folder storage.ClientImplCloser
}

type AggStats struct {
	MetadataReady, FilesTotal int32
	PeersUnique               int32
	ConnectionsTotal          uint64

	Completed bool
	Progress  float32

	BytesCompleted, BytesTotal uint64

	BytesDownload, BytesUpload uint64
	UploadRate, DownloadRate   uint64
}

func New(cfg *downloadercfg.Cfg) (*Downloader, error) {
	if err := portMustBeTCPAndUDPOpen(cfg.ListenPort); err != nil {
		return nil, err
	}

	// Application must never see partially-downloaded files
	// To provide such consistent view - downloader does:
	// add <datadir>/snapshots/tmp - then method .onComplete will remove this suffix
	// and App only work with <datadir>/snapshot s folder
	if dir.FileExist(cfg.DataDir + "_tmp") { // migration from prev versions
		_ = os.Rename(cfg.DataDir+"_tmp", filepath.Join(cfg.DataDir, "tmp")) // ignore error, because maybe they are on different drive, or target folder already created manually, all is fine
	}
	if err := moveFromTmp(cfg.DataDir); err != nil {
		return nil, err
	}

	db, c, m, torrentClient, err := openClient(cfg.ClientConfig)
	if err != nil {
		return nil, fmt.Errorf("openClient: %w", err)
	}

	peerID, err := readPeerID(db)
	if err != nil {
		return nil, fmt.Errorf("get peer id: %w", err)
	}
	cfg.PeerID = string(peerID)
	if len(peerID) == 0 {
		if err = savePeerID(db, torrentClient.PeerID()); err != nil {
			return nil, fmt.Errorf("save peer id: %w", err)
		}
	}

	d := &Downloader{
		cfg:               cfg,
		db:                db,
		pieceCompletionDB: c,
		folder:            m,
		torrentClient:     torrentClient,
		clientLock:        &sync.RWMutex{},

		statsLock: &sync.RWMutex{},
	}
	if err := d.addSegments(); err != nil {
		return nil, err
	}
	return d, nil
}

func (d *Downloader) SnapDir() string {
	d.clientLock.RLock()
	defer d.clientLock.RUnlock()
	return d.cfg.DataDir
}

func (d *Downloader) ReCalcStats(interval time.Duration) {
	//Call this methods outside of `statsLock` critical section, because they have own locks with contention
	torrents := d.torrentClient.Torrents()
	connStats := d.torrentClient.ConnStats()
	peers := make(map[torrent.PeerID]struct{}, 16)

	d.statsLock.Lock()
	defer d.statsLock.Unlock()
	prevStats, stats := d.stats, d.stats

	stats.Completed = true
	stats.BytesDownload = uint64(connStats.BytesReadUsefulIntendedData.Int64())
	stats.BytesUpload = uint64(connStats.BytesWrittenData.Int64())

	stats.BytesTotal, stats.BytesCompleted, stats.ConnectionsTotal, stats.MetadataReady = 0, 0, 0, 0
	for _, t := range torrents {
		select {
		case <-t.GotInfo():
			stats.MetadataReady++
			for _, peer := range t.PeerConns() {
				stats.ConnectionsTotal++
				peers[peer.PeerID] = struct{}{}
			}
			stats.BytesCompleted += uint64(t.BytesCompleted())
			stats.BytesTotal += uint64(t.Length())
			if !t.Complete.Bool() {
				progress := float32(float64(100) * (float64(t.BytesCompleted()) / float64(t.Length())))
				log.Debug("[downloader] file not downloaded yet", "name", t.Name(), "progress", fmt.Sprintf("%.2f%%", progress))
			}
		default:
			log.Debug("[downloader] file has no metadata yet", "name", t.Name())
		}

		stats.Completed = stats.Completed && t.Complete.Bool()
	}

	stats.DownloadRate = (stats.BytesDownload - prevStats.BytesDownload) / uint64(interval.Seconds())
	stats.UploadRate = (stats.BytesUpload - prevStats.BytesUpload) / uint64(interval.Seconds())

	if stats.BytesTotal == 0 {
		stats.Progress = 0
	} else {
		stats.Progress = float32(float64(100) * (float64(stats.BytesCompleted) / float64(stats.BytesTotal)))
		if stats.Progress == 100 && !stats.Completed {
			stats.Progress = 99.99
		}
	}
	stats.PeersUnique = int32(len(peers))
	stats.FilesTotal = int32(len(torrents))

	d.stats = stats
}

func moveFromTmp(snapDir string) error {
	tmpDir := filepath.Join(snapDir, "tmp")
	if !dir.FileExist(tmpDir) {
		return nil
	}

	snFs := os.DirFS(tmpDir)
	paths, err := fs.ReadDir(snFs, ".")
	if err != nil {
		return err
	}
	for _, p := range paths {
		if p.Name() == "." || p.Name() == ".." || p.Name() == "tmp" {
			continue
		}
		src := filepath.Join(tmpDir, p.Name())
		if err := os.Rename(src, filepath.Join(snapDir, p.Name())); err != nil {
			if os.IsExist(err) {
				_ = os.Remove(src)
				continue
			}
			return err
		}
	}
	_ = os.Remove(tmpDir)
	return nil
}

func (d *Downloader) verify() error {
	total := 0
	for _, t := range d.torrentClient.Torrents() {
		select {
		case <-t.GotInfo():
			total += t.NumPieces()
		default:
			continue
		}
	}
	logInterval := 20 * time.Second
	logEvery := time.NewTicker(logInterval)
	defer logEvery.Stop()

	wg := &sync.WaitGroup{}
	j := atomic.NewInt64(0)

	for _, t := range d.torrentClient.Torrents() {
		wg.Add(1)
		go func(t *torrent.Torrent) {
			defer wg.Done()
			<-t.GotInfo()
			for i := 0; i < t.NumPieces(); i++ {
				j.Inc()
				t.Piece(i).VerifyData()

				select {
				case <-logEvery.C:
					log.Info("[snapshots] Verifying", "progress", fmt.Sprintf("%.2f%%", 100*float64(j.Load())/float64(total)))
				default:
				}
				//<-t.Complete.On()
			}
		}(t)
	}
	wg.Wait()

	return nil
}

func (d *Downloader) addSegments() error {
	logEvery := time.NewTicker(20 * time.Second)
	defer logEvery.Stop()
	_, err := BuildTorrentFilesIfNeed(context.Background(), d.SnapDir())
	if err != nil {
		return err
	}
	files, err := seedableSegmentFiles(d.SnapDir())
	if err != nil {
		return fmt.Errorf("seedableSegmentFiles: %w", err)
	}
	files2, err := seedableHistorySnapshots(d.SnapDir())
	if err != nil {
		return fmt.Errorf("seedableHistorySnapshots: %w", err)
	}
	files = append(files, files2...)
	wg := &sync.WaitGroup{}
	i := atomic.NewInt64(0)
	for _, f := range files {
		wg.Add(1)
		go func(f string) {
			defer wg.Done()
			_, err := AddSegment(f, d.cfg.DataDir, d.torrentClient)
			if err != nil {
				log.Warn("[snapshots] AddSegment", "err", err)
				return
			}

			i.Inc()
			select {
			case <-logEvery.C:
				log.Info("[snpshots] initializing", "files", fmt.Sprintf("%s/%d", i.String(), len(files)))
			default:
			}
		}(f)
	}
	wg.Wait()
	return nil
}

func (d *Downloader) Stats() AggStats {
	d.statsLock.RLock()
	defer d.statsLock.RUnlock()
	return d.stats
}

func (d *Downloader) Close() {
	d.torrentClient.Close()
	if err := d.folder.Close(); err != nil {
		log.Warn("[Snapshots] folder.close", "err", err)
	}
	if err := d.pieceCompletionDB.Close(); err != nil {
		log.Warn("[Snapshots] pieceCompletionDB.close", "err", err)
	}
	d.db.Close()
}

func (d *Downloader) PeerID() []byte {
	peerID := d.torrentClient.PeerID()
	return peerID[:]
}

func (d *Downloader) StopSeeding(hash metainfo.Hash) error {
	t, ok := d.torrentClient.Torrent(hash)
	if !ok {
		return nil
	}
	ch := t.Closed()
	t.Drop()
	<-ch
	return nil
}

func (d *Downloader) Torrent() *torrent.Client {
	d.clientLock.RLock()
	defer d.clientLock.RUnlock()
	return d.torrentClient
}

func openClient(cfg *torrent.ClientConfig) (db kv.RwDB, c storage.PieceCompletion, m storage.ClientImplCloser, torrentClient *torrent.Client, err error) {
	snapDir := cfg.DataDir
	db, err = mdbx.NewMDBX(log.New()).
		Flags(func(f uint) uint { return f | mdbx2.SafeNoSync }).
		Label(kv.DownloaderDB).
		WithTableCfg(func(defaultBuckets kv.TableCfg) kv.TableCfg { return kv.DownloaderTablesCfg }).
		SyncPeriod(15 * time.Second).
		Path(filepath.Join(snapDir, "db")).
		Open()
	if err != nil {
		return nil, nil, nil, nil, err
	}
	c, err = NewMdbxPieceCompletion(db)
	if err != nil {
		return nil, nil, nil, nil, fmt.Errorf("torrentcfg.NewMdbxPieceCompletion: %w", err)
	}
	m = storage.NewMMapWithCompletion(snapDir, c)
	cfg.DefaultStorage = m

	for retry := 0; retry < 5; retry++ {
		torrentClient, err = torrent.NewClient(cfg)
		if err == nil {
			break
		}
		time.Sleep(10 * time.Millisecond)
	}
	if err != nil {
		return nil, nil, nil, nil, fmt.Errorf("torrent.NewClient: %w", err)
	}

	return db, c, m, torrentClient, nil
}

func MainLoop(ctx context.Context, d *Downloader, silent bool) {
	var sem = semaphore.NewWeighted(int64(d.cfg.DownloadSlots))

	go func() {
		for {
			torrents := d.Torrent().Torrents()
			for _, t := range torrents {
				<-t.GotInfo()
				if t.Complete.Bool() {
					continue
				}
				if err := sem.Acquire(ctx, 1); err != nil {
					return
				}
				t.AllowDataDownload()
				t.DownloadAll()
				go func(t *torrent.Torrent) {
					defer sem.Release(1)
					//r := t.NewReader()
					//r.SetReadahead(t.Length())
					//_, _ = io.Copy(io.Discard, r) // enable streaming - it will prioritize sequential download

					<-t.Complete.On()
				}(t)
			}
			time.Sleep(30 * time.Second)
		}
	}()

	logEvery := time.NewTicker(20 * time.Second)
	defer logEvery.Stop()

	statInterval := 20 * time.Second
	statEvery := time.NewTicker(statInterval)
	defer statEvery.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-statEvery.C:
			d.ReCalcStats(statInterval)

		case <-logEvery.C:
			if silent {
				continue
			}

			stats := d.Stats()

			if stats.MetadataReady < stats.FilesTotal {
				log.Info(fmt.Sprintf("[Snapshots] Waiting for torrents metadata: %d/%d", stats.MetadataReady, stats.FilesTotal))
				continue
			}

			if stats.Completed {
				log.Info("[Snapshots] Seeding",
					"up", common2.ByteCount(stats.UploadRate)+"/s",
					"peers", stats.PeersUnique,
					"connections", stats.ConnectionsTotal,
					"files", stats.FilesTotal)
				continue
			}

			log.Info("[Snapshots] Downloading",
				"progress", fmt.Sprintf("%.2f%% %s/%s", stats.Progress, common2.ByteCount(stats.BytesCompleted), common2.ByteCount(stats.BytesTotal)),
				"download", common2.ByteCount(stats.DownloadRate)+"/s",
				"upload", common2.ByteCount(stats.UploadRate)+"/s",
				"peers", stats.PeersUnique,
				"connections", stats.ConnectionsTotal,
				"files", stats.FilesTotal)
			if stats.PeersUnique == 0 {
				ips := d.Torrent().BadPeerIPs()
				if len(ips) > 0 {
					log.Info("[Snapshots] Stats", "banned", ips)
				}
			}
		}
	}
}