package torrent

import (
	"encoding/gob"
	"fmt"
	"math"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/debridmediamanager.com/zurg/internal/config"
	"github.com/debridmediamanager.com/zurg/pkg/logutil"
	"github.com/debridmediamanager.com/zurg/pkg/realdebrid"
	"github.com/hashicorp/golang-lru/v2/expirable"
	"go.uber.org/zap"
)

type TorrentManager struct {
	requiredVersion   string
	torrents          []Torrent
	inProgress        []string
	checksum          string
	config            config.ConfigInterface
	cache             *expirable.LRU[string, string]
	workerPool        chan bool
	directoryMap      map[string][]string
	processedTorrents map[string][]string
	mu                *sync.Mutex
	log               *zap.SugaredLogger
}

// NewTorrentManager creates a new torrent manager
// it will fetch all torrents and their info in the background
// and store them in-memory; it is called only once at startup
func NewTorrentManager(config config.ConfigInterface, cache *expirable.LRU[string, string]) *TorrentManager {
	t := &TorrentManager{
		requiredVersion:   fmt.Sprintf("4.11.2023 - retain:%v", config.EnableRetainFolderNameExtension()),
		config:            config,
		cache:             cache,
		workerPool:        make(chan bool, config.GetNumOfWorkers()),
		directoryMap:      make(map[string][]string),
		processedTorrents: make(map[string][]string),
		mu:                &sync.Mutex{},
		log:               logutil.NewLogger().Named("manager"),
	}

	// Initialize torrents for the first time
	t.mu.Lock()
	t.torrents = t.getFreshListFromAPI()
	t.checksum = t.getChecksum()
	t.mu.Unlock()

	// log.Println("First checksum", t.checksum)

	var wg sync.WaitGroup

	for i := range t.torrents {
		wg.Add(1)
		go func(idx int) {
			defer wg.Done()
			t.workerPool <- true
			t.addMoreInfo(&t.torrents[idx])
			<-t.workerPool
		}(i)
	}

	if t.config.EnableRepair() {
		go t.repairAll(&wg)
	}

	wg.Wait()
	t.mapToDirectories()
	go t.startRefreshJob()

	return t
}

// GetByDirectory returns all torrents that have a file in the specified directory
func (t *TorrentManager) GetByDirectory(directory string) []Torrent {
	var torrents []Torrent
	for i := range t.torrents {
		for _, dir := range t.directoryMap[t.torrents[i].Name] {
			if dir == directory {
				torrents = append(torrents, t.torrents[i])
			}
		}
	}
	return torrents
}

// HideTheFile marks a file as deleted
func (t *TorrentManager) HideTheFile(torrent *Torrent, file *File) {
	file.Unavailable = true
	t.repair(torrent.ID, torrent.SelectedFiles, false)
}

// FindAllTorrentsWithName finds all torrents in a given directory with a given name
func (t *TorrentManager) FindAllTorrentsWithName(directory, torrentName string) []Torrent {
	var matchingTorrents []Torrent
	torrents := t.GetByDirectory(directory)
	for i := range torrents {
		if torrents[i].Name == torrentName || strings.HasPrefix(torrents[i].Name, torrentName) {
			matchingTorrents = append(matchingTorrents, torrents[i])
		}
	}
	return matchingTorrents
}

// findAllDownloadedFilesFromHash finds all files that were  with a given hash
func (t *TorrentManager) findAllDownloadedFilesFromHash(hash string) []File {
	var files []File
	for _, torrent := range t.torrents {
		if torrent.Hash == hash {
			for _, file := range torrent.SelectedFiles {
				if file.Link != "" {
					files = append(files, file)
				}
			}
		}
	}
	return files
}

type torrentsResponse struct {
	torrents   []realdebrid.Torrent
	totalCount int
}

func (t *TorrentManager) getChecksum() string {
	torrentsChan := make(chan torrentsResponse)
	countChan := make(chan int)
	errChan := make(chan error, 2) // accommodate errors from both goroutines

	// GetTorrents request
	go func() {
		torrents, totalCount, err := realdebrid.GetTorrents(t.config.GetToken(), 1)
		if err != nil {
			errChan <- err
			return
		}
		torrentsChan <- torrentsResponse{torrents: torrents, totalCount: totalCount}
	}()

	// GetActiveTorrentCount request
	go func() {
		count, err := realdebrid.GetActiveTorrentCount(t.config.GetToken())
		if err != nil {
			errChan <- err
			return
		}
		countChan <- count.DownloadingCount
	}()

	var torrents []realdebrid.Torrent
	var totalCount, count int

	for i := 0; i < 2; i++ {
		select {
		case torrentsResp := <-torrentsChan:
			torrents = torrentsResp.torrents
			totalCount = torrentsResp.totalCount
		case count = <-countChan:
		case err := <-errChan:
			t.log.Errorf("Checksum API Error: %v\n", err)
			return ""
		}
	}

	if len(torrents) == 0 {
		t.log.Error("Huh, no torrents returned")
		return ""
	}

	checksum := fmt.Sprintf("%d%s%d", totalCount, torrents[0].ID, count)
	return checksum
}

// startRefreshJob periodically refreshes the torrents
func (t *TorrentManager) startRefreshJob() {
	t.log.Info("Starting periodic refresh")
	for {
		<-time.After(time.Duration(t.config.GetRefreshEverySeconds()) * time.Second)

		checksum := t.getChecksum()
		if checksum == t.checksum {
			continue
		}
		t.cache.Purge()

		newTorrents := t.getFreshListFromAPI()
		var wg sync.WaitGroup

		for i := range newTorrents {
			wg.Add(1)
			go func(idx int) {
				defer wg.Done()
				t.workerPool <- true
				t.addMoreInfo(&newTorrents[idx])
				<-t.workerPool
			}(i)
		}
		wg.Wait()

		// apply side effects
		t.mu.Lock()
		t.torrents = newTorrents
		t.checksum = t.getChecksum()
		t.mu.Unlock()

		// log.Println("Checksum changed", t.checksum)
		if t.config.EnableRepair() {
			go t.repairAll(&wg)
		}
		go t.mapToDirectories()
		go OnLibraryUpdateHook(t.config)
	}
}

// getFreshListFromAPI returns all torrents
func (t *TorrentManager) getFreshListFromAPI() []Torrent {
	torrents, _, err := realdebrid.GetTorrents(t.config.GetToken(), 0)
	if err != nil {
		t.log.Errorf("Cannot get torrents: %v\n", err)
		return nil
	}

	// convert to own internal type without SelectedFiles yet
	// populate inProgress
	var torrentsV2 []Torrent
	t.inProgress = t.inProgress[:0] // reset
	for _, torrent := range torrents {
		torrent.Name = strings.TrimSuffix(torrent.Name, "/")
		torrentV2 := Torrent{
			Torrent:       torrent,
			SelectedFiles: nil,
			ForRepair:     false,
			lock:          &sync.Mutex{},
		}
		torrentsV2 = append(torrentsV2, torrentV2)

		if torrent.Progress != 100 {
			t.inProgress = append(t.inProgress, torrent.Hash)
		}
	}

	t.log.Infof("Fetched %d torrents", len(torrentsV2))
	return torrentsV2
}

// addMoreInfo updates the selected files for a torrent
func (t *TorrentManager) addMoreInfo(torrent *Torrent) {
	// file cache
	torrentFromFile := t.readFromFile(torrent.ID)
	if torrentFromFile != nil {
		// see if api data and file data still match
		// then it means data is still usable
		if len(torrentFromFile.Links) == len(torrent.Links) {
			torrent.Name = t.getName(torrentFromFile)
			torrent.ForRepair = torrentFromFile.ForRepair
			torrent.SelectedFiles = torrentFromFile.SelectedFiles[:]
			return
		}
	}
	// no file data yet as it is still downloading
	if torrent.Progress != 100 {
		return
	}

	// t.log.Println("Getting info for", torrent.ID)
	info, err := realdebrid.GetTorrentInfo(t.config.GetToken(), torrent.ID)
	if err != nil {
		t.log.Errorf("Cannot get info: %v\n", err)
		return
	}

	// SelectedFiles is a subset of Files with only the selected ones
	// it also has a Link field, which can be empty
	// if it is empty, it means the file is no longer available
	// Files+Links together are the same as SelectedFiles
	var selectedFiles []File
	var streamableFiles []File
	// if some Links are empty, we need to repair it
	forRepair := false
	for _, file := range info.Files {
		if isStreamable(file.Path) {
			streamableFiles = append(streamableFiles, File{
				File: file,
				Link: "",
			})
		}
		if file.Selected == 0 {
			continue
		}
		selectedFiles = append(selectedFiles, File{
			File: file,
			Link: "",
		})
	}
	if len(selectedFiles) > len(info.Links) && info.Progress == 100 {
		t.log.Debugf("Some links has expired for %s %s: %d selected but only %d link(s)", info.ID, info.Name, len(selectedFiles), len(info.Links))
		// chaotic file means RD will not output the desired file selection
		// e.g. even if we select just a single mkv, it will output a rar
		var isChaotic bool
		selectedFiles, isChaotic = t.organizeChaos(info, selectedFiles)
		if isChaotic {
			t.log.Infof("Torrent %s %s is unfixable, it's always returning an unstreamable link, ignoring", info.ID, info.Name)
			t.log.Debugf("You can try fixing it yourself magnet:?xt=urn:btih:%s", info.Hash)
		} else {
			if len(streamableFiles) > 1 {
				t.log.Infof("Torrent %s %s marked for repair", info.ID, info.Name)
				forRepair = true
			} else {
				t.log.Infof("Torrent %s %s is unfixable, the lone streamable link has expired, ignoring", info.ID, info.Name)
				t.log.Debugf("You can try fixing it yourself magnet:?xt=urn:btih:%s", info.Hash)
			}
		}
	} else {
		// all links are still intact! good!
		for i, link := range info.Links {
			selectedFiles[i].Link = link
		}
	}
	// update file cache
	torrent.OriginalName = info.OriginalName
	torrent.Name = t.getName(torrent)
	if len(selectedFiles) > 0 {
		// update the torrent with more data!
		torrent.SelectedFiles = selectedFiles
		torrent.ForRepair = forRepair
		t.writeToFile(torrent)
	}
}

func (t *TorrentManager) getName(torrent *Torrent) string {
	// drop the extension from the name
	if t.config.EnableRetainFolderNameExtension() && strings.Contains(torrent.Name, torrent.OriginalName) {
		return torrent.Name
	} else {
		ret := strings.TrimSuffix(torrent.OriginalName, ".mp4")
		ret = strings.TrimSuffix(ret, ".mkv")
		return ret
	}
}

// mapToDirectories maps torrents to directories
func (t *TorrentManager) mapToDirectories() {
	// Map torrents to directories
	switch t.config.GetVersion() {
	case "v1":
		configV1 := t.config.(*config.ZurgConfigV1)
		groupMap := configV1.GetGroupMap()
		// for every group, iterate over every torrent
		// and then sprinkle/distribute the torrents to the directories of the group
		for group, directories := range groupMap {
			counter := make(map[string]int)
			for i := range t.torrents {
				// don't process torrents that are already mapped if it is not the first run
				alreadyMappedToGroup := false
				for _, mappedGroup := range t.processedTorrents[t.torrents[i].Name] {
					if mappedGroup == group {
						alreadyMappedToGroup = true
					}
				}
				if alreadyMappedToGroup {
					continue
				}

				for _, directory := range directories {
					var filenames []string
					for _, file := range t.torrents[i].SelectedFiles {
						filenames = append(filenames, file.Path)
					}
					if configV1.MeetsConditions(directory, t.torrents[i].ID, t.torrents[i].Name, filenames) {
						found := false
						// check if it is already mapped to this directory
						for _, dir := range t.directoryMap[t.torrents[i].Name] {
							if dir == directory {
								found = true
								break // it is already mapped to this directory
							}
						}
						if !found {
							counter[directory]++
							t.mu.Lock()
							t.directoryMap[t.torrents[i].Name] = append(t.directoryMap[t.torrents[i].Name], directory)
							t.mu.Unlock()
							break // we found a directory for this torrent, so we can stop looking for more
						}
					}
				}
				t.mu.Lock()
				t.processedTorrents[t.torrents[i].Name] = append(t.processedTorrents[t.torrents[i].Name], group)
				t.mu.Unlock()
			}
			sum := 0
			for _, count := range counter {
				sum += count
			}
			if sum > 0 {
				t.log.Infof("Group processing completed: %s %v total: %d", group, counter, sum)
			} else {
				t.log.Infof("No new additions to directory group %s", group)
			}
		}
	default:
		t.log.Error("Unknown config version")
	}
}

// getByID returns a torrent by its ID
func (t *TorrentManager) getByID(torrentID string) *Torrent {
	for i := range t.torrents {
		if t.torrents[i].ID == torrentID {
			return &t.torrents[i]
		}
	}
	return nil
}

// writeToFile writes a torrent to a file
func (t *TorrentManager) writeToFile(torrent *Torrent) {
	filePath := fmt.Sprintf("data/%s.bin", torrent.ID)
	file, err := os.Create(filePath)
	if err != nil {
		t.log.Fatalf("Failed creating file: %s", err)
		return
	}
	defer file.Close()

	torrent.Version = t.requiredVersion
	dataEncoder := gob.NewEncoder(file)
	dataEncoder.Encode(torrent)
}

// readFromFile reads a torrent from a file
func (t *TorrentManager) readFromFile(torrentID string) *Torrent {
	filePath := fmt.Sprintf("data/%s.bin", torrentID)
	fileInfo, err := os.Stat(filePath)
	if err != nil {
		return nil
	}

	if time.Since(fileInfo.ModTime()) > time.Duration(t.config.GetCacheTimeHours())*time.Hour {
		return nil
	}

	file, err := os.Open(filePath)
	if err != nil {
		return nil
	}
	defer file.Close()

	var torrent Torrent
	dataDecoder := gob.NewDecoder(file)
	err = dataDecoder.Decode(&torrent)
	if err != nil {
		return nil
	}
	if torrent.Version != t.requiredVersion {
		return nil
	}
	return &torrent
}

func (t *TorrentManager) repairAll(wg *sync.WaitGroup) {
	wg.Wait()
	for _, torrent := range t.torrents {
		if torrent.ForRepair {
			t.log.Infof("Issues were detected on %s %s; fixing...", torrent.ID, torrent.Name)
			t.repair(torrent.ID, torrent.SelectedFiles, true)
		}
		if len(torrent.Links) == 0 && torrent.Progress == 100 {
			// If the torrent has no links
			// and already processing repair
			// delete it!
			t.log.Infof("Deleting broken torrent %s %s as it doesn't contain any files", torrent.ID, torrent.Name)
			realdebrid.DeleteTorrent(t.config.GetToken(), torrent.ID)
		}
	}
}

func (t *TorrentManager) repair(torrentID string, selectedFiles []File, tryReinsertionFirst bool) {
	torrent := t.getByID(torrentID)
	if torrent == nil {
		return
	}

	// check if it is already "being" repaired
	found := false
	for _, hash := range t.inProgress {
		if hash == torrent.Hash {
			found = true
			break
		}
	}
	if found {
		t.log.Infof("Repair in progress, skipping %s", torrentID)
		return
	}

	// check if it is already repaired
	foundFiles := t.findAllDownloadedFilesFromHash(torrent.Hash)
	var missingFiles []File
	for _, sFile := range selectedFiles {
		if sFile.Link == "" || sFile.Unavailable {
			found := false
			for _, fFile := range foundFiles {
				// same file but different link, then yes it has been repaired
				if sFile.Path == fFile.Path && sFile.Link != fFile.Link {
					found = true
					break
				}
			}
			if !found {
				missingFiles = append(missingFiles, sFile)
			}
		}
	}
	if len(missingFiles) == 0 {
		t.log.Infof("Torrent %s %s is already repaired", torrent.ID, torrent.Name)
		return
	}

	// then we repair it!
	t.log.Infof("Repairing torrent %s %s", torrent.ID, torrent.Name)
	// check if we can still add more downloads
	proceed := t.canCapacityHandle()
	if !proceed {
		t.log.Error("Cannot add more torrents, exiting")
		return
	}

	// first solution: add the same selection, maybe it can be fixed by reinsertion?
	success := false
	if tryReinsertionFirst {
		success = t.reinsertTorrent(torrent, "", true)
	}
	if !success {
		// if all the selected files are missing but there are other streamable files
		var otherStreamableFileIDs []int
		for _, file := range torrent.Files {
			found := false
			for _, selectedFile := range selectedFiles {
				if selectedFile.ID == file.ID {
					found = true
					break
				}
			}
			if !found && isStreamable(file.Path) {
				otherStreamableFileIDs = append(otherStreamableFileIDs, file.ID)
			}
		}
		if (len(missingFiles) == len(selectedFiles) || len(missingFiles) == 1) && len(otherStreamableFileIDs) > 0 {
			// we will download 1 extra streamable file to force a redownload of the missing files
			// or if there's only 1 missing file, we will download 1 more to prevent a rename
			missingFilesPlus1 := strings.Join(getFileIDs(missingFiles), ",")
			t.log.Infof("Redownloading %d missing files", len(missingFiles))
			t.reinsertTorrent(torrent, missingFilesPlus1, false)
		} else if len(selectedFiles) > 1 {
			// if not, last resort: add only the missing files but do it in 2 batches
			half := len(missingFiles) / 2
			missingFiles1 := strings.Join(getFileIDs(missingFiles[:half]), ",")
			missingFiles2 := strings.Join(getFileIDs(missingFiles[half:]), ",")
			if missingFiles1 != "" {
				t.log.Infof("Redownloading %d missing files; batch 1 of 2", len(missingFiles1))
				t.reinsertTorrent(torrent, missingFiles1, false)
			}
			if missingFiles2 != "" {
				t.log.Infof("Redownloading %d missing files; batch 2 of 2", len(missingFiles2))
				t.reinsertTorrent(torrent, missingFiles2, false)
			} else {
				t.log.Info("No other missing files left to reinsert")
			}
		} else {
			t.log.Infof("Torrent %s %s is unfixable as the only link cached in RD is already broken", torrent.ID, torrent.Name)
			t.log.Debugf("You can try fixing it yourself magnet:?xt=urn:btih:%s", torrent.Hash)
			return
		}
		t.log.Info("Waiting for downloads to finish")
	}
}

func (t *TorrentManager) reinsertTorrent(torrent *Torrent, missingFiles string, deleteIfFailed bool) bool {
	// if missingFiles is not provided, look for missing files
	if missingFiles == "" {
		t.log.Info("Redownloading whole torrent", torrent.Name)
		var selection string
		for _, file := range torrent.SelectedFiles {
			selection += fmt.Sprintf("%d,", file.ID)
		}
		if selection == "" {
			return false
		}
		if len(selection) > 0 {
			missingFiles = selection[:len(selection)-1]
		}
	}

	// redownload torrent
	resp, err := realdebrid.AddMagnetHash(t.config.GetToken(), torrent.Hash)
	if err != nil {
		t.log.Errorf("Cannot redownload torrent: %v", err)
		return false
	}
	newTorrentID := resp.ID
	err = realdebrid.SelectTorrentFiles(t.config.GetToken(), newTorrentID, missingFiles)
	if err != nil {
		t.log.Errorf("Cannot start redownloading: %v", err)
	}

	if deleteIfFailed {
		if err != nil {
			realdebrid.DeleteTorrent(t.config.GetToken(), newTorrentID)
			return false
		}
		time.Sleep(1 * time.Second)
		// see if the torrent is ready
		info, err := realdebrid.GetTorrentInfo(t.config.GetToken(), newTorrentID)
		if err != nil {
			t.log.Errorf("Cannot get info on redownloaded torrent: %v", err)
			if deleteIfFailed {
				realdebrid.DeleteTorrent(t.config.GetToken(), newTorrentID)
			}
			return false
		}
		time.Sleep(1 * time.Second)

		if info.Progress != 100 {
			t.log.Infof("Torrent is not cached anymore so we have to wait until completion, currently %d%%", info.Progress)
			realdebrid.DeleteTorrent(t.config.GetToken(), newTorrentID)
			return false
		}

		if len(info.Links) != len(torrent.SelectedFiles) {
			t.log.Infof("It didn't fix the issue, only got %d files but we need %d, undoing", len(info.Links), len(torrent.SelectedFiles))
			realdebrid.DeleteTorrent(t.config.GetToken(), newTorrentID)
			return false
		}
		t.log.Info("Redownload successful, deleting old torrent")
		realdebrid.DeleteTorrent(t.config.GetToken(), torrent.ID)
	}
	return true
}

func (t *TorrentManager) organizeChaos(info *realdebrid.Torrent, selectedFiles []File) ([]File, bool) {
	type Result struct {
		Response *realdebrid.UnrestrictResponse
	}

	resultsChan := make(chan Result, len(info.Links))
	var wg sync.WaitGroup

	// Limit concurrency
	sem := make(chan struct{}, t.config.GetNumOfWorkers())

	for _, link := range info.Links {
		wg.Add(1)
		sem <- struct{}{}
		go func(lnk string) {
			defer wg.Done()
			defer func() { <-sem }()

			unrestrictFn := func() (*realdebrid.UnrestrictResponse, error) {
				return realdebrid.UnrestrictCheck(t.config.GetToken(), lnk)
			}
			resp := realdebrid.RetryUntilOk(unrestrictFn)
			if resp != nil {
				resultsChan <- Result{Response: resp}
			}
		}(link)
	}

	go func() {
		wg.Wait()
		close(sem)
		close(resultsChan)
	}()

	isChaotic := false
	for result := range resultsChan {
		found := false
		for i := range selectedFiles {
			if strings.HasSuffix(selectedFiles[i].Path, result.Response.Filename) {
				selectedFiles[i].Link = result.Response.Link
				found = true
			}
		}
		if !found {
			// "chaos" file, we don't know where it belongs
			isChaotic = !isStreamable(result.Response.Filename)
			selectedFiles = append(selectedFiles, File{
				File: realdebrid.File{
					Path:     result.Response.Filename,
					Bytes:    result.Response.Filesize,
					Selected: 1,
				},
				Link: result.Response.Link,
			})
		}
	}

	return selectedFiles, isChaotic
}

func (t *TorrentManager) canCapacityHandle() bool {
	// max waiting time is 45 minutes
	const maxRetries = 50
	const baseDelay = 1 * time.Second
	const maxDelay = 60 * time.Second
	retryCount := 0
	for {
		count, err := realdebrid.GetActiveTorrentCount(t.config.GetToken())
		if err != nil {
			t.log.Errorf("Cannot get active downloads count: %v", err)
			if retryCount >= maxRetries {
				t.log.Error("Max retries reached. Exiting.")
				return false
			}
			delay := time.Duration(math.Pow(2, float64(retryCount))) * baseDelay
			if delay > maxDelay {
				delay = maxDelay
			}
			time.Sleep(delay)
			retryCount++
			continue
		}

		if count.DownloadingCount < count.MaxNumberOfTorrents {
			t.log.Infof("We can still add a new torrent, we have capacity for %d more", count.MaxNumberOfTorrents-count.DownloadingCount)
			return true
		}

		if retryCount >= maxRetries {
			t.log.Error("Max retries reached, exiting")
			return false
		}
		delay := time.Duration(math.Pow(2, float64(retryCount))) * baseDelay
		if delay > maxDelay {
			delay = maxDelay
		}
		time.Sleep(delay)
		retryCount++
	}
}