package qbittorrent

import (
	"context"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log/slog"
	"os"
	"path"
	"strings"
	"sync"
	"time"

	"git.kmsign.ru/royalcat/tstor/pkg/qbittorrent"
	"git.kmsign.ru/royalcat/tstor/pkg/rlog"
	"git.kmsign.ru/royalcat/tstor/pkg/uring"
	"git.kmsign.ru/royalcat/tstor/src/vfs"
	"github.com/iceber/iouring-go"
)

type FS struct {
	mu      sync.Mutex
	client  *cacheClient
	name    string
	hash    string
	dataDir string // directory where torrent files are stored

	ur *iouring.IOURing

	entries map[string]fileEntry

	log *rlog.Logger

	vfs.FilesystemPrototype
}

type fileEntry struct {
	fs.FileInfo
	Content *qbittorrent.TorrentContent
}

var _ vfs.Filesystem = (*FS)(nil)

func newTorrentFS(ctx context.Context, ur *iouring.IOURing, client *cacheClient, name string, hash string, dataDir string) (*FS, error) {
	ctx, span := trace.Start(ctx, "newTorrentFS")
	defer span.End()

	cnts, err := client.listContent(ctx, hash)
	if err != nil {
		return nil, fmt.Errorf("failed to list content for hash %s: %w", hash, err)
	}

	entries := make(map[string]fileEntry, len(cnts))
	for _, cnt := range cnts {
		if cnt.Priority == qbittorrent.PriorityDoNotDownload {
			continue
		}

		entries[vfs.AbsPath(cnt.Name)] = fileEntry{
			Content:  cnt,
			FileInfo: vfs.NewFileInfo(cnt.Name, cnt.Size),
		}
	}

	return &FS{
		client: client,
		name:   name,
		hash:   hash,

		dataDir: dataDir,

		entries: entries,

		ur: ur,

		log: rlog.Component("qbittorrent", "fs"),

		FilesystemPrototype: vfs.FilesystemPrototype(name),
	}, nil
}

// Open implements vfs.Filesystem.
func (f *FS) Open(ctx context.Context, name string) (vfs.File, error) {
	if name == vfs.Separator {
		return vfs.NewDirFile(name), nil
	}

	if entry, ok := f.entries[name]; ok {
		return openFile(ctx, f.ur, f.client, f.dataDir, f.hash, entry.Content)
	}

	for p := range f.entries {
		if strings.HasPrefix(p, name) {
			return vfs.NewDirFile(name), nil
		}
	}

	return nil, vfs.ErrNotExist
}

// ReadDir implements vfs.Filesystem.
func (f *FS) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, error) {
	infos := make(map[string]fs.FileInfo, len(f.entries))
	for k, v := range f.entries {
		infos[k] = v.FileInfo
	}

	return vfs.ListDirFromInfo(infos, name)
}

// Stat implements vfs.Filesystem.
func (f *FS) Stat(ctx context.Context, name string) (fs.FileInfo, error) {
	name = vfs.AbsPath(path.Clean(name))

	if vfs.IsRoot(name) {
		return vfs.NewDirInfo(f.name), nil
	}

	if entry, ok := f.entries[name]; ok {
		return entry.FileInfo, nil
	}

	for p := range f.entries {
		if strings.HasPrefix(p, name) {
			return vfs.NewDirInfo(name), nil
		}
	}

	return nil, vfs.ErrNotExist
}

// Unlink implements vfs.Filesystem.
func (f *FS) Unlink(ctx context.Context, filename string) error {
	filename = vfs.AbsPath(path.Clean(filename))

	// we cannot delete a torrent itself, cause it will be added on next source scan and all delited files will be restored

	if entry, ok := f.entries[filename]; ok {
		return f.removeFile(ctx, f.hash, entry.Content)
	}

	for p, entry := range f.entries {
		if strings.HasPrefix(p, filename) {
			return f.removeFile(ctx, f.hash, entry.Content)
		}
	}

	return vfs.ErrNotExist
}

func (f *FS) Rename(ctx context.Context, oldpath string, newpath string) error {
	oldpath = vfs.AbsPath(path.Clean(oldpath))
	newpath = vfs.AbsPath(path.Clean(newpath))

	if _, ok := f.entries[oldpath]; ok {
		err := f.client.qb.Torrent().RenameFile(ctx, f.hash, vfs.RelPath(oldpath), vfs.RelPath(newpath))
		if err != nil {
			return fmt.Errorf("failed to rename file %s to %s: %w", oldpath, newpath, err)
		}

		f.mu.Lock()
		defer f.mu.Unlock()

		f.entries[newpath] = f.entries[oldpath]

		return nil
	}

	return vfs.ErrNotExist
}

func (f *FS) removeFile(ctx context.Context, hash string, content *qbittorrent.TorrentContent) error {
	log := f.log.With(slog.String("hash", hash), slog.String("file", content.Name))

	f.mu.Lock()
	defer f.mu.Unlock()

	fpath := vfs.AbsPath(content.Name)

	if _, ok := f.entries[fpath]; !ok {
		return fmt.Errorf("file %s is does not found", fpath)
	}
	delete(f.entries, fpath)

	err := f.client.qb.Torrent().SetFilePriority(ctx, f.hash, content.Index, qbittorrent.PriorityDoNotDownload)
	if err != nil {
		return fmt.Errorf("failed to set priority for torrent %s for file %s: %w", hash, content.Name, err)
	}

	err = os.Remove(path.Join(f.dataDir, vfs.RelPath(content.Name)))
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		log.Warn(ctx, "failed to remove file", rlog.Error(err))
		return fmt.Errorf("failed to remove file %s: %w", content.Name, err)
	}
	return nil
}

func openFile(ctx context.Context, ur *iouring.IOURing, client *cacheClient, torrentDir string, hash string, content *qbittorrent.TorrentContent) (*File, error) {
	props, err := client.getProperties(ctx, hash)
	if err != nil {
		return nil, err
	}

	// FIXME error when file not started downloading
	file, err := os.OpenFile(path.Join(torrentDir, content.Name), os.O_RDONLY, 0)
	if err != nil {
		return nil, err
	}

	return &File{
		client:     client,
		hash:       hash,
		torrentDir: torrentDir,

		filePath:     content.Name,
		contentIndex: content.Index,
		pieceSize:    props.PieceSize,
		fileSize:     content.Size,

		file: uring.NewFile(ur, file),

		offset: 0,
	}, nil
}

type File struct {
	client       *cacheClient
	hash         string
	torrentDir   string
	filePath     string // path inside a torrent directory
	contentIndex int
	pieceSize    int
	fileSize     int64

	mu     sync.Mutex
	file   *uring.File
	offset int64
}

var _ vfs.File = (*File)(nil)

// Info implements vfs.File.
func (f *File) Info() (fs.FileInfo, error) {
	return &fileInfo{name: path.Base(f.filePath), size: f.fileSize}, nil
}

// IsDir implements vfs.File.
func (f *File) IsDir() bool {
	return false
}

// Seek implements vfs.File.
func (f *File) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekStart:
		f.offset = offset
	case io.SeekCurrent:
		f.offset += offset
	case io.SeekEnd:
		f.offset = f.fileSize + offset
	}
	return f.offset, nil
}

// Name implements vfs.File.
func (f *File) Name() string {
	return path.Base(f.filePath)
}

func (f *File) canExpectSoon(ctx context.Context) (bool, error) {
	info, err := f.client.getInfo(ctx, f.hash)
	if err != nil {
		return false, err
	}

	return info.Completed == info.Size || info.State == qbittorrent.TorrentStateCheckingUP || info.State == qbittorrent.TorrentStateDownloading || info.State == qbittorrent.TorrentStateForcedDL, nil
}

func (f *File) isRangeComplete(ctx context.Context, offset int64, size int) (bool, error) {
	startPieceIndex := int(offset / int64(f.pieceSize))
	pieceCount := (size + f.pieceSize - 1) / f.pieceSize // rouding up

	for i := range pieceCount {
		ok, err := f.client.isPieceComplete(ctx, f.hash, startPieceIndex+i)
		if err != nil {
			return false, err
		}
		if !ok {
			return false, nil
		}
	}

	return true, nil
}

func (f *File) waitPieceAvailable(ctx context.Context, offset int64, size int) error {
	complete, err := f.isRangeComplete(ctx, offset, size)
	if err != nil {
		return err
	}
	if complete {
		return nil
	}

	canExpectSoon, err := f.canExpectSoon(ctx)
	if err != nil {
		return err
	}
	if !canExpectSoon {
		return fmt.Errorf("torrent is not downloading")
	}

	const checkingInterval = 1 * time.Second

	ticker := time.NewTicker(checkingInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			complete, err := f.isRangeComplete(ctx, offset, size)
			if err != nil {
				return err
			}
			if complete {
				return nil
			}
		}
	}
}

// Read implements vfs.File.
func (f *File) Read(ctx context.Context, p []byte) (int, error) {
	f.mu.Lock()
	defer f.mu.Unlock()

	if err := f.waitPieceAvailable(ctx, f.offset, len(p)); err != nil {
		return 0, err
	}

	n, err := f.file.ReadAt(ctx, p, f.offset)
	f.offset += int64(n)
	return n, err
}

// ReadAt implements vfs.File.
func (f *File) ReadAt(ctx context.Context, p []byte, off int64) (int, error) {
	if err := f.waitPieceAvailable(ctx, f.offset, len(p)); err != nil {
		return 0, err
	}

	return f.file.ReadAt(ctx, p, off)
}

// Size implements vfs.File.
func (f *File) Size() int64 {
	return f.fileSize
}

// Type implements vfs.File.
func (f *File) Type() fs.FileMode {
	return fs.ModeDir
}

// Close implements vfs.File.
func (f *File) Close(ctx context.Context) error {
	return f.file.Close(ctx)
}

type fileInfo struct {
	name string
	size int64
}

var _ fs.FileInfo = (*fileInfo)(nil)

// IsDir implements fs.FileInfo.
func (f *fileInfo) IsDir() bool {
	return false
}

// ModTime implements fs.FileInfo.
func (f *fileInfo) ModTime() time.Time {
	return time.Time{}
}

// Mode implements fs.FileInfo.
func (f *fileInfo) Mode() fs.FileMode {
	return vfs.ROMode
}

// Name implements fs.FileInfo.
func (f *fileInfo) Name() string {
	return f.name
}

// Size implements fs.FileInfo.
func (f *fileInfo) Size() int64 {
	return f.size
}

// Sys implements fs.FileInfo.
func (f *fileInfo) Sys() any {
	return nil
}