package torrent

import (
	"context"
	"fmt"
	"io"
	"io/fs"
	"log/slog"
	"path"
	"slices"
	"strings"
	"sync"
	"sync/atomic"
	"time"

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

type TorrentFS struct {
	name string

	Torrent *Controller

	filesCacheMu sync.Mutex
	filesCache   map[string]vfs.File

	lastTorrentReadTimeout atomic.Pointer[time.Time]

	resolver *vfs.Resolver
}

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

const shortTimeout = time.Millisecond
const lowTimeout = time.Second * 5

func (s *Daemon) NewTorrentFs(ctx context.Context, _ string, f vfs.File) (vfs.Filesystem, error) {
	c, err := s.loadTorrent(ctx, f)
	if err != nil {
		return nil, err
	}

	if err := f.Close(ctx); err != nil {
		s.log.Error(ctx, "failed to close file", slog.String("name", f.Name()), rlog.Error(err))
	}

	return &TorrentFS{
		name:     f.Name(),
		Torrent:  c,
		resolver: vfs.NewResolver(vfs.ArchiveFactories),
	}, nil
}

var _ fs.DirEntry = (*TorrentFS)(nil)

// Name implements fs.DirEntry.
func (tfs *TorrentFS) Name() string {
	return tfs.name
}

// Info implements fs.DirEntry.
func (tfs *TorrentFS) Info() (fs.FileInfo, error) {
	return tfs, nil
}

// IsDir implements fs.DirEntry.
func (tfs *TorrentFS) IsDir() bool {
	return true
}

// Type implements fs.DirEntry.
func (tfs *TorrentFS) Type() fs.FileMode {
	return fs.ModeDir
}

// ModTime implements fs.FileInfo.
func (tfs *TorrentFS) ModTime() time.Time {
	return time.Time{}
}

// Mode implements fs.FileInfo.
func (tfs *TorrentFS) Mode() fs.FileMode {
	return fs.ModeDir
}

// Size implements fs.FileInfo.
func (tfs *TorrentFS) Size() int64 {
	return 0
}

// Sys implements fs.FileInfo.
func (tfs *TorrentFS) Sys() any {
	return nil
}

// FsName implements Filesystem.
func (tfs *TorrentFS) FsName() string {
	return "torrentfs"
}

func (fs *TorrentFS) files(ctx context.Context) (map[string]vfs.File, error) {
	fs.filesCacheMu.Lock()
	defer fs.filesCacheMu.Unlock()

	if fs.filesCache != nil {
		return fs.filesCache, nil
	}

	ctx, span := tracer.Start(ctx, "files", fs.traceAttrs())
	defer span.End()

	files, err := fs.Torrent.Files(ctx)
	if err != nil {
		return nil, err
	}

	fs.filesCache = make(map[string]vfs.File)
	for _, file := range files {
		props, err := file.Properties(ctx)
		if err != nil {
			return nil, err
		}
		if props.Excluded {
			continue
		}

		p := vfs.AbsPath(file.Path())
		tf, err := openTorrentFile(ctx, path.Base(p), file.file, &fs.lastTorrentReadTimeout)
		if err != nil {
			return nil, err
		}
		fs.filesCache[p] = tf
	}

	// TODO optional
	// if len(fs.filesCache) == 1 && fs.resolver.IsNestedFs(fs.Torrent.Name()) {
	// 	filepath := "/" + fs.Torrent.Name()
	// 	if file, ok := fs.filesCache[filepath]; ok {
	// 		nestedFs, err := fs.resolver.NestedFs(ctx, filepath, file)
	// 		if err != nil {
	// 			return nil, err
	// 		}
	// 		if nestedFs == nil {
	// 			goto DEFAULT_DIR // FIXME
	// 		}
	// 		fs.filesCache, err = listFilesRecursive(ctx, nestedFs, "/")
	// 		if err != nil {
	// 			return nil, err
	// 		}

	// 		return fs.filesCache, nil
	// 	}
	// }
	// DEFAULT_DIR:

	rootDir := "/" + fs.Torrent.Name() + "/"
	singleDir := true
	for k, _ := range fs.filesCache {
		if !strings.HasPrefix(k, rootDir) {
			singleDir = false
		}
	}
	if singleDir {
		for k, f := range fs.filesCache {
			delete(fs.filesCache, k)
			k, _ = strings.CutPrefix(k, rootDir)
			k = vfs.AbsPath(k)
			fs.filesCache[k] = f
		}
	}

	return fs.filesCache, nil
}

func listFilesRecursive(ctx context.Context, fs vfs.Filesystem, start string) (map[string]vfs.File, error) {
	out := make(map[string]vfs.File, 0)
	entries, err := fs.ReadDir(ctx, start)
	if err != nil {
		return nil, err
	}
	for _, entry := range entries {
		filename := path.Join(start, entry.Name())
		if entry.IsDir() {
			rec, err := listFilesRecursive(ctx, fs, filename)
			if err != nil {
				return nil, err
			}
			maps.Copy(out, rec)
		} else {
			file, err := fs.Open(ctx, filename)
			if err != nil {
				return nil, err
			}
			out[filename] = file
		}
	}

	return out, nil
}

func (fs *TorrentFS) rawOpen(ctx context.Context, filename string) (file vfs.File, err error) {
	ctx, span := tracer.Start(ctx, "rawOpen",
		fs.traceAttrs(attribute.String("filename", filename)),
	)
	defer func() {
		if err != nil {
			span.RecordError(err)
		}
		span.End()
	}()

	files, err := fs.files(ctx)
	if err != nil {
		return nil, err
	}
	file, err = vfs.GetFile(files, filename)
	return file, err
}

func (fs *TorrentFS) rawStat(ctx context.Context, filename string) (fs.FileInfo, error) {
	ctx, span := tracer.Start(ctx, "rawStat",
		fs.traceAttrs(attribute.String("filename", filename)),
	)
	defer span.End()

	files, err := fs.files(ctx)
	if err != nil {
		return nil, err
	}

	file, err := vfs.GetFile(files, filename)
	if err != nil {
		return nil, err
	}
	return file.Info()
}

func (fs *TorrentFS) traceAttrs(add ...attribute.KeyValue) trace.SpanStartOption {
	return trace.WithAttributes(append([]attribute.KeyValue{
		attribute.String("fs", fs.FsName()),
		attribute.String("torrent", fs.Torrent.Name()),
		attribute.String("infohash", fs.Torrent.InfoHash()),
	}, add...)...)
}

func (tfs *TorrentFS) readContext(ctx context.Context) (context.Context, context.CancelFunc) {
	lastReadTimeout := tfs.lastTorrentReadTimeout.Load()
	if lastReadTimeout != nil && time.Since(*lastReadTimeout) < secondaryTimeout { // make short timeout for already faliled files
		trace.SpanFromContext(ctx).SetAttributes(attribute.Bool("short_timeout", true))

		return context.WithTimeout(ctx, shortTimeout)
	}

	return ctx, func() {}
}

// Stat implements Filesystem.
func (tfs *TorrentFS) Stat(ctx context.Context, filename string) (fs.FileInfo, error) {
	ctx, span := tracer.Start(ctx, "Stat",
		tfs.traceAttrs(attribute.String("filename", filename)),
	)
	defer span.End()

	if vfs.IsRoot(filename) {
		return tfs, nil
	}

	var err error
	ctx, cancel := tfs.readContext(ctx)
	defer func() {
		cancel()
		if err == context.DeadlineExceeded {
			now := time.Now()
			tfs.lastTorrentReadTimeout.Store(&now)
		}
	}()

	fsPath, nestedFs, nestedFsPath, err := tfs.resolver.ResolvePath(ctx, filename, tfs.rawOpen)
	if err != nil {
		return nil, err
	}
	if nestedFs != nil {
		return nestedFs.Stat(ctx, nestedFsPath)
	}

	return tfs.rawStat(ctx, fsPath)
}

func (tfs *TorrentFS) Open(ctx context.Context, filename string) (file vfs.File, err error) {
	ctx, span := tracer.Start(ctx, "Open",
		tfs.traceAttrs(attribute.String("filename", filename)),
	)
	defer span.End()

	if vfs.IsRoot(filename) {
		return vfs.NewDirFile(tfs.name), nil
	}

	ctx, cancel := tfs.readContext(ctx)
	defer func() {
		cancel()
		if err == context.DeadlineExceeded {
			now := time.Now()
			tfs.lastTorrentReadTimeout.Store(&now)
		}
	}()

	fsPath, nestedFs, nestedFsPath, err := tfs.resolver.ResolvePath(ctx, filename, tfs.rawOpen)
	if err != nil {
		return nil, err
	}
	if nestedFs != nil {
		return nestedFs.Open(ctx, nestedFsPath)
	}

	return tfs.rawOpen(ctx, fsPath)
}

func (tfs *TorrentFS) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, error) {
	ctx, span := tracer.Start(ctx, "ReadDir",
		tfs.traceAttrs(attribute.String("name", name)),
	)
	defer span.End()

	var err error
	ctx, cancel := tfs.readContext(ctx)
	defer func() {
		cancel()
		if err == context.DeadlineExceeded {
			now := time.Now()
			tfs.lastTorrentReadTimeout.Store(&now)
		}
	}()

	fsPath, nestedFs, nestedFsPath, err := tfs.resolver.ResolvePath(ctx, name, tfs.rawOpen)
	if err != nil {
		return nil, err
	}
	if nestedFs != nil {
		return nestedFs.ReadDir(ctx, nestedFsPath)
	}
	files, err := tfs.files(ctx)
	if err != nil {
		return nil, err
	}

	return vfs.ListDirFromFiles(files, fsPath)
}

func (fs *TorrentFS) Unlink(ctx context.Context, name string) error {
	ctx, span := tracer.Start(ctx, "Unlink",
		fs.traceAttrs(attribute.String("name", name)),
	)
	defer span.End()

	name = vfs.AbsPath(name)

	files, err := fs.files(ctx)
	if err != nil {
		return err
	}

	if !slices.Contains(maps.Keys(files), name) {
		return vfs.ErrNotExist
	}

	file := files[name]

	fs.filesCacheMu.Lock()
	delete(fs.filesCache, name)
	fs.filesCacheMu.Unlock()

	tfile, ok := file.(*torrentFile)
	if !ok {
		return vfs.ErrNotImplemented
	}

	return fs.Torrent.ExcludeFile(ctx, tfile.file)
}

// Rename implements vfs.Filesystem.
func (s *TorrentFS) Rename(ctx context.Context, oldpath string, newpath string) error {
	return vfs.ErrNotImplemented
}

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

type torrentFile struct {
	name string

	mu sync.RWMutex

	tr torrent.Reader

	lastReadTimeout        atomic.Pointer[time.Time]
	lastTorrentReadTimeout *atomic.Pointer[time.Time]

	file *torrent.File
}

const secondaryTimeout = time.Hour * 24

func openTorrentFile(ctx context.Context, name string, file *torrent.File, lastTorrentReadTimeout *atomic.Pointer[time.Time]) (*torrentFile, error) {
	select {
	case <-file.Torrent().GotInfo():
		break
	case <-ctx.Done():
		return nil, ctx.Err()
	}

	r := file.NewReader()
	_, err := r.ReadContext(ctx, make([]byte, 128))
	if err != nil && err != io.EOF {
		return nil, fmt.Errorf("failed initial file read: %w", err)
	}
	_, err = r.Seek(0, io.SeekStart)
	if err != nil {
		return nil, fmt.Errorf("failed seeking to start, after initial read: %w", err)
	}

	return &torrentFile{
		name:                   name,
		tr:                     r,
		file:                   file,
		lastTorrentReadTimeout: lastTorrentReadTimeout,
	}, nil
}

// Name implements File.
func (tf *torrentFile) Name() string {
	return tf.name
}

// Seek implements vfs.File.
func (tf *torrentFile) Seek(offset int64, whence int) (int64, error) {
	tf.mu.Lock()
	defer tf.mu.Unlock()

	return tf.tr.Seek(offset, whence)
}

// Type implements File.
func (tf *torrentFile) Type() fs.FileMode {
	return vfs.ModeFileRO | fs.ModeDir
}

func (tf *torrentFile) Info() (fs.FileInfo, error) {
	return vfs.NewFileInfo(tf.name, tf.file.Length(), time.Time{}), nil
}

func (tf *torrentFile) Size() int64 {
	return tf.file.Length()
}

func (tf *torrentFile) IsDir() bool {
	return false
}

func (rw *torrentFile) Close(ctx context.Context) error {
	rw.mu.Lock()
	defer rw.mu.Unlock()

	return rw.tr.Close()
}

func (tf *torrentFile) readTimeout(ctx context.Context) (context.Context, context.CancelFunc) {
	lastReadTimeout := tf.lastReadTimeout.Load()
	if lastReadTimeout != nil && time.Since(*lastReadTimeout) < secondaryTimeout { // make short timeout for already faliled files
		trace.SpanFromContext(ctx).SetAttributes(attribute.Bool("short_timeout", true))
		return context.WithTimeout(ctx, shortTimeout)
	}

	lastTorrentReadTimeout := tf.lastTorrentReadTimeout.Load()
	if lastTorrentReadTimeout != nil && time.Since(*lastTorrentReadTimeout) < secondaryTimeout { // make short timeout for already faliled files
		trace.SpanFromContext(ctx).SetAttributes(attribute.Bool("low_timeout", true))
		return context.WithTimeout(ctx, lowTimeout)
	}

	return ctx, func() {}
}

// Read implements ctxio.Reader.
func (tf *torrentFile) Read(ctx context.Context, p []byte) (n int, err error) {
	ctx, span := tracer.Start(ctx, "Read",
		trace.WithAttributes(attribute.Int("length", len(p))),
	)
	defer func() {
		span.SetAttributes(attribute.Int("read", n))
		span.End()
	}()

	tf.mu.Lock()
	defer tf.mu.Unlock()

	ctx, cancel := tf.readTimeout(ctx)
	defer cancel()
	defer func() {
		if err == context.DeadlineExceeded {
			now := time.Now()
			tf.lastReadTimeout.Store(&now)
			tf.lastTorrentReadTimeout.Store(&now)
		}
	}()

	return tf.tr.ReadContext(ctx, p)
}

func (tf *torrentFile) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
	ctx, span := tracer.Start(ctx, "ReadAt",
		trace.WithAttributes(attribute.Int("length", len(p)), attribute.Int64("offset", off)),
	)
	defer func() {
		span.SetAttributes(attribute.Int("read", n))
		span.End()
	}()

	tf.mu.RLock()
	defer tf.mu.RUnlock()

	ctx, cancel := tf.readTimeout(ctx)
	defer cancel()
	defer func() {
		if err == context.DeadlineExceeded {
			now := time.Now()
			tf.lastReadTimeout.Store(&now)
			tf.lastTorrentReadTimeout.Store(&now)
		}
	}()

	_, err = tf.tr.Seek(off, io.SeekStart)
	if err != nil {
		return 0, err
	}

	// return tf.tr.ReadContext(ctx, p)
	n, err = readAtLeast(ctx, tf.tr, p, len(p))

	_, err = tf.tr.Seek(0, io.SeekStart)
	if err != nil {
		return 0, err
	}

	return n, err
}

func readAtLeast(ctx context.Context, r torrent.Reader, buf []byte, min int) (n int, err error) {
	if len(buf) < min {
		return 0, io.ErrShortBuffer
	}
	for n < min && err == nil {
		var nn int

		nn, err = r.ReadContext(ctx, buf[n:])
		n += nn
	}
	if n >= min {
		err = nil
	} else if n > 0 && err == io.EOF {
		err = io.ErrUnexpectedEOF
	}
	return
}