package cache

import (
	"fmt"
	"io"
	"os"
	"sync"
	"time"

	"gitlink.org.cn/cloudream/common/pkgs/logger"
	cdssdk "gitlink.org.cn/cloudream/common/sdks/storage"
	"gitlink.org.cn/cloudream/common/utils/io2"
	"gitlink.org.cn/cloudream/common/utils/lo2"
	"gitlink.org.cn/cloudream/common/utils/math2"
	"gitlink.org.cn/cloudream/common/utils/serder"
	"gitlink.org.cn/cloudream/storage/client2/internal/mount/fuse"
)

type FileInfo struct {
	// 文件总大小。可能会超过对应的远端文件的大小。
	// 此大小可能与本地缓存文件大小也不同，需要定时将本地缓存文件大小修正到与这个值相同。
	Size int64
	// 本文件是否有未提交的修改
	Dirty bool
	// 数据段列表，按照段开始位置从小到大排列
	Segments []*Range
	// 文件对应的对象ID，仅在文件是一个缓存文件时才有值
	// ObjectID cdssdk.ObjectID
	// 文件对应的对象大小，仅在文件是一个缓存文件时才有值。
	// 此值代表有多少数据应该从远端加载，所以可能会小于远端实际大小
	ObjectSize int64
	// 如果本文件完全是一个缓存文件，那么这个字段记录了其内容的哈希值，用于在下载缓存数据时，检查远端文件是否被修改过
	// Hash cdssdk.FileHash
	// 文件的最后修改时间
	ModTime time.Time
	// 文件的权限
	Perm os.FileMode
}

func (f *FileInfo) Clone() FileInfo {
	n := *f
	n.Segments = make([]*Range, len(f.Segments))
	for i, seg := range f.Segments {
		n.Segments[i] = &Range{
			Position: seg.Position,
			Length:   seg.Length,
		}
	}

	return n
}

type Range struct {
	Position int64
	Length   int64
}

func (r *Range) GetPosition() int64 {
	return r.Position
}

func (r *Range) SetPosition(pos int64) {
	r.Position = pos
}

func (r *Range) GetLength() int64 {
	return r.Length
}

func (r *Range) SetLength(length int64) {
	r.Length = length
}

func (r *Range) End() int64 {
	return r.Position + r.Length
}

// 所有读写过程共用同一个CacheFile对象。
// 不应该将此结构体保存到对象中
type CacheFile struct {
	cache          *Cache
	pathComps      []string
	name           string
	info           FileInfo
	remoteObj      *cdssdk.Object
	infoRev        int64
	rwLock         *sync.RWMutex
	readers        []*CacheFileReadWriter
	writers        []*CacheFileReadWriter
	savingMetaChan chan any
	isDeleted      bool

	metaFile  *os.File
	dataFile  *os.File
	writeLock *sync.RWMutex
}

func createNewCacheFile(cache *Cache, pathComps []string) (*CacheFile, error) {
	metaPath := cache.GetCacheMetaPath(pathComps...)
	dataPath := cache.GetCacheDataPath(pathComps...)

	info := FileInfo{
		Dirty:   true,
		ModTime: time.Now(),
		Perm:    0777,
	}

	infoData, err := serder.ObjectToJSON(info)
	if err != nil {
		return nil, err
	}

	metaFile, err := os.OpenFile(metaPath, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		return nil, fmt.Errorf("create cache meta file: %w", err)
	}

	err = io2.WriteAll(metaFile, infoData)
	if err != nil {
		metaFile.Close()
		return nil, fmt.Errorf("save cache meta file: %w", err)
	}

	dataFile, err := os.OpenFile(dataPath, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		metaFile.Close()
		return nil, fmt.Errorf("create cache data file: %w", err)
	}

	ch := &CacheFile{
		cache:          cache,
		pathComps:      pathComps,
		name:           pathComps[len(pathComps)-1],
		info:           info,
		rwLock:         &sync.RWMutex{},
		savingMetaChan: make(chan any, 1),
		metaFile:       metaFile,
		dataFile:       dataFile,
		writeLock:      &sync.RWMutex{},
	}

	go ch.savingMeta()

	return ch, nil
}

func loadCacheFile(cache *Cache, pathComps []string) (*CacheFile, error) {
	metaPath := cache.GetCacheMetaPath(pathComps...)
	dataPath := cache.GetCacheDataPath(pathComps...)

	metaFile, err := os.OpenFile(metaPath, os.O_CREATE|os.O_RDWR, 0644)
	if err != nil {
		return nil, fmt.Errorf("open cache meta file: %w", err)
	}

	info := &FileInfo{}
	err = serder.JSONToObjectStream(metaFile, info)
	if err != nil {
		metaFile.Close()
		return nil, err
	}

	dataFile, err := os.OpenFile(dataPath, os.O_CREATE|os.O_RDWR, 0644)
	if err != nil {
		metaFile.Close()
		return nil, fmt.Errorf("open cache data file: %w", err)
	}

	ch := &CacheFile{
		cache:          cache,
		pathComps:      pathComps,
		name:           pathComps[len(pathComps)-1],
		info:           *info,
		rwLock:         &sync.RWMutex{},
		savingMetaChan: make(chan any, 1),
		metaFile:       metaFile,
		dataFile:       dataFile,
		writeLock:      &sync.RWMutex{},
	}

	go ch.savingMeta()

	return ch, nil
}

func newCacheFileFromObject(cache *Cache, pathComps []string, obj *cdssdk.Object) (*CacheFile, error) {
	metaPath := cache.GetCacheMetaPath(pathComps...)
	dataPath := cache.GetCacheDataPath(pathComps...)

	info := FileInfo{
		Size:       obj.Size,
		ObjectSize: obj.Size,
		ModTime:    obj.UpdateTime,
		Perm:       0755,
	}

	infoData, err := serder.ObjectToJSON(info)
	if err != nil {
		return nil, err
	}

	metaFile, err := os.OpenFile(metaPath, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		return nil, fmt.Errorf("create cache meta file: %w", err)
	}

	err = io2.WriteAll(metaFile, infoData)
	if err != nil {
		metaFile.Close()
		return nil, fmt.Errorf("save cache meta file: %w", err)
	}

	dataFile, err := os.OpenFile(dataPath, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		metaFile.Close()
		return nil, fmt.Errorf("create cache file: %w", err)
	}

	ch := &CacheFile{
		cache:          cache,
		pathComps:      pathComps,
		name:           pathComps[len(pathComps)-1],
		info:           info,
		remoteObj:      obj,
		rwLock:         &sync.RWMutex{},
		savingMetaChan: make(chan any, 1),
		metaFile:       metaFile,
		dataFile:       dataFile,
		writeLock:      &sync.RWMutex{},
	}

	go ch.savingMeta()

	return ch, nil
}

func loadCacheFileInfo(cache *Cache, pathComps []string) (*CacheEntryInfo, error) {
	metaPath := cache.GetCacheMetaPath(pathComps...)

	metaData, err := os.ReadFile(metaPath)
	if err != nil {
		return nil, err
	}

	info := &FileInfo{}
	err = serder.JSONToObject(metaData, info)
	if err != nil {
		return nil, err
	}

	return &CacheEntryInfo{
		PathComps: pathComps,
		Size:      info.Size,
		Mode:      info.Perm,
		ModTime:   info.ModTime,
		IsDir:     false,
	}, nil
}

func (f *CacheFile) PathComps() []string {
	return f.pathComps
}

func (f *CacheFile) Name() string {
	return f.name
}

func (f *CacheFile) Size() int64 {
	return f.info.Size
}

func (f *CacheFile) Mode() os.FileMode {
	return f.info.Perm
}

func (f *CacheFile) ModTime() time.Time {
	return f.info.ModTime
}

func (f *CacheFile) IsDir() bool {
	return false
}

func (f *CacheFile) Info() CacheEntryInfo {
	return CacheEntryInfo{
		PathComps: f.pathComps,
		Size:      f.info.Size,
		Mode:      f.info.Perm,
		ModTime:   f.info.ModTime,
		IsDir:     false,
	}
}

func (f *CacheFile) Delete() {
	f.writeLock.Lock()
	defer f.writeLock.Unlock()

	f.rwLock.Lock()
	defer f.rwLock.Unlock()

	metaPath := f.cache.GetCacheMetaPath(f.pathComps...)
	dataPath := f.cache.GetCacheDataPath(f.pathComps...)
	os.Remove(metaPath)
	os.Remove(dataPath)
	f.isDeleted = true

	f.letSave()
}

func (f *CacheFile) Move(newPathComps []string) {
	f.writeLock.Lock()
	defer f.writeLock.Unlock()

	f.rwLock.Lock()
	defer f.rwLock.Unlock()

	f.pathComps = newPathComps
	f.name = newPathComps[len(newPathComps)-1]

	f.letSave()
}

func (f *CacheFile) SetRemoteObject(obj *cdssdk.Object) {
	f.remoteObj = obj
}

// 打开一个写入句柄，同时支持读取
func (f *CacheFile) Open(flags uint32) *CacheFileReadWriter {
	logger.Tracef("CacheFile.Open: %v, %#x", f.name, flags)

	f.rwLock.Lock()
	defer f.rwLock.Unlock()

	h := &CacheFileReadWriter{
		file:       f,
		remoteLock: &sync.Mutex{},
	}

	if flags&uint32(os.O_RDWR) == uint32(os.O_RDWR) {
		h.readable = true
		h.writeable = true
	} else if flags&uint32(os.O_WRONLY) == uint32(os.O_WRONLY) {
		h.writeable = true
	} else if flags&uint32(os.O_RDONLY) == uint32(os.O_RDONLY) {
		h.readable = true
	}

	if f.remoteObj != nil {
		h.remote = newRemoteLoader(f)
	}

	if h.writeable {
		f.writers = append(f.writers, h)
	} else {
		f.readers = append(f.readers, h)
	}

	return h
}

func (f *CacheFile) SetModTime(modTime time.Time) error {
	logger.Tracef("CacheFile.SetModTime: %v, %v", f.pathComps, modTime)

	f.rwLock.Lock()
	f.info.ModTime = modTime
	f.infoRev++
	f.rwLock.Unlock()

	f.letSave()
	return nil
}

func (f *CacheFile) Truncate(size int64) error {
	logger.Tracef("CacheFile.Truncate: %v, %v", f.pathComps, size)

	// 修改文件大小前不允许写入
	f.writeLock.Lock()
	defer f.writeLock.Unlock()

	err := f.dataFile.Truncate(size)
	if err != nil {
		return err
	}

	f.rwLock.Lock()
	defer f.rwLock.Unlock()

	// 调整能从远端下载的大小
	f.info.ObjectSize = math2.Min(f.info.ObjectSize, size)

	// 调整本地缓存文件里的有效数据大小
	if size < f.info.Size {
		f.info.Segments = TruncateRange(f.info.Segments, size)
	} else if size > f.info.Size {
		f.info.Segments = AddRange(f.info.Segments, &Range{Position: f.info.Size, Length: size - f.info.Size})
	}
	if f.info.Size != size {
		f.info.Dirty = true
	}
	f.info.Size = size
	f.infoRev++

	f.letSave()
	return nil
}

// 不再使用缓存文件
// func (f *CacheFile) Release() {

// }

func (f *CacheFile) savingMeta() {
	savedInfoRev := int64(0)
	ticker := time.NewTicker(time.Second * 5)
	defer ticker.Stop()

	for {
		select {
		case _, ok := <-f.savingMetaChan:
			if !ok {
				return
			}

		case <-ticker.C:
		}

		f.rwLock.Lock()

		// 如果文件已被删除，则不能再保存元数据，防止覆盖掉新创建的同名文件
		if f.isDeleted {
			f.rwLock.Unlock()
			break
		}

		for {
			if f.infoRev == savedInfoRev {
				break
			}

			jsonData, err := serder.ObjectToJSON(f.info)
			if err != nil {
				// TODO 日志
				break
			}

			err = f.metaFile.Truncate(0)
			if err != nil {
				// TODO 日志
				break
			}

			_, err = f.metaFile.Seek(0, io.SeekStart)
			if err != nil {
				// TODO 日志
				break
			}

			err = io2.WriteAll(f.metaFile, jsonData)
			if err != nil {
				// TODO 日志
				break
			}

			savedInfoRev = f.infoRev
			break
		}

		f.rwLock.Unlock()
	}
}

func (f *CacheFile) letSave() {
	select {
	case f.savingMetaChan <- nil:
	default:
	}
}

type CacheFileReadWriter struct {
	file       *CacheFile
	readable   bool
	writeable  bool
	remote     *RemoteLoader
	remoteLock *sync.Mutex
}

func (h *CacheFileReadWriter) ReadAt(buf []byte, off int64) (int, error) {
	if !h.readable {
		return 0, fuse.ErrPermission
	}

	logger.Tracef("CacheFileReadWriter.ReadAt: %v, %v, %v", h.file.name, off, len(buf))

	totalReadLen := 0
	for totalReadLen < len(buf) {
		curBuf := buf[totalReadLen:]
		curOff := off + int64(totalReadLen)

		h.file.rwLock.RLock()

		if curOff >= h.file.info.Size {
			h.file.rwLock.RUnlock()
			break
		}

		// 先尝试从本地缓存文件里读取
		rngIdx := FirstContainsIndex(h.file.info.Segments, curOff)
		if rngIdx >= 0 && h.file.info.Segments[rngIdx].End() > curOff {
			readLen := math2.Min(int64(len(curBuf)), h.file.info.Segments[rngIdx].End()-curOff)
			realReadLen, err := h.file.dataFile.ReadAt(curBuf[:readLen], curOff)
			totalReadLen += realReadLen
			h.file.rwLock.RUnlock()

			logger.Tracef("read from local cache, n: %v, err: %v", realReadLen, err)
			if err != nil {
				return totalReadLen, err
			}
			continue
		}

		// 否则从远端下载
		loadLen := math2.Min(int64(len(curBuf)), h.file.info.ObjectSize-curOff)
		if rngIdx+1 < len(h.file.info.Segments) {
			// 最多加载到下一个段的开头
			loadLen = math2.Min(loadLen, h.file.info.Segments[rngIdx+1].Position-curOff)
		}

		h.file.rwLock.RUnlock()

		if h.remote == nil {
			return totalReadLen, fmt.Errorf("no remote file")
		}

		fmt.Printf("load from remote\n")

		// 加锁，防止并发Seek
		h.remoteLock.Lock()
		realLoadLen, err := h.remote.Load(curBuf[:loadLen], curOff)
		totalReadLen += realLoadLen
		if err != nil {
			h.remoteLock.Unlock()
			return totalReadLen, err
		}
		h.remoteLock.Unlock()

		logger.Tracef("load from remote: %v", realLoadLen)

		// 在写入到本地之前，先停止其他的写入，防止冲突
		h.file.writeLock.Lock()

		// 停止其他写入后，就可以计算一下实际要写回的长度。
		h.file.rwLock.RLock()
		loadRng := &Range{Position: curOff, Length: int64(realLoadLen)}
		DifferentRange(loadRng, h.file.info.Segments)
		h.file.rwLock.RUnlock()

		if loadRng.Length == 0 {
			h.file.writeLock.Unlock()
			continue
		}

		// 写入到本地缓存文件
		writeStart := loadRng.Position - curOff
		_, err = h.file.dataFile.WriteAt(curBuf[writeStart:writeStart+loadRng.Length], curOff)
		if err != nil {
			h.file.writeLock.Unlock()

			logger.Tracef("save to local file: %v", err)
			return totalReadLen, fmt.Errorf("save to local file: %w", err)
		}

		logger.Tracef("save to local: %v", loadRng.Length)

		h.file.writeLock.Unlock()

		// 提交到段列表里
		h.file.rwLock.Lock()
		h.file.info.Segments = AddRange(h.file.info.Segments, loadRng)
		h.file.infoRev++
		h.file.letSave()
		h.file.rwLock.Unlock()
	}

	return totalReadLen, nil
}

func (h *CacheFileReadWriter) WriteAt(buf []byte, off int64) (int, error) {
	if !h.writeable {
		return 0, fuse.ErrPermission
	}

	logger.Tracef("CacheFileReadWriter.WriteAt: %v, %v, %v", h.file.name, off, len(buf))

	// 允许多线程并行写入，但在数据加载期间不能写入
	h.file.writeLock.RLock()
	defer h.file.writeLock.RUnlock()

	// 写入到本地缓存文件
	writeLen, err := h.file.dataFile.WriteAt(buf, off)
	if err != nil {
		return writeLen, fmt.Errorf("save to local file: %w", err)
	}

	// 提交到段列表里
	h.file.rwLock.Lock()
	defer h.file.rwLock.Unlock()

	h.file.info.Segments = AddRange(h.file.info.Segments, &Range{Position: off, Length: int64(writeLen)})
	h.file.info.Size = math2.Max(h.file.info.Size, off+int64(writeLen))
	h.file.info.Dirty = true
	h.file.infoRev++

	h.file.letSave()

	return writeLen, nil
}

func (f *CacheFileReadWriter) Sync() error {
	return f.file.dataFile.Sync()
}

func (f *CacheFileReadWriter) Close() error {
	f.Sync()

	if f.remote != nil {
		f.remote.Close()
	}

	f.file.rwLock.Lock()
	if f.writeable {
		f.file.writers = lo2.Remove(f.file.writers, f)
	} else if f.readable {
		f.file.readers = lo2.Remove(f.file.readers, f)
	}
	f.file.rwLock.Unlock()
	return nil
}