package cache

import (
	"errors"
	"io"
	"os"
	"path/filepath"
	"sync"
	"syscall"
	"time"

	"github.com/inhies/go-bytesize"
	"github.com/samber/lo"
	"gitlink.org.cn/cloudream/common/pkgs/logger"
	"gitlink.org.cn/cloudream/common/pkgs/trie"
	"gitlink.org.cn/cloudream/common/utils/io2"
	"gitlink.org.cn/cloudream/common/utils/lo2"
	"gitlink.org.cn/cloudream/storage2/client/internal/db"
	"gitlink.org.cn/cloudream/storage2/client/internal/downloader"
	"gitlink.org.cn/cloudream/storage2/client/internal/mount/config"
	"gitlink.org.cn/cloudream/storage2/client/internal/mount/fuse"
	"gitlink.org.cn/cloudream/storage2/client/internal/uploader"
	clitypes "gitlink.org.cn/cloudream/storage2/client/types"
)

type CacheEntry interface {
	fuse.FsEntry
	// 在虚拟文件系统中的路径，即不包含缓存目录的路径
	PathComps() []string
}

type CacheEntryInfo struct {
	PathComps []string
	Size      int64
	Mode      os.FileMode
	ModTime   time.Time
	IsDir     bool
}

type Cache struct {
	cfg         *config.Config
	db          *db.DB
	uploader    *uploader.Uploader
	downloader  *downloader.Downloader
	lock        *sync.RWMutex
	cacheDone   chan any
	activeCache *trie.Trie[*CacheFile]
}

func NewCache(cfg *config.Config, db *db.DB, uploader *uploader.Uploader, downloader *downloader.Downloader) *Cache {
	return &Cache{
		cfg:         cfg,
		db:          db,
		uploader:    uploader,
		downloader:  downloader,
		lock:        &sync.RWMutex{},
		cacheDone:   make(chan any),
		activeCache: trie.NewTrie[*CacheFile](),
	}
}

func (c *Cache) Start() {
	go c.scanningCache()
	go c.scanningData()
}

func (c *Cache) Stop() {
	close(c.cacheDone)
}

func (c *Cache) GetCacheDataPath(comps ...string) string {
	comps2 := make([]string, len(comps)+1)
	comps2[0] = c.cfg.DataDir
	copy(comps2[1:], comps)
	return filepath.Join(comps2...)
}

func (c *Cache) GetCacheMetaPath(comps ...string) string {
	comps2 := make([]string, len(comps)+1)
	comps2[0] = c.cfg.MetaDir
	copy(comps2[1:], comps)
	return filepath.Join(comps2...)
}

// 获取指定位置的缓存条目信息。如果路径不存在，则返回nil。
func (c *Cache) Stat(pathComps []string) *CacheEntryInfo {
	c.lock.RLock()
	defer c.lock.RUnlock()

	node, ok := c.activeCache.WalkEnd(pathComps)
	if ok && node.Value != nil {
		info := node.Value.Info()
		return &info
	}

	dataPath := c.GetCacheDataPath(pathComps...)
	stat, err := os.Stat(dataPath)
	if err != nil {
		// TODO 日志记录
		return nil
	}

	if stat.IsDir() {
		info, err := loadCacheDirInfo(c, pathComps, stat)
		if err != nil {
			return nil
		}

		return info
	}

	info, err := loadCacheFileInfo(c, pathComps, stat)
	if err != nil {
		return nil
	}

	return info
}

// 创建一个缓存文件。如果文件已经存在，则会覆盖已有文件。如果加载过程中发生了错误，或者目标位置是一个目录，则会返回nil。
//
// 记得使用Release减少引用计数
func (c *Cache) CreateFile(pathComps []string) *CacheFile {
	c.lock.Lock()
	defer c.lock.Unlock()

	node, ok := c.activeCache.WalkEnd(pathComps)
	if ok && node.Value != nil {
		node.Value.Delete()
		if node.Value.state.uploading != nil {
			node.Value.state.uploading.isDeleted = true
		}
	}

	ch, err := createNewCacheFile(c, pathComps)
	if err != nil {
		logger.Warnf("create new cache file %v: %v", pathComps, err)
		return nil
	}

	ch.state.refCount++
	c.activeCache.CreateWords(pathComps).Value = ch

	logger.Debugf("create new cache file %v", pathComps)
	return ch
}

// 尝试加载缓存文件，如果文件不存在，则使用obj的信息创建一个新缓存文件，而如果obj为nil，那么会返回nil。
//
// 记得使用Release减少引用计数
func (c *Cache) LoadFile(pathComps []string, obj *clitypes.Object) *CacheFile {
	c.lock.Lock()
	defer c.lock.Unlock()

	node, ok := c.activeCache.WalkEnd(pathComps)
	if ok && node.Value != nil {
		if !node.Value.state.isLoaded {
			err := node.Value.Load()
			if err != nil {
				logger.Warnf("load cache %v: %v", pathComps, err)
				return nil
			}
		}

		return node.Value
	}

	ch, err := loadCacheFile(c, pathComps)
	if err == nil {
		ch.remoteObj = obj
		ch.state.refCount++
		c.activeCache.CreateWords(pathComps).Value = ch

		logger.Debugf("load cache %v", pathComps)
		return ch
	}

	if !os.IsNotExist(err) {
		// TODO 日志记录
		logger.Warnf("load cache %v: %v", pathComps, err)
		return nil
	}

	if obj == nil {
		return nil
	}

	ch, err = newCacheFileFromObject(c, pathComps, obj)
	if err != nil {
		logger.Warnf("create cache %v from object: %v", pathComps, err)
		return nil
	}

	ch.state.refCount++
	c.activeCache.CreateWords(pathComps).Value = ch

	logger.Debugf("create cache %v from object %v", pathComps, obj.ObjectID)
	return ch
}

// 创建一个缓存目录。如果目录已经存在，则会重置目录属性。如果加载过程中发生了错误，或者目标位置是一个文件，则会返回nil
func (c *Cache) CreateDir(pathComps []string) *CacheDir {
	c.lock.Lock()
	defer c.lock.Unlock()

	ch, err := createNewCacheDir(c, pathComps)
	if err != nil {
		logger.Warnf("create cache dir: %v", err)
		return nil
	}
	return ch
}

type CreateDirOption struct {
	ModTime time.Time
}

// 加载指定缓存目录，如果目录不存在，则使用createOpt选项创建目录，而如果createOpt为nil，那么会返回nil。
func (c *Cache) LoadDir(pathComps []string, createOpt *CreateDirOption) *CacheDir {
	c.lock.Lock()
	defer c.lock.Unlock()

	ch, err := loadCacheDir(c, pathComps)
	if err == nil {
		return ch
	}

	if !os.IsNotExist(err) {
		// TODO 日志记录
		return nil
	}

	if createOpt == nil {
		return nil
	}

	// 创建目录
	ch, err = makeCacheDirFromOption(c, pathComps, *createOpt)
	if err != nil {
		// TODO 日志记录
		return nil
	}
	return ch
}

// 加载指定路径下的所有缓存条目信息
func (c *Cache) StatMany(pathComps []string) []CacheEntryInfo {
	c.lock.RLock()
	defer c.lock.RUnlock()

	var infos []CacheEntryInfo

	exists := make(map[string]bool)

	node, ok := c.activeCache.WalkEnd(pathComps)
	if ok {
		for name, child := range node.WordNexts {
			if child.Value != nil {
				infos = append(infos, child.Value.Info())
				exists[name] = true
			}
		}
	}

	osEns, err := os.ReadDir(c.GetCacheDataPath(pathComps...))
	if err != nil {
		return nil
	}

	for _, e := range osEns {
		if exists[e.Name()] {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}

		if e.IsDir() {
			info, err := loadCacheDirInfo(c, append(lo2.ArrayClone(pathComps), e.Name()), info)
			if err != nil {
				continue
			}

			infos = append(infos, *info)
		} else {
			info, err := loadCacheFileInfo(c, append(lo2.ArrayClone(pathComps), e.Name()), info)
			if err != nil {
				continue
			}

			infos = append(infos, *info)
		}
	}

	return infos
}

// 删除指定路径的缓存文件或目录。删除目录时如果目录不为空，则会报错。
func (c *Cache) Remove(pathComps []string) error {
	c.lock.Lock()
	defer c.lock.Unlock()

	node, ok := c.activeCache.WalkEnd(pathComps)
	if ok {
		if len(node.WordNexts) > 0 {
			return fuse.ErrNotEmpty
		}

		if node.Value != nil {
			node.Value.Delete()
			if node.Value.state.uploading != nil {
				node.Value.state.uploading.isDeleted = true
			}
		}

		node.RemoveSelf(true)

		logger.Debugf("active cache %v removed", pathComps)
		return nil
	}

	metaPath := c.GetCacheMetaPath(pathComps...)
	dataPath := c.GetCacheDataPath(pathComps...)

	os.Remove(metaPath)
	err := os.Remove(dataPath)
	if err == nil || os.IsNotExist(err) {
		logger.Debugf("local cache %v removed", pathComps)
		return nil
	}

	if errors.Is(err, syscall.ENOTEMPTY) {
		return fuse.ErrNotEmpty
	}

	return err
}

// 移动指定路径的缓存文件或目录到新的路径。如果目标路径已经存在，则会报错。
//
// 如果移动成功，则返回移动后的缓存文件或目录。如果文件或目录不存在，则返回nil。
func (c *Cache) Move(pathComps []string, newPathComps []string) error {
	c.lock.Lock()
	defer c.lock.Unlock()

	_, ok := c.activeCache.WalkEnd(newPathComps)
	if ok {
		return fuse.ErrExists
	}

	newMetaPath := c.GetCacheMetaPath(newPathComps...)
	newDataPath := c.GetCacheDataPath(newPathComps...)

	_, err := os.Stat(newDataPath)
	if err == nil {
		return fuse.ErrExists
	}

	if !os.IsNotExist(err) {
		return err
	}

	oldMetaPath := c.GetCacheMetaPath(pathComps...)
	oldDataPath := c.GetCacheDataPath(pathComps...)

	// 确定源文件存在，再进行后面的操作
	_, err = os.Stat(oldDataPath)
	if err != nil {
		if os.IsNotExist(err) {
			return fuse.ErrNotExists
		}
		return err
	}

	// 创建父目录是为了解决被移动的文件不在本地的问题。
	// 但同时也导致了如果目的路径的父目录确实不存在，这里会意外的创建了这个目录
	newMetaDir := filepath.Dir(newMetaPath)
	err = os.MkdirAll(newMetaDir, 0755)
	if err != nil {
		return err
	}

	newDataDir := filepath.Dir(newDataPath)
	err = os.MkdirAll(newDataDir, 0755)
	if err != nil {
		return err
	}

	// 每个缓存文件持有meta文件和data文件的句柄，所以这里移动文件，不影响句柄的使用。
	// 只能忽略这里的错误
	os.Rename(oldMetaPath, newMetaPath)
	os.Rename(oldDataPath, newDataPath)

	// 更新缓存
	oldNode, ok := c.activeCache.WalkEnd(pathComps)
	if ok {
		newNode := c.activeCache.CreateWords(newPathComps)
		newNode.Value = oldNode.Value
		newNode.WordNexts = oldNode.WordNexts
		oldNode.RemoveSelf(false)

		if newNode.Value != nil {
			newNode.Value.Move(newPathComps)
		}
		newNode.Iterate(func(path []string, node *trie.Node[*CacheFile], isWordNode bool) trie.VisitCtrl {
			if node.Value != nil {
				node.Value.Move(lo2.AppendNew(newPathComps, path...))
			}
			return trie.VisitContinue
		})
	}

	logger.Debugf("cache moved: %v -> %v", pathComps, newPathComps)
	return nil
}

type uploadingPackage struct {
	bktName string
	pkgName string
	pkg     clitypes.Package
	upObjs  []*uploadingObject
}

type uploadingObject struct {
	pathComps []string
	cache     *CacheFile
	reader    *CacheFileHandle
	isDeleted bool
	isSuccess bool
}

func (c *Cache) scanningCache() {
	ticker := time.NewTicker(time.Second * 5)
	defer ticker.Stop()

	lastScanPath := []string{}
	for {

		select {
		case _, ok := <-c.cacheDone:
			if !ok {
				return
			}

		case <-ticker.C:
		}

		c.lock.Lock()

		type packageFullName struct {
			bktName string
			pkgName string
		}

		uploadingPkgs := make(map[packageFullName]*uploadingPackage)

		visitCnt := 0
		visitBreak := false

		node, _ := c.activeCache.WalkEnd(lastScanPath)
		node.Iterate(func(path []string, node *trie.Node[*CacheFile], isWordNode bool) trie.VisitCtrl {
			ch := node.Value
			if ch == nil {
				return trie.VisitContinue
			}

			if ch.state.refCount > 0 {
				logger.Debugf("skip cache %v, refCount: %v", path, ch.state.refCount)
				return trie.VisitContinue
			}

			visitCnt++

			shouldUpload := true
			// 不存放在Package里的文件，不需要上传
			if len(ch.pathComps) <= 2 {
				shouldUpload = false
			}

			if ch.Revision() > 0 && shouldUpload {
				// 1. 本地缓存被修改了，如果一段时间内没有被使用，则进行上传
				if time.Since(ch.state.freeTime) > c.cfg.UploadPendingTime && ch.state.uploading == nil {
					fullName := packageFullName{ch.pathComps[0], ch.pathComps[1]}
					pkg, ok := uploadingPkgs[fullName]
					if !ok {
						pkg = &uploadingPackage{
							bktName: ch.pathComps[0],
							pkgName: ch.pathComps[1],
						}
						uploadingPkgs[fullName] = pkg
					}
					obj := &uploadingObject{
						pathComps: lo2.ArrayClone(ch.pathComps),
						cache:     ch,
						reader:    ch.OpenReadWhenScanning(),
					}
					pkg.upObjs = append(pkg.upObjs, obj)
					ch.state.uploading = obj
				}
			} else if ch.state.isLoaded {
				// 2. 本地缓存没有被修改，如果一段时间内没有被使用，则进行卸载

				if time.Since(ch.state.freeTime) > c.cfg.CacheActiveTime {
					ch.Unload()
					ch.state.isLoaded = false
					ch.state.unloadTime = time.Now()
				}
			} else {
				// 3. 卸载后的缓存，如果一段时间内没有被使用，则进行删除。
				if time.Since(ch.state.unloadTime) > c.cfg.CacheExpireTime {
					// 如果文件已经同步到远端，则可以直接删除本地缓存
					if ch.Revision() == 0 {
						ch.Delete()
					}

					node.RemoveSelf(true)
				}
			}

			// 每次最多遍历500个节点，防止占用锁太久
			if visitCnt > 500 {
				lastScanPath = lo2.ArrayClone(path)
				visitBreak = true
				return trie.VisitBreak
			}
			return trie.VisitContinue
		})
		if !visitBreak {
			lastScanPath = []string{}
		}

		c.lock.Unlock()

		if len(uploadingPkgs) > 0 {
			go c.doUploading(lo.Values(uploadingPkgs))
		}
	}
}

func (c *Cache) scanningData() {
	ticker := time.NewTicker(c.cfg.ScanDataDirInterval)
	defer ticker.Stop()

	var walkTrace []*os.File
	var walkTraceComps []string
	for {
		select {
		case <-ticker.C:
		case <-c.cacheDone:
			return
		}

		logger.Infof("begin scanning data dir")

		if len(walkTrace) == 0 {
			dir, err := os.Open(c.cfg.DataDir)
			if err != nil {
				logger.Warnf("open data dir: %v", err)
				continue
			}

			walkTrace = []*os.File{dir}
			walkTraceComps = []string{c.cfg.MetaDir}
		}

		const maxVisitCnt = 5000
		const maxUntrackedFiles = 500

		var untrackedFiles [][]string
		visitCnt := 0

		// 一次最多遍历5000个文件（包括路径上的文件夹），一次最多添加500个未跟踪文件
		for len(walkTrace) > 0 && visitCnt < maxVisitCnt && len(untrackedFiles) < maxUntrackedFiles {
			lastNode := walkTrace[len(walkTrace)-1]
			visitCnt++

			e, err := lastNode.ReadDir(1)
			if err == io.EOF {
				lastNode.Close()
				walkTrace = walkTrace[:len(walkTrace)-1]
				walkTraceComps = walkTraceComps[:len(walkTraceComps)-1]
				continue
			}
			if err != nil {
				logger.Warnf("read dir %v: %v", lastNode.Name(), err)
				lastNode.Close()
				walkTrace = walkTrace[:len(walkTrace)-1]
				walkTraceComps = walkTraceComps[:len(walkTraceComps)-1]
				continue
			}

			if e[0].IsDir() {
				child, err := os.Open(filepath.Join(lastNode.Name(), e[0].Name()))
				if err != nil {
					logger.Warnf("open dir %v: %v", e[0].Name(), err)
					continue
				}
				walkTrace = append(walkTrace, child)
				walkTraceComps = append(walkTraceComps, e[0].Name())
				continue
			}

			// 对于不在Package层级的文件，不跟踪
			if len(walkTrace) <= 2 {
				continue
			}

			walkTraceComps = append(walkTraceComps, e[0].Name())
			fileMetaPath := filepath.Join(walkTraceComps...)
			_, err = os.Stat(fileMetaPath)
			if err == nil || !os.IsNotExist(err) {
				walkTraceComps = walkTraceComps[:len(walkTraceComps)-1]
				continue
			}

			untrackedFiles = append(untrackedFiles, lo2.ArrayClone(walkTraceComps[1:]))
			walkTraceComps = walkTraceComps[:len(walkTraceComps)-1]
		}

		if len(untrackedFiles) > 0 {
			for _, comps := range untrackedFiles {
				ch := c.LoadFile(comps, nil)
				if ch != nil {
					ch.Release()
				}
			}
		}

		logger.Infof("%v file visited, %v untracked files found", visitCnt, len(untrackedFiles))
	}
}

func (c *Cache) doUploading(pkgs []*uploadingPackage) {
	/// 1. 先尝试创建Package
	var sucPkgs []*uploadingPackage
	var failedPkgs []*uploadingPackage
	for _, pkg := range pkgs {
		p, err := db.DoTx21(c.db, c.db.Package().TryCreateAll, pkg.bktName, pkg.pkgName)
		if err != nil {
			logger.Warnf("try create package %v/%v: %v", pkg.bktName, pkg.pkgName, err)
			failedPkgs = append(failedPkgs, pkg)
			continue
		}

		pkg.pkg = p
		sucPkgs = append(sucPkgs, pkg)
	}

	/// 2. 对于创建失败的Package，直接关闭文件，不进行上传
	// 在锁的保护下取消上传状态
	c.lock.Lock()
	for _, pkg := range failedPkgs {
		for _, obj := range pkg.upObjs {
			obj.cache.state.uploading = nil
		}
	}
	c.lock.Unlock()
	// 关闭文件必须在锁外
	for _, pkg := range failedPkgs {
		for _, obj := range pkg.upObjs {
			obj.reader.Close()
		}
	}

	/// 3. 开始上传每个Package
	for _, p := range sucPkgs {
		uploader, err := c.uploader.BeginUpdate(p.pkg.PackageID, 0, nil, nil)
		if err != nil {
			logger.Warnf("begin update package %v/%v: %v", p.bktName, p.pkgName, err)

			// 取消上传状态
			c.lock.Lock()
			for _, obj := range p.upObjs {
				obj.cache.state.uploading = nil
			}
			c.lock.Unlock()

			for _, obj := range p.upObjs {
				obj.reader.Close()
			}
			continue
		}

		upSuc := 0
		upSucAmt := int64(0)
		upFailed := 0
		upStartTime := time.Now()

		logger.Infof("begin uploading %v objects to package %v/%v", len(p.upObjs), p.bktName, p.pkgName)
		for _, o := range p.upObjs {
			rd := cacheFileReader{
				rw: o.reader,
			}

			counter := io2.Counter(&rd)

			err = uploader.Upload(clitypes.JoinObjectPath(o.pathComps[2:]...), counter)
			if err != nil {
				logger.Warnf("upload object %v: %v", o.pathComps, err)
				upFailed++
				continue
			}

			o.isSuccess = true
			upSuc++
			upSucAmt += counter.Count()
		}

		// 在锁保护下登记上传结果
		c.lock.Lock()

		upCancel := 0
		upRename := 0

		// 检查是否有文件在上传期间发生了变化
		var sucObjs []*uploadingObject
		for _, o := range p.upObjs {
			o.cache.state.uploading = nil
			if !o.isSuccess {
				continue
			}

			oldPath := clitypes.JoinObjectPath(o.pathComps[2:]...)
			newPath := clitypes.JoinObjectPath(o.cache.pathComps[2:]...)

			if o.isDeleted {
				uploader.CancelObject(oldPath)
				upCancel++
				continue
			}

			// 如果对象移动到了另一个Package，那么也要取消上传
			if !lo2.ArrayEquals(o.pathComps[:2], o.cache.pathComps[:2]) {
				uploader.CancelObject(oldPath)
				upCancel++
				continue

			}

			// 只有仍在同Package内移动的对象才能直接重命名
			if newPath != oldPath {
				uploader.RenameObject(oldPath, newPath)
				upRename++
			}

			sucObjs = append(sucObjs, o)
		}

		_, err = uploader.Commit()
		if err != nil {
			logger.Warnf("commit update package %v/%v: %v", p.bktName, p.pkgName, err)
		} else {
			for _, obj := range sucObjs {
				obj.cache.RevisionUploaded(obj.reader.revision)
			}

			upTime := time.Since(upStartTime)
			logger.Infof("upload package %v/%v in %v, upload: %v, size: %v, speed: %v/s, cancel: %v, rename: %v",
				p.bktName, p.pkgName, upTime, upSuc, upSucAmt, bytesize.New(float64(upSucAmt)/upTime.Seconds()), upCancel, upRename)
		}

		c.lock.Unlock()

		// 在Cache锁以外关闭文件。
		// 关闭文件会影响refCount，所以无论是上传失败还是上传成功，都会在等待一段时间后才进行下一阶段的操作
		for _, obj := range p.upObjs {
			obj.reader.Close()
		}
	}
}

type cacheFileReader struct {
	rw  *CacheFileHandle
	pos int64
}

func (r *cacheFileReader) Read(p []byte) (int, error) {
	n, err := r.rw.ReadAt(p, r.pos)
	r.pos += int64(n)
	if err != nil {
		return n, err
	}

	if n != len(p) {
		return n, io.EOF
	}

	return n, nil
}