// vfs/disk/disk.go
package disk

import (
	"container/list"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"s1d3sw1ped/SteamCache2/steamcache/logger"
	"s1d3sw1ped/SteamCache2/vfs"
	"s1d3sw1ped/SteamCache2/vfs/vfserror"
	"strings"
	"sync"
	"time"

	"github.com/docker/go-units"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

var (
	diskCapacityBytes = promauto.NewGauge(
		prometheus.GaugeOpts{
			Name: "disk_cache_capacity_bytes",
			Help: "Total capacity of the disk cache in bytes",
		},
	)

	diskSizeBytes = promauto.NewGauge(
		prometheus.GaugeOpts{
			Name: "disk_cache_size_bytes",
			Help: "Total size of the disk cache in bytes",
		},
	)

	diskReadBytes = promauto.NewCounter(
		prometheus.CounterOpts{
			Name: "disk_cache_read_bytes_total",
			Help: "Total number of bytes read from the disk cache",
		},
	)

	diskWriteBytes = promauto.NewCounter(
		prometheus.CounterOpts{
			Name: "disk_cache_write_bytes_total",
			Help: "Total number of bytes written to the disk cache",
		},
	)
)

// Ensure DiskFS implements VFS.
var _ vfs.VFS = (*DiskFS)(nil)

// DiskFS is a virtual file system that stores files on disk.
type DiskFS struct {
	root string

	info     map[string]*vfs.FileInfo
	capacity int64
	size     int64
	mu       sync.RWMutex
	keyLocks sync.Map // map[string]*sync.RWMutex
	sg       sync.WaitGroup
	LRU      *lruList
}

// lruList for LRU eviction
type lruList struct {
	list *list.List
	elem map[string]*list.Element
}

func newLruList() *lruList {
	return &lruList{
		list: list.New(),
		elem: make(map[string]*list.Element),
	}
}

func (l *lruList) MoveToFront(key string) {
	if e, ok := l.elem[key]; ok {
		l.list.MoveToFront(e)
	}
}

func (l *lruList) Add(key string, fi *vfs.FileInfo) *list.Element {
	e := l.list.PushFront(fi)
	l.elem[key] = e
	return e
}

func (l *lruList) Remove(key string) {
	if e, ok := l.elem[key]; ok {
		l.list.Remove(e)
		delete(l.elem, key)
	}
}

func (l *lruList) Back() *vfs.FileInfo {
	if e := l.list.Back(); e != nil {
		return e.Value.(*vfs.FileInfo)
	}
	return nil
}

// New creates a new DiskFS.
func new(root string, capacity int64, skipinit bool) *DiskFS {
	if capacity <= 0 {
		panic("disk capacity must be greater than 0") // panic if the capacity is less than or equal to 0
	}

	if root == "" {
		panic("disk root must not be empty") // panic if the root is empty
	}

	fi, err := os.Stat(root)
	if err != nil {
		if !os.IsNotExist(err) {
			panic(err) // panic if the error is something other than not found
		}
		os.Mkdir(root, 0755)    // create the root directory if it does not exist
		fi, err = os.Stat(root) // re-stat to get the file info
		if err != nil {
			panic(err) // panic if the re-stat fails
		}
	}
	if !fi.IsDir() {
		panic("disk root must be a directory") // panic if the root is not a directory
	}

	dfs := &DiskFS{
		root:     root,
		info:     make(map[string]*vfs.FileInfo),
		capacity: capacity,
		mu:       sync.RWMutex{},
		keyLocks: sync.Map{},
		sg:       sync.WaitGroup{},
		LRU:      newLruList(),
	}

	os.MkdirAll(dfs.root, 0755)

	diskCapacityBytes.Set(float64(dfs.capacity))

	if !skipinit {
		dfs.init()
		diskSizeBytes.Set(float64(dfs.Size()))
	}

	return dfs
}

func New(root string, capacity int64) *DiskFS {
	return new(root, capacity, false)
}

func NewSkipInit(root string, capacity int64) *DiskFS {
	return new(root, capacity, true)
}

func (d *DiskFS) init() {
	tstart := time.Now()

	d.walk(d.root)
	d.sg.Wait()

	logger.Logger.Info().
		Str("name", d.Name()).
		Str("root", d.root).
		Str("capacity", units.HumanSize(float64(d.capacity))).
		Str("size", units.HumanSize(float64(d.Size()))).
		Str("files", fmt.Sprint(len(d.info))).
		Str("duration", time.Since(tstart).String()).
		Msg("init")
}

func (d *DiskFS) walk(path string) {
	d.sg.Add(1)
	go func() {
		defer d.sg.Done()
		filepath.Walk(path, func(npath string, info os.FileInfo, err error) error {
			if path == npath {
				return nil
			}

			if err != nil {
				return err
			}

			if info.IsDir() {
				d.walk(npath)
				return filepath.SkipDir
			}

			d.mu.Lock()
			k := strings.ReplaceAll(npath[len(d.root)+1:], "\\", "/")
			fi := vfs.NewFileInfoFromOS(info, k)
			d.info[k] = fi
			d.LRU.Add(k, fi)
			d.size += info.Size()
			d.mu.Unlock()

			return nil
		})
	}()
}

func (d *DiskFS) Capacity() int64 {
	return d.capacity
}

func (d *DiskFS) Name() string {
	return "DiskFS"
}

func (d *DiskFS) Size() int64 {
	d.mu.RLock()
	defer d.mu.RUnlock()
	return d.size
}

func (d *DiskFS) getKeyLock(key string) *sync.RWMutex {
	mu, _ := d.keyLocks.LoadOrStore(key, &sync.RWMutex{})
	return mu.(*sync.RWMutex)
}

func (d *DiskFS) Create(key string, size int64) (io.WriteCloser, error) {
	if key == "" {
		return nil, vfserror.ErrInvalidKey
	}
	if key[0] == '/' {
		return nil, vfserror.ErrInvalidKey
	}

	// Sanitize key to prevent path traversal
	key = filepath.Clean(key)
	if strings.Contains(key, "..") {
		return nil, vfserror.ErrInvalidKey
	}

	d.mu.RLock()
	if d.capacity > 0 {
		if d.size+size > d.capacity {
			d.mu.RUnlock()
			return nil, vfserror.ErrDiskFull
		}
	}
	d.mu.RUnlock()

	keyMu := d.getKeyLock(key)
	keyMu.Lock()
	defer keyMu.Unlock()

	// Check again after lock
	d.mu.Lock()
	if fi, exists := d.info[key]; exists {
		d.size -= fi.Size()
		d.LRU.Remove(key)
		d.Delete(key)
	}
	d.mu.Unlock()

	path := filepath.Join(d.root, key)
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return nil, err
	}

	file, err := os.Create(path)
	if err != nil {
		return nil, err
	}

	return &diskWriteCloser{
		Writer: file,
		onClose: func(n int64) error {
			fi, err := os.Stat(path)
			if err != nil {
				os.Remove(path)
				return err
			}

			d.mu.Lock()
			finfo := vfs.NewFileInfoFromOS(fi, key)
			d.info[key] = finfo
			d.LRU.Add(key, finfo)
			d.size += n
			d.mu.Unlock()

			diskWriteBytes.Add(float64(n))
			diskSizeBytes.Set(float64(d.Size()))

			return nil
		},
		key:  key,
		file: file,
	}, nil
}

type diskWriteCloser struct {
	io.Writer
	onClose func(int64) error
	n       int64
	key     string
	file    *os.File
}

func (wc *diskWriteCloser) Write(p []byte) (int, error) {
	n, err := wc.Writer.Write(p)
	wc.n += int64(n)
	return n, err
}

func (wc *diskWriteCloser) Close() error {
	err := wc.file.Close()
	if e := wc.onClose(wc.n); e != nil {
		os.Remove(wc.file.Name())
		return e
	}
	return err
}

// Delete deletes the value of key.
func (d *DiskFS) Delete(key string) error {
	if key == "" {
		return vfserror.ErrInvalidKey
	}
	if key[0] == '/' {
		return vfserror.ErrInvalidKey
	}

	// Sanitize key to prevent path traversal
	key = filepath.Clean(key)
	if strings.Contains(key, "..") {
		return vfserror.ErrInvalidKey
	}

	keyMu := d.getKeyLock(key)
	keyMu.Lock()
	defer keyMu.Unlock()

	d.mu.Lock()
	fi, exists := d.info[key]
	if !exists {
		d.mu.Unlock()
		return vfserror.ErrNotFound
	}
	d.size -= fi.Size()
	d.LRU.Remove(key)
	delete(d.info, key)
	d.mu.Unlock()

	path := filepath.Join(d.root, key)
	if err := os.Remove(path); err != nil {
		return err
	}

	diskSizeBytes.Set(float64(d.Size()))

	return nil
}

// Open opens the file at key and returns it.
func (d *DiskFS) Open(key string) (io.ReadCloser, error) {
	if key == "" {
		return nil, vfserror.ErrInvalidKey
	}
	if key[0] == '/' {
		return nil, vfserror.ErrInvalidKey
	}

	// Sanitize key to prevent path traversal
	key = filepath.Clean(key)
	if strings.Contains(key, "..") {
		return nil, vfserror.ErrInvalidKey
	}

	keyMu := d.getKeyLock(key)
	keyMu.RLock()
	defer keyMu.RUnlock()

	d.mu.Lock()
	fi, exists := d.info[key]
	if !exists {
		d.mu.Unlock()
		return nil, vfserror.ErrNotFound
	}
	fi.ATime = time.Now()
	d.LRU.MoveToFront(key)
	d.mu.Unlock()

	path := filepath.Join(d.root, key)
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}

	// Update metrics on close
	return &readCloser{
		ReadCloser: file,
		onClose: func(n int64) {
			diskReadBytes.Add(float64(n))
		},
	}, nil
}

type readCloser struct {
	io.ReadCloser
	onClose func(int64)
	n       int64
}

func (rc *readCloser) Read(p []byte) (int, error) {
	n, err := rc.ReadCloser.Read(p)
	rc.n += int64(n)
	return n, err
}

func (rc *readCloser) Close() error {
	err := rc.ReadCloser.Close()
	rc.onClose(rc.n)
	return err
}

// Stat returns the FileInfo of key. If key is not found in the cache, it will stat the file on disk. If the file is not found on disk, it will return vfs.ErrNotFound.
func (d *DiskFS) Stat(key string) (*vfs.FileInfo, error) {
	if key == "" {
		return nil, vfserror.ErrInvalidKey
	}
	if key[0] == '/' {
		return nil, vfserror.ErrInvalidKey
	}

	// Sanitize key to prevent path traversal
	key = filepath.Clean(key)
	if strings.Contains(key, "..") {
		return nil, vfserror.ErrInvalidKey
	}

	keyMu := d.getKeyLock(key)
	keyMu.RLock()
	defer keyMu.RUnlock()

	d.mu.RLock()
	defer d.mu.RUnlock()

	if fi, ok := d.info[key]; !ok {
		return nil, vfserror.ErrNotFound
	} else {
		return fi, nil
	}
}

func (d *DiskFS) StatAll() []*vfs.FileInfo {
	d.mu.RLock()
	defer d.mu.RUnlock()

	// hard copy the file info to prevent modification of the original file info or the other way around
	files := make([]*vfs.FileInfo, 0, len(d.info))
	for _, v := range d.info {
		fi := *v
		files = append(files, &fi)
	}

	return files
}