// Package upstream provides utility functionality to union.
package upstream

import (
	"context"
	"errors"
	"fmt"
	"io"
	"math"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/rclone/rclone/backend/union/common"
	"github.com/rclone/rclone/fs"
	"github.com/rclone/rclone/fs/cache"
	"github.com/rclone/rclone/fs/fspath"
	"github.com/rclone/rclone/fs/operations"
)

var (
	// ErrUsageFieldNotSupported stats the usage field is not supported by the backend
	ErrUsageFieldNotSupported = errors.New("this usage field is not supported")
)

// Fs is a wrap of any fs and its configs
type Fs struct {
	fs.Fs
	RootFs      fs.Fs
	RootPath    string
	Opt         *common.Options
	writable    bool
	creatable   bool
	usage       *fs.Usage     // Cache the usage
	cacheTime   time.Duration // cache duration
	cacheExpiry atomic.Int64  // usage cache expiry time
	cacheMutex  sync.RWMutex
	cacheOnce   sync.Once
	cacheUpdate bool // if the cache is updating
	writeback   bool // writeback to this upstream
	writebackFs *Fs  // if non zero, writeback to this upstream
}

// Directory describes a wrapped Directory
//
// This is a wrapped Directory which contains the upstream Fs
type Directory struct {
	fs.Directory
	f *Fs
}

// Object describes a wrapped Object
//
// This is a wrapped Object which contains the upstream Fs
type Object struct {
	fs.Object
	f *Fs
}

// Entry describe a wrapped fs.DirEntry interface with the
// information of upstream Fs
type Entry interface {
	fs.DirEntry
	UpstreamFs() *Fs
}

// New creates a new Fs based on the
// string formatted `type:root_path(:ro/:nc)`
func New(ctx context.Context, remote, root string, opt *common.Options) (*Fs, error) {
	configName, fsPath, err := fspath.SplitFs(remote)
	if err != nil {
		return nil, err
	}
	f := &Fs{
		RootPath:  strings.TrimRight(root, "/"),
		Opt:       opt,
		writable:  true,
		creatable: true,
		cacheTime: time.Duration(opt.CacheTime) * time.Second,
		usage:     &fs.Usage{},
	}
	f.cacheExpiry.Store(time.Now().Unix())
	if strings.HasSuffix(fsPath, ":ro") {
		f.writable = false
		f.creatable = false
		fsPath = fsPath[0 : len(fsPath)-3]
	} else if strings.HasSuffix(fsPath, ":nc") {
		f.writable = true
		f.creatable = false
		fsPath = fsPath[0 : len(fsPath)-3]
	} else if strings.HasSuffix(fsPath, ":writeback") {
		f.writeback = true
		fsPath = fsPath[0 : len(fsPath)-len(":writeback")]
	}
	remote = configName + fsPath
	rFs, err := cache.Get(ctx, remote)
	if err != nil && err != fs.ErrorIsFile {
		return nil, err
	}
	f.RootFs = rFs
	rootString := fspath.JoinRootPath(remote, root)
	myFs, err := cache.Get(ctx, rootString)
	if err != nil && err != fs.ErrorIsFile {
		return nil, err
	}
	f.Fs = myFs
	cache.PinUntilFinalized(f.Fs, f)
	return f, err
}

// Prepare the configured upstreams as a group
func Prepare(fses []*Fs) error {
	writebacks := 0
	var writebackFs *Fs
	for _, f := range fses {
		if f.writeback {
			writebackFs = f
			writebacks++
		}
	}
	if writebacks == 0 {
		return nil
	} else if writebacks > 1 {
		return fmt.Errorf("can only have 1 :writeback not %d", writebacks)
	}
	for _, f := range fses {
		if !f.writeback {
			f.writebackFs = writebackFs
		}
	}
	return nil
}

// WrapDirectory wraps an fs.Directory to include the info
// of the upstream Fs
func (f *Fs) WrapDirectory(e fs.Directory) *Directory {
	if e == nil {
		return nil
	}
	return &Directory{
		Directory: e,
		f:         f,
	}
}

// WrapObject wraps an fs.Object to include the info
// of the upstream Fs
func (f *Fs) WrapObject(o fs.Object) *Object {
	if o == nil {
		return nil
	}
	return &Object{
		Object: o,
		f:      f,
	}
}

// WrapEntry wraps an fs.DirEntry to include the info
// of the upstream Fs
func (f *Fs) WrapEntry(e fs.DirEntry) (Entry, error) {
	switch e := e.(type) {
	case fs.Object:
		return f.WrapObject(e), nil
	case fs.Directory:
		return f.WrapDirectory(e), nil
	default:
		return nil, fmt.Errorf("unknown object type %T", e)
	}
}

// UpstreamFs get the upstream Fs the entry is stored in
func (e *Directory) UpstreamFs() *Fs {
	return e.f
}

// UpstreamFs get the upstream Fs the entry is stored in
func (o *Object) UpstreamFs() *Fs {
	return o.f
}

// UnWrap returns the Object that this Object is wrapping or
// nil if it isn't wrapping anything
func (o *Object) UnWrap() fs.Object {
	return o.Object
}

// IsCreatable return if the fs is allowed to create new objects
func (f *Fs) IsCreatable() bool {
	return f.creatable
}

// IsWritable return if the fs is allowed to write
func (f *Fs) IsWritable() bool {
	return f.writable
}

// Put in to the remote path with the modTime given of the given size
//
// May create the object even if it returns an error - if so
// will return the object and the error, otherwise will return
// nil and the error
func (f *Fs) Put(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
	o, err := f.Fs.Put(ctx, in, src, options...)
	if err != nil {
		return o, err
	}
	f.cacheMutex.Lock()
	defer f.cacheMutex.Unlock()
	size := src.Size()
	if f.usage.Used != nil {
		*f.usage.Used += size
	}
	if f.usage.Free != nil {
		*f.usage.Free -= size
	}
	if f.usage.Objects != nil {
		*f.usage.Objects++
	}
	return o, nil
}

// PutStream uploads to the remote path with the modTime given of indeterminate size
//
// May create the object even if it returns an error - if so
// will return the object and the error, otherwise will return
// nil and the error
func (f *Fs) PutStream(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
	do := f.Features().PutStream
	if do == nil {
		return nil, fs.ErrorNotImplemented
	}
	o, err := do(ctx, in, src, options...)
	if err != nil {
		return o, err
	}
	f.cacheMutex.Lock()
	defer f.cacheMutex.Unlock()
	size := o.Size()
	if f.usage.Used != nil {
		*f.usage.Used += size
	}
	if f.usage.Free != nil {
		*f.usage.Free -= size
	}
	if f.usage.Objects != nil {
		*f.usage.Objects++
	}
	return o, nil
}

// Update in to the object with the modTime given of the given size
//
// When called from outside an Fs by rclone, src.Size() will always be >= 0.
// But for unknown-sized objects (indicated by src.Size() == -1), Upload should either
// return an error or update the object properly (rather than e.g. calling panic).
func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) error {
	size := o.Size()
	err := o.Object.Update(ctx, in, src, options...)
	if err != nil {
		return err
	}
	o.f.cacheMutex.Lock()
	defer o.f.cacheMutex.Unlock()
	delta := o.Size() - size
	if delta <= 0 {
		return nil
	}
	if o.f.usage.Used != nil {
		*o.f.usage.Used += size
	}
	if o.f.usage.Free != nil {
		*o.f.usage.Free -= size
	}
	return nil
}

// GetTier returns storage tier or class of the Object
func (o *Object) GetTier() string {
	do, ok := o.Object.(fs.GetTierer)
	if !ok {
		return ""
	}
	return do.GetTier()
}

// ID returns the ID of the Object if known, or "" if not
func (o *Object) ID() string {
	do, ok := o.Object.(fs.IDer)
	if !ok {
		return ""
	}
	return do.ID()
}

// MimeType returns the content type of the Object if known
func (o *Object) MimeType(ctx context.Context) (mimeType string) {
	if do, ok := o.Object.(fs.MimeTyper); ok {
		mimeType = do.MimeType(ctx)
	}
	return mimeType
}

// SetTier performs changing storage tier of the Object if
// multiple storage classes supported
func (o *Object) SetTier(tier string) error {
	do, ok := o.Object.(fs.SetTierer)
	if !ok {
		return errors.New("underlying remote does not support SetTier")
	}
	return do.SetTier(tier)
}

// Metadata returns metadata for an object
//
// It should return nil if there is no Metadata
func (o *Object) Metadata(ctx context.Context) (fs.Metadata, error) {
	do, ok := o.Object.(fs.Metadataer)
	if !ok {
		return nil, nil
	}
	return do.Metadata(ctx)
}

// Writeback writes the object back and returns a new object
//
// If it returns nil, nil then the original object is OK
func (o *Object) Writeback(ctx context.Context) (*Object, error) {
	if o.f.writebackFs == nil {
		return nil, nil
	}
	newObj, err := operations.Copy(ctx, o.f.writebackFs.Fs, nil, o.Object.Remote(), o.Object)
	if err != nil {
		return nil, err
	}
	// newObj could be nil here
	if newObj == nil {
		fs.Errorf(o, "nil Object returned from operations.Copy")
		return nil, nil
	}
	return &Object{
		Object: newObj,
		f:      o.f,
	}, err
}

// About gets quota information from the Fs
func (f *Fs) About(ctx context.Context) (*fs.Usage, error) {
	if f.cacheExpiry.Load() <= time.Now().Unix() {
		err := f.updateUsage()
		if err != nil {
			return nil, ErrUsageFieldNotSupported
		}
	}
	f.cacheMutex.RLock()
	defer f.cacheMutex.RUnlock()
	return f.usage, nil
}

// GetFreeSpace get the free space of the fs
//
// This is returned as 0..math.MaxInt64-1 leaving math.MaxInt64 as a sentinel
func (f *Fs) GetFreeSpace() (int64, error) {
	if f.cacheExpiry.Load() <= time.Now().Unix() {
		err := f.updateUsage()
		if err != nil {
			return math.MaxInt64 - 1, ErrUsageFieldNotSupported
		}
	}
	f.cacheMutex.RLock()
	defer f.cacheMutex.RUnlock()
	if f.usage.Free == nil {
		return math.MaxInt64 - 1, ErrUsageFieldNotSupported
	}
	return *f.usage.Free, nil
}

// GetUsedSpace get the used space of the fs
//
// This is returned as 0..math.MaxInt64-1 leaving math.MaxInt64 as a sentinel
func (f *Fs) GetUsedSpace() (int64, error) {
	if f.cacheExpiry.Load() <= time.Now().Unix() {
		err := f.updateUsage()
		if err != nil {
			return 0, ErrUsageFieldNotSupported
		}
	}
	f.cacheMutex.RLock()
	defer f.cacheMutex.RUnlock()
	if f.usage.Used == nil {
		return 0, ErrUsageFieldNotSupported
	}
	return *f.usage.Used, nil
}

// GetNumObjects get the number of objects of the fs
func (f *Fs) GetNumObjects() (int64, error) {
	if f.cacheExpiry.Load() <= time.Now().Unix() {
		err := f.updateUsage()
		if err != nil {
			return 0, ErrUsageFieldNotSupported
		}
	}
	f.cacheMutex.RLock()
	defer f.cacheMutex.RUnlock()
	if f.usage.Objects == nil {
		return 0, ErrUsageFieldNotSupported
	}
	return *f.usage.Objects, nil
}

func (f *Fs) updateUsage() (err error) {
	if do := f.RootFs.Features().About; do == nil {
		return ErrUsageFieldNotSupported
	}
	done := false
	f.cacheOnce.Do(func() {
		f.cacheMutex.Lock()
		err = f.updateUsageCore(false)
		f.cacheMutex.Unlock()
		done = true
	})
	if done {
		return err
	}
	if !f.cacheUpdate {
		f.cacheUpdate = true
		go func() {
			_ = f.updateUsageCore(true)
			f.cacheUpdate = false
		}()
	}
	return nil
}

func (f *Fs) updateUsageCore(lock bool) error {
	// Run in background, should not be cancelled by user
	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()
	usage, err := f.RootFs.Features().About(ctx)
	if err != nil {
		f.cacheUpdate = false
		if errors.Is(err, fs.ErrorDirNotFound) {
			err = nil
		}
		return err
	}
	if lock {
		f.cacheMutex.Lock()
		defer f.cacheMutex.Unlock()
	}
	// Store usage
	f.cacheExpiry.Store(time.Now().Add(f.cacheTime).Unix())
	f.usage = usage
	return nil
}

// Check the interfaces are satisfied
var (
	_ fs.FullObject = (*Object)(nil)
)