// Package mega provides an interface to the Mega
// object storage system.
package mega

/*
Open questions
* Does mega support a content hash - what exactly are the mega hashes?
* Can mega support setting modification times?

Improvements:
* Uploads could be done in parallel
* Downloads would be more efficient done in one go
* Uploads would be more efficient with bigger chunks
* Looks like mega can support server side copy, but it isn't implemented in go-mega
* Upload can set modtime... - set as int64_t - can set ctime and mtime?
*/

import (
	"fmt"
	"io"
	"path"
	"strings"
	"sync"
	"time"

	"github.com/ncw/rclone/fs"
	"github.com/ncw/rclone/fs/config/flags"
	"github.com/ncw/rclone/fs/config/obscure"
	"github.com/ncw/rclone/fs/fshttp"
	"github.com/ncw/rclone/fs/hash"
	"github.com/ncw/rclone/lib/pacer"
	"github.com/ncw/rclone/lib/readers"
	"github.com/pkg/errors"
	mega "github.com/t3rm1n4l/go-mega"
)

const (
	minSleep      = 10 * time.Millisecond
	maxSleep      = 2 * time.Second
	decayConstant = 2    // bigger for slower decay, exponential
	useTrash      = true // FIXME make configurable - rclone global
)

var (
	megaDebug   = flags.BoolP("mega-debug", "", false, "If set then output more debug from mega.")
	megaCacheMu sync.Mutex                // mutex for the below
	megaCache   = map[string]*mega.Mega{} // cache logged in Mega's by user
)

// Register with Fs
func init() {
	fs.Register(&fs.RegInfo{
		Name:        "mega",
		Description: "Mega",
		NewFs:       NewFs,
		Options: []fs.Option{{
			Name:     "user",
			Help:     "User name",
			Optional: true,
		}, {
			Name:       "pass",
			Help:       "Password.",
			Optional:   true,
			IsPassword: true,
		}},
	})
}

// Fs represents a remote mega
type Fs struct {
	name       string       // name of this remote
	root       string       // the path we are working on
	features   *fs.Features // optional features
	srv        *mega.Mega   // the connection to the server
	pacer      *pacer.Pacer // pacer for API calls
	rootNodeMu sync.Mutex   // mutex for _rootNode
	_rootNode  *mega.Node   // root node - call findRoot to use this
	mkdirMu    sync.Mutex   // used to serialize calls to mkdir / rmdir
}

// Object describes a mega object
//
// Will definitely have info but maybe not meta
//
// Normally rclone would just store an ID here but go-mega and mega.nz
// expect you to build an entire tree of all the objects in memory.
// In this case we just store a pointer to the object.
type Object struct {
	fs     *Fs        // what this object is part of
	remote string     // The remote path
	info   *mega.Node // pointer to the mega node
}

// ------------------------------------------------------------

// Name of the remote (as passed into NewFs)
func (f *Fs) Name() string {
	return f.name
}

// Root of the remote (as passed into NewFs)
func (f *Fs) Root() string {
	return f.root
}

// String converts this Fs to a string
func (f *Fs) String() string {
	return fmt.Sprintf("mega root '%s'", f.root)
}

// Features returns the optional features of this Fs
func (f *Fs) Features() *fs.Features {
	return f.features
}

// parsePath parses an mega 'url'
func parsePath(path string) (root string) {
	root = strings.Trim(path, "/")
	return
}

// shouldRetry returns a boolean as to whether this err deserves to be
// retried.  It returns the err as a convenience
func shouldRetry(err error) (bool, error) {
	// Let the mega library handle the low level retries
	return false, err
	/*
		switch errors.Cause(err) {
		case mega.EAGAIN, mega.ERATELIMIT, mega.ETEMPUNAVAIL:
			return true, err
		}
		return fserrors.ShouldRetry(err), err
	*/
}

// readMetaDataForPath reads the metadata from the path
func (f *Fs) readMetaDataForPath(remote string) (info *mega.Node, err error) {
	rootNode, err := f.findRoot(false)
	if err != nil {
		return nil, err
	}
	return f.findObject(rootNode, remote)
}

// NewFs constructs an Fs from the path, container:path
func NewFs(name, root string) (fs.Fs, error) {
	user := fs.ConfigFileGet(name, "user")
	pass := fs.ConfigFileGet(name, "pass")
	if pass != "" {
		var err error
		pass, err = obscure.Reveal(pass)
		if err != nil {
			return nil, errors.Wrap(err, "couldn't decrypt password")
		}
	}

	// cache *mega.Mega on username so we can re-use and share
	// them between remotes.  They are expensive to make as they
	// contain all the objects and sharing the objects makes the
	// move code easier as we don't have to worry about mixing
	// them up between different remotes.
	megaCacheMu.Lock()
	defer megaCacheMu.Unlock()
	srv := megaCache[user]
	if srv == nil {
		srv = mega.New().SetClient(fshttp.NewClient(fs.Config))
		srv.SetRetries(fs.Config.LowLevelRetries) // let mega do the low level retries
		srv.SetLogger(func(format string, v ...interface{}) {
			fs.Infof("*go-mega*", format, v...)
		})
		if *megaDebug {
			srv.SetDebugger(func(format string, v ...interface{}) {
				fs.Debugf("*go-mega*", format, v...)
			})
		}

		err := srv.Login(user, pass)
		if err != nil {
			return nil, errors.Wrap(err, "couldn't login")
		}
		megaCache[user] = srv
	}

	root = parsePath(root)
	f := &Fs{
		name:  name,
		root:  root,
		srv:   srv,
		pacer: pacer.New().SetMinSleep(minSleep).SetMaxSleep(maxSleep).SetDecayConstant(decayConstant),
	}
	f.features = (&fs.Features{
		DuplicateFiles:          true,
		CanHaveEmptyDirectories: true,
	}).Fill(f)

	// Find the root node and check if it is a file or not
	_, err := f.findRoot(false)
	switch err {
	case nil:
		// root node found and is a directory
	case fs.ErrorDirNotFound:
		// root node not found, so can't be a file
	case fs.ErrorIsFile:
		// root node is a file so point to parent directory
		root = path.Dir(root)
		if root == "." {
			root = ""
		}
		f.root = root
		return f, err
	}
	return f, nil
}

// splitNodePath splits nodePath into / separated parts, returning nil if it
// should refer to the root
func splitNodePath(nodePath string) (parts []string) {
	nodePath = path.Clean(nodePath)
	parts = strings.Split(nodePath, "/")
	if len(parts) == 1 && (parts[0] == "." || parts[0] == "/") {
		return nil
	}
	return parts
}

// findNode looks up the node for the path of the name given from the root given
//
// It returns mega.ENOENT if it wasn't found
func (f *Fs) findNode(rootNode *mega.Node, nodePath string) (*mega.Node, error) {
	parts := splitNodePath(nodePath)
	if parts == nil {
		return rootNode, nil
	}
	nodes, err := f.srv.FS.PathLookup(rootNode, parts)
	if err != nil {
		return nil, err
	}
	return nodes[len(nodes)-1], nil
}

// findDir finds the directory rooted from the node passed in
func (f *Fs) findDir(rootNode *mega.Node, dir string) (node *mega.Node, err error) {
	node, err = f.findNode(rootNode, dir)
	if err == mega.ENOENT {
		return nil, fs.ErrorDirNotFound
	} else if err == nil && node.GetType() == mega.FILE {
		return nil, fs.ErrorIsFile
	}
	return node, err
}

// findObject looks up the node for the object of the name given
func (f *Fs) findObject(rootNode *mega.Node, file string) (node *mega.Node, err error) {
	node, err = f.findNode(rootNode, file)
	if err == mega.ENOENT {
		return nil, fs.ErrorObjectNotFound
	} else if err == nil && node.GetType() != mega.FILE {
		return nil, fs.ErrorNotAFile
	}
	return node, err
}

// lookupDir looks up the node for the directory of the name given
//
// if create is true it tries to create the root directory if not found
func (f *Fs) lookupDir(dir string) (*mega.Node, error) {
	rootNode, err := f.findRoot(false)
	if err != nil {
		return nil, err
	}
	return f.findDir(rootNode, dir)
}

// lookupParentDir finds the parent node for the remote passed in
func (f *Fs) lookupParentDir(remote string) (dirNode *mega.Node, leaf string, err error) {
	parent, leaf := path.Split(remote)
	dirNode, err = f.lookupDir(parent)
	return dirNode, leaf, err
}

// mkdir makes the directory and any parent directories for the
// directory of the name given
func (f *Fs) mkdir(rootNode *mega.Node, dir string) (node *mega.Node, err error) {
	f.mkdirMu.Lock()
	defer f.mkdirMu.Unlock()

	parts := splitNodePath(dir)
	if parts == nil {
		return rootNode, nil
	}
	var i int
	// look up until we find a directory which exists
	for i = 0; i <= len(parts); i++ {
		var nodes []*mega.Node
		nodes, err = f.srv.FS.PathLookup(rootNode, parts[:len(parts)-i])
		if err == nil {
			if len(nodes) == 0 {
				node = rootNode
			} else {
				node = nodes[len(nodes)-1]
			}
			break
		}
		if err != mega.ENOENT {
			return nil, errors.Wrap(err, "mkdir lookup failed")
		}
	}
	if err != nil {
		return nil, errors.Wrap(err, "internal error: mkdir called with non existent root node")
	}
	// i is number of directories to create (may be 0)
	// node is directory to create them from
	for _, name := range parts[len(parts)-i:] {
		// create directory called name in node
		err = f.pacer.Call(func() (bool, error) {
			node, err = f.srv.CreateDir(name, node)
			return shouldRetry(err)
		})
		if err != nil {
			return nil, errors.Wrap(err, "mkdir create node failed")
		}
	}
	return node, nil
}

// mkdirParent creates the parent directory of remote
func (f *Fs) mkdirParent(remote string) (dirNode *mega.Node, leaf string, err error) {
	rootNode, err := f.findRoot(true)
	if err != nil {
		return nil, "", err
	}
	parent, leaf := path.Split(remote)
	dirNode, err = f.mkdir(rootNode, parent)
	return dirNode, leaf, err
}

// findRoot looks up the root directory node and returns it.
//
// if create is true it tries to create the root directory if not found
func (f *Fs) findRoot(create bool) (*mega.Node, error) {
	f.rootNodeMu.Lock()
	defer f.rootNodeMu.Unlock()

	// Check if we haven't found it already
	if f._rootNode != nil {
		return f._rootNode, nil
	}

	// Check for pre-existing root
	absRoot := f.srv.FS.GetRoot()
	node, err := f.findDir(absRoot, f.root)
	//log.Printf("findRoot findDir %p %v", node, err)
	if err == nil {
		f._rootNode = node
		return node, nil
	}
	if !create || err != fs.ErrorDirNotFound {
		return nil, err
	}

	//..not found so create the root directory
	f._rootNode, err = f.mkdir(absRoot, f.root)
	return f._rootNode, err
}

// clearRoot unsets the root directory
func (f *Fs) clearRoot() {
	f.rootNodeMu.Lock()
	f._rootNode = nil
	f.rootNodeMu.Unlock()
	//log.Printf("cleared root directory")
}

// Return an Object from a path
//
// If it can't be found it returns the error fs.ErrorObjectNotFound.
func (f *Fs) newObjectWithInfo(remote string, info *mega.Node) (fs.Object, error) {
	o := &Object{
		fs:     f,
		remote: remote,
	}
	var err error
	if info != nil {
		// Set info
		err = o.setMetaData(info)
	} else {
		err = o.readMetaData() // reads info and meta, returning an error
	}
	if err != nil {
		return nil, err
	}
	return o, nil
}

// NewObject finds the Object at remote.  If it can't be found
// it returns the error fs.ErrorObjectNotFound.
func (f *Fs) NewObject(remote string) (fs.Object, error) {
	return f.newObjectWithInfo(remote, nil)
}

// list the objects into the function supplied
//
// If directories is set it only sends directories
// User function to process a File item from listAll
//
// Should return true to finish processing
type listFn func(*mega.Node) bool

// Lists the directory required calling the user function on each item found
//
// If the user fn ever returns true then it early exits with found = true
func (f *Fs) list(dir *mega.Node, fn listFn) (found bool, err error) {
	nodes, err := f.srv.FS.GetChildren(dir)
	if err != nil {
		return false, errors.Wrapf(err, "list failed")
	}
	for _, item := range nodes {
		if fn(item) {
			found = true
			break
		}
	}
	return
}

// List the objects and directories in dir into entries.  The
// entries can be returned in any order but should be for a
// complete directory.
//
// dir should be "" to list the root, and should not have
// trailing slashes.
//
// This should return ErrDirNotFound if the directory isn't
// found.
func (f *Fs) List(dir string) (entries fs.DirEntries, err error) {
	dirNode, err := f.lookupDir(dir)
	if err != nil {
		return nil, err
	}
	var iErr error
	_, err = f.list(dirNode, func(info *mega.Node) bool {
		remote := path.Join(dir, info.GetName())
		switch info.GetType() {
		case mega.FOLDER, mega.ROOT, mega.INBOX, mega.TRASH:
			d := fs.NewDir(remote, info.GetTimeStamp()).SetID(info.GetHash())
			entries = append(entries, d)
		case mega.FILE:
			o, err := f.newObjectWithInfo(remote, info)
			if err != nil {
				iErr = err
				return true
			}
			entries = append(entries, o)
		}
		return false
	})
	if err != nil {
		return nil, err
	}
	if iErr != nil {
		return nil, iErr
	}
	return entries, nil
}

// Creates from the parameters passed in a half finished Object which
// must have setMetaData called on it
//
// Returns the dirNode, obect, leaf and error
//
// Used to create new objects
func (f *Fs) createObject(remote string, modTime time.Time, size int64) (o *Object, dirNode *mega.Node, leaf string, err error) {
	dirNode, leaf, err = f.mkdirParent(remote)
	if err != nil {
		return nil, nil, leaf, err
	}
	// Temporary Object under construction
	o = &Object{
		fs:     f,
		remote: remote,
	}
	return o, dirNode, leaf, nil
}

// Put the object
//
// Copy the reader in to the new object which is returned
//
// The new object may have been created if an error is returned
// PutUnchecked uploads the object
//
// This will create a duplicate if we upload a new file without
// checking to see if there is one already - use Put() for that.
func (f *Fs) Put(in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
	exisitingObj, err := f.newObjectWithInfo(src.Remote(), nil)
	switch err {
	case nil:
		return exisitingObj, exisitingObj.Update(in, src, options...)
	case fs.ErrorObjectNotFound:
		// Not found so create it
		return f.PutUnchecked(in, src)
	default:
		return nil, err
	}
}

// PutUnchecked the object
//
// Copy the reader in to the new object which is returned
//
// The new object may have been created if an error is returned
// PutUnchecked uploads the object
//
// This will create a duplicate if we upload a new file without
// checking to see if there is one already - use Put() for that.
func (f *Fs) PutUnchecked(in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (fs.Object, error) {
	remote := src.Remote()
	size := src.Size()
	modTime := src.ModTime()

	o, _, _, err := f.createObject(remote, modTime, size)
	if err != nil {
		return nil, err
	}
	return o, o.Update(in, src, options...)
}

// Mkdir creates the directory if it doesn't exist
func (f *Fs) Mkdir(dir string) error {
	rootNode, err := f.findRoot(true)
	if err != nil {
		return err
	}
	_, err = f.mkdir(rootNode, dir)
	return errors.Wrap(err, "Mkdir failed")
}

// deleteNode removes a file or directory, observing useTrash
func (f *Fs) deleteNode(node *mega.Node) (err error) {
	err = f.pacer.Call(func() (bool, error) {
		err = f.srv.Delete(node, !useTrash)
		return shouldRetry(err)
	})
	return err
}

// purgeCheck removes the directory dir, if check is set then it
// refuses to do so if it has anything in
func (f *Fs) purgeCheck(dir string, check bool) error {
	f.mkdirMu.Lock()
	defer f.mkdirMu.Unlock()

	rootNode, err := f.findRoot(false)
	if err != nil {
		return err
	}
	dirNode, err := f.findDir(rootNode, dir)
	if err != nil {
		return err
	}

	if check {
		children, err := f.srv.FS.GetChildren(dirNode)
		if err != nil {
			return errors.Wrap(err, "purgeCheck GetChildren failed")
		}
		if len(children) > 0 {
			return fs.ErrorDirectoryNotEmpty
		}
	}

	err = f.deleteNode(dirNode)
	if err != nil {
		return errors.Wrap(err, "delete directory node failed")
	}

	// Remove the root node if we just deleted it
	if dirNode == rootNode {
		f.clearRoot()
	}
	time.Sleep(100 * time.Millisecond) // FIXME give the callback a chance
	return nil
}

// Rmdir deletes the root folder
//
// Returns an error if it isn't empty
func (f *Fs) Rmdir(dir string) error {
	return f.purgeCheck(dir, true)
}

// Precision return the precision of this Fs
func (f *Fs) Precision() time.Duration {
	return fs.ModTimeNotSupported
}

// Purge deletes all the files and the container
//
// Optional interface: Only implement this if you have a way of
// deleting all the files quicker than just running Remove() on the
// result of List()
func (f *Fs) Purge() error {
	return f.purgeCheck("", false)
}

// move a file or folder (srcFs, srcRemote, info) to (f, dstRemote)
//
// info will be updates
func (f *Fs) move(dstRemote string, srcFs *Fs, srcRemote string, info *mega.Node) (err error) {
	var (
		dstFs                  = f
		srcDirNode, dstDirNode *mega.Node
		srcParent, dstParent   string
		srcLeaf, dstLeaf       string
	)

	if dstRemote != "" {
		// lookup or create the destination parent directory
		dstDirNode, dstLeaf, err = dstFs.mkdirParent(dstRemote)
	} else {
		// find or create the parent of the root directory
		absRoot := dstFs.srv.FS.GetRoot()
		dstParent, dstLeaf = path.Split(dstFs.root)
		dstDirNode, err = dstFs.mkdir(absRoot, dstParent)
	}
	if err != nil {
		return errors.Wrap(err, "server side move failed to make dst parent dir")
	}

	if srcRemote != "" {
		// lookup the existing parent directory
		srcDirNode, srcLeaf, err = srcFs.lookupParentDir(srcRemote)
	} else {
		// lookup the existing root parent
		absRoot := srcFs.srv.FS.GetRoot()
		srcParent, srcLeaf = path.Split(srcFs.root)
		srcDirNode, err = f.findDir(absRoot, srcParent)
	}
	if err != nil {
		return errors.Wrap(err, "server side move failed to lookup src parent dir")
	}

	// move the object into its new directory if required
	if srcDirNode != dstDirNode && srcDirNode.GetHash() != dstDirNode.GetHash() {
		//log.Printf("move src %p %q dst %p %q", srcDirNode, srcDirNode.GetName(), dstDirNode, dstDirNode.GetName())
		err = f.pacer.Call(func() (bool, error) {
			err = f.srv.Move(info, dstDirNode)
			return shouldRetry(err)
		})
		if err != nil {
			return errors.Wrap(err, "server side move failed")
		}
	}

	// rename the object if required
	if srcLeaf != dstLeaf {
		//log.Printf("rename %q to %q", srcLeaf, dstLeaf)
		err = f.pacer.Call(func() (bool, error) {
			err = f.srv.Rename(info, dstLeaf)
			return shouldRetry(err)
		})
		if err != nil {
			return errors.Wrap(err, "server side rename failed")
		}
	}

	time.Sleep(100 * time.Millisecond) // FIXME give events a chance...
	return nil
}

// Move src to this remote using server side move operations.
//
// This is stored with the remote path given
//
// It returns the destination Object and a possible error
//
// Will only be called if src.Fs().Name() == f.Name()
//
// If it isn't possible then return fs.ErrorCantMove
func (f *Fs) Move(src fs.Object, remote string) (fs.Object, error) {
	dstFs := f

	//log.Printf("Move %q -> %q", src.Remote(), remote)
	srcObj, ok := src.(*Object)
	if !ok {
		fs.Debugf(src, "Can't move - not same remote type")
		return nil, fs.ErrorCantMove
	}

	// Do the move
	err := f.move(remote, srcObj.fs, srcObj.remote, srcObj.info)
	if err != nil {
		return nil, err
	}

	// Create a destination object
	dstObj := &Object{
		fs:     dstFs,
		remote: remote,
		info:   srcObj.info,
	}
	return dstObj, nil
}

// DirMove moves src, srcRemote to this remote at dstRemote
// using server side move operations.
//
// Will only be called if src.Fs().Name() == f.Name()
//
// If it isn't possible then return fs.ErrorCantDirMove
//
// If destination exists then return fs.ErrorDirExists
func (f *Fs) DirMove(src fs.Fs, srcRemote, dstRemote string) error {
	dstFs := f
	srcFs, ok := src.(*Fs)
	if !ok {
		fs.Debugf(srcFs, "Can't move directory - not same remote type")
		return fs.ErrorCantDirMove
	}

	// find the source
	info, err := srcFs.lookupDir(srcRemote)
	if err != nil {
		return err
	}

	// check the destination doesn't exist
	_, err = dstFs.lookupDir(dstRemote)
	if err == nil {
		return fs.ErrorDirExists
	} else if err != fs.ErrorDirNotFound {
		return errors.Wrap(err, "DirMove error while checking dest directory")
	}

	// Do the move
	err = f.move(dstRemote, srcFs, srcRemote, info)
	if err != nil {
		return err
	}

	// Clear src if it was the root
	if srcRemote == "" {
		srcFs.clearRoot()
	}

	return nil
}

// DirCacheFlush an optional interface to flush internal directory cache
func (f *Fs) DirCacheFlush() {
	// f.dirCache.ResetRoot()
	// FIXME Flush the mega somehow?
}

// Hashes returns the supported hash sets.
func (f *Fs) Hashes() hash.Set {
	return hash.Set(hash.None)
}

// PublicLink generates a public link to the remote path (usually readable by anyone)
func (f *Fs) PublicLink(remote string) (link string, err error) {
	root, err := f.findRoot(false)
	if err != nil {
		return "", errors.Wrap(err, "PublicLink failed to find root node")
	}
	node, err := f.findNode(root, remote)
	if err != nil {
		return "", errors.Wrap(err, "PublicLink failed to find path")
	}
	link, err = f.srv.Link(node, true)
	if err != nil {
		return "", errors.Wrap(err, "PublicLink failed to create link")
	}
	return link, nil
}

// MergeDirs merges the contents of all the directories passed
// in into the first one and rmdirs the other directories.
func (f *Fs) MergeDirs(dirs []fs.Directory) error {
	if len(dirs) < 2 {
		return nil
	}
	// find dst directory
	dstDir := dirs[0]
	dstDirNode := f.srv.FS.HashLookup(dstDir.ID())
	if dstDirNode == nil {
		return errors.Errorf("MergeDirs failed to find node for: %v", dstDir)
	}
	for _, srcDir := range dirs[1:] {
		// find src directory
		srcDirNode := f.srv.FS.HashLookup(srcDir.ID())
		if srcDirNode == nil {
			return errors.Errorf("MergeDirs failed to find node for: %v", srcDir)
		}

		// list the the objects
		infos := []*mega.Node{}
		_, err := f.list(srcDirNode, func(info *mega.Node) bool {
			infos = append(infos, info)
			return false
		})
		if err != nil {
			return errors.Wrapf(err, "MergeDirs list failed on %v", srcDir)
		}
		// move them into place
		for _, info := range infos {
			fs.Infof(srcDir, "merging %q", info.GetName())
			err = f.pacer.Call(func() (bool, error) {
				err = f.srv.Move(info, dstDirNode)
				return shouldRetry(err)
			})
			if err != nil {
				return errors.Wrapf(err, "MergDirs move failed on %q in %v", info.GetName(), srcDir)
			}
		}
		// rmdir (into trash) the now empty source directory
		fs.Infof(srcDir, "removing empty directory")
		err = f.deleteNode(srcDirNode)
		if err != nil {
			return errors.Wrapf(err, "MergDirs move failed to rmdir %q", srcDir)
		}
	}
	return nil
}

// About gets quota information
func (f *Fs) About() (*fs.Usage, error) {
	var q mega.QuotaResp
	var err error
	err = f.pacer.Call(func() (bool, error) {
		q, err = f.srv.GetQuota()
		return shouldRetry(err)
	})
	if err != nil {
		return nil, errors.Wrap(err, "failed to get Mega Quota")
	}
	usage := &fs.Usage{
		Total: fs.NewUsageValue(int64(q.Mstrg)),           // quota of bytes that can be used
		Used:  fs.NewUsageValue(int64(q.Cstrg)),           // bytes in use
		Free:  fs.NewUsageValue(int64(q.Mstrg - q.Cstrg)), // bytes which can be uploaded before reaching the quota
	}
	return usage, nil
}

// ------------------------------------------------------------

// Fs returns the parent Fs
func (o *Object) Fs() fs.Info {
	return o.fs
}

// Return a string version
func (o *Object) String() string {
	if o == nil {
		return "<nil>"
	}
	return o.remote
}

// Remote returns the remote path
func (o *Object) Remote() string {
	return o.remote
}

// Hash returns the hashes of an object
func (o *Object) Hash(t hash.Type) (string, error) {
	return "", hash.ErrUnsupported
}

// Size returns the size of an object in bytes
func (o *Object) Size() int64 {
	return o.info.GetSize()
}

// setMetaData sets the metadata from info
func (o *Object) setMetaData(info *mega.Node) (err error) {
	if info.GetType() != mega.FILE {
		return fs.ErrorNotAFile
	}
	o.info = info
	return nil
}

// readMetaData gets the metadata if it hasn't already been fetched
//
// it also sets the info
func (o *Object) readMetaData() (err error) {
	if o.info != nil {
		return nil
	}
	info, err := o.fs.readMetaDataForPath(o.remote)
	if err != nil {
		if err == fs.ErrorDirNotFound {
			err = fs.ErrorObjectNotFound
		}
		return err
	}
	return o.setMetaData(info)
}

// ModTime returns the modification time of the object
//
//
// It attempts to read the objects mtime and if that isn't present the
// LastModified returned in the http headers
func (o *Object) ModTime() time.Time {
	return o.info.GetTimeStamp()
}

// SetModTime sets the modification time of the local fs object
func (o *Object) SetModTime(modTime time.Time) error {
	return fs.ErrorCantSetModTime
}

// Storable returns a boolean showing whether this object storable
func (o *Object) Storable() bool {
	return true
}

// openObject represents a download in progress
type openObject struct {
	mu     sync.Mutex
	o      *Object
	d      *mega.Download
	id     int
	skip   int64
	chunk  []byte
	closed bool
}

// get the next chunk
func (oo *openObject) getChunk() (err error) {
	if oo.id >= oo.d.Chunks() {
		return io.EOF
	}
	var chunk []byte
	err = oo.o.fs.pacer.Call(func() (bool, error) {
		chunk, err = oo.d.DownloadChunk(oo.id)
		return shouldRetry(err)
	})
	if err != nil {
		return err
	}
	oo.id++
	oo.chunk = chunk
	return nil
}

// Read reads up to len(p) bytes into p.
func (oo *openObject) Read(p []byte) (n int, err error) {
	oo.mu.Lock()
	defer oo.mu.Unlock()
	if oo.closed {
		return 0, errors.New("read on closed file")
	}
	// Skip data at the start if requested
	for oo.skip > 0 {
		_, size, err := oo.d.ChunkLocation(oo.id)
		if err != nil {
			return 0, err
		}
		if oo.skip < int64(size) {
			break
		}
		oo.id++
		oo.skip -= int64(size)
	}
	if len(oo.chunk) == 0 {
		err = oo.getChunk()
		if err != nil {
			return 0, err
		}
		if oo.skip > 0 {
			oo.chunk = oo.chunk[oo.skip:]
			oo.skip = 0
		}
	}
	n = copy(p, oo.chunk)
	oo.chunk = oo.chunk[n:]
	return n, nil
}

// Close closed the file - MAC errors are reported here
func (oo *openObject) Close() (err error) {
	oo.mu.Lock()
	defer oo.mu.Unlock()
	if oo.closed {
		return nil
	}
	err = oo.o.fs.pacer.Call(func() (bool, error) {
		err = oo.d.Finish()
		return shouldRetry(err)
	})
	if err != nil {
		return errors.Wrap(err, "failed to finish download")
	}
	oo.closed = true
	return nil
}

// Open an object for read
func (o *Object) Open(options ...fs.OpenOption) (in io.ReadCloser, err error) {
	var offset, limit int64 = 0, -1
	for _, option := range options {
		switch x := option.(type) {
		case *fs.SeekOption:
			offset = x.Offset
		case *fs.RangeOption:
			offset, limit = x.Decode(o.Size())
		default:
			if option.Mandatory() {
				fs.Logf(o, "Unsupported mandatory option: %v", option)
			}
		}
	}

	var d *mega.Download
	err = o.fs.pacer.Call(func() (bool, error) {
		d, err = o.fs.srv.NewDownload(o.info)
		return shouldRetry(err)
	})
	if err != nil {
		return nil, errors.Wrap(err, "open download file failed")
	}

	oo := &openObject{
		o:    o,
		d:    d,
		skip: offset,
	}

	return readers.NewLimitedReadCloser(oo, limit), nil
}

// Update the object with the contents of the io.Reader, modTime and size
//
// If existing is set then it updates the object rather than creating a new one
//
// The new object may have been created if an error is returned
func (o *Object) Update(in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (err error) {
	size := src.Size()
	//modTime := src.ModTime()
	remote := o.Remote()

	// Create the parent directory
	dirNode, leaf, err := o.fs.mkdirParent(remote)
	if err != nil {
		return errors.Wrap(err, "update make parent dir failed")
	}

	var u *mega.Upload
	err = o.fs.pacer.Call(func() (bool, error) {
		u, err = o.fs.srv.NewUpload(dirNode, leaf, size)
		return shouldRetry(err)
	})
	if err != nil {
		return errors.Wrap(err, "upload file failed to create session")
	}

	// Upload the chunks
	// FIXME do this in parallel
	for id := 0; id < u.Chunks(); id++ {
		_, chunkSize, err := u.ChunkLocation(id)
		if err != nil {
			return errors.Wrap(err, "upload failed to read chunk location")
		}
		chunk := make([]byte, chunkSize)
		_, err = io.ReadFull(in, chunk)
		if err != nil {
			return errors.Wrap(err, "upload failed to read data")
		}

		err = o.fs.pacer.Call(func() (bool, error) {
			err = u.UploadChunk(id, chunk)
			return shouldRetry(err)
		})
		if err != nil {
			return errors.Wrap(err, "upload file failed to upload chunk")
		}
	}

	// Finish the upload
	var info *mega.Node
	err = o.fs.pacer.Call(func() (bool, error) {
		info, err = u.Finish()
		return shouldRetry(err)
	})
	if err != nil {
		return errors.Wrap(err, "failed to finish upload")
	}

	// If the upload succeded and the original object existed, then delete it
	if o.info != nil {
		err = o.fs.deleteNode(o.info)
		if err != nil {
			return errors.Wrap(err, "upload failed to remove old version")
		}
		o.info = nil
	}

	return o.setMetaData(info)
}

// Remove an object
func (o *Object) Remove() error {
	err := o.fs.deleteNode(o.info)
	if err != nil {
		return errors.Wrap(err, "Remove object failed")
	}
	return nil
}

// Check the interfaces are satisfied
var (
	_ fs.Fs              = (*Fs)(nil)
	_ fs.Purger          = (*Fs)(nil)
	_ fs.Mover           = (*Fs)(nil)
	_ fs.PutUncheckeder  = (*Fs)(nil)
	_ fs.DirMover        = (*Fs)(nil)
	_ fs.DirCacheFlusher = (*Fs)(nil)
	_ fs.PublicLinker    = (*Fs)(nil)
	_ fs.MergeDirser     = (*Fs)(nil)
	_ fs.Abouter         = (*Fs)(nil)
	_ fs.Object          = (*Object)(nil)
)