// Package cmount implents a FUSE mounting system for rclone remotes.
//
// This uses the cgo based cgofuse library

// +build cgo
// +build linux darwin freebsd windows

package cmount

import (
	"fmt"
	"log"
	"os"
	"os/signal"
	"runtime"
	"syscall"
	"time"

	"github.com/billziss-gh/cgofuse/fuse"
	"github.com/ncw/rclone/cmd"
	"github.com/ncw/rclone/cmd/mountlib"
	"github.com/ncw/rclone/fs"
	"github.com/pkg/errors"
	"github.com/spf13/cobra"
)

// Globals
var (
	noModTime    = false
	debugFUSE    = false
	noSeek       = false
	dirCacheTime = 5 * 60 * time.Second
	// mount options
	readOnly                         = false
	allowNonEmpty                    = false
	allowRoot                        = false
	allowOther                       = false
	defaultPermissions               = false
	writebackCache                   = false
	maxReadAhead       fs.SizeSuffix = 128 * 1024
	umask                            = 0
	uid                              = ^uint32(0) // these values instruct WinFSP-FUSE to use the current user
	gid                              = ^uint32(0) // overriden for non windows in mount_unix.go
	// foreground                 = false
	// default permissions for directories - modified by umask in Mount
	dirPerms  = os.FileMode(0777)
	filePerms = os.FileMode(0666)
)

func init() {
	cmd.Root.AddCommand(commandDefintion)
	commandDefintion.Flags().BoolVarP(&noModTime, "no-modtime", "", noModTime, "Don't read/write the modification time (can speed things up).")
	commandDefintion.Flags().BoolVarP(&debugFUSE, "debug-fuse", "", debugFUSE, "Debug the FUSE internals - needs -v.")
	commandDefintion.Flags().BoolVarP(&noSeek, "no-seek", "", noSeek, "Don't allow seeking in files.")
	commandDefintion.Flags().DurationVarP(&dirCacheTime, "dir-cache-time", "", dirCacheTime, "Time to cache directory entries for.")
	// mount options
	commandDefintion.Flags().BoolVarP(&readOnly, "read-only", "", readOnly, "Mount read-only.")
	commandDefintion.Flags().BoolVarP(&allowNonEmpty, "allow-non-empty", "", allowNonEmpty, "Allow mounting over a non-empty directory.")
	commandDefintion.Flags().BoolVarP(&allowRoot, "allow-root", "", allowRoot, "Allow access to root user.")
	commandDefintion.Flags().BoolVarP(&allowOther, "allow-other", "", allowOther, "Allow access to other users.")
	commandDefintion.Flags().BoolVarP(&defaultPermissions, "default-permissions", "", defaultPermissions, "Makes kernel enforce access control based on the file mode.")
	commandDefintion.Flags().BoolVarP(&writebackCache, "write-back-cache", "", writebackCache, "Makes kernel buffer writes before sending them to rclone. Without this, writethrough caching is used.")
	commandDefintion.Flags().VarP(&maxReadAhead, "max-read-ahead", "", "The number of bytes that can be prefetched for sequential reads.")
	commandDefintion.Flags().IntVarP(&umask, "umask", "", umask, "Override the permission bits set by the filesystem.")
	//commandDefintion.Flags().BoolVarP(&foreground, "foreground", "", foreground, "Do not detach.")
}

var commandDefintion = &cobra.Command{
	Use:   "cmount remote:path /path/to/mountpoint",
	Short: `Mount the remote as a mountpoint. **EXPERIMENTAL**`,
	Long: `
rclone mount allows Linux, FreeBSD and macOS to mount any of Rclone's
cloud storage systems as a file system with FUSE.

This is **EXPERIMENTAL** - use with care.

First set up your remote using ` + "`rclone config`" + `.  Check it works with ` + "`rclone ls`" + ` etc.

Start the mount like this

    rclone mount remote:path/to/files /path/to/local/mount

Or on Windows like this where X: is an unused drive letter

    rclone mount remote:path/to/files X:

When the program ends, either via Ctrl+C or receiving a SIGINT or SIGTERM signal,
the mount is automatically stopped.

The umount operation can fail, for example when the mountpoint is busy.
When that happens, it is the user's responsibility to stop the mount manually with

    # Linux
    fusermount -u /path/to/local/mount
    # OS X
    umount /path/to/local/mount

### Limitations ###

This can only write files seqentially, it can only seek when reading.
This means that many applications won't work with their files on an
rclone mount.

The bucket based remotes (eg Swift, S3, Google Compute Storage, B2,
Hubic) won't work from the root - you will need to specify a bucket,
or a path within the bucket.  So ` + "`swift:`" + ` won't work whereas
` + "`swift:bucket`" + ` will as will ` + "`swift:bucket/path`" + `.
None of these support the concept of directories, so empty
directories will have a tendency to disappear once they fall out of
the directory cache.

Only supported on Linux, FreeBSD and OS X at the moment.

### rclone mount vs rclone sync/copy ##

File systems expect things to be 100% reliable, whereas cloud storage
systems are a long way from 100% reliable. The rclone sync/copy
commands cope with this with lots of retries.  However rclone mount
can't use retries in the same way without making local copies of the
uploads.  This might happen in the future, but for the moment rclone
mount won't do that, so will be less reliable than the rclone command.

### Filters ###

Note that all the rclone filters can be used to select a subset of the
files to be visible in the mount.

### Directory Cache ###

Using the ` + "`--dir-cache-time`" + ` flag, you can set how long a
directory should be considered up to date and not refreshed from the
backend. Changes made locally in the mount may appear immediately or
invalidate the cache. However, changes done on the remote will only
be picked up once the cache expires.

Alternatively, you can send a ` + "`SIGHUP`" + ` signal to rclone for
it to flush all directory caches, regardless of how old they are.
Assuming only one rclone instance is running, you can reset the cache
like this:

    kill -SIGHUP $(pidof rclone)

### Bugs ###

  * All the remotes should work for read, but some may not for write
    * those which need to know the size in advance won't - eg B2
    * maybe should pass in size as -1 to mean work it out
    * Or put in an an upload cache to cache the files on disk first

### TODO ###

  * Check hashes on upload/download
`,
	Run: func(command *cobra.Command, args []string) {
		cmd.CheckArgs(2, 2, command, args)
		fdst := cmd.NewFsDst(args)
		err := Mount(fdst, args[1])
		if err != nil {
			log.Fatalf("Fatal error: %v", err)
		}
	},
}

// mountOptions configures the options from the command line flags
func mountOptions(device string, mountpoint string) (options []string) {
	// Options
	options = []string{
		"-o", "fsname=" + device,
		"-o", "subtype=rclone",
		"-o", fmt.Sprintf("max_readahead=%d", maxReadAhead),
	}
	if debugFUSE {
		options = append(options, "-o", "debug")
	}

	// OSX options
	if runtime.GOOS == "darwin" {
		options = append(options, "-o", "volname="+device)
		options = append(options, "-o", "noappledouble")
		options = append(options, "-o", "noapplexattr")
	}

	if allowNonEmpty {
		options = append(options, "-o", "nonempty")
	}
	if allowOther {
		options = append(options, "-o", "allow_other")
	}
	if allowRoot {
		options = append(options, "-o", "allow_root")
	}
	if defaultPermissions {
		options = append(options, "-o", "default_permissions")
	}
	if readOnly {
		options = append(options, "-o", "ro")
	}
	if writebackCache {
		// FIXME? options = append(options, "-o", WritebackCache())
	}
	return options
}

// mount the file system
//
// The mount point will be ready when this returns.
//
// returns an error, and an error channel for the serve process to
// report an error when fusermount is called.
func mount(f fs.Fs, mountpoint string) (*mountlib.FS, <-chan error, func() error, error) {
	fs.Debugf(f, "Mounting on %q", mountpoint)

	// Check the mountpoint
	if runtime.GOOS != "windows" {
		fi, err := os.Stat(mountpoint)
		if err != nil {
			return nil, nil, nil, errors.Wrap(err, "mountpoint")
		}
		if !fi.IsDir() {
			return nil, nil, nil, errors.New("mountpoint is not a directory")
		}
	}

	// Create underlying FS
	fsys := NewFS(f)
	host := fuse.NewFileSystemHost(fsys)

	// Create options
	options := mountOptions(f.Name()+":"+f.Root(), mountpoint)
	fs.Debugf(f, "Mounting with options: %q", options)

	// Serve the mount point in the background returning error to errChan
	errChan := make(chan error, 1)
	go func() {
		var err error
		ok := host.Mount(mountpoint, options)
		if !ok {
			err = errors.New("mount failed")
			fs.Errorf(f, "Mount failed")
		}
		errChan <- err
	}()

	// unmount
	unmount := func() error {
		fs.Debugf(nil, "Calling host.Unmount")
		if host.Unmount() {
			fs.Debugf(nil, "host.Unmount succeeded")
			return nil
		}
		fs.Debugf(nil, "host.Unmount failed")
		return errors.New("host unmount failed")
	}

	// Wait for the filesystem to become ready
	<-fsys.ready
	return fsys.FS, errChan, unmount, nil
}

// Mount mounts the remote at mountpoint.
//
// If noModTime is set then it
func Mount(f fs.Fs, mountpoint string) error {
	// Set permissions
	dirPerms = 0777 &^ os.FileMode(umask)
	filePerms = 0666 &^ os.FileMode(umask)

	// Show stats if the user has specifically requested them
	if cmd.ShowStats() {
		stopStats := cmd.StartStats()
		defer close(stopStats)
	}

	// Mount it
	FS, errChan, _, err := mount(f, mountpoint)
	if err != nil {
		return errors.Wrap(err, "failed to mount FUSE fs")
	}

	// Note cgofuse unmounts the fs on SIGINT etc

	sigHup := make(chan os.Signal, 1)
	signal.Notify(sigHup, syscall.SIGHUP)

waitloop:
	for {
		select {
		// umount triggered outside the app
		case err = <-errChan:
			break waitloop
		// user sent SIGHUP to clear the cache
		case <-sigHup:
			root, err := FS.Root()
			if err != nil {
				fs.Errorf(f, "Error reading root: %v", err)
			} else {
				root.ForgetAll()
			}
		}
	}

	if err != nil {
		return errors.Wrap(err, "failed to umount FUSE fs")
	}

	return nil
}