package main

import (
	"bufio"
	"errors"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

type unixVolumeAdder struct {
	*volumeSet
}

func (vs *unixVolumeAdder) Set(value string) error {
	if dirs := strings.Split(value, ","); len(dirs) > 1 {
		log.Print("DEPRECATED: using comma-separated volume list.")
		for _, dir := range dirs {
			if err := vs.Set(dir); err != nil {
				return err
			}
		}
		return nil
	}
	if len(value) == 0 || value[0] != '/' {
		return errors.New("Invalid volume: must begin with '/'.")
	}
	if _, err := os.Stat(value); err != nil {
		return err
	}
	var locker sync.Locker
	if flagSerializeIO {
		locker = &sync.Mutex{}
	}
	*vs.volumeSet = append(*vs.volumeSet, &UnixVolume{
		root:     value,
		locker:   locker,
		readonly: flagReadonly,
	})
	return nil
}

func init() {
	flag.Var(
		&unixVolumeAdder{&volumes},
		"volumes",
		"Deprecated synonym for -volume.")
	flag.Var(
		&unixVolumeAdder{&volumes},
		"volume",
		"Local storage directory. Can be given more than once to add multiple directories. If none are supplied, the default is to use all directories named \"keep\" that exist in the top level directory of a mount point at startup time. Can be a comma-separated list, but this is deprecated: use multiple -volume arguments instead.")
}

// Discover adds a UnixVolume for every directory named "keep" that is
// located at the top level of a device- or tmpfs-backed mount point
// other than "/". It returns the number of volumes added.
func (vs *unixVolumeAdder) Discover() int {
	added := 0
	f, err := os.Open(ProcMounts)
	if err != nil {
		log.Fatalf("opening %s: %s", ProcMounts, err)
	}
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		args := strings.Fields(scanner.Text())
		if err := scanner.Err(); err != nil {
			log.Fatalf("reading %s: %s", ProcMounts, err)
		}
		dev, mount := args[0], args[1]
		if mount == "/" {
			continue
		}
		if dev != "tmpfs" && !strings.HasPrefix(dev, "/dev/") {
			continue
		}
		keepdir := mount + "/keep"
		if st, err := os.Stat(keepdir); err != nil || !st.IsDir() {
			continue
		}
		// Set the -readonly flag (but only for this volume)
		// if the filesystem is mounted readonly.
		flagReadonlyWas := flagReadonly
		for _, fsopt := range strings.Split(args[3], ",") {
			if fsopt == "ro" {
				flagReadonly = true
				break
			}
			if fsopt == "rw" {
				break
			}
		}
		if err := vs.Set(keepdir); err != nil {
			log.Printf("adding %q: %s", keepdir, err)
		} else {
			added++
		}
		flagReadonly = flagReadonlyWas
	}
	return added
}

// A UnixVolume stores and retrieves blocks in a local directory.
type UnixVolume struct {
	// path to the volume's root directory
	root string
	// something to lock during IO, typically a sync.Mutex (or nil
	// to skip locking)
	locker   sync.Locker
	readonly bool
}

// Touch sets the timestamp for the given locator to the current time
func (v *UnixVolume) Touch(loc string) error {
	if v.readonly {
		return MethodDisabledError
	}
	p := v.blockPath(loc)
	f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
	if err != nil {
		return err
	}
	defer f.Close()
	if v.locker != nil {
		v.locker.Lock()
		defer v.locker.Unlock()
	}
	if e := lockfile(f); e != nil {
		return e
	}
	defer unlockfile(f)
	now := time.Now().Unix()
	utime := syscall.Utimbuf{now, now}
	return syscall.Utime(p, &utime)
}

// Mtime returns the stored timestamp for the given locator.
func (v *UnixVolume) Mtime(loc string) (time.Time, error) {
	p := v.blockPath(loc)
	fi, err := os.Stat(p)
	if err != nil {
		return time.Time{}, err
	}
	return fi.ModTime(), nil
}

// Lock the locker (if one is in use), open the file for reading, and
// call the given function if and when the file is ready to read.
func (v *UnixVolume) getFunc(path string, fn func(io.Reader) error) error {
	if v.locker != nil {
		v.locker.Lock()
		defer v.locker.Unlock()
	}
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()
	return fn(f)
}

// stat is os.Stat() with some extra sanity checks.
func (v *UnixVolume) stat(path string) (os.FileInfo, error) {
	stat, err := os.Stat(path)
	if err == nil {
		if stat.Size() < 0 {
			err = os.ErrInvalid
		} else if stat.Size() > BlockSize {
			err = TooLongError
		}
	}
	return stat, err
}

// Get retrieves a block identified by the locator string "loc", and
// returns its contents as a byte slice.
//
// Get returns a nil buffer IFF it returns a non-nil error.
func (v *UnixVolume) Get(loc string) ([]byte, error) {
	path := v.blockPath(loc)
	stat, err := v.stat(path)
	if err != nil {
		return nil, v.translateError(err)
	}
	buf := bufs.Get(int(stat.Size()))
	err = v.getFunc(path, func(rdr io.Reader) error {
		_, err = io.ReadFull(rdr, buf)
		return err
	})
	if err != nil {
		bufs.Put(buf)
		return nil, err
	}
	return buf, nil
}

// Compare returns nil if Get(loc) would return the same content as
// expect. It is functionally equivalent to Get() followed by
// bytes.Compare(), but uses less memory.
func (v *UnixVolume) Compare(loc string, expect []byte) error {
	path := v.blockPath(loc)
	if _, err := v.stat(path); err != nil {
		return v.translateError(err)
	}
	return v.getFunc(path, func(rdr io.Reader) error {
		return compareReaderWithBuf(rdr, expect, loc[:32])
	})
}

// Put stores a block of data identified by the locator string
// "loc".  It returns nil on success.  If the volume is full, it
// returns a FullError.  If the write fails due to some other error,
// that error is returned.
func (v *UnixVolume) Put(loc string, block []byte) error {
	if v.readonly {
		return MethodDisabledError
	}
	if v.IsFull() {
		return FullError
	}
	bdir := v.blockDir(loc)
	if err := os.MkdirAll(bdir, 0755); err != nil {
		log.Printf("%s: could not create directory %s: %s",
			loc, bdir, err)
		return err
	}

	tmpfile, tmperr := ioutil.TempFile(bdir, "tmp"+loc)
	if tmperr != nil {
		log.Printf("ioutil.TempFile(%s, tmp%s): %s", bdir, loc, tmperr)
		return tmperr
	}
	bpath := v.blockPath(loc)

	if v.locker != nil {
		v.locker.Lock()
		defer v.locker.Unlock()
	}
	if _, err := tmpfile.Write(block); err != nil {
		log.Printf("%s: writing to %s: %s\n", v, bpath, err)
		tmpfile.Close()
		os.Remove(tmpfile.Name())
		return err
	}
	if err := tmpfile.Close(); err != nil {
		log.Printf("closing %s: %s\n", tmpfile.Name(), err)
		os.Remove(tmpfile.Name())
		return err
	}
	if err := os.Rename(tmpfile.Name(), bpath); err != nil {
		log.Printf("rename %s %s: %s\n", tmpfile.Name(), bpath, err)
		os.Remove(tmpfile.Name())
		return err
	}
	return nil
}

// Status returns a VolumeStatus struct describing the volume's
// current state, or nil if an error occurs.
//
func (v *UnixVolume) Status() *VolumeStatus {
	var fs syscall.Statfs_t
	var devnum uint64

	if fi, err := os.Stat(v.root); err == nil {
		devnum = fi.Sys().(*syscall.Stat_t).Dev
	} else {
		log.Printf("%s: os.Stat: %s\n", v, err)
		return nil
	}

	err := syscall.Statfs(v.root, &fs)
	if err != nil {
		log.Printf("%s: statfs: %s\n", v, err)
		return nil
	}
	// These calculations match the way df calculates disk usage:
	// "free" space is measured by fs.Bavail, but "used" space
	// uses fs.Blocks - fs.Bfree.
	free := fs.Bavail * uint64(fs.Bsize)
	used := (fs.Blocks - fs.Bfree) * uint64(fs.Bsize)
	return &VolumeStatus{v.root, devnum, free, used}
}

var blockDirRe = regexp.MustCompile(`^[0-9a-f]+$`)
var blockFileRe = regexp.MustCompile(`^[0-9a-f]{32}$`)

// IndexTo writes (to the given Writer) a list of blocks found on this
// volume which begin with the specified prefix. If the prefix is an
// empty string, IndexTo writes a complete list of blocks.
//
// Each block is given in the format
//
//     locator+size modification-time {newline}
//
// e.g.:
//
//     e4df392f86be161ca6ed3773a962b8f3+67108864 1388894303
//     e4d41e6fd68460e0e3fc18cc746959d2+67108864 1377796043
//     e4de7a2810f5554cd39b36d8ddb132ff+67108864 1388701136
//
func (v *UnixVolume) IndexTo(prefix string, w io.Writer) error {
	var lastErr error = nil
	rootdir, err := os.Open(v.root)
	if err != nil {
		return err
	}
	defer rootdir.Close()
	for {
		names, err := rootdir.Readdirnames(1)
		if err == io.EOF {
			return lastErr
		} else if err != nil {
			return err
		}
		if !strings.HasPrefix(names[0], prefix) && !strings.HasPrefix(prefix, names[0]) {
			// prefix excludes all blocks stored in this dir
			continue
		}
		if !blockDirRe.MatchString(names[0]) {
			continue
		}
		blockdirpath := filepath.Join(v.root, names[0])
		blockdir, err := os.Open(blockdirpath)
		if err != nil {
			log.Print("Error reading ", blockdirpath, ": ", err)
			lastErr = err
			continue
		}
		for {
			fileInfo, err := blockdir.Readdir(1)
			if err == io.EOF {
				break
			} else if err != nil {
				log.Print("Error reading ", blockdirpath, ": ", err)
				lastErr = err
				break
			}
			name := fileInfo[0].Name()
			if !strings.HasPrefix(name, prefix) {
				continue
			}
			if !blockFileRe.MatchString(name) {
				continue
			}
			_, err = fmt.Fprint(w,
				name,
				"+", fileInfo[0].Size(),
				" ", fileInfo[0].ModTime().Unix(),
				"\n")
		}
		blockdir.Close()
	}
}

// Delete deletes the block data from the unix storage
func (v *UnixVolume) Delete(loc string) error {
	// Touch() must be called before calling Write() on a block.  Touch()
	// also uses lockfile().  This avoids a race condition between Write()
	// and Delete() because either (a) the file will be deleted and Touch()
	// will signal to the caller that the file is not present (and needs to
	// be re-written), or (b) Touch() will update the file's timestamp and
	// Delete() will read the correct up-to-date timestamp and choose not to
	// delete the file.

	if v.readonly {
		return MethodDisabledError
	}
	if v.locker != nil {
		v.locker.Lock()
		defer v.locker.Unlock()
	}
	p := v.blockPath(loc)
	f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
	if err != nil {
		return err
	}
	defer f.Close()
	if e := lockfile(f); e != nil {
		return e
	}
	defer unlockfile(f)

	// If the block has been PUT in the last blobSignatureTTL
	// seconds, return success without removing the block. This
	// protects data from garbage collection until it is no longer
	// possible for clients to retrieve the unreferenced blocks
	// anyway (because the permission signatures have expired).
	if fi, err := os.Stat(p); err != nil {
		return err
	} else {
		if time.Since(fi.ModTime()) < blobSignatureTTL {
			return nil
		}
	}
	return os.Remove(p)
}

// blockDir returns the fully qualified directory name for the directory
// where loc is (or would be) stored on this volume.
func (v *UnixVolume) blockDir(loc string) string {
	return filepath.Join(v.root, loc[0:3])
}

// blockPath returns the fully qualified pathname for the path to loc
// on this volume.
func (v *UnixVolume) blockPath(loc string) string {
	return filepath.Join(v.blockDir(loc), loc)
}

// IsFull returns true if the free space on the volume is less than
// MinFreeKilobytes.
//
func (v *UnixVolume) IsFull() (isFull bool) {
	fullSymlink := v.root + "/full"

	// Check if the volume has been marked as full in the last hour.
	if link, err := os.Readlink(fullSymlink); err == nil {
		if ts, err := strconv.Atoi(link); err == nil {
			fulltime := time.Unix(int64(ts), 0)
			if time.Since(fulltime).Hours() < 1.0 {
				return true
			}
		}
	}

	if avail, err := v.FreeDiskSpace(); err == nil {
		isFull = avail < MinFreeKilobytes
	} else {
		log.Printf("%s: FreeDiskSpace: %s\n", v, err)
		isFull = false
	}

	// If the volume is full, timestamp it.
	if isFull {
		now := fmt.Sprintf("%d", time.Now().Unix())
		os.Symlink(now, fullSymlink)
	}
	return
}

// FreeDiskSpace returns the number of unused 1k blocks available on
// the volume.
//
func (v *UnixVolume) FreeDiskSpace() (free uint64, err error) {
	var fs syscall.Statfs_t
	err = syscall.Statfs(v.root, &fs)
	if err == nil {
		// Statfs output is not guaranteed to measure free
		// space in terms of 1K blocks.
		free = fs.Bavail * uint64(fs.Bsize) / 1024
	}
	return
}

func (v *UnixVolume) String() string {
	return fmt.Sprintf("[UnixVolume %s]", v.root)
}

// Writable returns false if all future Put, Mtime, and Delete calls are expected to fail.
func (v *UnixVolume) Writable() bool {
	return !v.readonly
}

func (v *UnixVolume) Replication() int {
	return 1
}

// lockfile and unlockfile use flock(2) to manage kernel file locks.
func lockfile(f *os.File) error {
	return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
}

func unlockfile(f *os.File) error {
	return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
}

// Where appropriate, translate a more specific filesystem error to an
// error recognized by handlers, like os.ErrNotExist.
func (v *UnixVolume) translateError(err error) error {
	switch err.(type) {
	case *os.PathError:
		// stat() returns a PathError if the parent directory
		// (not just the file itself) is missing
		return os.ErrNotExist
	default:
		return err
	}
}