package btrfs

import (
	"bytes"
	"os"
	"syscall"
)

const (
	xattrPrefix      = "btrfs."
	xattrCompression = xattrPrefix + "compression"
)

type Compression string

const (
	CompressionNone = Compression("")
	LZO             = Compression("lzo")
	ZLIB            = Compression("zlib")
)

func SetCompression(path string, v Compression) error {
	var value []byte
	if v != CompressionNone {
		var err error
		value, err = syscall.ByteSliceFromString(string(v))
		if err != nil {
			return err
		}
	}
	err := syscall.Setxattr(path, xattrCompression, value, 0)
	if err != nil {
		return &os.PathError{Op: "setxattr", Path: path, Err: err}
	}
	return nil
}

func GetCompression(path string) (Compression, error) {
	var buf []byte
	for {
		sz, err := syscall.Getxattr(path, xattrCompression, nil)
		if err == syscall.ENODATA || sz == 0 {
			return CompressionNone, nil
		} else if err != nil {
			return CompressionNone, &os.PathError{Op: "getxattr", Path: path, Err: err}
		}
		if cap(buf) < sz {
			buf = make([]byte, sz)
		} else {
			buf = buf[:sz]
		}
		sz, err = syscall.Getxattr(path, xattrCompression, buf)
		if err == syscall.ENODATA {
			return CompressionNone, nil
		} else if err == syscall.ERANGE {
			// xattr changed by someone else, and is larger than our current buffer
			continue
		} else if err != nil {
			return CompressionNone, &os.PathError{Op: "getxattr", Path: path, Err: err}
		}
		buf = buf[:sz]
		break
	}
	buf = bytes.TrimSuffix(buf, []byte{0})
	return Compression(buf), nil
}