#!/usr/bin/env python3
#
#  Copyright (C) 2016 Stavros Korokithakis
#  Copyright (C) 2017 Codethink Limited
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
#
#  The filesystem operations implementation here is based
#  on some example code written by Stavros Korokithakis.

import os
import sys
import stat
import errno
import shutil
import signal
import tempfile

from multiprocessing import Process
from .fuse import FuseOSError, Operations

from .mount import Mount


# SafeHardlinks()
#
# A FUSE mount which implements a copy on write hardlink experience.
#
# Args:
#     root (str): The underlying filesystem path to mirror
#     tmp (str): A directory on the same filesystem for creating temp files
#
class SafeHardlinks(Mount):

    def __init__(self, directory, tempdir):
        self.directory = directory
        self.tempdir = tempdir

    def create_operations(self):
        return SafeHardlinkOps(self.directory, self.tempdir)


# SafeHardlinkOps()
#
# The actual FUSE Operations implementation below.
#
class SafeHardlinkOps(Operations):

    def __init__(self, root, tmp):
        self.root = root
        self.tmp = tmp

    def _full_path(self, partial):
        if partial.startswith("/"):
            partial = partial[1:]
        path = os.path.join(self.root, partial)
        return path

    def _ensure_copy(self, full_path):
        try:
            # Follow symbolic links manually here
            real_path = os.path.realpath(full_path)
            file_stat = os.stat(real_path)

            # Dont bother with files that cannot be hardlinked, oddly it
            # directories actually usually have st_nlink > 1 so just avoid
            # that.
            #
            # We already wont get symlinks here, and stat will throw
            # the FileNotFoundError below if a followed symlink did not exist.
            #
            if not stat.S_ISDIR(file_stat.st_mode) and file_stat.st_nlink > 1:
                with tempfile.TemporaryDirectory(dir=self.tmp) as tempdir:
                    basename = os.path.basename(real_path)
                    temp_path = os.path.join(tempdir, basename)

                    # First copy, then unlink origin and rename
                    shutil.copy2(real_path, temp_path)
                    os.unlink(real_path)
                    os.rename(temp_path, real_path)

        except FileNotFoundError:
            # This doesnt exist yet, assume we're about to create it
            # so it's not a problem.
            pass

    ###########################################################
    #                     Fuse Methods                        #
    ###########################################################
    def access(self, path, mode):
        full_path = self._full_path(path)
        if not os.access(full_path, mode):
            raise FuseOSError(errno.EACCES)

    def chmod(self, path, mode):
        full_path = self._full_path(path)

        # Ensure copies on chmod
        self._ensure_copy(full_path)
        return os.chmod(full_path, mode)

    def chown(self, path, uid, gid):
        full_path = self._full_path(path)

        # Ensure copies on chown
        self._ensure_copy(full_path)
        return os.chown(full_path, uid, gid)

    def getattr(self, path, fh=None):
        full_path = self._full_path(path)
        st = os.lstat(full_path)
        return dict((key, getattr(st, key)) for key in (
            'st_atime', 'st_ctime', 'st_gid', 'st_mode',
            'st_mtime', 'st_nlink', 'st_size', 'st_uid'))

    def readdir(self, path, fh):
        full_path = self._full_path(path)

        dirents = ['.', '..']
        if os.path.isdir(full_path):
            dirents.extend(os.listdir(full_path))
        for r in dirents:
            yield r

    def readlink(self, path):
        pathname = os.readlink(self._full_path(path))
        if pathname.startswith("/"):
            # Path name is absolute, sanitize it.
            return os.path.relpath(pathname, self.root)
        else:
            return pathname

    def mknod(self, path, mode, dev):
        return os.mknod(self._full_path(path), mode, dev)

    def rmdir(self, path):
        full_path = self._full_path(path)
        return os.rmdir(full_path)

    def mkdir(self, path, mode):
        return os.mkdir(self._full_path(path), mode)

    def statfs(self, path):
        full_path = self._full_path(path)
        stv = os.statvfs(full_path)
        return dict((key, getattr(stv, key)) for key in (
            'f_bavail', 'f_bfree', 'f_blocks', 'f_bsize', 'f_favail',
            'f_ffree', 'f_files', 'f_flag', 'f_frsize', 'f_namemax'))

    def unlink(self, path):
        return os.unlink(self._full_path(path))

    def symlink(self, name, target):
        return os.symlink(target, self._full_path(name))

    def rename(self, old, new):
        return os.rename(self._full_path(old), self._full_path(new))

    def link(self, target, name):

        # When creating a hard link here, should we ensure the original
        # file is not a hardlink itself first ?
        #
        return os.link(self._full_path(name), self._full_path(target))

    def utimens(self, path, times=None):
        return os.utime(self._full_path(path), times)

    def open(self, path, flags):
        full_path = self._full_path(path)

        # If we're opening for writing, ensure it's a copy first
        if flags & os.O_WRONLY or flags & os.O_RDWR:
            self._ensure_copy(full_path)

        return os.open(full_path, flags)

    def create(self, path, mode, fi=None):
        full_path = self._full_path(path)

        # If it already exists, ensure it's a copy first
        self._ensure_copy(full_path)
        return os.open(full_path, os.O_WRONLY | os.O_CREAT, mode)

    def read(self, path, length, offset, fh):
        os.lseek(fh, offset, os.SEEK_SET)
        return os.read(fh, length)

    def write(self, path, buf, offset, fh):
        os.lseek(fh, offset, os.SEEK_SET)
        return os.write(fh, buf)

    def truncate(self, path, length, fh=None):
        full_path = self._full_path(path)
        with open(full_path, 'r+') as f:
            f.truncate(length)

    def flush(self, path, fh):
        return os.fsync(fh)

    def release(self, path, fh):
        return os.close(fh)

    def fsync(self, path, fdatasync, fh):
        return self.flush(path, fh)